545 / 2019-03-20 11:59:57

High Temperature and High Pressure Sintering of Nanocrystalline B4C/SiC Composite Ceramics

B4C,SiC,nano-ceramic,high pressure sintering

全体主题 > High Pressure Physics and Materials Science

Boron carbide (B4C), a lightweight, refractory semiconductor with a hardness ranking behind those of diamond and cubic boron nitride (c-BN), has been increasingly applied in the industry. This increased usage is mainly benefited from the superior properties of the material, such as low density (2.5 g/cm3), high Young' s modulus (~440 GPa), high melting point (>2400˚C), small thermal extension coefficient (5.73 ×10-6 K-1), high resistance to chemical attacks, high thermal stability, high Seebeck coefficient, and large neutron absorption cross section. However, the shortage that low fracture toughness and strength as well as poor machinability has significantly becomes a bottleneck for further application of B4C, which are serious obstacles for any structural material.
Nanocrystalline ceramics are known to exhibit numerous outstanding properties compared with conventional polycrystals. In particular, these ceramics are expected to have a combination of high strength and enhanced ductility. So a great deal of effort has been performed to reinforce B4C ceramics using higher chemical activity B4C powders with a smaller nano size and controlling grain growth during the sintering process. In addition, adding toughing phase such as TiB2, Al2O3, CeO2, and SiC can also improve the sintering density and mechanical properties.
In this study, we have successfully prepared B4C/SiC nanocomposite ceramics by using high temperature and high pressure instead of SPS or hot pressing sintering method. Unlike the previous method of sintering boron carbide nano-powder mixed with silicon carbide nano-powder, we use self-prepared carbon-coated nano-powders and pure silicon powders as precursors. Nano-composite ceramics can be prepared by high pressure method at lower sintering temperature. Boron carbide retains the same particle size as the precursor, and the particle size is ~92 nm. And the average size of SiC nanocrystals is ~136 nm. The hardness and fracture toughness of samples doped with 15 wt% Si reached 35 GPa and 5.5 MPa·m1/2 respectively. Compared with the sample prepared under the same sintering conditions without adding Si, the hardness and fracture toughness of the samples increased by 40% and 150% respectively.