Simultaneously improving the strength and ductility of an oxide dispersion-strengthened high-entropy alloy by employing innovative precursors for oxide formation

The engineering of a composite microstructure, achieved by coupling heterogeneous grain distribution with oxide dispersion, has been demonstrated as an effective strategy for enhancing the strength-ductility synergy of alloys at both room and elevated temperatures. The effectiveness of this approach is strongly correlated with the micro-features of dispersed oxides. In this study, we selected the Ni₃₈Co₂₀Cr₂₀Fe₁₈Ti₄ high-entropy alloy (HEA) as the base material, which could achieve the desired composite structure through preparation using mechanical alloying and spark plasma sintering methods. Our primary objective was to investigate the effects of incorporating Y₂O₃ or utilizing hydrides (TiH₂ and YH₃) as alternative precursors on the modification of oxide precipitates, evolution of a bimodal grain microstructure, and alteration in mechanical properties for the oxide dispersion strengthened (ODS) HEA. The results show that the incorporation of Y₂O₃ promotes the formation of ultrafine and semi-coherent Y₂Ti₂O₇ ternary oxide particles, in addition to the pre-existing coarse binary TiO in the HEA matrix. Moreover, this leads to a significant increase in the fraction and a decrease in the average size of ultrafine grains (UFGs) within the bimodal microstructure. Notably, utilizing Ti- and Y-hydrides instead of Y₂O₃ and Ti as oxide-forming precursors within an equivalent composition remarkably amplifies the precipitation proportion of Y₂Ti₂O₇ among dispersoids while further refining UFGs. The ODS-HEA synthesized using hydrides exhibits a simultaneous enhancement of 12 % in yield strength and 13 % in elongation to fracture, compared to that prepared from Ti and Y₂O₃. This intriguing phenomenon primarily arises from the heightened strengthening and toughening contributions, facilitated by the increased precipitation of advantageous Y₂Ti₂O₇ nanoparticles.