Anisotropic creep behaviour of single crystal superalloy CMSX-4 and its modelling

Single crystal superalloys exhibit highly anisotropic creep behaviour. Three-dimensional constitutive equations of the ''Microstructure Dependent Model'' have been adapted for the prediction of the anisotropic viscoplastic behaviour. At low temperature, the prediction of a cubic Hill's formulation gives a good agreement for <001> and <111> oriented specimens, whereas weaker creep behaviour in <011> direction can not be predicted. At high temperature (950 degrees C), the anisotropy is modified by the directional coarsening of the gamma'-particles. <001> oriented specimens become weaker than <111> oriented ones. A microstructure dependent potential with coefficients connected to the normalised edge lengths of the gamma'-particles, is expressed in order to predict the influence of the rafted structure on the overall behaviour. A good agreement is found between the prediction of the model and the experimental creep results at 950 degrees C.