Study on Surface Integrity and Fatigue Properties of TC4 Titanium Alloy by Surface Ultrasonic Rolling

In this paper, the influence of a surface ultrasonic rolling process on the surface integrity of TC4 titanium alloy and its influence on the fatigue properties were studied. By comparing and analyzing the surface roughness, microhardness, residual stress, microstructure, and fatigue fracture, the surface strengthening and modification mechanism of TC4 titanium alloy is discussed. The results show that the surface roughness of titanium alloy is observably decreased after the suitable surface ultrasonic rolling process, and the maximum Ra value can be reduced to 0.052 μm. The axial residual stress on the specimen surface can be increased to −685 MPa. The hardening rate of the surface hardness of the sample was 35%. The residual compressive stress and hardness of the sample surface increased with the increase of static pressure. However, the increase of feed rate and rational speed was less. After surface ultrasonic rolling, the sample surface exhibited obvious grain refinement, the number of high-angle boundaries increased to include the formation of nano-equiaxed grains. The fatigue strength increased by 52% from 280 MPa to 425 MPa. Under 450 MPa, the fatigue life of samples with SUR 2 was the highest, at about 7.7 times that of the original samples. The surface integrity of titanium alloy samples after surface ultrasonic rolling treatment is greatly improved, which is the reason for the significant increase in fatigue life of the samples.