Recent Progress in the Theory of Bordoni-Type Relaxation Processes

Abstract

While it is well established by experiment that the relaxation processes in face-centred cubic metals discovered by P. G. Bordoni as well as related phenomena are due to the thermally activated formation of kink pairs on dislocation lines, the quantitative aspects of the theory as developed since Bordoni's discovery still reveal gaps or even inconsistencies. The paper reports on recent progress in solving the open problems. An improved formula has been derived for the mean number of (thermal as well as geometrical) kinks on dislocation segments of length L under the action of a homogeneous applied shear stress. It is shown how the change-over in the temperature dependence of the number of kink pairs, nkp, from the low-temperature exp(-2H k /kT) law to the high temperature exp(-H k /kT) law depends on L, on the number of geometrical kinks n g , and on the applied stress. H k is the formation energy of an isolated kink. The mean dislocation velocity, which is the essential quantity determining the relaxation time, shows a similar temperature dependence. The dependence of the relaxation time and strength of the relaxation process by kink-pair generation on internal stresses is discussed in some detail.