Self-propagating High-temperature Synthesis Technique Research Articles

Synthesis of non-stoichiometric carbides and carbohydrides of Ti and Ti-Nb using self-propagating high-temperature synthesis technique

Non-stoichiometric monocarbides are of great interest because they can be used as additives at production of hard alloys. Interestingly, the non-stoichiometric carbides of IV group metals provided with a wide range of homogeneity interact with hydrogen and form ternary compounds, carbohydrides. These compounds attract the researches as the bases for creating new hydrogen containing materials resistant at temperatures above those for known binary hydrides of transition metals. They are promising as materials for biological protection in nuclear energy. In the present work the single-phase non-stoichiometric face-centered cubic (FCC) carbides and hexagonal close packed (HCP) and FCC carbohydrides based on Ti and Ti-Nb were synthesized using Self-propagating High-temperature Synthesis (SHS) method. These syntheses were implemented in one technological stage. The high hydrogen content in the synthesized non-stoichiometric carbohydrides promoted their dispersion down to particle sizes of < 5 µm and even smaller, to the nanoscale crystallite sizes of < 50 nm. The mechanism of formation of non-stoichiometric carbides and carbohydrides in SHS was discussed. Significant advantages of a highly efficient non-energy-intensive SHS method for the synthesis of non-stoichiometric titanium and titanium-niobium carbides and carbohydrides can be of commercial and industry interest.

Influence of Co content on microstructure and hardness of AlCoxCrFeNi (0 ≤ x ≤ 1) high-entropy alloys produced by self-propagating high-temperature synthesis

In an effort to reduce energy consumption and expensive Co content, herein we report the effects of Co content on microstructure and microhardness of widely studied AlCoxCrFeNi high-entropy alloys produced by cost-efficient aluminothermic self-propagating high-temperature synthesis (SHS) method. Accordingly, the feasibility of SHS technique in the production of AlCoxCrFeNi master high-entropy alloys was discussed. In order to investigate the effect of further casting, the SHS alloys were also subjected to vacuum arc melting/suction casting process. Prior to SHS; phase diagram, raw material amounts and adiabatic temperatures were calculated via thermochemical modelling. The calculated equilibrium phase diagram suggested a full BCC structure over the whole Co range. However, according to XRD results, as-cast alloys consisted of BCC and FCC phases, having microhardness values ranging in between 385 HV and 504 HV, depending on Co content. The increase in Co content, enlarged the grains, altered the spinodal decomposition morphology and led to the formation of dual-phase (FCC + BCC) alloys, which in return had a significant effect on the microhardness values. Overall hardness values were increased due to finer microstructure obtained by suction casting. Also, Widmanstätten plate-like growth of the FCC phase inside the BCC cores was kinetically suppressed due to higher cooling rate. It was concluded that AlCoxCrFeNi master high-entropy alloys can be successfully produced by SHS method and the attained dual-phase microstructures could be beneficial in tailoring mechanical properties as well as reducing the total cost of the AlCoxCrFeNi HEAs system in addition to the significant energy reduction obtained via SHS route.

Preparation of Submicron Metastable Spherical β-Bi₂O₃ Particles by Self-Propagating High-Temperature Synthesis Method.

Sub-micrometer particles of β-Bi₂O₃ were successfully synthesized via a one-step self-propagating high-temperature synthesis (SHS) method for the first time. The experiments were carried out in the air at room temperature. The products were characterized by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). In this study, three experiments were designed to optimize the heat source, Bi source and additive for the reaction system. Results showed that the system composed of Al, Bi₂O₃ and Al₂O₃ powders could synthesize monodisperse high-purity β-Bi₂O₃ spherical particles with the average diameter of 369 nm and the as-prepared products kept stable after being exposed in air for one month. Then, the influences of the ratio of the three components on system were investigated. Interestingly, it was found that a slight adjustment on the ratio of Al:Bi₂O₃:Al₂O₃ had significant effects on the reactions happening in a system. Specifically, when the amount of Al₂O₃ exceeds the molar ratio of 2:1:1 (Al:Bi₂O₃:Al₂O₃), it is difficult to ignite the reaction system; when the amount is less than 2:1:0.5, the reaction system becomes too violent to obtain pure products. However, there are no obvious differences on the morphology and structure of final products with the two ratios because of few changes in adiabatic temperature. Preparation of β-Bi₂O₃ by SHS technique enjoying many advantages, such as high efficiency, inexpensive experimental equipment and simple processes, would has a promising prospect for industrial application.

Novel processing route for the fabrication of bulk high-entropy metal diborides

A single high-entropy phase material with hexagonal structure is produced by a two-steps processing method. Elemental reactants are first remarkably converted by Self-propagating High-temperature Synthesis (SHS). The completion of the chemical transformation to the desired (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2 phase and its concurrent consolidation up to 92.5% relative density is achieved by processing the SHS powders at 1950 °C via Spark Plasma Sintering. It is clearly evidenced that the use of the SHS technique is extremely beneficial to promote the formation of high-entropy ceramics, as compared to the time consuming ball milling treatment alternatively adopted.

Optimizations of RZ5-TiC magnesium matrix composite wear parameters using Taguchi approach

PurposeThe advancement in modern manufacturing technology generated the need to develop new materials for better wear resistance. The purpose of this paper is to use the Taguchi optimization approach to examine which wear parameter significantly affects weight loss and coefficient of friction for RZ5-TiC composite. It is a simple and efficient method to find performance of wear parameter using minimum experimental runs.Design/methodology/approachRZ5-TiC composites were prepared using RZ5 as matrix, reinforced with TiC through self-propagating high-temperature synthesis technique. In the present work, an attempt has been made to study the influence of wear parameters like applied load (AL), sliding distance (SD) and Wt.% of TiC (WTC) on responses like weight loss and coefficient of friction of RZ5/TiCp composites. The pin-on-disc apparatus used to conduct abrasive wear test. The wear process parameters are optimized for minimum wear based on L27 Taguchi orthogonal design. The Taguchi technique using design of experiments (DOE) is used to obtain the data. The ANOVA and an orthogonal array are used to examine the influence of wear parameters on responses. The purpose is to examine parametric significances which affect responses.FindingsIt observed that wear parameters have the significant influence on responses of RZ5/TiCp composites. The interaction of sliding distance/Wt.% of TiC is observed and found significant influence on both responses. The optimum level of the significant wear parameters is achieved based on the maximum S/N ratio for RZ5/TiCp composites. The optimal interaction for weight loss and coefficient of friction is AL1-SD1-WTC3 and AL3-SD1-WTC3, respectively. Finally, the confirmation test is conducted and the results are obtained within the confidence interval.Originality/valueThe current manuscript provides an optimization of wear parameters using Taguchi approach. The extensive experimental data are used for this purpose and effects of wear parameters on responses are analyzed from the presented results. The results obtained are useful in improving the wear resistance of the RZ5-TiC composite.

Ultrafast Synthesis and Related Phase Evolution of Mg2Si and Mg2Sn Compounds

Both Mg2Si and Mg2Sn compounds were synthesized by an ultra-fast self-propagating high-temperature synthesis (SHS) method. The data regarding SHS were obtained via theoretical calculation combined with experiments, showing that the adiabatic temperature Tad and ignition temperature Tig of Mg2Si are a little higher than those of Mg2Sn. The mechanism of phase evolution and the concomitant microstructure evolution during the synthesis process of Mg2Si and Mg2Sn compounds were investigated by adopting SHS technique coupled with a sudden quenching treatment. Differential scanning calorimetry (DSC), field emission scanning electron microscopy (FESEM), and x-ray powder diffraction (XRD) results indicate that Mg2Si compound can be directly synthesized through the reaction of Mg and Si elements at around 850 K. Correspondingly, the formation of Mg2Sn needs to undergo melting of Sn and the subsequent feeble reaction between Mg and Sn elements before the large scale transformation at 730 K. As the groundwork, this research embodies great significance for future study on the ultrafast SHS process of the ternary Mg2Si1−xSnx solid solutions.

Scalable Self-Propagating High-Temperature Synthesis of Graphene for Supercapacitors with Superior Power Density and Cyclic Stability.

An ultrafast self-propagating high-temperature synthesis technique offers scalable routes for the fabrication of mesoporous graphene directly from CO2 . Due to the excellent electrical conductivity and high ion-accessible surface area, supercapacitor electrodes based on the obtained graphene exhibit superior energy and power performance. The capacitance retention is higher than 90% after one million charge/discharge cycles.

Mechanical and Chemical Characterization of a TiC/C System Synthesized Using a Focus Plasma Arc.

Titanium carbide-graphite (TiC/C) composite was successfully synthesized from Ti and C starting elemental powders using self-propagating high-temperature synthesis technique in an ultra-high plasma inert medium in a single stage. The TiC was exposed to a high-temperature inert medium to allow recrystallization. The product was then characterized using field emission scanning electron microscopy (FESEM) coupled with energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), Rietveld refinement, nanoindentation, and micro-hardness to determine the product’s properties. The recorded micro-hardness of the product was 3660 HV, which is a 14% enhancement and makes is comparable to TiC materials.

Dry sliding friction behavior of copper–matrix composites by self-propagating high-temperature synthesis

This paper presents a simple approach to preparing copper–matrix composites (CMCs) by using self-propagating high-temperature synthesis technique. The dry sliding friction behavior of CMCs was systematically investigated. Results showed that the strengthening layer presented a compact metallurgical joint to copper substrate without a distinct boundary. The running-in period for copper substrate at any load was approximately 125 s but decreased to less than 30 s for CMCs. Increasing the applied load resulted in shorter running-in periods. The average friction coefficients for pure copper substrate and CMCs presented slight variation at the steady state, with minor enhancement in CMCs. The wear loss rates of the two different sections in CMCs rapidly increased with increased load, and the wear loss rate of CMCs was always lower than that of pure copper substrate at any load. Typical adhesion wear character was observed according to the wear scar of pure copper substrate; the wear mechanism of CMCs was dominated by abrasive wear, accompanied by oxidized wear with increased applied load.

Ultra-fast synthesis and thermoelectric properties of Te doped skutterudites

The self-propagating-high-temperature-synthesis (SHS) technique is applied here for the first time to synthesize CoSb3 thermoelectric materials. Mixtures of Co and Sb powders were compacted into pellets which were ignited from one end. A single-phase skutterudite material was obtained in a very short period of time using the SHS process which is maintained by the heat released from the chemical reaction of Co with Sb. Thermodynamic parameters and kinetics of the SHS reaction are investigated. The ignition temperature, adiabatic temperature, and the propagation speed of the combustion wave in the synthesis of CoSb3 are 723 K, 861 K, and 1.25 mm s−1, respectively. Using the SHS technique followed by Plasma Activated Sintering (PAS), we synthesized high performance bulk skutterudites of composition CoSb2.85 Te0.15 with a ZT of 0.98 at 820 K, one of the highest ZT values for an unfilled form of skutterudites. Compared with the samples synthesized by the traditional methods, the synthesis time is shortened from the typical several days to less than 20 minutes. Our work opens a new avenue for ultra-fast, low cost, mass production fabrication of skutterudite-based materials, which may also be universally applicable for the synthesis of other thermoelectric materials.

Bonding characteristics of the Al2O3-metal composite coating fabricated onto carbon steel by combustion synthesis

Abstract The fabrication of an alumina-metal composite coating onto a carbon steel substrate by using a self-propagating high-temperature synthesis technique was demonstrated. The effects of the type and thickness of the pre-coated layer on the binding structure and surface quality of the coating were systematically investigated. The macrostructure, phase composition, and bonding interface between the coating and the substrate were investigated by scanning electronic microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectrometry (EDS). The diffraction patterns indicated that the coating essentially consisted of α-Al2O3, Fe(Cr), and FeO·Al2O3. With an increase in the thickness of the pre-coated working layer, the coating became more smooth and compact. The transition layer played an important role in enhancing the binding between the coating and the substrate. When the pre-coated working layer was 10 mm and the pre-coated transition layer was 1 mm, a compact structure and metallurgical bonding with the substrate were obtained. Thermal shock test results indicated that the ceramic coating exhibited good thermal shock resistance when the sample was rapidly quenched from 800°C to room temperature by plunging into water.

The difference of synthesis mechanism between Ti3SiC2 and Ti3AlC2 prepared from Ti/M/C (M=Al or Si) elemental powders by SHS technique

Ti3MC2 ternary compounds (M=Al or Si) have been prepared by a self-propagating high-temperature synthesis (SHS). The difference of synthesis mechanism between Ti3SiC2 and Ti3AlC2 using Ti/M/C(M=Al or Si) powder mixtures and some TiC or some intermetallic compounds as raw materials has been investigated. The phase composition and the relative content of Ti3MC2 materials in the final products were determined by X-ray diffraction (XRD). The results show that TiC and intermetallic compounds of TiAl have played an important role in synthesis of Ti3AlC2. The relative content of Ti3AlC2 in the products increases with increased addition of TiC or TiAl in the raw materials. In contrast, the relative content of Ti3SiC2 in the products changes less with increasing of TiSi2 content, even decreases with increasing of TiC content in the raw materials. The difference of synthesis mechanism between them has been explained thermodynamically.

Effect of Mg on the Synthesis of TiB&lt;sub&gt;2&lt;/sub&gt; Powder by a Self-Propagating High-Temperature Synthesis Technique

Micro-nanoTiB2 ceramic was prepared through increasing the molar ratio of Mg and leaching with suitable acid by the combustion synthesis reaction of Mg, TiO2 and B2O3, which could get higher temperature and purer product. The Samples were investigated by XRD and SEM, and the results showed the diameter of the TiB2 was 200 nm ~ 300 nm and the shape of the TiB2 was irregular hexagonal crystal. The diameter of the TiB2 was decreased with the increase of Mg powder. The formation mechanism of TiB2 has been studied.

Strengthening of a high strength Fe85Ni15 alloy by tempering treatment

A high-strength Fe85Ni15 alloy with lath martensitic structure was obtained by the self-propagating high-temperature synthesis technique. After tempering at 500°C for 2h, the hardness increased from 3.8 to 5.1GPa, and the compression yield strength increased from about 1100 to 1500MPa without much sacrifice of ductility. The strengthening effect might be attributed to the evolution of lath martensitic morphology and the reverse martensitic transformation.

Pulse electric current effect on mechanical properties of titanium aluminide produced by the self-propagating high-temperature synthesis technique

We present results of study on the effect of pulse electric current treatment on bending strength and hardness of intermetallic titanium aluminide produced by the self-propagating high-temperature synthesis technique. It is shown such treatment results in some increase in strength and plasticity of the intermetallide in comparison with the initial state, while its hardness decreases. The results of microstructural analysis show that reduction of the material brittleness after treatment is a consequence of current-induced change of thin structure of a material, redistribution of pores and reduction of the residual tensile stresses.

Fabrication of Ti3SiC2-based ceramic matrix composites by a powder-free SHS technique

A powder-free technique for fabrication of Ti3SiC2-based composite ceramics via self-propagating high-temperature synthesis (SHS) is developed. The essence of the method is that the SHS-compaction of a multilayer stack comprised alternating layers of titanium foils and polymer films filled with either microsized silicon carbide particles or microsized silicon carbide particles mixed with charcoal particles. It is shown that SHS-compaction of non-powder materials can be used to synthesize dense particulate-reinforced ceramic matrix composites of Ti3SiC2TiSi2SiCp. Effects of the initial reactant composition and the synthesis conditions on the microstructure of the prepared materials are discussed.

Formation mechanism of Ti2AlC under the self-propagating high-temperature synthesis (SHS) mode

Ti2AlC was fabricated by the self-propagating high-temperature synthesis (SHS) technique from a compacted powder mixture consisting of Ti:Al:C=2:1:1 (molar ratio) of mortar mixing, planetary mixing and various packing densities. A thermocouple was placed directly into the green compact body in order to monitor the combustion temperature during the SHS process. When the green compact with planetary mixing treatment and a packing density of 17% as well as 60% was used, propagation of the reaction exothermicity could occur, and the starting compact completely changed to Ti2AlC. Formation mechanism of Ti2AlC using a SHS technique was discussed. In addition, the melting point of the resultant sample was determined to be 1570°C.

자전연소합성법으로 제조된 SiO2첨가된 MoSi2분말 내에서의 SiO2의 거동 연구

In order to investigate the behavior of SiO 2 in the molybdenum silicide powders, crystal structure of these powders was measured by XRD, in addition, surface composition and surface phase (or chemical states) and microstructure were analysed by XPS and TEM, respectively. Mo-silicide powders containing SiO 2 were synthesized by SHS (Self-Propagating High-Temperature Synthesis) technique. In XRD result, according to increase of SiO 2 contents, the crystal structure for synthesized MoSi 2 powders was still typical MoSi 2 bct without any other phases. By XPS analysis, the surface of Mo and Si source powders was covered with MoO 3 and SiO 2 , respectively, and the surface of synthesized MoSi 2 powder was also covered with MoO 3 and SiO 2 , which were stable oxides at room temperature. However, according to increase of SiO 2 addition, MoSi 2 phase in XPS spectra decreased and SiO 2 phase increased relatively in synthesized MoSi 2 powders. From the results by XPS and XRD, we found that the existent SiO 2 has amorphous structure. In the microstructure, the small particulates of the synthesized products added SiO 2 agglomerated together to form larger clusters (from ~10 nm to ~1 μm). From TEM, XPS, and XRD results, we found that the out layer of agglomeration of synthesized MoSi 2 powder is surrounded by amorphous SiO 2 .

Aging of electrolyte La0.88Sr0.12Ga0.82Mg0.18O3 − δ made using magnetic-pulse compaction

Ceramics of the La0.88Sr0.12Ga0.82Mg0.18O3 − δ solid electrolyte was obtained by magnetic-pulse compaction (MPC) of a powder synthesized using the self-propagating high-temperature synthesis technique with further sintering at 1380°C. Conductivity and its change in time were studied. It was shown that conductivity of fresh samples coincides with conductivity of ceramics obtained using the classical solid-phase synthesis. It was established that conductivity of electrolyte decreased by 18% during isothermal exposure at 700°C for 1 year.

Preparation, and magnetic and electromagnetic properties of La-doped strontium ferrite films

SrLaxFe12−xO19 films (x=0–1.0) with large magneto-crystalline anisotropy were synthesized on SiO2 substrate by sol–gel and self-propagating high-temperature synthesis technique. The films were characterized by various experimental techniques including X-ray diffraction analysis, Field Emission Scanning Electron Microscope, Atomic Force Microscopy, Vibrating Sample Magnetometry and vector network analyzer. The results show that La ions completely enter into strontium ferrite lattice without changing the ferrite appearance; its grain size is approximately 40–80nm, its length is 100nm; the magnetoplumbite structure is proved through testing a concertina form of the crystal grain; the maximum coercivity is 5986Oe at x=0.2; La-doped films possess a wider microwave absorption frequency range with better gross loss angle tangent (tanδ>0.1), from 9 to 10.5GHz at x=0.2, where the maximum value of tanδ reaches 0.2709. The La-doped films reach smaller nanometer size, better magnetic properties and microwave absorption properties with the doping of lanthanum.