Influence of alpha-case layer on the low cycle fatigue properties of Ti-6Al-2Sn-4Zr-2Mo alloy

Strain-controlled low cycle fatigue properties of Ti-6Al-2Sn-4Zr-2Mo with different thickness of alpha-case layers were investigated. Results show that at strain amplitudes 0.3% and 0.4%, the fatigue life of the alloy is reduced for the specimens with alpha-case layer compared to the ones without any alpha-case. It was noted that with a 2 μm thick alpha-case layer the low cycle fatigue life is reduced about 50% at the higher strain amplitude. The degrading effect of the alpha-case layer on fatigue life increased with increasing thickness. The alpha-case layer at the surface is enriched with oxygen making the surface harder and brittle, which results in easier crack initiation and thus decrease in fatigue life.