Oxide dispersion strengthened Ni-rich high entropy alloy synthesized via mechanical alloying and spark plasma sintering: Attribution of nano-Y2O3 dispersoid on mechanical properties

Abstract

Current study investigates the effect of Y₂O₃ content (0, 1, 3, and 5 vol. %) on microstructural evolution and deformation behavior of a novel Ni₄₇Al₆Co₁₈Cr₈Fe₁₂Ti₈W₁ (at. %) Ni-rich oxide dispersion strengthened (ODS) high entropy alloy (HEA) synthesized via mechanical alloying and spark plasma sintering. Y₂O₃ addition up to 3 vol. % resulted in significant increase in both hardness and compressive strength of the ODS HEA. Specifically, the ODS HEA containing 3 vol. % Y₂O₃ demonstrated an outstanding combination of strength and ductility, with a compressive yield strength of 1517 MPa and 27% compressive strain. However, increasing Y₂O₃ content to 5 vol. % resulted in poor densification due to agglomeration of the nanoscale oxide particles resulting in lower hardness and compressive strength in comparison to 1 and 3 vol. % Y₂O₃ containing ODS HEAs. Further, the microstructural characterization of fractured samples revealed that the deformation was primarily mediated by dislocation slip in both the pristine (0 vol. % Y₂O₃) HEA and 3 vol. % Y₂O₃ ODS HEAs, along with occurrence of dynamic recrystallization (DRX). Interestingly, in case of 3 vol. % Y₂O₃ ODS HEA, the extent of DRX was found to be higher in comparison to the pristine HEA, as confirmed from transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD) analysis. TEM characterization of 3 vol. % Y₂O₃ fractured sample revealed simultaneous occurrence of continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) during deformation process, contributing in retaining impressive ductility.