Revisiting MP35N and MP159: The route to ultra-strong Co–Cr–Ni medium entropy alloys

The recently emerged CoCrNi-based medium-entropy alloys (MEAs)/high-entropy alloys (HEAs) have a good combination of high strength and ductility. However, there are still challenges for further increasing their mechanical properties by finding optimal composition with simple processing. In this investigation, we revisited the commercial superalloys MP35N and MP159 with similar composition and entropy to CoCrNi-based MEAs/HEAs to find inspirations for designing CoCrNi-based MEAs. After a simple thermomechanical process, MP35N/MP159 can achieve a high tensile strength over 2.2 GPa at ambient temperature, better than a majority of present CoCrNi-based MEAs/HEAs. At intermediate temperature tensile tests, the aged MP159 also has a considerable tensile strength (1.8 GPa) and tensile elongation (12.5%). The underlying strengthening factors of aged MP35N/MP159 were investigated by transmission electron microscope. It indicated that precipitation strengthening, solid solution strengthening, and work-hardening could be introduced in CoCrNi-based MEAs through alloying, and simple thermomechanical treatments to significantly improve the performance. The present findings and perspectives provide useful enlightenment for developing ultra-strong CoCrNi-based MEAs/HEAs.