First prize deep case hardening of titanium alloys with oxygen

Abstract

In order for such engineering components as bearings and gears to withstand the high Hertzian contact stresses encountered in service, deep case hardening is necessary. Oxygen diffusion (OD) and thermal oxidation (TO) techniques have been successfully applied to the low strength Ti–6Al–4V alloy to develop a deep hardened case and a thin, hard, wear resistant surface layer. These techniques have been used to produce homogeneous, composition controlled, and highly reproducible alloyed surface layers in the Ti–6Al–4V alloy. It was the objective of the present investigation to develop and apply the novel duplex OD–TO surface treatment to the high strength titanium alloy Timet550. The higher strength of Timet550, compared with Ti–6Al–4V, would have the advantage of increasing the bending strength of a component under load. Various oxidation and diffusion treatments were carried out to optimise the OD–TO process and consequently a post-diffusion heat treatment was developed to maximise the depth and hardness of the OD case for Timet550. The surface layers were characterised using XRD, GDS, and SEM, which revealed a rutile surface with an oxygen rich case. The loadbearing capacities of duplex treated Timet550 specimens were evaluated using friction monitored scratch tests and a wheel on block Amsler wear tester. It was found that the OD, heat treated, and TO processed Timet550 specimens had the greatest loadbearing capacity.