Developing metallic materials with a good combination of strength and ductility has been an unending pursuit of materials scientists. The emergence of high/medium-entropy alloys (HEA/MEA) provided a novel strategy to achieve this. Here, we further strengthened a strong-and-ductile MEA using a traditional solid solution strengthening theory. The selection of solute elements was assisted by mechanical property and microstructure predictive models. Extensive microstructural characterizations and mechanical tests were performed to verify the models and to understand the mechanical behavior and deformation mechanisms of the designated CoCrNi–3W alloy. Our results show good experiment-model agreement. The incorporation of 3 at.% W into the ternary CoCrNi matrix increased its intrinsic strength by ∼20%. External strengthening through microstructural refinement led to a yield strength nearly double that of the parent alloy, CoCrNi. The increase in strength is obtained with still good ductility when tested down to 77 K. Nanoscale twin boundaries are observed in the post-fracture microstructure under 77 K. The combination of strength and ductility after W additions deviate from the traditional strength-ductility-trade-off contour.

Alnico alloys have long been used as strong permanent magnets because of their ferromagnetism and high coercivity. Understanding their structural details allows for better prediction of the resulting magnetic properties. However, quantitative three-dimensional characterization of the phase separation in these alloys is still challenged by the spatial quantification of nanoscale phases. Herein, we apply a dual tomography approach, where correlative scanning transmission electron microscopy (STEM) energy-dispersive X-ray spectroscopic (EDS) tomography and atom probe tomography (APT) are used to investigate the initial phase separation process of an alnico 8 alloy upon non-magnetic annealing. STEM-EDS tomography provides information on the morphology and volume fractions of Fe–Co-rich and Νi–Al-rich phases after spinodal decomposition in addition to quantitative information of the composition of a nanoscale volume. Subsequent analysis of a portion of the same specimen by APT offers quantitative chemical information of each phase at the sub-nanometer scale. Furthermore, APT reveals small, 2–4 nm Fe-rich α1 phases that are nucleated in the Ni-rich α2 matrix. From this information, we show that phase separation of the alnico 8 alloy consists of both spinodal decomposition and nucleation and growth processes. The complementary benefits and challenges associated with correlative STEM-EDS and APT are discussed.