Enhanced properties of additively manufactured W/ODS steel multimaterials by modulating the distribution of intermediate phases

Abstract

In the process of fabricating immiscible bimetallic structures using Laser powder bed fusion (LPBF), the formation of brittle intermetallic compounds at the interface is common, significantly degrading the mechanical properties of the materials. This study aimed to enhance the mechanical properties of As-built W/ODS-316L by adjusting the phase distribution at the interface through solid solution heat treatment. The transition zone of As-built W/ODS-316L was found to contain large intermetallic compound (CIC) clusters composed of Fe₂W, Fe₇W₆, and Fe₆W₆C phases along the grain boundaries of the γ-Fe matrix. These CIC, featuring a core-shell structure, hindered dislocation motion and grain boundary slippage, leading to stress accumulation. Following solution heat treatment, the ultimate tensile strength of W/ODS-316L increased from 283.8 ± 8.4 MPa to 327.5 ± 7.8 MPa, while elongation improved from 7.97 ± 0.67 % to 20.34 ± 0.84 %. The mechanical property enhancement is attributed to two factors. First, the decomposition of Fe₇W₆, reduction in CIC size, and precipitation of fine Fe₆W₆C within the γ-Fe matrix reduced stress levels. Second, heat treatment transformed the transition zone interfaces into semi-coherent interfaces with the γ-Fe matrix, improving compatibility and facilitating dislocation motion, which prevented macroscopic crack formation. These findings confirm that solution heat treatment effectively improves the strength and ductility of As-built W/ODS-316L multi-material structures by transforming the interface into semi-coherent phases and reducing stress accumulation.