Thermally activated dislocation glide in moderately concentrated solid solutions

Abstract

Abstract A recent theory of the activation volume in the thermally activated glide of a dislocation in a solid solution in the Labusch regime is tested quantitatively. The dependence of the activation volume V + on the flow stresses [sgrave](T) of a series of alloys of the same solvent metal under standard conditions of temperature and strain rate is explained rather satisfactorily, but the temperature dependence of the activation volume is not predicted correctly. An alternative mechanism of thermal activation is investigated. In the standard model, the sequence of configurations of a dislocation segment as it overcomes a potential barrier is the same at all temperatures. The displacements of the dislocation produced by the long-wavelength thermal vibrations are added to those produced by the applied stress. In the new model, short-wave components of the thermal vibration suppress the relaxation of the dislocation into the potential wells of solute atoms, thereby increasing the length of dislocation segment which moves forward coherently. The flow stress decreases inversely as the square root of this length. The reduction in flow stress by this process is less than that produced by the long wavelengths at high temperatures, but may be several times larger than the latter at intermediate temperatures, and should dominate at very low temperatures. Both processes show stress equivalence and the relation V + ∝ [[sgrave](0)]−2/3, and make the same erroneous prediction that for a series of alloys of the same solvent the range of temperature over which the flow stress varies rapidly with temperature is proportional to [[sgrave](0)]1/2.