The Internal Friction of Single Metal Crystals

The internal friction of crystalline copper, tin, lead, and zinc has been measured by the composite piezoelectric oscillator method. It is found that the decrement of an unannealed crystal may be as large as that of the polycrystalline material, that annealing reduces the decrement to a value of the order ${10}^{-4\mathrm{}}$ to ${10}^{-5\mathrm{}}$, and that both Young's modulus and the decrement vary with the vibrational strain amplitude at strain amplitudes as low as ${10}^{-6\mathrm{}}$. In the case of zinc crystals, a detailed study has been made of the way in which the elastic modulus and internal friction depend on the previous history of the specimen, on the vibration frequency and amplitude, and on the orientation of the vibration axis with respect to the crystal slip planes. The results suggest that the mechanism involved is a propagated "dislocation" of the sort proposed by Taylor, Polanyi and Orowan to account for macroscopic plastic flow, and that the application of a stress is accompanied by a plastic strain, together with an associated strain hardening in consequence of which the stress-strain relation on removal of the applied stress is nearly elastic.