激光熔覆大厚度纳米热障陶瓷涂层成形控制及强韧化机理

Preparation of thick thermal barrier coatings (TBCs) is a hot research topic at this stage. In this project, the thick nanostructured thermal barrier ceramic coating would be fabricated by squash presetting type laser multi-layer cladding with nanostructured agglomerated powders, and preparation control and reinforced mechanism of laser-clad TBCs will be studied. The crack of clad layer would be controlled by preheating and slow cooling rate of sample with incubator, applying the ultrasonic vibration and closed-loop controlling temperature of molten pool during laser cladding process. The main research as follows: experimental research and preparation control of thick nanostructured ceramic coating by squash presetting type laser multi-layer cladding; process parameters optimization based on neural networks and genetic algorithms; thermal-mechanical coupling finite element analysis of laser multi-layer cladding; discussion of the crack forming during laser cladding process; suggestion of cladding layer crack control measure; nanoparticles growth model during laser cladding process based on brook's theory; reinforced mechanism of nanoparticles; microstructure and property of laser-clad thick nanostructured thermal barrier ceramic coating. It can expand the application scope of TBCs and establish a new preparation method of thick TBCs through this project.

制备大厚度热障涂层是现阶段研究的一个热点。本项目拟在激光熔覆过程中用保温箱对试样进行预热和缓冷处理、引入超声振动及对熔池温度闭环控制等系列熔覆层裂纹控制措施基础上，以压片预置式纳米团聚体陶瓷粉末作为熔覆对象，基于激光多层熔覆的方法，在镍基高温合金表面进行激光熔覆大厚度纳米陶瓷热障涂层的制备技术及强韧化机理研究。课题的主要研究内容包括：压片预置式激光多层熔覆纳米陶瓷涂层试验研究及成形控制；基于遗传神经网络的激光熔覆工艺参数多目标优化；对激光多层熔覆进行热力耦合有限元分析，讨论熔覆层裂纹形成机理，并研究熔覆层裂纹控制措施；建立基于Brook理论的激光熔覆过程中纳米陶瓷颗粒生长模型，并分析纳米陶瓷颗粒对熔覆层的强韧化机理；研究所制备厚纳米陶瓷热障涂层的组织及性能。通过该项目，能够拓展热障涂层的应用范围，建立起一种新的制备大厚度热障涂层的加工方法。

随着航空发动机向高推重比、高流量比、高涡轮进口温度方向发展，发动机的工作温度越来越高，从而对热障涂层提出了更高的要求。而热障涂层的隔热性能与其厚度成正比，因此制备大厚度热障涂层成为现阶段研究的一个热点。本研究在激光熔覆过程中用保温箱对试样进行预热和缓冷处理、引入超声振动及对熔池温度闭环控制等系列熔覆层裂纹控制措施基础上，以压片预置式纳米团聚体Al2O3-13%TiO2(质量分数)陶瓷粉末作为熔覆对象，基于激光多层熔覆的方法，进行激光熔覆大厚度纳米陶瓷热障涂层的探索，所完成的主要工作如下：.(1)在分析熔覆层裂纹形成机理和控制方法的基础上，提出了一种可减小熔覆层裂纹的凸字形激光光束实现方法和装置，另外提出了一种激光多层熔覆热障涂层裂纹综合控制措施。.(2)在Brook晶粒生长经典理论基础上，结合有限元软件ANSYS数值模拟的激光熔覆温度场，计算了激光多层熔覆纳米热障涂层过程中纳米陶瓷颗粒尺寸变化，并讨论了纳米颗粒初始尺寸及不同熔覆区域对其生长的影响。.(3)分别采用正交试验法和遗传神经网络对激光多层熔覆大厚度热障涂层工艺参数进行了优化，建立了熔覆工艺参数(熔池闭环控制温度、超声振动频率及保温箱预热温度)与涂层性能(结合强度和显微硬度)之间的遗传神经网络预测模型，并采用遗传算法对涂层结合强度和显微硬度进行了单目标和多目标参数优化。.(4)在对激光多层熔覆纳米热障涂层组织结构分析的基础上，研究了涂层厚度（熔覆层数）对其结合强度的影响，并对比了等离子喷涂常规热障涂层、等离子喷涂纳米结构热障涂层及激光熔覆热障涂层的隔热性能。