A. S. Rogachev

Institute of Structural Macrokinetics and Materials Science RAS | ISM

The dependence of the ignition temperature, combustion rate and composition of the resulting products on the concentration of Ti + C in mixtures with powder of a high-entropy alloy (HEA) FeNiCoCrCu and the initial mixture of metals forming it (MIX) has been studied. HEA was obtained by mechanical activation (MA) of a mixture of metal powders in arg...

The stability of high-entropy alloys is of great importance for their fundamentals and practical applications. We experimentally studied the phase and microstructural evolution of near-equiatomic Co0.18Cr0.20Fe0.24Ni0.19Ti0.19 alloy during long-term (up to 204 days) isothermal annealing at 873, 1073, and 1273 K. The as-synthesized material fabricat...

Reactive multilayer nano-foils possess high heat release and combustion temperature, which makes them very attractive for advanced applications, such as materials joining materials, tuning ignition and actuation, energy microsources, and others. The combustion mechanism of CuO/Al foils has not been adequately described yet. In this work, we report...

Self-propagating high-temperature synthesis (SHS) is an attractive technique to synthesize a variety of advanced materials [1]. It is based on the concept that once initiated locally by means of a thermal source of short-term-service, highly exothermic reactions become self-sustaining and yield the final product progressively without requiring addi...

The formation dynamics of medium- entropy alloy CoFeNi has been studied both experimentally and theoretically in terms of molecular dynamic simulation. The results of experiments and modelling showed good qualitative agreement and supplemented each other. The synthesis was found to occur in two stages. (a) Refinement of crystallites and accumulatio...

A two-phase powder alloy based on substitutional solid solutions with bcc and fcc lattices has been obtained by the high-intensity mechanical treatment (HMT) of a multicomponent powder mixture Fe + Cr + Co + Ni + Ti. Sections of the samples and particles of the resulting mixtures are studied on an ultra-high resolution scanning electron microscope...

Spark plasma sintering (SPS) is an efficient method for fabricating various bulk dense materials, including ceramics. Reactive spark plasma sintering (RSPS) of the exothermic reaction systems involves an initial powder mixture that allows chemical transformation with release of an additional energy during the SPS process. Thus, a deep understanding...

Combustion of Me + 2B, (Me1 + Me2 + Me3 + Me4) + 8B, and (Me1 + Me2 + Me3 + Me4 + Me5) + 10B mixtures (Me = Ti, Hf, Nb, Zr, Ta) aiming at the preparation of a high-entropy metal diboride by SHS method was studied by using XRD and SEM analyses. We succeeded to prepare high-entropy diboride [TiHfZrNbTa]B2 by SHS method from the above mixtures in a co...

A two-phase powder alloy based on substitutional solid solutions with BCC and FCC lattices was obtained by highintensity mechanical treatment (HMT) of a multicomponent Fe–Cr–Co–Ni–Ti powder mixture. Sample sections and particles of mixtures obtained were studied using an ultra high resolution field emission scanning electron microscope by scanning...

A powder of equiatomic CoCrFeNiCu high entropy alloy (HEA) was prepared by short-term (120 min) high energy ball milling (HEBM). Our structural and chemical analysis showed that microsized particles of fcc CoCrFeNiCu with a grain size of 8 nm were obtained after 120 min of HEBM at 694/1388 rpm. The structural/phase evolution of CoCrFeNiCu HEA powde...

A family of high-entropy alloys (HEA) composed of 3d-transitional metals is attracting great interest due to the mechanical, magnetic, and electrical properties that are valuable in the development of advanced structural and functional materials. In this work, we studied X-CoCrFeNi HEAs, where X = Al, Ti, or Cu, produced by mechanical alloying by m...

Reactive joining with Ni/Al nanocomposites is an innovative technology that provides an alternative to more common bonding techniques. This work focuses on a class of energetic material, produced by high energy ball milling and cold rolling. The initial microstructure is more complex than that of reactive multilayer nanofoils, produced by magnetron...

A powder of uniform high entropy alloy AlCoCrFeNi was produced by relatively short-term (90 min) mechanical alloying in a planetary mill followed by annealing at 873, 1073 and 1273 K for 5.5 h. Results of high-temperature in situ XRD analyses demonstrated the occurrence of specific crystal lattice transformations taking place in major fcc and bcc p...

The reactivity of the Ti–Al system was investigated experimentally in the case of reactive laminated particles produced by high energy ball milling. The ignition temperature for a self-sustaining reaction was measured as a function of the heating rate. By means of the Kissinger analysis, two activation energies were evaluated. The first one is asso...

In this study, nonstoichiometric hafnium carbonitrides (HfCxNy) were fabricated via short-term (5 min) high-energy ball milling of Hf and C powders, followed by combustion of mechanically induced Hf/C composite particles in a nitrogen atmosphere (0.8 MPa). The obtained HfC0.5N0.35 powder exhibited a rock-salt crystal structure with a lattice parame...

Ceramic-metal composites TiC–High-Entropy Alloy (HEA) CoCrFeNiMe (Me = Mn, Ti or Al) were first produced by combustion synthesis method. Self-sustained synthesis occurs due to heat release from exothermic reaction Ti + C = TiC; the binder content was varied between zero and 40–50 wt.%. The combustion velocity and temperature gradually decreased wit...

Direct high-speed micro-video records prove the existence of highly overheated zones at the contacts of powder particles during short (~ 1 ms) electric current pulses. The value of overheating can exceed 1600 degrees and lead to the formation of liquid-phase sintering necks, the dimensions of which are well correlated with the size of the overheate...

A powder of equiatomic CuCrFeTiNi high-entropy alloy (HEA) was prepared by short-term (30 min) high-energy ball milling (HEBM). Our structural and chemical analysis showed that micron sized particles of bcc CuCrFeTiNi consisting of nanosized crystalline grains (∼6 nm) could be obtained after 30 min of HEBM. The influence of milling time (30 ÷ 240 m...

Direct high-speed micro video recording data proved the existence of highly overheated zones at contacts of powder particles through which electric current pulses about 1 ms long were sent. The overheating might exceed 1600 K and could give rise to liquid-phase sintering necks, the sizes of which correlated well with the sizes of the overheated zon...

The process of phase formation during short-term (80 and 120 min) high-energy ball milling of Fe84B16, Fe80B20, and Fe70B30 powder mixtures was studied by Mössbauer spectroscopy. Hyperfine field Bhf on the nuclei of resonant atoms as a function of the number of boron atoms (nB) in the nearest neighborhood of Fe atoms was also found to be a linear f...

Mechanochemical synthesis of hafnium nitride ceramic powder was accomplished through direct nitridation of hafnium particles in nitrogen atmosphere during high-energy milling in a planetary ball mill. The nitrogen content was measured and evaluated to determine the reaction kinetics for hafnium – nitrogen across a range of treatment durations. The...

High-entropy alloy CoCrFeNiMn was produced by short high energy ball milling (90 min) and spark plasma sintering (10 min at 1073 K). Co-existence of two fcc-phases with lattice parameters 0.360 nm and 0.356 nm was demonstrated via HRTEM, XRD and other methods. The matrix fcc-phase with larger parameter transforms into the more compact phase during...

Ball motion and microstructure formation in the mixtures of Al with metals (Ti, Ni) during high-energy planetary ball milling are studied by means of high-speed video recording, scanning electron microscopy and computer modeling, including molecular dynamics simulation. Possibility of production reactive composite powders with rounded particles for...

A molecular dynamics simulation method was applied for estimation of critical cooling rates (vc) that required for amorphization of pure metals: Mg, Al, Ti, Fe, Co, Ni, Cu, Zr, Mo, Pd, Ag, Ta, W, Pt, Au, and Pb. The range of values vc was found to be from 7.9 × 1011 K/s for Al to 3.8 × 1013 K/s for Zr. The atomic structure obtained at different coo...

The critical cooling rates \({{{v}}_{{\text{c}}}}\) at which pure metals Mg, Al, Ti, Fe, Co, Ni, Cu, Zr, Mo, Pd, Ag, Ta, W, Pt, Au, and Pb transit to an amorphous state (vitrify), have been calculated for some alloys using the method of molecular dynamic modeling. These rates range from 7.9 × 10¹¹ for Al to 3.8 × 10¹³ for Zr. The atomic structures...

The results of studying the influence of mechanical alloying (MA) on the surface morphology, microstructure, and atomic–crystalline structure of particles of the Fe–Cr–Co–Ni–Mn multicomponent powder mixture are presented. The initial components are as follows: the R-10 radio-engineering carbonyl iron powder with average particle size d = 3.5 μm, th...

TiZrNiCuAl and TiNbNiCuAl alloys were prepared by thermal explosion and high-energy ball milling, characterized by SEM, XRD and tested for their thermal stability.

The effect of different regimes of high-energy ball milling (HEBM) on the morphology of reactive Ti–Al powders was studied. It is shown that a “soft” regime of mechanical treatment can be readily used to prepare spheroidal reactive Ti–Al powders with the flow ability suitable for selective laser melting applications. Size distribution of milled pow...

Molecular dynamic simulation was used to study mechanism of self-propagating waves of explosive crystallization (devitrification) in the CuTi metallic glass. Processes in thin rectangular samples composed of one to two million atoms were simulated and compared with experimental data. It was shown that the nucleation of primary crystalline clusters...

We report the fabrication of high porous cellular material (HPCM) by a combination of spray-solution combustion synthesis (SSCS) and spark plasma sintering (SPS) approaches. It was shown that unique morphological features of the hollow nickel nanostructured spheres, produced by solution combustion, permit rapid (15 min) low temperature (763 K) sint...

The results of the investigation into the formation of amorphous structures in the Cu–Ti system and their subsequent crystallization under the effect of high-energy ball milling (HEBM) are presented. To form amorphous Cu–Ti powders, powders of copper (MPS-V grade with average particle size d = 45–100 μm, GOST (State Standard) 4960–75) and titanium...

Room-temperature crystallization of ‘explosive’ amorphous antimony was found to exhibit the phenomenon of non-uniqueness: it may spontaneously proceed (in identical samples) either within 27 days or within 67 days to yield crystallites with different preferential orientation. Apparently, this happens due to structural fluctuations in the initial am...

This paper presents the results of studying the mechanical alloying (MA) effect on the surface morphology, microstructure and atomic-crystal structure of multicomponent Fe–Cr–Co–Ni–Mn powder mixture particles. The following materials were used as initial components: radio-engineering carbonyl iron powder (R-10 with an average particle size d = 3,5...

Amorphous Cu50Ti50 alloy was prepared by short-term (20 min) high-energy ball milling (HEBM). According to TEM, electron diffraction, and HAADF STEM results, the material was 93% amorphous with an admixture of nanocrystalline particles 2–8 nm in their size. Thermal stability and crystallization of amorphous Cu50Ti50 was studied by differential scan...

Microcrystalline and nanocrystalline Cu/Cr pseudo-alloy electrodes were prepared from elemental powders using high-energy ball milling and spark plasma sintering, and were characterized by SEM, TEM, EDS, and AFM. Vacuum discharge tests were conducted in order to reveal how the microstructure influences the material resistance to surface damage by v...

A comparative experimental study of self-sustained exothermal waves in electrodeposited amorphous antimony (Sb) films, quenched glassy copper-titanium (CuTi) alloy, and magnetron deposited multilayer nickel-aluminum (Ni/Al) films was accomplished using a single approach. It is shown that self-propagating thermal waves can be initiated in all three...

High-speed micro video recording and electron and atomic force microscopy have been used to obtain new experimental data at the initial stage of the titanium melt spreading along a carbon material (oriented pyrolytic graphite) and the formation of a reaction product. It has been shown that the melt spreading at the initial stages takes place along...

The atomic structure and amorphous-crystalline transition dynamics in CuTi metallic glass synthesized by high-energy ball milling have been studied. Using high-resolution transmission electron microscopy (HRTEM), it has been shown that the initial amorphous phase contains crystalline inclusions, which are up to 8 nm in size and may serve as crystal...

The high-temperature (1300-1600 K) kinetics for the Ti-Si reactive system were investigated using electro-thermal analysis. The influence of short-term (1-3 min) high-energy ball milling (HEBM) of Ti+0.6Si heterogeneous powder mixtures on the kinetic parameters was also studied. It was shown that HEBM leads to a significant decrease of the apparent...

Self-propagating thermal waves of the amorphous-crystalline transformation in Fe-based metallic glasses, obtained by melt spinning, were observed using a high-speed infrared camera and reported here. Some experimental results are also reported concerning oscillating waves in the CuTi glassy foils. The thermal characteristics and wave propagating ve...

The transition of the TiCu alloy from an amorphous state to the crystalline state has been studied by time-resolved X-ray diffraction. An analysis of the diffraction pattern has shown that the crystallization of the amorphous TiCu alloy upon heating occurs for a short time (no longer than 0.5 s). A sharp transition is observed at the instant of cry...

Copper-based nanocomposite pseudoalloys with a chromium content of 25 to 45 wt % have been obtained via the spark plasma sintering. The treatment of powder blends with various chromium contents in the planetary mills is found to cause pronounced changes in the electrical and mechanical properties of materials. The electric resistance of materials w...

The SHS waves in multilayer Ni/Al nanofilms and the explosive crystallization waves in Sb films deposited onto a thin copper substrate were comparatively explored by IR imaging and SEM. Despite a markedly lower thermal effect of crystallization, the waves of chemical reaction and crystallization were found to have much in common in their temperatur...

Nanostructured powders of pseudoalloys of immiscible Cu and Mo metals are prepared by highenergy ball milling (HEBM). Mechanical alloying in an Activator-2S planetary ball mill for 60 min provides a uniform distribution of refractory Mo particles in a moldable Cu matrix on submicron and nanoscopic levels. Nanostructured Cu–Mo powders are consolidat...

Self-propagating crystallization waves are detected and experimentally demonstrated in the Ti50Cu50 amorphous alloy obtained by the melt spinning (ultrafast quenching) method. High-speed thermographic recording has shown that crystallization waves can appear spontaneously at the heating of an amorphous strip to 300–350°С or at the local initiation...

Self-propagating high-temperature synthesis (SHS) or combustion synthesis (CS) is a rapidly developing research area. SHS materials are being used in various fields, including mechanical and chemical engineering, medical and bioscience, aerospace and nuclear industries. The goal of the present paper is to provide a comprehensive state-of-the-art re...

Heterogeneous nanostructured foils produced by magnetron deposition or mechanical processing represent a new class of reactive materials. They are composed of layers or clusters of different phases (typically with a size of 10–100 nm) that can react with each other with strong heat release. The reaction, being initiated locally, spontaneously propa...

A combination of High Energy Ball Milling in the planetary mills (HEBM) with Spark Plasma Sintering (SPS) allows production of dense (>97%) nano-composites of immiscible metals, Cu and Cr, so-called pseudo-alloys. New results on electrical resistance of the pseudo-alloys have been obtained from cryogenic to elevated temperatures, in comparison with...

Using combustion synthesis approach we fabricated B2 NiAl intermetallic compound as well as quasi-binary Ni(Al50Ti50) alloy, where half Al atoms are randomly substituted by transitional metal Ti. Young's modulus for synthesized materials was measured and appeared to be 222 ± 10 GPa for NiAl and 175 ± 15 GPa for Ni(Al50Ti50) phases. Using first-prin...

The results of measurement of electric resistivity and thermal conductivity of materials obtained by spark plasma sintering from powders of Cu, Cr, and their mixtures in the range of 300–600 K are presented. It is shown that the grinding of powders in planetary mills results in a reasonably substantial change in the electric and thermal properties...

Single-stage fabrication of SiC ceramics by a combination of self-propagating high temperature synthesis (SHS) and spark plasma sintering (SPS) is reported. SHS+SPS is demonstrated to be an efficient method for production of SiC ceramics with density 3.1 g/cm3, hardness of 24 GPa and toughness of 5 MPa∙m1/2. The starting material for the process is...

A comparative study, including experiments and molecular dynamic simulation, of the combustion waves in the Ni/Al multilayer reactive nanofoils reveals unknown mechanisms of the process. High speed macro-video recording, brightness pyrometry and thermal imaging proved that the combustion wave consists of two stages; the first stage can propagate in...

New classes of reactive systems that are characterized by nano-scale heterogeneity and possess extremely high reactivity, as compared to that for similar reactive systems with micro-scale heterogeneity, have attracted a vast attention of many researchers. The recent developments and trends in combustion science toward such “nano” reactive media are...

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+...

In this work silicon carbide (SiC) sub-micron powders were synthesized using four different combustion routes, which include the following reactive systems: Si/C/Teflon (T); Si/C/N2 (N); Si/C mechanically activated composite particles (MA) and reduction SiO2/Mg/C reaction (R). The specific surface area of the as-synthesized SiCT, SiCN, SiCMA and Si...

A new electrothermographic method, viz. high-speed temperature scanning, was applied to kinetic studies of reactions taking place in the Ni-Al system, including those after mechanical activation in a planetary ball mill. Treatment of the temperature profiles taken at different heating rates in terms of the Kissinger-Akahira-Sunose (KAS) approximati...

This paper presents an analytical review of modern quasihomogeneous and discrete models of gasless combustion. Particular attention is given to experiments that make it possible to distinguish between homogeneous and microheterogeneous regimes of this process. It is shown that in the cases where different theoretical models predict different behavi...

Solution combustion synthesis (SCS) is typically used to produce nanostructured oxides and bulk metallic materials for a variety of application including catalysis. Here, we report in situ, one-step SCS of high surface area (155 m2/g) Ni catalysts supported on fumed silica (SiO2). Time-resolved X-ray diffraction is used to investigate the dynamics...

The extremely rapid gasless reactions in binary Ni/Al reactive multilayer nanofoils (RMNFs) are investigated both experimentally and theoretically. The quenching technique is used to study the dynamics of structural transformation on the micro- and nanoscales. The experimentally obtained patterns of structural evolution related to the heterogeneous...

Investigation of the micro- and atomic structures for the planetary ball-milled Ni + Al mixtures has revealed existence of intermediate nano-crystalline and amorphous phases, which are not detectable by XRD analysis, but can be observed by means of HRTEM. Annealing of the milled mixtures at moderate temperature, 205-280 °C, transforms the nano-phas...

The mechanism of structural transformation during combustion of nickel nitrate (oxidizer)−glycine (fuel) system is investigated by using different in situ techniques, including time-resolved X-ray diffraction (TRXRD), thermogra-vimetric analysis (TGA), differential scanning calorimetry (DSC) with dynamic mass spectrometry (MS), and high-speed infra...

For SHS reactions in Ti-Ni-C powder blends yielding TiC-TiNi composites, investigated was the effect of initial temperature (T 0), green composition, and nanosized refractory additive (alloying agent) on combustion parameters and structure formation in combustion products. An increase in T 0 elevated combustion temperature T and burning velocity U,...

Experimental study of reactive powder blends (largely Ni + Al mixures) was made in order to reveal a role of micro to nano structural transformations during mechanical activation in improving the reactivity of activated blends. The blends were processes in planetary ball mills, and the temperature (T ig) of reaction initiation (self-ignition) was m...

Combustion joining of carbon/carbon (C/C) composites using a mixture of titanium and mechanically activated Ni/Al powders as a reactive medium is reported. A minimum preheating of the sample stack to 630 K is required to initiate the joining process. A robust crack- and pore-free joint layer (similar to 75-100 mu m in thickness), which is composed...