Investigation of the CNTD Mechanism and Its Effect on Microstructure and Properties of Silicon Nitride.

摘要

Silicon carbide and silicon nitride have been recognized as prime candidate materials for numerous high temperature applications, based on their properties such as oxidation resistance, chemical stability, creep resistance, strength, and thermal shock resistance. As a result, a number of different consolidation techniques are being investigated for potential use. Ceramics produced by CVD are thought to have considerable potential in these applications in offering greater purity and density than ceramics produced by more conventional consolidation techniques. At Chemetal, an advanced state of the art CVD process, called Controlled Nucleation thermochemical Deposition has been developed. The influence of the process on the microstructures is readily apparent. The characteristics of the resultant deposit are quite different in that the columnar crystal growth, which is typical of CVD, is interrupted so as to provide instead a fine grained non-columnar deposit. This program was directed toward achieving a better understanding of the mechanism of the CNTD process as it relates to silicon nitride deposition.