新型抗烧结热障涂层多功能孔隙协同设计及特征共优化服役机理

Thermal barrier coatings (TBCs) are used to protect metallic components against heat flux in aircraft engines and land-based gas turbines. Application of TBCs enables the engines to operate at higher temperatures, thus improving their overall efficiency. In addition, the TBCs decrease the temperature experienced by the coated components, thereby extending their lifetime. Therefore, TBCs have been playing a crucial role in the development of engines since the past few decades. Nowadays, advanced engines often require TBCs to be characterized by high thermal insulation and a long lifetime; and hence, these are the key requirements for advanced TBCs in future applications..The challenge is to retain high performances despite the significant changes in the ceramic structure caused by sintering during thermal exposure. For example, in conventional plasma sprayed TBCs, both the thermal insulation and the strain tolerance can be decreased by approximately 50%. The reason is that the functional pores are significantly healed by sintering. Since degradation tremendously threatens the lifetime as well as the thermal insulative function of the TBCs, there is an urgent need for designing a TBCs structure capable of degradation-resistant behavior..However, it is a huge challenge to simultaneously enhance thermal insulation and lifetime. Regarding the thermal barrier effect, in-plane pores vertical to heat flux are designed to prevent heat flux. However, these in-plane pores are prone to cause spallation of TBCs during service. As a result, these TBCs often have poor performance on lifetime. Regarding the lifetime, the vertical pores have proven their benefit in enhancing strain tolerance, and thus extending the lifetime of TBCs. However, the current TBCs with vertical pores often have dense microstructure, which has low thermal insulation. .This study proposed a novel sintering-resistant TBCs structure based on co-design of multi-functional pores: macro-vertical-pores and micro-parallel-pores. Therefore, this novel structure of TBCs can achieve co-enhanced performances of lifetime and thermal insulation. To begin with, a hybrid-layered model will be developed to analyze the formation and co-existence of the multi-functional pores. The aim is to provide guide for the following experimental preparation. Subsequently, the novel TBCs will be prepared by a new method to form multi-functional pores. Effects of parameters on the scale of multi-oriented pores will be investigated. Finally, the novel TBCs are evaluated by a gradient thermal cyclic test. The sintering-resistant behavior will be investigated, along with the exploration of mechanism on co-enhanced lifetime and thermal insulation. Overall, the novel TBCs are expected to simultaneously prolong the lifetime and increase the thermal barrier performance, which is the main objective of advanced TBCs in next-generation applications.

实现长寿命隔热防护，是先进航机和燃机用热障涂层(TBCs)的核心目标。然而，TBCs服役后隔热功能降低~50%，且极易开裂剥落，根源是高温烧结引发其内部功能微孔隙大量消失。遗憾的是，目前的单取向功能造孔抗烧结设计难以兼顾隔热与寿命。本研究提出了多功能孔隙多取向协同设计的方法，解决TBCs抗烧结“顾此失彼”的瓶颈难题，以实现新型抗烧结TBCs隔热、寿命共优化。首先，建模分析多取向孔隙的成孔及尺度共存机制，阐明新型涂层宏/微观双尺度孔隙的设计要求；随后，基于多功能孔隙的双取向复合成孔新方法，发展新型TBCs的制备调控工艺；最后，采用梯度热循环测试，探究多取向孔隙的抗烧结机制，揭示新型TBCs隔热、寿命共优化的服役机理。本项目的新型抗烧结TBCs，兼具高隔热、长寿命的优越综合性能，对发展先进航机和燃机具有重要理论价值和技术支撑意义。

热障涂层(TBCs)用以保护高温合金免受高温热流的影响，这对于开发高性能燃气轮机是非常必要的。TBCs具有多孔结构，高温热暴露导致烧结致密化，由此产生的刚化是导致TBCs失效的主要原因。因此，需要减少对TBCs寿命的负面烧结效应。本研究，通过实验揭示了烧结机理和导致刚度和力学性能变化的主要因素。结果表明，原本光滑的二维（2D）孔隙内表面的多尺度起伏触发了上下内表面之间的多点接触，导致在热暴露过程中孔隙愈合。2D孔隙的愈合是热暴露后TBCs的主要结构特征变化，也是其刚化和力学性能变化的主要原因。然后，设计并模拟了对具有纵向裂纹结构的TBCs的烧结效果。研究发现，在陶瓷层中植入纵向裂纹可以使烧结效果和开裂驱动力分别降低87.9%和79.9%。减少程度很大程度上取决于纵向裂纹之间的距离。随后，分析和讨论了抗烧结TBCs的机理。纵向裂纹结构表现出对尺度敏感的刚化，表明宏观刚化远低于微观刚化。因此，宏观烧结效应降低，TBCs在热暴露期间保持对整体高应变容限。由此产生的应变能释放率远低于传统TBCs的释放率。最后，基于反向变形发展了在层状热障涂层内生成纵向裂纹的方法。本研究将对先进燃气轮机中使用的高温合金部件的长寿命热防护提供一定的帮助。