Abstract
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.
Up to date, the intention to make cost-effective titanium parts by PM is a challenge. One of the main issues is the presence of interstitials. Oxygen modifies the mechanical properties of titanium alloys by decreasing its ductility when a certain amount is exceeded. However, very little is known about the impact of oxygen on the fatigue properties of MIM titanium. Ti-Al-7Nb is an attractive alloy to use in powder metallurgy (PM) due to its biocompatibility and mechanical properties sufficient for load bearing medical implants. This study will contribute to the field by studying the effect of oxygen on the fatigue behaviour of MIM Ti-6Al-7Nb. Thus, it will be possible to evaluate which measures are necessary to take in order to control oxygen presence. On the other hand, another issue in PM titanium is the impact of residual porosity on mechanical behaviour. Under cyclic forces, pores act as crack initiation sites. This study will present the impact of residual porosity on fatigue properties of MIM Ti-6Al-7Nb. Then, it will be possible to have an idea of the efforts that are necessary to make in order to control residual porosity with respect to cost efficiency.
