In-Situ Synthesis Of Aluminum Nitride Materials

In-situ synthesis technology is a novel method of materials fabrication. The application of in-situ synthesis technology in AIN materials fabrication was studied in this paper. Moreover, AIN/SiC CMCs(Ceraniic-Matrix Composites) and A1N whiskers were prepared via directed nitridation of molten Al-Mg-Y alloy. Firstly, a selection criterion of Al alloy system used in in-situ AIN materials was proposed. which provides a basis to broaden the rang of alloy system selection. Then thermodynamics and kinetics of the nitridation reaction of molten Al-Mg-Y alloy were systematically analyzed. The influence on the reaction and products, such as alloy composition and technological conditions, was also considered. The results show that AIN can be synthesized by this nitridation reaction because of the deoxidization of Mg and Y. The reaction can be significantly intensified by the ebullience of Mg, and be accelerated by increasing Y content or processing temperature which are also able to improve the nitridation rate A N and the compactness of nitride products. Furthermore, the phenomena of the enrichment of Y in the forms of micro and macro were interpreted with transferring model of micro channel. The ill-situ fabricating process of AIN/SiC composites and the interface condition were analyzed. Meanwhile, morphologic characters of in-situ composites and the relationship between technological conditions and products were also investigated. The results show that in-situ AIN/S1C composite was not formed through the penetration growth of AIN crystal among SiC filler. Essentially, the synthesizing process of composite was that AIN is synthesized by nitridation of Al alloy permeated among filler. Moreover, there are distinctive differences between morphology of A1N crystal in in-situ composites and those of A1N in nitride, and the former is remarkably influenced by processing temperature. During the fabricating process of in-situ AlN/SiC~ composite, the composition of SiC-AIN powder can not only adjust the ratio between matrix and reinforcements but also remarkably influence the kinetic process. In-situ synthesis of AIN whiskers was studied. A1N whiskers were grown by VLS mechanism, and VLS may change to VS mechanism at high temperature. Finally, a novel fabrication method of A1N whiskers was presented in which SIC fibers are used as growth template and VS is the main growth mechanism.