The deformation behavior of single crystals of CaF2 was investigated at homologous temperatures of 0.45. Stress changes involving reductions by a factor up to about 2 were done to separate the dislocation processes. In agreement with previous results for pure Al and LiF, it was found that the response to stress-reductions in the steady state of deformation starts with a period of declining deformation rate before the normal transient reaction with work softening sets in. This first period shrinks significantly when the stress-reduction tests were performed at lower strains, i.e. earlier in the primary transient. Correlation with results for the microstructural evolution during the primary transient allowed one to conclude that the transient response with declining strain-rate after stress-reductions was due to sub-grain boundary migration under concentrated stress. The results indicated that dislocation walls in the form of cell and sub-grain boundaries controlled the accumulation of dislocations in strain hardening and that the deformation resistance in the steady state reflects the kinetics of sub-grain boundary migration under stress. Consequences for the interpretation of dip tests and stress relaxation tests were considered.

Control of Dynamic Recovery and Strength by Subgrain Boundaries - Insights from Stress-Change Tests on CaF2 Single Crystals. S.Mekala, P.Eisenlohr, W.Blum: Philosophical Magazine, 2011, 91[6], 908-31