Precipitation and micromechanical behavior of the coherent ordered nanoprecipitation strengthened Al-Cr-Fe-Ni-V high entropy alloy

Abstract

Coherent ordered nanoprecipitation (CON) hardening is an efficient strategy for breaking the strength-ductility trade-off. Revealing the precipitation mechanism and its influence on mechanical property is significant for further optimization of CON-strengthened alloys. In this work, we investigated the precipitation and mechanical behavior of the coherent FCC/L12 spinodal nanostructure and nano-lamellar BCC phase in a newly developed CON-strengthened Al0.5Cr0.9FeNi2.5V0.2 high entropy alloy (HEA). We found that high-density defects induced by pre-deformation promoted the segregation of Cr, resulting in composition redistribution. The thermodynamics state of the matrix shifted into a spinodal regime and the ordering energy of L12 phase increased, facilitating the formation of coherent FCC/L12 spinodal nanostructure. Meanwhile, the Cr segregation promoted the precipitation of Cr-enriched nano-lamellar BCC phase. During tensile deformation, the FCC phase yielded first, followed by L12 and BCC phases in sequence. The L12 and BCC strengthening phases contributed to an ultrahigh macroscopic yield strength. Due to the low-misfit interconnected spinodal nanostructure, the differences in phase stress between FCC and L12 phases was insignificant, which could avoid the stress concentration and retain ductility. The nano-lamellar feature of the stiff BCC phase delayed the crack initiation and propagation. Our research revealed not only the significant effect of pre-deformation on CONs formation and refinement, but also the deformation mechanism of CONs, which shed new light on the microstructural optimization and mechanical property improvement of CON-strengthened alloys.