The Role of Oxygen in the Fatigue Behaviour of Ti-6Al-7Nb Processed by Metal Injection MouldingThursday (29.09.2016) 10:00 - 10:15 Part of:
Interstitial elements play a critical role in the properties of titanium alloys. Previous studies have demonstrated that interstitials change the microstructure and mechanical properties of titanium alloys reducing drastically their ductility. The aim of this research is to explore the influence of oxygen on the tensile and fatigue properties of Ti-6Al-7Nb. In fact, this would be useful to estimate the level of oxygen that is tolerable in the alloy and thus, design production processes in accordance. In the study, tensile and fatigue specimens were produced by metal injection moulding (MIM) using gas atomized Ti-6Al-7Nb powder. Different interstitial contents (O, N, C) were introduced into the specimens and expressed as “oxygen equivalent” values. Tensile and yield strength values showed a 12% increase when the oxygen equivalent raised from 0.15 to 0.34 wt.%. However, the ductility rapidly deteriorated when 0.46 wt.% was reached. Moreover, the fatigue strength of shot peened MIM Ti-6Al-7Nb specimens was reduced by the presence of interstitials. High cycle 4-point bending fatigue test results showed that the endurance strength at N=107 decreased from 450 MPa to 325 MPa when the oxygen equivalent content increased from 0.18 wt.% to 0.50 wt.%. Finally, the effect of oxygen content on fatigue behaviour was preliminarily examined by the observation of microstructures and fracture surfaces using scanning electron microscopy.