Dynamic response of surface materials and topography control on TC4 titanium alloy subjected to laser shock imprinting

Abstract

Laser shock imprinting (LSI) can improve the fatigue performance of workpieces by controlling the surface topography. In this paper, TC4 titanium alloy was treated with LSI. The dynamic response of the surface material at the imprinted area was investigated with finite element modeling (FEM), and the simulated results were evaluated by experiments. The results show that a special shape with the convex on both sides and concave on the center is formed, which may not be beneficial to the fatigue performance of the workpiece. Increasing the shock wave pressure will aggravate the residual stress difference (the compressive residual stress is at the non-direct contact area and the tensile residual stress is at the direct contact area) and this problem can be effectively solved by multiple impacts with a thicker contact foil. Multiple impacts with thin contact foils will cause irregular deformation (tilting) of micro-protrusions, whereas utilizing thicker contact foils for multiple impacts can flatten the micro-protrusion surface and prevent tilting. In the overlapping LSI experiment, with the increasing of the contact foil thickness (CFT), the height of the micro-protrusion decreases, and the “laser spot boundary effect” (LSBE) is effectively alleviated, which decreases the surface roughness.