Grain Boundary Sliding in High-Purity Aluminium Bicrystal during Tensile Deformation at High Temperature

High-purity aluminium bicrystals which have grain boundaries making an angle of 45° with the tensile axis were prepared by the recrystallization method. During the creep and the constant-rate heating tests under constant tensile load in argon atmosphere at high temperatures, the grain boundary sliding and the shear deformation were observed near the boundary. The grain boundary sliding increased stepwise against the time in the tensile creep test. The grain boundary sliding was accompanied by the shear deformation of the crystals near the boundary, and the grain boundary displacement had no relation with the boundary misorientation angle θ, but depended upon the angles, αA or αB, between the slip traces and the boundary trace on the observed surface. The contribution of grain boundary sliding to the total deformation of the specimen became larger with the increase of the testing time at 300° and 350°C, and showed the maximum value of about 36% at 400°C for 300 min. Grain boundary migration took place in the direction to release the strain energy of plastic deformation that occurred locally at the boundary irregulalities. The initial grain boundary displacement was proportional to the heating temperature, and the obtained activation energy for the boundary sliding of the specimens with αA+αB\simeq18°∼71° was 11600∼26400 cal/mol.