Issue No 1, April

Abstract

In this paper, we focus on some historical aspects, as well as on recent achievements in the field of self-propagating high-temperature synthesis (SHS) of ceramics. While giving the tributes to the pioneers of the SHS, we overview the wide variety of recently established SHS-based routes for fabrication of advanced ceramics, including nanopowders and nanostructured bulk materials. Both, the conventional heterogeneous SHS and solution combustion synthesis (SCS) approaches are considered. Advantages and challenges for using of the self-sustained reactions for fabrication of ceramics are also discussed.

Abstract

In order to maintain and extend sustainable activities of humans, the availability of renewable energies or high efficient energy systems is essential and plays an important role in the design and implementation for further developments forwards. Self-propagation high-temperature synthesis (SHS) which features oxygen-free heat release and high-performance materials synthesis is an economical and energy saving technology effective in exergy loss minimization. The SHS process has been successfully applied to super high heat supplies and high-temperature materials formations under the conditions of inertia forces and steep gradients of pressure and temperature. With such technological merits, various SHS related technologies have been widely performed for in-situ resource utilizations in space exploration and geothermal developments toward space and underground environments utilizations. By validating the experimental conditions and the achievements obtained from the studies on (1) inertia forced composite formations, (2) nitride synthesis with liquid nitrogen and (3) carbon allotropes formation with oxygen deficient flame and plasma spraying, the SHS related technologies would work efficiently even in the environments of low gravity and atmospheric carbon dioxide and nitrogen like Mars. The establishment of the SHS related technologies performed in space and underground environments utilizations would be able to promote further technological progresses exerting actively and flexibly also in other extreme environments such as underwater and disaster-area.

Abstract

Since the inception of self-propagating high-temperature synthesis (SHS), the production of refractory carbides and borides was one of the main areas of SHS application. SHS provides unique reaction conditions, including extremely high reaction temperature and rapid heating/cooling, and produces materials with novel microstructures and outstanding mechanical properties. SHS is generally characterized by short processing cycle, decreased energy consumption, and reduced cost, and provides an efficient way for the production of refractory and hard materials. In this review, we summarize the recent developments in this field with the two main foci: first, the latest advances in SHS of carbide- and boride-based ceramics, including ultra-high temperature ceramics (UHTCs) and high-entropy ceramics (HECs), and second, the properties and industrial applications of synthesized materials. Most prominent features of SHS ceramics are summarized, and prospective directions for further developments are discussed.

Abstract

The paper presents a summary of the experimental works made in the Nalbandyan Institute of Chemical Physics of Armenian NAS during the period of 2008-2018. Here the results of studies on the synthesis of multicomponent compounds containing transition metals of IV and V groups, chromium, molybdenum, cobalt and carbon at combustion in the atmosphere of argon, hydrogen, nitrogen and nitrogen/hydrogen mixture are described. Using SHS, single-phase carbides, carbohydrides, carbonitrides and carbohydridonitrides, based on titanium, vanadium, zirconium, niobium and chromium were synthesized in one technological step. It was shown that over the entire range of changes in the metal/carbon ratio at low concentrations of carbon, carbohydrides and carbonitrides with a cubic FCC lattice formed. The influence of the metal/nonmetal ratio on the phase composition of the final products was studied, and the X-ray densities of the obtained compounds were calculated. It is shown that the increasing of the carbon and vanadium content, as well as the doping carbides, carbonitrides and carbohydrides with molybdenum and cobalt lead to the increasing of X-ray density.

Abstract

Cylindrical disks composed of HfB₂-26 vol%SiC_f are successfully fabricated by combining the Self-propagating High temperature Synthesis (SHS) and Spark Plasma Sintering (SPS) processes. Specifically, HfB₂ powders synthesized by SHS are mixed with SiC fibers and the resulting mixture is consolidated by SPS. The presence of SiC fibers was retained in the nearly full dense materials sintered at 1800 °C. The measured values of Vickers hardness, fracture toughness, flexural strength and elastic modulus at room temperature are 21.6±0.8 GPa, 6.2±0.5 MPa·m^0.5, 429±45 MPa and 312±17 GPa, respectively. The obtained products are found to well resist to ablation, with weight losses below 0.25% when exposed to the most aggressive heat flux conditions (1250 W/cm²). A nozzle component of the desired shape and size is finally obtained for space propulsion applications after electrical discharge machining the SPS material.

Abstract

Titanium diboride-silicon composite was fabricated by innovative method of self-propagating high-temperature synthesis (SHS) from the mixtures of titanium, magnesium dodecaboride and silicon in constant pressure reactor in argon atmosphere at 0.5-2 MPa pressure. The key influence of initial mixture composition, sample geometry and external gas pressure on the combustion features, products phases and microstructure characteristics were examined. Direct fabrication of fully dense TiB₂-(30-44)wt.%Si composite with improved physico-mechanical properties was performed using spark plasma sintering (SPS) at a relatively low temperatures (1250-1350 °C) with a dwelling time of 3 min at pressure of 50 MPa. Erosive wear behavior of the composites was studied both at room and elevated temperatures. The highest erosion resistance against silica particles impact was demonstrated by composite with the lowest silicon content.

Abstract

Ni-W nanocomposite material was synthesized by self propagating high temperature synthesis method from the NiO-WO₃ oxides mixture using Mg+C combined reducers via thermo-kinetic coupling approach. Thermodynamic modeling was performed to design combustion synthesis in the NiO-WO₃-yMg-xC system to find out optimum values for x and y in a moderate temperature conditions. Combustion peculiarities and reduction mechanism were explored using copper wedge technique combined with XRD analysis of the quenched products disclosing the preferential participation of magnesium rather than carbon in the primary stage of reduction process. The obtained Ni-W nanocomposite material with up to 50 nm average particle size subjected to spark plasma sintering exhibited high relative density and improved microhardness.

Abstract

A novel technique on hot explosive welding has been developed for fabricating layered composites consisting of ceramics and metal. The technique uses a simple processing which combines shock loading and combustion synthesis. The two types of trilayer composites which consisted of TiB₂+TiN ceramics, TiNi and steel, or TiB₂ ceramics, TiNi and steel, were fabricated by the hot explosive welding with a cohesive and strongly joined interface. Optimum fabrication conditions such as flying method of flyer plate, the amount of explosive, time window and buffer materials were investigated. Consequently, time window and the quantity of explosive affected their welding states significantly. After thermal shock test of the specimens at temperature of 500 °C into water, no exfoliation at the interfaces of the composite were shown. It was suggested that pseudo elasticity of TiNi intermetallic layer was effective for relaxation of thermal stress operated between ceramics and steel at elevated temperatures.