Proposal of Delamination Strengh Evaluation Method of Thermal Barrier Coatings Based on Interface Cohesive Model with Interface Oxidation Process
Masayuki ARAI
Abstract:Thermally grown oxide layer formation between ceramic top coating layer and metal bond coating layer in "Thermal Barrier Coating (TBC)" is known to cause reduction of interface cohesion. This cohesion reduction is practically associated with a serious damage such as coating spallation due to thermal cycling, prolonged isothermal exposure and thermo-mechanical fatigue. Interface crack mechanics have been used widely to evaluate such interface strength. In the mechanics, an ideal interface condition was considered, because of the difficulty of mathematic treatment for stress field solution. However, actual interface strength is predominated by the effect of interface oxidation growth by Al diffusion process and interface instinctive problem such as a wavy interface geometry. In this study, the interface cohesive model, which is based on a spring connection between the interface nodes in the top coating and the substrate, is developed for evaluating TBC interface delamination strength with taking into account coating instinctive characterization, such as thermally grown oxide formation. Application of finite element analysis included with the developed model to the TBC delamination test by four-point bending is shown. Also, delamination energy, which is defined by energy stored in the interface spring until interface fracture surface formation, is proposed newly as TBC delamination strength. Key Words:Gas turbine, Thermal barrier coating, Delamination strength, Interface cohesion model, Finite element analysi