Coating-assisted deterioration mechanism of creep resistance at a nickel-based single-crystal superalloy

Abstract

Pt-aluminide (PtAl) bond coats have been applied to advanced turbine blades due to their good performance in oxidation and corrosion environment, however, the complex interaction between coats and nickel-based single crystal superalloys deteriorates mechanical performance. In this work, the creep properties of samples with different coating cross-section to superalloy cross-section ratio, under 850 °C/450 MPa, 980 °C/250 MPa, 1100 °C/137 MPa conditions, have been investigated. The coating-assisted creep deterioration exhibits elevating minimum strain rate and lowering ductility limit, and the creep performance shows strong temperature and stress dependence. The prediction by using load-bearing area reduction role fails to suit the fact, such that the surface damage accumulation is taken into the consideration. The composition/phase - microhardness - surface crack initiation relation is established, and the surface crack propagation mechanisms, including surface layer spallation and cracks blunting at high temperatures and stress concentrated-induced propagation at low temperature, are revealed. Base on the above, the deterioration is suggested to be explained by coupling of above surface damage accumulation and the load-bearing area reduction. This should provide insight into the coat-superalloy interaction and usefully guide modifying performance prediction and designing advanced coats.