The Oxidation and Interdiffusion of a Chromia Forming Multilayered TBC System

Current thermal barrier coating systems (TBCs) rely on an alumina-forming bond coat to provide protection against oxidation. At bond coat temperatures below 900 °C, however, optimum protection against oxidation and hot corrosion is best achieved by a chromia layer. TBC systems using this approach are currently being developed and an example is examined in this paper. The multilayered bond coat in the present TBC system consisted of: a NiCrAlY layer aluminised at its surface; a 50:50 NiCr layer (containing 1.8 wt% Si); an air plasma sprayed yttria stabilised zirconia top coat. These samples were oxidised in laboratory air at 750, 800 and 850 °C for durations up to 1,000 h. Post-test characterisation was undertaken using SEMs and energy dispersive X-ray spectroscopy to determine the growth rate of the TGO and to investigate interdiffusion within the layered coating structure. The interdiffusion process was also modelled using the ODIN finite difference code.