Mechanical and thermal stability of mechanically induced near-surface nanostructures

Mechanical surface treatments, such as deep rolling, shot peening, hammering, etc., can significantly improve the fatigue behaviour of metallic materials owing to near-surface nanocrystallisation, strain hardening and compressive residual stresses. In this paper, we investigate the stability of near-surface microstructures of deep rolled austenitic stainless steel AISI 304 and turbine blade alloy Ti-6Al-4V during high temperature fatigue (up to 600 deg. C) by transmission electron microscopy and X-ray diffraction. The investigated nanocrystalline regions are stable during short time annealing and unstable during long time annealing at 600 deg. C. Isothermal fatigue in the low cycle fatigue regime at high stress amplitudes does not alter the nanocrystalline region up to 600 deg. C