Discontinuous coarsening leads to unchanged tensile properties in high-entropy alloys with different recrystallization volume fractions

Heterogeneous microstructure alloys provide a possibility for the combination of strength and ductility. As a typical heterogeneous microstructure, a partially recrystallized microstructure is attractive because of the convenient processing route and great potential for industrial applications. However, the mechanical properties of this microstructure vary dramatically with different morphology factors, especially the recrystallization fraction, which restricts the processing window and the property consistency. In this study, we found that the yield strength (∼1.3 GPa) and ductility (∼20%) of the partially recrystallized Ni2CoCrFeTi0.24Al0.2 do not change when the recrystallization fraction increases from 21% to 72%. This novel phenomenon is attributed to an additional hetero-deformation induced (HDI) strain hardening effect produced by heterogeneous precipitates. With the increased recrystallization fraction, this additional HDI stress keeps the ductility unchanged by offsetting the decreased HDI stress arising from the hetero-deformation between recrystallized (RX) and non-recrystallized (NRX) areas. The unchanged yield strength comes from the increased strengthening effects of the lamellar precipitates and grain boundaries. We also confirmed that the discontinuous coarsening contributes to the formation of heterogeneous precipitates. These findings would open a new pathway for enhancing the consistency and processability of hetero-structured alloys and thus promote their broader industrial applications.