TiAl合金激光冲击强化表面微观形貌演变分析

Surface Microstructure Evolution Analysis of TiAl Alloy by Laser Shock Peening

针对TiAl合金进行激光冲击强化,研究多晶体在强化过程中表面微观形貌演变,发现经过单点激光冲击的试样表面形成的凹坑中存在一些分布不均匀的凸起结构,凸起结构相对高度范围为100～300 nm,凸起边缘为环状凸台;研究激光冲击能量密度对表面凸起结构的影响,发现随着激光能量密度增加凸起结构的数量明显增加,凸起相对高度有增加的趋势,同时凹坑中心平均表面粗糙度明显增加;研究搭接率为50%的多次冲击形貌变化,发现相比于单次冲击,多次冲击凸起数量明显减少,表面粗糙度略有增加,这是因为随着冲击次数增加弹性变形和塑性变形趋于一种饱和状态,弹性变形部分发生回弹。分析表面凸起结构形成机制,建立不均匀塑性变形流模型和冲击波叠加模型,激光冲击强化形成的表面形貌是2种模型相互耦合作用的结果。

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.