Issue No. 3, December

Abstract

Basic stages of progress in composite materials, prepared by SHS method, from a scientific approach to a promising and rapidly developing applications are discussed in this paper. The systematic review of different forms of composites prepared directly by SHS or by SHS-origin precursors is presented. Powders are usually the starting material for manufacturing of ceramic and a lot of attention has been paid to find new routes for synthesis powders in form of nano or micro particles. The present work is aimed at efficient and convenient powder processing by SHS as an important target for future composites technology. The use of SHS may bring a considerable development in ceramic technology, by enabling a manufacturing of sinterable, high-purity nano or micro powders. It can be demonstrated in different ceramic systems explored by the authors and coworkers using SHS e.g. (a) Si-C-N, (b) Al-O-N as well as (c) Ti-Si-C-N. Rapid combustion conditions were successfully used to manufacturing composite powders and nanopowders suitable for preparing multiphase composite materials having controlled properties.

Abstract

The presentation will report on the adoption of two different approaches based on selfpropagating high-temperature synthesis (SHS) to produce cermets. The first of these concerns the formation of the solid solution carbide, (Ti,V)C, of various compositions in an iron matrix by starting with elemental powders. It was observed that two types of carbide particles were generated within the matrix; a (Ti,V)C carbide of submicron size and a TiC-rich carbide of slightly higher size. Comparison of SHS Fe-TiC products showed that the addition of vanadium led to refinement of the carbide dispersions. The mechanism of formation of Fe-(Ti,V)C cermets will be discussed using chemical thermodynamic analysis. The second SHS approach involves the reaction between titanium and graphite by dropping compacted powders into a copper melts at 1250˚C. The process yielded dispersions of TiC within the matrix as well as graphite flakes. The reaction mechanism will be discussed and the potential of SHS to yield dispersions within metal matrices will be assessed.

Abstract

Some of ternary materials in the Ti-Al-C system are called MAX-phases and are characterised by heterodesmic layer structure. Their specific structure consisting of covalent and metallic chemical bonds influence its semi-ductile features locating them on the boundary between metals and ceramics, which may lead to many potential applications, for example as a part of a ceramic armour. Ti₂AlC is one of this nanolaminate materials. Self-propagating High-temperature Synthesis (SHS) was applied to obtain sinterable powders of Ti₂AlC Utilization of heat produced in exothermal reaction in adiabatic conditions to sustain process until all substrates are transformed into product is one of the advantages of the method that result in low energy consumption and low cost combined with high efficiency. Different substrates were used to produce fine powders of ternary material. Phase compositions of obtained powder were examined by XRD method. Than selected powders were used for sintering in various temperature both in a presureless sintering and hot-pressing in argon atmosphere. Properties and phase composition of obtained products were examined.

Abstract

The Self-Propagating High-Temperature Synthesis (SHS) method has been used to produce a new class of active catalyst materials based on metals, metal oxides and spinels for various applications. The method is characterized by very fast processing times (of the order of minutes), relatively low preheating temperatures and very high reaction temperatures produced as a result of carefully designed exothermic reactions. A large range of materials have been produced and characterized by a variety of physico-chemical and mechanical tests. This review devoted to Catalytic properties of SHS products. A number of catalytically active materials all over the world have been identified which offer promise for applications ranging from oxidation of CO and hydrocarbons to reduction of NO_x, methane dehydrogenation and other.

Abstract

In the work, interrelations between morphology of porous metalloceramics and thermal modes of SHS wave have been revealed on the basis of complex investigations including highspeed microvideo filming and dynamic pyrometry of processes, the physical and chemical analysis of products by the example of various intermetallic and hybrid (Ni, Co, Сr-Al, Ti-B-Cu, Ti-Si), metallothermic (FeTiO₃-Al, Si, C; FeO-Al₂O₃-MgO-Al, etc.) systems.

Abstract

Self-propagating High-temperature Synthesis (SHS) technology is characterized with high-temperature generation, spontaneous reaction propagation and rapid synthesis. Our research and development on simultaneous synthesis and sintering has progressed by applying mass force effects to SHS technologies; metal-ceramic composite pipe formation with centrifugal force on thermite reactions (“Centrifugal-thermite Process”) and fine ceramic composite synthesis under micro-gravity environments (MGE) formed with a free-fall, parabolic flight and sounding rocket. The process has successfully attained to produce more than 3 m long composite-layered pipes with significant feature for the production in its reaction propagation under centrifugal effect as well as the centrifugal force and reaction heat. In the latter, the TiB₂-Al composite synthesis under a free fall MGE, for example, has made clear that the lack of mass migration and the improvement of wetting between TiB₂ and Alunder the MGE affect the formation of a fine and dense cermet-like structure in the products. Anapproach on the mass-forced SHS technologies performed is introduced by designingproduct densities and SHS reaction system.

Abstract

The work deals with the review, analysis, systematization and classification SHS- refractories of a «Furnon» class are. The chronology of researches, introduction into industry are given, economic feasibility of their application in industries are shown. Comparative characteristics and distinctions of SHS- refractories with classical refractory are given. Current status, prospects and possible fields of using refractories produced by SHS method are considered.

Abstract

Functionally Grated Materials (FGMs) have usually been expected as candidates for a wide variety of industrial applications due to their desirable properties such as high heat resistance capability, good wear resistance, bio-compatibility, chemical stability and so on. Scaling-up and three dimensional (3-D) near-net shape forming technique for FGMs are one of the most important key-factor to produce the industrial engineering components and products in practical use. On the other hand, it is generally well known that the Spark Plasma Sintering (SPS) method is a novel process to produce homogeneous FGMs, nano-structural sintered compact, thermoelectric semiconductors and bio-medical materials in shorter sintering time with finer microstructure. This paper will present development of FGMs fabricated by SPS and future prospects of SPS on research and industrialization activities in Japan. A brief historical review progress of SPS technology is also given and the applicable field is exemplified. Then, the paper is focused on manufacturing processes on FGM by SPS technology.

Abstract

The low thermal conductivity of Lanthanum hexaaluminate, abbreviated as LHA, combined with high structural reliability of alumina matrix ceramics attracted our attention to develop a new functionally graded layered LHA-Al₂O₃-composite, with a LHA and a porosity gradient along the thickness of a bulk oxide ceramic. LHA is formed by in–situ reaction during sintering of the alumina/LHA composite. The high sintering temperature required for completion of LHA formation in LHA-rich layers causes grain growth and a degradation of mechanical strength in alumina-rich layers. Therefore, microwave hybrid heating was investigated as a method to enhance the reaction rate without excessive grain growth. Comparison of conventionally and microwave assisted sintered homogenous composite ceramics with 20–80 volume percent LHA showed that utilization of microwave heating could enhance the solid–state reaction and densification in samples containing more than 20 volume percent LHA. Enhanced microwave absorption in LHA rich layers assisted the sintering of a functionally graded composite at lower temperatures, enabling LHA formation without any abnormal grain growth in alumina rich layers.

Abstract

Functionally graded zirconia toughened alumina (ZTA) ceramics have been fabricated from aqueous suspension with an open porous and aligned lamellae structure on one side and a dense layer on the other side. A novel combination of two processes has been merged to achieve such graded structures, i.e. unidirectional freeze casting and electrophoretic deposition (EPD). A custom-designed apparatus has been built in which a controlled double side cooling has been realized in conjunction with the possibility to introduce an electric field over the ceramic slurry prior to the freezing process. A square wave pulsed DC voltage has been used in the EPD process in order to avoid electrolysis of water. Suitable duty cycle of applied pulse voltage could gain bubble-free deposition. The thickness of the dense layer is controlled by tuning voltage, duty of cycle, pulse width and deposition time. It was shown that thicknesses up to 500μm could be achieved. The microstructure of the porous part is controlled by adjusting the temperature during the freezing process. Using temperatures between -1 and -25°C the channel width changed from 220 to 40μm, respectively.

Abstract

In a flow forming process of automobile wheels of Al-based alloys, plastic deformation of the rim part is performed by rollers from the periphery side, while the inner periphery is fixed on a steel mandrel and is slightly deformed. Therefore, the rim part has a strain-graded microstructure in the thickness direction. In this study, the effects of the strain-graded plastic deformation on mechanical properties of an Al-Si cast alloy have been investigated. The strain-graded plastic deformation in this study was done by hot rolling of an Al alloy plate together with a steel plate. The two plates were joined at one end in the longitudinal direction and were rolled from the joined edge at 330 oC using a roller with a roll diameter of 200 mm and a rotation speed of 66 per minute. The chemical composition of the alloy was Al-7mass%Si-0.3mass%Mg-0.3mass%Fe. The rolled Al alloy plate had a strain-graded microstructure in the thickness direction; the strain was the highest at the roller side surface and the lowest at the steel plate side surface. The rolling also brought about a Si particle size graded microstructure. The eutectic Si rods were broken by the rolling deformation and the Si particle size was the smallest at the roller side surface and the largest at the steel plate side surface. On the other hand, a normal rolling deformation of the Al alloy plate without the steel plate was also performed for comparison. The rolled sample having the strain-graded and Si particle size graded microstructure exhibited much more excellent bending strength and ductility compared with the normally rolled sample.

Abstract

Crystal structures of Li₂MO₃ (M=Sn, Ti) and TiO(OH)₂ have been studied in detail and refined using X-ray powder diffraction data. All compounds posses a high concentration of defects in the structure. The crystal structures of the Li₂MO₃ salts obtained at 700°C reveal stacking faults of LiM₂ metal layers, which leads to the appearance of short-range order in three possible space groups: C2/c, C2/m, P3₁12. The possibility to stabilize this imperfect state increases the mobility of the Li⁺ ions in the Li₂TiO₃ structure and allows the complete exchange of lithium by hydrogen in acid water solutions with formation of TiO(OH)₂. The crystal structure of TiO(OH)₂ belongs to the layered double hydroxide structure type with the 3R₁ sequence of oxygen layers and can be described as a stacking of charge-neutral metal oxyhydroxide slabs [(OH)₂OTi₂O(OH)₂].