Titanium case-hardening

Titanium alloys have some very useful properties, including a high strength-to-weight ratio and excellent corrosion resistance, but exhibit very poor tribological characteristics. The latter can be improved significantly by oxygen diffusion to form a hard surface layer. If this is superimposed with a "rutile" oxide layer, a surface capable of acting as the wear face of a high-performance gear is produced. To date, it has only been possible to confer an appropriate oxygen diffusion layer by oxidation followed by diffusion in a vacuum. A third step is required to produce the surface oxide. The work reported in this paper was aimed at imparting the duplex surface in a single treatment, without recourse to expensive vacuum technology. It was found that the required layer could be attained, in a highly-controllable manner by using mixtures of argon and oxygen at atmospheric pressure.