Crack propagation studies and bond coat properties in thermal barrier coatings under bending

Ceramic based thermal barrier coatings (TBC) are currently considered as a candidate material for advanced stationary gas turbine components. Crack pr opagation studies under bending are described that were performed on plasma sprayed ZrO2, bonded by MCrAIY layer to Ni base superalloy, The crack prop agation behaviour of the coatings at room temperature in as received and ox idized conditions revealed a linear growth of the cracks on the coating til l the yield point of the super alloy was reached, High threshold load at th e interface between the ceramic Layer and the bond coat was required to pro pagate the crack further into the bond coat, Once the threshold load was su rpassed the crack propagated into the brittle bond coat without an apprecia ble increase in the load, At temperatures of 800 degreesC the crack propaga ted only in the TBC (ceramic layer), as the ductile bond coat offered an at tractive sink for the stress relaxation, Effects of bond coat oxidation on crack propagation in the interface region have been examined and are discus sed.