Evolution and anti-fatigue mechanism of surface characteristics of Ti60 alloy induced by ball burnishing and shot peening during tensile-compression fatigue

To clarify the evolution of surface characteristics of Ti60 alloy induced by ball burnishing and shot peening and their anti-fatigue mechanism during tensile-compression fatigue, room temperature and 450℃ elevated temperature fatigue tests were conducted on burnished and shot peened round bar Ti60 samples. Residual stresses, microhardness, and microstructures were analyzed during fatigue, and the fracture mechanism was investigated through fractography. The results show that the residual stress relaxation rate of the burnished sample is lower than that of the shot peened sample. After fatigue, the strengthened samples showed reduced microhardness and fewer low angle grain boundaries. The strengthened samples are both subsurface initiation, and the depth of initiation of the burnished sample is greater than that of the shot peened sample. The fatigue initiation mode at room temperature and 450℃ high temperature is quasi cleavage. No fatigue striations are observed at room temperature fatigue propagation zone, but they can be observed at 450℃ elevated temperature. The dimples can be observed at room temperature fatigue transient fracture zone. However, at 450℃ elevated temperature fatigue transient fracture zone, the dimples and quasi-cleavage can be observed simultaneously, indicating a mixed fracture mode. In addition, the crack shape of the strengthened sample is a wide top and narrow bottom shape due to the compressive residual stress layer.