Single crystals of CaF2 oriented along <111> for glide on three equally stressed

slip systems were used to study the evolution of the dislocation structure during

deformation at 873 to 1315K. Structure quantification was done by the etch-pit

method using atomic force microscopy for high resolution. Evolution begins with

free dislocations forming a cellular structure. The average spacings of free

dislocations and of cell boundaries were generally close to their stress-dependent

steady state values. The sub-grain structure developed more slowly with strain. As

it superimposes on the free dislocations, the crystals work harden and the creep rate

decreased. The rates of change of the characteristic spacings of sub-grain and cell boundaries, of free dislocations and of dislocations in sub-grain boundaries were

formulated as functions of stress, strain and the empirical steady state values of

spacings. Combining the laws of structure evolution with those of deformation

kinetics in the framework of the composite model, the creep behaviour was

modelled in a large range of homologous temperatures in consistence with the

general picture of plasticity of crystalline materials.

Evolution of Dislocation Structure and Deformation Resistance in Creep

Exemplified on Single Crystals of CaF2. P.Sadrabadi, P.Eisenlohr, G.Wehrhan,

J.Stäblein, L.Parthier, W.Blum: Materials Science and Engineering A, 2009, 510-

511, 46-50