CALCULATION OF THE INTERNAL-STRESSES AND STRAINS IN THE MICROSTRUCTURE OF A SINGLE-CRYSTAL NICKEL-BASE SUPERALLOY DURING CREEP

The evolution of internal stresses and strains in the microstructure o f a single crystal nickel-base alloy during annealing and during creep in [001] direction has been calculated using a visco-plastic model. T wo limiting conditions are considered: an ''overloading'' case where t he internal stresses reach the critical resolved shear stress of the w hole gamma' volume and an ''underloading'' case where the critical res olved shear stress of the gamma' precipitate is reached only at distin ct areas. During creep deformation a triaxial stress state evolves in the microstructure and large pressure gradients are built up. The infl uence of an initial coherency misfit is shown to be negligible after s hort times of creep. The calculations allow the prediction of flow pat terns in the microstructure, creep-induced lattice parameter changes, type and arrangement of interfacial dislocations and of the dependence of the stationary strain rate on the cube or plate morphology of the gamma' phase.