Superlubric-Locked Transition of Twist Grain Boundaries in 3D Crystals

J Wang and E Tosatti, PHYSICAL REVIEW LETTERS, 135, 026202 (2025).

DOI: 10.1103/7bbs-q17w

Properties of twist grain boundaries (TGB), long known structurally but not tribologically, are simulated under sliding and load, with Au(111) our test case. The load-free TGB moire is smooth and superlubric at incommensurate twists. Surprisingly, load provokes a first-order structural transformation, where the highest energy moire nodes are removed-an unexpected Aubry-type transition for which we provide a Landau theory leading to a full twist- load phase diagram. Upon frictional sliding, the transformation causes a superlubric-locked transition, with a huge friction jump, and irreversible plastic flow. The predicted phenomena are robust, also recovered in a Lennard-Jones lattice TGB, and not exclusive to gold or to metals. Both superlubricity and strong Aubry locking hold promises for studies and applications in micro and nano mechanics and devices.

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