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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 M 23 C 6 -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.

The present study describes the application of hot tension experiments in order to predict the creep and tensile behaviour of the highly loaded superalloy CoCr 2 2Ni 22 W 14 . The results of mechanical tests and transmission electron microscopy (TEM) investigations have been used as input data in a model which describes the high temperature plastic deformation. A common log ɛ - log σ plot of tensile and creep data shows a systematic shift of about 10% towards higher stresses in the case of tensile loading. In creep tests the dislocation densities reach their steady-state values at the points of minimal strain rates, whereas in tensile tests the dislocation densities increase at any given time until the tensile strength is reached at significantly higher strains. Under the condition of equal true stresses subgrain formation is more pronounced after tensile than after creep deformation. By including the experimentally determined dislocation densities, the constitutive model yields qualitatively correct predictions of the creep and tensile behaviour.