MODELING OF CREEP IN A NI BASE SUPERALLOY USING A SINGLE-CRYSTAL PLASTICITY MODEL

In this article the creep behaviour of Ni base superalloy single cryst al 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 ga mma matrix. The gauge section of a single crystal tube is modelled usi ng finite elements. In the model the material is represented as a homo geneous FCC single crystal with two sets of slip systems, octahedral s lip systems and artificial cubic slip systems, to account for dislocat ion climb in the gamma channels. Large deformation, rate dependent cry stal plasticity theory is used to describe the constitutive behaviour of the crystal. In the simulations the emphasis is on qualitative pred ictions and qualitative comparisons with experiment. The results predi ct 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 artificia l slip systems, the model predictions are in goad qualitative agreemen t with experimental observations in terms of relative creep rates for the different loading directions. (C) 1997 Elsevier Science B.V.