Effect of Laser Shock Processing on Residual Stress and Microstructure of Ti834 Titanium Alloy

Laser shock processing (LSP), also known as laser shot peening, is a novel surface strengthening treatment technology. The surface roughness, residual stress and microhardness distribution of Ti834 alloy before and after LSP were analyzed by surface roughometer, X-ray diffraction and microhardness tester, respectively. And the surface morphology and microstructure of the impact area were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the surface roughness, microhardness and residual compressive stress of Ti834 titanium alloy increase after LSP. Moreover, the depth of the strengthening layer formed after one impact and two impacts is 170 and 265 mu m, respectively. After LSP treatment, a high compressive stress field is produced on the surface of Ti834 alloy. The peak value of residual compressive stress, after one impact and two impacts, appears in the subsurface layer, and reaches -369 and -511 MPa, respectively. A large amount of dislocation entanglement can be observed in the plastic deformation layer induced by laser shock wave. The increase of dislocation density and the formation of deformation twins are conducive to improvement of mechanical properties of Ti834 alloy subjected to LSP.