A parametric study of the double-ceramic-layer thermal barrier coatings part I: Optimization design of the ceramic layer thickness ratio based on the finite element analysis of thermal insulation (take LZ7C3/8YSZ/NiCoAlY DCL-TBC for an example)

The double-ceramic-layer thermal barrier coating (DCL-TBC) consists of a top ceramic layer (TC1), an inside ceramic layer (TC2), bond coat (BC) and alloy substrate (SUB). As a parametric study, this new coating system (DCL-TBC) is studied from two different topics: the study on the heat insulation behavior of the DCL-TBC and the study on the stress state of the DCL-TBC. The works reported in the present paper is focused on the former. Based on the structure of the DCL-TBC, a FE numerical model had been developed to calculate the temperature of the DCL-TBC under the thermal loading, and three kinds of heat transport mechanisms, which are heat conduction, heat convection and heat radiation, were considered in the model. y, based upon the calculation results, the relationships between the temperature of each layer in the DCL-TBC and the two structure parameters: the thickness of the TC1 layer (HTC1) and the total thickness of two ceramic layer (Htot) were mainly studied. Results had shown that the DCL-TBC with large values of HTC1 and Htot has better heat insulation ability which reduces the temperature of TC2 and BC. However, the temperature of the TC1 layer will be increased with the increase in HTC1 and Htot. These two points indicate that too large values of HTC1 (and Htot) and too small values of HTC1 (and Htot) are all unfavorable to the temperatures in the whole DCL-TBC. A reasonable range of HTC1 and Htot should exist and could ensure that the temperatures in the whole DCL-TBC could be in the safe state. Then for further study, the reasonable values of the thickness of TC1 and total thickness of two ceramic layers were investigated based on the temperature calculation results and temperature resistance of each layer, and the “temperature safe region” is obtained in the HTC1–Htot map. Based on the “temperature safe region”, it has been concluded that the total thickness of two ceramic layers should not exceed 370 μm, and the thickness range of the TC1 layer can be obtained in the condition that the total thickness of two ceramic layers is a certain value.