Enhanced Strength-Ductility Synergy in Crfe2ni2ti0.2 High-Entropy Alloys by Non-Metallic Element Si and Solution-Aging Treatment

Abstract

Solution-ageing treatment is considered to be an effective method to enhance the mechanical properties of alloys. In this paper, CrFe2Ni2Ti0.2Six (x = 0, 0.125, 0.25, 0.375, 0.5, 0.625，denoted as Six) HEAs are prepared by vacuum arc melting, and all the HEAs are subjected to aging treatment at 800°C according to phase diagram calculations (CALPHAD). The phase compositions, microstructures and mechanical properties of the alloys after solution-aging are investigated. From XRD, SEM and EBSD experiments, it can be concluded that CrFe2Ni2Ti0.2Six (x=0.375,0.5,0.625) HEAs have a two-phase hybrid structure of FCC+G-phase (Ni16Ti6Si7), which corroborates the results of CALPHAD. And the two-phase hybrid structure of the alloys exhibits a labyrinth-like shape. Following the solution-ageing treatment, the alloys show a substantial increase in G-phase, which effectively enhances the strength-ductility synergy. Particularly, the Si03.75 alloys exhibits optimal mechanical properties among the considered alloys, achieving an ultimate strength of 1325.2 MPa while maintaining a ductility of 37.3%. The strengthening mechanisms of heat-treated CrFe2Ni2Ti0.2Six HEAs are also studied. The results show that heat treatment significantly enhances grain boundary strengthening and precipitation strengthening, which are the primary contributors to the improved mechanical properties of the alloys.

Keywords: High-entropy alloys, Heat treatment, Microstructures, Mechanical properties, Strengthening mechanisms