Effects of heat treatment combined with laser shock peening on wire and arc additive manufactured Ti17 titanium alloy: Microstructures, residual stress and mechanical properties

Wire and arc additive manufactured (WAAM) metal parts usually contain large columnar grains and detrimental tensile residual stress, affecting their mechanical performance. In this work, a post-treatment method combining heat treatment (HT) and laser shock peening (LSP) was employed to alter the microstructure and mechanical properties of WAAM Ti17 titanium alloy. The results show severe plastic deformation was induced in the surface layer, which, in turn, led to a high-level surface compressive residual stress (similar to -763 MPa) by combination treatment of HT and LSP. Meanwhile, high-density dislocations and mechanical twins were observed in coarse a phases after treatment by laser shock wave, and gradually evolved into refined a phases. The elongation of samples was significantly improved by 15% while ensuring original ultimate tensile strength (UTS, 1153 +/- 13 MPa) after HT and LSP treatment. This combined HT and LSP method helps enhance the mechanical performance of WAAM parts through changing their microstructure and residual stress distribution.