A New Solid-state Diffusion Welding Method for Fe- and Ni- based Superalloys

J.-B. Hwang, E.-S. Kim
Korea Atomic Energy Research Institute,

Keywords: superalloys, diffusion welding, surface treatment, mechanical properties


Fe- and Ni-based superalloys have been widely used as structural materials in hot sections of nuclear reactors and aerospace engines. However, the welding defects should be appropriately controlled because they can be the origin of the failure. While solid-state diffusion welding methods have been investigated to avoid typical welding defects, secondary precipitates, such as Ti-rich carbides and Al-rich oxides, along the welding interface significantly affect the load-bearing capacity of the diffusion weldment. To address this issue, we have formulated a surface treatment dissolving the secondary precipitates into the matrix, increasing the solubility product (Ksp) to exceed the reaction quotient (Q) on the surface of the superalloys. Two sheets of surface-treated Alloy 800H and Alloy 617 having dimensions of 17.3 (L) × 17.3 (W) × 1.5 (T) mm3 were diffusion welded at 1140 °C for two hours and uni-axially compressed with a hand-tightened clamp, respectively. Post-weld heat treatment was carried out at 1100 °C for 20 hours without compressive pressure for the additional atomic diffusion. The equiaxed grains at/near the interface indicated that the grain boundary migration occurred due to the reduction of the secondary precipitates. Furthermore, four plates of Alloy 800H having dimensions of 110.0 (L) × 80.0 (W) × 25.0 (T) mm3 were diffusion welded to examine tensile, stress-to-rupture, and low-cycle fatigue behaviors. The mechanical properties of the diffusion weldment will be presented and further discussed compared to the current industry standards.