COMPARISON OF THERMO-PHYSICAL PROPERTIES AND THERMAL PERFORMANCE OF MACRO-CRACKED THERMAL BARRIER COATING PROCESSED BY APS WITH EBPVD TBCS
The performance of a gas turbine engines may be improved by increasing the tolerance of the turbine blades to hot gases emerging from the combustor. One approach to achieving high operating temperatures involves application of thermal barrier coating (TBC) to the exterior surface of the blade while passing cooling air through the blade. Three TBC products, air plasma spray (APS), dense vertically cracked (DVC) and electron beam physical vapour deposition (EBPVD) are analysed in this study. The advantage of the air plasma spray process over EB-PVD is that the thermal conductivity of TBCs produced by the air plasma spray process is lower than EB-PVD. But the main draw back is that it has less strain tolerance to the thermal stresses at high temperatures. Because of which spallation failure takes place in TBCs. By introducing vertical segmented cracks into the coating structure which is also called macro-cracked TBCs can increase the strain tolerance in the air plasma coatings. The present study involves thermal properties characterization of macro-cracked TBCs as a function of the thickness of the coating and temperature. Measured and data of thermo-physical properties from literature are used in a model to assess the insulating effects of the TBC on a superalloy substrate in a simulated high temperature environment. The radiative transport is considered within the semi-transparent TBC layer. The results of the simulation show that the substrate with an EB-PVD or macro-cracked layer has a higher temperature than when it has an APS TBC layer. Thus, confirming better insulating effects of APS layers. These results are used for stress analysis studies to investigate effect of induced thermal stress gradients. For this study a preliminary elastic stress analysis carried out showed that the in-service stresses in the EBPVD and DVC coating was lower compared to the APS processed TBC.