Unveiling high ductility in boron carbide crystal at room temperature

Ductility is critical for preventing materials catastrophic fracture. However, achieving tensile ductility in covalent materials remains challenging and unexplored because of the strong, directional covalent bonds. Here, we unveiled the remarkable tensile ductility driven by vacancies in boron carbide (B₄C). Using advanced electron ptychography techniques, we identified the presence of carbon-vacancy-carbon chains with boron vacancies in B₄C lattice. The fabricated B₄C beams exhibit a high ductility (~26.8%) at room temperature, a characteristic previously unattained in covalent materials and comparable to metals. In situ high-resolution transmission electron microscopy revealed that the formation of local amorphous regions after B₄C lattice exceeded its elastic strain limit, causing plastic deformation. Atomistic simulations, using experimentally observed B₄C models, reveal that the creation of carbon-carbon bonds in chains containing boron vacancies causes localized amorphization and contributes to the plastic deformation. This research highlights the significance of vacancies in facilitating plastic deformation in B₄C and suggests a potential strategy to improve the ductility of strong covalent materials.