Super Strengthening Nano-Polycrystalline Diamond through Grain Boundary Thinning

摘要

Introducing nanostructures into diamonds is quite appealing for the synthesisof superhard materials with superior properties. However, as thegrain size decreases to nanoscale, grain boundary effects become crucial yetcomplicated in the nanopolycrystalline diamond (NPD), making it challengingto tailor nanostructures. Here, atomistic simulations are combined withexperiment to demonstrate a strengthening strategy for the sintered NPD byintroducing thin amorphous grain boundary (AGB). The additive of small percentageof fullerene into precursors during sintering can significantly reducecrushed amorphous-like nanodomains in diamond nanocrystals, leading tothe formation of thin AGB. Such sintered NPD exhibits a significant hardnessand fracture toughness enhancement, exceeding that of single crystaldiamonds. These atomistic simulations show that upon straining the plasticdeformation, crack initiation and propagation in NPD is AGB thicknessdependent, and thin AGB can reduce crack nucleation and block crack propagation,well explaining the experimental observations. This study indicatesthat grain boundary modulation provides a promising approach for rationaldesigns of high-performance superhard materials with desired high strength.