Jiaqi Duan

Most of the face-centered cubic (FCC) multi-principal element alloys (MPEAs) developed thus far contain cobalt. For many applications, it is either required or beneficial to avoid cobalt, since cobalt has long-term activation issue (for nuclear applications), is expensive, and is considered a critical material. In addition, FCC structured solid-solution MPEAs tend to have relatively low strength. A FCC solid-solution Fe30Ni30Mn30Cr10 (at %) MPEA was fabricated via arc melting, followed by homogenization at 1100 °C for 12 h. The alloy was hot rolled at 1100 °C with a total reduction of up to 97 %. The microstructure was characterized and mechanical properties were investigated at various stages. Tensile testing showed that yield strength (YS) increased by 285–595 MPa and ultimate tensile strength (UTS) increased by 520–710 MPa. This increase in YS and UTS occurred with a total elongation (ductility) of 40 %. Meanwhile, hot rolling at high reductions led to evident decreases in size and area fraction of Mn-rich inclusions. Overall, after hot rolling, this FCC solid-solution MPEA is both strong and ductile.

Two Co-free multi-principal-element alloys (MPEAs), viz. single-phase face-centered cubic (FCC) Fe30Ni30Mn30Cr10 and (Fe30Ni30Mn30Cr10)94Ti2Al4 (all in atomic percent) with FCC matrix containing Ni-Ti-Al enriched L12 (ordered FCC) secondary phase (γ′), have been developed and investigated. The alloys were ion irradiated at 300°C and 500°C to peak damage of 120 displacements per atom (dpa). Compared with the (Fe30Ni30Mn30Cr10)94Ti2Al4 alloy, in the Fe30Ni30Mn30Cr10 alloy, the dislocation loops were smaller, with a higher number density. The difference in loop size between the two MPEAs was attributed to the addition of Ti to the matrix, which was anticipated to lower the stacking fault energy and stabilize the faulted Frank loops. The γ′ phase showed good stability under irradiation, with no new γ′ precipitation or growth in existing precipitates. Both alloys showed similar irradiation-induced hardening at 300°C, but the (Fe30Ni30Mn30Cr10)94Ti2Al4 alloy exhibited lower irradiation-induced hardening at 500°C compared with the Fe30Ni30Mn30Cr10 alloy.