Strain-rate cycling tests, in conjunction with ultrasonic oscillation, were carried out at 80 to 239K on 2 types of Sr2+-doped (0.05mol% in the melt) single crystals: quenched and annealed. By examining the relationship between the temperature and the dislocation velocity effective stress exponent, m*, it was possible to deduce a suitable force-distance relationship between the dislocation and an impurity. The force-distance relationship for the quenched specimen approached a Fleischer model which took account of the Friedel relationship, rather than the original Fleischer model. For annealed specimens, the square model was the most appropriate one among the square, parabolic and triangular force-distance profiles. The 3 force-distance relationships took account of the Friedel relationship. Upon annealing the quenched specimen, m* became low at a given temperature. This was attributed to 2 phenomena. Firstly, the concentration of weak obstacles to dislocation motion had decreased after heat treatment. Secondly, the resistance to movement of a dislocation in the quenched specimens was weakened by annealing. That is, F0 was reduced to about one-third and θ0 increased from 154 to 172º. Here, F0 and θ0 were the force acting on the dislocation and the bending angle of dislocations by a weak obstacle such as an impurity. It was concluded that the dislocation velocity in the quenched specimens was more sensitive to the effective stress due to impurities than was that in annealed specimens at the same temperature.

Study of the Interaction between a Dislocation and Impurities in KCl:Sr2+ Single Crystals by the Blaha effect – III. Influence of Heat Treatment on Various Characteristics. Y.Kohzuki, T.Ohgaku: Journal of Materials Science, 2004, 39[1], 107-12