Effect of the holding time on the mechanical properties of gradient-hardened pure titanium

Abstract The vacuum rapid nitriding process is a surface modification technique that is used mainly to increase the wear resistance and surface hardness of titanium and its alloys. Using this simple process, the surface of titanium can be hardened within a relatively short time by a continuous process. The holding times were controlled to improve the titanium surface and mechanical properties. The hardened layers consisted of continuous layers with high hardness and deep thickness, which differed from the conventional discrete over-layer coating. The diffusion layers were composed of gradient-hardened inner layers of Ti2N, TiNx, and Ti[N]. The thickness and hardness increased with increasing holding time, but the tensile strength decreased until 1 h at 800 °C. The tensile strength was influenced by the relative combination of the softening effect by the high temperature and the hardening effect by the hardened area, as a function of the holding times.