Advanced High Temperature Si3N4 Ceramics with Refractory Grain Boundaries

小行星9362087 目前对具有可保持至高温的上级机械性能的材料存在很大的需求。 氮化硅已被确定为满足这些材料要求的最有前途的陶瓷之一。 迄今为止，对Si3N4陶瓷的研究已经产生了上级的室温性能，但尚未实现将这些性能保持到高温。 这主要是为了致密化和晶粒生长而引入的液相的结果，但其仍然是在高温下软化的玻璃状晶界相。 提出了一种新的方法，该方法允许致密化和微观结构控制的Si3N4没有额外的玻璃相。 该技术涉及使用瞬时液相，其随后转化为难熔氧化物，使得不存在熔点为1850 ℃的相。 此外，Si4N4颗粒表面上存在的任何二氧化硅都应转化为SiC。 这将导致具有显著改善的抗蠕变性的材料能够在更高温度下操作。 拟议的研究涉及广泛的表征固结材料的相分析和微观结构的检查。 将在室温和1400 ℃下测量优化样品的机械性能。

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.