For any application a user must consider a number of factors when choosing a tool material. Such factors including: cost; toughness; wear rate/hardness; ability to process a desired working surface such as a cutting edge; useful lifetime; and inertness to chemical effects with the material to be processed.
An ideal tool material is one which is both hard and tough. These two properties of materials used in wear and tear applications are often presented on two perpendicular axes. Very simply, wear is a measurement of the amount of material removed per unit of operation. Toughness is a measure of a material's resistance to crack propagation.
There is an ongoing desire to provide materials which are harder, tougher, stronger and more wear resistant. There is also an ongoing desire to provide faster, more precise and cleaner production methods which add up to cost efficiency and improved performance. It is an aim of certain embodiments of the present invention to at least partially address some of these needs.
Diamond materials are the materials of choice for many premium performance cutting, drilling, grinding and polishing tools. Diamond materials are used in tooling solutions across a range of industries including a variety of metal, stone and woodworking industries. Examples include aerospace and automotive manufacturing, furniture production, stone quarrying, construction, mining and tunnelling, mineral processing, and the oil and gas industries.
Diamond's hardness properties make it the ultimate material in terms of wear. However, diamond's limited ability to plastically deform under stress at the tool's working temperature leads to more rapid crack propagation in comparison to much tougher materials such as steel.
Previous attempts to improve the durability of diamond have involved either adapting the method of forming the diamond material or treating the diamond material after forming the material. For example, WO 01/79583 teaches a process for improving the durability of a diamond-type tool to increase the impact strength and fracture toughness. The process involves implanting ions into the surface of a diamond-type tool. Ion implantation is a materials engineering process by which ions of a material can be implanted into another solid, thereby changing the physical properties of the solid. Under typical circumstances ions are implanted to a depth in the range 10 nanometers to 1 micrometer. WO 01/79583 teaches ion implantation which penetrates a diamond surface to a depth in the range 0.02 μm to 0.2 μm. Preferred ions include chromium, nickel, ruthenium, tantalum, titanium and yttrium.
U.S. Pat. No. 4,184,079 and GB 1588445 also teach a method for toughening diamond by bombarding the diamond with ions of sufficient energy to penetrate the diamond surface. Various ions are suggested including carbon, nitrogen and hydrogen ions. It is described that the ions form a dislocation network in the diamond crystal lattice thereby inhibiting microcleavage of the diamond. It is further described that the dislocations can be confined to a depth of from 10 nanometers to 1 micrometer below the surface of the diamond crystals in order to form a hard skin on the surface thereof. It is taught that the dose of ions should be quite small, in the range 1016 to 1018 ions cm−2, and have energies in the range 10 keV to 10 MeV, more preferably less than 100 keV so that the species implanted by the bombardment do not have a detrimental effect on the diamond material. As ion bombardment of diamond results in the amorphisation and softening of the surface unless the temperature is held sufficiently high to maintain the crystal structure, it is taught to use a temperature of at least 500° C. during ion bombardment.
GB 1588418 discloses a process for improving the wear characteristics of industrial diamonds. The process comprises implanting ions into the surface of the diamond. Carbon and nitrogen ions are suggested for this purpose.
U.S. Pat. No. 4,012,300 discloses a method of altering the friability of abrasive particles, particularly diamond and cubic boron nitride particles, by subjecting the particles to irradiation. Proton, neutrons and gamma radiation are suggested with neutrons being preferred.
US2006065187 discloses a tough CVD diamond material which is grown in an atmosphere having a nitrogen to methane ratio of about 4% N2/CH4 at about 1050° C.-1200° C. and then annealed.
US2009110626 teaches that nitrogen containing single crystal CVD diamonds treated by a low pressure, high temperature annealing process have a high toughness.
It is an aim of certain embodiments of the present invention to improve the toughness and/or wear resistance of diamond tools. It is a further aim of certain embodiments of the present invention to avoid some of the problems associated with the aforementioned methods.