Studies and Optimization of Surface Roughness and Residual Stress in Ball Burnishing of Ti60 Alloy

In this study, the response surface experiment of the turning combined with ball burnishing was carried out. The surface topography of turning and ball burnishing was observed and analyzed. The characteristics of the surface roughness profile curve corresponding to surface topography were analyzed, and the stress concentration factor of the profile curve was calculated. The distribution characteristics of residual stress in the surface layer were revealed, and a distribution model was proposed. Nondominated sorting genetic algorithm-II was used to optimize the surface residual stress and surface residual stress in the axial direction. Additionally, the microstructure under optimized burnishing parameters was observed and analyzed. The results show that only turning marks can be observed after burnishing, and the stress concentration factor decreases significantly. A spoon-shaped distributed residual compressive stress layer is formed after burnishing, and the proposed model can effectively predict the distribution of residual stress along the depth. The optimal burnishing parameters are 18 MPa, 0.05 mm/r, 600 r/min, and 2 for the burnishing force, burnishing feed, burnishing speed, and number of passes. Moreover, under the optimized parameters, the second α phase (α_s) was deflected obviously, and the grains close to the surface are refined and the mean grain size is 11.31 μm.