On the Dependence of Durability of Thermal Barrier Coatings on the Oxidation Resistance of Composite Substrate Systems Produced by Diffusing Platinum into Selected Ni-Based Superalloys

Platinum is diffused into the single-crystal superalloys CMSX-4 and CMSX-10 to integrate a surface protection layer consisting of a mixture of γ′- and γ-phases. It is shown that the Pt/CMSX-10 system is characterized by higher thermal stability and resistance to oxidation in comparison with the Pt/CMSX-4 system. Such difference is correlated with the initial microstructure and composition of the two systems and is reflected on their performance in thermal barrier coatings utilizing yttria-stabilized zirconia as top coating. Based upon cyclic oxidation tests, the Pt/CMSX-10 system is found to provide about threefold increase in useful life. However, both coatings are found to fail by spallation of the top coating due to decohesion of the thermally grown oxide developed by each system. It is concluded that the higher performance provided by the Pt/CMSX-10 stems from decelerated kinetics of interdiffusion and oxidation.