text:
HVOF coatings.pdf
August 10, 2017 | Author: Radu Haiducu | Category: Gases, Continuum Mechanics, Materials Science, Chemical Product Engineering, Physical Sciences
DOWNLOAD PDF - 7.4MB
Download HVOF coatings.pdf...
Coatings 2011, 1, 17-52; doi:10.3390/coatings1010017 OPEN ACCESS
coatings ISSN 2079-6412 www.mdpi.com/journal/coatings/ Article
Optimization and Characterization of High Velocity Oxy-fuel Sprayed Coatings: Techniques, Materials, and Applications Maria Oksa 1, *, Erja Turunen 1 , Tomi Suhonen 1, Tommi Varis 1 and Simo-Pekka Hannula 2 1
VTT Technical Research Centre of Finland, POB 1000, VTT 02044, Finland; E-Mails: [email protected] (E.T.); [email protected] (T.S.); [email protected] (T.V.) Department of Materials Science and Engineering, Aalto University School of Chemical Technology, POB 16200, Aalto 00076, Finland; E-Mail: [email protected]
* Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +358-20-722-5412; Fax: +358-20-722-7069. Received: 28 July 2011; in revised form: 19 August 2011 / Accepted: 19 August 2011 / Published: 2 September 2011
Abstract: In this work High Velocity Oxy-fuel (HVOF) thermal spray techniques, spraying process optimization, and characterization of coatings are reviewed. Different variants of the technology are described and the main differences in spray conditions in terms of particle kinetics and thermal energy are rationalized. Methods and tools for controlling the spray process are presented as well as their use in optimizing the coating process. It will be shown how the differences from the starting powder to the final coating formation affect the coating microstructure and performance. Typical properties of HVOF sprayed coatings and coating performance is described. Also development of testing methods used for the evaluation of coating properties and current status of standardization is presented. Short discussion of typical applications is done. Keywords: thermal spray; coating; HVOF; optimization; characterization; standardization
1. Introduction to Thermal Spray Processes Thermal spraying is a general term to describe all methods in which the coating is formed from melted or semi-melted droplets. In thermal spraying the material is in the form of powder, wire or rod
Coatings 2011, 1
and is fed into the flame produced by a spray gun, where it melts and the formed droplets are accelerated towards the substrate to be coated. The thermal and kinetic energy of the flame can be produced either with burning mixtures of fuel gas and oxygen, or by using an electrical power source. Based on the energy source, thermal spray methods can be divided into a few main groups: plasma spray methods (atmospheric plasma APS, vacuum plasma VPS, and low pressure plasma LPPS), combustion flame spray methods (flame spray), high velocity oxy/air-fuel methods (HVOF/HVAF), electrical arc methods (wire arc), detonation method (D-Gun), and, as the latest technology, cold gas methods (CGS). Since coating is built up from flattened, fast solidified droplets the velocity plays an important role for the obtained density of the lamella structured coating. Temperature of the flame has a strong effect on the suitable materials to be sprayed. Ceramic coatings are mainly manufactured by using atmospheric plasma spray method, while temperature sensitive materials, such as cermets, are more preferably sprayed by methods with a lower flame temperature. In Figure 1 the typical operation ranges for various spray systems are presented. Figure 1. Typical flame temperature and particle velocity operation ranges for various thermal spray systems.
Thermal spray coatings are often applied for better corrosion and wear resistance. Therefore, low porosity and good adhesion are desired properties for the coating. High velocity processes—especially HVOF (High velocity oxy-fuel) spraying—are the preferred methods for producing coating with low porosity and high adhesion. In HVOF spraying, heat is produced by burning mixture of oxygen and
fuel such as hydrogen, kerosene, propane, propylene, natural gas, ethylene, or acetylene. Due to the special nozzle design, a jet with supersonic speed is produced. The ability to produce dense coatings with low amount of degradation, oxidation of metallic materials, and phase transformations is the main feature of the HVOF process. This is due to the short dwell time of the particles in a relatively cold flame. It is widely used to produce cermet and metal coatings, but the HVOF process has also been demonstrated to be able to deposit dense ceramic coatings. In the HVOF process, fuel and oxygen are introduced to the combustion chamber together with the spray powder. The combustion of the gases produces a high temperature and high pressure in the chamber, which causes the supersonic flow of the gases through the nozzle. The powder particles melt or partially melt in the combustion chamber and during the flight through the nozzle. The flame temperature varies in the range of 2500 °C–3200 °C, depending on the fuel, the fuel gas/oxygen ratio and the gas pressure. In the HVOF process the particles melt completely or only partially, depending on the flame temperature, particle dwell time, material melting point and thermal conductivity. A few different HVOF spray systems exist with partly different gun designs and capacities. Each one has differences in design, but all are based on the same fundamental principles. The combination of high pressure (over 3 bar) and gas flow rates of several hundred liters per minute generate supersonic gas velocities. These systems can be roughly divided into the first, second and third generation. In all first and second generation guns, the pressurized burning of gaseous fuel with oxygen is used to produce an exhaust jet traveling at a speed of about 2000 m/s. The main fundamental difference between first and second generation is the design of the nozzle. In the first generation HVOF systems there is typically relatively large combustion chamber and a straight nozzle. With this design maximum of 1 Mach (gas velocity related to the sonic speed) velocities can be produced. The second generation is based on the de Laval nozzle, which enables over 1 Mach velocities at the diverging part of the nozzle. Under standard spray conditions the systems are operated at a power level of about 100 kW and are capable of spraying about 2–3 kg/h of WC-Co. The third generation systems are for power levels ranging from 100 to 300 kW and for higher chamber pressures ranging from 8 bar up to as far as 25 bars, being capable of spray rates up to about 10 kg/h. Table 1 summarizes the key differences between generations. Table 1. The differences between three generations of HVOF systems. Nozzle type Power level (kW)*
Chamber pressure (bar)
Kg/h (WC-Co)
De laval
80 to120
8 to 12 (up to 25)
*Total Heat Output
From a scientific point of view, particle velocity (v) and particle temperature (T) together with substrate characteristics are the main parameters affecting the deposit formation. They determine the deposit build-up process and deposit properties. Particle velocity and temperature affect the deposit efficiency as well as the microstructure. Trend in HVOF process development has been towards higher
gas pressures, faster particle velocities and lower particle temperatures as shown schematically in Figure 2. This has a clear influence on the coating microstructure, where amount of oxidation in the lamella boundary is decreased and flattening rate is increased, and due to this the coating density is improved generation by generation, as presented in the Figure 3. Figure 2. The trend in HVOF process development has been towards higher gas pressures, faster particle velocities and lower particle temperatures.
Figure 3. Faster particle velocities and lower particle temperatures in HVOF process have a clear influence on the coating microstructure, where amount of oxidation in the lamella boundary is lowered, the flattening rate increased, and due to this the coating density is improved.
2. HVOF Process Optimization HVOF spraying is a very complex process, which has a large variety of variables affecting the deposit formation and hence coating properties. These variables include hardware characteristics (e.g., nozzle geometry and spraying distance) and process parameters, e.g., fuel gas, gas flow density, and powder feedstock. In the spray process, the powder particles experience very high speed combined with fast heating up to its melting point or above. This high temperature may cause evaporation of the powder or some components of it, dissolution, and phase transformations. Due to this complex nature of HVOF technique, the control and optimization of the process in order to achieve coating with desired properties is a highly challenging task. There are different ways of optimizing and analyzing the thermal spray processes and deposit formation. These include statistical methods such as Taguchi and design of experiments (DoE), numerical modeling and simulation, and FE methodology [1-5]. In the Taguchi method, for example, the test matrix can be significantly reduced and the relative importance between variables can be determined sufficiently. The result in Taguchi is dependent on the design and selection of variables and their levels and the result may therefore be misleading. Determining the importance and weight of a large number of variables is very difficult with the HVOF process. This applies to different modeling procedures as well. Good coating quality with suitable properties and required performance for specific applications is the goal in producing thermal spray coatings. In order to reach this goal, a deeper understanding of the spray process as a whole is needed. Starting material, spray process and particle-substrate interactions all affect the formation of coating with different microstructure and hence the coating properties and eventually the coating performance. Use of submicron and nanostructured powders sets demands for the coating process in order to maintain the fine-scaled structures and enhance the coating properties. For better control of thermal spraying, different sensing devices have been developed during the last decade. These diagnostic tools have enabled better investigation and measuring of the spray process, and helped to understand the impact of different process variables on in-flight particle state (flux, temperature and velocity). In tandem with the diagnostic tool development, a novel comprehensive optimization tool has been developed for thermal spray processes. The process mapping concept was first introduced by Professor Sanjay Sampath [6], and its use has increased since introduction [7-10]. In this chapter the diagnostic equipments are introduced, as well as the process mapping tool and factors related to it. Examples of applying the process maps for process control and coating design are presented. 2.1. Diagnostic Tools for Process Optimization For the last fifteen years active development of spray process sensing systems has taken place. These diagnostic tools are nowadays robust, user-friendly and cost-effective, and therefore their use has increased strongly. Principle objectives of diagnostic tools are to measure the variables of particles within the spray stream, i.e., velocity, temperature, flux, trajectory, and size distribution, which all have influence on the microstructure and properties of sprayed coatings [9]. The sensors are mainly based on two-wavelength pyrometry and time triggered measurement of velocity. Examples of sensors for thermal spraying are Tecnar DPV2000, Oseir SprayWatch, Tecnar Accuraspray, Inflight Particle
Pyrometer, and Spray Position Trajectory sensor. These are based on either individual particle (DPV2000) or ensemble (group of particles) measurement (SprayWatch, Accuraspray). In its simplest form, the sensors are used for measuring the temperature and velocity of the powder particles in the spray stream. The placing of the sensors can either be fixed on the spray torch or on the side of it. With the former sensors, it is possible to monitor the process continuously, and any variation can be instantly detected. Ensemble measurement is the faster of the two, a few seconds against a few minutes [11]. The diagnostic tools have differences in measuring the spray stream, including volume, number of particles and the ability to scan the spray stream. These differences with single particle and ensemble sensors may lead to different results when measuring temperature and velocity. Comparison with single and ensemble sensors has shown good relation for ceramic and metallic coatings when velocity was measured [12]. However, average particle temperature measured by single and ensemble sensors did not correlate for metallic materials. The reason for this might be that high-temperature ceramic materials have higher total radiated intensity due to higher temperature and higher emissivity, but metals are influenced by oxidation and change of emissivity [12]. Therefore the results of diagnostic tools need careful consideration. 2.2. Process Optimization Procedures The spraying process is monitored with diagnostic sensors, which measure the particle surface temperature and velocity in the spray stream. It is very important to place the equipment correctly in-line with the spray stream. By controlling the gas flow, the fuel/oxygen ratio, or back-pressure of the chamber, different particle states are formed. In order to examine coating formation in detail, individual splats can be sprayed in parallel with using diagnostic tools. By splat studies on the polished substrate, the particle melting state can be analyzed, and hence it is possible to get more information of the diverse coating build-up process. With splat analysis, it has been shown e.g., that small NiCr particles suffer more oxidation when particle temperatures are high [10]. It is common that high speed particles form air pockets when deposited on the substrate, especially when particles are not fully melted. Fully molten NiCr particles have formed smaller grain sized splats compared to feedstock material [10]. Examples of splats of Al2O3 are presented in Figure 4, showing different melting states of sprayed particles resulting from different spray parameters. Characterization of the formed coating by microscopic means and testing the coating after spraying, thickness, porosity, lamellar structure with fully or partially molten particles, flattening ratio, oxidation level, bonding, hardness, elastic modulus etc. are revealed, and can be linked to process variables. When the linkages between process variables, coating microstructure and properties are done, the reverse deduction is also possible. When a certain property is the goal, it is possible to go backwards by process maps and identify the correct process parameters in order to achieve the desired property.
Figure 4. In the SEM figures of splats different melting, flattening and splashing behavior of HV2000 (Praxair) sprayed Al2O3 particles can be detected. The used spray parameters have been (a) 776 L/min H2 / 272 L/min O2 / 20 L/min N2 (fuel ratio 2.85), 150 mm stand-off distance, (b) 776/272/20 (2.85) 200 mm, (c) 699/349/20 (2.00) 150 mm, and (d) 747/301/20 (2.48) 150 mm.
Three operational gas/liquid flow variables can be used for the control of HVOF process: (i) choice of used gases/liquids; (ii) total volume flow of gases/liquids; and (iii) the ratio between them (oxygen/fuel). All these have influence on particle velocity (backpressure of the chamber) and particle temperature. Independent operational parameters with HVOF can be oxygen, fuel, nitrogen and air flow. Other variables, which play an important role, include spray distance and deposition rates (combination of e.g., feed rate and robot speed). Gas flow control can be used as a tool for particle state measurements (T, v), as well as a tool for using different fuels, chamber and nozzle designs, which change the particle state significantly. The spraying process must be calibrated, so that errors in the measurement can be prevented or estimated. Use of feedback control in the process enables this. Repeating a certain condition whilst performing the process map procedure indicates the data scatter and error, both to temperature and velocity measurement. Errors rise from input parameters (emissivity), instruments, control of gas flows and feed rate, and degradation effects of nozzle and injection wear [8]. These may have influence on the achieved temperature-velocity values during a long process time, and therefore calculation, re-calculation and re-adjusting of spraying parameters are needed throughout the spraying process.
An example of the HVOF spraying of NiCr powder has shown the influence of oxygen-rich flame, resulting in higher temperature and lower velocity [10]. When fuel-rich flame was used, the temperature decreased (as the flame energy decreased), and particle velocity increased. Kinetic and thermal energy transferred to the particles is dependent on the flame energy (enthalpy of the used fuel, fuel density, and ratio of fuel to oxygen). Higher energy levels of the flame yield higher kinetic and thermal energies to the particles. Increment of airflow to the flame decreases the temperature and increases the particle velocity slightly by increasing the drag force to the particles and shortening of their dwell time. Changes in fuel-oxygen mixture cause stronger effect. Feed rate plays also a role on the kinetic and thermal energy. A flame quenching effect has been observed when increasing the feed rate of NiCr powder [10] The oxide content of the coatings is predominantly determined by the in-flight reactions. Longer flame protects the particles from oxidation by shortening the interaction with the surroundings, and by burning the oxygen within the flame, a so-called shielding effect. Therefore the fuel-rich conditions produce metallic coatings with less oxidation [10]. Higher particle speeds reduce particle overheating, thus preventing the oxidation and decarburization of carbides [13]. On the other hand, higher particle temperature leads to slightly higher oxide content [10]. 2.3. Process Mapping Particle state is influenced by fuel gas chemistry (fuel/oxygen ratio), total gas flow, and energy input, which affect the particle temperature, velocity and hence coating formation dynamics and properties. The process-structure-property relations can be presented by process maps, which can be used as design tool for coating processing. Process maps are interrelationships among the process variables and output responses [12]. The process mapping optimization tool has been widely applied for plasma spray process [12,14], but it can be successfully used for HVOF process as well [10,15]. 2.3.1. Concept of Process Mapping The process map methodology is developed for process control and coating properties optimization. In the process mapping concept, the diagnostic tools are used for understanding the fundamentals of relationships in the thermal spray process, starting from powder to thermal spraying process, to deposit formation, to coating characteristics, and finally to coating performance. In Figure 5, the process map concept for HVOF spraying is presented. A first order process map expresses the relationship between torch parameters and particles in the spray stream, which are measured by diagnostics. A second order process map represents relationship between the spray stream measured responses and coating properties. Systematic evaluation of the processes, eventually leading to optimization of coating properties for specified performance and an assessment of process reliability, can be performed by creating first and second order maps for certain material and thermal spray process. A third order process map, which links coating microstructure and properties to coating performance can also be constructed.
Figure 5. The process map concept for the HVOF process. The relationship between process parameters, measured particle state, coating microstructure and coating properties are described as process maps of different order. The goal of process mapping is to understand the process-structure-properties in order to be able to use the tool for coating design.
2.3.2. First-Order Process Map A first order process map relates the process variables to particle state (temperature and velocity). The results acquired with diagnostic tools are plotted in a T-v diagram, which is called a first order process map. An example of first-order (T-v) process map is shown in Figure 6, which presents different temperature and velocity ranges for two different fuel mixtures for HVOF sprayed Al2O3 [15]. A generalized first-order process map in Figure 1 for different thermal spray processes, presenting the typical temperature and velocity ranges. In the figure it can be seen that HVOF process has moderate temperature and high velocity compared to other common thermal spray processes. First-order process map helps to understand how the particle state influences on the formation of the coating microstructure.
Figure 6. A first-order process map for HVOF alumina, showing particle temperature and velocity ranges for propylene-oxygen and hydrogen-oxygen fuel mixtures [15].
2.3.3. Second-Order Process Map A second-order process map links the process and deposit interactions. It describes the influence of coating microstructure on the coating properties. In order to produce a second-order map, a certain T-v process window from the first-order map is selected. After the spraying, the coating properties, such as weight, elastic modulus and thermal conductivity, are measured, and thus linked to the process parameters (temperature, velocity). The purpose of the second order map is to provide a tool for designer to choose coatings of selected combination of properties and specify the values of T-v of the particle state. Actual operational parameters are specified from the first-order map. A second-order process map for HVOF sprayed NiCr is presented in Figure 7, showing values of elastic modulus and hardness reflected with different particle temperature and velocity values [10]. A schematic illustration of an idea of the second-order process map is presented in Figure 3, where different HVOF processes are compared in T-v diagram, linking the formed microstructure to the process parameters. Figure 7. Second-order process maps for HVOF NiCr of elastic modulus and hardness with different particle temperatures and velocities [10].
2.4. Reliability through Process Optimization More stringent requirements for coatings in different applications enhance the use of process optimization, repeatability, reproducibility and reliability (3 R's) of the coating process as a goal [16]. However, reliance and manufacturing reproducibility is a complex task due to the multitude of interrelated parameters that influence spraying process and the deposit formation dynamics. The complexity of the process and material variables has made it difficult to understand the process-structure-property relationships as well as industry/application related attributes, such as coating design, property characterization and reliability [8]. Process optimization is used for process development by parameter improvement, tracking instabilities and examining reproducibility, and that way for improved coating manufacturing. A strategy for coating design can be obtained by careful use of process maps, because process parameters can be linked to coating characteristics and hence understanding of the process-microstructure-property relationships is possible [12]. Through process optimization it is possible to produce reliable and reproducible coatings with designed performance together with predictable life of operation [15]. Therefore the process map concept is an excellent tool for analyzing and controlling the effects of spraying parameters in production of coatings. The method can be applied for any thermal spray technology [10]. Also deposition efficiency (DE) can be improved, as well as process efficiency. Materials usage and the amount of defective coated components can be minimized, and that way it is possible to lower the coating production costs. 2.5. Case Studies of Process Optimization with Process Map Concept Challenges arise when spraying nanoscale carbides, because with fine carbide sizes the dissolution of carbides and carbon loss becomes easier. The powder quality is important, as the size distribution, density, carbon and oxygen content have influence on the deposit formation. Choosing right spray process and optimizing control parameters are essential in generating good coating quality. Agglomerated and sintered WOKA 3652, −45+45 µm WC-10Co4Cr powder was sprayed with DJ Hybrid HVOF spray, with hydrogen as fuel gas. The goal was to increase both wear resistance and fracture toughness. As can be seen in the generalized second order process map for WC-CoCr in Figure 8, a small process window to achieve such characteristics combination was found. The goal of using WC-CoCr with nanoscale carbides was to achieve high hardness combined with good fracture toughness. Thermico CJS (carbide jet spray), a colder HVOF thermal spray process with broader process window, was applied for maintaining the nanoscale carbides within the matrix. With careful process optimization, both the characteristics were enhanced [17].
Figure 8. A generalized second order process map for WC-CoCr HVOF coating. Different coating properties are placed into the temperature-velocity diagram. This process map can be used as a design tool to optimize coating process conditions in order to achieve desired coating property or coating property combinations.
Process map methodology has been used for HVOF spraying of Ni-20%Cr coatings [10]. Design of experiments was used to prepare a first order process map. According to the map, different conditions were chosen to produce the coatings with a low feed rate, and to analyze them with an in-situ coating property sensor (ReliaCoat Technology ICP). It was noted that increase in the feed rate decreased both the particle temperature and velocity. In the same process optimization trials, an increment on airflow feeding was detected to result in lower particle temperature but higher velocity. When spraying distance was increased, the particle temperature was risen and the velocity was reduced. In order to enhance the thermal conductivity, high kinetic energy with high thermal energy of particles was required so as to deposit dense coatings with improved intersplat bonding (metallurgical, intimate mechanical contact), but oxide content must be kept relatively low. Electrical resistivity was enhanced with high thermal-kinetic energy as well. Stiffer coatings were formed with high particle velocity and sufficient melting state. An example of plasma spray process optimization for yttrium stabilized zirconium (YSZ) plasma sprayed coating showed possibility of controlling the particle state within a small process window (±10 °C average temperature and ±2 m/s average velocity) by using a first order process map while varying process parameters (e.g., gas flow, current). However, different melting states were observed in the temperature distribution diagrams for various sprayings, as well as differences for deposition efficiencies, and modulus between the coatings. These results indicate that temperature and velocity measurement solely do not describe the melting state of the particles [15]. 2.6. Thermal Energy and Kinetics of Particles in Spray Stream In order to better understand the melting behavior of particles in the spray stream, another factor has been developed besides the use of temperature. Especially with ceramic materials, with low thermal conductivity, the particle surface temperature does not directly indicate the particle melting status due
to large temperature gradient within the particle [9,18]. The particle surface may even evaporate before the core melts. In the case of metallic materials, the oxidation of particles occurs in the spray stream. This phenomenon can have an effect on the measured temperature values and emissivity value. Melting index (MI) also takes into account the time particles stay under the influence of flame and particle size. It can be expressed as [12]: (1) where T = measured particle surface temperature [K], D = particle size [m], and Δtfly particle in-flight time assuming constant acceleration of particles [s]. In the MI formula the Δtfly = 2L/v, where L = spray distance [m], and v = particle velocity [m/s]. MI can be defined as the ratio of particle residence time in the flame to the total time needed for particle to melt: MI = Δtfly/Δtmelt [9]. There is also more thorough description of melting index, which attaches thermal resistance and energy balance analysis to the formula [9]: (2) where k is the thermal conductivity [W/mK], ρ is the density of the material in liquid state [kg/m3], is the enthalpy of fusion [J/kg], and
is the flame temperature near the in-flight particle [K],
is the
melting point of the material [K], is the particle size [m], and Bi is the Biot number [9]. With this approach MI is non-dimensional, which allows cross-comparison of melting state among a range of materials. From Equation 2, it can be detected that if the flame temperature is higher than the melting point of the material, a positive MI value will be obtained, which corresponds to fully molten particles. Otherwise, the material will be unmolten (MI < 0) or partially molten (0 ≤ MI < 1). Since it is difficult to monitor the real time flame temperature in the vicinity of the flying particles, for simplifications particle surface temperature, T, has been often used instead of . Metallic particles oxidize during the spraying process, which has effect on the measured temperature by diagnostic sensors. Oxidation reactions are exothermic, which raises the particle temperature in-flight. Extent of oxidation taking place with the metallic particles is described by Oxidation index (OI) [9]. Like temperature, the velocity values alone do not give sufficient information of the particles impinging on the substrate material and hence the deposit build-up process. Therefore either kinetic energy (KE) or Reynolds number (Re) can be used for describing the kinetic behavior of the particles. Kinetic energy is related to particle mass (m) and velocity (v) [9]: (3) Reynolds number can be described with factors such as particle size, material density and viscosity [17]: (4)
where D = particle diameter [m], ρ = density of the material in liquid state [kg/m3] and µ = dynamic viscosity [kg/ms]. Both the kinetic energy and Re are important factors describing the impact, extent of spreading and flattening, and hence the nature of splat-substrate and splat-splat contact [9]. Melting state, kinetic energy and local deposition temperature are likely the most important factors controlling the microstructure and properties of the coatings [10]. Other factors besides particle state correlations that strongly effect deposit formation dynamics (wetting, spreading-splashing, flattening, solidification, and interlocking/bonding dynamics) and hence deposit characteristics, are substrate temperature and roughness, deposit conditions (rate, spray angle), and deposit rate [12]. Another factor affecting particle behavior and temperature is exothermic reaction of oxide formation (e.g., Cr2O3), which generates additional heat during flight [10]. 2.7. Monitoring Deposit Formation In-Situ Analysis of coating characteristics is mainly performed after the actual coating process. However, the actual deposit formation process is difficult to monitor. An in-situ coating property sensor (ICP) has been developed to monitor coating curvature evolution and substrate temperature during the spraying process [12]. Measuring curvature is possible by monitoring the substrate displacement with non-contact lasers. Temperature measurement is performed with multiple thermocouples attached to the back of the substrate material during both deposition and cooling. With this information, it is possible to calculate residual stresses, CTE, and elastic modulus of the coatings. The technique and the measurement method are described in detail by Matejicek et al. [19]. The particle state influences stress build-up during spraying process and coating residual stresses have an effect on the coating properties. The residual stresses depend strongly on the particle velocity and on the particle temperature [12]. Compressive stresses are formed due to peening at high particle velocities. As an example, in curvature measurements of NiCr it has been noticed that in the first pass, the quenching stresses prevail due to limited plastic deformation of the substrate [10]. Following passes induce compressive stresses due to the peening effect. The higher the velocity, the higher is the buildup of the compressive stresses. Peening intensity of the impacting particles can be monitored during spraying through an in-situ curvature technique. Correlation of it can be made to the microstructure, splats, residual stress and hardness of deposits [10]. Difference in CTE's (coefficient of thermal expansion) between the coating and substrate material also causes stress in the coating. Evolving stress and substrate temperature are main factors when considering strain hardening of the coating, compaction, and residual stress development [10]. 2.8. Effect of Feedstock Properties on Coating Formation Powder properties and characteristics (e.g., particle shape, structure and size, powder density and flow ability, purity, phase content, agglomeration) depend on the detailed powder manufacturing method, i.e., crushing and milling, water and gas atomization, spray drying, agglomeration and sintering [13]. Studies have shown implication of different feedstock for the formed coating, as the particle characteristics are very different in the spray process (e.g., temperature and velocity). When powders from the same material, but with different morphologies or different size distribution, have been sprayed with similar temperature and velocity range, the formed coatings have shown substantial
differences in several properties e.g., elastic modulus [12]. Examples of different spray powder morphologies are presented in Figure 9. The feedstock characteristics (particle form, size distribution, density and chemistry) have an effect on deposit evolution and process efficiency by change in thickness per pass, and to other properties, such as thermal conductivity. Figure 9. SEM images of thermal spray powders representing different morphologies. a) Ball mill mixed, agglomerated and sintered Al2O3/SiC; b) spray dried Cr2O3; c) gas atomized Ni20Cr; and d) fused and crushed Al2O3 powder by Praxair.
3. Characterization of HVOF Coatings and their Properties The optimization of the coating microstructures and properties is a challenging task, not to mention the performance of the coating in a particular environment or application as presented in Figure 10. There are a number of influencing factors and interdependencies that influence the intrinsic coating properties as discussed above. These interdependencies are complicated and sometimes even impossible to handle although the systematic process optimization approach described in the previous chapter shows promise as an effective tool for such a task.
Figure 10. A typical optimization route of coating performance by controlling the intrinsic coating properties via optimization of coating microstructure and coating/substrate system interactions.
As described in previous chapters, the typical route for the optimization of coatings performance is via its intrinsic properties that in turn are controlled by the microstructure and coating/substrate— system interactions. For example, in wear applications such coating properties as hardness, elastic modulus and fracture toughness, along with porosity of the coating, are under focus. If the application requires environmental resistance, whether against corrosive media or oxidation, it is important to control the phase structure of the coating as well as its porosity. In both cases, also the system properties, i.e., adhesion of the coating to the substrate and internal stresses must be under control to obtain a coating that has an optimal performance at the particular applications. Before discussing the typical properties and the range of their variance in HVOF coatings we will introduce the most usual methods for characterizing the properties of HVOF coatings. It is important to acknowledge that although most of them are quite generally applied in materials characterization, thermal spray coatings bear many special features that must be taken into account when their properties are evaluated. 3.1. Characterization of Intrinsic Coating Properties: Special Features and Limitations Characterization of coating microstructures and properties are usually carried out by methods developed for microstructural characterization in general. While most of these are directly applicable for HVOF coatings as well, there are certain precautions, which should be considered and taken into account. This concerns especially the preparation of samples for characterization of microstructural features of coatings. 3.1.1. Coating Hardness Hardness of the coating is usually measured either from the cross section or the surface of the coating. Two types of methods are commonly used, i.e., traditional hardness measurement preferably
carried out by Vickers' method or instrumented indentation techniques, where the hardness is evaluated from the load-displacement data. When Vickers hardness is measured from the cross-section of thermal sprayed coating the applied loads should not lead to the formation of cracks. According to standard EN ISO 14923 the thickness of the coating should be at least three times the indentation diagonal d. This is observed to be the absolute minimum thickness required to make reliable measurements and, to be on the safe side, the upper corner of the indentation should be located at least at a distance of one diagonal from the surface of the coating, and the lower corner a similar distance away from the substrate. When Vickers hardness is measured from the top surface of the coating, the thickness is recommended to be ten times the plastic depth of the indentation to avoid any effect from the substrate on the measurement. Therefore, nanoindentation is currently used for a more detailed mechanical property characterization, such as for measuring hardness and elastic modulus of individual phases like carbides or matrix material of the coating or even from single splats [20-22]. 3.1.2. Elastic Modulus There are several methods to deduce the elastic modulus or Young´s modulus of the coating (E). Among them impulse excitation technique (IET), ICP sensor, and instrumented indentation test are most common. IET-standard procedures are described in ASTM E 1876-99 [23] and ENV 843-2 [24]. Elastic modulus can conveniently be determined by instrumented indentation. Values of E are calculated from the load-displacement data usually following the procedure proposed by Oliver and Pharr [25]. Because of the elastic field of the indentation is always larger than the plastic field, the boundary conditions of hardness measurement described above should be considered to be minimum requirements for elastic modulus measurements. Since elastic modulus is very sensitive to coating microstructure and especially to coating porosity and other faults, its value can also be used when estimating the uniformity and quality of the coating in comparison to other thermally sprayed coatings. 3.1.3. Coating Toughness The toughness of a material describes its ability to absorb energy before and during fracture [26]. Because of the brittle nature of many thermal sprayed coatings, fracture mechanics play an important role in evaluation of the usability and performance of the coatings. Fracture mechanical theories, equations and measuring techniques of bulk ceramics, also possessing brittle nature, have been the starting point for studying the fracture behavior in the thermal sprayed coatings. Because of the required sample size in the methods developed for bulk materials, the indentation fracture toughness (IF) technique seems to be the only reasonable and suitable test for thermal sprayed coatings. The basic idea is to apply a large enough load with Vickers diamond pyramid tip to initiate cracks from the diagonal corners of the indentation mark. From the measured average crack length and applied indentation load, the fracture toughness (KIC) can be calculated. It describes the critical stress intensity factor of mode I crack. Indentation fracture toughness KIC can be measured from the cross-section or the surface of thermal sprayed coating. From the surface, one usually gets four corner cracks with the same length, and the boundary conditions described e.g., in JIS R 1668-2005 [27] can be used.
Because the applied loads needed for the initiation of cracks in the fracture toughness measurement are higher than those used in the hardness measurements, one must check that the maximum plastic depth of the indentation is less than one tenth of the coating thickness. When measuring fracture toughness from the cross-section of the coating, the obtained result describes the lamellar cohesion. Cracks in the coatings grow more easily in the direction parallel to the substrate—vertical cracks are usually produced only in the brittle ceramic coatings. The cracks parallel to the substrate will usually initiate and propagate in the lamella boundary. Because of this preferred crack growth direction, the equations and boundary conditions developed for homogenous bulk ceramics do not apply and some modifications are needed. If the cracks grow only in the parallel direction, the average crack length (l) should be calculated by dividing the total crack length (= sum of the cracks) by two, not by four as when measured from the surface. One requirement is that the cracks should initiate near the diagonal corners. If other major cracks than the corner cracks are developed, the measurement is not anymore valid. This prerequisite may lead to difficulties of finding valid measurements, especially if the coating possesses large residual stresses [22]. 3.1.4. Coating Porosity There are a number of different methods that can be used for determination of the coating porosity. Nondestructive methods such as water adsorption, mercury intrusion porosimetry, helium pycnometry, Archimedean method, and other more sophisticated and tedious methods such as small angle neutron scattering (SANS) or x-ray computed microtomography (CMT) [28] have all been employed for quantitative measurement of porosity. Accurate counts of porosity and its distribution can be obtained by the latter two methods, but they both require special instrumentation, which is not generally available for industrial use. The most common practice to analyze the porosity of a coating is to prepare a metallographic cross-section sample of the coating and to determine its porosity from the micrographs taken with light microscope or a scanning electron microscope (SEM) e.g., by image analysis. Porosity within a microstructure can in principle be easily detected by image analysis because of the contrast difference between the dark pores (voids) and the more highly reflective coating material with sufficient resolution. Some reports claim that image analysis can reproducibly detect and measure microstructural features (pores, cracks, etc.) to a 95% confidence level within thermal spray coatings [29]. There is a lot of criticism presented on this procedure since the preparation of the samples has a large influence on the values obtained, i.e., the preparation may result in formation of pores (in brittle coatings such as ceramics) or closure of pores (in ductile metallic coatings) resulting in erroneous values of porosity. In ISO/TC107/WG1, porosity measurement of thermal sprayed ceramic coatings by SEM cross-sectional photography and image analysis has been evaluated by a number of participating members. In a round robin test organized by the working group, five samples having a different ceramic coating were tested by each participant to obtain the respective porosity values. Further examinations have also been conducted by NIMS in Japan about the role of image analysis software, SEM and surface polishing procedures to rationalize the reasons for the observed differences. A preliminary and partial analysis of these results is given in ref. [30], and the final report is published as
an ISO Technical Report TR 26946. The findings can be summarized as follows. The differences in grinding/polishing conditions of the cross-sectional sample have a major influence on the porosity value obtained. Especially the pressure during polishing has an important role. It could be hypothesized that if the grinding pressure in the beginning of the polishing procedure is too low, the defects formed during the specimen cutting and preparation are not removed completely and too high value of porosity is obtained. If the pressure applied in the polishing is too high the sample preparation itself results in pull offs and too high porosity value. Furthermore, it is important to recognize that the imaging mode in SEM has an influence such that secondary electron image (SEI) typically yields lower values of porosity than the backscattered electron image (BEI) because the distinction of the coating matrix and the pores is more difficult in the SEI image, and the fraction of image judged to be a pore as a result has decreased. Based on this hypothesis an optimum pressure can be found, which results in a minimum value of porosity. Whether this is the actual porosity of the coating or higher than the real value depends on the mechanical properties of the particular coating. An additional challenge is that the total percentage of porosity does not always give enough information on the quality of the coating even if determined correctly. A more detailed account of pores and cracks is actually needed if the coating properties and performance are to be judged or predicted in more detail. Therefore it would be advantageous to divide the net porosity into classes, such as coarse and fine globular pores and crack networks according to their process of formation [31]. Coarse pores refer to the size range of 3–10 µm pores, which are formed due to incomplete filling of interstices between impacting particles and previously deposited particles and typically formed, when the impacting particles are not completely molten. Fine pores are approximately 0.1–3 µm in size resulting from incomplete contact between lamellae during coating formation, and are therefore more or less oriented parallel to the substrate surface. The fine cracks approximately 0.01–0.5 µm in thickness result from relaxation of stresses generated within the splats during cooling and are thus oriented typically perpendicular to the lamellar plane. 3.2. Characterization of Coating Substrate System Properties: Challenges and Special Features 3.2.1. Coating Adhesion Adhesion is one of the most important parameters, which influences the performance of thermal spray coatings—substrate system in practical applications of coatings. For many applications the adhesion of the coating is crucial to the performance of the coated part (e.g., [32]]. Since no metallurgical bonds are formed between the rapidly cooling deposit and the substrate, the surface finish and the deposition conditions during the first spray pass are of uttermost importance in obtaining good adhesion. A standard method for the measurement of adhesion of thermal spray coatings is by tensile adhesive test [33]. This test is widely used although according to [34] more than 80 other methods are reported for the measurement of coating adhesion. However, in case of porous ceramic coatings tensile adhesion testing has an inherent problem of being prone to penetration of the adhesive used for gluing the tensile test holder through the coating. This may result in too high a value of adhesion in the test. Therefore, other types of tests have been proposed for the measurement of adhesion of thermal spray
ceramic coatings. Two of these are currently used or studied as an alternative for the tensile test, i.e., shear test and scratch test. Shear test developed in the frame of the EU-CRAFT-project "Shear Test for Thermally Sprayed Coatings" presents the main advantage of being possibly used in real time, i.e., during the production process [34]. The small size of the substrate specimens allows them to be prepared in advance in large quantities, and no limitation of porosity or adhesive strength of the adhesive occurs. Therefore the shear test is more relevant to represent the real stress state acting on the mechanical parts during service. The main disadvantages are the samples characteristics (coating should be thicker than 150 µm) and the need of special equipment to perform the test. Scratch test, which is widely used for testing adhesion of thin films to substrate, is with modifications currently considered also for determining the thermal spray coating adhesion. ISO TC 107 WG 1 is carrying out an international round robin test to study the feasibility of this test for the determination of the coating adhesion of ceramic thermal spray coatings. Preliminary results of this round robin test will be available by the end of 2011. 3.2.2. Evaluation of Internal Stresses An important coating-substrate system property is the residual stress state of the coating after spraying. There are only few methods that can be used to measure the residual stresses of thermally sprayed coatings. The generally applied method for measuring the residual stresses in metallic materials is by XRD using standard d vs. sin2 Ψ XRD techniques (see e.g., [35]]. In order to apply this method for the determination of residual stresses of thermally sprayed coating one needs to know the so-called X-ray elastic constants (XEC). XEC can be calculated using techniques based on the mechanical loading of the samples. However, the experimental behavior of the thermally sprayed coatings shows that the calculation of XEC is unreliable. Considering the characteristics of dense material to which the X-ray diffraction is sensitive, the use of XEC values calculated for the same phase of the bulk material can, according to [36], be used for the determination of stresses in the coatings with an engineering accuracy. When internal stresses are measured during spraying using the so called In-situ Coating Property (ICP) sensor, it is possible to adjust the residual stresses to a large extent during spray by controlling the deposition parameters. In this way, the various stages of stress build-up can be monitored and the various stress contributions can be evaluated separately. The ICP sensor can also be used to extract in-plane elastic modulus of the coatings deposited. It is based on laser sensing of deflections in a strip during thermal spraying which is converted to sample curvature. A simultaneous measurement of temperature is achieved via multiple thermocouples. Elastic modulus and CTE of the coating can be calculated from the coating-substrate composite curvature change due to thermal mismatch [37]. 3.2.3. Evaluation of Wear Resistance Wear resistance of thermally sprayed coatings is of high interest for many applications. In general, wear resistance of a coating in a particular environment is a system property influenced by the coating and substrate material and in particular the type of wear environment. Therefore, it is impossible to quantify the wear resistance of the coating accurately without knowing these factors. However, for
particular types of wear environments there are tests, which give relative performance of different coatings quite accurately. One of the most used wear tests for thermally sprayed coating is the rubber wheel abrasion test (e.g., ASTM G-65), which is meant for testing material's resistance against abrasive type of wear. These tests are also extensively used for a wider screening of coatings, since the possible problems in coating microstructure (not so easily observed e.g., by metallographic means) are often manifested in the results of the abrasion test. Other tests exist for other types of wear situations, such as tests for adhesive wear (e.g., pin-on-disc types of test) and tests for erosive conditions (various modifications exists, e.g., slurry test depicted in standard ASTM G75-95 [38]). 3.2.4. Evaluation of Wet Corrosion Resistance Corrosion resistance of thermally sprayed coating is always a system property. This is influenced first of all by the corrosive environment in question, but also by the coating properties (composition, phase structure and microstructure including the cracks and the pores) and the coating-substrate-environment interactions. It is very rarely possible to produce fully liquid or gas impenetrable coatings even by sealing the coatings afterwards. Therefore, it is not only the corrosion resistance of the coating, but of the substrate-coating system, which should be considered in each particular application where corrosion is a factor. Measurement of the corrosion resistance of a coating-substrate system is typically carried out by immersion tests in actual conditions or by accelerated immersion tests in the laboratory. These tests in combination with metallographic and analytical studies help to identify the corroding parts of the system, whether this is corrosion of coating in general, selective corrosion of some specific phase of the coating, or corrosion of substrate via cracks or open porosity of the coating finally leading to coating detachment. Electrochemical measurements may also be used to evaluate the response of coating⎯substrate system to corrosive environments. Typical measurement may include the determination of the free corrosion potential and the polarization behavior of the system. If the environment is selected such that the electrolyte causes corrosion only in the substrate, the corrosion current may yield information on the through porosity of the coating as well as on the possible passivation system while the pores of the coating are filled with corrosion products from the substrate. 4. Typical Properties of HVOF Coatings Coatings prepared by various HVOF techniques have properties typically different from those produced by other thermal spray methods. As discussed in the previous chapter this results mainly from the characteristics of the HVOF process and in particular the combination of particle velocities and temperatures. Therefore, it is important to recognize that nominally similar coating compositions may have a wide variance in properties depending on the details of the processing. On the other hand, this also implies that properties of the coatings can be adjusted according to demands of the application at least to some extent.
4.1. Wear Resistant HVOF Coatings Wear control is of uttermost importance for many applications of thermally sprayed coatings. These applications include various moving parts such as rotating rolls and axels e.g., for printing equipment, paper and pulp machinery, etc. Among different thermal spray methods high velocity oxy fuel (HVOF) spraying has proven to be especially suitable for deposition of carbide and metallic coatings because of relatively low flame temperature and supersonic particle velocities [16]. Under certain restrictions it can also be used to produce high quality ceramic coatings for wear protection. 4.1.1. Wear Resistant Cermets Typical wear resistant coatings are based on cermet, i.e., metal-ceramic composites, predominantly combining various mixtures of metal matrix including cobalt (Co), chromium (Cr) and nickel (Ni), and tungsten carbide (WC) or chromium carbide (Cr3C2). The most common combinations—WC-12 wt.% Co or WC-17 wt.% Co—are widely used in applications where high wear resistance is required. Theoretically the compositions correspond to 20% and 27% of cobalt in volume, but may slightly vary depending on spraying conditions and decomposition of WC during spraying. For WC-Co-based material it is well known that during flight sprayed particles melt to different extents depending on their size, density and dwell times. Molten Co dissolves the WC grains whereas carbon loss occurs by diffusion through the liquid followed by reaction with the oxygen from the surroundings. There can be large amounts of carbon and tungsten dissolved in the matrix metal, especially in the outer regions of sprayed particles. During cooling, Co-rich liquid becomes supersaturated resulting from the formation of W2C and other mixed carbides. High cooling rates can even be responsible for the formation of amorphous/nanocrystalline matrix phase. During cooling, precipitation of mixed carbides like eta-carbide [(Co6W6)C] phase may occur in the Co-rich material. All of these effects are most visible on the outer core of the particles. In the small size particles, the whole particle can be influenced by decarburization [39]. If cooling is fast enough, the matrix will stay amorphous and supersaturated of W and C. When the coating is heat-treated afterwards, precipitation of eta-carbide starts at temperatures above 600 °C resulting in marked increase of hardness and reduction of residual stresses in the coating [22,40]. In oxidizing atmospheres or at temperatures above approximately 450°C the resistance of Co-WC is not adequate, and alloying of cobalt binder e.g., with chromium or use of other type of cermet coatings such as Cr3C2-25 wt.% NiCr are frequently employed to protect against wear at such elevated temperatures [41]. However, in comparison to WC-Co coatings Cr3C2-NiCr coatings are less wear resistant in many cases. Likewise to WC powders Cr3C2 containing powders are susceptible to a range of decomposition reactions during thermal spraying and require careful optimization of the spraying process in order to obtain desired coating properties. This has prompted efforts to look for other type of cermet for high temperature applications. TiC and TiB2 are potentially attractive alternatives to Cr3C2 for use in high temperature wear resistant cermet applications since it exhibits a high hardness, low density and good oxidation resistance. Wear properties of TiB2-containing cermet coatings have been addressed e.g., in refs. [42,43]. HVOF spraying of Ni(Cr)-65 wt.% TiB2 and Fe(Cr)-70 wt.% TiB2 powders resulted in TiB2-containing coatings that were found to perform better in abrasive wear with
alumina than conventional Cr3C2-NiCr deposits. Coatings having composition of Ni(Cr)-65 wt.% TiB2, Ni(Cr)-40 wt.% TiB2, and Ni(Cr)-40 wt.% TiB2 with 5 at.% excess boron in order to promote matrix amorphization have also been studied [42]. The size of the TiB2 particles within the cermet was found to depend critically on the initial composition; large particles were favored by low binder fractions and the presence of the excess boron. The presence of the larger boride particles was concluded to impart the wear resistance of these coatings in abrasion by alumina or silica abrades [43]. Other cermets studied for high temperature erosion include e.g., WC-CoCr, TiC-CoCr, NbC-CoCr [7]. In a study of the erosion-corrosion resistance of these coatings, Wang [44] noticed that peak wastage occurred at intermediate carbide contents at both shallow and steep impact angles for all of the HVOF carbide-cermet coatings tested. At shallow impact angles, this peak occurred on the side of lower carbide contents, while at steep impact angles the peak occurred on the side of higher carbide contents. At both shallow and steep impact angles, wastage in erosion-corrosion test decreased with decreasing carbide size of homogeneous distribution in the HVOF carbide-metal cermet coatings. It was concluded that the erosion-corrosion behavior of carbide/metal cermet coatings and the dependence of mass loss on carbide content are related to the morphology of the coatings and characteristics of erodent particles. Also Hawthorne et al. [45] noted that coating composition and microstructural integrity are the main factors determining the relative erosion resistance of the cermet coatings. They also noted that the WC-10Co-4Cr matrix coating was more resistant to erosion–corrosion damage in aqueous slurry testing than was the WC-12Co cermet coating. Similarly WC-10Co-5Cr coating has been found in simulative laboratory test to be a potential candidate for coating of hydro turbine components by Mann and Arya [46]. At low erosive conditions the erosion-corrosion resistance has been found to increase when increasing Cr-content from 5 to 8.5 wt.% [47]. An interesting development in the corrosion resistant HVOF coatings is being made with the amorphous coatings. Amorphous coatings with a composition of Fe48Cr15Mo14C15B6Y2 have been prepared by means of high velocity oxygen fuel (HVOF) thermal spraying under different conditions by Zhou et al. [48]. These coatings present dense layered structure and low porosity with some fraction of nanocrystals. The coatings are spontaneously passivated with wide passive region and low passive current density in chloride containing acidic solutions exhibiting excellent ability to resist localized corrosion. 4.1.2. Wear Resistant Ceramic Coatings by HVOF HVOF spraying is applied mainly to cermet and metallic coatings because of the limited melting power of most of the HVOF spraying guns and systems. However, due to the higher kinetic energy, shorter dwell time of particles in the flame, and lower flame temperature compared to the plasma spray, HVOF offers an interesting combination to produce dense coatings with controlled phase transformations [49]. For high quality coatings particle melting state and possible phase transformations during particle flight in the thermal spray flame as well as coating build up mechanism including splat interface and stress stages must be controlled. Despite some limitations there are several reports on successful depositions of ceramic coatings by HVOF spraying techniques (e.g., [7,15,49-51]).
In order to produce high quality ceramic coatings by HVOF, the spraying system should have a high enough melting power to melt the powder particles during the short flight. It has been shown that the particle temperature and the melting state control the deposit efficiency and the build-up rate while the flattening behavior is dominated by particle kinetic energy [15]. The powders used for spraying must have a narrow size distribution and their average size should be somewhat smaller than for powders generally used for HVOF spraying. Selection of fuel gas is of high importance and the necessity of finding correct temperature-velocity combination is a must for successful deposition of high quality ceramic coatings. The coating density and mechanical properties are strongly affected by particle velocity when complete melting is achieved. The particle state in the case of HVOF is very sensitive to the standoff distance and is found to be an influential parameter controlling microstructure and properties. It has been noted that in HVOF the interpass interfaces play a dominant role in thermal, electrical and tribological properties [16]. 4.1.3. Comparison of APS and HVOF Wear Resistant Coatings It has been quite generally recognized that the wear resistance properties of HVOF coatings are superior to their APS counterparts. Li et al. [41] have compared the impact wear resistance of Cr3C2-25%NiCr coatings prepared by APS- and HVOF- spraying. They found that the wear resistance of Cr3C2-25%NiCr coatings under different impact conditions increases in the order of APS-Ar/H2, APS-Ar/He and HVOF spraying. The HVOF sprayed Cr3C2-25%NiCr coatings showed the best impact wear resistance due to the denser structure and fewer defects since the wear mechanisms of Cr3C2-25%NiCr coatings under impact are influenced by the cohesive defects such as stratification, porosity and microcracks in the lamella, and therefore control of these factors has a large impact on the wear resistance of the coatings. Similar findings have been made by the present authors on HVOF sprayed ceramic coatings. Although only a few HVOF spraying guns exist on the market that are suitable for depositing ceramic coatings, the coating properties obtained by the HVOF techniques have shown quite amazing improvements in comparison to coatings deposited by APS [52]. HVOF sprayed coatings show clearly improved density and less pores and cracks than the APS sprayed as depicted in Figure 11. The abrasion wear resistance of the coatings as measured in a standardized rubber wheel abrasion test is improved more than tenfold when the coating is made by HVOF spraying. The difference is more than 15 times with the alumina and chromia coatings where the spray parameters have been optimized. The HVOF zirconia coatings perform more than 20 times better than the corresponding APS coatings. It must be noted though that the reference value for comparison is for Thermal Barrier Coating (TBC), where maximum density is not aimed. However, the obtained results show that HVOF spraying of ceramics can be an effective method to produce dense, well-adhered ceramic coatings with good environmental protection capability. This can be attributed mainly to the lower porosity and improved cohesion of the ceramic coating structure when produced by HVOF techniques.
Figure 11. Comparison of abrasive wear resistance of plasma sprayed and HVOF sprayed oxide ceramic coating coatings: yttria-stabilized zirconia (YSZ), aluminia (Al2O3), and chromia (Cr2O3). Compiled based on [52].
These findings were later confirmed by Bolelli et al. [53], who compared Al2O3 and Cr2O3 coatings deposited onto steel substrates by high velocity oxygen-fuel (HVOF) flame spraying using H2 as fuel gas, and by conventional atmospheric plasma spraying (APS). In this study it was recognized that HVOF-sprayed coatings exhibited lower porosity and smaller average pore area than the APS ones. The HVOF-sprayed coatings possessed higher Vickers micro hardness, higher indentation fracture toughness and higher elastic modulus than the APS ones. During ball-on-disk tests against SiC, various wear mechanisms were observed. At room temperature and at low normal load, all of the coatings developed stable tribofilms under mild wear regime (
Report "HVOF coatings.pdf"
Share & Embed "HVOF coatings.pdf"


Hilary Holland, Linda Hutton, Tony Mascia, Rick Riccardo, Jackson D. Kane, Bernie Casey, Buck Henry, Candy Clark, Rip Torn,... Good. 1976 Run time: 140. Ships Fast! Satisfaction Guaranteed!
Hilary Holland, Linda Hutton, Tony Mascia, Rick Riccardo, Jackson D. Kane, Bernie Casey, Buck Henry, Candy Clark, Rip Torn,... Good. 1976 Run time: 139. Connecting viewers with great movies since 1972. All used discs are inspected and guaranteed. Used discs may not include digital copies. Customer service is our top priority!
Rick Riccardo, Rip Torn, Candy Clark, Buck Henry, Bernie Casey, Jackson D. Kane, Tony Mascia, Linda Hutton, Hilary Holland,... Good. 1976 Run time: 139. Connecting viewers with great movies since 1972. All used discs are inspected and guaranteed. Used discs may not include digital copies. Customer service is our top priority!
Acceptable. EX-LIBRARY DVD ONLY COME IN PLAIN CASE NO ART WORK DVD ONLY EX-LIBRARY SHIPPED WITH DELIVERY CONFIRMATION SHIPPED FROM OREGON Used-Acceptable.
Fine. 013131578799 Ships with outer slipcover, as pictured. This item is guaranteed to play perfectly, with all original artwork and materials.
Great sellar would use them again. Thanks for having them.
PLOT: An alien comes to Earth to get water for his desert-like home world. Some memory flashes indicated his preparation was based on views of Earth life from 100 years ago meaning his planet is nearby, and, he is unprepared for what those years have meant to our society. He parlays his advanced scientific technologies into big bucks which he eventually spends to have a return vessel built. Along the way to that point is the interesting journey he takes of self discovery. Being an alien, he begins as a true individual but as time passes and he is made aware that he won't get back to his family because of the nature of space travel, he becomes a member of this society, and the costs he pays in membership dues are examined.
RETURN ON INVESTMENT: 8.5 of 10; As we follow him through thirty or so years of his development, the other characters also develop (except for the driver who is static until...). The sets are well done. The animations and graphics, where applied, help the story. The cosmetics of Bowie there and here and the aging done on the other characters is exceptional (except for one bit in a liqour store which could have been left on the cutting room floor). The excentricity of the costumes help to impress the difference of his species from ours.
ADDED NOTES: A friend reflected that even Bowie will not claim this as one of his better efforts, but I disagree. For the scope of the story being told this film gets most of the important parts done right.


text:
Q: Using range operator gives error predefined type 'System.range' is not defined or imported I discovered the range and index feature which was (apparently) released with c# 8 ([1..4] and [^2]) back in 2019 and I tried using them, but Visual Studio is giving me following errors in the editor:
CS0518: The predefined Typ "System.Range" is not defined or imported
CS0518: The predefined Typ "System.Index" is not defined or imported

(Note: I translated the errors as good as I can, the original errors are:
CS0518: Der vordefinierte Typ "System.Range" ist nicht definiert oder importiert
CS0518: Der vordefinierte Typ "System.Index" ist nicht definiert oder importiert

)
My Code
using System;

namespace TestApp
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] myArray = {0, 1, 2, 3, 4};
            Console.WriteLine(myArray[1..3].ToString());
        }
    }
}

I changed my Visual Studio LangVersion in the .csproj to <LangVersion>8.0</LangVersion>
dotnet --info in cmd gives me following output:
.NET SDK (gemäß "global.json"):
 Version:   6.0.100-preview.4.21255.9
 Commit:    950e4949a7

Laufzeitumgebung:
 OS Name:     Windows
 OS Version:  10.0.18363
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\6.0.100-preview.4.21255.9\

Host (useful for support):
  Version: 6.0.0-preview.4.21253.7
  Commit:  bfd6048a60

.NET SDKs installed:
  5.0.200 [C:\Program Files\dotnet\sdk]
  5.0.300 [C:\Program Files\dotnet\sdk]
  6.0.100-preview.4.21255.9 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-preview.4.21253.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-preview.4.21253.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.0-preview.4.21254.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download

Im using Visual Studio Community 2019 16.10.0

redpajama_set_name: RedPajamaStackExchange


ad notam is a celebrated inventor, pioneer, and leader in the LED Mirror TV industry. The product lines are the integration of the ad notam LED behind a glass or mirror surface.
Eclusive design TV, mirror TV, bathroom TV, for hospitality and residential high end markets.
Bowers & Wilkins makes the world's most advanced home cinema and hi-fi speakers, including Abbey Road's reference system.
Barco Residential brings the very pinnacle of image and sound technology to the high-end home-entertainment environment.
Control4 manufactures a complete line of affordable wired and wireless home automation products.
Our unique range of products at Future Automation allows such elements to be integrated within the fabric of a room like never before, making them as unobtrusive, effective and as easy to operate as possible.
Integra designs and creates A/V components that set higher standards for system integration, upgrade capability and multi-zone expansion.
JBL Synthesis systems combine the most advanced signal processors, equalizers, amplifiers and loudspeakers to create the most realistic listening experience possible in rooms of any size.
KNX is a standardized (EN 50090, ISO/IEC 14543), OSI-based network communications protocol for intelligent buildings.
Leaf is a market leading manufacturer of audio and video switching and distribution systems.
The Mark Levinson brand has become synonymous with extraordinary levels of audio performance and has a reputation in high-end audio design like no other.
Strong partnerships with artisans and designers among the most important in the world ( Ron Arad , Marta Gatti ... ) propose the right combination of high acoustic fidelity and formal beauty.
At NuVo Technologies, we focus just as much energy on our products' value and ease of use as we do on their quality, design, energy efficiency and engineering, striving for the highest levels in all aspects.
Revel designs and produces innovative, no-compromise loudspeakers that expand the art of home sound reproduction.
Setting new standards for the industry, our advanced products include the patented ClearPix2™ acoustically transparent screen.


Four women from the small southern Ohio town of Chillicothe have turned up dead since May, 2014. Two other women are missing.
All of the dead women worked as escorts and are believed to have known each other, prompting the community to fear a serial killer who targets prostitutes is on the loose.
Investigators are looking to see if there is a connection between Neal Falls and Chillicothe.
Serial killer's daughter joins hunt for Chillicothe killer, on Huffingtonpost.com.
As women keep washing up dead, Ohio town fears a serial killer is on the loose, on WashingtonPost.com.
Chillicothe police look for link between W. Va. shooting, dead Ohio women, on USAToday.com.
A woman was found dead, hanging from a fence, in Chillicothe, Ohio. A suspect is in custody. Authorities do not believe the case is related to the four dead and two missing women from the same town.


For a limited time we are offering 10% off plumbing services, call today!
**Offer does not include Drain Cleaning or any Emergency or Trip Charges.
When it comes to residential plumbers in Eagan, there is really only one clear choice, and that is Do It Right Plumbing, Sewer, & Drain Service. We have all of your home's plumbing needs covered. Our friendly and attentive staff will cater to your every need and listen to your requests. We also provide residential plumbing services in Minneapolis, so no matter where you live in the Twin Cities, one of our trained staff members will be happy to come to your home to take care of your plumbing repairs.
If you have drain clearing needs, we have the resources and know-how to get your drains flowing as if they were brand new. Having your drains in top working order will improve the overall effectiveness of your complete plumbing system and help prevent future issues. Needing a drain repair may seem like a small problem, but it could be a sign of greater problems to come. That is why it is very important to have these fixed as soon as they are noticed. Our team of trained professionals will gladly provide this and other drain services.
If you have water standing in your sink or bathtub for too long, then you most likely need a drain clearing service. If your kitchen sink is having draining issues, you might need garbage disposal repair. Removing any build up will help water drain better and will lead to a more efficient plumbing system, whether in the bathroom or the kitchen.
Do It Right Plumbing is one of the best in the area when it comes to water heater repair. Keeping your water heater in good working order will improve your home's energy consumption and, as a result, save you money. If your water heater needs leak repair or just isn't functioning properly, give us a call to schedule water heater repair.
With several years of experience in sewer cleaning, we will be able to provide unparalleled service in this area. Having a properly functioning sewer system is of the utmost importance, and Do It Right Plumbing will be there to deliver. Our drain services are among the best in the industry. Having poor drainage will lead to unnecessary frustration and most likely cause more issues in your plumbing.
Do It Right Plumbing has all of your plumbing needs covered, from toilet repair to sink repair and so much more. Give us a call today to let us know how we can help!


My passion for Italy inspired me to live here.
My discoveries inspired me to share.
Pack your dreams in your suitcase and bring them to us.
Several times a year, a small group of food and wine lovers gather together on a journey that we hope is life-changing. Sounds a little silly maybe, but when you get down and deep with the locals this can happen! Sometimes it's a private group of friends or family, and sometimes it is a group of strangers soon to become friends The tours are offered in different parts of Italy, the South of France Spain and Portugal. The landscape of each region, typical and special foods, small production wines, the cast of special characters whom you'll meet, and beautiful architecture affect me, in the same way, I hope to affect you, perhaps even to change and re-invigorate you, and give you a new perspective about life. To approach it in a new and different way….The European Way!
It's not easy to describe a feeling. Translating to paper is almost impossible, so we invite you to come and see for yourself. We bird-dog until we find the best of everything. Beautiful architecture, delicious wine, memorable restaurants, cozy accommodations, unforgettable guides, and the most authentic experiences. We have a dream that you will somehow be transformed. And when you come home, you may still be the same, and yes, you may go back to the same old job, but something in your mind will have changed. And trust me….that changes everything.
Send us an email to whyman1@aol.com to get information and itineraries!
Join us soon for one of our adventures, and ask us how, when, and where for 2018 and 2019 bookings.
Dates will be added for 2020 as we plan them.
Thank You for your recognition on Trip Advisor!


Check- In - All athletes must check in at North Durham CrossFit between 7AM and 745AM EST.
Where Am I Going? – Check-in occurs at North Durham CrossFit (124 Latta Rd., Durham, NC 27712).
Parking – There's parking available at our location!
Come Prepared – You'll need to provide a valid ID to complete check-in. You'll also want to bring water bottle, any snacks/food you may want, and other gear you'll need for the Throwdown.
No Take-Backs – Life happens—we totally get that. But please be aware that if you cannot participate in the weekend's events, we cannot offer a refund for any reason. In the event of incliment weather, we will update atheltes according.
Durham's most supportive CrossFit gym specializing in group instruction, personal training, and more!


The foreign exchange rates used for the purposes of any If you wish to access our foreign exchange services or find out the foreign the UK's deposit guarantee.
Feb 03, 2017Yearly Average Currency Exchange Rates Translating foreign currency into U. S. dollars. You must express the amounts you report on your U. S. tax return in U. Important economic data announcements can have significant effects on foreign exchange rates. This is evidenced by the fact that immediately preceding and following. Foreign currency exchange available at optimal rates at UAE Exchange. Exchange your money and obtain travellers cheques at best rates possible. View foreign exchange rates and use our currency exchange rate calculator for more than 30 foreign currencies.
Reuters. co. uk for the latest currency news, currency exchange rates and an easy to use currency converter and currency calculator. Online currency exchange with Travelex means you get great rates with home delivery or bureau pickup. Or get travel money via our Supercard or Cash Passport. Currency exchange rates View todays foreign currency exchange rates below and sign up to our newsletter to stay uptodate on the latest currency news, happy hours.
Make fast and secure international money transfers with OFX. Register today and save with better exchange rates than the big banks. Moneycorp are an awardwinning foreign exchange specialist with over 35 years experience in currency exchange. You could save money online with moneycorp now.
Get the best deal on your travel money by comparing all the latest offers on foreign currency and exchange rates. See all of our commission free currency offers Historical Rates Exchange Rates API Corporate FX Transfers FX News Support Currency I have: Currency I want: Interbank Download. Compare Holiday Money is a fast, free travel money comparison site helping you find the best currency exchange rates available online today.
LIVE RATES AND GRAPHS Exchange rates are moving all the time and can change in the space of a week, day or even an hour. Check the rates in the tables below. This Free Currency Exchange Rates Calculator helps you convert US Dollar to Euro from any amount.
Moneycorp are an awardwinning foreign exchange specialist with over 35 years experience in currency exchange. You could save money online with moneycorp now.
LIVE RATES AND GRAPHS Exchange rates are moving all the time and can change in the space of a week, day or even an hour. Check the rates in the tables below.


text:
RUSS HONS: Photo Gallery — University Of North Dakota Vs. University Of Nebraska-Omaha
Posted on March 10, 2019 by Russell Hons
The University of North Dakota defeated the University of Nebraska-Omaha 5-4 in overtime Saturday night in Ralph Engelstad Arena to complete a National Collegiate Hockey Conference weekend sweep of Mavericks. The Fighting Hawks (18-15-2 overall, 12-11-1 NCHC) won Friday night's game 2-1. UNO dropped to 9-22-3 overall and 5-17-2 in the NCHC. Jordan Kawaguchi scored two goals, including the game-winner in Saturday night's game. Also scoring for UND were Nick Jones, Cole Smith and Gavin Hain. UNO goal scorers were Tyler Weiss, Zach Jordan, Tristen Keck and Nate Knoepke. UND goalie Peter Thome stopped 17 shots, while UNO's Evan Weniger had 41 saves. UND travels to Denver next weekend to play the Pioneers in a best-of-three NCHC first round playoff series. (Check out more photos from Russ Hons here.)
March 9, 2019 NCAA men's ice hockey game between the University of Nebraska-Omaha Mavericks and the University of North Dakota Fighting Hawks at Ralph Engelstad Arena in Grand Forks, ND. Photo by Russell Hons
national collegiate hockey conferencenchcralph engelstad arenarussell honsrussell hons photographyundund men's hockeyunheralded.fishuniversity of nebraska-omaha men's hockeyUniversity of North Dakotauniversity of north dakota men's hockeyuno men's hockey
JIM FUGLIE: View From The Prairie — What Does A State Treasurer Do, Anyway?
RON SCHALOW: Holier Than Thou, Part One

redpajama_set_name: RedPajamaCommonCrawl


Excellent, informative post. Thanks for taking the time!
Steve, a great post. As a point of clarity, I believe that Roger has distanced himself from Slottech and that Morris Clark is responsible for the day to day Slottech operations.
Right, and Roger trades as RMS. So far he has made gears and axle condoms. Both are highly rated.
None of these high performance chassis builders has a proper online store on their website, which is hampering every aspect of their business unnecessarily.
Viper have a decent looking site, and a webstore. They are also active on social media, youtube etc.
if the 'Hobby chassis' side of HO is to survive, it will probably be because of those guys.
(Unless Roger P starts producing a chassis).
The situation in Great Britain is unique as clubs can, and do, build large temporary tracks for their races. That trend hasn't caught on in the US.
Which is a huge shame. If HO racing is to survive the continuing passing of old racers stateside, it needs to be more visible and accessible, and offer something people cannot have at home, in my opinion.
Last edited by NicoRosberg.; 01-15-2019, 01:00 AM.
Indeed, Viper/VSR have been doing well, and their web store keeps improving. JAG Hobbies also has a great online store, and their TR-3/DR-1 inline chassis are total game-changers for still using bodies meant for the aging pancakes. If more slot car companies embraced online commerce, and actually made their websites useful for the average consumer, they might see an improvement in sales.
I also think back to the 80s-90s, when Saturday morning cartoons had commercials for TYCO race sets. The internet has largely replaced that type of advertising nowadays, so the bigger we can make the presence of "slot cars" on the internet in general, the more people all over the world will see them and start to take notice. Exposure is our biggest issue at present--there are not many people really doing a good job of publicizing anything they're doing, and nowhere to post it but Facebook (a closed system) or this site (broken for years). Other hobby forum sites are just as arcane and unusable as this one.
This site could have (and should have) been leading the world in slot car news, reviews, etc. It could have been THE place to gather for slot car fans of all stripes all over the world, but instead it's the same few old guys arguing about nothing because no one else is even able to log in to post anything interesting. The downfall of this site is directly tied to the downfall of slot cars in general in the last 5 years. Nobody can post what they're doing, nobody can post questions, nobody talks, nothing is happening, so people take one look at the apparent "lack of activity" and never come back, unless it's to cherry-pick the vast amount of reference info.


Owners of a wholesale warehouse in Dunstable were left reeling after £250,000 worth of clothing was stolen in a major heist last week.
Nationwide Auctions Ltd based at Woodside Industrial Estate, was burgled at around 6.30pm on Wednesday, January 6 – just minutes after workers left the warehouse.
Director David McLean said the firm discovered the theft after returning to the building on Monday and checking CCTV.
He said: "The majority of stuff taken was high street clothing. It was about 1,000 Kardashian dresses, Bhs babywear and a large quantity of Bhs clothing.
"We still have a lot of stock here but it was certainly a good chunk of the value.
Mr McLean said Bedfordshire Police was now stepping up its efforts to find those responsible but an officer was not assigned to the case until two days after it was reported.
Mr McLean said: "The initial response has been quite slow, considering it took two days to get through to CID.
Mr McLean added that the remaining stock continues to be sold wholesale from the warehouse, following their usual practice.
A Beds Police spokesman insisted the force was taking the theft seriously.
He said: "We're just trying to establish whether there is CCTV footage in any of the surrounding buildings.
"I can also confirm that the case has been assigned to an officer today (Wednesday, January 13).
Anyone with information contact Beds Police on 101.


A Senate panel today revived a plan to replace ISTEP with an "off-the-shelf" test by dismantling another bill central to Gov. Mike Pence's legislative agenda.
Sweeping amendments made to a bill that initially intended to overhaul the state's school intervention process have taken away much of its punch.


text:
Posted on April 5, 2022 by morrowcountysentinel
Fire department seeks new levy on May 3
By Rhonda Bletner - [email protected]
Corrected figures and costs 4/6/2022
MOUNT GILEAD — The Mount Gilead Fire Department is asking voters to approve a new fire levy on the May 3 primary ballot. The .25% income tax will allow the department to continue its services undeterred.
The last levy voters passed was a 1.5 mill for staffing in 2005 and it was renewed in 2012. Of course, the cost of doing business has increased since 2012, and the levy is critical to maintaining the department at its current level of operation, if not providing for improvements.
"I'm actually deficit spending at the moment," Chief Chad Swank said, "and I've been doing some staffing reductions already."
"And $5 gas, I never saw that coming," he added. "I don't have any way to replace capital. My fleet is aging. We have a new tanker coming, but I only paid 5% of the bill. Just to give you an idea on inflation: that truck, when it went out last month to do the final on the factory, they asked, 'If we ordered that truck today, what would it cost? They said add $100,000."
He noted the increase in firefighting gear as well. A set of turnout gear: pants, coat, just two items is approximately $3,000 for one fireman's set. And the gear has a lifespan: it is supposed to be replaced every 10 years—those are unfunded mandates for the department.
The fire department's fleet of vehicles is aging and they operate out of what was the city's original 1852 waterworks building with a vehicle bay added in 1974. The layout does not allow the department to grow and there are some needed updates.
The Mount Gilead department made 437 runs in 2021, a 35% increase in call volume since 2016. Approximately 30 runs a year are structure fires.
Chief Swank is the only full time firefighter. The department has 34 volunteer and part time firefighters and paramedic personnel. The department provides paramedic services with five department members serving trained paramedics, three more firefighters will begin paramedic school in May. The department has 15 EMTs. And training costs are increasing as well.
"We're the only fire department in the county, right now, that can function as a paramedic," Swank said. "A paramedic can provide advanced life support and an EMT is basic life support. When it comes to IVs and medications for the patient, we can do that."
He continued, "A dual-trained person is a better fit than a single trained because they see the bigger picture. Being an EMT makes you a better fireman; like when you're on an extraction. For a car crash—we're not just there because a car crashed. We're there for the people inside the car. The majority of our calls outside of fire are people-related. The county has limited resources: there aren't that many fire departments; there aren't that many squads.
"Why not be a resource for the county. We use the CARES Act money to do what we're doing, so it didn't cost us any money. The CARES Act was to help with COVID-19 and that's how we were able to purchase cardiac monitors, drugs, bags, and actually helped a couple of guys go to paramedic school."
This is an income tax not a property tax. The cost at a $36,945 income will cost approx. $92 annually, which is the average income for the Village of Mount Gilead.
"I've cut as much as I can; I've reduced staffing. My discretionary spending between maintenance and my supplies is $60,000 for 34 guys. That's everything from turnout gear to toilet paper, and maintenance," he said. Swank added he's only used 85% of his payroll budget to try to stretch funds the last two years.
"I'm very passionate about what I do," said Swank." Whatever I do, I always try to leave it better than I found it. My predecessors laid a great foundation for me to try to do that. And when I say I have the best department, I really mean it. That's truly how I feel; they're my family."
https://www.morrowcountysentinel.com/wp-content/uploads/sites/29/2022/04/web1_IMG-8761-1.jpgRhonda Bletner | Morrow County Sentinel
By Rhonda Bletner
Hi! A visitor to our site felt the following article might be of interest to you: Fire department seeks new levy on May 3. Here is a link to that story: https://www.morrowcountysentinel.com/news/42990/fire-department-seeks-new-levy-on-may-3


Living Room : Beautiful Bathroom Wallpaper Black Pendant Light Mirror Over The Toilet Cabinet A Designer's Imaginarium: How Does Designer Home Look Like Sitting Ideas Dining Decor Latest Table Designs ~ Acdflorida Inc.
Published at Friday, February 16th, 2018 - 13:09:44 PM. Living Room. By Della Friedrich.


text:
Q: Does Eshrah ap Niht from Gaunt's Ghosts speak Middle English? On planet Gereon Ghosts meet "partisans" that speak language other than Low Gothic. After a bit of concentration, Gaunt recalls that he was learning something similar in scholam

Gaunt's brow creased as he concentrated. He could almost see old Boniface now, smell the
  musty scholam room, Vaynom Blenner at the desk beside Gaunt, doodling cross-eyed eldar on the
  cover of his slate.
  "No looking at your vocab primer now, Scholar Gaunt," Boniface called. "Parse the verb form
  now, young man! Begin! 'Ayeam yclept… Heyth yclept…' Come on, now! Blenner? What's that
  you're drawing, boy? Show the class!"
  "Histye, soule," Gaunt said, more deliberately now. "Ayeam yclept Gaunt of Tanith His Worlde.
  Preyathee, hwat yclepted esthow?"
  "Cynulff ayeam yclept," the partisan replied. "Of Geryun His Worlde." His voice dripped like
  glue in the sweaty air.
  "Histye, Cynulff," said Gaunt. "Biddye hallow, andso of sed hallow yitt meanye goode rest."

There are more examples later on, i.e:

"Preyathee, soule," Gaunt asked, tapping the bow. "Hwat yclept beyit?"
  "Reynbow, beyit," Eszrah replied. He was delicately picking meat from a spindly frog-bone with
  his small, white teeth.
  "Reyn-bow, seythee?" Gaunt repeated.
  Eszrah nodded. "Thissen brande sowithe yitt we shalle reyn yron dartes thereon the heddes of
  otheren kinde, who gan harm makeyit on us."
  A rain-bow, to rain quarrels on the heads of the enemy. Gaunt smiled. He'd seen that. Emperor
  bless the nightwalkers.

While of course this might be completely fictional language, it does sound look similar to Middle English. Could someone with more linguistic skills confirm or deny it?
Edit: TvTropes describe it as an example of "Ye Olde Butcherede Englishe":

Used in Traitor General to represent the old, proto-Low Gothic language used by the Nihtganes. Although there, it was a combination of normal Butcherede Englishe, random "misspellings" that make everything look like it's weirdly pronounced and some words that Abnett just plain made up.

So I guess question is answered.

A: Your friendly amateur linguistic anthropologist is here to answer simply....ish.
Alright, so first things first. Let's define Middle English.

Thanks google! To be more precise (or at least more verbose) Middle English is the culmination of Norman French and Olde English. This happened because William the great big ol' Conqueror better known as the Duke of Normandy and William I of England (all these titles belonged to the same dude) invaded the island of Britain from his home base back in northern France. The English were stubborn, the French were arrogant and no one wanted to give up their root language...so old French and old English had a verbal baby and voila, Middle English was born.
So this.

Became this:

You can see the Germanic influence of the Anglo-Saxon root language shift to take on some of the romantic parlance of the French. Good luck picking out what the Old English is saying (It's an excerpt of Beowulf, there are lots of spark notes) but the middle English is a little easier to understand as our common modern English comes from this. Excess letters have been dropped, the thorn (the symbol for the 'th' sound) disappears, the 'eth' also goes away, but the big thing to note is declensions (which help know what the word is ding in the sentence you are reading, provided you can read the sentence).
So what separates Middle English from modern? Well, there are four big things.

*

*Spelling (No one really agreed on spelling yet...)

*Latin (rather than German)

*Punctuation (The punctuation mark hadn't been invented yet)

*Lacking in the Shakespearean "thee/thine/thou"

Alright, so let's take a piece of the literature that you used.

"Parse the verb form now, young man! Begin! 'Ayeam yclept… Heyth yclept…"

Neat.
Okay, written language is broken down into two parts, grammar and punctuation. Let's break down the punctuation first.
Alrighty. So we can see that while the speaking is talking in their regular language, everything is normal grammatically. There is familiar punctuation and most notably an exclamation point. Yay!
Moving on, the most noted punctuation is that of the ellipsis, which is ancient Greek in origin, and this fits Middle English, but originally meant the omission of a word (or even a phrase). I do not think that is what it means here.
However! It was, according to Cambridge, originally used 1588 edition of the Roman dramatist Terence's play Andria, this means that the punctuation of your piece is not Middle English.
But what about the grammar, the words? Arguably the more important part of this question. The speaker is asking the student to parse the verb, or break down the verb in the sentence.
I CAN say that "yclept" IS a Middle English word meaning to 'call or name', the student begins to do just that, call and name.
Thissen means you or yourself
Preyathee is a bastardization of 'prithee' (though that's not Middle English, just archaic)
While I wont go and break down and define each and every word (I do have a day job) I can say that there are plenty of words here that are found in Middle English, but not all.
What I think is that this particular writer did use Middle English as inspiration, but did not stick to the language in its entirety.