DETWINNING AND CRACK INITIATION DURING CYCLIC LOADING IN MULTILAYER COPPER/COPPER SAMPLES WITH NANOSCALE TWINNING

摘要

High-purity Cu samples containing aligned nanotwins arranged in adjoining columns were fatigued in tension-tension load control or were subjected to indentation. Cycling to failure between stresses of 450 and 45 MPa left much of the original structure intact but highly distorted. Enough of the original structure remained to preserve the original strength but softer de-nanotwinned regions developed that became sites for fatigue crack initiation. In the indentation experiments, results of varying the orientation of the faces of an indenter tip with respect to the planes of twin boundaries demonstrate the importance of twin boundaries in impeding dislocation motion.