热障涂层中表-界面裂纹间的竞争机理

Coatings debonding is the major failure mechanism of thermal barrier coating system (TBCs),which is important for the strength and durability evaluation of such structures. It is demonstrated that the presence of multiple vertical surface cracks in the top coat was beneficial in improving the TBCs durability by reducing the crack driving force developed by thermally induced strain. However, the complex micro and macro structures and service enviromental makes it difficult to understand the competitive mechanisms of multiple surface cracks and interfacial delamination. The effects of vertical surface cracks on the initiation and propagation of interfacial delamination are investigated in this project. The strain energy release rates at multiple surface cracks tips are calculated for different surface crack length, density and morphology. The effect of multiple surface cracks on the interfacial delamination of brittle thin coatings on elastic substres is investigated. Furthermore, the necessary conditions for the appearance of concomitant interfacial delamination are certificated for various elastic mismatch, geometry parameters, and interface toughness. This project aims at the competitive mechanisms of multiple vertical surface cracks and interfacial delamination, which can be used as engineering guidances for improving the durability and reliability of TBCs.

陶瓷涂层与粘结层间的界面破坏是影响热障涂层系统（TBCs）耐久性的关键因素，表面垂直裂纹是延缓乃至抑制涂层早期剥落失效的有效途径。然而，TBCs复杂的自身结构、组织成分和服役环境等，使得表面垂直裂纹与界面裂纹间的竞争机理尚不清晰，从而制约了热障涂层粘结强度的合理评价。本项目以陶瓷涂层内表面垂直裂纹与陶瓷层/粘结层界面裂纹为对象，研究表面垂直裂纹与界面裂纹的竞争机制，具体包括：采用理论分析与数值计算研究表面垂直裂纹长度、距离及形貌等对断裂主控参数的影响规律；通过分析表面垂直裂纹对界面裂纹萌生及扩展的影响，揭示表-界面裂纹相互竞争机理；基于试验及数值分析研究材料失配和几何尺寸对表面与界面裂纹断裂力学行为的影响规律。本项目旨在揭示陶瓷涂层内制备网状分布表面裂纹对界面裂纹萌生及扩展的影响规律，为有效延迟或抑制陶瓷涂层早期剥落和研制新型抗剥落失效TBCs结构提供理论基础。

本项目以陶瓷涂层内表面垂直裂纹与陶瓷层/粘结层界面裂纹为对象，结合数值和实验方法研究了界面裂纹断裂行为及其关键影响参数、表面垂直裂纹与界面裂纹的相互影响，揭示了陶瓷涂层内周期分布表面垂直裂纹对界面裂纹萌生及扩展的影响规律、高温氧化生成物对界面裂纹的影响规律以及表-界面裂纹间竞争机理。.研究表明：（1）对于不同材料属性，夹层存在未改变界面裂纹稳态扩展时的裂纹扩展驱动力；而对于不同位置及厚度的夹层，界面裂纹断裂行为受到显著影响。（2）不同厚度及材料属性的陶瓷层与粘结层对TBCs的失效模式有着显著影响。对于较厚的陶瓷层，主要以界面脱粘失效为主；而对于较薄的陶瓷层，则以表面裂纹断裂为主导。（3）混合氧化物生长率对界面完整性影响明显，其生长会引起界面裂纹的萌生及扩展，进而加速涂层的剥离。尤其是在混合氧化物具有很高的生长率时候，会明显加速涂层界面裂纹的扩展及剥离。在TBCs选材时，应尽可能考虑添加可抑制有害混合氧化物的形成。（4）粘塑性仅减缓了界面裂纹扩展，但对起裂并无显著影响。高孔隙率和低混合氧化物生长速率有助于减缓界面裂纹萌生和扩展。然而，初始孔洞大小对界面断裂行为影响可以忽略。为实现较好的抗烧结性能，应采用粘性强、混合氧化物含量低的多孔陶瓷材料。