The near singular boundaries in BCC iron

For BCC metals, it is almost impossible to bring in a considerable amount of singular boundaries because the twinning plane is the third closest plane {1 1 2}. As a concessional approach, trying to make use of the near singular (vicinal) boundaries would be significant to the grain boundary design and control for BCC metals. In the present work, a high purity (99.999%, mass fraction) iron sample with a uniform microstructure was prepared by multi-directional forging and recrystallisation annealing. Then the grain boundary characteristics were analysed by an integrated method involving electron backscatter diffraction, grain boundary filtration, five-parameter analysis and grain boundary inter-connection determination. The results indicate that the most frequent grain boundaries are those with {0 1 1}/{0 1 1} inter-connections. The forming ability of such boundaries is about 10 times higher compared to that of the singular boundaries. Near coincidence site and O-lattice theory analyses illustrate that the boundaries with {0 1 1}/{0 1 1} inter-connections have particular atomic structures of periodic good matching sites isolated by periodic dislocations, showing a higher degree of structural ordering compared to the random boundaries. Surface etching test demonstrates that these boundaries are much more resistant to intergranular corrosion attacks in comparison to random boundaries. Therefore, the grain boundaries with {0 1 1}/{0 1 1} inter-connections are suggested to be the near singular boundaries in BCC iron. It is significant to the grain boundary engineering research and application for BCC metals.