Face-centered-cubic (FCC) to body-centered-cubic (BCC) phase-transformation-induced strengthening of nanoscale harmonic-like high-entropy alloys

Abstract

An heterostructured high-entropy alloy (HEA) effectively overcomes the constraint relationship between the strength and ductility. The transformation-induced plasticity (TRIP) phenomenon induced by the FCC-BCC phase transformation has been proven to significantly improve the comprehensive mechanical properties of HEAs. However, due to the limitations of existing experimental technologies, there are few reports on the synergistic effects of these two mechanisms. In this study, we employed molecular dynamics (MD) to investigate the influence of the harmonic structure and TRIP on the tensile deformation behavior of a Co₂₅Ni₂₅Fe₂₅Al_7.5Cu_17.5 HEA. The results indicate that the harmonic structure can effectively enhance the alloy's strength, increasing from 1.5 GPa in a polycrystalline structure to 2.2 GPa. With the increase in the coarse-grain diameter (D_sp), the volume fraction of the FCC to BCC transformation increases, and the phase transformation is advanced. The phase transformation mainly occurs in the coarse-grain regions, where the high hardness of BCC phases mismatches mechanically with the surrounding soft grain regions, inducing a heterogeneous deformation-induced (HDI) strengthening mechanism. Therefore, this study opens a new avenue for the subsequent development of HEAs with high strength and high ductility.