Effect of combined treatment of laser shock peening and shot peening on fatigue performance of laser-powder-bed-fusioned GH4169 nickel-based alloy

Abstract

The laser-powder-bed-fusioned (LPBFed) GH4169 nickel-based alloys were respectively surface-strengthened by laser shock peening (LSP), shot peening (SP), and a combination of LSP and SP (LSP + SP). The surface roughness, microhardness, residual stress, and microstructures of the un-peened, (LSP + SP)ed, LSPed, and SPed sample were comparatively studied. The fatigue gain mechanism of the LSP + SP combined treatment on the LPBFed alloy was finally revealed. The vibration fatigue life of the (LSP + SP)ed sample under 680 MPa is at least 37.76 times, 1.58 times, and 0.79 times longer compared with the un-peened LSPed and SPed samples. The LSP + SP treatment decreased the stress concentration coefficient K_t compared with LSP treatment. The maximum compressive residual stress (CRS) of the (LSP + SP)ed sample is 68 % larger than that of the LSPed sample, and the CRS layer thickness is 1.12 times thicker compared with the SPed sample. The average grain size for the (LSP + SP)ed sample is the smallest, and the LAGBs fraction increases by 96 % and 50.9 % compared with the LSPed and SPed samples. The fatigue gain mechanism of the LSP + SP combined treatment on the LPBFed alloy is concluded that the largest maximum CRS, a thick CRS layer, the refined grains, and the decreased K_t extend the crack initiation life, and the smallest grain size, the highest density of dislocation substructures, as well as the highest fraction of LAGBs extend the crack propagation life. The results demonstrated that the LSP + SP combined treatment is an efficient surface strengthening method that can improve fatigue life of LPBFed nickel-based alloys.