Cyclic deformation of ultrafine-grained aluminum

Cyclic deformation of ultrafine-grained (UFG) Al with different grain sizes has been studied. it was found that UFG At had shorter fatigue life than its coarse-grained counterparts. For UFG At, the fatigue life decreases with decreasing grain size. Shear bands (SBs) shorten fatigue life. SBs are always inclined at 45 degrees to the loading axis, and extend across the whole specimen. A SB is a thin sheet of tangled dislocations that have different Burgers vectors; its thickness is much less than the grain size. The strain-stress field inside a SB is very high. SBs produce shear steps, but not surface extrusions/intrusions, on the specimen surface. Thick shear bands (TSBs), about 200-300 mu m, were found in the 6.36 mu m grain size specimens, which also inclined 45 degrees to the loading axis. TSBs consist of dislocation cells. The formation of TSBs does not reduce the fatigue life. (c) 2006 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.