Internal friction of β brass

Abstract

The internal friction of polycrystals and single crystals of β brass has been investigated by the method of low-frequency, free, torsional vibration. Six separate anelastic phenomena have been detected by varying the composition and heat treatment of the specimens. These are observed as distinct relaxation peaks at approximately 70°, 177°, 190°, 285°, and 300°C and an increase in internal friction to very high values at temperatures close to the order-disorder transformation temperature. The peak at 70°C is unstable and decays with an activation energy of 15,000 cal/mole. The peaks at 70° and 177°C are interpreted in terms of Zener's pair-reorientation mechanism; that at 70°C is considered to be due to stress-induced reorientation of zinc pairs made possible by an excess concentration of vacancies resulting from quenching, and that at 177°C to stress-induced reorientation of copper pairs. On the basis of this model, diffusion coefficients for the diffusion of copper in β brass are calculated. The peak at 190°C is attributed to stress relaxation at β-γ interfaces and that at 285°C to stress relaxation at β-γ. interfaces. The peak at 300°C is attributed to stress relaxation by grain-boundary slip. The very high internal friction at temperatures close to the order-disorder transformation temperature is in agreement with theoretical prediction.