The Initiation of Fatigue Cracks in the Grain Boundary Affected-regions in Aluminum Isoaxial Bicrystals

Abstract

In order to examine the effects of the screw component of the dislocations parallel to the grain boundary planes on the initiation of fatigue cracks in the boundary affected-regions, aluminum isoaxial bicrystals in which the screw components of the dislocations parallel to the boundary planes in the primary slip systems were varied from 100 to 0% were prodused by a modified Bridgman method. They were tested by the bending fatigue testing machine under constant strain amplitudes of 0.20 and 0.18%, and cyclic frequencies of 30.4 Hz.
In the component crystals with the screw components larger than about 83% of the dislocations parallel to the boundary planes in the primary slip systems, the initiation of fatigue cracks occurred along the primary slip bands in the boundary affected-regions. On the other hand, the initiation of fatigue cracks was observed not along the primary slip bands in the component crystals with the screw components less than about 45%, but along those in the edges of the specimens or at the hollows formed by the development of the deformation bands.