Progress in pressureless sintering of boron carbide ceramics – a review

Abstract

Boron carbide (B 4 C) ceramics has many outstanding performance, such as extremely high hardness, low density, high melting point, high elastic modulus, high thermoelectromotive force, high chemical resistance, high neutron absorption cross section, high impact and excellent wear resistance. Therefore, B 4 C ceramics can be used in various industrial applications, such as lightweight ceramic armour, high temperature thermocouples, neutron absorber, reactor control rods in nuclear power engineering, polishing media for hard materials, abrasive media for lapping and grinding, and wear resistant components (blasting nozzles, die tips and grinding wheels). Pressureless sintering is the method with industrialised application value for B 4 C ceramics, however, it is impossible to sinter pure B 4 C ceramics to high densities without additives by pressureless sintering. So sintering additives must be used to promote the densification of B 4 C ceramics. The different sintering additives used to promote the densification of boron carbide will be described in this review, including carbon additives, metallic additives, oxide additives, non-oxide additives, combined additives and rare earth oxide additives. Finally, the recent research trends for sintering methods and sintering additives of B 4 C ceramics will also be proposed.

Demonstrating low‐temperature sintering of boron carbide powders

“…As reviewed earlier and also in Ref. 13,15, methods to densify B 4 C include pressureless sintering, hot pressing, and spark plasma sintering; their typical densification conditions and results of monolithic B 4 C samples without additives are compared with our results in Table . First, much studies exist about pressureless sintering, in which green bodies are prepared and fired .…”

“…Sintering of B 4 C, either hot or cold, is more challenging than sintering of oxides, due to its strong covalent bonding, low self‐diffusion coefficient, thermodynamic stability, and its high sintering temperature (>2000°C vs 2450°C melting point) . The sintering temperature of B 4 C has been lowered by introducing additives such as carbon, ductile metals, and metal borides , but only down to ~ 1800‐1900 °C with pressureless sintering and pressure‐assisted sintering such as hot pressing and spark plasma sintering . The resulted B 4 C samples are not monolithic, potentially degrading the unique properties of B 4 C.…”

Properties of B4C-TiB2 ceramics prepared by spark plasma sintering*

“…To calculate fracture toughness, an oscilloscope was used to measure the shear and longitudinal wave sound velocities and then the Poisson ratio μ was calculated using Equation (5). Data for the Young ' s modulus calculation was then obtained using Equation (6). Finally, the fracture toughness of the B 4 C-TiB 2 composite ceramics was calculated according to Equation 7.…”

“…The third hardest material known to man, black diamond, or B 4 C ceramic [3][4] , is an attractive ceramic because of its excellent properties such as low density (2.51 g•cm 3 ), high melting point (2447 °C), high hardness (2931 GPa), outstanding chemical stability and excellent absorption neutron cross-section (600 b). It has many applications, such as abrasive cutting, as a coating material, for light-weight armour and for controlling nuclear fission [5][6] . B 4 C ceramic also has high Young's modulus (390440 GPa) and low fracture toughness (2.162.52 MPa•m 1/2 ) [7][8] .…”

Microstructure and mechanical property of (TiB2‐SiC) agglomerate‐toughened B4C‐TiB2‐SiC composites

“…Boron carbide (B 4 C) with a combination of unique properties, such as superior hardness, low density (2.52 g/cm 3 ), high melting point, good abrasion resistance, and excellent neutron absorption ability, 1,2 has attracted great attention in recent years and has been broadly applied in lightweight armors, wear‐resistant components, abrasive materials, and absorbent nuclear materials. However, some drawbacks of B 4 C limit its further application.…”