Die Rolle der Bondcoat-Oxidation fuer die Lebensdauer von Waermedaemmschichten Abschlussbericht

Materials for front stage blades and vanes of land based gas turbine and aero engines must be resistant to the extreme service conditions, which include thermal, chemical and mechanical effects. To ensure a sufficient service life time at continuous operating temperatures in excess of 1000 C the combined advantages of both metallic and ceramic materials are recently used by applying a ceramic thermal barrier coating (TBC) of partially yttria stabilised zirconia (P-YSZ) on top of the vacuum plasma sprayed protective bond coat (BC), which protects the underlying substrate material from oxidative attack. The main aim of this project was to develop a life time prediction model for the top coat of the APS-TBC systems for isothermal and cyclic oxidation conditions. This model should emphasize the oxidation induced failure mechanisms as well as take into account the appropriate thermal mechanical loading parameters as well as the relevant material properties and provide a reasonable description of the damage evolution process. Additionally, the model should quantify the relevant bond coat parameters that influence the spallation life time. The advancements that this project has made in ex-situ and in-situ measurement technology are still providing a large amount of insight with regard to the adhesion and the degradation of the top coat. Consequently it is now possible to propose life time prediction models that are based on semi-detailed information about the top coat and the thermally grown oxide degradation process. Two new measurement approaches have been developed and both have provided interesting results with regards to the thermal barrier coating system degradation. The first uses a four point bend test to measure critical strains of the APS top coat. The second uses in-situ acoustic emission analysis to measure the damage accumulation of the thermally grown oxide and top coat. The most recent advance made by this project was the classification of spallation into three cases, namely, case 1 thermal fatigue failure, case 2 thermal ageing failure and case 3 Al depletion failure. Cases 1 and 2 are considered to be, more or less, oxidation induced ''mechanical'' failures, where case 3 is considered to be a type of ''chemical'' failure. This classification produces a conceptual framework that separates ''mechanical'' and ''chemical'' spallation mechanisms, which can in turn be modeled separately when the appropriate measurement data is available. (orig.)SIGLEAvailable from TIB Hannover: F04B1074 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDeutsche Forschungsgemeinschaft, Bonn (Germany)DEGerman