Microstructure, microhardness and residual stress of laser additive manufactured CoCrFeMnNi high -entropy alloy subjected to laser shock peening

摘要

Laser shock peening (LSP) is a surface modification technology to synthesize nanostructures on the surface layer of materials, thereby improving mechanical performances. In this work, a laser additive manufactured CoCrFeMnNi high -entropy alloy (HEA) is processed using LSP. The microstructure evolution during LSP is in- vestigated via electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) observations. The micro -hardness distributions on cross -sections and subsurface residual stress states as functions of the laser energy are also determined. Results indicate that the LSP results in a thick hardened layer with high micro - hardness, and transforming the tensile stress in the subsurface into compressive stress. The microstructure ap- parently refines because of the formation of nanoscale grains on the surface after LSP. A novel grain refinement mechanism under ultra -high plastic strain is proposed. Surface strengthening modes are proposed to describe the relationship between strengthening behaviors and microstructure characteristics, thereby revealing the strengthening mechanism.