A preparation method for reducing the sintering temperature of a dense ultrafine-grained boron carbide ceramic material

Abstract

The invention discloses a method for preparing a compact ultrafine-grain boron carbide ceramic material with a reduced sintering temperature. The method comprises the following steps: selecting coarse boron carbide powder with an average particle size of less than 20 [mu]m and carrying out ball milling and settlement so as to obtain ultrafine boron carbide powder with a particle size of less than 1 [mu]m; mixing the ultrafine boron carbide powder with MnNiCoCrFeX high-entropy alloy powder and carrying out ball milling so as to obtain B4C-MnNiCoCrFeX mixed powder; and subjecting the mixed powder to pressure sintering so as to obtain the compact ultrafine-grain boron carbide ceramic material with a reduced sintering temperature. According to the invention, the MnNiCoCrFeX high-entropy alloy powder is added into a boron carbide matrix, so a liquid phase is formed during high-temperature sintering and can fill in pores, and thus, the sintering densification temperature of the boron carbide ceramic material is effectively reduced, and energy consumption is decreased; and a boron carbide product with a density of greater than 99% is obtained after a temperature of 1900 DEG C is maintained for 5 min, and compared with the prior art, sintering temperature is reduced by 200 DEG C and heat preservation time is substantially shortened.

Description

technical field [0001] The invention relates to a dense ultra-fine-grain boron carbide material, in particular to a preparation method capable of reducing the sintering temperature of a dense ultra-fine-grain boron carbide ceramic material. Background technique [0002] The molecular formula of boron carbide is B 4 C, black gray powder under normal temperature and pressure, high hardness (Mohs hardness 9.3, second only to diamond and cubic boron nitride), low density (theoretical density 2.52g / cm 3 , is the lightest ceramic material), high melting point (2350 ° C) and good thermal stability. Therefore, boron carbide materials can be used as friction, drilling, and polishing materials. [0003] An extremely important application of boron carbide is as a bearing material for gyrodynamic motors. As a sensor sensitive to angular displacement and angular velocity, gyroscope is an indispensable part of the inertial guidance system of aerospace equipment. In the 1970s, the Brit...

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Problems solved by technology

[0006] (2) The melting point of boron carbide is relatively high, 2350°C. If the traditional pressureless sintering is adopted, 2200°C or a long time of heat preservation is required to achieve full densification, which not only consumes high energy, but also has harsh production conditions.

With low sintering temperature or low holding time, the product has low relative density, many internal residual pores, low hardness, fracture toughness, bending strength and friction and wear strength, and the product cannot be applied

[0007] (3) The prepared pure boron carbide bearing material adopts traditional pressure sintering, that is, hot pressing sintering or spark plasma sintering. Although the sintering temperature is lowered, it still needs 2100°C. The temperature is relatively high, and the production conditions are still harsh. The sintering process When the holding time is too long, the grain grows obviously, the average grain size is >5μm, the bending strength is low, there are many internal cracks in the bearing, and the hardness and wear performance are poor