Grain size dependent deformation behavior of a metastable Fe40Co20Cr20Mn10Ni10 high-entropy alloy

Abstract The effects of grain size on the deformation behavior in a metastable Fe40Co20Cr20Mn10Ni10 high-entropy alloy (HEA) were investigated. The dislocation substructures with two different grain sizes of 12 µm (FG) and 41 µm (CG) upon straining were revealed, of which the strong grain size dependent of martensite phase transformation was observed. The HCP martensite plates appear earlier in the CG sample than the FG sample, along with the formation of much thicker and higher fraction of the HCP plates. This is ascribed to the impediment of stacking faults (SFs) movement and further the growth of the HCP lamellae from grain boundaries. The differences between the strain hardening behavior of the FG and CG HEAs were clarified in terms of the deformation microstructural evolution. The FG HEA shows higher strain hardening rates at original stage of deformation resulted from pinning effects to dislocation movements by grain boundaries, yet values of strain hardening rates are lower for the FG HEA at later stage of deformation due to the lower level of martensite phase transformation.