Influence of interlayer on interfacial microstructure of diffusion bonded Ni-Cr-W superalloy

To research the microstructural characterization of diffusion-bonded new Ni-Cr-W alloy interfaces, taking Cu, Ni, Cu/Ni/Cu foil as interlayer or without interlayer, the vacuum solid-state diffusion bonding processes were successfully carried out to join Ni-Cr-W alloy at 950 °C, 30 MPa, 45 min. The influences of different interlayer on the microstructure and elements concentration distribution of new Ni-based alloy across the interface were investigated in details. Results show that several pores and M₂₃C₆ particles could be found in the joint of direct diffusion bonding. These defects and precipitates slowed down the diffusion of elements, leading to poor bonding quality. Using Cu foil interlayer, a reaction layers with thickness of 1.3 μm was formed between the Cu and Ni-Cr-W alloy. However, a sound bounding was obtained without any reaction layer when the Ni was used as interlayer. When used Cu/Ni/Cu multilayers, reaction layer and solution layer (thickness is about 9 μm) could be found in Ni-Cr-W/Cu and Ni/Cu interface, respectively. Further investigation indicates that the existence of M₂₃C₆ blocked the diffusion of Cu atoms across the diffusion interface.