A study on microstructure evolution and mechanical properties of PVD TiAlN/TiAlCrSiN deposited on Re doped Ti(C,N)-based cermets

Abstract

Re doped TiCN-based cermet substrates were prepared and coated with bilayer TiAlN/TiAlCrSiN to investigate the influencing mechanism of Re on structural evolution and mechanical performance of substrates and coatings. The results showed the grain size of hard phase particles decreased with the increase of Re content. The existence form of Re in cermets was characterized by high resolution transmission electron microscope (HRTEM) and energy spectrum analysis (EDS). Conclusions could be drawn that Re existed in solid solution and free state. Meanwhile, fcc-Co expanded to form hcp-Co structure, and twins was detected. According the generalized stacking fault energy (GSFE) curves calculated by first principles, it showed that the dissolution of Re into Co reduced the stable SFE γsf, unstable twinning SFE γut and twinning SFE γtsf of fccCo, promoting the formation of hcp-Co and twins. Cermets containing 0 wt% Re exhibited the strong preferred textures of {001}. However, the preferred orientation was obviously weakened in cermets containing 5 wt% Re, which indicated Re added into ceramic metals could restrain the preferred growth of {001} textures. The nanoindentation curves showed coatings on substrates with 5 wt% Re had the highest nanohardness value of 31.258GPa, which attributed to Re diffusion into TiAlCrSiN/TiAlN and refinement of core-rim grains. However, it was found that coatings on cermets with 5 wt% Re showed the lowest bonding strength due to the huge lattice structural difference between fcc-TiAlCrSiN and hcp-co substrate. In conclusion, bilayer TiAlCrSiN/TiAlN coatings deposited on TiCN-based cermets with 3 wt% Re possessed the best comprehensive performance, combining the various factors such as nanohardness, surface roughness, bonding strength and wear resistance.