Spatial confinement imposed by bifunctional nanoprecipitates enhances strength and ductility of medium-entropy alloys (MEAs) by impeding dislocation motion and modulating transformation-induced plasticity. Precipitate characteristics and alloy chemistry can be precisely tailored to activate deformation mechanisms exactly when needed to thwart the strength-ductility tradeoff.
The researchers investigated model Fe-Ni-Al-Ti medium-entropy alloys with and without nanoprecipitates. Precipitate characteristics (size and spacing) were varied while their volume fraction and matrix compositions were kept constant. In the absence of nanoprecipitates, the matrix undergoes a face-centered cubic to body-centered cubic transformation upon quenching from elevated temperature. In contrast, when nanoprecipitates are present, the transformation is suppressed during quenching but activated during subsequent tensile testing resulting in TRIP. By tuning precipitate characteristics, researchers adjusted the balance between conventional precipitation hardening and TRIP, allowing specific deformation mechanisms to be activated, exactly when needed, to optimize strength and ductility. These findings open novel pathways to overcome the strength-ductility tradeoff, which has long been the bane of structural materials.
