Status of available testing methods and standardization

Abstract

Investigations of damage evolution and life prediction methodologies of thermal barrier coating (TBC-) systems pose a current challenge. In order to determine properties of TBC system components (bond coat, thermal grown oxide layer (TGO) and ceramic top coat) testing methods have been developed following the strategy to identify mechnical and phyiscal properties prior to lifing studies. Testing methods comprise experiments for • individual components of TBC systems and • TBC systems without/with TGO layer. The simulation of complex loading and damage evolution requires data e.g. for elastic plastic (time independent) behaviour and time dependent (creep) behaviour of bond coat as well as TGO layer. Further adhesion experiments distinguish between global experiments and local experiments. Hardness test is of interest with respect to getting local data of top coat. Further crack propagation experiments lead to e.g. energy release rate, which can directly feed in a life prediction model. Herefrom the problem arises that properties may depend on specimen design. In addition, morphology of individual TBC system components cause problems at the generation of data and their interpretation. Consequently, efforts are necessary to harmonise • specimen geometry • testing methods and • assessment procedures. The purpose of this presenation deals with the aim to give an overview about typical testing methodologies and corresponding specimen design. The harmonisation of testing practices followed by a standard is a future challenge of interest for research as well as for industry as the end user of components operating with TBC systems. Among all existing test methods the thermocyclic exposure test as an unsophisticated and widely used test in industry is presently in the ISO standardization procedure. The talk will dwell on this test and the present standardization situation to a significant extent.