Surface hardening of age-hardenable Cu–Ti alloy by plasma carburization

•Specimens of a commercially used age-hardenable Cu–Ti alloy are plasma carburized.•The resulting changes in their surface hardness and wear toughness are determined.•A TiC surface layer and a Cu3Ti3O sublayer are formed after carburization.•These layers improve the surface hardness and wear toughness significantly.•The thicknesses of the layers increase with the carburization temperature.

Plasma carburization was performed on specimens of a commercially used age-hardenable Cu–Ti alloy, in order to improve its surface hardness and wear toughness. Specimens of a Cu–4 mol% Ti alloy were carburized in a methane gas glow discharge plasma at temperatures of 1073 K and 1123 K for 6 h. The plasma-carburization treatment resulted in the formation of two layers of crystalline compounds on the surfaces of the Cu–4 mol% Ti alloy specimens: (i) a TiC top layer containing 11 at.% oxygen and (ii) a Cu3Ti3O sublayer. The thicknesses of the TiC and Cu3Ti3O layers were approximately 100 nm and 900 nm, respectively, in the case of the specimen plasma-carburized at 1073 K. This led to significant improvements in the surface hardness and wear toughness of the specimen. It was interesting to note that the presence of a carbon-friendly alloying element (Ti) at a concentration of only 4 mol% resulted in the formation of a hard TiC layer, leading to the surface hardening of the Cu-based alloy. Furthermore, plasma carburization at a higher temperature of 1123 K resulted in the formation of thicker layers of hard TiC and Cu3Ti3O, causing a greater degree of surface hardening. Thus, it was demonstrated that plasma carburization is highly suitable for the surface modification of age-hardenable Cu–Ti dilute alloys.