Combination of annealing and laser shock peening for tailoring microstructure and mechanical properties of laser directed energy deposited CrMnFeCoNi high-entropy alloy

Abstract

In this study, a post-treatment method combining annealing and laser shock peening (LSP) is used to tailor the microstructure and mechanical properties of CrMnFeCoNi high-entropy alloy (HEA) prepared by laser directed energy deposition (LDED). The microstructure, microhardness, residual stress and tensile property of the as-built, annealed, LSP and annealed + LSP specimens are compared. Results indicate that LSP produces greater plastic deformation on the surface of annealed specimen compared to the pristine as-built specimen, as manifested by a thicker plastically-affected layer. Recrystallization, dislocation network annihilation and thermal stress relaxation caused by annealing contribute to an increase in the plasticity of LDED-prepared specimens, which provides great strengthening conditions for LSP. Gradient strain hardening and compressive residual stress are gained in the surface layer of the annealed specimen subjected to LSP. Moreover, plastic deformation induces a gradient microstructure consisting of ultra-fine grains, high-density mechanical twins and slip bands in order. An excellent strength–ductility synergy is achieved in LDED-prepared CrMnFeCoNi HEA after combined post-treatment of annealing and subsequent LSP.