Relaxation effects in solid solutions arising from changes in local order. II. Theory of the relaxation strength

Abstract

The lattice dimensions of an alloy depend upon the degree of short-range order σ. Thus the equilbrium value of σ in a strained crystal will in general differ from that in the unstrained crystal and in addition to the elastic strain following an applied stress, there will be an anelastic strain arising from the change to the new stress induced equilibrium value of σ. An internal friction peak frequently found in substitutional solid solutions is attributed to this type of anelastic effect and on the basis of the regular solution model a calculation is made of the associated relaxation strength δ. Very satisfactory agreement is found between the theoretical values of δ and the measured values for α-CuZn, α-AgZn and CuAl alloys. The theory is critically compared with an earlier interpretation of the experimentally observed effect by Zener, who employed a concept of stress induced reorientation of solute atom pairs.