Ultrastrong and ductile FeNi-based alloys through Pd-containing multicomponent L12-type precipitates

Precipitation strengthening stands as a paramount strategy for enhancing the mechanical properties of FeNi-based alloys. Conventional precipitates used for strengthening typically contain only two major constituent elements selected from Ni, Al, and Ti. However, knowledge about the intrinsic properties and strengthening mechanisms of multicomponent precipitates remains limited. Here, we propose introducing novel multicomponent L12-type precipitates containing palladium (Pd) to strengthen FeNi-based alloys. The strengthened FeNi alloy achieves an eightfold increase in strength compared to the FeNi matrix while maintaining good ductility. Using meticulous micro-characterization and energy-dispersive X-ray spectroscopy (EDS) techniques, in conjunction with first-principles calculations, this study investigated the effects of Pd addition on the thermodynamic stability, morphology, coherency, and strengthening mechanisms of the precipitates. Results indicate that the addition of Pd induces the nucleation of L12-type precipitates, increases their ductility, and eliminates anisotropy in the shear modulus of the precipitates. Excessive Pd content can alter the shape of precipitates from spherical to acicular due to increased interfacial mismatch between the precipitates and the FeNi matrix. These insights shed light on the impact of Pd addition on the intrinsic properties of L12-type precipitates, offering a promising pathway for the design of advanced FeNi-based alloys with optimized mechanical performance.