碳/碳复合材料硅酸钇晶须增韧莫来石涂层的制备、性能及抗氧化机理研究

Ceramics coating coated carbon/carbon composites(C/C composites) are very improtant high temperature structural materials for aviation and spaceflight appications. In oder to solve the cracking, peeling off and short time oxidation protection of the ceramics coating under high temperature wind tunnel atmosphere, this project provide and develop a new kind of yttrium silicates whisker reinfoced mullite coating. Firstly, a porous SiC bonding layer will be prepared by pack cemetation process. Then yttrium silicates whiskers will be deposited in to the microholes of the SiC caoting via a electrophoretic deposition with the asistant of ultrasonic irradiation as the choice method. As a result, the inserted yttrium silicates layer will be achieved. After that, the nanometer mullite crystallites will be deposited into the inserted yttrium silicates layers and a dense yttrium silicates whisker reinforced mullites coating will be obtained through the discharge sintering effect under the hydrothermal eletrophoretic deposition process. The purpose of the composites coating is to enhence the eroding and oxidation resistance of the coated composites. The corresponding physical and chemical reaction happened during the deposition process and the deposition mechanism of the coating will be investigated. And the depositions condition will be optimized. The method that how to get dense coating structure and good interface combination will be researched. Also the oxidation protective and failure mechanism of the prepared coating will be investigated and discovered. The projest will provide new method and theroy foundation for the improving of the oxidation resistance of C/C composites under gas eroding condition.

陶瓷涂层碳/碳复合材料（C/C）是非常重要的航空航天用高温结构材料，本项目针对涂层C/C在高速燃气冲刷环境下陶瓷涂层易脱落及氧化保护时间短的难题，提出并开发一种新型硅酸钇晶须增韧莫来石涂层。首先在C/C表面通过固渗反应制备一层多孔SiC内涂层，然后通过超声电泳选择性组装沉积技术将带电的硅酸钇晶须嵌入SiC内层的孔隙中，形成钉扎的晶须层；再通过水热电泳沉积将纳米莫来石充填于硅酸钇晶须层中，通过沉积过程中的放电烧结形成致密的硅酸钇晶须增韧莫来石涂层。旨在增强莫来石涂层的抗冲刷和抗氧化性能。系统深入研究涂层沉积过程中发生的相关物理化学变化和涂层形成机理，优化复合涂层的制备工艺，探索形成致密复合涂层的同时提高涂层内聚力以及复合涂层界面结合强度的方法，探讨所制备的复合涂层在高温静态和动态条件下对C/C的保护和失效机制。为进一步提高C/C在燃气冲刷气氛下的抗氧化性能和拓展其应用提供新的思路和理论基础。

碳/碳复合材料具有优异的高温稳定性以及优异的高温力学性能，从而被应用于航空航天领域。但是，C/C复合材料在超过723 K的有氧环境下就会被氧化，限制了其在氧化气氛下的广泛应用。陶瓷涂层被认为是解决碳/碳复合材料氧化问题的有效途径。. 本项目以碳/碳复合材料高温抗氧化涂层的关键基础科学问题为核心。采用包埋法制备SiC内涂层。采用溶剂热法制备了硅酸钇晶须,获得优化的硅酸钇晶须制备工艺。采用熔盐法制备了β-Y2Si2O7晶须，研究了熔盐温度对制备硅酸钇晶须晶相、显微结构的影响以及β-Y2Si2O7晶须的合成机理。另外，研究了对应β-Y2Si2O7陶瓷的热物理性能。所制备β-Y2Si2O7晶须有较低的热膨胀系数（3.88×10−6•K−1）和较低的热导率（1.84 W•m-1•K-1）。采用脉冲电弧放电沉积法制备了β-Y2Si2O7晶须增韧莫来石涂层。为进一步提高涂层的抗氧化性能，在制备了β-Y2Si2O7晶须增韧莫来石涂层的基础上，通过热浸渍法在其表面制备了硅酸盐玻璃涂层。研究了涂层的晶相组成、显微结构、界面结合强度、抗氧化性能及抗热震性能。所制备涂层在经过从室温到1673 K的50次热循环后，失重仅有1.05%。经过210 h的高温氧化后，失重仅为0.85%。. 采用熔盐法结合热浸渍法制备了莫来石晶须增韧硅酸盐玻璃涂层。研究了涂层的晶相组成、显微结构、界面结合强度及抗热震性能。结果表明莫来石晶须层以及莫来石晶须的引入有效地提高了涂层的界面结合，同时缩小了裂纹尺寸。所制备涂层在经过从室温到1573 K的100次热循环后，失重仅有2.21%。. 采用超声辅助水热电泳沉积法结合脉冲电弧放电沉积法制备了碳化硅纳米线（SiCNW）增韧莫来石复合外涂层，研究了涂层的晶相组成、显微结构、抗氧化性能及抗热震性能。SiCNW的引入缩小了裂纹尺寸并通过各种增韧机理：析晶，纳米线桥接，裂纹偏转，纳米线拔出等阻止了裂纹的扩展。所制备涂层在经过从室温到1773 K的50次热循环后，失重仅有0.03%。经过235 h的高温氧化后，单位面积的失重量仅为107 g•m-2。涂层失效的主要原因是玻璃相的挥发以及涂层中裂纹的产生。