Research On Analysis And Design System For Ceramic/Metal Gradient Thermal Barrier Coatings

With the increasing demand of intensity for internal combustion engines, the problem of the reliability of internal combustion engines stands out more and more clearly. In order to improve the economy and reliability of internal combustion engines, ceramic materials are sprayed on the metal surface of the combustion chamber components as ceramic thermal barrier coating to subject both thermal loading and mechanical loading. The large difference of thermal expansion coefficient between ceramic and metal materials causes large thermal stresses and thermal fatigue, which may lead to cracking and spalling of the coating. The conception of functionally gradient material is introduced into the ceramic thermal barrier coating to decrease the high thermal stresses caused by the mismatch of the thermal expansion coefficient. This kind of ceramic thermal barrier coating, which has gradient microstructure as well as gradient material properties, is called as ceramic/metal gradient thermal barrier coating. Theoretical analysis, numerical calculation and optimization design for ceramic/metal gradient thermal barrier coating are carried out in this paper, the relating procedures are programmed, and finally the ceramic/metal gradient thermal barrier coating analysis and design software (CCDS) which has user-friendly interface, is successfully developed according to software engineering methodology.Both the multi-layer plate model and multi-layer cylinder model adopted in this paper are composed of four layers: substrate layer, metal bond layer, ceramic/metal gradient layer and ceramic work layer. The polynomial function and exponential function are adopted for the structure model of the ceramic/metal gradient layer respectively. The analytical and finite difference solutions of temperature fields and stress fields in the two mathematical models (plate model and cylinder model) are derived, the relating procedures are programmed, and the existing finite element procedures are improved. In order to reduce the thermal stress in the ceramic/metal gradient thermal barrier coating as much as possible, the optimization design of thecoating structure is carried out by genetic algorithm based on SAAS or ANSYS Parameter Design Language (APDL).The CCDS software is developed for analyzing the heat transfer and the thermal stress in the ceramic/metal gradient thermal barrier coatings, and for designing the optimal coating schemes. The CCDS is developed according to software engineering methodology with C++ Builder 5.0 and has user-friendly interface. It is composed of three functional modules: preprocess module, analysis module and post process module. Initial data are input in the preprocess module, calculation of the temperature and thermal stress is carried out in the analysis module, and visualization is realized by the post process module. Calculation is carried out by analytical method, finite difference method and finite element method. In addition, the CCDS is enhanced by attaching an optimization design module which completes optimization design for ceramic/metal gradient thermal barrier coatings by genetic algorithm based on SAAS or ANSYS Parameter Design Language (APDL) and an expert system module which may propose schemes and suggestions for coating design.CCDS software not only can be used to implement the theoretical calculation and numerical calculation of temperature fields and thermal stress fields in the ceramic/metal gradient thermal barrier coating, but also can be used to optimize the structure design of the ceramic/metal gradient thermal barrier coating. With respect to the analysis and design of the ceramic/metal gradient thermal barrier coating, CCDS software has general use and utility to some extent. At the meantime, CCDS software has some reference value for the development of similar engineering application software.