GRAIN-BOUNDARY EFFECTS ON THE FATIGUE DEFORMATION AND CRACKING BEHAVIOR OF COPPER BICRYSTALS

Fatigue tests were performed on two types of [(1) over bar 34] iso-axi al copper bicrystals for studying the grain boundary (GB) effects on t he cyclic deformation and fatigue cracking behavior and the correspond ing mechanism in copper bicrystals. One bicrystal contains a perpendic ular GB and the other contains a tilting one with respect to the loadi ng axis. Both the grain boundaries are nearly 180 degrees rotated. It was shown that both the perpendicular and tilting grain boundaries hav e little effect on the cyclic hardening and saturation behavior of the bicrystals, but show strong effects on the slip deformation and fatig ue cracking behavior. The microcracks were found to prefer to nucleate and propagate at the GB, leading to intergranular cracking. However, the crack nucleation behavior was found to be different for the above two iso-axial copper bicrystals. Two types of intergranular fatigue cr acking mechanisms were proposed based on the specimen geometry with re spect to the dominant slip system and the GB orientation. (C) 1998 Els evier Science Ltd.