Sub-volt high-speed silicon MOSCAP microring modulator driven by high-mobility conductive oxide.pdf
Article https://doi.org/10.1038/s41467-024-45732-y Manufacturing of high strength and high conductivity copper with laser powder bed fusion Yingang Liu 1,11, Jingqi Zhang 1,11, Ranming Niu 2,3 , Mohamad Bayat4, Ying Zhou5, Yu Yin 1, Qiyang Tan 1, Shiyang Liu1, Jesper Henri Hattel4, Miaoquan Li6, Xiaoxu Huang 7,8, Julie Cairney 2,3, Yi-Sheng Chen 2,3, Mark Easton 9, Christopher Hutchinson 10 & Ming-Xing Zhang 1 Additive manufacturing (AM), known as 3D printing, enables rapid fabrication of geometrically complex copper (Cu) components for electrical conduction and heat management applications. However, pure Cu or Cu alloys produced by 3D printing often suffer from either low strength or low conductivity at room and elevated temperatures. Here, we demonstrate a design strategy for 3D printing of high strength, high conductivity Cu by uniformly dispersing a minor portion of lanthanum hexaboride (LaB6) nanoparticles in pure Cu through laser powder bed fusion (L-PBF). We show that trace additions of LaB6 to pure Cu results in an improved L-PBF processability, an enhanced strength, an improved thermal stability, all whilst maintaining a high conductivity. The presented strategy could expand the applicability of 3D printed Cu compo- nents to more demanding conditions where high strength, high conductivity and thermal stability are required. The ability to fabricate fully dense, highly conductive, and mechani- cally robust copper (Cu) components is essential for electrical con- duction and heat management applications. Additive manufacturing (AM)1–11, or 3D printing, offers unprecedented opportunities for pro- ducing Cu components with complex geometry and tailored perfor- mance which are inaccessible by conventional manufacturing processes. However, pure Cu has a high reﬂectivity for infrared lasers and hence pure Cu components fabricated by the most commonly used laser AM machines often suffers from high porosity12–14, leading to poor mechanical and conductivity properties. Although AM using green lasers or electron beams enables the fabrication of pure Cu components with relatively high density15–17, the intrinsically low strength of pure Cu at room temperature and its inability to resist thermal softening hinders the applications of additively manufactured Cu components in demanding mechanical loading and high tem- perature conditions. Alloying Cu with elements such as Cr and Zr improves the laser absorptivity and strengthens the metal12,18,19, but this approach degrades the conductivity due to their high solid solubility in Cu20. An alternative approach is to add immiscible foreign particles to reinforce the Cu while maintaining the high conductivity21,22. In practice, it has proven exceedingly difﬁcult to achieve a sufﬁciently well dispersed Received: 12 May 2023 Accepted: 1 February 2024 Check for updates 1School of Mechanical and Mining Engineering, The University of Queensland, St. Lucia, QLD, Australia. 2Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW, Australia. 3School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW, Australia. 4Department of Mechanical Engineering, Technical University of Denmark, Lyngby, Denmark. 5State IJR Center of Aerospace Design and Additive Manufacturing, Northwestern Polytechnical University, Xi’an, China. 6School of Materials Science and Engineering, Northwestern Polytechnical University, Xi’an, China. 7International Joint Laboratory for Light Alloys (Ministry of Education), College of Materials Science and Engineering, Chongqing University, Chongqing, China. 8Shenyang National Laboratory for Materials Science, Chongqing University, Chongqing, China. 9Centre for Additive Manufacturing, School of Engineering, RMIT University, Melbourne, VIC, Australia. 10Department of Materials Science and Engineering, Monash University, Clayton, VIC, Australia. 11These authors contributed equally: Yingang Liu, Jingqi Zhang. e-mail: ranming.niu@sydney.edu.au; christopher.hutchinson@monash.edu; mingxing.zhang@uq.edu.au Nature Communications|        (2024) 15:1283  1 1234567890():,; 1234567890():,; and uniform distribution of externally added nanoparticles to obtain a signiﬁcant strengthening increment, without particle agglomeration degrading the ductility and damage tolerance21,23. The challenge of simultaneously obtaining high strength and high conductivity in 3D printed Cu parts limits its applications where a good balance of mechanical and physical properties is required. Here, we present a design strategy that enables laser AM of Cu parts with high density and high performance through the addition of minute amounts of lanthanum hexaboride (LaB6) nanoparticles. Our LaB6-doped Cu exhibits a yield strength of 347 ± 2 MPa (which is 3.7 times higher than pure Cu), together with an elongation to failure of 22.8 ± 1.2%, electrical conductivity of 98.4% IACS (International Annealed Copper Standard), thermal conductivity of 387 W m−1 K−1 and the ability to resist softening at 1050 °C. Additionally, we further demonstrate the applicability of our design strategy to geometrically complex components. Results Design strategy The key feature of our design strategy is that we select additives, of which the constituent elements have negligible solubility in solid Cu (and therefore have negligible detrimental effects on the con- ductivity), but will dissolve in the melt pools during laser melting (therefore not too high melting point) and subsequently re-precipitate with a very ﬁne dispersion during solidiﬁcation (and hence provide excellent strengthening). Criteria are as follows: (1) the constituent elements of the particles should have negligible solid solubility in Cu in order to minimize their detrimental inﬂuence on the conductivity19,20,24,25 and to maximize the re- precipitation of nanoparticles; (2) particles should have a relatively low melting point26, to maximize the chance of dissolution in the melt pool and to minimise coar- sening of the re-precipitated nanoparticles during solidiﬁca- tion; and (3) particles should possess a low wetting angle with liquid Cu27, minimizing nanoparticle clustering in the liquid Cu. Microstructural characterization Following this design strategy, we identiﬁed LaB6 as a suitable additive candidate. LaB6 met the criteria due to its lower melting point, minimal solid solubility of constituent elements in Cu, and low wetting angle with molten Cu (see Supplementary Note 1). The initial LaB6 particles that were added to the pure Cu powder feedstock exhibited an irre- gular morphology and sizes up to 300 nm (Supplementary Fig. 1). The laser reﬂectivity test clearly demonstrates that pure Cu powder exhi- bits exceptionally high laser reﬂectivity within the infrared laser range (Fig. 1b), speciﬁcally at a wavelength of 1060 nm, as used by the laser powder bed fusion (L-PBF) system in our study. The reﬂectivity was noticeably decreased upon the incorporation of 1.0 weight per cent (wt%) LaB6 nanoparticles. This reduction can be attributed to two factors: the inherently low laser reﬂectivity of LaB6 and the introduc- tion of LaB6 nanoparticles, which enhance the surface roughness of pure Cu particles, facilitating multiple reﬂections within the pow- der bed. We then produced pure Cu parts using L-PBF and compared them with parts produced from Cu with 1 wt% LaB6 nanoparticles (hereafter denoted as 1.0LaB6-Cu) (see Methods). Despite the rela- tively high energy density being used for laser melting, the pure Cu parts produced by L-PBF shows discontinuous scanning tracks with a rough surface (Fig. 1a2), indicating a balling effect resulting from the high reﬂectivity of infrared lasers12,13,28. This leads to lack-of- fusion defects when successive layers are fused29. Micro-computed tomography (Micro-CT) shows pores with a diameter range of 10- 130 μm (Supplementary Fig. 2a, b). In contrast, the 1.0LaB6-Cu part demonstrates well-deﬁned scanning tracks and no obvious defects (Fig. 1a3), which were attributed to the increased laser absorptivity due to the LaB6 addition (Fig. 1b). Micro-CT and electron back- scatter diffraction (EBSD) conﬁrm the much higher density (Sup- plementary Fig. 2e, f) and relatively large grains of the 1.0LaB6-Cu as compared with pure Cu (Fig. 1a3). With an improvement in laser processability, highly dense 1.0LaB6-Cu parts can be fabricated effectively over a broader laser power range, spanning 325 W to 400 W (Supplementary Fig. 3). a BD Surface morphology Elemental mapping Electron backscatter diffraction map Pure Cu particle LaB6-doped  Cu particle LaB6 Laser beam b a1 a2 a3 Fig. 1 | Laser AM of Cu and LaB6-doped Cu. a A schematic diagram of laser AM process (a1), and top surface morphology, cross-sectional EDS elemental mapping and EBSD inverse pole ﬁgure map of the L-PBF fabricated pure Cu (a2) and 1.0LaB6- Cu (a3). The pores are visible in pure Cu and high density can be achieved after addition of LaB6. b Laser reﬂectivity of pure Cu, LaB6 and 1.0 wt% LaB6 nanoparticles doped Cu powder feedstock at various laser wavelengths. After introducing 1.0 wt% LaB6 nanoparticles, the powder mixture shows lower laser reﬂectivity compared with pure Cu powder, indicating the increased laser absorptivity. SD Scanning direction, BD Building direction. Source data are pro- vided as a Source Data ﬁle. Article https://doi.org/10.1038/s41467-024-45732-y Nature Communications|        (2024) 15:1283  2 and the nanoparticle agglomeration was observed in the 2.0LaB6-Cu due to the excessive addition (Supplementary Fig. 7d), leading to a reduction in the strength and ductility. After the feedstock prepara- tion, the powder mixture was characterized in a SEM (Hitachi SU3500) equipped with EDS. LaB6 nanoparticles electrostatically adhere to almost all Cu particles with uniform distribution (Supplementary Fig. 1). As a comparison to the experiment, high purity (99.9%) TiB2 nanoparticles with an average size of 100 nm were also mixed with pure Cu powder (Supplementary Fig. 13a). Furthermore, micrometre- scaled LaB6 powder with particle size ranging from 1 µm to 10 µm was also employed as the additive and mixed with pure Cu powder to show the microstructure and property response (Supplementary Fig. 7a). The laser reﬂectivity of the as-received powder and powder mixtures was measured using a double-beam UV-Visible-NIR Lambda 1050 Per- kinElmer spectrophotometer equipped with a 150 mm integrating sphere in the 400–2000 nm wavelength range. Pure Cu powder and the powder mixtures were subsequently subjected to laser powder bed fusion (L-PBF) AM in an SLM125HL system and the processing para- meters are listed in Supplementary Table 1. The L-PBF fabricated dog- bone-shaped blocks with gauge length of 10 mm, gauge width of 2.5 mm, and thickness of 40 mm were used for tensile testing54. The chemical compositions of the L-PBF fabricated samples were mea- sured using inductively coupled plasma atomic emission spectroscopy (ICP-AES) for metallic elements and using LECO combustion analysis for non-metallic elements, as listed in Supplementary Table 2. More- over, in order to analyse the microstructure of directly solidiﬁed metal, single-track samples were prepared with the same L-PBF processing parameters as the bulk sample on a pure Cu substrate (Fig. 2e). In addition, the sheet-based gyroid lattice with porosity of 70% and overall dimension of 30 mm (length) × 30 mm (width) × 30 mm (height) was designed to contain 5 × 5 × 5 arrays of unit cells and fab- ricated by L-PBF using both pure Cu and LaB6 nanoparticles doped Cu powder feedstocks for compression tests (Fig. 5a). Heat treatment In order to show the thermal stability of the L-PBF fabricated 1.0LaB6- Cu, annealing treatments were performed at various temperatures ranging from550 °C to 1050 °C for 1 h in a vacuum furnace, followed by furnace cooling at a cooling rate of 5 °C min−1 to ambient temperature. Hardness of heat-treated samples was measured in a LECO Vickers hardness tester at a load of 3 kg and a dwell time of 12 s. Six random positions were tested to obtain the average value for each sample. Microstructure characterization All metallographic samples were ﬁrstly ground using SiC papers fol- lowed by polishing with Struers OP-S suspension and ﬁnally etching with 50 ml HCl, 20 ml Fe3Cl, and 30 ml C2H5OH for 3 s. The micro- structure was examined in a Hitachi SU3500A SEM. Grain size, grain morphology and crystallographic orientation were characterized through electron backscatter diffraction (EBSD) analysis at a scan step size of 1.2 µm in a JEOL JSM-7800F ﬁeld emission SEM and the corre- sponding geometrically necessary dislocation (GND) density was cal- culated. The detailed description of the method used for GND density calculation can be found in ref. 55. Prior to EBSD, surfaces of samples were electropolished in a Struers electrolyte D2. In addition, typical element distributions in the samples were analysed using EDS in the SEM operated at an accelerating voltage of 20 kV. To examine the nanoparticle distribution, the electropolished samples were etched with gallium ions using a focused ion beam (FIB), and SEM images were acquired at a 52° tilt to expose the nanoparticles in a FEI Scios FIB-SEM. Phase analysis of the L-PBF fabricated samples was accomplished using XRD in a Brücker D8 Advance system at a scan rate of 1° min−1 and step size of 0.02° with the diffraction angle 2θ ranging from 20° to 100°. FIB was used to prepare the TEM thin foils. A Hitachi HF5000 TEM, equipped with a probe aberration corrector and symmetrically opposed dual EDS detectors and operated at an acceleration voltage of 200 kV, was used for in-depth characterization of the L-PBF fabricated 1.0LaB6-Cu. The diondo d2 micro-CT system was used to analyse the micropores in the L-PBF fabricated samples. 2D slice image data were acquired through an X-ray source with the voltage of 120 kV and cur- rent of 100 µA. The exposure time was 2000 ms with a spatial solu- tion of 4 μm. Atom probe tomography The nanoscale elemental distribution in the L-PBF fabricated 1.0LaB6-Cu was analysed using APT in a local electrode atom probe CAMECA LEAP 4000X SI, which has a detection rate of 57%. APT matchstick specimens with dimension of 1.0 mm × 1.0 mm × 10 mm were ﬁrst cut from the as- built sample, and then electropolished using alternating current under voltages of 5 V, 3 V and 1 V. The electrolyte was 70% orthophosphoric acid in water, as suggested by ref. 31. The electropolished APT samples were then annular polished using a Thermo Fisher G4 Plasma FIB-SEM. A Xe+ beam with a voltage of 5 kV and a current of 30 pA were used to ﬁnalize the APT sample preparation. The laser APT experiment was conducted under a high vacuum of 2 × 10−11 torr, at a temperature of 50 K, a laser pulse frequency of 200 kHz, and a laser pulse energy of 70 pJ. The APT data was reconstructed using a CAMECA integrated visualization and analysis software (AP Suite version 6.1.0.29). Mechanical property testing The tensile specimens with gauge dimension of 10 mm (length) × 2.5 mm (width) × 2 mm (thickness) were cut from the as-built blocks54. Tensile testing was performed perpendicular to the building direction on an Instron 5584 universal testing machine equipped with an advanced Instron video extensometer at a constant strain rate of 0.001 s−1. Four tensile samples were tested for each L-PBF fabricated part with the same addition and heat treatment conditions, and the average value was used as the testing result. After tensile testing, the fracture surface was examined in an SEM. Uniaxial compression tests of the sheet-based gyroid lattices were conducted along the building direction on the same Instron machine. During compression, the samples were centrally located between two pressure plates at a strain rate of 0.001 s−1 in accordance with standard ISO13314-2011. The compression process was recorded using a video camera at a rate of 50 frames per second. Frames extracted from these videos were then correlated with features in the associated stress-strain data, providing detailed information regarding the failure modes of both pure Cu and LaB6-doped Cu. All lattices were compressed until densiﬁcation. Electrical conductivity testing The resistance of pure Cu and 1.0LaB6-Cu was measured on three samples with dimension of 15 mm (length) × 2 mm (width) × 5 mm (height) using a four-point probe method on a ZEM-3 electric resis- tance measurement system at room temperature. Because the length according to ASTM standard (300 mm) is far beyond the currently available L-PBF machine’s capacity to build, the non-standard length was used56. The volume resistivity can be calculated as follows: ρν = ðA=lÞr ð1Þ where ρv is the volume resistivity (Ω mm2 m−1), A is the cross-sectional area (mm2), l is the gage length (6 mm), and r is the measured resistance (Ω). The volume resistivity was determined to be 0.019527 Ω mm2 m−1 for the L-PBF fabricated pure Cu, and 0.017528 Ω mm2 m−1 for 1.0LaB6-Cu. The electrical conductivity σ can be expressed as follows: σ = 1 ρν = l Ar ð2Þ Article https://doi.org/10.1038/s41467-024-45732-y Nature Communications|        (2024) 15:1283  7 Accordingly, the electrical conductivity was calculated to be 5.121 × 107S m−1 for the pure Cu, and 5.705 × 107S m−1 for 1.0LaB6-Cu. In addition, based on ASTM B193, 100% IACS (International Annealed Copper Standard) is deﬁned as the electrical conductivity corre- sponding to a volume resistivity at 293 K of 0.017241 Ω mm2 m−1. Therefore, it is 88.3% IACS for the L-PBF fabricated pure Cu, and 98.4% IACS for 1.0LaB6-Cu. Thermal conductivity calculation The thermal conductivity of the L-PBF fabricated pure Cu and 1.0LaB6- Cu can be calculated through their electrical conductivity based on the Wiedemann-Franz law57. κ=σ = KL ð3Þ where κ is the thermal conductivity (W m−1 K−1), σ is the electrical con- ductivity (S m−1), K is the absolute temperature (K), and L is a Lorenz constant (W Ω K−2). For the annealed pure Cu with the electrical con- ductivity of 5. 916 × 107S m−1 and thermal conductivity of 401 W m−1 K−1, Lorenz constant can be calculated to be 2.31 × 10−8W Ω K−2. Therefore, the thermal conductivity of the L-PBF fabricated pure Cu and 1.0LaB6-Cu can be estimated to be 347 W m−1 K−1 and 387 W m−1 K−1, respectively. Data availability The experimental data generated in this study have been deposited in Dryad58. Source data are provided with this paper. References 1. DebRoy, T. et al. Additive manufacturing of metallic components – process, structure and properties. Prog. Mater. 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M.B. acknowledge the funding from Independent Research Fund Denmark, DIGI-3D project (Contract number: 0136–00210B). The authors from Northwestern Polytechnical University thank the State Key Laboratory of Solidiﬁcation Processing in NWPU for funding support (Grant number: SKLSP202319). The authors from The University of Queensland thank Australian Micro- scopy & Microanalysis Research Facility at the Centre for Microscopy and Microanalysis (CMM), The University of Queensland for the facilities and technical assistance. The authors are grateful for the scientiﬁc and technical support from the Australian Centre for Microscopy and Microanalysis (ACMM) as well as the Microscopy Australia Node at the University of Sydney. Author contributions Y.L., J.Z., C.H. and M.-X.Z. conceived the concept and designed the experiments. M.-X.Z. supervised the project. Y.L. and J.Z. carried out the main experiments. R.N., J.C. and Y.-S.C. conducted the APT character- ization. M.B. and J.H.H. contributed idea for the research. Y.Z. conducted dataanalysis and lattice experiment. Q.T. and J.Z. prepared TEM samples and conducted the TEM characterization. Y.Y., Y.L. and S.L. prepared EBSD samples and carried out the EBSD characterization. Y.L., J.Z., Y.Z., M.L., X.H., M.E., C.H. and M.-X.Z. wrote the manuscript. All authors contributed to the discussion of the data. Competing interests The authors declare no competing interests. Additional information Supplementary information The online version contains supplementary material available at https://doi.org/10.1038/s41467-024-45732-y. Correspondence and requests for materials should be addressed to Ranming Niu, Christopher Hutchinson or Ming-Xing Zhang. Peer review information Nature Communications thanks Raiyan Seede, Katsuyoshi Kondoh and the other, anonymous, reviewer for their con- tribution to the peer review of this work. A peer review ﬁle is available. 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To view a copy of this licence, visit http://creativecommons.org/ licenses/by/4.0/. © The Author(s) 2024 Article https://doi.org/10.1038/s41467-024-45732-y Nature Communications|        (2024) 15:1283  9
Title: Manufacturing of high strength and high conductivity copper with laser powder bed fusion
Authors: Yingang Liu, Jingqi Zhang, Ranming Niu, Mohamad Bayat, Ying Zhou, Yu Yin, Qiyang Tan, Shiyang Liu, Jesper Henri Hattel, Miaoquan Li, Xiaoxu Huang, Julie Cairney, Yi-Sheng Chen, Mark Easton, Christopher Hutchinson, Ming-Xing Zhang
Publisher: Nature Communications
Date: 2024-02-12 00:00:00
Abstract: Additive manufacturing (AM), known as 3D printing, enables rapid fabrication of geometrically complex copper (Cu) components for electrical conduction and heat management applications. ​ However, pure Cu or Cu alloys produced by 3D printing often suffer from either low strength or low conductivity at room and elevated temperatures. ​ Here, we demonstrate a design strategy for 3D printing of high strength, high conductivity Cu by uniformly dispersing a minor portion of lanthanum hexaboride (LaB6) nanoparticles in pure Cu through laser powder bed fusion (L-PBF). ​ We show that trace additions of LaB6 to pure Cu results in an improved L-PBF processability, an enhanced strength, an improved thermal stability, all whilst maintaining a high conductivity. ​ The presented strategy could expand the applicability of 3D printed Cu components to more demanding conditions where high strength, high conductivity and thermal stability are required. ​ 