4.7 Article

Enhanced mechanical properties of nanocrystalline B4C-SiC composites by in-situ high pressure reactive sintering

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ELSEVIER
DOI: 10.1016/j.jmrt.2023.10.110

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Boron carbide; High-pressure sintering; Hardness; Toughening

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A core-shell structured B4C nanopowder, Si as a sintering aid additive, and high-pressure sintering technique were used to process nanocrystalline B4C-SiC ceramics with improved mechanical properties. The addition of Si reacted with carbon layer and nanoshell to form dispersed SiC nanocrystals and Si-C phase. Furthermore, deflection of nanoscale cracks and covalent bonding at grain boundaries were responsible for the superior performance in hardness and fracture toughness.
A unique optimized of core-shell structural B4C nanopowder, sintering aid additive of Si, and high-pressure sintering technique has been used to process nanocrystalline B4C-SiC ceramics with enhanced mechanical properties. C-coated B4C nanopowder was initially uniformly mixed with micron Si of different content by ballmilling. B4C-SiC composites with a homogenous distribution of SiC in B4C matrix were subsequently obtained by sintering the mixed powders at 6 GPa and 1600 degrees C. The added Si reacted with submicron amorphous carbon layer and amorphous carbon nanoshell to form dispersed SiC nanocrystals and Si-C phase filled at B4C grain boundaries and pores, respectively. The prepared composite had the most outstanding mechanical properties when the Si content in the precursor was 15 wt%, with a hardness reaching 37.8 GPa and a fracture toughness reaching 7.3 MPa & sdot;m1/2. Microstructural characterizations indicated that the multi deflection of nanoscale crack caused by intergranular fracture, the covalent bonding of Si-C phase at the grain boundary, and the abundant nanotwin substructure were jointly responsible for the superior performance in hardness and fracture toughness.

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