Thermal barrier coatings systems are composed of a zirconium dioxide-(6 to 8 wt.%) yttrium oxide ceramic top coat about 300-500 micrometer in thickness, deposited either by air plasma spraying or electron beam assisted physical vapour deposition, over an MCrAlY (M = Ni, Co or NiCo) bond coat, about 100 micrometer thick, deposited by vacuum plasma spraying. In this paper, the stiffness of as-sprayed zirconia is measured using three different techniques, namely cantilever beam bending, ultrasonic resonance and nanoindentation. The paper explores the effect of post-deposition heat treatment on the value obtained. The results show that the cantilever bend technique, employed with a high precision scanning laser method of displacement measurement, was found to be the most reliable procedure. Paper includes a German-language abstract.

Test pieces were machined from vacuum plasma sprayed (VPS) deposits of the bond coat materials Ni-22Cr-10Al-1Y and Co-32Ni-21Cr-8Al-0.5Y. Changes in gauge length at high temperatures under various applied stresses were measured using a scanning laser extensometer. In this way, isothermal creep data and, using no applied load, expansivity data were obtained. The CoNiCrAlY creeps faster than the NiCrAlY at low stresses, but the reverse is true at high stresses. The CoNiCrAlY has an appreciably higher expansivity than the NiCrAlY. These data were used in a numerical process model to evaluate the effect of bond coat creep on the stress state of a TBC system. Comparisons between measured and predicted curvature histories during deposition were used to evaluate the quenching stress for the two materials. This is considerably higher for the CoNiCrAlY. Although creep generally results in reduced stress levels at service temperatures, it can generate residual stresses which are raised after cooling down to ambient temperature, particularly for the CoNiCrAlY. Evaluation of the strain energy release rates associated with various stress distributions, and comparison with measured interfacial fracture energy values, confirmed that debonding will tend to occur at the top coat / bond coat interface, rather than between the bond coat and the substrate. However, bond coat spallation is more likely with CoNiCrAlY than with NiCrAlY.