Modelling and validation of anisotropic creep deformation in single crystal superalloys: Variable and multiaxial loading

Anisotropic creep in single crystal superalloys under steady isothermal and uniaxial loading has previously been described by a number of crystallographic slip-based models 1,2,3); the Imperial College approach, based on the concepts of Continuum Damage Mechanics (CDM), is particularly effective in accounting for (he progressive increase in creep rate that occurs over most of the creep life of the material, This model has been extended to account for deformation under (a) changing uniaxial tensile stresses and variable temperatures, (b) multiaxial loading and (c) through-zero cyclic axial loading. Theoretical simulations are compared with experimental measurements on the Second Generation SX alloy CMSX4 for step-changes in load and for Bridgman notch creep specimens. Characterisation of the spatial heterogeneity of lattice rotation resulting from creep, using Electron Back Scatter Diffraction, allows the active slip systems in multiaxial stresses to be identified. These are consistent with the assumptions of the model.