Enhanced strength-ductility synergy in CrFe2Ni2Ti0.2 high-entropy alloys by metalloid element Si and solution-aging treatment

Solution-aging treatment is a critical approach for optimizing the mechanical properties of HEAs. In this study, CrFe₂Ni₂Ti_0.2Si_x (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 composition, microstructure and mechanical properties of the alloys are systematically investigated. CALPHAD predictions and experimental results reveal that Si addition (x = 0.325, 0.5, 0.625) promotes the formation of a dual-phase structure comprising an FCC and G-phase (Ni₁₆Ti₆Si₇). And the two-phase hybrid structure of the alloys exhibits a labyrinth-like shape. Particularly, the Si0.375 alloys exhibit optimal strength-ductility synergy among the considered alloys, achieving an ultimate strength of 1325.2 MPa while maintaining a ductility of 37.3 %. This represents a 67 % improvement in yield strength compared to the as-cast alloys. The fracture surface of the Si0.375 alloys exhibit characteristic dimples of varying sizes, indicating a predominantly ductile fracture mechanism. Moreover, heat treatment significantly increases the G-phase volume fraction, thereby enhancing both grain boundary and precipitation strengthening effects.