Study on the tensile and fatigue properties of the heat-treated HIP Ti-6Al-4V alloy after ultrasonic surface rolling treatment

This paper was mainly study on the tensile and fatigue performance change of HIP Ti-6Al-4V alloy treated by heat treatment combined with ultrasonic surface rolling (USR). Based on the use of heat treatment process to improve the microstructure and increase the mechanical properties, then USR treatment was used to further refine the grains in material surface modification layer and increase the residual stress and microhardness. The results showed that the plastic deformation layer of material surface was comparatively thin, and had a poorer grain refining effect. The SAED had the discontinuous ring spot pattern. Compared with the cut sample, the compressive residual stress value was −724 ± 23 MPa and increased by 50%, surface roughness was reduced to 0.17 ± 0.025 μm and decreased by 74.6%, and surface microhardness were increased to 467 ± 7.4 HV and increased by 43.6%. Finally, the tensile and yield strength increased by 3.6% and 3%, and the rate of reduction in area and the elongation decreased by 12.9% and 3.4% respectively. The fatigue strength at the high-cycle mechanism changed from 530 MPa to 570 MPa. The fatigue lifetime was increased by several times at the cycle stress of 700 MPa, and the only initial point of fatigue crack was located at the subsurface of the sample. Therefore this method could effectively improve tensile strength, fatigue strength and fatigue lifetime of HIP Ti-6Al-4V alloy.