Abstract
The surfaces of gas turbine components are coated with thermal barrier coatings (TBCs) using a plasma spraying technique. A lot of effort has been expended examining the TBC interfacial strength, however studies examining how residual stress is formed after the process and how the coating stress changes with temperature are limited. In this report, the residual stress prediction model is proposed based on the splat deposition process. A simplified model including the plasma sprayed process is developed based on shear-lag theory. The simplification is given in continuous particle deposition process. That is, continuous particle deposited coating is modeled as a single layer, which is called by "deposition layer". This deposition layer is assumed to impact directly onto the substrate. The binding layer is also introduced to express multiple cracks caused by quenching stress in splats and sliding deformation at splat boundary. It is shown that the numerical analysis has good agreement with the associated experiments.
Highlights
Ceramic thermal barrier coatings (TBCs), which play an important role in insulating components such as blades of gas turbines from high heat flux and/or high-temperature environments, are generally deposited using plasma-spraying technology
We develop a comprehensive numerical model to estimate residual stress in TBCs generated during the plasma spraying process, based on the assumption of layer build-up structure modeled as the continuous splat deposition process
Residual stress comprises both quenching stress, which is caused by contraction of the deposition layer on the underlying substrate, and thermal stress, which is generated by a thermal expansion mismatch between the deposition layer and the substrate
Summary
Ceramic thermal barrier coatings (TBCs), which play an important role in insulating components such as blades of gas turbines from high heat flux and/or high-temperature environments, are generally deposited using plasma-spraying technology. We develop a comprehensive numerical model to estimate residual stress in TBCs generated during the plasma spraying process, based on the assumption of layer build-up structure modeled as the continuous splat deposition process. A continuous molten particle deposition process is idealized by impingement of a single layer (called the “deposition layer”.) onto a substrate Residual stress comprises both quenching stress, which is caused by contraction of the deposition layer on the underlying substrate, and thermal stress, which is generated by a thermal expansion mismatch between the deposition layer and the substrate. The coating stress generated in the deposition layer can be given by [1]:
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