Microstructure evolution and deformation behavior during stretching of a compositionally inhomogeneous TWIP-TRIP cantor-like alloy by laser powder deposition

Abstract

A TWIP-TRIP high-entropy alloy with inhomogeneous chemical composition was prepared by laser powder deposition (LPD). The microstructure and properties of the alloy were quite different from those of compositionally homogeneous alloy with the same composition produced via electric arc melting + hot forging (EAM-HF) technique. During stretching, deformation twinning occurred under low strain, while FCC-HCP transformation was observed under high strain. The yield strength, tensile strength, and elongation were 425 MPa, 715 MPa, and 83%, respectively. For comparison, a sample with the same chemical composition was fabricated by EAM-HF. While twinning was detected under high strain during stretching, no FCC-HCP transformation was observed. Its yield strength, tensile strength, and elongation were found to be 69.6%, 86.9%, and 90% of those of LPD sample, respectively. In order to discuss the evolution of hardening behavior, a constitutive model based on dislocation density evolution was established, taking the contribution from twinning and FCC-HCP transformation into account. Since deformation twinning could be generated at a moderate speed in a wide tensile strain range and FCC-HCP transformation occurred under high strains, the high strain hardening rate could be guaranteed under high strain, thus avoiding strain localization, which endowed the LPD sample with good plasticity. It was shown to be possible to adjust the mechanical behaviors of alloys by increasing their stacking fault energy span through LPD.