Regulation of interfacial microstructure and mechanical properties of CuNi/X65 cladding fabricated by pulsed GTAW

Direct fusion of corrosion-resistant copper–nickel (CuNi) cladding to X65 steel can cause Fe–Cu intermixing, segregation, and interface-associated cracking. This study comparatively evaluates whether an ERNiCu-7 transition layer regulates the interface more effectively than preheating/slow cooling under otherwise comparable pulsed gas tungsten arc welding conditions. Four cladding schemes were characterized by optical microscopy, SEM-EDS, EBSD, Vickers hardness, and Charpy impact testing. In direct ERCuNi cladding, preheating/slow cooling widened the measured Fe–Cu–Ni interdiffusion zone from approximately 10 to 30 μm. This change coincided with coarse Fe-rich bcc-indexed segregation, a maximum interfacial hardness of approximately 280 HV, severe fusion-line cracking, and a decrease in single-specimen impact energy from 35 J to 18 J. In contrast, the ERNiCu-7 transition-layer schemes exhibited continuous interfaces, high-angle grain-boundary fractions above 82.9%, smoother hardness transitions, and impact energies of 86 J and 68 J. Because one impact specimen and one complete hardness traverse were available per scheme, these mechanical results are interpreted as comparative screening data. Overall, the converging microstructural and mechanical evidence shows that the Ni-Cu transition layer reduces direct Fe–Cu interaction and improves interfacial continuity. Transition-layer design is therefore more reliable than preheating/slow cooling alone for suppressing cracking in CuNi-clad X65 components.