Microstructure and wear resistance of CVD TiN-coated and induction surface hardened steels

CVD hard coated (e.g. TiN) steels need a post coating heat treatment, to restore their mechanical properties. This can successfully be done by induction surface hardening instead of through hardening. The coatings withstand induction surface hardening without macroscopic damage. The load support of the steel substrates, the residual stress state and the distortion can be positively influenced. In this work, the coating microstructures and hardnesses as well as the coating/substrate wear resistances of the combined CVD TiN-coated+induction surface hardened steels AISI 4140, 52100, A2 and D2 were investigated. The CVD TiN-coating microstructures were investigated by cross-section TEM (XTEM) analysis. They looked very similar in the as-deposited and in the induction surface hardened state. By ultramicro-hardness measurements no significant difference in CVD TiN-coating hardnesses between as-deposited state and induction surface hardened state was detected. In pin-on-disc wear tests against Al2O3-balls, induction surface hardening of the most coating/substrate compounds increased the wear resistance significantly. After induction surface hardening of the compound CVD TiN/D2 in air, the wear resistance slightly decreased. Due to inductive heating of D2 for longer periods in air, these samples exhibited thin oxide layers at the CVD TiN-coating surface.