In-situ studies of forming and developing Kirkendall porosity in a joint of Ni/Ni-base superalloy CMSX-4

Kirkendall porosity forms and develops in joints made of different materials exposed to high temperatures over a long period of time. This is due to the diffusion of elements accompanied by a vacancy flux. Hence, in a materials combination of pure Ni and Ni-base superalloy CMSX-4 joined by diffusion welding, alloying elements move from CMSX-4 to pure Ni, while Ni atoms and vacancies move in the opposite direction. However, the detailed development of the Kirkendall porosity, such as the time of the start of the pore formation and then of further growth, also in relation to the distance to the diffusion-welded interface, is still unknown. Furthermore, the shape of the developing voids depends on time, temperature and crystallographic orientations. In-situ 3D µ-tomography can answer the kinetics of the forming and developing Kirkendall porosity.