Thermal Properties of Novel Thermal Barrier Coatings

The focus of the research is to select oxides with low thermal conductivity. Currently 7-weight percent yttria stabilized zirconia is the thermal barrier coating (TBC) in use. At high temperatures 7YSZ partitions into a mixture of tetragonal and cubic zirconia. As 7YSZ cools a transformation occurs. The tetragonal phase changes to a monoclinic phase resulting in the delamination of the coating. We are exploring material systems with a lower thermal conductivity as a potential TBC. We substituted hafnia for zirconia using a mass substitution technique. We did ten comparisons of ranging Zr and Hf ratios with two levels of yttria concentrations, one at 7 weight percent yttria and the other at 14 weight percent yttria in two groups of five. A thermal flash technique is used to measure thermal diffusivity and heat capacity of the sample from which thermal conductivity can be calculated. Applications include the use of TBCs in gas powered turbine engines and other applications where protection against high temperatures is required. This increases the engine efficiency and life of the components coated by the oxide. The research will explore oxides that are capable of operating at temperatures required for the next generation of gas powered turbine engines.