Self-propagating High-temperature Synthesis Research Articles

Annealing of a (Hf0.2Ta0.2Ti0.2Nb0.2Zr0.2)C high-entropy ceramic up to 2100 °C: In-situ removal of oxide impurities and microstructural modification

A (Hf0.2Ta0.2Ti0.2Nb0.2Zr0.2)C high-entropy ceramic (HEC) prepared by the combination of self-propagation high-temperature synthesis (SHS) and spark plasma sintering (SPS), was annealed at 2000 °C and 2100 °C in order to remove the impurities and modify the microstructure. The microstructure and phase composition of the HECs were characterized by X-ray diffraction, scanning electron microscopy, and transmission electronic microscopy. Moreover, the mechanical properties were examined by nanoindentation. It is found that the as-prepared HEC contains the impurities of (Hf, Zr)O2 and amorphous carbon. The oxide and amorphous carbon can be in-situ removed by further carbothermal reduction reaction during the annealing, followed by dissolution of the reduction products into the HEC phase. In other words, the heat treatment can significantly improve the microstructure of the HEC by the removal of impurity and uniform distribution of the compositional elements. In addition, the annealing at 2000 °C and 2100 °C enhance the mechanical properties of the HEC. The nano-hardness, elastic modulus and fracture toughness are 34.04±1.49 GPa, 525.82±14.51 GPa and 3.60±0.55 MPa m1/2, respectively, for the HEC annealed at 2100 °C for 1 h, which are 1.13–2.08 times of the as-prepared HEC.

The Influence of Ultrasonic Activation on Microstructure, Phase Transformation and Mechanical Properties of Porous Ni-Ti Shape Memory Alloys via Self-Propagating High-Temperature Synthesis.

Porous Ni-Ti shape memory alloys (SMAs) have been widely studied in biomedical and engineering applications. Porous Ni-Ti SMAs were obtained via self-propagating high-temperature synthesis (SHS), and their microstructure, phase transformation, and mechanical properties were investigated. This article presents the results of a study of changes in the microstructure, phase transformation, and mechanical properties of porous Ni-Ti SMAs when Ni and Ti metal powders were preliminarily subjected to ultrasonic activation at various periods. It was determined that the porosity of the obtained alloy samples was 62-68 vol%. The microstructure was composed of the main matrix Ni-Ti phase and the accompanying Ti and Ti2-Ni phases. The results show that the hardness 34.1-86.8 HB and elastic modulus 4.2-10.8 GPa increased with an increase in the ultrasonic activation time of the samples. The phase transformation temperature of the Ni-Ti shape memory alloy remained almost unchanged under the influence of ultrasonic treatment.

Effects of TiC, Si, and Al on Combustion Synthesis of Ti3SiC2/TiC/Ti5Si3 Composites.

The fabrication of Ti3SiC2 from TiC-containing reactant compacts was investigated by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS). The initial sample composition was formulated based on (3 - x)Ti + ySi + (2 - x)C + xTiC + zAl, with stoichiometric parameters of x from 0 to 0.7, y = 1.0 and 1.2, and z = 0 and 0.1. For all samples studied, combustion was sufficiently exothermic to sustain the reaction in the SHS manner. Due to the dilution effect of TiC, combustion wave velocity and reaction temperature substantially decreased with TiC content. When compared with the TiC-free sample, the TiC-containing sample facilitated the formation of Ti3SiC2 and the TiC content of x = 0.5 produced the highest yield. Excess Si (y = 1.2) to compensate for the evaporation loss of Si during combustion and the addition of Al (z = 0.1) to promote the phase conversion were effective in improving the evolution of Ti3SiC2. All final products were composed of Ti3SiC2, TiC, and Ti5Si3. For the TiC-containing samples of x = 0.5, the weight fraction of Ti3SiC2 increased from 67 wt.% in the sample without extra Si and Al to 72 wt.% in the Si-rich sample of y = 1.2 and further up to 85 wt.% in the Si-rich/Al-added sample of y = 1.2 and z = 0.1. As-synthesized Ti3SiC2 grains were in a thin plate-like shape with a thickness of 0.5-1.0 μm and length of about 10 μm. Ti3SiC2 platelets were closely stacked into a layered structure.

Microstructure evolution of Ni-Cr-Mo superalloy fabricated by microwave-assisted combustion synthesis

In this study, the microwave-assisted self-propagation high-temperature synthesis (SHS) technique was utilized to successfully synthesize the Nistelle super C commercial alloy with the chemical composition of Ni59Cr23Mo18. The precursors used for this purpose were NiO, Cr2O3, and MoO3 oxide compounds. The thermodynamicall calculations were carried out by the Factsage software. The synthesized alloys' chemical composition, phase, and microstructure were evaluated by induction-coupled plasma, X-ray diffraction, optical microscopy, and scanning electron microscopy. The findings revealed considerable residual silicon in the final product due to using Si as the reducing agent. The presence of residual Si in the chemical composition led to forming a eutectic Niγ-FCC+ Mo2Ni3Si microstructure in the alloys produced by the alumino/silicothermic method. The high silicon content in the excess Al-containing sample led to forming of proeutectic Mo2Ni3Si phases with a petaloid morphology. Besides, this alloy displayed small islands of the interdendritic nickel silicide phase. Conversely, the aluminothermic sample showed a nearly single-phase structure with low amounts of the precipitates of chromium and molybdenum-rich phases. The phase diagram plotted for this sample indicated that the precipitates were probably TCP phases like σ and P. In all the samples, the segregation of Mo occurred significantly, while Cr was distributed almost uniformly in all regions. The formation of the Mo2Ni3Si intermetallic phase resulted in the significant segregation of Mo and depletion of the Niγ-FCC matrix from this element. However, the segregation of Mo was also observed near the grain boundaries in the single-phase sample. The results showed that the dissolution of the alloying elements, especially molybdenum, caused severe offset in some peaks of the Niγ-FCC XRD pattern.

Oxygen blocking enhancement of HfB2-SiC coating using HfB2-HfSi2 alloyed composite powders by self-propagating high-temperature synthesis

To suppress the oxidation loosening of HfB2-SiC coating, the HfB2 was alloyed with HfSi2 in the form of composite powders through self-propagating high-temperature synthesis (SHS) technique, which was then used to prepare HfB2-HfSi2-SiC coatings. Compared to the 60HfB2-SiC coating, the 60(HfB2-HfSi2)SHS-SiC coating exhibited lower oxidation activity and better inert oxygen blocking at 1700 °C. The addition of HfSi2 promoted the homogenization of the Hf-oxides distribution on the glass layer and the formation of the protective phase HfSiO4, further inhibiting oxygen diffusion. The 60(80HfB2-20HfSi2)SHS-SiC coating exhibited optimal oxygen blocking protection after oxidation at 1700 °C, with 87.96% and 92.33% reductions in oxygen permeability and carbon loss rate, respectively.

Self-Propagating High-Temperature Synthesis and Consolidation of MoSi2–MoB Heterophase Ceramics Alloyed with ZrB2

Self-Propagating High-Temperature Synthesis and Consolidation of MoSi2–MoB Heterophase Ceramics Alloyed with ZrB2

A practical high-energy lithium-ion capacitor enabled by multiple conducting bridges triggered electrode current reallocation

Lithium-ion capacitors (LICs), consisting of a battery-type anode and capacitive cathode, hold great promise for achieving high-energy and high-power densities. However, the sluggish migration of electrons and ions in the anode hinders the attainment of the "dual-high" target. To circumvent this obstacle, we propose a novel strategy employing multiple conducting bridges to augment charge dynamics for the hard carbon (HC) anode and activated carbon (AC) cathode. In this approach, graphene nanosheets are deposited in-situ via a self-propagating high-temperature synthesis methodology to establish connections between isolated HC (or AC) powders. Subsequently, carbon nanotubes are introduced to fill the inter-particle gaps, forming a network of multiple conducting bridges. Through the experimental investigation and finite elemental simulation, we demonstrate that this approach triggers prompt inter-particle electrons and ions migration, resulting in a homogeneous redistribution of the current at the electrode scale. This engenders a substantial enhancement in electronic conductivity (∼3 fold), and a significant improvement in the ion diffusion. Consequently, we fabricate a 1000 F LIC pouch cell displaying a state-of-the-art device performance of 30.3 W h kg−1 and 8.1 kW kg−1, coupled with a remarkable cycle life of 87.9% retention after 10,000 cycles. This study thus represents a distinctive avenue for regulating charge dynamics at the electrode scale and optimizing the performance of practical LICs.

Research on Self-Propagating High-Temperature Synthesis of Ceramic Matrix Composites

Research on Self-Propagating High-Temperature Synthesis of Ceramic Matrix Composites

Liquid matrix SHS manufacturing and heat treatment of Al–Mg composites reinforced with fine titanium carbide

Aluminum matrix composites reinforced with ultra-fine refractory titanium carbide feature a unique combination of properties. They are promising structural materials. Self-propagating high-temperature synthesis (SHS) is an affordable and energy-saving composite making process. It involves the exothermic reaction between titanium and carbon (or their compounds) directly in the melt. We studied the properties of SHS composites based on the AMg2 and AMg6 commercially available alloys reinforced with 10 wt.%TiC. We investigated the macroand microstructure of the samples with XRD and EDS analysis. It was found that the β-phase is separated from α-solid solution of aluminum as early as the air cooling stage. We conducted experiments aimed at studying the effects of additional heating on the sample structure and properties and found the optimal temperature and time values. We also proposed a phenomenological model of the structural transformation sequence. We compared the physical, mechanical, and manufacturing properties and corrosion resistance of the original cold-hardened AMg2N and AMg6N alloys and the composites before and after heat treatment. It was found that additional heating reduces porosity and maintains electrical conductivity. It was also found that the compressive strength and relative strain of the composite based on the AMg2 alloy change insignificantly, while for the AMg6-based composite the reduction is more significant. Heat treatment increases the composite hardness while maintaining sufficient plastic deformation. It is confirmed by the measured values of the relative strain and the reduction ratio close to that of the original matrix alloys. It was also found that the composites retain high resistance to carbon dioxide and hydrogen sulfide corrosion.

Use of Few-Layer Graphene Synthesized under Conditions of Self-Propagating High-Temperature Synthesis for Supercapacitors Applications.

Graphene nanostructures (GNSs) are among the most promising materials for producing supercapacitors. However, GNSs are still not used in creating supercapacitors due to the impossibility of obtaining large volumes of high-quality material at an acceptable cost. In our previous works, we have shown the possibility of synthesizing large volumes of few-layer graphene (FLG, the number of layers is not more than five) from cyclic biopolymers under conditions of self-propagating high-temperature synthesis (SHS). Using the SHS process makes it possible to synthesize large volumes of FLG without Stone-Wales defects. This work is devoted to the study of the possibility of using FLG synthesized under the conditions of the SHS process in the creation of supercapacitors. It was found that the synthesized FLG makes it possible to obtain better results than using classical materials, namely activated carbon (AC). It was found that the sample based on FLG had a higher specific capacitance of 65 F × g-1 compared to the sample from AC, the specific capacitance of which was 35 F × g-1; for a speed of 5 mV × s-1, these values were170 and 64 F × g-1, respectively. The drop in capacitance over 1000 cycles was 4%, indicating a sufficiently high FLG stability, allowing us to consider FLG as a prospective material for use in supercapacitors.

Influence of Layer-Thickness Proportions and Their Strength and Elastic Properties on Stress Redistribution during Three-Point Bending of TiB/Ti-Based Two-Layer Ceramics Composites

A mathematical model was developed to determine the order of failure of layers in a two-layer ceramics composite and to determine the conditions for achieving the maximum limit load under three-point loading. The model was set in the space of three “bilayer parameters”: the ratio of the thickness of the lower layer to the whole thickness of the beam, the ratio of Young’s moduli of the lower layer to the upper layer, and the ratio of flexural strengths of the materials of the lower layer to the upper layer. The adequacy of the model obtained was confirmed by experimental results on the three-point bending of the experimental specimens. The experimental samples were two-layer composites consisting of a cermet layer TiB/Ti and a layer of α-Ti. The samples were obtained by free self-propagating high-temperature synthesis (SHS) compression and with varying their thickness. The results obtained make it possible to predict in advance which layer, based on the specific bilayer parameters, will trigger the brittle fracture mechanism as well as to set the maximum destructive load of bilayer composites.

Production of Zirconium-Niobium Alloys for Nuclear Reactors Fuel Rods via SHS Process

This article presents the results of studies of the self-propagating high-temperature synthesis (SHS) for obtaining zirconium alloys with niobium by the method of calcium-thermal reduction of nuclear-grade zirconium tetrafluoride in the presence of niobium powder. The optimal heating temperature of the initial charge and the methods of charge mixture with different calcium content were determined. The safety of the SHS process is ensured by the formation of an optimal combustion front of the mixture to remove the released high-pressure gases. A setup for the furnace reduction of zirconium alloys with charge preheating, discharge of molten products into molds of various designs, and control of the time and rate of slag and alloy crystallization has been tested. The required performance of the installation, the degree of transition of zirconium from salt into the alloy, and the purity, structure, and uniformity of the alloy were achieved.

Synthesis of low-cost Ti3AlC2-Ti2AlC dual MAX phase with high-electrical conductivity using economical raw materials and novel compositions

Titanium-aluminum-carbide (Ti3AlC2-Ti2AlC) dual MAX phases produced with mechanical alloying (MA) of raw materials followed by a self-propagating high-temperature synthesis (SHS) approach. The low-cost dual MAX phases have been manufactured from commercial powders of Ti, Al, TiC, and agricultural wastes-based activated carbon (AC). The effects of Ti/Al/C mole ratios and carbon sources with various prices on the surface morphology, microstructure, chemical structure, and electrical conductivity of dual MAX phases have been investigated. All synthesized MAX phases have acceptable surface morphology with hexagonal particles and high purity (78.87–99.26 %). The FESEM, EDS, XRD, and XPS analyses revealed that the AC and TiC are appropriate as carbon sources for the manufacture of Ti3AlC2-Ti2AlC dual and Ti3AlC2 single MAX phases, respectively. Moreover, the purity of the MAX phases can be controlled with Al/C ratios in raw materials composition. The AC-produced Ti3AlC2-Ti2AlC dual MAX phase with 3Ti:1.25Al:2 C displayed the highest electrical conductivity (5.631 ×106 S/m), while TiC-produced Ti3AlC2 single MAX phase with 3.25Ti:2.2Al:2 C composition has comparable electrical conductivity (2.203 ×106 S/m) and highest purity (99.26 %). This study makes available an advantageous method for low-cost synthesis of high-purity MAX phases. These understandings open up a pathway to improve synthesis protocols for low-cost and high-conductivity MAX phases in the future.

An overview of the synthesis of silicon carbide–boron carbide composite powders

Abstract Recently, silicon carbide–boron carbide composite ceramics have attracted more and more attention. The most important achievements of the silicon carbide–boron carbide composite ceramics should be applied in terms of mechanical, physical, and chemical for use in various advanced industries, such as armor plates, nozzles, abrasive tools, mechanical seals, etc. To prepare silicon carbide–boron carbide composite ceramics with good performance, the synthesis of silicon carbide–boron carbide composite powders is the basis. The synthesis approaches of silicon carbide–boron carbide composite powders are systematically summarized in this review, including ball milling, high-energy ball milling, self-propagating high-temperature synthesis (SHS), and sol–gel. Particularly, nanosized silicon carbide–boron carbide composite powders can be in situ synthesized by high-energy ball milling, SHS, or sol–gel. When commercial silicon carbide and/or boron carbide powders are used as raw materials to synthesize silicon carbide–boron carbide composite powders, the pretreatment of acid etching can significantly remove oxide layers existing on the surfaces of initial powders.

Combustion synthesis of ultra-high-temperature solid solutions (ZrxNb1-x)B2. Part 1: The mechanisms of combustion and structure formation

The self-propagating high-temperature synthesis (SHS) in Zr–Nb–B system has been thoroughly investigated with a focus on its macrokinetics and phase formation mechanisms. The activation energies were determined by analyzing the relationship between the combustion rate and temperature. For compositions NbB2–40%ZrB2 and NbB2–50%ZrB2, the increase in the initial temperature has resulted in a significant change in combustion rate's dependence on temperature, signifying a possible shift in the reaction mechanisms. The quenched combustion front technique (QCF) method in conjunction with thermodynamic and ab initio calculations were used to analyze the sequence of phase formation events, including the formation of niobium and zirconium borides through gas transport reactions involving volatile boron suboxide BO in the heating zone, followed by the emergence of a zirconium-boron melt in the combustion zone and formation of main fraction of niobium and zirconium borides. Interactions between the primary niobium and zirconium borides and the melt result in the formation of solid solutions; however, at sub-optimal combustion conditions multiple non-equilibrium solid solutions are retained in the products. To address this issue, a machine learning model was developed, attaining coefficients of determination (R2) of 89% for combustion temperature and rate predictions, thus enabling the fine-tuning of macrokinetic parameters of the SHS process in the system.

COLD UNIAXIAL PRESSING OF COMOSITE MATERIALS BASED ON PTFE WITH FUNCTIONAL ADDITIVES TIC AND TIB2

In the current work a solid-phase technology of composite materials based on polytetrafluoroethylene (PTFE) with functional additives is investigated. The mentioned additives are titanium carbides and diborides was obtained by self-propagating high-temperature synthesis (SHS). The process of pressing bulk density composite powders into compact blanks in a special mold by loading in a constant speed mode has been studied. Rheological strainstress curves were obtained. The time when a progressive increasing of stress inside the sample was determined. The results of these studies were compared with data for samples without additives (pure PTFE), as well as for compositions with basalt fiber. It is shown that at stresses 171-177 MPa it is possible to achieve a density corresponding to the calculated compact density of 2.24-2.25 g/cm3. The dependence of density variation over the volume of compact specimens has been studied, and a comparative analysis of the compressibility moduli G under uniaxial cold pressing has been carried out.

Coatings Prepared by Electro-Spark Alloying with SHS Electrode Materials Based on Ti-B-Fe-AlN

In this work, the features of the phase composition, structures, and properties of coatings obtained on a high-speed steel substrate (steel R6M5) were studied. The coatings were prepared using the ESA method (electro-spark alloying). Electrode materials prepared through self-propagating high-temperature synthesis (SHS) based on (Ti-B-Fe)xAlN with the addition of nanosized AlN particles in the amount of x = 0.5, 10, 15 wt % were used as electrodes. The structure, phase composition, and physical and mechanical properties of the SHS electrode materials are reported. It was found that the coatings inherited the structure of the SHS electrode material and formed two characteristic zones for x = 0 and three zones for x = 5, 10, 15. The surface hardness of the substrate made of the high-speed steel R6M5 with the developed coatings was found to increase up to five times compared to the uncoated substrate. It was found that the wear resistance of the samples with the coating was four to six times higher than that of uncoated samples.

Microstructure and tribocorrosion behaviors of Fe–Al–Ti coatings prepared by the aluminothermic reaction

To improve the tribocorrosion resistance of 316L stainless steel in acidic media, Fe–Al–Ti coatings were prepared on 316L substrate by self-propagating high-temperature synthesis (SHS) using an aluminothermic reaction. The effects of Ti content on the tribocorrosion behaviors of Fe–Al–Ti coatings in 0.5 mol/L H2SO4 solutions were investigated. The Fe–Al–Ti coatings exhibited a multi-phase microstructure. The open circuit potential (OCP) of the Fe–Al–Ti coatings and 316L substrate decreased significantly with the onset of sliding, indicating a strong wear-corrosion synergistic effect. The hardness and tribocorrosion resistance of Fe–Al–Ti coatings increase with increasing the Ti content. The tribocorrosion volume loss of the Fe–25Al–25Ti coating was about one order of magnitude lower than that of the 316L substrate. The Fe–25Al–25Ti coating was more suitable as a tribocorrosion-resistant material than the 316L substrate.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ ВИДА ФЛЮСА НА СИНТЕЗ ЛИТОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА АМг2-TiC

The results are presented devoted to the study of the influence of flux type on the process of self-propagating high-temperature synthesis (SHS) of titanium carbide in aluminum flux, as well as on the structure and properties of the resulting composite material AMg2-TiC. During the research, the most promising halide salts for use as fluxes were analyzed and selected: Na3AlF6, Na2TiF6, K2TiF6, K1-3AlF4-6 (Nocolok ™ made in Germany). During the experimental synthesis, the most active signs of an exothermic reaction between titanium and carbon powders in the flux were recorded having a flux additive Na2TiF6. Then microstructural, micro X-ray spectral analysis and quantitative X-ray phase analyses were carried out, according to their results it was found out that the most homogeneous distribution in terms of material volume, the maximum content of a high dispersion of carbide phase close to the stoichiometric composition is also observed in samples obtained with the use of Na2TiF6 salt. The synthesized samples of the composite material were assessed according to physical and mechanical characteristics: hardness, porosity and electrical conductivity. It was found out that composite samples with an optimal structure are also characterized by a decrease in porosity by 1.33%, an increase in hardness by 94 MPa and a reduction of electrical conductivity by 0.3 MSm/m compared with samples obtained using other fluxes. According to the results of the studies carried out, Na2TiF6 flux is recommended for use to implement SHS composite AMg2-TiC material.

Structure of Nb-Si-C-based composite obtained by self-propagating high-temperature synthesis

Alumothermic self-propagating high-temperature synthesis was used for obtaining 2Nb-1Si-1C composite material. The morphology, structure and phase composition of the composite were studied by X-ray diffraction and scanning electron microscopy. It was found that γ- Nb5Si3, NbC, NbSi2 phases were formed in the sample.