HIGH TEMPERATURE INTERNAL FRICTION AND DISLOCATION MOTION IN POLY AND SINGLE CRYSTALS OF F.C.C. METALS

Abstract
High temperature internal friction experiments were performed on different poly and single crystals of four (Al, Ag, Cu, Ni) FCC metals in the Hz frequency range. Damping spectra exhibits relaxation peaks even for vibration amplitude corresponding to strains as low as 2.5 10_-7. For higher stress levels (corresponding to strains ranging between 2.5 10_-7 and 5 10_-6) damping proved to be very sensitive to the strain amplitude. In the 0.4 - 0.5 T_M temperature range, one peak have been found associated with an activation energy of about 1 ev. This peak is not present on strongly cold-worked specimens and appear after annealing at medium temperature. He disappears after high temperature annealing whereas new peaks appear at 0.6 - 0.7 T_M, associated to a large activation energy. The importance of the microstructural state and specially of the dislocation network, as regards the presence of internal friction maxima, was confirmed by the fact that same peak behaviour was observed on single and poly crystals.