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

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-4mol% Ti alloy were carburized in a methane gas glow discharge plasma at temperatures of 1073K and 1123K for 6h. The plasma-carburization treatment resulted in the formation of two layers of crystalline compounds on the surfaces of the Cu-4mol% Ti alloy specimens: (i) a TiC top layer containing 11at.% oxygen and (ii) a Cu₃Ti₃O sublayer. The thicknesses of the TiC and Cu₃Ti₃O layers were approximately 100nm and 900nm, respectively, in the case of the specimen plasma-carburized at 1073K. 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 4mol% 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 1123K 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.