Surface Microstructure Evolution Analysis of TiAl Alloy by Laser Shock Peening

The evolution of surface microstructure of the poly crystals formed in TiAl alloy treated by laser shock processing was studied in this paper. After a single laser shock peening treatment, some unevenly distributed briefs in the pits formed on the surface of the sample are found, the relative height of briefs ranges from 100 to 300 nm and the raised edge is an annular boss. When the samples are treated with different energy density lasers, the number of briefs increases significantly and the relative height has an increasing tendency, and the average surface roughness of the pits increases obviously. Further study on the changes in shape of multiple impacts on the spot overlap rate of 50% reveals that the number of briefs significantly declines compared with a single laser shock processing treatment, and the surface roughness is slightly increased. This is because the elastic deformation and plastic deformation tend to be saturated with the increase of laser shock processing treatment times, and the elastic deformation partially gets rebound. The formation mechanism of the surface protrusions was analyzed, and the uneven plastic deformation flow model and shock wave superposition model were established. The surface topography formed by laser shock processing results from the coupling effect of the two models