Advanced High Temperature Si3N4 Ceramics with Refractory Grain Boundaries

9362087利斯基目前对一种具有优异机械性能的材料的需求很大，这种材料可以在高温下保持。氮化硅被认为是最有希望满足这些材料要求的陶瓷之一。到目前为止，对Si3N4陶瓷的研究已经导致了优异的室温性能，但这些性能在高温下的保持还没有实现。这主要是为了致密化和晶粒生长而加入的液态相的结果，但它仍然是一种玻璃晶界相，在高温下会软化。提出了一种新的方法，使Si3N4的致密化和微观结构控制，而不是决定性的玻璃相。这项技术包括使用瞬变的液态，然后将其转化为难熔的氧化物，因此不存在熔点为1850℃的相。此外，Si4N4颗粒表面的任何二氧化硅都应该转化为碳化硅。这将导致材料具有显著改善的蠕变抗力，能够在更高的温度下运行。拟议的研究涉及在物相分析和微观结构检查方面对固结材料进行广泛的表征。优化后的样品将在RT和1400℃下测量机械性能。

9362087 Leaskey There is much currently great demand for a material with superior mechanical properties that can be maintained to high temperatures. Silicon nitride has been identified as one of the most promising ceramics to meet these material requirements. To date, research on Si3N4 ceramics has resulted in superior room temperature properties but retention of these properties to high temperatures has not been achieved. This is mainly a result of liquid phase incorporated for densification and grain growth, but which remains as a glassy grain boundary phase which softens at high temperatures. A Novel method is proposed which allows for densification and microstructural control of Si3N4 without deterimental glassy phases. This technique involves use of a transient liquid phase which is subsequently converted to refractory oxides so that no phases with melting points 1850 C are present. Also, any silica present on the surface of the Si4N4 particles should be converted to SiC. This will result in materials with substantially improved creep resistance capable of operation at higher temperatures. The proposed research involves extensive characterization of consolidated materials in terms of phase analyses and examination of microstructures. The mechanical properties of optimized samples will be measured at RT and 1400 C.