Reactive phase formation at AlN-Ti and AlN-TiAl interfaces

Ti specimens with embedded AIN particles, as well as AlN-Ti and AlN-TiAl diffusion couples were annealed at 900 to 1100 degrees C for up to 40 h. The microstructure and phase composition of the reacted interfaces were characterized using electron probe x-ray microanalysis (EPMA) and electron backscatter diffraction (EBSD) in scanning electron microscope and x-ray diffraction (XRD). In AlN-TiAl diffusion couples, a ternary Ti2AlN compound was formed at the interface. A more complex AlN-TiN + Ti3AlN-Ti3Al-(Ti)(Al)-Ti reaction zone was observed at the AlN-Ti interface. The morphology of the two-phase (TiN + Ti3AlN) layer changed with time so that the ternary nitride dominated after longer exposures. The kinetics of the reaction zone growth was two-stage, with a significant decrease of the growth rate at the second stage. Such behavior is believed to be caused by the changing morphology of the (TiN + Ti3AlN) layer accompanied by decreasing diffusivity of the components. (C) 2000 Elsevier Science S.A. All rights reserved.