Synchrotron Sub-μ X-ray Tomography of Kirkendall Porosity in a Diffusion Couple of Nickel-Base Superalloy and Nickel after Annealing at 1250 °C

Kirkendall porosity that forms during interdiffusion in a diffusion couple of nickelbase superalloy CMSX-10 with pure nickel is investigated. The diffusion experiments are conducted at a temperature of 1250 degrees C, where the strengthening gamma'-phase is partially dissolved. The porosity is studied by X-ray sub-mu tomography with a spatial resolution of about 0.35(3) mu m(3) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. It is found that depending on the distance from the interface the Kirkendall pores take different shapes: octahedral, rounded pyramidal, drop shaped, dendritic, pear shaped, and joint shapes. Such a variety of pore morphologies indicates a complex multistage process of porosity nucleation and growth under vacancy supersaturation of different degrees. The experimental findings are interpreted on the basis of the results of diffusion modeling. It is shown that the kinetics of porosity growth is essentially influenced by the dissolution of the. phase.