A dislocation perspective on heterointerfacial strengthening in nanostructured diamond and cubic boron nitride composites

The nanometer-scale diamond/cBN (C/BN) heterointerface is believed to significantly enhance the mechanical properties of diamond-cBN nanocomposites, however, the underlying mechanisms remain largely unexplored and poorly understood. In this study, we conduct a comprehensive investigation of the dislocation slip resistance at perfect C/BN heterointerfaces and their corresponding nanotwinned and stacking-faulted structures, utilizing the ab initio-informed Peierls-Nabarro model. Our findings show that the nanotwinned defects at the heterointerface, characterized by negative formation energy, are more thermodynamically stable than those in the cBN and diamond bulk. Stacking faults tend to favor the cBN side over the diamond side at the heterointerface, which is consistent with experimental observations. The perfect C/BN heterointerface exhibits notably lower slip resistance to parallel dislocation than bulk diamond and cBN due to shear-induced Friedel oscillation. Conversely, a much higher dislocation slip resistance is observed at the nanotwinned and stacking-faulted C/BN heterointerfaces than that of bulk cBN, suggesting that the mirror symmetry presented across the nanotwinned and stacking-faulted heterointerfaces offers an effective strategy for strengthening. These insights not only offer a novel perspective on the ubiquitous heterointerfacial strengthening in diamond-cBN nanocomposites, but also underscore the pivotal role of atomic-scale interfaces in designing superhard nanostructures.