Densification Of Boron Carbide Research Articles

Reactive Sintering of Boron Carbide Based Ceramics by SPS

Boron carbide is a highly covalent non-oxide ceramic with a high melting temperature. Therefore, the densification of boron carbide via a thermally activated process is extremely hard and requires additional driving forces. In addition to searching alternative production techniques for boron carbide, the production of boron carbide composites is one of the most interested subjects. In this study, BxC-TiB2-SiC ceramic was produced through an in-situ reaction between B4C and Ti3SiC2 and excess amorphous boron using spark plasma sintering method at 1600°C-1800°C. XRD and microstructure analysis of the sintered sample show that boron rich boron carbide phase is present in the sintered specimen, which did not develop a continuous matrix through the sample. The three phases present in ceramics formed agglomerate throughout the microstructure and did not show homogeneous distribution.

Densification of boron carbide under high pressure

Additive-free boron carbide (B4C) powders were densified at 4 GPa using the high-pressure “anvil-type with hollows” apparatus in the temperature range of 1500–1900 °C. The boron carbide ceramics prepared by this method showed a hardness of 37 GPa, which is very close to the hardness of mono-crystal boron carbide. The study showed that the boron carbide grains are uniformly sized without observed grain growth in the sintered materials. Obtained results revealed that high-pressure sintering can be a very effective low-temperature densification method for the obtainment of additive-free B4C ceramics. Moreover, the process can be scaled-up for the production of large-size composites required in various cutting tools and other extreme condition applications.

In-situ synthesis and densification of boron carbide and boron carbide-graphene nanoplatelet composite by reactive spark plasma sintering

Simultaneous synthesis and densification of boron carbide and boron carbide- graphene nano platelets (GNP) were carried out by reactive spark plasma sintering of amorphous boron and graphene nano platelets at temperature ranging from 1200 to 1600 °C, pressure of 50 MPa and heating rate of 50 °C/min and 100 °C/min. X-ray diffraction and Raman spectroscopy confirmed the formation of required phases. Electron microscopic images revealed the formation of sub-micron and nano sized grains of plate like morphology. Sintered product with high relative density of 96%TD was achieved at a temperature of 1600 °C and heating rate of 50 °C/min for B4C stoichiometric composition and also exhibited maximum hardness of 21.10 GPa.

Influence of spark plasma sintering parameters on densification and mechanical properties of boron carbide

The densification behavior of boron carbide without sintering additives is reported for temperatures in the range of 1100°C to 1800°C by spark plasma sintering (SPS) technique together with the sintering parameters (Holding Time and Pulsed DC). The influence of porosity on mechanical properties (hardness, fracture toughness and elastic modulus) of boron carbide prepared by SPS is measured. Pulsed DC current is found to play a dominant role in the densification of boron carbide and in achieving near theoretical density at lower sintering temperature compared to conventional sintering techniques. Hardness, fracture toughness and elastic modulus of fully dense B4C are measured as 37.2GPa, 2.8MPa.m1/2 and 570GPa respectively. Microstructural analysis indicates the presence of deformation twins in boron carbide grains.

Densification behavior and related phenomena of spark plasma sintered boron carbide

In this work, boron carbide ceramics were sintered in the temperature range of 1400–1600°C by spark plasma sintering (SPS). The influence of sintering temperature, heating rate, and holding time on the microstructure, densification process and physical property was studied. The heating rate was found to have greater influence than that of the holding time on the microstructure and the densification of boron carbide. The optimal sintering temperature was 1600°C under the heating rate higher than 100°C/min. The relative density, flexural strength, Vickers hardness and fracture toughness of the sample synthesized at 1600°C were 98.33%, 828MPa, 31GPa and 2.66±0.29MPam1/2, respectively. The densification mechanism was also investigated.

Synthesis, Densification and Characterization of Boron Carbide

This paper presents the experimental results on synthesis of boron carbide from its elements. Boron to carbon ratio of 4:1 and a synthesis temperature of 1850°C was found optimum to obtain stoichiometric B4C. Higher boron in charge resulted in the formation of boron rich phase B8C along with B4C but was not effective in eliminating free carbon in the product. Effect of hot pressing parameters on densification of boron carbide was investigated and the optimum operating parameters to obtain B4C pellets with a density of ≥95% TD were identified. Mechanical and thermal properties were characterized and compared with literature values.

Investigation on reactive sintering process of boron carbide ceramics by XRD

Boron carbide ceramics were simultaneously synthesised and densified from B and C elemental powders by a spark plasma sintering method. The reactive sintering process was investigated, and two stages of large shrinkage corresponding to synthesis and densification of boron carbide were observed. At stage I (1300–1700°C), B reacted with C and the product in phase of free C and B rich boron carbide (B4+xC) was synthesised. With increasing the sintering temperature, C atoms diffused into the B4+xC lattice, resulting in the reduction in free C content and the decreasing in lattice parameters of B4+xC. At stage II from 1700 to 1900°C, the densification of the synthesised boron carbide occurred. The product was densified gradually and a high relative density (95%) was obtained by spark plasma sintering at 1900°C.

Pressureless sintering of boron carbide ceramics

Densification of boron carbide (B4C) was studied by pressureless sintering at temperatures ranging from 2108° to 2226°C with Al gas and Si compound gas derived from SiC. High purity boron carbide compacts attained a bulk density of a nearly full density (2.455 g/cm3) after being sintered at 2226°C.

The effect of the sintering atmosphere on the densification of B 4C ceramics

Densification of boron carbide during sintering may be improved by a two-stage process, namely heating to 2000°C under vacuum and sintering at 2190°C under argon. This sintering regime allows achieving a relative density of the ceramic bodies fabricated from a fine powder higher than 95%. The nitrogen treatment of the boron carbide phase at 1900°C leads to the formation of the BN phase and precipitation of graphite. Vacuum treatment of these samples at 2000°C leads to decomposition of the boron nitride phase. The liberated free boron may again react with graphite to form in situ boron carbide particles. The experimental investigations of the sintering behavior of the boron carbide phase under various atmospheres supported the thermodynamic predictions regarding the phase transformation. No evidence, however, was found for enhanced sintering under a nitrogen atmosphere.