Dislocation-ledge coupling governs semicoherent precipitate growth
Many crystalline materials acquire their properties as one crystal phase grows through another, but a long-standing defect-kinetic puzzle remains: how dense interfacial dislocation networks between two crystals advance, reorganize, and accommodate strain without relying on ordinary glide. Here, using in situ transmission electron microscopy, O-lattice analysis, and three-dimensional phase-field crystal simulations, we identify how semicoherent interfaces overcome this constraint during lath precipitate growth. In situ observations of austenite precipitates in duplex stainless steel reveal nanometer-high growth ledges propagating laterally along migrating habit planes. O-lattice analysis shows how lattice misfit prescribes a closed network across habit planes, side facets, and end faces. Simulations resolve the hidden three-dimensional dynamics: the network undergoes diffusion-assisted, non-conservative motion, producing steady end-face advance and ledge-mediated broad-facet migration while accommodating transformation strain. These results reveal a general defect-kinetic route linking point-defect transport, dislocation-network motion, interface migration, and morphology evolution.