Correlating microstructure, corrosion behavior and wear resistance in an additively manufactured heterogeneous CoCrNi-based medium entropy alloy with outstanding mechanical properties

It remains challenging to simultaneously achieve excellent strength-ductility synergy, corrosion resistance and wear resistance in medium/high entropy alloys (M/HEAs). Here, we report a promising design and fabrication strategy for heterogeneous MEA, which is composed of two CoCrNi-based alloy powders with different Al and Ti contents alternately deposited via laser directed energy deposition (LDED). Additionally, a two-step heat treatment is implemented to optimize the microstructure and heterogeneous precipitation of nano-L1₂ phases. This study systematically characterizes and investigates the microstructural evolution, corrosion behavior and tribological behavior of heterogeneous MEA and the homogeneous counterparts. It is found that compared with other counterparts, the nano-L1₂ strengthened heterogeneous MEA not only overcomes the trade-off between the strength and ductility, but also exhibits anomalous corrosion resistance enhancement while maintaining superior wear resistance. Notably, the improved corrosion resistance originates from grain refinement and a passive film with higher stability and protection composed predominantly of Cr₂O₃, Al₂O₃ and minor TiO₂ and Co₃O₄. Specifically, the enhanced tribological properties are attributed to the increased overall hardness and protective oxide debris formation. These findings provide new insights for designing additive manufactured M/HEAs with integrated mechanical and chemical durability.