Grain-interior planar defects induced by heteroatom monolayer

A new type of grain-interior planar defect in a ceramic phase in TiC doped cemented tungsten carbides was discovered. It is unique in that the monolayers of metal atoms exist stably in ceramic grains. The planar defects were induced by the ordered heteroatoms distributing on certain crystal planes of the matrix, which are distinct from the known planar defects such as phase-, grain-, and twin-boundaries, stacking faults, and complexions. Detailed characterization on the atomic scale was performed for the composition, structure, and crystallography of the planar defects, and their energy state and stability were evaluated by modeling. It was found that the Ti monolayer assists nucleation of the new WC crystal along the normal direction to its basal plane. Due to the disturbance of the heteroatom layer, the deposition of W and C atoms deviates from the regular sites occupied in the perfect crystal lattice, resulting in variations of the W–C arrangement in the grain structure. Experiments confirmed that tailoring the distribution density of the planar defects could give the best comprehensive mechanical performance with simultaneously outstanding strength and fracture toughness in the materials containing the grain-interior planar defects. This study provides a new strategy to greatly enhance the mechanical properties of materials by introducing and tailoring planar defects in the grain interiors. We report a discovery of a new type of grain-interior planar defects induced by the heteroatom monolayer, e.g., a monolayer of metal atoms inside the covalent crystal of ceramic grains. It is of great significance that the planar defects hinder the long-distance motion of stacking faults and dislocations in the grain interiors, and act as obstructions against propagation of the transgranular cracks. This work provides a novel strategy to enhance the mechanical properties of materials by introducing and tailoring the grain-interior planar defects.