Effects of Ultrasonic Surface Rolling Process on Microstructure and Surface Integrity of Ti-6Al-4V Alloy

The ultrasonic surface rolling process (USRP) was performed on the annealed Ti-6Al-4V alloy using employing the rectangular-ambulatory-plane machining path. The microstructure and surface integrity of Ti-6Al-4V alloy after USRP were characterized by equipments such as optical microscope, transmission electron microscope, vickers indenter, X-ray diffraction residual stress analyzer and surface three-dimensional topography. The results show that a plastic deformation layer with around 300 μm thickness was formed on the surface of Ti-6Al-4V alloy after USRP. The surface of plastic deformation layer was the equiaxial nanocrystal layer and the subsurface was the long strip shaped nanocrystalline laminar layer with the same grain orientation. The maximum mirco-hardness of Ti-6Al-4V alloy was 390 HV and the surface roughness reduced from 0.76 μm to 0.23 μm after USRP. The residual compressive stress of Ti-6Al-4V alloy increased first and then decreased with the increase of distance from surface.