Influence of Aluminum Additives on the Content and Parameters of the Fine Structure of Titanium Silicon Carbide in SHS Powders

The dependence of the phase composition and parameters of a fine structure of titanium silicon carbide in powders formed by the self-propagating high-temperature synthesis on the aluminum concentration in the 5Ti/2Si/1C reaction mixture is investigated. The aluminum content is varied in a range of 0.1–0.4 mole fraction with the conservation of the total carbon content. It is established that the additives of aluminum not only affect the yield of titanium silicon carbide, but also promote the preferential formation of Ti5Si3 in synthesis products instead of TiSi2 identified in powders containing no aluminum. The introduction of a small amount of aluminum (0.1 mole fraction) leads to the formation of the Ti3Si1 – xAlxC2 solid solution and makes it possible to decrease the content of impurity phases in SHS powders by 6%. The silicon carbide concentration in SHS powders decrease at a higher aluminum content in the reaction mixture, while that of binary compounds (TiC, Ti5Si3, TiAl) correspondingly increases. No noticeable effect from the introduction of aluminum on the parameters of the crystal lattice of titanium silicon carbide in SHS powders is found in concentration limits of 0.1–0.25 mol %. A noticeable increase in parameters of a and c for Ti3Si1 – xAlxC2 (from a = 3.067 Å, c = 17.67 Å to a = 3.07 Å, c = 17.73 Å) with the conservation of the c/a ratio in limits of known values (c/a = 5.78) is observed only with the aluminum concentration of 0.4 mole fraction. The crystallite size of titanium silicon carbide depends, first and foremost, on the combustion parameters. At the same time, the deformation of the crystal lattice of Ti3Si1 – xAlxC2 in SHS powders increases monotonically with an increase in the aluminum content in the reaction mixture in the concentration range under study.     

SHS Metallurgy of Cr<Subscript>2</Subscript>AlC MAX Phase-Based Cast Materials

A review of publications on the structure, properties, fabrication methods, and application fields of materials based on the Cr₂AlC MAX phase is given. It is noted that the most promising method of formation of such materials is self-propagating high-temperature synthesis (SHS), one of the directions of which is SHS metallurgy. A powder mixture of chromium III and chromium VI oxides of the analytical grade, aluminum of ASD-1 grade, and carbon is used as the base charge in investigations. The adiabatic combustion temperature and composition of final products is calculated using the THERMO special program. Experiments were performed in an SHS reactor with volume V = 3 dm³ under the initial pressure of inert gas (Ar) P₀ = 5 MPa. The influence of the ratio of initial reagents on SHS parameters (the combustion rate, pressure increment, and yield of the target product), composition, and microstructure of target products is investigated experimentally. A scientific approach of the formation of cast materials in the Cr–Al–C system consisting of the Cr₂AlC MAX phase and phases Cr₃C₂ and Cr₅Al₈ by the SHS metallurgy method is developed. The structural-phase states of target products are studied. It is established experimentally that, varying the content of initial reagents (aluminum and carbon) in the charge, it is possible to substantially affect the synthesis regularities, composition, and microstructure of final products. An increase in the content of the Cr₂AlC MAX phase in the final product and a decrease in the Cr₅Al₈ content occur with an increase in the carbon content (above stoichiometric) in the initial mixture. An increase in the aluminum content (above stoichiometric) in the initial mixture leads to an increase in the content of the Cr₂AlC MAX phase in the final product and a decrease in the content of the Cr₃C₂ phase.     

Structure and phase formation of combustion products during the synthesis of γ-AlON in self-propagating high-temperature synthesis

Synthesis of aluminum oxynitride (γ-AlON) in conditions of self-propagating high-temperature synthesis (SHS) gas-statting under high pressures (10–100 MPa) of gaseous nitrogen, including the mode of so-called coupled combustion reactions (chemical furnaces) is investigated. It is shown that chemical and phase compositions of combustion products, as well as their structure and morphology of powder particles, depend on the reagent ratio in Al–Al₂O₃ initial mixture, as well as on nitrogen pressure, combustion temperature of highly exothermic components of chemical furnaces, and grade of initial reagents. The structure of γ-AlON powder particles are determind and its relation with operation conditions of SHS. Optimal SHS parameters for Al₅O₆N (γ-AlON) formation are established.     

Composite SHS materials based on titanium carbide and nikelide doped with a refractory component

This study is devoted to the synthesis and investigation of composite ceramic materials based on titanium carbide and nickelide with the use of the effect of dispersion strengthening by force of the dedicated alloying of reactionary mixtures with a nanodispersed refractory component. The influence of nanodispersed particles on the main combustion parameters in conditions of quasi-isostatic compression is shown. The phase composition and the structure of compact synthesis products, in which the main phase components are TiC and the Ti _x Ni _y intermetallic compound, are investigated. It is established that doping with a nanocomponent does not vary the phase composition qualitatively but leads to a substantial modification of the structure of the materials, at which the average grain size of the main refractory component decreases by a factor of 1.5–3.5. In addition, a similar effect is observed with a decrease in the TiC concentration in the composition of the samples. Complex investigations into the physicomechanical properties and heat resistance of fabricated materials are performed. The effect of the positive influence of refractory nanoparticles on such characteristics of alloys as hardness, strength, Young modulus, and durability to high-temperature oxidation are shown.     

Tic-Ni-based composite materials dispersion-strengthened by nanoparticles for electrospark deposition

The macrokinetic characteristic properties of the combustion process of mixtures in the TiC-Ni system with additives of nanosized ZrO₂, Al₂O₃, Mo-Al₂O₃ powders, as well as the phase composition, structure, and properties of the STIM-2 alloy dispersion-hardened by nanoparticles of the composition 80%TiC–20%Ni, are studied. These new materials were produced by the method of self-propagating high-temperature synthesis (SHS), in particular using the technology of power SHS-compacton. The addition of nanosized components with a higher melting point was shown to decrease both the combustion temperature (on average by 300–400 K) and its rate (by a factor of 1.5–2.0) and to modify the structure of synthetic products, where an average size of carbide grains decreases by a factor of 1.5–3.0. The optimal composition of the STIM-2 alloy dispersion hardened by nanoparticles with the addition of the composition powder on the basis of 0.5%Al₂O₃-cladded molybdenum, which provides a high level of physical and mechanical properties, is found.     

Effect of the oxygen content of titanium powder on the synthesis of titanium carbide by the self-propagating high-temperature method

Conclusions An investigation was carried out into the possibility of employing various grades of titanium powder for the production of titanium carbide by the SHS process. The relationship between the chemical composition of the end product and synthesis parameters has been established. The completeness of chemical transformation, degree of purification of the titanium carbide from oxygen, and velocity of propagation of the synthesis wave depend on the oxygen content and particle size of the titanium powder as well as on the synthesis (combustion) temperature and time of residence of the reaction mass in the inert atmosphere at high temperature. Raising the CO concentration in synthesis increases the contamination of the titanium carbide with oxygen and the amount of free carbon in the synthesis product. The authors wish to thank Professor A. G. Merzhanov for helpful advice and discussion.The authors wish to thank Professor A. G. Merzhanov for helpful advice and discussion.Translated from Poroshkovaya Metallurgiya, No. 12(228), pp. 49–54, December, 1981.     

The self-propagating high-temperature synthesis of a nanostructured titanium nitride powder with the use of sodium azide and haloid titanium-containing salt

The use of the “ammonium hexafluorotitanate (NH₄)₂TiF₆-sodium azide NaN₃” system during self-propagating high-temperature synthesis (SHS) allows researchers to obtain nanostructured titanium nitride powder. Nanopowders of silicon, boron, and aluminum nitrides are formed from similar “halogenide of nitrided element-sodium azide” systems by SHS. It is confirmed that the use of compounds rather than pure elements in the starting powder mixtures for SHS makes it possible to substantially decrease the dimensionality of the combustion products and obtain them in the form of nanostructured particles, nanofibers, and nanopowders.     

Optimization of self-propagating high-temperature synthesis using a halogen fluoride as an igniter for reagents

The minimum quantity of the high-activity chemical reagent (HACR) that is required for the initiation of self-propagating high-temperature synthesis (SHS) is determined. The experimental results show that 1–1.3 mg ClF₃ (gravity flow from a dosing device), BrF₃ on the end of a filling knife, or a few ClF₂ ⁺ SbF₆ ^- crystals are sufficient for the initiation of titanium–boron or titanium–carbon high-energy powder charge compositions. Since the quantity of HACR required for SHS initiation is very small, the chemical method of initiation can be used for the development of a mobile ignition device for estimating the ignition of various SHS charge compositions under laboratory conditions and for application in standard reactors.     

Synthesis of Ceramic Materials Based on Titanium Carbide with a Cobalt Binder for the Pulsed Electrospark Deposition of Bioactive Coatings with an Antibacterial Effect

The goal of this study was to produce biocompatible ceramic materials in the Ti–C–Co–Ca₃(PO₄)₂–Ag–Mg system by combustion mode synthesis. The influence of cobalt on combustion parameters of the mixture, structure, and properties of the products was investigated. Compact ceramics consist of a combined grain frame of nonstoichiometric titanium carbide (TiC_0.5–TiC_0.6) with the titanium phosphate (Ti₃PO_x) phase homogeneously distributed along grain boundaries and local isolations of calcium oxide (CaO). The introduction of cobalt promotes the formation of a complex phosphide CoTiP and TiCo intermetallic compound. Alloying with silver and magnesium leads to the formation of a silver-based solid solution.     

Characteristic Features of Boron Carbide Synthesis for Iron Triad Borides

We have studied the characteristic features of synthesis of iron, cobalt, and nickel borides by boron carbide reduction of oxides. We have shown that the reaction of boron carbide with iron triad metal oxides occurs through a stages involving formation of the metals, lower boride phases, carbides and borates of the corresponding metals. A characteristic feature of such a reaction is the higher reactivity of boron carbide compared with carbon in the initial stages, leading to the appearance of B₂O₃ and C which react at higher temperatures to form boron carbide. The method of boron carbide reduction of oxides allows us to obtain rather pure higher borides of iron, cobalt, and nickel.     

Features of Production and High-Temperature Oxidation of SHS Ceramics Based on Zirconium Boride and Zirconium Silicide

This article is devoted to the investigation into the combustion kinetics and mechanism of reaction mixtures in Zr–Si–B and Zr–B systems formed according to the forced SHS-pressing of compact ceramic materials, as well as to studying their heat resistance. It is shown that dependences of the combustion temperature and rate on the initial temperature (T₀) for compositions in the Zr–Si–B system are linear; i.e., staging of chemical reactions of formation of zirconium diboride and disilicide remains invariable with an increase in T₀. The values of effective activation energy of SHS process, which evidence the leading role of the reaction interaction of zirconium with boron and silicon in the melt, are calculated. Staging of chemical transformations in the combustion wave of the Zr–Si–B system is investigated: initially the ZrB₂ phase is formed by crystallization from the melt, and then the ZrSi₂ phase appears with a delay of 0.5 s; unreacted Si crystallizes after 1 s. The phase composition of synthesis products, in which the main component is ZrB₂ diboride, and zirconium disilicide, Si, and ZrB₁₂ boride are contained depending on the composition of the reaction charge, is investigated. Compact samples having high hardness and low residual porosity are fabricated according to forced SHS-pressing technology. High-temperature oxidation of SHS samples results in the formation of SiO₂–ZrO₂–B2O₃ oxide films and ZrSiO₄ complex oxide on their surface depending on the composition, which serve the effective diffusion barrier and lower the oxidation rate.     

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).     

Microstructural characterization of self-propagating high-temperature synthesis/ dynamically compacted and hot-pressed titanium carbides

Titanium-Carbide produced by combustion synthesis followed by rapid densification in a high-speed forging machine was characterized by optical microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). The density of the combustion synthesized/dynamically compacted TiC reached values greater than 96 pct of theoretical density, based on TiC_0.9, while commercially produced hot-pressed TiC typically exceeded 99 pct of theoretical density. The higher density of the hot-pressed TiC was found to be attributable to a large volume fraction of heavy element containing inclusions. The microstructure of both TiCs consists of equiaxed TiC grains with some porosity located both at grain boundaries and within the grain interiors. In both cases, self-propagating high-temperature synthesis (SHS)/dynamically compacted (DC) and hot-pressed, the TiC is ordered cubic (NaCl-structure,B ₁; Space Group Fm3m) with a lattice parameter of ≈0.4310 nm, indicative of a slightly carbon deficient structure; stoichiometric TiC has a lattice parameter of 0.4320 nm. For the most part, the grains were free of dislocations, although some dislocation dipoles were found associated with the voids within the grain interiors. In one SHS/DC specimen, a new, complex Ti-Al-O(C) phase was observed. The structure could not be matched with any previously published phases but is believed to be hexagonal, with a c-axis/a-axis ratio of ≈6.6, similar to the AlCTi₂ phase which has a point group 6 mmm. In all other SHS/DC TiC samples, the grains and grain boundaries were devoid of any second-phase particles. The hot-pressed TiC exhibited a greater degree of porosity than the SHS/densified specimens and a large concentration of second-phase particles at grain boundaries and within grains. The structure and composition of these second-phase particles were determined by con-vergent beam electron diffraction (CBED) and X-ray microanalysis. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

Fabrication of metal matrix composites of

Fine fibrous titanium carbide (TiC) was processed through the self-propagating high-temperature synthesis (SHS) method and employed to fabricate aluminum matrix composites. Two consol-idation methods were investigated: (1) combustion synthesis of TiC fiber/Al composites directly using titanium powders and carbon fibers ignited simultaneously with varying amounts of the matrix metal powder and (2) combustion synthesis of TiC using titanium powders and carbon fibers followed by consolidation into different amounts of the metal matrix powder, Al,via hot isostatic pressing (HIP). In the former method, when the amount of the Al in the matrix was increased, the maximum temperature obtained by the combustion reaction decreased and the propagation of the synthesis reactions became difficult to maintain. Preheating was required for the mixture of reactants with more than approximately 5 mole pct aluminum matrix powders in order to ignite and maintain the propagation rate. Microstructural analysis of the products from the Al/C/Ti reaction without preheating shows that small amounts of an aluminum carbide phase (AI4C3) are present. In the second method, following separation of the individual fibers in the TiC product, dense composites containing the SHS products were obtained by HIP of a mixture of the TiC fibers and Al powders. No ternary phase was formed during this procedure. Formerly Graduate Research Assistant, Department of Chemical Engineering, Michigan Technological University, is with Particle Technology, Inc., Hanover, MD 21076. This paper is based on a presentation made in the symposium “Reaction Synthesis of Materials” presented during the TMS Annual Meeting, New Orleans, LA, February 17–21, 1991, under the auspices of the TMS Powder Metallurgy Committee.     

自蔓延高温合成法制备WC－Al_2O_3复合陶瓷材料的研究

研究了ＷＣ－Ａｌ２Ｏ３复合陶瓷材料的自蔓延高温合成过程中，稀释剂含量、反应物类型（炭黑与石墨）、金属还原剂粒度，以及碳的配比含量对燃烧反应的速率、温度和燃烧合成物相组成的影响。结果表明，采用自蔓延高温合成技术制备ＷＣ－Ａｌ２Ｏ３复合陶瓷材料时，气相产物的生成及挥发是影响反应参数和合成产物相组成的重要因素。通过改变反应物的配比含量，可以有效地调整合成产物中ＷＣ，Ｗ２Ｃ以及Ｗ的相对含量。     

Wear of tungstenless hard alloys based on SHS-titanium carbide

The structure, porosity, strength, and wear resistance of tungstenless hard alloys based on titanium carbide are investigated. Titanium carbide is produced by self-propagating high-temperature synthesis (SHS). The strength of this alloy and normal hard alloy of similar composition is about the same, but SHS alloy exhibits higher wear resistance. The use of SHS titanium carbide alloyed with molybdenum results in an increase in strength. Addition of molybdenum to the nickel binder results in a twofold increase in wear resistance.Institute of Structural Microkinetics, Russian Academy of Sciences, Chernogolovka. Translated from Poroshkovaya Metallurgiya, Nos. 1/2(383), pp. 61–64, January–February, 1996. Original article submitted April 13, 1994.     

Formation of the structure and phase composition of the Ti–Al–Ta-based materials

The experiments on the fabrication of materials based on the Ti–3Al–0.5Ta and 3Ti–2Al–Ta systems by self-propagating high-temperature synthesis (SHS) are performed. The influence of the composition of the initial mixture, dispersity of powders, and preliminary mechanical activation on the phase composition and structure of the SHS product is investigated. The optimal ratio between the mechanically activated and initial powder in a mixture for the synthesis of materials is determined. The dependence of the structure of final products on the structure of initial powders is established. The use of porous tantalum leads to the formation of the intermetallic matrix based on titanium aluminide with the uniform distribution of Ta particles. It is noteworthy that tantalum powders of both studied series (which differ by dispersity and morphology) partially reacted already at the stage of mechanical activation with the formation of the Al₂Ta phase. It is shown that aluminum plays the leading role in processes of mechanical activation in Ti–Al–Ta reaction mixtures. Indeed, a considerable rise of unreacted tantalum particles in the microstructure of sintered samples is observed with a decrease in the amount of aluminum in the reaction mixture.     

Effect of Nanocrystalline Powders on the Structure and Properties of Dispersion-Hardened Alloy TiC – 40% KhN70Yu

This article examines aspects of the effect of nanocrystalline powders of ZrO₂, Al₂O₃, W, WC, WC–Co, NbC, and Si₃N₄ on the combustion, structure, and physical and physico-mechanical properties of new dispersion-hardened electrode alloy TiC – 40%KhN70Yu. This heat-resistant hard alloy, based on titanium carbide and a nickel alloy, was obtained by self-propagating high-temperature synthesis (SHS). It is shown that the addition of a nanocrystalline powder decreases combustion rate, with the magnitude of the reduction depending on the specific surface of the addition. It was determined that the structure of the synthesis products is modified appreciably by introducing a mixture of nanocrystalline powders into the initial charge. Here, additions of ZrO₂ and NbC have a positive effect on the main physico-mechanical characteristics of the alloy (strength, hardness, fracture toughness). Nano-powders of Al₂O₃ and Si₃N₄ have a negative effect on the alloy's physico-mechanical properties. The addition of WC–Co increases the flexural strength of the material, while the addition of W and WC increases its fracture toughness.     

Effect the Actual Structure of Boron and Catalytic Additions on Boron Nitride Synthesis

The bahavior of boron with different degrees of purity, fineness, and crystal structure perfection during nitriding at high temperature is studied by electron microscopy, x-ray diffraction, and chemical analysis. The effect of additives (Li₂CO₃, H₃BO₃, and NH₄Cl) on boron nitride synthesis is studied. A marked reduction is established in the temperature for forming a highly-ordered boron nitride structure on introducing additives. The chemistry of the amorphizing effect of ammonium chloride on the crystal structure of boron is suggested.     

SHS Technology for Composite Ferroalloys. 2. Synthesis of Ferrosilicon Nitride and Ferrotitanium Boride

The combustion of ferrosilicon in nitrogen is very similar to the combustion of metallic silicon. With increase in silicon content in the initial ferrosilicon, its reaction rate with nitrogen increases, as is clear from the considerably more vigorous combustion. The nitrogen concentration in the combustion products increases here. Over the whole range of initial parameters (nitrogen pressure, grain size of the powder, batch composition), the combustion products consist mainly of β-Si₃N₄. No large quantity of α-Si₃N₄ is observed. In practice, FS75 and FS90 ferrosilicon is optimal for refractory production, while FS65 and FS75 ferrosilicon, with lower impurity content, is best for the production of components used in steel production. The introduction of iron in the Ti–B system (T_ad = 3190 K) considerably restricts the combustion concentration range. A mixture with 16.9% B burns in a narrow Ti:B concentration range close to 0.86. In combustion of the Fe–B + Ti mixture, increase in the initial temperature considerably expands the concentration range for synthesis. In all cases, increase in the initial temperature considerably boosts the combustion rate. Heating to T₀ ≥ 300°C permits the use of mixtures with titanium powder containing larger grains (r_me.Ti ≥ 0.4 mm) in self-propagating high-temperature synthesis (SHS). A wide range of B:Ti ratios may be used. The combustion of such mixtures permits the production of an alloy with 6–14% B and 30–60% Ti. Specialized industrial equipment has been constructed: a series of SHS reactors with working volumes of 0.06, 0.15, and 0.3 m³, permitting the large-scale production of materials based on refractory inorganic compounds for use in metallurgy. The industrial production of composites based on oxygen-free compounds by self-propagating hightemperature synthesis has been introduced.