Interfacial Reactions of Refractory Metals Niobium and Tantalum with Ceramics Silicon Carbide and Alumina

Recent interest in the development of advanced metal matrix composites has prompted research on interfacial reactions of Nb and Ta with candidate reinforcements such as silicon carbide and alumina. Formation of reaction layers as small as 0.1 μm can be detrimental to composite strength and ductility and in some instances to the corrosion behavior, which suggests the importance of understanding the early stages of interfacial reactions. Thin films of Nb and Ta were sputter deposited on single crystal and polycrystalline silicon carbide and on sapphire substrates, and the nature and extent of reaction evahiated using Auger depth profiling and electron microscopy. In the Nb/SiC system, NbCX is the first reaction product to form, but the overall extent of the reaction is dominated by the formation of the more stable NbCXSiY ternary phase. Little or no interfacial reaction was observed in the Nb/Al2O3 system for up to 4 hburs at 1100°C, which also suggests that Al2O3 may be a potential diffusion barrier to minimize reactions in the Nb/SiC system. Similar interesting observations were made in the Ta/SiC and Ta/Al2O3 systems.