The project involves the production of TBCs with different bond coats and with controlled surface morphologies, measurement of residual stress in the alumina thermally grown oxide (TGO) using luminescence, and measurement of YSZ mechanical properties and inter-layer adhesion by indentation.  Generation of stress in the coating on thermal cycling, and its relief by plastic deformation and fracture, was studied by finite element modelling (FEM).  The bond coats studied include two beta-structured Pt-Al types (differing in their aluminising temperature, LT and HT)) and a gamma-gamma prime structure produced by Pt diffusion without aluminising. 

In this contribution we describe some of the key findings of the project.  The TBCs with the LTPt-Al bond coat fail by a rumpling mechanism that generates isolated cracks at the interface between the TGO and the YSZ.  This reduces adhesion at this interface and the TBC delaminates when it can no longer resist the release of stored elastic energy of the YSZ, which stiffens with time due to sintering.  By contrast, the TBCs with Pt diffusion bond coats do not rumple, and the adhesion of interfaces in the coating does not significantly degrade.  These TBCs fail at the bond coat/TBC interface driven by release of stored elastic energy in both the TGO and YSZ.  The TBCs with HTPt-Al bond coats show mixtures of both failure mechanisms.  It is shown that the different failure mechanisms are caused by the different high temperature mechanical properties of the bond coats.