Research on influence of deep cryogenic treatment and ultrasonic rolling on improving surface integrity of Ti6Al4V alloy

The synergistic effects of deep cryogenic treatment (DCT) and the ultrasonic surface rolling process (USRP) on surface microstructure and properties of Ti6Al4V alloy were investigated. Surface roughness, surface topography, nano-hardness and residual stress were used to characterize the surface-modified layer. A plastic deformation layer with a deformation depth of 7.80 μm was formed in the DCT + USRP specimen. The content of the β phase in the surface of the DCT + USRP specimen was 3% less than that of USRP, making the surface hardness of the DCT + USRP specimen higher than that of USRP. Further, the surface roughness of the DCT + USRP specimen was lower. Especially, tension-tension fatigue tests showed that the fatigue life of the specimen after DCT + USRP treatment increased by 61.9% relative to the original specimen. The synergy mechanisms of surface quality, residual stress, microstructure and work hardening were analyzed in the DCT + USRP specimen.