Lifetime and failure modes of plasma sprayed thermal barrier coatings in thermal gradient rig tests with simultaneous CMAS injection

In this study a burner rig facility has been used for the evaluation of TBC performance, where a thermal gradient is applied across the TBC at cyclic load and CMAS is continuously injected to the combustion environment to simulate the conditions closer to actual service in an engine while allowing control of important degradation limiting parameters. Tests have been performed on the state of the art material YSZ while loading parameters as high temperature dwell time and CMAS deposition rate have been varied. Tests have been evaluated in terms of chemical degradation, failure mode and TBC spallation lifetime by means of SEM, EDS and XRD. Test conditions and relevance to in-service operating conditions are discussed. Major impacts on thermal gradient cycling lifetime and similarities and discrepancies related to reported failure mechanism are reviewed.