Continuous-Transition-Mediated Deformation Twinning in Cubic Boron Nitride

Abstract Deformation twinning, a phenomenon primarily documented within metallic systems, has remained essentially unexplored in covalent materials due to the formidable challenges posed by their inherent extreme hardness and brittleness. Utilizing our loading-specific twinning criterion, we have successfully activated extensive deformation twinning and quantified the consequent significant improvements in mechanical properties in -oriented cBN submicron pillars at room temperature, employing a five-degree-of-freedom nanomanipulation stage inside a transmission electron microscope. Extending beyond cBN, this criterion has also proven widely applicable across a spectrum of covalent materials, underscoring its broad potential. Building on the successful implementation of twinning, our investigations have unveiled the twinning dynamics at the atomic level in cBN. In contrast to metallic systems, the twinning observed in cBN is governed by a novel mechanism of continuous transitions involving the collective displacement of atoms beneath the (111) slip planes within the lattice. These findings substantially advance our comprehension of twinning mechanisms in covalent face-centered cubic materials, and herald a promising avenue for microstructural engineering aimed at enhancing the strength and toughness of these materials.