Fatigue deformation of silver single crystals: STM evidence for crack nucleation, measurements of slip irreversibility and verification of a new scaling relationship for fatigue life

Silver single crystals oriented in the single glide orientation were fatigued in air and vacuum. The surface morphology was observed using a scanning tunneling microscope. A gold film deposited on the silver surface was used as a reference marker so that the same region can be observed upon repeated fatigue cycling. Pit-shaped features were observed to form within a narrow range of cycles and to eventually develop into micro-sized cracks, lending support to the notion that cracks are formed by a nucleation process. In addition, by measuring the slip band height and spacing as a function of cycling, we were able to determine the slip irreversibility and the Coffin-Manson exponents in both environments. With these two sets of data, we were able to verify a new scaling relationship for fatigue life based on our earlier theoretical work.