Design and fabrication of HfC, SiC/HfC and HfC-SiC/HfC interlayers for improving the adhesion between diamond coatings and cemented carbides

Three types of interlayers named Hafnium carbide (HfC) single-interlayer, SiC/HfC double-interlayer, and HfC-SiC/HfC double-interlayer were designed and fabricated on cemented carbide (WC-Co) to seek out the optimal coating structure for well-adhered diamond coatings. The phase composition, microstructure, adhesion and effectiveness in diamond coating adhesion of these interlayers were investigated and compared. The results showed that the HfC single-interlayer was a HfC-dominant nanostructured layer composed of HfC, Si, and SiC. The SiC/HfC and the HfC-SiC/HfC double-interlayers had an inner layer with a structure similar to the HfC single-interlayer. However, the former had a SiC-dominant outer layer, while the latter had a gradient HfC-SiC mixed outer layer. The double-interlayers possessed better adhesion and higher hardness than those of the HfC single-interlayer. This could be attributed to the introduction of SiC in the outer layer, which endowed the substrates with significantly enhanced microhardness and decreased TEC, closer to those of diamond coatings. After the subsequent CVD process, dense nanocrystalline diamond coatings with a thickness of similar to 5.0 mu m were deposited onto the double-interlayered substrates. The coatings possessed good adhesion. Between them, the diamond coating on the HfC-SiC/HfC double-interlayered substrate had better adhesion (HF1 similar to HF2) and lower residual stress (-1.7 GPa) than those of the coating on the SiC/HfC double-interlayered substrate. These experimental results provide a feasible way for fabrication of well-adhered diamond coating on WC-Co tools. (C) 2019 Elsevier B.V. All rights reserved.