The Printability, Microstructure, and Mechanical Properties of FeMnCoCr High-Entropy Alloys Fabricated by Laser Powder Bed Fusion Additive Manufacturing.

This work investigated the effect of Fe/Mn ratio on the microstructure and mechanical properties of non-equimolar FeMnCoCr ( = 30% and 50%) high-entropy alloys (HEAs) fabricated by laser powder bed fusion (LPBF) additive manufacturing. Process optimization was conducted to achieve fully dense FeMnCoCr and FeMnCoCr HEAs using a volumetric energy density of 105.82 J·mm. The LPBF-printed FeMnCoCr HEA exhibited a single face-centered cubic (FCC) phase, while the FeMnCoCr HEA featured a hexagonal close-packed (HCP) phase within the FCC matrix. Notably, the fraction of HCP phase in the FeMnCoCr HEAs increased from 0.94 to 28.10%, with the deformation strain ranging from 0 to 20%. The single-phase FeMnCoCr HEA demonstrated a remarkable combination of high yield strength (580.65 MPa) and elongation (32.5%), which surpassed those achieved in the FeMnCoCr HEA system. Comparatively, the dual-phase FeMnCoCr HEA exhibited inferior yield strength (487.60 MPa) and elongation (22.3%). However, it displayed superior ultimate tensile strength (744.90 MPa) compared to that in the FeMnCoCr HEA (687.70 MPa). The presence of FCC/HCP interfaces obtained in the FeMnCoCr HEA resulted in stress concentration and crack expansion, thereby leading to reduced ductility but enhanced resistance against grain slip deformation. Consequently, these interfaces facilitated an earlier attainment of yield limit point and contributed to increased ultimate tensile strength in the FeMnCoCr HEA. These findings provide valuable insights into the microstructure evolution and mechanical behavior of LPBF-printed metastable FeMnCoCr HEAs.