Designing stronger γ′-hardened NiCoCr medium entropy alloys

The γ′ precipitates have extensively enhanced the yield strength of NiCoCr-based medium entropy alloys (MEAs). However, further improvement is challenging since the precipitates’ volume fraction and size, which are currently used to tune the strengthening effect, have reached an optimal limit. Instead, here we propose to tune the composition of γ′ phase to overcome the above challenge. Through Ta microalloying, the precipitation strengthening effect of γ′ phase is enhanced by ∼34 % when the volume fraction and size of precipitates are almost the same. Detailed experimental and theoretical analysis evidenced the feasibility of our new strategy.