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

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 Al_0.5Cr_0.9FeNi_2.5V_0.2 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.