SHS Products Research Articles

Study of the Phase Composition, Structure and Mechanical Properties of Synthetic Composites Produced by High-Temperature Vacuum Sintering of SHS-Fabricated CrNi-TiN Powders

This work studies the phase composition, structure and mechanical properties of composite materials obtained by high-temperature vacuum sintering of SHS-fabricated CrNi–TiN powders synthesized in semi-industrial-scale production conditions. It was found that changes in the synthesis conditions have no effect on the phase composition and structure of the final products. Additionally, a small increase in the average size of ceramic TiN particles was observed. Compacted rectangular samples were obtained by high-temperature vacuum sintering of fine-ground CrNi–TiN SHS products. A minimum sintering temperature was found at which specimens with a density of 95% of the theoretical one could be obtained. The structure of sintered composites inherits the metal-matrix structure of a part of SHS products. It was shown that CrNi–TiN composite materials are superior to NiTi–TiB2 composites in terms of hardness as well as binding strength for three-point bending at temperatures up to 550 °C.

Express-diagnostics of the properties of ЫРЫ materials using chrono-topographic analysis of thermal vision data

Subject of research: the article is devoted to the development of a methodology for express diagnostics of material properties based on the measurement of macrokinetic parameters of the SHS process.
 Purpose of research: plotting the dependence of the microhardness of SHS products on the propagation velocity of the SHS wave and its temperature.
 Methods and objects of research: the research objects were the SHS process in the Ni-Al system and the reaction products; To measure the propagation velocity of a high-temperature synthesis wave, an original method of chrono-topographic analysis of thermal imaging data was used; temperature control was carried out by an original method of spectral-brightness pyrometry. The study of the microhardness of experimental samples was carried out using an FM-800 microhardness tester.
 Main results of research: in the course of experimental studies, it was shown that the error in determining the propagation velocity of the SHS wave by the method of chrono-topographic analysis of thermal imaging data is 0.1 %, and the error in temperature measurement by the method of spectral-brightness pyrometry is estimated at 0.5 %. It is concluded that the main factor influencing the total error in the SHS wave propagation velocity in the experiment is the inaccuracy of setting the charge parameters for a set of samples. The absolute value of the total error was 3.2 %. A diagnostic trajectory has been constructed that makes it possible, based on the SHS propagation rate and reaction temperature, to evaluate the microhardness of the product and draw a conclusion about the quality of charge preparation for the production of a material with desired properties.

A theoretical and experimental investigation on the SHS synthesis of (HfTiCN)-TiB2 high-entropy composite

In this work, a fundamental possibility of obtaining a high-entropy ceramic (HfTiCN)-TiB2 composite material by the coupled self-propagating high-temperature synthesis is shown. To search for a stable fixed composition of the HfTiCN compound, the USPEX code was used with the CASTEP interface at 0K. According to the XRD analysis, the obtained SHS product is represented by HfTiCN phase (60 wt%) and TiB2 phase (40 wt%). Based on the results of XRD, elemental analysis, and the heat pattern of combustion of the Hf-Ti-C-N-B powder mixture, a probable mechanism for the formation of the (HfTiCN)-TiB2 composite material during the coupled self-propagating high-temperature synthesis was proposed.

Study of the Composition and Properties of Coatings being Formed during Combustion of Al + B<sub>2</sub>O<sub>3</sub> Mixtures on Steel Substrates

Within the scope of this work, the methods of the experimental research of SHS processes during HFC-heating, particularly of hardening coatings applied on samples by HFC-heating have been developed. A study of the composition and properties of the products formed during the SHS process in the basic mixture on the surface of S355 steel parts during HFC-heating has been made, and it has been shown that aluminum oxide, aluminum nitride (by-product), and amorphous boron are formed under these conditions, and composite porous inhomogeneous coatings up to 250 microns thick, based on aluminum oxide, SHS products in the basic mixture and traces of high-speed HFC-boriding products are formed on the workpiece surface.

Subtle Details in Crystal Structure of SHS Products by DFT Calculations

Total energy ab-initio calculations for some SHS products were performed by DFT method using VASP program package. The results of calculations along with XRD results and crystallographic modeling were used to explain specific features of the composition/structure of selected SHS products.

Melting Points of Refractory SHS Products: Evaluation by Molecular Dynamics Methods

Several approaches to theoretical estimation of melting points for refractory metals and compounds by molecular dynamics calculations were analyzed and a new time-saving approach applicable to small two-phase ensembles and personal computers was suggested. The results of numerical calculations for melting points of refractory metals (Ta, W, Mo, V, Cr, Ti, Zr, Hf) and compounds (TiC, TiN, TiB2, TaC) well agree with respective tabulated values.

Non-isothermal synthesis of materials based on the MAX phases in the Ti-Si-C and Nb-Al-C systems

The experimental results of self-propagating high-temperature synthesis of materials in Ti – Si – C and Nb – Al – C systems are presented. Mixtures of powders of Ti, Si, Nb, Al, and C were used as charge. The combustion thermograms of the Ti-Si-C system are investigated. It is shown that changes in the technological conditions of synthesis can substantially change the phase composition and microstructure of the final products. The optimal synthesis conditions were established, which made it possible to obtain a product with a maximum content of the target phases Ti3SiC2, Nb2AlC, Nb4AlC3. Under all conditions studied, the SHS method fails to obtain 100% of the MAX phase of stoichiometric composition. To obtain 100% stoichiometric MAX phases, additional heat treatment of the ground SHS products is necessary. The products obtained by high-temperature synthesis were characterized by X-ray, optical and scanning electron microstructural analysis methods.

Self-propagating high-temperature synthesis of oxide bronzes with regulated composition and properties

The work is devoted to the preparation of oxide tungsten bronzes of various compositions and various structures by the SHS method. The work is aimed at the realization of the ability to control the composition, structure and properties of SHS products. Brightness pyrometry technique was used for the experimental evaluation of the temperature in the combustion wave. The values of the electrical conductivity of the obtained samples of oxide tungsten bronzes with constant current: for K0.25WO3 — 0,029 S/cm; K0.50WO3 — 0,046 S/cm. Carbon paste electrode was produced and tested based on an oxide bronze K0.50WO3.

The influence of the ignition conditions of the SH-synthesis of intermetallic compounds on the combustion parameters of the Ti-15.82wt.%Al composition: computer simulation and computing experiments

Computational experiments (CEs) have been carried out to simulate the propagation of the combustion wave of the SH-synthesis process in a package of alternating layers of nanoscale crystal lattices of Ti and Al atoms by molecular dynamics method. The interatomic interaction potential in the embedded atom model (EAM) was used in the LAMMPS package. Using the LAMMPS configuration with parallel computing, the following results of CEs were obtained: sets of temperature profiles along the layers of the structure at successive instants of time (up to 16 ns) and the corresponding sets of snapshots (vertical cross-sections of the atomic arrangement along the layers), as well as a tables with the number and percentage of the content of various types of elementary cells (fcc, hcp, bcc, other) at the same instants of time. The influence of the initiation’s conditions of the SH-synthesis of intermetallic compounds on the combustion parameters of the nanoscale layered Ti-15.82wt.%Al composition was showed. The ignition conditions of SHS that are provided the stable motion of the combustion wave in the SHS-sample were determined. And the ignition conditions of SHS with dominance of either TiAl or Ti3Al phase formation in the SHS products was also determined.

Self-propagating high-temperature synthesis of ZrB2-B4C composites with the dispersed phase as hollow shells

The formation of the microstructure of ZrB2-B4C ceramic composites produced by SHS pressing has been studied. It has been shown that the exothermic interaction in a mixture of Zr, B, and C powders gives an equilibrium SHS product containing ZrB2 as a dispersed phase and B4C – as a ceramic binder. The effect of the ceramic binder (B4C) content on the formation of the microstructure of SHS composites has been studied. It is shown, at content of B4C 10-20 wt% homogeneous SHS composites were formed consisting monolithic the ZrB2 particles with a size of 10-12 pm, and at content of B4C 20-40 wt% – hollow shells consisting of the ZrB2 particles.

Self-Propagating High-Temperature Synthesis of ZrB2–B4C Composites with the Hollow-Shell Dispersed Phase

The formation of the microstructure of ZrB2–B4C ceramic composites produced by SHS pressing has been studied. It has been shown that the exothermic interaction in a mixture of Zr, B, and C powders gives an equilibrium SHS product containing ZrB2 as a dispersed phase and B4C as a ceramic binder. The effect of the ceramic binder (B4C) content on the formation of the microstructure of SHS composites has been investigated.

Самораспространяющийся высокотемпературный синтез тугоплавких порошковых материалов на основе диборида циркония из борсодержащего минерального сырья Республики Казахстан

The goal of the present work is the synthesis of the refractory zirconium diboride powder in the combustion mode. One of the most effective methods of synthesis of the refractory zirconium diboride powder is the self-propagating high-temperature synthesis method (SHS) with a preliminary mechanical activation of the initial components. Initial components of the SH-synthesis are borate ore, zircon, aluminum powder and magnesium. After the SH-synthesis obtained products were processed by 37.5% HCl and were washed with distilled water. Final composition and microstructure of SHS products were investigated with X-ray phase analysis and SEM. Boron-containing SHS-powders can be used as bio-protection in nuclear engineering, production of abrasive powders, ceramic, composite materials and coatings.

SHS TECHNOLOGY OF COMPOSITION FERROALLOYS. PART II. SYNTHESIS OF FERROSILICON NITRIDE AND FERROTITANIUM BORIDE

Consistent patterns in the combustion of ferrosilicium in nitrogen are rather similar to those of metal silicon. As the concentration of silicon in initial ferrosilicium is increased, the intensity of its interac­tion with nitrogen increases as well, resulting in a significant growth of the combustion rate. The concentration of nitrogen in the combus­tion products here increases as well. In the entire investigated range of initial parameters (nitrogen pressure, powder fineness, burden mix), the main phase in the combustion products is β-Si3N4. No considerable amounts of α-Si3N4 have been observed. In practical applications, the use of FS75 and FS90 ferrosilicium is optimal for producing fire-re­sistant materials, while FS65 and FS75 (being the purest alloy grades) are optimal for obtaining alloying steel compositions. Introducing iron into the (Ti – B) ( T ad = 3190 K) system significantly narrows down the concentration limits of combustion. ((Fe – B) + Ti) mixture with 16.9 % B alloy burns in a narrow range of Ti:B concentrations close to 0.86. When a ferroboron-titanium mixture burns, an increase in the initial temperature significantly expands the synthesis concentration limits. In all the cases, an increase in the initial temperature leads to a significant increase in the combustion rate. Heating up to T 0 ≥ 300 °C allows for involving mixtures with more coarse titanium powders ( r av. Ti ≥ 0.4 mm) into the SHS process. The synthesis is implemented in a wide range of B:Ti ratios. By burning such mixtures one can ob­tain alloys with 6 – 14 % B and 30 – 60 % Ti. Specialized industrial equipment has been built: a series of SHS reactors with the operation volume of 0.06, 0.15 and 0.3 m3 for the serial production of manufac­turing items based on hard-melting inorganic compositions (nitrides, borides, silicides, etc.) for metallurgical applications. Industrial SHS production of composite materials based on oxygenless compositions has been set up.

On the self-propagating high-temperature synthesis of tungsten boride containing composite powders from WO3–B2O3–Mg system

In this research, the self-propagating high-temperature synthesis characteristics of the 2WO3‒(1 + x)B2O3‒(9 + y)Mg system were studied using H3BO3 as the boron oxide source. The addition of extra B2O3 and Mg was considered as the main process parameter to obtain tungsten borides phases. XRD results showed that tungsten element was the only phase remained after leaching of the products obtained with the stoichiometric composition. The extra B2O3 and Mg acted as the diluent agents and decreased the adiabatic temperature and the reaction velocity as well as the products’ particle size. Moreover, tungsten boride containing composite powders were obtained. However, the type of the tungsten boride in the composites was dependent on the diluent agent. Fourier transformed infrared spectroscopy analysis showed that nearly-pure composite powders were obtained after acid leaching. Finally, based on the XRD phase analysis and differential thermal analysis results, a mechanism was suggested for the formation of the SHS products in this system.

Express-analysis of Phase Composition of SHS Products

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A Study on the Characterization of MASHS Processed Ti-Si-Al System

Many promising titanium aluminides and silicides could be synthesized in Ti-Si-Al system via mechanically activated self-propagating high-temperature synthesis (MASHS). The influence of mechanical activation and initial composition on phase formation, microstructure and synthesis behavior of mechanically activated Ti-rich mixtures in Ti-Si-Al system is investigated. Results indicate that Al can participate in the reaction and forms Ti3Al and TiAl3 phases beside Ti5Si3 phase by using mechanically activated reactants. Si and Al could be substituted each other in titanium aluminide and silicide to form solid solution of Ti3(Si,Al) and Ti5(Si,Al)3. In Ti-Si-Al system, combustion temperature is increased by increasing Si amount in the system while, ignition temperature is decreased profoundly from 1100 to 800 ∘C by applying mechanical activation prior to reaction and increasing Al in the system. In addition, Mechanical activation prior to synthesis gives rise to narrow grain size distribution and more uniform microstructure in comparison with SHS products.

The kinetics and mechanism of combusted Zr–B–Si mixtures and the structural features of ceramics based on zirconium boride and silicide

The study focuses on investigation of the combustion kinetics and mechanisms, as well as the phase- and structure formation processes, during elemental synthesis of ceramics based on zirconium diboride and silicide doped with aluminum. The effect of the degree of dilution with an inert component and initial temperature T0 on the combustion kinetics of the Zr–Si–Al–B mixture is studied. An increase in T0 in the range of 298–700K causes a directly proportional rise in the combustion temperature Tc and rate Uc, which demonstrates that staging of the reactions of formation of zirconium boride and silicide remains invariant. The effective activation energy Eeff of the combustion process is 225kJ/mol, suggesting that the liquid-phase processes have a decisive effect on the reaction kinetics. The interaction of zirconium with boron and silicon runs through the Zr–Si–Al–B melt that is formed in the combustion zone. Staging of chemical transformations during phase and structure formation of SHS products is studied. The primary ZrB2 grains crystallize from the melt in the combustion zone; the ZrSi silicide phase is formed with a delay of no longer than 0.5s. Compact ceramics with composition ZrB2–ZrSi–ZrSi2–ZrSiAl2 synthesized by forced SHS- pressing showing a great potential for high-temperature applications both as a construction material and as a precursor for ion-plasma deposition of coatings.

Conditions for fabricating single-phase (Ta, Zr)C carbide by SHS from mechanically activated reaction mixtures

The process parameters for the fabrication of binary carbide (Ta, Zr)C using MA–SHS were optimized. After MA processing in air, the SHS product was the virtually single-phase binary carbide (Ta, Zr)C with a ZrO2 content less than 3%. Activation of the exothermic mixture in argon or under vacuum did not give rise to the single-phase product because the TaC and ZrC phases were present in addition to (Ta, Zr)C.Introduction of excess carbon, an increase in the combustion and post-reaction temperatures, and an increase in the duration of thermal relaxation using a “chemical oven” yielded the single-phase (Ta, Zr)C solid solution with lattice parameter a=0.4493nm, which corresponds to 17.5at% of dissolved ZrC. Dense samples were fabricated from submicron-sized carbide powder via hot pressing and spark plasma sintering; their properties were studied.

SHS production of heat-shield materials from minerals and residual products: Influence of preliminary mechanochemical treatment and modifying agents

We report on preparation of porous refractory ceramics from natural quartz sand and industrial wastes (fly ash and wastes of concrete production) by SHS in a mode of thermal explosion with preliminary mechanochemical treatment of charge mixtures in the presence of carbonaceous modifying agents (activated carbon and polystyrene). The Al2O3–AlN-based composite synthesized in optimized conditions exhibited low thermal conductivity [0.185–0.228 W/(m K)], finely porous structure, and high compression strength (30–96 MPa).

Fluorophlogopite by metallothermic SHS from quartz sand and waste product

Using quartz sand (SiO2); Al and Mg powders as reducing agents; a waste product of aluminum production, cryolite Na3AlF6, as a source of fluorine; and commercial KClO4 as a source of oxygen, we made an attempt to synthesize cast fluorophlogopite, NaMg3Si3AlO10F2, by metallothermic SHS in open air. Synthesis conditions have been optimized with respect to preparation of either cast or porous resultant materials. The synthesized materials were found to contain NaMg3AlSi3O10F2, Na4Mg6Al4Si4O20F4, MgAl2O4, SiO2, and some amount of unreacted Si. Our results can be regarded as a technological basis for designing a process for SHS production of fluorophlogopites.