Boron carbide is a strategic material, finding applications in nuclear industry, armour for personnel and vehicle safety, rocket propellant, etc. Its high hardness makes it suitable for grinding and cutting tools, ceramic bearing, wire drawing dies, etc. Boron carbide is commercially produced either by carbothermic reduction of boric acid in electric furnaces or by magnesiothermy in presence of carbon. Since many specialty applications of boron carbide require dense bodies, its densification is of great importance. Hot pressing and hot isostatic pressing are the main processes employed for densification. In the recent past, various researchers have made attempts to improve the existing methods and also invent new processes for synthesis and consolidation of boron carbide. All the techniques on synthesis and consolidation of boron carbide are discussed in detail and critically reviewed.

Synthesis and consolidation of boron carbide: a review

On the influence of active element content on the thermal conductivity and thermal expansion of Cu-X (X = Cr, B) diamond composites

Processing and microstructural characterisation of AA 1070 and AA 6063 matrix B4Cp reinforced composites

Pressureless sintering of boron carbide

In this contribution, authors present a review on the state-of-the-art in the utilization of industrial and agricultural waste materials for the development of metal–matrix composites (MMCs), providing, through the judicious analysis of an ample and varied references source – from the oldest to the newest ones – an insight into the challenges and opportunities for the exploitation to their full potential. In addition to its topicality, the novelty of this contribution lies in the presentation of key statistical, technical, and property-related information of a comprehensive variety of waste materials classed into two main groups, namely, fly ash reinforced MMCs and MMCs derived from other waste materials. Although fly ash has been exploited in a broad range of applications, the attention paid for its use in the development of MMCs seems to be insufficient. A purposely designed chart helped to pinpoint the more demanding and profitable applications of fly ash, and establish strategic opportunity ar...

Development of metal-matrix composites from industrial/agricultural waste materials and their derivatives

The effect of TiO2 and of Ti additions on the sintering behavior of B4C was studied in the 1800 °C to 2190 °C temperature range. According to thermodynamic predictions that were verified by the experimental results, TiB2 is formed in situ in both instances. Titanium oxide is reduced by carbon that originates in B4C and decreases its carbon content. The activity of carbon in the boron carbide phase is reduced significantly with decreasing carbon content. By sintering at 2160 °C for 1 hour, a mixture of fine-sized B4C with 40 wt pct TiO2 is transformed into a 95 pct dense two-phase composite that consists of substoichiometric boron carbide and TiB2 and displays a bending strength of 420 MPa. The significantly improved sintering behavior of this composite ceramic is attributed to the enhanced mass transport processes that takes place in substoichiometric B4C. The low carbon activity values in substoichiometric B4C ensure that no deleterious carbide phases are produced by reaction with molten metals.

The effect of Ti and TiO2 additions on the pressureless sintering of B4C

Additions of TiO2 affect significantly the sintering behavior of B4C. The two powders react at approximately 1500°C according to the reaction: B4C+TiO2→B4C1−x+TiB2+CO↑ (or CO2↑). Above 2000°C, the resulting two-phase, B4C1−x+TiB2, mixture sinters at a higher rate than the single-phase boron carbide. The rate of sintering increases dramatically for mixtures that contained initially 40 wt% TiO2, yielding after sintering at 2190°C for 1 h a 95% dense, fine-grained composite material, consisting of sub-stoichiometric B4C1−x and TiB2. The boron-rich carbide displays very high affinity to carbon and reverts rapidly to stoichiometric composition when treated at high temperature in a carburizing atmosphere. The two-phased ceramic can be sintered to various levels of density and infiltrated with a molten metal. After infiltration with molten aluminum, the hardness of the resulting cermets ranges from 800 to 2500 HV and the flexural strength varies from 750 to 350 MPa depending on their ceramic-to-metal ratio.

A novel approach for the preparation of B4C-based cermets

A thermodynamic analysis of the Al-rich corner in the ternary Al-Ti-C diagram, providing phase relations and regions of phase stability, is presented. An invariant four-phase equilibrium between Al, Al4C3, Al3Ti, and TiC
 x
 takes place at 0.53 at. pct Ti, 7.10−6 at. pct C, and TiC0.883 at 966 K. The carbon content of the TiC
 x
 phase, which extends from x=0.48 to 0.98, exerts a significant effect on phase relationships in this ternary system. In particular, it is shown that stoichiometric TiC is not stable in the presence of liquid Al. For example, at 1300 K, a two-phase equilibrium between Al
 L
 and TiC
 x
 exists only in the 0.91<x<0.82 range. Thus, the interaction of Al
 L
 with stoichiometric TiC leads to the formation of the Al4C3 aluminum carbide phase, whereas for x<0.82, only the intermetallic compound Al3Ti can form at this temperature. The results of this analysis were confirmed by X-ray diffraction (XRD) measurements of relevant composites.

L. Levin

Papers

The effect of Ti and TiO2 additions on the pressureless sintering of B4C

A novel approach for the preparation of B4C-based cermets

High-temperature phase equilibria in the Al-rich corner of the Al-Ti-C system

Manufacturing B4C–(Al,Si) composite materials by metal alloy infiltration

Iron-titanium-carbon system. I. Equilibrium between titanium carbide (TiCx) of various stoichiometries and iron-carbon alloys