Detailed damage analyses of a plasma sprayed ZrO 2 /8 wt.-% Y 2 O 3 -MCrAlY-CMSX-4 TBC system during isothermal and cyclic oxidation tests with different dwell times at high temperature have been performed. The resulting failure mode, i.e. the particular delamination crack path, is strongly dependent on the temperature cycle applied. Isothermal exposure promotes crack propagation within the TGO, whereas thermal cycling shifts the crack path towards the TBC. Thermal cycling with dwell time at high temperature leads to a mixed delamination crack path (partly within TBC and TGO). The respective correlation between TBC lifetimes and duration of high temperature dwell time per cycle (cycle frequency) is shown and discussed.

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This paper describes a through‐process modelling on a microstructural level of the production of a coated turbine blade, including its in‐service properties and degradation, accompanied by the actual production and testing of a CMSX‐4 single crystal turbine blade dummy. The following steps are dealt with by modelling and experiment: solidification of the blade alloy during casting, microstructural changes during homogenization and aging heat treatments, chemical vapour deposition of an Al2O3 diffusion barrier coating, physical vapour deposition (sputtering) of a (Ni,Co)CrAlY bond coat, atmospheric plasma spraying of an Y2O3 stabilized ZrO2 thermal barrier coating and microstructural changes and development of critical stresses at in‐service conditions. This work forms a part of the Collaborative Research Centre 370 (SFB 370) “Integrative materials modelling”.

Abstract. The present contribution gives an overview about recent research on a thermal barrier coating (TBC) system consisted of (i) an intermetallic MCrAlY-alloy Bondcoat (BC) applied by vacuum plasma spraying (VPS) and (ii) an Yttria Stabilised Zirconia (YSZ) top coat air plasma sprayed (APS) at Forschungszentrum Juelich, Institute of Energy and Climate Research (IEK-1). The influence of high temperature dwell time, maximum and minimum temperature on crack growth kinetics during thermal cycling of such plasma sprayed TBCs is investigated using infrared pulse thermography (IT), acoustic emission (AE) analysis and scanning electron microscopy. Thermocyclic life in terms of accumulated time at maximum temperature decreases with increasing high temperature dwell time and increases with increasing minimum temperature. AE analysis proves that crack growth mainly occurs during cooling at temperatures below the ductile-to-brittle transition temperature of the BC. Superimposed mechanical load cycles accelerate delamination crack growth and, in case of sufficiently high mechanical loadings, result in premature fatigue failure of the substrate. A life prediction model based on TGO growth kinetics and a fracture mechanics approach has been developed which accounts for the influence of maximum and minimum temperature as well as of high temperature dwell time with good accuracy in an extremely wide parameter range.

Degradation evolution and failure mechanisms of air plasma-sprayed thermal barrier coatings during thermal cycling were investigated using microstructural and acoustic emission analysis. The microcrack evolution observed suggests that the life-time is governed by the kinetics of crack formation, growth and linking of individual cracks. The damage in the thermal barrier coatings mainly occurs during cooling due to thermal-expansion mismatch stresses at the metal – ceramic interface. The effect of the minimum cycling temperature on the lifetime was found to be much more pronounced than that of a variation in cooling rate. Experimental results were supported by finite element modeling of the stress distribution at the metal – ceramic interface during cooling at different rates.