Abstract
High-entropy alloys (HEAs) have inspired considerable interest due to their attractive physical and mechanical properties. In this work, the microstructural evolution induced by different heat treatments on rapidly solidified hypoeutectic precursors of a Fe26.7Co26.7Ni26.7Si8.9B11 HEA is investigated and correlated with the corresponding mechanical properties. The microstructures of the rapidly solidified precursors are composed of primary fcc solid solution dendrites embedded in a eutectic matrix. When the samples are annealed at different temperatures after furnace cooling or quenching, respectively, the eutectic structure gradually decomposes into fcc, tetragonal (Fe,Co)2B, and hexagonal Ni31Si12 crystals with increasing annealing temperature, leading to a gradual increase of the content of the fcc crystals and both their aggregation and coarsening. Then the dominant structural framework gradually transforms from eutectic structures to fcc dendrites and ultimately the (Fe,Co)2B crystals become isolated as dominant reinforcement particles distributed in the interdendritic regions. This gradual microstructural transition from hypoeutectic to quasi-duplex structures leads to the change of the dominant deformation mechanism from crack-controlled to dislocation-dominated deformation, which allows to control both ductility and strength in a wide range. Hence, this study provides some guideline for how to tune the microstructure and mechanical properties of HEAs.
Highlights
High-entropy alloys (HEAs) have inspired considerable interest due to their attractive physical and mechanical properties
Even though the samples were annealed at same temperatures but cooled under different cooling rates, no obvious crystalline phase changes can be observed based on the XRD results, implying that no fcc to bcc transition has occurred during quasi-equilibrium solidification
energy dispersive X-ray spectroscopy (EDX) mapping (Fig. S1 in the Supplementary Materials) preliminarily reveals that the primary dendritic phase is rich in Fe, Co, Ni, and Si while the eutectic structures are rich in Fe, Co, and B
Summary
High-entropy alloys (HEAs) have inspired considerable interest due to their attractive physical and mechanical properties. The microstructural evolution induced by different heat treatments on rapidly solidified hypoeutectic precursors of a Fe26.7Co26.7Ni26.7Si8.9B11 HEA is investigated and correlated with the corresponding mechanical properties. The dominant structural framework gradually transforms from eutectic structures to fcc dendrites and the (Fe,Co)2B crystals become isolated as dominant reinforcement particles distributed in the interdendritic regions This gradual microstructural transition from hypoeutectic to quasi-duplex structures leads to the change of the dominant deformation mechanism from crack-controlled to dislocation-dominated deformation, which allows to control both ductility and strength in a wide range. Recent studies have shown that when B, Si, P, or/and C with relatively small atomic weights are introduced into Fe-Co-Ni medium entropy alloys[35,36,37,38], high entropy metallic glasses and glass-matrix composites containing nanoscale fcc solid solution crystals can be achieved[39,40], which exhibit relatively good soft magnetic properties.
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