Steady state deformation and dislocation structure of pure and Mg-doped LiF single crystals. II. Etch pit studies of dislocation structure

The dislocation structure of pure and Mg-doped 〈100〉-LiF single crystals deformed in compression creep tests between 375 and 800°C has been investigated by means of etch pit technique. After transient creep an equilibrium substructure is established which consists of a three-dimensional equiaxed network of cell boundaries with extremely inhomogeneously grouped dislocations within them. Under conditions of steady state creep characterized by the constant steady state creep rate both the dislocation density within the cells and the cell diameter Ds are not only constant with respect to strain but also unique functions of applied stress σ and temperature T: ∼ σ1; Ds ∼ σ−2/3 (T = const), ∞ σ2; Ds ∞ σ−1 ( = const) independent of deformation history, viz., pre-deformation at room temperature and stress changes at high temperatures. The relative effective stress and the internal stress level have been calculated both during transient creep and steady state creep.