MICROSTRUCTURE OF A SIGMA-17B GRAIN-BOUNDARY IN MOLYBDENUM

A SIGMA17b boundary in molybdenum has high fracture strength, though this boundary has a poor atom matching compared with SIGMA9 and SIGMA11 coincidence boundaries. In order to clarify the reason from the viewpoint of grain boundary structure, the transmission electron microscopy observations have been conducted. The grain boundary of (334) SIGMA17b is shown to be a plane matching boundary which is regarded as one of the low energy boundaries. Interface dislocations to assure the coherency at the boundary are present in addition to DSC dislocations. Such a coherent nature of the boundary structure due to the presence of the dislocations is considered to be responsible for the fairly high fracture strength of the boundary.