Modelling of creep in a Ni base superalloy using a single crystal plasticity model

In this article the creep behaviour of Ni base superalloy single crystal tubes is simulated for three different loading directions: [100], [110] and [111] and fur three different loading cases: tension, torsion and combined tension and torsion. The material is assumed to have the gamma-gamma microstructure of gamma phase cuboids, imbedded in a gamma matrix. The gauge section of a single crystal tube is modelled using finite elements. In the model the material is represented as a homogeneous FCC single crystal with two sets of slip systems, octahedral slip systems and artificial cubic slip systems, to account for dislocation climb in the gamma channels. Large deformation, rate dependent crystal plasticity theory is used to describe the constitutive behaviour of the crystal. In the simulations the emphasis is on qualitative predictions and qualitative comparisons with experiment. The results predict nonuniform plastic deformation in the tubes for all but one of the cases considered. The results also show that, by choosing the relative values of the reference strain rates for the octahedral and artificial slip systems, the model predictions are in goad qualitative agreement with experimental observations in terms of relative creep rates for the different loading directions. (C) 1997 Elsevier Science B.V.