Enhanced precipitation strengthening of multi-principal element alloys by κ- and B2-phases

Abstract Discoveries of new multi-principal element alloys (MPEAs) with outstanding performance have been challenging due to the large complexity of the compositional space. Many existing highly alloyed steels already incorporate MPEA concepts and detailed research is readily available, which can be utilized for a more efficient design approach. Inspired by this consideration, Ni- and Co-additions to the Al14.6C4.9Fe53.6Mn26.9 (at.%) high‑manganese steel were assessed to introduce B2-precipitates in addition to the κ-carbides to increase strength. Thermodynamic screening in the Al-C-Co-Fe-Mn-Ni system was performed with a custom calphad database and combined with experimental screening to identify novel MPEAs with enhanced mechanical properties. The selected MPEAs were produced by thermo-mechanical processing and the mechanisms active during annealing and deformation were investigated experimentally. The modification with Co did not result in the formation of B2-precipitates and improved mechanical properties. The Ni-added MPEA, Al14.7C4.7Fe49.9Mn26.4Ni4.2, revealed significant precipitation and dispersion hardening by nanoscale κ- and B2-phases combined with excellent strain hardening capacity due to slip band refinement-induced plasticity (SRIP). A combination of 1 to 1.2 GPa yield strength (21.3% increase) with a total elongation of 20 to 10% was achieved. The chosen methodology was efficient in the design of a novel MPEA with an improved strength-ductility synergy.