Ionic interdiffusion as interaction mechanism between Al and Si₃N₄

Abstract

Al‐Si3N4 couples were heat‐treated at 850‐1150°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 × 10−9 m2/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 β‐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 β‐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.

In-situ scanning transmission electron microscopy study of Al-amorphous SiO2 layer-SiC interface

“…Our results clearly show that SiO 2 amorphous phase has different reaction mechanism with Al than the crystalline SiC. As mentioned before, the current theories suggest that reaction between metals and ceramics can either follow the dissolution [22,23,28,47] or the interdiffusion path [33][34][35][36][37][38]. The reason behind the different reaction mechanism for SiO 2 amorphous phase and SiC can be explained using the structural similarities of reaction products and the reactants for the crystalline ceramics.…”

“…On the other hand, Al 4 C 3 was formed within the SiC phase with a certain orientation relationship ((0004) SiC || (0006) Al4C3 ). In the previous research on a similar system (ex-situ TEM investigation on Al- Si 3 N 4 [33]), Adabifiroozjaei observed similar orientation relationship ((0001) AlN || (0001) Si3N4 )) between the reaction product (AlN) and the ceramic reactant (Si 3 N 4 ). Therefore, it was inferred that the reaction product is formed from the reactant through an elemental interdiffusion (Al 3?…”

“…The reason behind the different reaction mechanism for SiO 2 amorphous phase and SiC can be explained using the structural similarities of reaction products and the reactants for the crystalline ceramics. This was hypothesized in the previous study on crystalline oxides (CaAl 2 Si 2 O 8 -Al system [35]) and subsequently was applied to the Al-Si 3 N 4 system [33]. In Ref.…”

“…In contrast to first theory, the second theory is based on interdiffusion of elements across the interface of the metal and the ceramic. This theory was applied in the previous works on Al-Si 3 N 4 [33], Al-CaAl 2 Si 2 O 8 [34,35], Al-BaAl 2 Si 2 O 8 [36,37], and Al-MgAl 2 O 4 [38] systems, in which elemental interdiffusion (e.g. Al 3?…”