Plastic deformation of aluminium bicrystals having ∑7 and ∑21 coincidence tilt boundaries

Abstract

Three types of isoaxial summetrical bicrystals and their component single crystals were tested in tension to clarify the effect of the grain boundary on plastic properties. The 〈111〉 oriented bicrystal was deformed by the mode similar to that of the 〈111〉 oriented single crystal. Fine multiple slip which appeared from the early stage of plastic deformation was suppressed at the boundary. It was found that the flow stress of this bicrystal was almost equal to that of the component single crystal and the effect of grain boundary on the flow stress did not appear. Two bicrystals having the ∑7 and ∑21 coincidence tilt boundary were deformed by single slip at the early stage of plastic deformation. The flow stress of each bicrystal was increased by the presence of the boundary. The boundary strength rapidly increased from the yield point to 0.5% strain by the interaction between primary slip and additional slip in the vicinity of the boundary; only a slight increase was observed from about 1.0–5.0% strain. The effect of the grain boundary on the flow stress of the bicrystal is prominent by introducing multiple slip near the grain boundary in the stage 1 region of the component single crystal but not prominent in the stage II region. The effect of the grain boundary on the flow stress is negligible after multiple slip takes place away from the boundary in the adjoining grains.