LCF life improvement of biomedical Ti–13Nb–13Zr alloy through surface nanostructuring

Abstract

This investigation deals with the role of ultrasonic shot peening (USSP) on modification of microstructure of surface region and low cycle fatigue (LCF) behavior of the Ti–13Nb–13Zr alloy at room temperature. USSP was carried out with stainless steel shots of 3 mm diameter for 2, 4 and 6 min, at ultrasonic frequency of 20 kHz. There was no phase change due to USSP, and the coarse-grained microstructure was refined to nanoscale. The surface hardness of the USSP treated sample was increased by 15%–20% and gradually decreased towards interior. LCF life of all the specimens subjected to USSP treatment for varying durations of 2–6 min increased considerably and the optimum enhancement was in the specimen USSP treated for 4 min of which the LCF life at total strain amplitude of ±0.70% was enhanced nearly by three times. The increase in the LCF life of the specimens USSP treated for 4 min was nearly comparable over the total strain amplitudes from ±0.55% to ±0.90%. Fatigue crack initiation in the un-treated samples was found from the surface whereas it was from subsurface in the USSP treated samples. The improvement in LCF life from the USSP treatment may be attributed to surface nanostructuring and the compressive residual stresses associated with the USSP affected region.