Microstructural evolution and surface integrity of ultrasonic surface rolling in Ti6Al4V alloy

Abstract Ultrasonic surface rolling technology is a new mechanical surface treatment technology that can improve the surface integrity, increase the amplitude and depth of the residual compressive stress layer and improve the fatigue property of metal materials. In this paper, the effect of ultrasonic rolling on the surface layer's microstructure and properties of Ti6Al4V alloys is investigated. The microstructure, surface roughness, surface topography, microhardness and residual stress were used to characterise the surface-modified layer. Specimens treated by ultrasonic surface rolling obtained the smallest surface roughness (0.231 μm) and largest plastic deformation depth (304.38 μm), simultaneously, under sixteen processing stage numbers. The rule of surface compressive residual stress distribution had a similar tendency to the law of surface microhardness distribution. Furthermore, the grain size of the strengthened surface layer decreased, the texture type changed and the Schmidt factor increased compared with the matrix. The increase of microhardness and residual stress is due to grain refinement and dislocation strengthening.