Boundaries; kink versus ripplocation in graphite, MAX phases and other layered solids

K Sudhakar and G Plummer and GJ Tucker and MW Barsoum, CARBON, 213, 118221 (2023).

DOI: 10.1016/j.carbon.2023.118221

Kink boundaries, KBs, in metals are well defined entities that at low disregistry angles are identical to low angle grain boundaries, LAGBs. The latter are comprised of basal dislocations aligned normal to the basal planes in such a way that their strain fields cancel. A ripplocation is best defined as an atomic scale ripple. When ripplocations on adjacent planes nest, they define a ripplocation boundary, RB. Two oppositely signed adjacent RBs define a ripplocation band. Until recently, most RBs have been classified as KBs. In layered crystalline solids, LCS, when deformation is confined in two independent directions, with no possibility of twinning, most KBs should be classified as RBs. Herein, we show that in LCSs, RBs: i) are not atomically sharp; their strain fields are considerably delocalized, especially in comparison to KBs, ii) delaminate at high curvatures; iii) form nanobridges, and iv) are highly strained and, if not trapped, fully reversible. At extreme curvatures, the bonds are sundered and the RBs are no longer reversible and are reminiscent of KBs at the macroscopic scale. The distinction is important because whether delaminations nucleate and/or a material is highly strained has important and crucial ramifications on its deformation and ultimate failure.

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