Synergistic effects of the pure Ni interlayer on microstructural evolution and mechanical properties of diffusion-bonded GH5188 superalloy

This study systematically compares interfacial evolution and mechanical performance in GH5188 cobalt-based superalloy joints produced through direct diffusion bonding and nickel-interlayered diffusion bonding. Under the constant bonding pressure (6 MPa) and holding time (60 min), direct-bonded joints transition from macro-cracking (1130 °C) to micro-porosity (1190 °C), achieving 95 % interface integrity and 607 MPa shear strength at 1190 °C with brittle fracture morphology. Compared with the direct diffusion bonding of GH5188, the joint can be optimized to a certain extent by introducing a 10 μm thick Ni foil interlayer. Comparing the two bonding methods, it can be found that Ni foil can effectively eliminate the interface defects, dissolve the carbides, and avoid the deterioration of the mechanical properties of the joints. At the same time, by adjusting the bonding process parameters, the interface defects can be completely eliminated and the effective bonding of the interface can be achieved. Optimized Ni-interlayered joints demonstrate 6.7 % strength enhancement (648 MPa) with ductile fracture characteristics at 1190 °C. The results indicate that the nickel interlayer effectively improves joint performance through three ways: enhanced elemental interdiffusion, suppression of carbide precipitation, and restriction of grain boundary migration. This work establishes a reliable pathway for manufacturing high-integrity joints in cobalt-based superalloys under elevated temperature conditions.