The role of vicinal ∑3 boundaries and ∑9 boundaries in grain boundary engineering

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∑3 grain boundary planes and triple junctions containing ∑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 ∑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 ∑3/∑3/∑9 it was shown that a combination of one {111} and one vicinal-to-{111} ∑3 was more likely to occur than two {111} ∑3s or two not-{111} ∑3s. The explanation for the preferred {111}/vicinal-to-{111} combination is that mobile ∑9 boundaries with high deviations encounter {111} ∑3s, and in consequence regenerate a ∑3 at the triple junction which must be vicinal-to-{111} according to the crystallographic constraints at the junction. Analysis of the not-{111} ∑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.

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