填料增强先驱体转化法制备陶瓷涂层的研究进展

先驱体转化陶瓷法是一种原位制备陶瓷涂层的新型方法.在先驱体转化陶瓷法制备陶瓷涂层时,选择陶瓷产率较高的先驱体和添加填料是降低陶瓷涂层气孔率和收缩率的重要途径.填料在先驱体转化陶瓷法制备陶瓷涂层中起着重要作用,通过添加填料,可进一步提高陶瓷涂层的性能并扩展其功能特性.填料主要包括惰性填料、活性填料、熔融型填料和牺牲型填料4种.对比了4种填料的类型和特点,介绍了填料增强陶瓷涂层的作用机制和选取原则,综述了填料增强先驱体转化陶瓷法制备陶瓷涂层的研究现状.在裂解过程中,惰性填料的质量和体积均保持不变,可加入较高体积分数的惰性填料制备厚涂层;活性填料可与先驱体、裂解产生的小分子气体、保护气氛等反应,实现陶瓷涂层的近净成形;熔融型填料熔融后,填充到涂层空隙中,可提高涂层的致密化程度,消除基体和陶瓷涂层以及填料和先驱体之间由于热膨胀系数不匹配产生的应力;牺牲型填料分解后,形成孔状涂层,可控制陶瓷涂层中的应力,降低陶瓷涂层的有效弹性模量,增强陶瓷涂层的应变强度.针对陶瓷涂层的服役工况,选择合适的填料类型,确定填料的临界体积分数,揭示填料对陶瓷涂层组成、晶界结构、涂层致密化、裂纹缺陷及裂解反应过程的影响规律,研发新型裂解技术和工艺以控制先驱体转化为陶瓷涂层过程中产生的应力,是后续研究中需要重点关注的问题.

Research Progress on Preparation of Polymer Derived Ceramic Coatings Reinforced by Fillers

Polymer-derived ceramics is a new method of in-situ preparation of ceramic coating. The selection of precursor with higher ceramic yield and the addition of fillers are important ways to reduce the porosity and shrinkage of ceramic coatings in the preparation of polymer derived ceramic coatings. Filler can play a very important effect in the process of fabricating ceramic coatings. The performance of ceramic coatings can be further improved and their functional properties can be extended by adding fillers. The filler may be subdivided into four basic types:inert, active, fused and sacrificial fillers. In this paper, the types and characteristics of four different fillers were compared, the mechanism of action and selecting principles of filler reinforced ceramic coating were described, and the latest development about preparation of polymer-derived ceramics coatings reinforced by fillers were viewed. The mass and volume of inert filler remains unchanged in the pyrolysis process, so high volume fractions of inert filler can be added to receive thick ceramic coating. The active filler can react with the polymer, with gaseous products generated during pyrolysis or with the pyrolysis atmosphere, achieving near net shape of ceramic coating. The fused fillers may melt during pyrolysis, sealing porosity and densifying the coating, also enable the relaxation of thermomechanical stresses caused by thermal expansion mismatches between substrate and coating, and between fillers and precursor matrix. The sacrificial filler decomposes to form a porous coating, which can control the stress in the ceramic coating, reduce the effective elastic modulus of the ceramic coating, and enhance the strain strength of the ceramic coating. According to the service conditions of ceramic coating, select the appropriate type of filler, determine the critical volume fraction of filler, reveal the effecting laws of filler on ceramic coating composition, grain boundary structure, coating densification, crack defects and pyrolysis process, and develop novel processing techniques and strategies to control stresses arising during conversion into ceramic coatings should be paid much attention in subsequent study.