Induction-field-activated self-propagating high-temperature synthesis of AlN-SiC solid solutions in the Si3N4-Al-C system

The synthesis of AlN-SiC solid solutions from Si3N4, Al, and C was investigated using the induction-field-activated/self-propagating high-temperature synthesis/static pseudo-isostatic compaction technique. Careful x-ray diffraction analyses were made on the products of combustion to determine reaction routes. Optical microscopy as well as scanning electron microscopy with an electron probe microanalysis was used for microstructural analysis. It was found that initially molten aluminum reacted with silicon nitride producing an AI-Si alloy. At higher temperatures, aluminum evaporated from the Al-Si liquid and the synthesis of AlN via a vapor phase process took place. Subsequently, dissolution of AIN into molten Si resulted in the formation of an AlN-SiC solid solution from the Al-N-Si-C liquid phase. However, below 1850 degreesC, the resulting solid solution of 4AlN-3SiC was not fully crystallized. Combustion temperatures above or equal to 1850 OC were required to prepare a highly crystallized solid solution with a morphology exhibiting hexagonal platelets. Based on these observations, a model for the formation of AlN-SiC solid solution is proposed.