Modulating L12 precipitation behavior and mechanical properties in an Fe-rich medium-entropy alloy fabricated via laser powder bed fusion

This study systematically investigates the effects of different annealing treatments before identical aging on precipitation and mechanical properties of an L1₂-strengthened Fe-rich medium-entropy alloy (Fe-MEA) fabricated by laser powder bed fusion (L-PBF). These treatments result in distinct final microstructures characterized by either discontinuous precipitation (DP) or continuous precipitation (CP) dominance, accompanied by varied mechanical properties. The high-density dislocations and coarse grains induced by L-PBF promote CP. In contrast, the fine grains formed via L-PBF and the reduced dislocation density through annealing enhance DP, leading to grain refinement. The L-PBF Fe-MEA subjected to various post-printing heat treatments also demonstrates acceptable mechanical properties. It is revealed that the stacking fault energy (SFE) of the face-centered cubic (fcc) matrix in the direct-aged sample is sufficiently low to facilitate the formation of deformation-induced twinning and stacking faults (SFs) in both the CP and DP regions, indicating that both regions exhibit good deformation capacity. Additionally, hetero-deformation-induced (HDI) strengthening significantly contributes to the strength of the studied samples. In the annealing-aged samples, HDI strengthening primarily originates from the heterogeneous distribution of grains and precipitates (fine grains containing DP and coarse grain including CP). In contrast, in the direct-aged sample, HDI strengthening is attributed not only to the heterogeneous grains and precipitates but also to the heterogeneous dislocation structure. This work may provide guidance for modulating L1₂ precipitation behavior and mechanical properties of high/medium-entropy alloys (H/MEAs) fabricated by L-PBF.