In situ tuning of FCC–BCC dual phase and mechanical properties in multi‐principal element alloys via laser‐aided additive manufacturing
Lijia Chen, Sihao Zou, Shang Sui, Fei Weng, Shangxiong Huangfu, Lichao Cao, Hao Zhang, С. В. Гапоненко, Tao Yang, Jun Jiang, Lidong Zhao, Wenjun Lu, Guijun Bi
Abstract
Abstract A novel approach for fabricating multi‐principal element alloys with adjustable phase configurations and mechanical properties was developed using laser‐aided additive manufacturing (LAAM), combining FCC‐structured (face‐centered cubic) CoCrNi and BCC‐structured (body‐centered cubic) CoCrNiAl0.6TiFe feedstocks. During fabrication, CoCrNi powders and CoCrNiAl0.6TiFe powders were simultaneously fed into the melt pool at individually adjustable rates, allowing for controlled phase transitions. The resulting phase evolution demonstrated a gradual transition from a single FCC structure CoCrNi(Al0.6TiFe) x ( x = 0, 0.1, 0.2, 0.3) to a dual FCC‐B2 structure CoCrNi(Al0.6TiFe) x ( x = 0.4, 0.5) as the proportion of BCC‐structured powders increased. The B2 phase, enriched in Ti and Al due to their larger atomic radii and negative segregation enthalpy, precipitated around the FCC matrix, with volume fractions of 0.5% and 5.7% for CoCrNi(Al0.6TiFe)0.4 and CoCrNi(Al0.6TiFe)0.5, respectively. This phase transition resulted in significant mechanical enhancements. Yield and ultimate tensile strengths increased from 486.0 and 781.2 MPa (CoCrNi) to 887.2 and 1165.2 MPa (CoCrNi(Al0.6TiFe)0.5). Dislocation‐mediated hardening prevailed in single‐phase FCC alloys, exhibiting a characteristic dislocation density of 2.5 × 10 15 m −2 for CoCrNi(Al0.6TiFe)0.3 alloy. Once the B2 phase precipitated, precipitation strengthening became dominant, as observed in transmission electron microscopy (TEM), where dislocations accumulated around B2 precipitates. This study presents an innovative alloy fabrication strategy that enables precise tuning of FCC–BCC dual‐phase structures, facilitating the direct fabrication of components with spatially customized properties. These findings provide valuable insights for developing multi‐principal element alloys with heterogeneous microstructures for advanced engineering applications.