Development of Evaluation Methods for Thermal Stress Relief Type Ceramic Coating Design

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The objective of this research is to develop methods for evaluating thermal stress relief type ceramic coatings on the basis of transient thermal stress analyses. This study especially focuses on the development of functionally gradient materials ( FGMs ). The following evaluation and analysis methods were developed for evaluating the thermal shock resistance of FGMs in this study.(1) Evaluation of mechanical properties of constituent materials ( Small punch testing method )In order to determine the optimum microstructure of FGMs under the thermal environment, the mechanical properties as a function of the mixture ratio of the component are required for the materials design. For this purpose, the small punch ( SP ) method was developed for determining the elasticity modulus and fracture properties using a thin, miniaturized specimen ( 0.5*10*10mm ). By use of the SP method a material properties data base was established for SiC/C and ZrO_2/metal composiltes.(2) Computer simulation method for evaluating transient thermal stress using a finite element methodTransient thermal stress analyses were conducted on several FGMs such as SiC/C and ZrO_2/metal coating systems under the thermal environments of their applications. The analyses were also performed to simulate the test of laser heating in order to facilitate the fabrication- evaluation loop. Using the simulation method, the effect of varying the gradient microstructure on the transient thermal stresses was examined.(3) Thermal shock resistance evaluation method ( Laser and plasma-arc heating technique )Laser and plasma-arc heating methods supplemented by the transient thermal stress analysis were developed to evaluate the thermal shock resistance of FGMs. The tests demonstrated the usefulness of FGMs to mitigate the induced thermal stress within the ceramic coating materials.