Microstructure and Modeling of the High-Temperature Deformation Behavior of Carbide-Hardened Superalloys

Thermal barrier coatings (TBC) have the potential to improve considerably the efficiency of stationary gas or aircraft turbines by increasing the operating temperature. This report describes the use of creep experiments and microstructure investigations in order to predict the deformation behavior of uncoated and TBC-coated superalloys NiCr22Co12Mo9 and CoCr22Ni22W14. The results of mechanical tests and transmission electron microscopy investigations have been used as input data into two models in order to describe the hot deformation behavior. The deterioration in the creep properties of the superalloy NiCr22Co12Mo9 as a result of coating was due to the degraded state of the M23C6 precipitates in the substrate metal, as well as to the weakening of the solid solution- and precipitation-hardening mechanisms responsible for the creep strength of the material, in the region of the boundary surface.