Thermally Activated Dislocation Depinning in Dilute Copper Alloys

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Abstract
Internal friction and Young's modulus measurements have been performed on a series of dilute copper—silicon, copper—germanium, and copper—tin alloys at temperatures ranging from 4° to 300°K in order to determine the extent of thermally activated dislocation depinning from solute atoms. Specimens are in the form of singel-crystal bars, and are excited piezoelectrically in their fundamental longitudinal mode of vibration at 80 kHz. For temperatures in excess of 180°K, the amplitude-dependent internal friction is characterized by an Arrhenius temperature dependence with an activation energy that varies linearly with the stress amplitude. A low-temperature modification of the Granato—Lücke theory accounts for the temperature dependence of the internal friction below about 120°K; however, the stress dependence is contradictory to that predicted theoretically. In general, thermal depinning is enhanced at high temperatures and stress levels, and in crystals containing long dislocation segment lengths and solute atoms of low pinning strength.