Unraveling deformation mechanism in a hierarchical microstructured CrFeNiNb multi-principal element alloy via in-situ micropillar compression

Driven by the growing demand for metallic materials with exceptional mechanical performance in advanced structural applications, multi-principal element alloys (MPEAs) with hierarchical microstructures have attracted increasing attention. However, the deformation mechanisms of hexagonal close-packed (HCP) phase-dominated MPEAs remain poorly understood, which hampers the rational design of such alloys. Here, we report a CrFeNiNb MPEA with a hierarchical microstructure comprising a primary HCP matrix, a secondary face-centered cubic phase, (Nb, Cr)-rich oxides, and a high density of uniformly dispersed nanoscale precipitates. This hierarchical architecture endows the alloy with an ultrahigh microscale yield strength of approximately 4.0 GPa. Detailed microstructural and deformation analyses reveal that plastic deformation is governed by intense dislocation accumulation within the HCP matrix, accompanied by pronounced impediment of dislocation motion by the dispersed nano-precipitates. These findings provide mechanistic insights into the deformation behavior of HCP-based MPEAs and offer guidance for designing high-performance alloys with multiphase hierarchical microstructures.