Surface hardening of age-hardenable Cu–Ti dilute alloys by plasma nitriding

A plasma-nitriding procedure was applied to enhance the surface hardness and wear toughness of practical age-hardenable Cu–4 mol% Ti alloy. Plasma nitriding at 1073 K and 1173 K leads to the formation of TiN surface layers with thicknesses of 300 nm and 350 nm, respectively, above Cu3Ti3O layers with thicknesses of approximately 700 nm and 2200 nm. In other words, the thicknesses of the surface compound layers increase with plasma nitriding temperature, which also increases the surface hardening. In particular, the hard TiN and Cu3Ti3O on the surface contribute to hardening of the surface to Vickers hardness of around 10 GPa, which is much greater than the hardness of the substrate alloy of approximately 1.6 GPa. The surface layers also modified the wear resistance significantly. Thus, an optimized plasma-nitriding procedure is a promising surface modification technique for age-hardenable Cu–Ti dilute alloys.