A study of residual stress distribution and interfacial micro-crack development in TBCs with Cohesiv

• 作 者: Kai Lv Ying-qiang Xu Jian Sun Shu-wei Zhao Fei-fei Wang
• 机 构: School of Mechanical Engineering, Northwestern Polytechnical University, Xi'an 710072, China
• 出 处: 第十一届全国表面工程大会暨第八届全国青年表面工程学术会议
• 发表日期: 2016年4期
• 关键词: thermal barrier coatings Cohesive Zone Model residual stress micro-crack roughne

　　Thermal barrier coatings(TBCs) are applied to superalloy turbine blades to provide thermal insulation and oxidation protection. And the performance of these multi-layered and multi-material systems ,tailored for high temperature applications is closly linked to their microstrture evolution. In this work, the residual stress distribution and micro-crack development were calculated with finite element method. Residual stress distribution is the main driving force for micro-crack nucleation and propagation. A complicated sine curve, having various amplitude and wavelength was used to simulate interface morphologies between layers so as to study the stress behavior after cooling process in air plasma spraying TBCs. The elastic-plastic and creep deformation of thermally grown oxide(TGO) and bond coat(BC) were taken about. The material properties are all temperature dependent. Cohesive Zone element at the TGO-BC interface models the development of the interfacial micro-crack. The position of micro-crack nucleation was judged by stress distrbution around layers interface. The residual stress comparison between models with and without micro-crack shows the appearance of interfacial micro-crack makes the stress around layers interface fall dramaticlly. The effect of plastic and creep on interfacial micro-crack development were researched respectively, revealing these properties make micro-crack nucleation delay and slow down micro-crack propagation. Meanwhile, the analysis focused on the micro-crack propagation beside the TGO-BC interface, and took into account a broad spectrum of aspects, n mely thermal expansion mismatch, oxidation of TGO, cyclic loading and the interfacial roughness(A/B). The results show micro-crack forms already during the first cooling down to ambient and the micro-crack length stabilises after 3 cycles. Oxidation of TGO can accelerate micro-crack propagation. In addition, the bigger A/B is, the slower the micro-crack extend within a certain range. And micro-crack propagation rate(R) is linear relationship with the reciprocal of A/B.