Zener Relaxations in the Copper-Gold System

Abstract

Zener relaxation peaks have been observed by low-frequency internal-friction measurements in seven polycrystalline copper-gold alloys. Measurements of associated activation energies and relaxation strengths show maxima at the equiatomic composition of 50.5 kcal/mole and 0.4 (at 400° C), respectively. The activation energies for the relatively dilute alloys were slightly less than or equal to those reported for tracer-diffusion studies. A large variation in τ₀ with composition correlates roughly with entropy changes estimated from the temperature-dependence of the shear modulus. The maximum relaxation strength at equiatomic composition is in qualitative agreement with the predictions of Zener (“Elasticity and Anelasticity of Metals”, p. 106. 1948: Chicago (University Press)) and Shmatov (Physics Metals Metallography, 1960, 9, 98). Estimation of the ordering temperatures for Cu₃Au and two off-stoichiometric alloys from the temperature-dependence of the relaxation strength has yielded results that compare reasonably well with the phase diagram.