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.