ASYMMETRIC CREEP DEFORMATION OF A SINGLE-CRYSTAL SUPERALLOY

The anisotropic creep behaviour of single crystal superalloys leads to changes in the orientation and shape of specimens of arbitrary initia l orientations during high temperature deformation. A model of anisotr opic creep has been applied to a creep database for the single crystal superalloy SRR99 tested in uniaxial tension on [001] and [111] orient ations in order to evaluate the model parameters. These have been used to predict the changes in specimen cross-sectional shape resulting fr om creep deformation of more complex orientations. Experimental measur ements have been made of the cross-sectional dimensions of initially c ylindrical specimens as a function of local creep strain. The agreemen t between experimental measurement and model prediction is normally ve ry good. The biggest disagreement, for the [211] specimen, indicates t hat macroscopic cube slip is dominant rather than mixed cube and octah edral deformation as indicated by the model.