Evolution of residual stress distribution and microstructure in a platinum-aluminide coating

Abstract

In the present paper, we consider the evolution of residual stress and the corresponding microstructure in the thermally grown oxide (TGO) formed on a type of platinum-aluminide coating, RT22, on a single crystal superalloy CMSX4. Eight coated specimens were oxidised in a simulated gas turbine environment at 850, 950, 1000 and 1050°C for periods of time extended up to 10 000 h. Photo-stimulated luminescence piezo-spectroscopy (PLPS) was used to measure the residual stress in the TGO in order to provide a detailed evaluation of the stress developed at each temperature. The stress variation was evaluated using a random measurement approach, which demonstrated that up to 100 measurements provide data that allows the stress distributions to be determined with high confidence. Scanning electron microscope (SEM) and energy dispersive X-ray (EDX) microanalysis have been adopted to investigate microstructural and compositional changes in the TGO and the coating as a function of time and temperature. The results are discussed with respect to the correlation between the statistically analysed stress distribution, degradation of the TGO and coating overall integrity.