Thermal Properties of Thermal Barrier Coatings – Practical Evaluation Aspects

Thermal properties of thermal barrier coatings (TBC’s) are an important aspect of their initial design and development. Thermal properties, such as thermal conductivity, are related to the coating initial microstructure and materials used to produce it. However, thermal properties do not remain constant in service and will change with high temperature exposure. Monitoring the change in thermal properties is key to understanding the degradation of TBC’s and effective evaluation of TBC’s in the research and development stage. Evaluation of thermal properties has been carried out to a lesser or greater extent in many research publications over the last decades. However, specific technical aspects of the test process are often not discussed in detail and there are many potential pitfalls for those conducting the evaluation.

This paper will cover some practical aspects of thermal property evaluation of TBC ceramics and bond coats. Specifically: methods to measure specific heat capacity and density, advantages and disadvantages of free standing and multi-layer coating evaluation, the influence of thermal exposure on the evolution of thermal properties and challenges presented by new materials and coating microstructures.