Evolution of a diffusion aluminide bond coat for thermal barrier coatings during thermal cycling

The thermal cyclic durability of a TBC is thought to be strongly dependent on the physical and mechanical properties of the bond coat layer. A novel high temperature microsample tensile testing technique has been employed to characterize the mechanical behavior of a platinum modified nickel aluminide bond coat at 0% and 28% of cyclic life in the temperature range of 25 to 1150 degreesC. Values for the coefficient of thermal expansion and the Young's modulus are reported. The bond coat exhibits a ductile to brittle transition temperature at approximately 600 degreesC, and above this temperature the yield and creep strength decreases rapidly with temperature. A power law description of elevated temperature stress relaxation is developed. The intermediate temperature strength was found to increase with thermal cycling, while the high temperature strength remained the same. This evolution in properties has been related to the development of a martensitic transformation that occurs during each thermal cycle. (C) 2003 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.