Effect of Oxygen Scavenging by Yttrium Addition on Fatigue Properties of MIM Ti-6Al-4V Using HDH-Powder

Abstract

For this study, tensile test specimens and rectangular shaped fatigue test specimens were produced by MIM, using a mixture of hydride de-hydride (HDH) Ti-6Al-4V powder with high oxygen content (4200 µg/g) and 20% gas atomized Ti-6Al-4V powder with 1600 µg/g oxygen. Due to the oxygen-scavenging effect, the addition of 0.5 wt.-% yttrium powder with a particle size < 45 µm to the powder mixture led to a strong increase of ductility from 4.5% to 13.5%. The results of the fatigue tests, conducted by 4-point bending at room temperature with a load ratio of 0.2 show a totally different behaviour. While the ductility is increasing, the fatigue endurance limit drops from 420 MPa for the pure Ti-6Al-4V down to 350 MPa by the addition of yttrium. This decrease of fatigue strength is caused by the large irregular shaped Y2O3 filled pore clusters, which are forming during sintering.