热载荷下热障涂层表-界面裂纹间的相互影响

Interaction between surface and interface cracks in thermal barrier coatings under thermal load

针对高温热载荷条件下APS制热障涂层裂纹失效问题,基于涂层系统热弹、热弹塑性本构关系,考虑陶瓷层/氧化层/粘结层界面凹凸形貌,依据表、界面裂纹位置、性质不同,分别运用断裂力学和损伤力学理论建立裂纹演化模型,结合围线积分和内聚力单元法,分析了热载荷下表、界面裂纹断裂参量及开裂状态,研究了陶瓷层表面裂纹与粘结层/氧化层界面裂纹间的相互影响,揭示了热、力、化多场耦合下的裂纹失效机理。结果表明,表面裂纹大幅改变界面微区域的应力分布状态,靠近界面时能使界面裂纹扩展程度整体增加20%,且相邻凸峰处开裂非均匀性可达81%,表面裂纹断裂参量主要受多层结构热失配及缺陷主导,界面裂纹对其影响相对较小,分析结果与试验结果一致。

In view of the problem of crack failure of thermal barrier coatings(TBCs)prepared by means of APS,based on the thermal elastic and elastoplastic constitutive relations of the coating system,and taking into consideration the concave and convex morphology of ceramic coat(TC)/oxide layer(TGO)/bond coat(BC)interface,the crack evolution model was established by fracture mechanics and damage mechanics theory respectively according to the difference of position and nature of surface and interface cracks.In combination with contour integral and cohesive element method,the fracture parameters and cracking state of the surface and interface cracks under the thermal load were analyzed,the interaction between the surface cracks of the thermal barrier coating and the interface cracks of the BC/TGO was studied,and the crack failure mechanism under the coupling of thermal,force and chemical fields was revealed.The results showed that the surface cracks greatly changed the stress distribution state in the interface microregion.When the surface crack was near the interface,the interface crack propagation increased by 20%,and the nonuniformity of the crack in the adjacent convex peak can reach 81%.The fracture parameters of the surface crack were mainly dominated by the thermal mismatch and the defects of the multilayerstructure.The effect of interface crack on the surface crack was relatively small.The results of the analysis were in agreement with the test results.