Superhard composites of cubic silicon nitride and diamond

• Published in: Diamond and related materials Vol. 27-28; pp. 49 - 53
• Main Authors: Wang, Wendan, He, Duanwei, Tang, Mingjun, Li, Fengjiao, Liu, Lei, Bi, Yan
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2012; Elsevier
• Subjects: Atomic structure; Carbon; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Cubic silicon nitride; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Hardness; High pressure; Materials science; Mechanical and acoustical properties; Nanocrystalline materials; Nanocrystals; Nanodiamond; Nanoscale materials and structures: fabrication and characterization; Optical microscopes; Physical properties of thin films, nonelectronic; Physics; Scanning electron microscopy; Silicon nitride; Sintering; Specific materials; Structure and morphology; thickness; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Thin film structure and morphology; Cubic silicon nitride; Nanodiamond; High pressure; Cubic lattices; Vickers hardness; Synthetic diamond; XRD; Nanostructures; Optical microscopy; Hexagonal crystals; Hardness testing; Carbon nitrides; Silicon; Nanocrystal; Scanning electron microscopy; Reaction product; Silicon nitride; Mechanical properties; Carbon; Polycrystalline diamond; Composite materials; Transmission electron microscopy; Spinels; Sintering; Graphite; Nanostructured materials
• DOI: 10.1016/j.diamond.2012.05.013
• ISSN: 0925-9635

Powder mixture of graphite and silicon nitride with hexagonal structure (α/β-Si3N4) was ball-milled in nitrogen and compressed under ~16GPa/1800°C and ~18GPa/2000°C, to investigate the possibility for replacing Si atoms by C atoms in cubic spinel silicon nitride (c-Si3N4). The sintered samples were characterized by X-ray diffraction (XRD), hardness measurement, optical microscope, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The results show that the well-sintered compacts were composed of nanocrystalline c-Si3N4 and nanocrystalline diamond, and neither C3N4 and CSi2N4 nor other reaction products of Si3N4 and C were observed. Vickers hardness test shows that the average hardness of the samples is 41–42GPa. As a comparison, phase-pure c-Si3N4 bulks also have been synthesized and their hardness was confirmed to be about 31GPa. The pure c-Si3N4 sintered bulks exhibit a high frangibility, but their fracture toughness could be largely improved by adding carbon (nanocrystalline diamond) in the sintered compacts. ► Well-sintered compacts of c-Si3N4 and diamond composite have been synthesized. ► Nanodiamond improved the sintered compacts in hardness and fracture toughness. ► Vickers hardness of c-Si3N4 was confirmed to be 31GPa by synthesized pure bulks. ► Si atoms in Si3N4 cannot be replaced by C atoms up to 18GPa and 2000°C.