Formation mechanism of AlN-SiC solid solution with multiple morphologies in Al-Si-SiC composites under flowing nitrogen at 1300 °C

Abstract

The non-oxide-reinforced phase AlN-SiC solid solution with high performance was successfully synthesized in the resin-bonded Al-Si-SiC composites under flowing nitrogen at 1300 °C. The AlN-SiC solid solution was synthesized by three paths of liquid-solid, gas-solid and gas-gas reactions through modulation of Al/Si ratio, and controllable microstructure of AlN-SiC solid solution was attained. The phase composition and microstructure of the sintered samples were characterized by XRD and SEM, combined with thermodynamics, the formation mechanism of AlN-SiC solid solution was investigated and the reaction model was established. Al was not detected while Si was detested by XRD. Granular, short columnar and whisker-like AlN-SiC solid solution were generated and their positions varied. As the temperature increases, the partial pressure of oxygen decreases due to the oxidation of Al, Si and SiC on the surface of the sample, inside the sample, the active oxidation takes place, generating Al2O(g), SiO(g) and CO(g). Due to the low oxygen partial pressure, Al is preferentially nitrided to form a thin AlN layer on its surface. The AlN layer is broken as the temperature increases, then liquid Al with carbon from resin begins to flow, leaving the residual shell of AlN in situ. When it flows to the surface of Si, Al-Sialloy is formed locally inside the Si particles under the wetting effect of C, then hexagonal AlN-SiC solid solution is formed inside the Si shell. Part of SiO(g) + CO(g) diffuses into the interior of the AlN residual shell and reacts by aggregation to form a granular AlN-SiC solid solution in the shell wall; others diffuses into the pores of the sample for vapor deposition, and finally forms stacked hexagonal flaky whiskers. The in-situ generated of AlN-SiC solid solution with multiple morphologies in the composite plays a joint toughening effect, which can significantly enhance the comprehensive performance of the composite. In this experiment, the synthesis of AlN-SiC solid solution without sintering aids under normal pressure at a low temperature. It is expected to be applied to the blast furnace and to realize the longevity of blast furnace.