Hardening and toughening mechanisms in nanotwinned ceramics

Recent experiments have reported that nanotwinned ceramics with covalent or ionic bonds exhibit unprecedented hardness, enhanced fracture toughness and improved thermal stability. In this viewpoint paper, we highlight some preliminary studies on mechanical properties of nanotwinned ceramics either synthesized in the laboratory or extracted from biological materials, with an emphasis on their hardening and toughening mechanisms from the point of view of defects and bonding structures. Some discussions are also made on possible future research directions, such as exploring underlying deformation mechanisms via in situ TEM testing and large-scale atomistic simulations, and investigating the twin size and orientation effects.