Journal of the American Ceramic Society, Vol.102, No.8, 4835-4847, 2019
Ionic interdiffusion as interaction mechanism between Al and Si3N4
Al-Si3N4 couples were heat-treated at 850-1150 degrees C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre-coefficient of 5 x 10(-9) m(2)/s, indicating that the interaction is diffusion-dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al-Si transfer through the solid solution (Si3-xAlxN4-y) at the interface of Al alloy and beta-Si3N4 grains controls the kinetic of the interaction. When concentration of Al in solid solution exceeds a certain amount, it undergoes a topotactic phase transformation to form Al1-xSixN1+y (viz., AlN). Next, the Al1-xSixN1+y grains detach from the beta-Si3N4 grains and subsequently new Al-Si3N4 interfaces are established. These interfaces repeat the interaction process, continuing until all the reactant is depleted. Thus, the interaction kinetics consist of a sequence of associated parabolic stages, precluding the observation of parabolic kinetics.