Low cycle fatigue of a copper bicrystal under constant plastic strain control

Symmetrical tension-compression fatigue tests in an axial plastic strain range of 0.12x10(-3) to 2.75x10(-3) were performed on a copper bicrystal containing two highly misoriented component crystals one of which is oriented for single slip and another is oriented very closely for double slip. The grain boundary (GB) is roughly perpendicular to stress axis. Experimental results showed that this bicrystal exhibited a very high saturation stress and did not exhibit an apparent plateau in the cyclic stress-strain (CSS) curve. It seems that no persistent slip bands formed under higher strain amplitudes according to the analysis of the change of fatigue loop shape. Surface observation showed that at least three slip systems operated in both of the components of the bicrystal due to constraints of GB. The occurrence of multiple slip, which may result in very strong dislocation interaction, is considered to be responsible for the features of the CSS curve of the bicrystal. Intergranular microcracks and relatively large intergranular macro-cracks were frequently observed on the specimen surfaces even though small cumulative strains were applied. Apparently, the GB plays the most important role in the fatigue failure of the bicrystal to be studied. Copyright (C) 1997 Elsevier Science Limited.