Nickel-aluminum diffusion: A study of evolution of microstructure and phase

Microstructural and phase evolution of an aluminum deposit on nickel, after heat treatment at 883 K, is studied by means of various microscopy techniques, i.e. energy dispersive X-ray spectroscopy, backscattered electron imaging, electron backscatter diffraction, ion channeling contrast imaging and scanning transmission electron microscopy. AlNi3 crystallites are observed on the aluminum grain boundaries after only 3 min of heat treatment indicating that nickel and nickel rich phases are the initially diffusing and forming species. Heat treatment for 120 min or longer results in the formation of Al3Ni2 and a porous Al3Ni2/y-Al2O3 structure at the surface. The Al3Ni2 layer is composed of two different grain morphologies, indicating the position of a Kirkendall plane, and hence, there is a high diffusion rate of aluminum in this phase.