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

In the present investigation, the influence of B 4 C on the mechanical and Tribological behavior of Al 7075 composites is identified. Al 7075 particle reinforced composites were produced through casting, K 2 TiF 6 added as the flux, to overcome the wetting problem between B 4 C and liquid aluminium metal. The aluminium B 4 C composites thus produced were subsequently subjected to T6 heat treatment. The samples of Al 7075 composites were tested for hardness, tensile, compression, flexural strengths and wear behavior. The test results showed increasing hardness of composites compared with the base alloy because of the presence of the increased ceramic phase. The wear resistance of the composites increased with increasing content of B 4 C particles, and the wear rate was significantly less for the composite material compared to the matrix alloy. A mechanically mixed layer containing oxygen and iron was observed on the surface, and this acted as an effective insulation layer preventing metal to metal contact. The coefficient of friction decreased with increased B 4 C content and reached its minimum at 10 vol% B 4 C.

Influence of B4C on the tribological and mechanical properties of Al 7075–B4C composites

The challenge of ceramic/metal microcomposites and nanocomposites

This paper reviews the fundamental concepts and the terminology of wetting. In particular, it focuses on high temperature wetting phenomena of primary interest to materials scientists. We have chosen to split this review into two sections: one related to macroscopic (continuum) definitions and the other to a microscopic (or atomistic) approach, where the role of chemistry and structure of interfaces and free surfaces on wetting phenomena are addressed. A great deal of attention has been placed on thermodynamics. This allows clarification of many important features, including the state of equilibrium between phases, the kinetics of equilibration, triple lines, hysteresis, adsorption (segregation) and the concept of complexions, intergranular films, prewetting, bulk phase transitions versus “interface transitions”, liquid versus solid wetting, and wetting versus dewetting.

/pdf/a-review-of-wetting-versus-adsorption-complexions-and-2rni10tbod.pdf

A review of wetting versus adsorption, complexions, and related phenomena: the rosetta stone of wetting

Graphene has emerged as the most popular topic in the active research field since graphene's discovery in 2004 by Andrei Geim and Kostya Novoselov. Since then, graphene research has exponentially accelerated because of its extraordinary properties, which have attracted the interest of researchers all over the world. For example, among the key properties are its thermal conductivity, electrical conductivity, optical transparency, and mechanical properties. These remarkable properties of graphene show its promise for applications in different industries including optical electronics, photovoltaic systems and others. However, the large-scale production and transfer method onto target substrates of monolayer graphene for commercial and industrial applications are still under study in the improvement stage. Therefore, this review presents the state-of-the-art research activities and latest advancement in the synthesis of graphene using various carbon precursors including solid, liquid and gas carbon feedstocks. The characterization methods have also been critically discussed in this review. In addition, the advancement in the transfer methods onto target substrates for achieving clean and high-quality transferred graphene have been thoroughly reviewed. Furthermore, the current growth mechanisms of single and multilayer graphene have also been discussed.

/pdf/review-of-the-synthesis-transfer-characterization-and-growth-1lirj47kfe.pdf

Review of the synthesis, transfer, characterization and growth mechanisms of single and multilayer graphene

Site related nucleation and growth of hydrides on uranium surfaces

Magnetic pulse welding (MPW) is a solid-state impact welding technology that provides metallurgical joints while exhibiting a negligible heat-affected zone. The MPW process is a high speed single shot welding technique used mainly for joining tubular components in a lap configuration and characteristic length scales of few millimeters to centimeters. It is similar in operation to explosive welding and shares the same physical principles. The nature of bonding in MPW is not sufficiently understood yet and some controversial explanations are reported in the literature. The two major ideas are based on either solid state bonding or local melting and solidification. The present work summarizes our current understanding of the bonding mechanism and the structure in various similar and dissimilar metal pairs joined by MPW.

Interface Phenomena and Bonding Mechanism in Magnetic Pulse Welding

.The microstructural features of the bonding zone in magnetic pulse welds of similar and dissimilar metal pairs have been investigated. The nature of the reactions and phase formation that occur in the magnetic pulse joints displaying a discontinuous pocket type or a continuous transition layer along the bond interface is explained in terms of local melting followed by rapid solidification. The most significant feature of the transition zone created during the magnetic pulse welding process is the hardness increase of the interface layer. For similar base metals the main cause of the hardness increase is the fine grained microstructure created during the rapid local solidification. In the dissimilar base metal welds the increase in hardness is a result of the formation of stable or metastable intermetallic phases and of the fine grained microstructure of the bonding zone.

Bonding zone formation in magnetic pulse welds

Lanthanide-doped thoria is relevant both to nuclear energy and to solid oxide fuel cell technology. It is also a simple model system in which oxygen vacancy concentration is directly proportional to doping with no complication from oxidation–reduction reactions, ordered phases, or phase transitions in the tetravalent oxide. Despite this relevance, only few thermodynamic data are available for such systems. In the present study, La xTh1-xO2-0.5x (0< x <0.50) and Yx Th1-x O2-0.5x (0 < x < 0.18) have been synthesized, characterized, and systematically studied for the first time using high-temperature oxide melt solution calorimetry. Two competing effects contribute to the energetics: endothermic deviation from ideality related to cation size difference and partial stabilization of the system due to the exothermic formation of defect clusters. The former can be described by endothermic regular solution interaction parameters of 119.3 ± 11.4 kJ/mol for the yttria system and 27.8 ± 4.1 kJ/mol for the lanthana system. The latter can be described by exothermic vacancy clustering or defect association energies of –116.3 ± 23.3 kJ/mol for yttria-doped thoria and –98.6 ± 19.7 kJ/mol for lanthana-doped thoria.

Thermochemistry of Lanthana- and Yttria- Doped Thoria

The experimental study of the wetting phenomena in the boron carbide–copper system, using the sessile drop method at 1150 °C shows that molten Cu attacks boron carbide substrates forming a crater below the contact area. Boron additions prevent crater formation, improve wetting and, for a 10 at.% B alloy, reduce the equilibrium wetting angle to 40°. Thermodynamic analysis of the Cu–B–C system in the Cu-rich corner confirms the experimental results. These results and similar ones obtained in the TiC–Cu system suggest that the presence of a carbide phase over a concentration range is a key feature that governs wetting phenomena and chemical interaction at these metal–carbide interfaces.

Michael Aizenshtein

Papers

Site related nucleation and growth of hydrides on uranium surfaces

Interface Phenomena and Bonding Mechanism in Magnetic Pulse Welding

Bonding zone formation in magnetic pulse welds

Thermochemistry of Lanthana- and Yttria- Doped Thoria

Ceramic-metal interaction and wetting phenomena in the B4C/Cu system