Exceptional combination of mechanical and corrosion properties in partially recrystallized CoCrFeNiMo medium-entropy alloys

Corrosion-resistant materials with good mechanical properties are an endless goal to develop reliable structural materials. Multiple strengthening mechanisms stemming from diverse microstructural factors have been developed, while the effect of microstructural factors on corrosion properties in high-entropy alloys has not been clearly defined yet. Herein, the corrosion behaviors of CoCrFeNiMo medium-entropy alloys with different annealing times are investigated. The influences of microstructures are summarized as follows: alloyed Mo accelerates repassivation, Mo-rich precipitates form micro-galvanic couples, and unrecrystallized microstructures induce pitting corrosion. Regarding mechanical properties, the alloyed Mo, Mo-rich precipitates, and unrecrystallized region with profuse dislocations lead significant solid solution strengthening, precipitation strengthening, and dislocation strengthening, respectively. Particularly, the sample annealed for 60 min possesses dissolved Mo in the matrix, fine precipitates, wide recrystallized regions, and low dislocation density, resulting in a wide passivation range of 1.512 V and high yield strength × fracture strain of 220.3 MPa simultaneously. The sample annealed for 60 min reveals a synergistic combination of diverse microstructural factors affecting corrosion and mechanical properties.