Achieving strength-ductility synergy of an additively manufactured metastable high-entropy alloy via deep cryogenic treatment followed by laser shock peening
Zhaopeng Tong, Yuze Zhang, Yichen Wang, Yunxia Ye, Jie Yin, Yucheng Bao, Xudong Ren
Abstract
Abstract Laser powder bed fusion (LPBF) is an attractive additive manufacturing technology for preparing high-performance high-entropy alloys (HEAs) engineering components. Unfortunately, the existence of inherent thermal residual stress and non-equilibrium microstructures in the additively manufactured components results in unsatisfactory mechanical properties. Herein, we propose a novel strengthening strategy, namely deep cryogenic treatment (DCT) followed by laser shock peening (LSP), to tailor the microstructures and enhance performances of an LPBF additively manufactured metastable HEA. The post-treatment effects of DCT + LSP on the LPBF-fabricated Fe 50 Mn 30 Co 10 Cr 10 HEA are evaluated in terms of microstructural modifications, residual stress, and microhardness redistribution, as well as tensile properties. Results indicate that a gradient heterogeneous structure is formed on the as-built sample surface, featuring gradient variations in grain size, martensitic phase content, and dislocation density, due to the grain refinement and martensitic phase transformation under DCT + LSP. The initial tensile residual stress on the surface is fully transformed into compressive stress, achieving a peak of −289 MPa, and the surface microhardness attains a maximum of 380.8 HV. The various strengthening mechanisms of gradient heterogeneous structures, as well as the multiple effects of heterodeformation-induced (HDI) hardening, transformation-induced plasticity (TRIP), and twinning-induced plasticity (TWIP), are responsible for achieving strength-ductility synergy. This work provides a practical pathway and valuable scientific insights for enhancing the mechanical behaviors of additively manufactured metastable HEAs via microstructural engineering.