Wear-resistant ZrN/Ti functionally graded coating prepared on TA18 alloy by double glow plasma alloying

Despite being an excellent structural material, α-Ti alloy is with low shear deformation resistance, resulting in susceptibility to friction damage during service, and limits its further application. A wear-resistant ZrN/Ti functionally graded coating (FGC) was prepared on TA18 alloy by double glow plasma alloying technique in this paper. The morphology, phase structure, mechanical properties and wear behavior of ZrN/Ti FGCs were studied and analyzed. The results proved that a gradient structure formed in the coating: the topmost layer was ZrN ceramic phase, in the transition layer were ZrN, TiN, and Ti2N phases, and in the inner layer was α-Ti phase. The coating was dense and metallurgically bonded with the substrate. It exhibited better load bearing capacity and fracture toughness. Upon conclusion of wear tests under different loads, only slight damage was observed on the coating. The main wear form of the coating was delamination wear, and the ZrN layer on the topmost surface was not worn through. More specifically, the Zr pre-diffusion treatment was used to increase the content of ZrN in the transition layer, reducing the unfavorable Ti nitride phase formed. Therefore, the stress concentration caused by the difference in elastic modulus between the different phases was relieved. Thus, ZrN/Ti FGC with continuous properties and good wear resistance was successfully synthesized.