BEHAVIOUR OF AI-SINGLE CRYSTAL DURING EARLY STAGE OF PUSH-PULL FATIGUE

Push-pull fatigue deformation of [110] and [100] Al-single crystals was performed at room temperature at strain amplitudes in the range (1 to 6) × 10￣(-4). Variation of the stress σ, internal friction Q￣(-1), and ultrasonic attenuation △α vs cycle number N under various strain amplitudes were measured systematically, and the relative dislocation configuration at different stages of fatigue was observed by TEM. The results indicate that the σ-N curve goes through a hardening -softening-secondary hardening sequence during push-pull fatigue in the two kinds of Al-single crystals. The change in the internal friction vs cycle N is synchronous and reverse with that of the stress. The ultrasonic attenuation △α increases with N at the beginning, after reaching a hump, decreases gradually. The variation of this three parameter is controled by the mechanism of interaction between dislocation segments.