Fatigue behavior of columnar-grained Cu with preferentially oriented nano scale twins

Polycrystalline columnar-grained bulk Cu samples containing preferentially oriented nanoscale twins have been synthesized by means of direct current electrodeposition. The S-N curves under tension tension fatigue tests suggested that the fatigue limit (sigma(max) = 162 MPa at 10(7)) of nanotwin Cu is greatly improved over that of the coarse-grained Cu with essentially a similar grain size (sigma(max) = 110 MPa at 10(7)). It is found that the majority of twin boundaries are quite stable during cyclic deformation. Distinct zigzag slip bands acrossing a few twin planes are prevalently observed in the grain interiors. Schmid factor analysis shows that the zigzag slip bands result from one primary slip system activation of threading dislocations propagation within the twin lamellae, which is fundamentally different from that of polycrystal materials. The nanoscale twin confinement of activated threading dislocations suppresses the stress concentration, retards fatigue crack initiation and enhances the fatigue limit. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.