Subtask 6.5 - SiAION Coatings of Silicon Nitride and Silicon Carbide.

Nowok, J. W. ; Hurley, J. P. ; Kay, J. P.

Technical Information Center Oak Ridge Tennessee

关键词: Silicon carbides;    Silicon nitrides;    Protective coatings;    Chemical properties;    Corrosion resistance;   

RP-ID  :  DE2004824976

学科分类：工程和技术（综合）

美国|英语

来源: National Technical Reports Library

【 摘 要 】

The need for new engineering materials in aerospace applications and in stationary power turbine blades for high-efficiency energy-generating equipment has led to a rapid development of ceramic coatings. They can be tailored to have superior physical (high specific strength and stiffness, enhanced high-temperature performance) and chemical (high-temperature corrosion resistance in more aggressive fuel environments) properties than those of monolithic ceramic materials. Among the major chemical properties of SiAlON-Y ceramics are their good corrosion resistance against aggressive media combined with good thermal shock behavior. The good corrosion resistance results from the yttria-alumina-garnet (YAG), Al(sub 5)Y(sub 3)O(sub 12), formed during the corrosion process of SiAlON-Y ceramics in combustion gases at 1300 C. The interfacial chemical precipitation of the YAG phase is beneficial. This phase may crystallize in cubic and/or tetragonal modifications and if formed in SiAlON-Y ceramic may simultaneously generate residual stress. Also, this phase can contain a large number of point defects, which is a consequence of the large unit cell and complexity of the YAG structure because it has no close-packed oxygen planes. Therefore, the need exists to elucidate the corrosion mechanism of a multilayered barrier with respect to using SiAlON-YAG as a corrosion-protective coating. Stress corrosion cracking in the grain boundary of a silicon nitride (Si(sub 3)N(sub 4)) ceramic enriched in a glassy phase such as SiAlON can significantly affect its mechanical properties.