Microstructure and modeling of the high temperature deformation behavior of TBC-coated superalloys

The present study describes the application of hot deformation experiments and microstructure investigations in order to predict the deformation behaviour of uncoated and TBC-coated superalloys NiCr22Co12Mo9 and CoCr22Ni22W14. Estimating parameters like dislocation density and carbide spacing by transmission electron microscopy (TEM), the hot tensile, creep and relaxation behaviour has been connected with the evolution of microstructure. The results of mechanical tests and the TEM-investigations have been used as input data into two models (an effective stress model and a modified constitutive model by Kocks–Mecking), which describe the deformation behavior. The deterioration in the creep properties of the alloy NiCr22Co12Mo9 as a result of coating was a result both of the degraded state of the M23C6-precipitate in the substrate metal, and of 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.