Ultrastrong and ductile additively manufactured maraging medium-entropy alloy via cell network-assisted control of reversion transformation

Abstract

Maraging steels are extensively utilized in the aerospace, automotive, and defense industries due to their load-bearing capabilities, and recent advances in laser powder bed fusion (LPBF) have enabled their potential application in components with complex geometries. However, the inherently limited strain-hardenability of maraging steels, which is also observed under LPBF manufacturing, constrains their broader application. In this study, we present a novel LPBF-processed Fe60Co25Ni10Mo5 (at.%) maraging medium-entropy alloy (MEA) that demonstrates exceptional mechanical performance, achieved by tailoring the as-built cellular structure. Fully dense LPBF parts with <0.2% porosity are obtained through process optimization, and the as-built specimen exhibits a cellular structure featuring Mo segregation at cell boundaries. Aging at 650 °C leads to the transformation of the cell boundaries into film-like μ precipitates, the formation of reverted face-centered cubic (FCC) grains, and spherical μ phase precipitation within cells, which enhances strength but compromises ductility due to the deteriorative effects of film-like μ precipitates. In contrast, aging at 700 °C decreases the harmful film-like μ precipitates and promotes a higher rate of reversion into metastable FCC grains that are uniformly distributed on the ultrafine scale. The resulting microstructure delivers markedly improved strain-hardenability and ductility without significant loss of strength, attributed to the stress-shielding effect. An exceptional mechanical performance with ultrahigh strength (yield strength of (1 484.4 ± 13.1) MPa and tensile strength of (1 749.5 ± 0.7) MPa) and enhanced uniform elongation of (10.0 ± 0.9)% are achieved, indicating a record-high performance among LPBF-processed ultrahigh-strength ferrous alloys. The synergy of ultrahigh strength, excellent strain-hardening behavior, and near-net-shape capability highlights the broad applicability of this LPBF-processed maraging MEA for advanced structural applications.