Self-propagating High-temperature Synthesis Process Research Articles

Self-Propagating High-Temperature Synthesis of (Al–2% Mn)–10% TiC and (Al–5% Cu–2% Mn)–10% TiC Nanostructured Composite Alloys Doped with Manganese Powder

The influence of alloying with powder manganese on the preparation of nanostructured (Al‒2% Mn)–10% TiC and (Al–5% Cu–2% Mn)–10% TiC composite alloys with the application of the self-propagating high-temperature synthesis (SHS) of titanium carbide TiC nanoparticles from the Ti + C charge in a melt of matrix alloys is investigated. Powder metallic manganese in an amount of 2 wt % is preliminarily introduced into Al and Al–5%Cu matrix bases of composite alloys. This makes it possible to increase the ultimate tensile strength of the aluminum base from 81 MPa (for initial aluminum of the A7 brand) to 136 MPa and that of the aluminum–copper base to 169 MPa. It is revealed that, when alloying aluminum only with manganese, the SHS reaction proceeds weakly and incompletely, while the carbide phase size in the (Al‒2% Mn)–10% TiC alloy varies from a nanolevel to several microns. When adding 10% of the Na2TiF6 haloid salt into the SHS charge, the SHS process is intensified, but the resulting alloy contains numerous pores, inclusions of the unreacted charge, and coarse agglomerates of ceramic nanodimensional TiC particles. When using Ti + C and Ti + C + 10% Na2TiF6 SHS charges with coalloying matrix aluminum by copper and manganese, similar results are acquired. The difference is in the larger distribution uniformity of the nanodispersed TiC phase. The best results are attained with a decrease in the Na2TiF6 additive to 5% of the charge weight, which promotes the smoother and complete synthesis of preferentially nanodimensional TiC particles and the formation of the poreless homogeneous microstructure of the (Al–5% Cu–2% Mn)–10% TiC composite alloy with an ultimate tensile strength of 213 MPa and relative elongation of 6.6%.

Structural and phase states of titanium borides produced by the self-propagating high-temperature synthesis method in the field of ultrasound oscillations

The effect of ultrasound oscillations (USO) on the velocity and temperature of combustion during self-propagating high-temperature synthesis (SHS) in the Ti-B system and structural and phase states of the produced titanium borides is studied using the earlier developed experimental setup. The effect of USO on SHS is subdivided into thermal and physical (non-thermal). The thermal influence is connected with cooling of the specimen surface because of the occurrence of forced convection of the ambient gas, and the physical effect is due to the action of USO on complex interaction processes in the SHS wave such as melt spreading, heterogeneous reactions and mass transfer in the liquid phase. Imposition of USO on the SHS process brings about changes in the phase composition of the synthesis products. For charge composition Ti–1.0В the content of orthorhombic modification of phase TiB increases from 78.2 % without USO to 82.9 % at the USO amplitude ξ = 10 mm, while the content of the cubic modification of this phase decreases from 9.2 % at ξ= 0 to 6.8 % at ξ = 10 mm. For all the examined compositions, the amount of residual titanium and Ti3B4decreases and the content of TiB2increases. It is determined that carrying out SHS in the field of USO results in a change of the specific heat capacity of the target synthesis products: with raising the USO amplitude it increases by 4–5 %. Thereby it is shown that imposition of USO on SHS is an efficient physical method for purposeful regulation of structural and phase states and therefore properties of the synthesis products and can be used as a means for controlling the synthesis process.

Azide SHS of highly dispersed powder of titanium carbonitride with intermediate partial nitriding or partial carburizing titanium powder

It is noted that the powder of titanium carbonitride (TiC0.5N0.5) is the basis of the TiC1−xNx/Ni–Mo system cermets, which are considered as the most promising tool materials for the replacement of classical hard alloys based on tungsten carbide of the WC–Co system. The properties of these cermets are the higher the finer is the titanium carbonitride powder from which they are sintered. First, a simple energy-saving process of self-propagating high-temperature synthesis (SHS) was applied for the intermediate partial nitriding of the initial metal powder of titanium to the composition of TiN0.2 or partial carburizing to TiC0.3 composition in order to ensure fire safety and efficiency of the grinding process in the planetary ball mill to obtain superfine powders of partially nitrided or carburized titanium with ultrafine structure. Further, these powders were used in the azide SHS process for complete nitriding and carburizing to produce titanium carbonitride powder which was composed of superfine agglomerates of ultrafine and nano-particles of TiC0.5N0.5.

Self-propagating high-temperature synthesis of Fe2TiSn based Heusler alloys with following spark plasma sintering

The Fe2TiSn based Heusler alloys were synthesized and studied. The samples were fabricated by a combination of self-propagating high-temperature synthesis (SHS) followed by spark plasma sintering (SPS). An optimal mechanical activation (MA) regime, favoring for successful SHS process was experimentally defined for the stoichiometric mixture of elements powder. The phase evolution of the Fe2TiSni-xSix (x = 0, 0.10, 0.15, 1) compound and the morphology of a bulk specimens were studied. It was shown that with the presence of an impurity side phase Fe2Ti the electrical resistivity of material decreased by an order of magnitude, while the Seebeck coefficient remains unchanged in the range from 3 to 8 μ V K−1.

A Self-propagating high-temperature synthesis process for the fabrication of Fe(Cr)–Al2O3 nanocomposite

Self-propagating high-temperature synthesis (SHS) was used to fabricate a Fe(Cr)-Al2O3 nanocomposite. The composite was fabricated by the reactions between the powders of Fe, Fe2O3, Cr2O3, and Al. The effect of blending ratio and mechanical activation of the initial powders and the precursor compressing pressure on the microstructure of the final product was studied by optical microscopy, scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The significance of the effect of each of the aforementioned parameters on the quality of the composite (assessed by measuring the compressive strength and wear resistance) was determined using a full-factorial design of experiments method. The results showed that the best molar powder ratio that produced the most homogeneous product through a sustainable SHS reaction was Fe:Fe2O3:Cr2O3:Al = 10:1:1:4. A lower Fe content caused the Fe(Cr) phase to melt and separate from the rest of the materials.

Effect of post annealing on the microstructure, mechanical properties, and failure of MoxW1-xSi2 heaters produced by self-propagating high-temperature synthesis

High-performance tungsten molybdenum disilicide (MoxW1-xSi2) heating elements were prepared using a self-propagating high temperature synthesis process. The effect of post annealing on the degradation behavior of the alloy was experimentally investigated. Increasing the attrition milling time up to 20 min during powder preparation resulted in MoxW1-xSi2 heaters with the highest density, which increased the fracture strength compared to samples with shorter attrition times. Such samples were annealed and evaluated as heating elements using accelerated degradation tests and failure analysis in order to compare their structural characteristics and flexural strength with as-fabricated samples. The annealed MoxW1-xSi2 heater showed a relatively dense structure with few pores and no secondary phases, apart from a SiO2 layer. This favorable structure prevented bubble formation, which can result in fracturing of the heater, as revealed by evaluation at high temperatures with various heating rates. The flexural strength of the annealed specimen was 2.5-times higher than that of the as-fabricated specimen, which was attributed to removal of secondary phases during annealing. Failure time and surface load analyses were used to investigate the fracture mechanism of the MoxW1-xSi2 heaters in detail at 1790 °C by quantifying bubble formation and the presence of secondary phases.

Nitrided Ferroalloy Production By Metallurgical SHS Process: Scientific Foundations and Technology

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A Comparative Investigation of the Porous NiTi Alloys Synthesized by Self-Propagating High-Temperature Synthesis and Combined Process of Decomposition and Sintering

Porous NiTi alloys were successfully synthesized by two different processes, including self-propagating high-temperature synthesis (SHS), and a combined process of decomposition – sintering. A systematic comparison of micro-structures and mechanical properties of these alloys was investigated. The results showed that the SHS process was better than decomposition – sintering process. By controlling the processing parameters of SHS, the received porous NiTi alloys showed that the porosity and pore were larger, and ratio of opened-pore reached up to 80%. The porous NiTi alloys fabricated by SHS process also exhibited good properties, such as a high compressive strength (up to 250MPa), and elastic modulus in range of 6.1 – 7.0GPa. The porous NiTi alloys synthesized by decomposition – sintering process have lower porosity (26-43%), lower compressive strength (< 110MPa), lower elastic modulus (< 1.2GPa) but the strain could be reached to 10%.

Effect of powerful ultrasound on the combustion processes and phase composition of refractory compounds of titanium at the self-propagating high-temperature synthesis

The effect of ultrasound oscillations (USO) on the heat transfer conditions between a specimen and environment is examined using a specially developed experimental facility. The influence of the USO amplitude on the combustion temperature and velocity as well as on the phase composition and crystal lattice parameters of the synthesized compounds is studied for the self-propagating high-temperature synthesis (SHS) in Ti–С(Si,B) systems. The heat transfer coefficient on the surface of a specimen during its oscillations with an ultrasound frequency is assessed. Possible mechanisms of the effect of USO on the SHS process are considered. It is demonstrated that a decrease in the SHS temperature is connected with cooling the specimen due to forced convection of a surrounding gas, while a change in a phase composition of the synthesized material and the crystallographic parameters of the phases occurs due to changes in the conditions of high-temperature heterogeneous interactions in the SHS wave.

SHS process application in Ti3SiC2–Ni composite fabrication

The paper reviews the results of using the process of self-propagating high-temperature synthesis (SHS) to obtain high-temperature nickel alloys and composites based on titanium carbide (TiC) and nickel. In order to reduce the brittleness of these composites, it was proposed to replace the TiC ceramic phase by the MAX phase of titanium silicon carbide (Ti3SiC2) and use the SHS process to obtain a Ti3SiC2–Ni skeleton composite. Nickel for Ti3SiC2skeleton infiltration was introduced in three variants: by introducing to the reaction mixture; in the form of a briquette located between two SHS charge briquettes; and similar to the second variant, but with the barrier layers of paper between the Ni and SHS charge briquettes. It was shown that Ni melt in all three variants prevents the formation of the titanium silicon carbide MAX phase thus leading to its degradation. Ni introduction into the reaction mixture according to the first variant made it possible to obtain a homogeneous composite, which became almost non-porous with an increase in Ni concentration up to 50 %. When the Ni briquette was placed between two compacted briquettes of SHS charge, it was possible to melt a relatively small amount of Ni (23–29 % of the mass of synthesized composite samples), which was not enough to completely fill the porous layered skeletons of Ti3SiC2. 20 % of Si added to the Ni briquette increased infiltration depth, lowered the degree of MAX phase degradation at the infiltration point, and formed a more homogeneous composite consisting of a porous skeleton of TiC, TiSi2and Ti3SiC2phases partially filled with metallic nickel during Ni(Si) melt infiltration.

Application of SHS process for fabrication of copper-titanium silicon carbide composite (Cu-Ti3SiC2)

The results of the study of possibility of using a simple, energy-saving powder technology, based on the process of self-propagating high-temperature synthesis (SHS) or combustion synthesis, for the single-stage preparation of Cu-Ti3SiC2 composite from relatively inexpensive powders of its constituent elements are presented. Placing the Cu powder briquette between two adjacent charge briquettes 3Ti + 1,25Si + 2C for the synthesis of MAX-phase of Ti3SiC2, it was possible to use a large heat effect of SHS for melting the Cu briquette and infiltration of Ti3SiC2 porous skeleton by Cu melt. For the successful realization of this process, it is necessary to ensure the required fluidity of Cu melt and wetting Ti3SiC2 through a high temperature of the melt and the alloying of the melt with silicon, as well as to ensure the delay in the transfer of the melt into pores of SHS product.

Application of SHS auxiliary reaction of titanium carbide for introduction of AlN nanoparticles into aluminum melt

For ex-situ introduction of AlN nanopowder, obtained by azide technology of self-propagating high-temperature synthesis (SHS) or combustion synthesis in the mixture with the flux cryolite: (AlN-35%Na3AlF6), into the aluminum melt, an exothermic master powder composite (EMPC) of different composition (AlN-35%Na3AlF6) – (Ti + C) – Na2TiF6 was first used, leading to the realization of in-situ process of SHS of reinforcing phase TiC in the combustion mode in the aluminum melt. The conditions were found for reliable ignition of the EMPC and fabrication of cast hybrid nanocomposites Al-Al-TiC, including the calculated composition Al-7.7%AlN-19%TiC with an increased content of AlN reinforcing phase.

Chrono-topographic analysis of the fire focus dynamics in the SHS wave

The paper presents the means for measuring the spatial and temporal coherence of temperature in the micro regions of a wave of self-propagating high-temperature synthesis (SHS) and revealing the relationship between the events of ignition of individual foci. The method for determining the parameters of the thermal wave structure of the synthesis is based on the chronographical and topographical representation of micro thermal data in the form of maps that visualize the ergodicity of the SHS process and facilitate the recognition of individual foci of burning on thermal imaging images. The ergodicity of the phenomenon is used in the method to determine the time of induction of the combustion sites, the time of their growth, the growth rate of the foci tangentially to the front of the SHS wave, the size of the foci in the direction of the normal to the front. The error in measuring the velocity of the SHS front of the wave with the pro-posed technique was 0.05%.

Combustion Synthesis of Composition Ferroalloys.

The main objective of this paper is to present results of the research in the development of a specialized self-propagating high-temperature synthesis (SHS) technology for ferroalloy composites, as applied to steelmaking. The problem of creating such a production cycle has been solved by developing a new approach to the practical implementation of self-propagating high-temperature synthesis, as applied to metallurgy. The metallurgical variation of SHS is based on the use of different metallurgic alloys (including waste in the form of dust from ferroalloy production) as basic raw materials in the new process. Here, the process of synthesis by combustion is realized through exothermic exchange reactions. The process produces a composite, based on inorganic compositions with a bond of iron and/or alloy based on iron. It has been shown that in terms of the aggregate state of initial reagents, metallurgical SHS processes are either gasless or gas-absorbing. Combustion regimes significantly differ when realized in practice. To organize the metallurgical SHS process in weakly exothermic systems, different variations of the thermal trimming principle are used. In the present study, self-propagating high-temperature synthesis of ferrovanadium nitride, which is widely used in steel alloying, was investigated. It has been shown that the phase composition of the initial alloy has a profound impact on the regular patterns in ferrovanadium combustion in nitrogen and on the mechanism itself. During the nitriding of σ-(Fe-V), process activation is taking place. The activation is due to the transformation of the intermetallide into an α-solid solution, when the temperature of phase transition is reached (~1200 °C). The composite structure of the products of ferrovanadium is nitriding by the fusion of particles-droplets composed of molten Fe and solid VN.

Self-propagating high-temperature synthesis of (Al–2%Mn)–10%TiC and (Al–5%Cu–2%Mn)–10%TiC nanostructured composite alloys when doped with manganese powder

The paper studies the effect of doping with manganese powder on the production of (Al–2%Mn)–10%TiC and (Al–5%Cu– 2%Mn)–10%TiC nanostructured composite alloys by self-propagating high-temperature synthesis (SHS) of TiC titanium carbide nanoparticles from Ti + C charge in the melt of matrix alloys. First, manganese metal powder was added to the matrix bases of Al and Al–5%Cu composite alloys in the amount of 2 wt%. This improved aluminum base tensile strength from 81 MPa (for the original A7 grade aluminum) to 136 MPa and aluminum-copper base tensile strength to 169 MPa. It was found that when aluminum was doped with manganese only, the SHS reaction proceeded weakly and not completely, and the carbide phase size in the resulting alloy (Al–2%Mn)–10%TiC varied from nanoscale to several micrometers. When 10% Na2TiF6halide salt was added to the SHS charge, the SHS process intensified, but the resulting alloy contained a considerable amount of pores, inclusions of unreacted charge and large agglomerates of TiC ceramic nanosized particles. Similar results were obtained in cases of using Ti + C and Ti + C + 10%Na2TiF6SHS charges, but with joint doping of matrix aluminum with copper and manganese, providing more uniform distribution of the TiC nanodispersed phase. The best results were obtained by reducing the Na2TiF6salt additive to 5 % of the SHS charge mass, which facilitated smoother and complete synthesis of predominantly TiC nanosized particles and the formation of a non-porous uniform microstructure of (Al–5%Cu–2%Mn)–10%TiC composite alloy with an ultimate tensile strength of 213 MPa and 6,6 % elongation.

Ultrafast Synthesis and Thermoelectric Properties of Mn1+xTe Compounds

MnTe compounds show great potential for thermoelectric applications in the intermediate temperature range (500-800 K) because of their large Seebeck coefficient and intrinsically low thermal conductivity. So far, the existing methods for the synthesis of MnTe compounds remain constrained to multistep processes that are time- and energy-intensive. Herein, we demonstrate ultrafast synthesis of high-density bulk MnTe compounds using a combination of self-propagating high-temperature synthesis (SHS) and plasma activated sintering. The entire synthesis and processing procedure takes less than 1 h. The thermodynamic consideration suggests that the SHS process includes two steps: (1) Mn + 2Te → MnTe2 + Q1 and (2) MnTe2 → MnTe + Te. With the heat released by step (1), the process moved in cycle and finished in a rather short time. The effect of extra Mn content on the structure and thermoelectric properties was investigated. There is some solubility limit of extra Mn in the Mn1+ xTe compound. The extra Mn occupy interstitial sites, leading to a decrease of carrier concentration while enhancing Seebeck coefficient and decreasing thermal conductivity. Low-temperature heat capacity data indicates that the Mn1.06Te compound has a high effective mass of 8.34 m0 and a low Debye temperature of 186 K, which are beneficial for the large Seebeck coefficient and low thermal conductivity. Therefore, the maximum ZT value reaches 0.57 at 850 K for the Mn1.06Te compound.

Synthesis of TiB2–Al2O3–FeAl composites via self-sustaining combustion with Fe2O3/TiO2-based thermite mixtures

A novel fabrication route combining combustion synthesis and thermite reactions was applied to prepare TiB2–Al2O3–FeAl composites with a broad composition range. The staring materials including Fe2O3, TiO2, Fe, Al, and amorphous boron powders formulated two reaction systems which were conducted in a self-propagating high-temperature synthesis (SHS) manner. Formation of xFeAl–0.6TiB2–Al2O3 composites with x = 2.5–3.6 and 3FeAl–yTiB2–Al2O3 composites with y = 0.6–1.0 was achieved through the SHS process. The increase of FeAl and TiB2 caused a decrease in reaction exothermicity, and therefore, a lower combustion propagation rate. Based upon a correlation between the measured combustion front velocity and temperature, the activation energy Ea = 90.84 kJ/mol was determined for the thermite-type SHS reaction. The thermite reduction of Fe2O3 was considered as the governing step to trigger the reaction sequence.

Self-Propagating High-Temperature Synthesis of Titanium Carbide Powder under Pressure–Shear Conditions

This paper presents results of an experimental study of the self-propagating high temperature synthesis (SHS) of titanium carbide powder under pressure in combination with high-temperature shear deformation. We have studied the effect of technologically important parameters, primarily that of the pressure and strain rate, on the synthesis process under pressure–shear conditions. The results demonstrate that a shear load applied to an incompletely formed material during synthesis may have a significant effect on the grain size and morphology, as well as on the mutual arrangement of structural constituents throughout the reaction system. Running the technological SHS process under pressure in combination with shear allows for the synthesis of refractory metals and comminution of the reaction products before cooling to room temperature in a single processing cycle.

Toward a better conversion in magnesiothermic SHS of zirconium diboride

Zirconium diboride (ZrB2) is a promising ultra-high-temperature ceramic material. Magnesiothermic self-propagating high-temperature synthesis (SHS) is an attractive method for its fabrication from relatively inexpensive oxides of zirconium and boron. However, prior studies on magnesiothermic, combustion-based methods for synthesis of ZrB2 have revealed incomplete conversion. The present work aims to determine optimal conditions for magnesiothermic SHS of ZrB2 from ZrO2 and B2O3. The addition of MgO, NaCl, and excess Mg was investigated experimentally. Mechanical activation (short-time high-energy ball milling) was used to facilitate ignition of the powder mixtures. After combustion in an argon environment, the products were leached by diluted HCl to remove magnesium compounds and NaCl. The results show that NaCl is a better additive than MgO; it effectively improves milling and decreases the amount of zirconia in the products. Further, NaCl decreases the particle size of the products, which is beneficial for sintering. The addition of excess Mg also has a positive effect on the conversion because it compensates for the loss of Mg through vaporization during the SHS process. In the products obtained by combustion and leaching of the mixtures with 20% excess Mg and 10–30 wt% NaCl, the oxygen content was below 4 wt%. Nanoscale polycrystalline ZrB2 particles were obtained using the mixture with 20% excess Mg and 30 wt% NaCl.

SHS Technology for Composite Ferroalloys. 1. Metallurgical SHS: Nitrides of Ferrovanadium and Ferrochromium

The development of specialized self-propagating high-temperature synthesis (SHS) for complex ferroalloys used in steel smelting and in blast-furnace technology is discussed. To that end, a new approach to the SHS process has been conceived: the metallurgical SHS process, in which the basic raw material consists of various metallurgical alloys including dusty waste from ferroalloy production. In that case, synthesis involves exchange exothermal reactions. The product is a composite based on the initial inorganic compounds; the binder is iron or an iron alloy. Depending on the state of the initial reagents, the metallurgical SHS processes may be gas-free, gas-absorbing, or gas-liberating. For each case, the combustion conditions will be very different. Thermal matching may be used in organizing the metallurgical SHS process in systems that are not strongly exothermal. The self-propagating high-temperature synthesis of nitrided ferrovanadium and ferrochrome is investigated. It is shown that the phase composition of the initial alloy strongly affects the combustion of ferrovanadium in nitrogen. In the nitriding of σ ferrovanadium, transformation of the intermetallide to an α solid solution is activated on reaching the phase-transition temperature (~1200°C). The composite structure of the nitriding products of ferrovanadium is formed under the influence of solid–liquid droplets consisting of molten iron and solid vanadium nitride. Solid-phase reaction of ferrochrome with nitrogen facilitates high degrees of nitriding. The combustion rate of ferrochrome on nitriding during coflow filtration, as in chromium, increases with increase in the nitrogen flow rate. The degree of nitriding of the ferrochrome in forced filtration (4.7–7.5% N) is much less than that in natural filtration (8.8–14.2% N).