An in situ transmission electron microscopy study of the thermalstability of near-surface microstructures induced by deep rolling andlaser-shock peening

Mechanical surface treatments are known to be effective at improving the fatigue resistance of metallic alloys at elevated temperatures ({approx}550-600 C), even though the near-surface compressive residual stress fields have been annealed out. We have investigated the thermal stability of near-surface microstructures induced by deep rolling and laser-shock peening in an austentic stainless steel (AISI 304) and a titanium alloy (Ti-6Al-4V) using in situ hot-stage transmission electron microscopy. It is found that the improvements in fatigue resistance at elevated temperature are related to the high-temperature stability of the work-hardened near-surface microstructure in each case.