纳米结构稀土硅酸盐环境障涂层的激光熔凝合成机制研究

Researches show the future direction of development that Non-oxide silicon-based ceramics ( NOSBC ) is the leading candidates to displace Ni based super-alloys for high temperature structural components in the aero-engine, for their excellent high temperature mechanical properties, light weight, good insulation effect, and other comprehensive performance. In order to prevent the ceramic material performance from the degradation influence of engine working environment, it need to prepare environment barrier coating outside the ceramic surface .To solve the coating(which is prepared through currently widely used plasma spraying method)'s shortcomings of reducing the coating life like the weak impact resistant ability, poor toughness, low interfacial bonding capacity, the coating's porosity and cavity , after the theoretical analysis and the research results, owing to Laser Surface Melting method's helpful to eliminate the coating internal defects as well as the improving of the interface bonding force advantages and Nano-ceramic itself outstanding characteristics, The project put forward to put the Laser Surface Melting technology into ceramic surface Nanostructural environment barrier coating's preparation, study the influence of the Laser Surface Melting on coating microstructure and performance, discuss the reason for the Laser Surface Melting's influence of coating surface stress change rule and crack reduce, research in the structural features in the coating of Nano-particles under the action of the laser, to play the Nano-particles' dispersion strengthened role on the coating that has excellent strong toughness, so as to solve the environmental barrier coating's problem of thermo-stress ,crack, low binding force and coating failure in the thermal cycle.

由于具备优异的高温力学性能、质量轻、隔热效果好等综合性能，硅基非氧化物陶瓷取代高温镍基合金作为航空发动机热端主体结构材料是未来的发展方向。为了防止发动机工作环境对陶瓷材料性能的恶劣影响，需要在陶瓷表面制备环境障涂层。针对解决目前广泛使用的等离子喷涂法制备的涂层抗冲击能力弱、韧性差、界面结合强度低、涂层中存在孔隙和空洞等会降低涂层寿命的诸多不足，通过理论分析和前期研究结果，结合激光熔凝法有利于消除涂层内部缺陷，提高界面结合力等优势以及纳米陶瓷本身的优异特性，本项目提出激光熔凝技术应用于陶瓷表面纳米环境障涂层的制备方法，研究激光熔凝对涂层显微结构及性能的影响，解析激光熔凝对涂层表面应力变化影响的规律和裂纹减少的原因，研究纳米颗粒在激光作用下在涂层中的结构特征，发挥纳米颗粒的弥散强化使涂层具有优异的强韧性的作用，解决目前环境障涂层在热循环过程中存在热应力，产生裂纹，结合力低、导致涂层失效等问题。

结题报告摘要.硅基非氧化物陶瓷及其复合材料（SiC、Cf/SiC、SiCf/ SiC，etc.）具有比重轻、比强度大、相较高温合金具有更好的高温力学性能和热学性能，在大推重比航空发动机中具有广泛的应用前景。 然而，在航空发动机工作的高温，氧气，水蒸气和熔盐等腐蚀气氛环境下，硅基非氧化物陶瓷表面会被严重侵蚀， 最终失效。.保护硅基非氧化物陶瓷材料常用且有效的方法是采用稀土硅酸盐作为保护涂层，成为最有潜力的环境障涂层材料。.等离子喷涂技术制备的稀土硅酸盐环境障涂层常伴随气孔较多，表面较粗糙、具有典型的层状结构等缺陷。这些缺陷的存在严重影响环境障涂层的使用寿命。通过激光熔凝重熔处理大气等离子喷涂制备的涂层，可以有效地消除等离子喷涂层结构中的层状结构、细化组织、消除涂层内部缺陷、调节层与层元素的分布、提高涂层的硬度和抗热振性能。纳米级硅酸盐材料由于超细的晶粒尺寸、极高的表面积以及弥散强化作用，具备优异的力学性能。而目前对纳米级稀土硅酸盐，尤其是可直接用作等离子喷涂填料的纳米级球形稀土硅酸盐的精准合成及相关热学、力学性能等尚无系统研究。.通过大量系统的试验和宏观与微观的表征，得到如下具备科学参考价值和实际应用价值的试验结果。.（1）精准合成出粒度大小可控、形貌均匀的高纯纳米级球形（Y, Yb, Er, Lu）2Si2O7.（2）精准合成出粒度介于200-500nm之间的高纯，高度结晶的纳米级（Y, Yb, Er, Lu）PO4.（3）系统研究了纳米级球形Yb2Si2O7 的高温相稳定性及高温条件下晶型转变规律.（4）采用优化的等离子喷涂参数制备SiC/Si/mullite/Lu2Si2O7 -Lu2SiO5 环境障涂层体系；并首次将激光熔凝方法应用于环境障涂层体系的改性研究，系统研究了不同激光熔凝工艺参数重熔处理后涂层的表面形貌、成分分布、涂层硬度变化等情况，获得了适用于SiC/Si/mulllite/Lu2Si2O7-Lu2SiO5涂层体系的最佳激光熔凝参数。.（5）采用优化的激光熔凝参数重熔处理经大气等离子喷涂制备的涂层；在模拟发动机工作环境下重熔处理后涂层的抗热振寿命提高了1.05倍。