Study on the applicability of the Friedel relation with dislocation velocity-stress exponent

It was investigated at 77–178 K whether the Friedel relation is appropriate for the interaction between a dislocation and the impurity in KCl:Mg²⁺ (0.035 mol% in the melt) single crystal. This was carried out by fitting of m₌₀ to the temperature versus dislocation velocity-effective stress exponent, m^*, curves with respect to the two models: one is the Fleischer's model taking account of the Friedel relation and the other the Fleischer's model. The former model is termed the F-F. m₌₀ is the m value at zero strain. m is a dislocation velocity-applied stress exponent. The m^* for the F-F was examined fromm^* = 2F₀b(T_c/T)^1/2 – 1/(3kT_c)where F₀ is the force acted on the dislocation at 0 K, b is the magnitude of the Burgers vector, k is the Boltzmann's constant and T_c is the critical temperature T, at which the effective stress due to the impurities is zero. As a result, it was found that the m₌₀ values tend to increase with decreasing temperature and further approach to the m^* for the Fleischer's model in contrast to the F-F. That is, the interaction between a dislocation and the impurity in the specimen could be approximated to the Fleischer's model rather than to the F-F. Similar result was also deduced on the basis of the data analyzed in terms of strain-rate sensitivity versus stress decrement due to oscillation. Consequently, it was considered that the Friedel relation is inappropriate for the specimen within the temperature range.