Regain the fatigue strength of laser additive manufactured Ti alloy via laser shock peening

Abstract

Laser additive manufacturing was one attractive method to rebuild the geometric features and regain a part of the mechanical properties of metallic alloys. But some adverse effects, such as tensile stress and heat-affected zone, were introduced and resulted in the low fatigue strength. Laser shock peening (LSP) is a technique to produce compressive residual stress and change microstructure. In this paper, the surface and profile residual stress distributions were presented on laser additive TC17 titanium alloy with and without LSP treatment. The tensile stress changed into compressive stress after LSP treatment. The microhardness and tensile properties of the laser additive specimens were presented and compared before and after LSP treatment. In addition, the microstructure characteristics in different regions of laser additive TC17 titanium alloy were characterized by scanning electron microscope and transmission electron microscope observations. Moreover, three kinds of specimens, namely substrate, laser additive and LSP post-laser additive, were subjected to fatigue tests. The fatigue strength of laser-additive specimens reduced from 401 MPa (substrate) to 365 MPa. Relatively, LSP improved the fatigue strength to 451 MPa. Lastly, the fatigue morphologies were observed and the possible regain mechanism of fatigue strength was discussed.