Outstanding weld-crack resistance of NiCrFe-7A cladding alloys via Hf microalloying

Cracking susceptibility remains a major challenge in nickel-based welding alloys, particularly in strip cladding alloys subjected to high heat input. This study demonstrates that appropriate hafnium (Hf) microalloying significantly enhances the cracking resistance of NiCrFe-7A strip cladding alloys. Comprehensive microstructural analyses — including SEM, EDS, EBSD, TEM, DSC, and ToF-SIMS — reveal that microalloying with 20 ppm Hf (Hf20) promotes the segregation of strengthening elements (Mo, Ta, and Nb) at grain boundaries (GBs), thereby improving GB cohesion. Additionally, γ′/γ″-reinforced island platforms form at some GBs, facilitating carbide precipitation and introducing GB curvature that disperses stress and suppresses crack initiation. However, excessive Hf addition (Hf40) increases the cracking susceptibility due to the formation of low-melting-point mixed phases (Mn/Cr oxides embedded in Nb 3 Ni 2 Si eutectics) at crack-susceptible high-angle grain boundaries (S-HAGBs). These phases, together with thermal stresses during rapid cladding cycles, induce cracking. This work provides new mechanistic insights into the design of nickel-based welding alloys with superior resistance to cracking.