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/L1(2) spinodal nanostructure and nano-lamellar BCC phase in a newly developed CON-strengthened Al(0.5)Cr(0.9)FeNi(2.5)V(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 L1(2) phase increased, facilitating the formation of coherent FCC/L1(2) 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 L1(2) and BCC phases in sequence. The L1(2) 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 L1(2) phases was insignificant, which could avoid the stress concentration and retain ductility. The nanolamellar 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. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

Coherent ordered nanoprecipitation (CON) hardening is an effective strategy for overcoming the strength-ductility trade-off in alloys. Understanding the precipitation mechanisms and their effects on mechanical properties is crucial for optimizing CON-strengthened materials. In this study, the precipitation and mechanical behavior of FCC/L1(2) spinodal nanostructure and BCC phase in a newly developed CON-strengthened high entropy alloy were investigated, revealing the impact of pre-deformation on composition redistribution and phase strengthening.