Stronger yet Ductile NiCrFe-7A Weld Metals through Hf Microalloying

Microalloying is a proven strategy for enhancing the mechanical performance of weld metals. To address the insufficient tensile strength of nuclear-grade Ni-based welding materials, this study investigates the effects of Hf microalloying on the microstructure and mechanical properties of NiCrFe-7A weld metals. Hf microalloying promotes the formation of island platforms that facilitate the nucleation of nanoscale γ′ and γ′′ phases, and also refines austenitic columnar grains. These microstructural changes, particularly the fine γ′ phases and increased amount of grain boundaries, inhibit grain boundary migration and dislocation movement, leading to improved strength primarily via precipitation strengthening. Furthermore, stacking faults within the Nb3Ni2Si phase contribute to energy absorption and stress relief, enhancing ductility. Combining modeling with experimental results, this work provides insights into the design of high-performance, nuclear-grade Ni-based welding materials through targeted microalloying.