It was determined, at 77 to 178K, whether the Friedel relationship was applicable to the interaction between a dislocation and an impurity in Mg2+-doped (0.035mol% in the melt) single crystals. This was done by fitting mε = 0 to temperature versus dislocation velocity-effective stress exponent, m*, curves using 2 models. One was a Fleischer model which took account of the Friedel relationship. The other was Fleischer's model. The former model was termed F-F. Here, mε = 0 was the m-value at zero strain, m was a dislocation velocity-applied stress exponent. The m* for the F-F model was deduced from m* = 2F0b{(Tc/T)1/2 - 1}/(3kTc), where F0 was the force acting on the dislocation at 0K, b was the magnitude of the Burgers vector, k was Boltzmann’s constant and Tc was the critical temperature at which the effective stress due to impurities was zero. It was found that the mε = 0 values tended to increase with decreasing temperature, and approached the m*-value for the Fleischer model rather than that for the F-F model. Thus, the interaction between a dislocation and an impurity could be approximated by the Fleischer model rather than by the F-F model. A similar result was also deduced on the basis of data which were analyzed in terms of the strain-rate sensitivity versus the stress decrement due to oscillations. It was concluded that the Friedel relationship was unsuitable for treating specimens within the present temperature range.

Study of the Applicability of the Friedel Relation with Dislocation Velocity-Stress Exponent. Y.Kohzuki, T.Ohgaku: Journal of Materials Science, 2003, 38[22], 4487-92