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

• Published in: Journal of alloys and compounds 2018-06, Vol.750, p.626-635
• Main Authors: Luo, Sihai, He, Weifeng, Chen, Kai, Nie, Xiangfan, Zhou, Liucheng, Li, Yiming
• Format: Article
• Language: English
• Subjects: Alloying additive; Compressive properties; Compressive strength; Fatigue strength; Fatigue tests; Heat affected zone; Laser additive manufacturing; Laser shock processing; Lasers; Materials fatigue; Mathematical morphology; Mechanical properties; Microhardness; Microstructure; Peening; Residual stress; Shot peening; Substrates; TC17 titanium alloy; Tensile properties; Tensile stress; Titanium alloys; Titanium base alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2018.04.029

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. •The fatigue strength of Ti-alloys degraded from 401 MPa to 365 MPa after LAM.•LSP effectively eliminated the tensile stress and changed the microstructure.•The fatigue strength of LAMed Ti-alloys improved to 451 MPa.•The regain mechanism of fatigue strength was discussed due to LSP.