Stress Induced Preferential Orientation of Pairs of Solute Atoms in Metallic Solid Solution

Abstract

In a non-stressed cubic crystal the axes of pairs of adjacent solute atoms are randomly orientated along the several permissible crystallographic directions. It is shown that in the presence of a stress the equilibrium orientation is no longer random, but that certain directions become preferred, and it is further shown that the continual striving of the crystal to maintain equilibrium causes it to manifest all the characteristic anelastic effects, stress relaxation, internal friction, etc. In particular, its internal friction will be anomalously high in that temperature range where the time of relaxation for the establishment of equilibrium is comparable with the period of oscillation. The theory is developed for the dependence of anelastic effects upon temperature and upon crystallographic orientation, and it is found that in b.c.c. crystals these effects vanish for a tensile stress applied along one of the 100> axes. The magnitude of the anelastic effects associated with this stress induced preferential orientation may be very large. Thus in alpha-brass past experiments indicate that under optimum conditions the associated internal friction is at least 20 times as large as that due to all other causes.