Micron diamond composites with nanocrystalline silicon carbide bonding

Diamond composites with nanocrystalline cubic silicon carbide bonding were sintered from diamond/amorphous silicon mixtures under high pressure and high temperature (p = 5 GPa and temperatures up to 1673 K). Differential scanning calorimetry, ex situ x-ray, and Raman spectroscopy investigations showed that amorphous silicon partially transformed into nanocrystalline silicon at 873 K under 5 GPa. This was followed by the formation of nanocrystalline silicon carbide from the reaction between the silicon and diamond after silicon melting. Refinement of the x-ray diffraction patterns of composites with the Rietveld method revealed that considerable microstrain (0.3-0.5%) remained within the nanocrystalline silicon carbide grains. Small strain (0.1-0.2%) was observed in the compacted diamonds, but after the reaction they became almost strain free (<0.1%). Enhanced fracture toughness was obtained for hybrid composites compared to liquid-infiltrated composites.