1997-CMS-Modelling of creep in aNibasesuperalloy using asinglecrystalplasticitymodel.pdf

ELSEVIER Computational Materials Science Y (I 997) 134- 140 COMPUTATIONAL MATERIALS SCIENCE Modelling of creep in a Ni base superalloy using a single crystal plasticity model P.E. McHugh a, ‘, R. Mohrmann ’ Abstract In this article the creep behaviour of Ni base superalloy smgle crystal tubes is simulated for three different loading directions: [ 1001, [I IO] and [l 111 and for three different loading cases: tension, torsion and combined tension and torsion, The material is assumed to have the y-y’ microstructure of y’ phase cuboids, imbedded in a y matrix. The gauge section of a single crystal tube is modellcd 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 y 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 Jeformatton 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 good quahtative agreement with experimental observations in terms of relative creep rates for the different loading directions. 0 1997 Elsevier Science B.V. 1. Introduction Ni base single crystal superalloys are materials that are receiving considerable attention nowadays due to their excellent high temperature creep bc- haviour. This behaviour makes them suitable for high performance components such as gas and jet turbine blades. Typical materials such as CMSX-3 or CMSX-4. when suitably heat treated and for temper- atures below approximately 900°C take the form of two phase single crystals with the y-