Enhanced precipitation strengthening of D024 precipitates in a nanograined Fe-Ni based alloy

Realizing the greater potential for precipitation strengthening in nanograined alloys is highly desirable but often challenging. In this study, an Fe-Ni based alloy was subjected to plastic deformation followed by aging treatment to further strengthen nanograins through high-density precipitates. Microstructural characterization showed that nanograins account for ∼64% of the volume, with an average size of 44 nm. Notably, the nanoprecipitates in the nanograins exhibit utterly different characteristics from those in the coarse grains. As a result, the sample has an ultra-high yield strength of 1677 MPa. Further analyses indicated that the D0₂₄-structured nanoprecipitates at the nanograin boundaries provide a greater precipitation strengthening than conventional L1₂-structured nanoprecipitates within the coarse grains, the reason of which is that the precipitates inhibit partial dislocation emission and grain boundary migration of the nanograins. This work deepens the understanding of precipitation strengthening in nanograined materials and proposes a novel strategy to further strengthen nanograined alloys.