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Vacuum pressureless sintering of boron carbide ceramics with additives

Boron carbide ceramic materials have many excellent properties, such as: high melting point (2450°C), ultra-high hardness (HV>30GPa), low density (2.51g/cm³), high modulus, good wear resistance, oxidation resistance, Strong acid and alkali resistance, good neutron absorption capacity, and high tensile strength at high temperature, it is often used in bulletproof, nuclear energy, military, energy and other fields. However, the fracture toughness of boron carbide ceramics is very low, and the covalent bond content is as high as 94%, so it is an extremely difficult ceramic material to sinter.

The relatively mature process for preparing high-density boron carbide is hot pressing sintering, and technologies such as hot isostatic pressing, microwave sintering, reaction sintering, pressureless sintering or spark plasma sintering are also used for boron carbide sintering. Among them, pressureless sintered B4C ceramics have been widely valued due to their simple preparation process, superior product performance and low cost. Boron carbide superfine powder with suitable particle size can be used, and a small amount of forming and sintering aids can be added. Afterwards, B4C ceramic products with a relative density of 96% to 97% can be prepared through the grouting molding process and pressureless sintering, which can reduce the densification sintering temperature of boron carbide ceramics.

Process flow

Boron carbide powder is selected, SiC and C are used as sintering aids, and pressureless sintering is carried out under vacuum conditions. The mass fraction of carbon in the sintering aid is 5%, and the mass fraction of silicon carbide is 6%. As the sintering temperature increased from 1925 °C to 2000 °C, the bulk density and flexural strength of pressureless sintered B4C ceramic composites showed a trend of increasing first and then decreasing, the hardness showed an increasing trend, and the fracture toughness showed a decreasing trend. small trend. When the sintering temperature is 1975°C, the material exhibits the best mechanical properties: the bulk density is 2.45g/cm³, the Vickers hardness is 35GPa, the flexural strength is 240MPa, and the fracture toughness is 3.0 MPa.

Through multiple process experiments, the following points can be learned:

1) The best sintering process for pressureless sintering of BaC ceramic material is 1975℃ for 30min.

2) The effects of the addition of sintering aids SiC and C on the density, hardness and flexural strength of the material all increase first and then decrease. The fracture toughness of the material increases with the increase of the mass fraction of C. The increase of SiC decreases firstly, and increases slightly after the SiC mass fraction is higher than 6%.

3) When the sintering aids SiC and C are added at 6% and 5%, respectively, the best mechanical properties of the pressureless sintered BAC ceramic material are obtained: the bulk density is 2.45g/cm³, and the Vickers hardness is 35 GPa , the flexural strength is 240 MPa, and the fracture toughness is 3.0 MPa.

Selection of sintering equipment: Pressureless sintering is a key link in the production of silicon carbide ceramics. The processing effect of this link will directly determine the quality of the finished product. Therefore, the selection of equipment for silicon carbide sintering furnace is very important.

The RVS-S series pressureless silicon carbide sintering furnace produced by SIMUWU can well meet the needs of silicon carbide pressureless sintering. It can be heated up to 2400 degrees Celsius and has good temperature uniformity and vacuum.

SIMUWU has more than ten years of sales and manufacturing experience in the field of vacuum furnaces, and can effectively meet the different process needs of customers. The mature engineer team can help manufacturers complete a series of needs from installation to after-sales. In the field of silicon carbide sintering, many factories have chosen this brand. Its technology is mature and reliable, and it is an outstanding brand in the field of pressureless silicon carbide sintering furnaces.