Structures and impurity effect on symmetric tilt boundaries of molybdenum

In order to clarify the grain-boundary structure of molybdenum and influence of impurities on the microstructures, bicrystals with symmetric tilt boundary ([001](1 (3) over bar 0)Sigma 5, [001](1 (2) over bar 0)Sigma 5, [001](1 (4) over bar 0)Sigma 17, [001](1 (5) over bar 0) Sigma 13 and [110](33 (2) over bar)Sigma 11 coincidence boundaries) were prepared, and the boundary structures were observed by transmission electron microscopy. For the purified specimens, periodic structures were observed along the boundary, and well explained by geometric models (coincidence site lattice and O-lattice theories) for the periodicity and by molecular dynamics calculation for microstructures. It was found that the grain boundary structures consist of the combination of structure units of stable boundaries ((0 (1) over bar 0) and (1 (1) over bar 0) Sigma 1 single crystals, and (1 (3) over bar 0) Sigma 5 coincidence boundary). On the other hand, in the not-purified specimens, precipitates and lattice bendings, which were probably caused by impurities, were observed at the boundaries. From these findings, it is concluded that impurities are one of the most important factors affecting the boundary structures in molybdenum. However, the effect was very different from each boundary.