The effect of shot peening on the microstructure and properties of a near-alpha titanium alloy following high temperature exposure

The effect of shot peening on the microstructure, oxygen ingress and high-cycle fatigue properties of a near-α titanium alloy is investigated. Microstructural characterization of shot-peened material is performed through light microscopy, scanning electron microscopy and electron backscatter diffraction. Oxygen uptake during thermal exposure is analytically determined using secondary ion mass spectrometry. Shot peening leads to an increase in subsurface oxygen content following thermal exposure in air and the increased levels of oxygen content are accompanied by the precipitation of silicides along (or in close proximity to) the mechanical twin boundaries and in regions of high dislocation density. Preliminary fatigue data obtained through a staircase loading method show that a decrease in room temperature fatigue performance occurs in shot-peened material following prolonged thermal exposure in air at 650 °C. The observed phenomena suggest that shot peening may be deleterious to the mechanical integrity of titanium alloy components that are subject to high temperature exposure in oxidizing environments.