Effect of Pt-aluminide bond coat on tensile and creep behavior of a nickel-base single crystal superalloy

The effect of Pt-aluminide bond coat on the mechanical properties, namely tensile and creep, of a Ni-base single crystal superalloy has been investigated. Tensile properties of both uncoated and bond coated specimens were evaluated in the temperature range of room temperature (RT)-1100 °C. Creep testing was carried out using four combinations of temperature and stress, viz. 850 °C/500 MPa, 982 °C/240 MPa, 1038 °C/138 MPa and 1100 °C/90 MPa. By and large, the presence of bond coat reduced the tensile strength of the superalloy at all temperatures. However, the coated alloy exhibited a higher ductility than the uncoated alloy in the above temperature range. The lowering of strength in the coated alloy can be explained in terms of the significantly lower strength of the coating as compared to that of the substrate, which caused a decrease in the strength of the coating-substrate composite structure. The higher ductility of the coated alloy, especially at elevated temperatures, can be attributed to the surface protection provided by the oxidation resistant bond coat to the substrate. The creep properties (strain-to-fracture and creep life) of the coated alloy were somewhat inferior to those of the uncoated alloy at all test temperatures. This can be ascribed to the low strength of the bond coat at high temperatures and also to the microstructural changes that took place in and near the coating during the creep test.