Temperature and rate dependence of saturation stress for low amplitude fatigue of Cu crystals between 4.2 and 350 K

Abstract

Copper single crystals oriented for single glide were fatigued at temperatures from 4.2 to 350 K in inert atmosphere. Fatigue behaviour was similar at all temperatures. Saturation stress decreased smoothly with increasing fatigue temperature from ≈85 MPa at 4.2 K to ≈27 MPa at 350 K. The effect of cycling rate on saturation stress was also measured. The observations suggest that the same fundamental mechanism, which must be mechanical in nature, operates throughout the temperature interval studied. The activation energy of the operating mechanism, calculated from the observed temperature and rate dependence of the saturation stress, increases linearly with temperature, from ≈0.175 eV at 77.4 K to ≈ 0.7 eV at room temperature. At 77.4 K (as at room temperature) fatigue life is shorter in reactive than in inert environment.