Effects of Deep Rolling on the Fatigue Behavior of Ti-6Al-4V at Ambient and Elevated Temperatures

摘要

Mechanical surface treatments such as deep rolling (DR), shot peening and laser-shock peening (LSP) can significantly improve fatigue behavior of highly-stressed metallic components. DR is particularly attractive as it generates deep, near-surface compressive residual stresses and work hardening, while retaining a relatively smooth surface finish. This study seeks to examine the effect of DR on the fatigue behavior of the turbine-engine alloy, Ti-6Al-4V, with emphasis on the thermo-mechanical stability of the residual stress case and near-surface microstructures. Based on cyclic deformation and stress/life behavior, coupled with X-ray diffraction and microstructural observations, it was found that DR and LSP can be very effective in improving fatigue resistance even at high temperatures, despite the almost complete relaxation of the near-surface residual stresses. This implies that, in addition to residual stresses, the near-surface ultrafine microstructures play a critical role in fatigue lifetime enhancement. In light of this, the stability of the nanostructured layer with increasing temperature is examined using an in situ transmission electron microscopy study.