Effect of post-weld heat treatment on microstructure and mechanical properties of dissimilar TRIP- and slip-assisted high-entropy alloy welds

초록

Joining HEAs with fundamentally different deformation mechanisms enables the integration of complementary strain-hardening behaviors, while simultaneously introducing challenges related to mechanical mismatch across the weldment. Importantly, welding such dissimilar HEAs gives rise to inherent challenges arising from compositional and microstructural mismatches, for which laser beam welding (LBW), owing to its high precision and low heat input, is particularly suitable. This study investigates the microstructure and mechanical behavior of LBW joints between two precipitation-hardened high-entropy alloys (HEAs) exhibiting distinct deformation mechanisms of transformation-induced plasticity (TRIP) and dislocation slip. Since fusion welding introduces compositional heterogeneity and residual stresses that can deteriorate joint performance, post-weld heat treatment (PWHT) was applied to promote precipitation evolution and enhance mechanical compatibility across the weldment. Aging at 750 degrees C promotes the formation of transgranular L12 and intergranular B2 precipitates across both base metals and the weld zone, establishing a continuous gradient in precipitate density and composition. This microstructure reconciles hardness mismatch, increases the weld-zone strength, and enables sequential strain transfer from the TRIP base metal through the weld into the slip base metal. As a result, the PWHT joint achieves a yield strength of 781 MPa and elongation of 15.9%, corresponding to similar to 50% higher yield strength and a threefold increase in ductility compared with the as-welded condition. These findings highlight the role of precipitation evolution in establishing mechanically gradient structures and demonstrate an effective strategy to reconcile strength and ductility in dissimilar HEA weldments.

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