The effects of oxygen on the fatigue behaviour of MIM Ti-6Al-7Nb alloy

The control of interstitial elements is an important aspect in titanium alloys processing. Oxygen changes the mechanical behaviour of titanium alloys. Nevertheless, much uncertainty still exists about the influence of oxygen on dynamic properties of titanium alloys. This study investigates the effect of oxygen in fatigue behaviour of Ti-6Al-7Nb processed by metal injection moulding (MIM) and the influence of residual porosity in fatigue properties. Four-point bending fatigue specimens with varying contents of oxygen were produced by MIM. Some of the specimens were subjected to hot isostatic pressing (HIP) after MIM process. The specimens show a sharp drop in ductility when oxygen content increases from 0.15 to 0.45 wt.%. However, high cycle four-point bending fatigue results reveal just a slight decrease in the fatigue properties. Finally, the impact of residual porosity and oxygen on crack initiation and propagation was evaluated by the observation of microstructures and fractured surfaces