Microstructure and mechanical performance study of CrMnFeCoNi high-entropy alloys after cryogenic treatment

Abstract

In recent years, significant progress has been made in the development of high-entropy alloys (HEAs) that possess both high strength and high ductility. The application of the metastable engineering strategy to enhance the strength and ductility of materials has also gradually been employed, and cryogenic treatment is one of the important techniques in this regard. Through cryogenic liquid nitrogen treatment, this study significantly enhanced the strength and ductility of (CrMnFeCoNi)₄₅Fe₅₅ and (CrMnFeCoNi)₄₀Fe₆₀ HEAs prepared by laser melting deposition (LMD). Compared to the initial samples, the fracture strength of (CrMnFeCoNi)₄₅Fe₅₅ increased from 480 MPa (at room temperature) to 980 MPa (after cryogenic treatment), and the fracture elongation alloy increased from 60 % (at room temperature) to 62 % (after cryogenic treatment). The fracture strength of (CrMnFeCoNi)₄₀Fe₆₀ alloy increased from 550 MPa (at room temperature) to 1150 MPa (after cryogenic treatment), and the fracture elongation decreased from 55 % (at room temperature) to 45 % (after cryogenic treatment). The reduction in stacking fault energy (SFE) through cryogenic liquid nitrogen treatment enables the formation of stacking faults in the alloy system. These stacking faults act as nucleation sites for phase transformations, encouraging the shift of the matrix from a face-centered cubic (FCC) phase to a body-centered cubic (BCC) phase or other phases. This triggers phase transformation-induced plasticity effects (TRIP). The occurrence of phase transformation was confirmed using in-situ cryo-TEM. Simultaneously, the coexistence of two phases mechanism achieves an advantageous balance between strength and ductility. Our study offers novel insights and methodologies for acquiring high-entropy alloys with exceptional comprehensive mechanical properties.