Revealing the progressive stress relaxation mechanism in fine-grained AlCoCrFeNi high-entropy alloys with structural-functional integration

In the present work, the fundamental mechanism underlying the structural-functional integration in hot-extruded AlCoCrFeNi high-entropy alloys (HEAs) is systematically elucidated. Dynamic recrystallization (DRX) process occurs in equiatomic AlCoCrFeNi HEAs fabricated via hot extrusion, yielding extremely refined grains (with an average grain size below 5 μm) and soft FCC phases distributed along the grain boundaries. Enabled by the cocktail effect, the evolution of BCC/B2 and FCC phases before and after hot extrusion exhibits distinguishable magnetic responses, providing a sensitive non-destructive characterization approach for AlCoCrFeNi HEAs. The refined grains, rationally combined with the reticular FCC phase of a volume fraction exceeding 10%, synergistically facilitate the homogeneous relaxation of deformation energy under compression. Collectively, these microstructural features markedly retard crack nucleation, alleviate stress concentration at crack tips, induce crack blunting and drive crack propagation along grain boundaries. Such a mechanism effectively impedes the crack propagation, preventing AlCoCrFeNi HEAs from catastrophic transgranular fractures. Relative to counterparts fabricated via alternative methods, the hot-extruded AlCoCrFeNi HEA achieves significantly improved compressive strength and plasticity of 3600 MPa and 41%, respectively. Furthermore, the electron back scattering diffraction (EBSD) and transmission electron microscopy (TEM) results are thoroughly discussed to reveal the dynamic evolution of progressive stress relaxation and dislocation configurations at various compression strains. These findings not only provide available guidelines for large-scale industrial manufacturing of such HEAs, but also offer valuable insights for designing and developing numerous structural-functional integrated HEAs with cocktail effect.