The role of vicinal Σ3 boundaries and Σ9 boundaries in grain boundary engineering

Σ 3 grain boundary planes and triple junctions containing Σ 3 boundaries have been investigated in grain boundary engineered brass using an adaptation of electron backscatter diffraction (EBSD) data combined with a single surface trace analysis methodology. The data have been analysed from the standpoint of whether or not the interface planes in the Σ 3 boundaries are close to {111} (i.e. coherent annealing twins), vicinal to {111} (i.e. a small deviation from the {111} reference structure) or not on {111}. At triple junctions composed of Σ 3/Σ 3/Σ 9 it was shown that a combination of one {111} and one vicinal-to-{111} Σ 3 was more likely to occur than two {111} Σ 3s or two not-{111} Σ 3s. The explanation for the preferred {111}/vicinal-to-{111} combination is that mobile Σ 9 boundaries with high deviations encounter {111} Σ 3s, and in consequence regenerate a Σ 3 at the triple junction which must be vicinal-to-{111} according to the crystallographic constraints at the junction. Analysis of the not-{111} Σ 3s indicated that more than half the boundaries in this category could not have {211}{211}, {774}{855}, {111}{511}, {001}{221} or {110}{411} planes. The possible distribution of these planes types, based on information from the single-surface trace analysis, had a high rank correlation coefficient, 0.925, with previous data from nickel which was based on a two-surface, full boundary planes analysis.