Synthesizing SiC layer on diamond by heat treatment and its effects on density and thermal conductivity of diamond/W composite

In order to improve the thermal conductivity of W composites as plasma-facing materials, the interface bonding and interfacial thermal resistance of the composites are the key issues to be solved. Based on our previous study, although Si coating on diamond surface can improve the interface bonding and thermal conductivity of the composite, there still existed the interfacial reaction between W and diamond, which produced more low thermal conductivity compounds (WC/W ₂C) and added the interfacial thermal resistance of the composites. To further improve the interface bonding and increased the thermal conductivity of diamond/W composites, the Si-coated diamonds were used to prepare the Si-SiC dual layer on diamond via vacuum heat treatment and then to fabricate diamond/W composites (HT-coated diamond/W composite). The effects of temperature and holding time of the heat treatment on coating and its interface bonding with the composites were investigated by scanning electron microscopy, X-ray diffraction and transmission electron microscopy. The results showed that a stable and dense Si-SiC-diamond structure was formed after heat treatment at 1200 °C for 1 h, and the thickness of SiC transition layer was about 20 nm. Thermodynamic analysis demonstrated the reaction rate of SiC increased gradually first and then sharply from 1000 °C to 1400 °C. The integrity of the coating on the diamond surface was strongly impacted by residual compressive stress of the SiC layer, and its value increased with the SiC thickness. The Si-SiC dual layer evidently improved the interface bonding and thermal conductivity of diamond/W composite under the combined influence of reaction diffusion at SiC-W interface, inter-diffusion at W-Si interface, and the orientation relationship at diamond-SiC interface. Theoretical thermal analysis proved that HT-coated diamond/W composite possessing lower interface thermal resistance than that of Si-coated diamond/W composite and raw diamond/W composite achieved higher thermal conductivity of 205 W m ⁻¹ K ⁻¹.