The internal friction in a high-purity nickel was measured as a function of temperature, using a torsion pendulum at a low frequency of vibration. The internal-friction curve consists of a background damping which increases as the temperature increases, and a peak at 510°C (0.44 cps) due to grain-boundary stress relaxation with an associated activation energy of 63,500 cal/mol. The limited data reviewed lead to the conclusion that neither the lattice self-diffusion nor the grain-boundary self-diffusion is the rate-determining process for grain-boundary stress relaxation, although this value for the activation energy associated with grain-boundary stress relaxation in nickel is consistent with that for lattice self-diffusion, and with the value for creep. The coefficient of viscosity of the grain boundary at the melting point, estimated from internal-friction measurements, using a modified Ke's equation, is much smaller than (all the experimentally) determined values for many other liquid metals. Oxygen in nickel reduces the peak due to grain-boundary stress relaxation substantially.
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