Combination Of Self-propagating High-temperature Synthesis Research Articles

High homogeneity and ultralow lattice thermal conductivity in Se/Te-doped skutterudites obtained by self-propagating high-temperature synthesis and pulse plasma sintering

Traditional ways to obtain homogeneous and efficient skutterudite-based thermoelectric materials usually require long processing time. In this study thermoelectric properties of Se and Te co-doped CoSb 3 bulk materials fabricated using a combination of self-propagating high-temperature synthesis and pulse-plasma sintering techniques were investigated. The proposed short-term fabrication route enabled synthesis of thermoelectric materials with high chemical homogeneity. Moreover, simultaneous doping with Se and Te beneficially influenced the electrical and thermal transport properties of the materials. As a result, an ultralow lattice thermal conductivity of 0.86 W m −1 K −1 has been attained while simultaneously doping and filling the voids in the skutterudite structure. The ultralow lattice thermal conductivity could be attributed to the unique lattice dynamics, enhanced point-defect, and electron-phonon scattering. Owing to these synergetic effects, a dimensionless figure of merit of 1.1 was obtained at 723 K. The findings show that combination of self-propagating high-temperature synthesis and pulse-plasma sintering techniques allow to fabricate chemically homogeneous and efficient thermoelectric materials as well as offer numerous advantages, such as time, energy efficiency, and potential scalability, to carry out large-scale production. • Se/Te modified skutterudites were fabricated via SHS-PPS route. • Seebeck potential mapping confirms high homogeneity of the fabricated materials. • The record low lattice thermal conductivity 0.86 W m −1 K −1 at 723 K was achieved. • Co 4 Sb 10.8 Te 0.6 Se 0.6 sample exhibits the maximum ZT of 1.1 at 723 K.

Mechanical Properties and Thermal Stability of the High-Thermoelectric-Performance Cu2Se Compound.

The Cu2Se compound possesses extraordinary thermoelectric performance at high temperatures and shows great potential for the application of waste heat recycling. However, a thermoelectric device usually undergoes mechanical vibration, mechanical and/or thermal cycling, and thermal shock in service. Therefore, mechanical properties are of equal importance as thermoelectric performance. However, the mechanical performance and stability of the Cu2Se compound during long-term service at high temperatures have rarely been reported. In this study, we systematically investigated the mechanical properties of Cu2Se compounds synthesized by three varied methods (melting (M), self-propagating high-temperature synthesis (SHS), and a combination of SHS and ultrasonic treatment (UT)) and investigated the thermal stability of the SHS-UT compound under different annealing temperatures. The SHS-UT process effectively refines the grain size from 19 μm for the melting sample to 5 μm for the SHS-UT sample. The high density of grain boundaries in the SHS-UT sample effectively dissipates the energy of crack propagation; thus, the mechanical properties are greatly improved. The compressive strength, bending strength, and Vickers hardness of the SHS-UT sample are 147 MPa, 52.6 MPa, and 0.46 GPa, respectively, which are 21.5, 16.6, and 35.3% higher than those of the melting sample, respectively. Moreover, excellent thermal stability is achieved in the compound prepared by SHS and ultrasonication at a temperature below 873 K. After annealing at temperatures up to 873 K for 7 days, the excellent thermoelectric performance of the Cu2Se compound is well maintained with a ZT value exceeding 1.80 at 873 K. However, with further increasing the annealing temperature to 973 K, the volatilization of Se and the precipitation of Cu result in the instability and significantly deteriorated thermoelectric performance of the material. This work provides an avenue for boosting the mechanical properties and commercial application of Cu2Se.

Synthesis of Ceramic and Composite Materials Using a Combination of Self-Propagating High-Temperature Synthesis and Spark Plasma Sintering (Review)

Synthesis of Ceramic and Composite Materials Using a Combination of Self-Propagating High-Temperature Synthesis and Spark Plasma Sintering (Review)

Influence of Heat Treatment on Microstructure and Properties of NiTi46 Alloy Consolidated by Spark Plasma Sintering.

Ni-Ti alloys are considered to be very important shape memory alloys with a wide application area including, e.g., biomaterials, actuators, couplings, and components in automotive, aerospace, and robotics industries. In this study, the NiTi46 (wt.%) alloy was prepared by a combination of self-propagating high-temperature synthesis, milling, and spark plasma sintering consolidation at three various temperatures. The compacted samples were subsequently heat-treated at temperatures between 400 °C and 900 °C with the following quenching in water or slow cooling in a closed furnace. The influence of the consolidation temperature and regime of heat treatment on the microstructure, mechanical properties, and temperatures of phase transformation was evaluated. The results demonstrate the brittle behaviour of the samples directly after spark plasma sintering at all temperatures by the compressive test and no transformation temperatures at differential scanning calorimetry curves. The biggest improvement of mechanical properties, which was mainly a ductility enhancement, was achieved by heat treatment at 700 °C. Slow cooling has to be recommended in order to obtain the shape memory properties.

Heretophase Ceramics in the Hf–Si–Mo–B System Fabricated by the Combination of SHS and Hot Pressing Methods

This work is devoted to the fabrication of heterophase powder and consolidated ceramics based on hafnium and molybdenum borides and silicides by combining self-propagating high-temperature synthesis (SHS) and hot pressing (HP). Composite ceramic HfB2–HfSi2–MoSi2 SHS powders are fabricated according to the magnesium-thermal reduction flowsheet from oxide raw materials, in which the combustion wave has temperatures of 1750–2119 K and rather high mss combustion rates of 8.4–9.3 g/s. The structure of synthesized SHS powders consists of relative coarse MoSi2 grains up to 10 μm in size, submicron elongated HfB2 grains mainly located inside the MoSi2 grains, and rounded Si precipitates. The composition with a lower boron concentration contains numerous polyhedral HfSi2 grains smaller than 10 μm in size. The resulting powders have an average particle size of ~6 μm with a maximal size up to 26 μm. The phase compositions of the ceramics consolidated by the HP method and synthesized SHS powders are identical. The microstructure of compact samples consists of faceted elongated HfB2 grains 0.5–10.0 μm in size, polyhedral HfSi2 and MoSi2 grains up to 8–10 μm in size, and silicon interlayers. The consolidated ceramics have a high structural and chemical homogeneity, low residual porosity of 1.1–1.7%, high hardness of 11.7–12.6 GPa, and thermal conductivity of 62–87 W/(m K).

Heterophase ceramics in the Hf–Si–Mo–B system obtained by a combination of SHS and hot pressing methods

The paper focuses on obtaining heterophase powder ceramics and consolidated ceramics based on borides and silicides of hafnium and molybdenum by combining the methods of self-propagating high-temperature synthesis (SHS) and hot pressing (HP). Composite ceramic SHS powders HfB2–HfSi2–MoSi2 were obtained according to the scheme of magnesium-thermal reduction from oxide raw materials where the combustion wave is characterized by temperatures of 1750–2119 K and high mass combustion rates of 8,4– 9,3 g/s. The structure of synthesized SHS powders consists of relatively large MoSi2 grains up to 10 μm in size and submicron elongated HfB2 grains located mainly inside the MoSi2 grains and rounded Si precipitates. The composition with a lower concentration of boron contains a large number of polyhedral HfSi2 grains with a size of less than 10 μm. The resulting powders are characterized by an average particle size of ~6 μm with a maximum size up to 26 μm. Phase compositions of ceramics consolidated by the HP method and SHS synthesized powders are identical. The microstructure of compact samples consists of faceted HfB2 elongated grains 0,5– 10,0 μm in size, polyhedral HfSi2 and MoSi2 grains up to 8–10 μm in size and silicon interlayers. Consolidated ceramics has a high structural and chemical homogeneity, low residual porosity of 1,1–1,7 %, high hardness of 11,7–12,6 GPa and thermal conductivity of 62–87 W/(m·K).

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

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

One-step ultra-rapid fabrication and thermoelectric properties of Cu2Se bulk thermoelectric material.

Cu2Se is a promising material for high temperature thermoelectric energy conversion due to its unique combination of excellent electronic properties and low thermal conductivity owing to its ionic liquid characteristics at high temperature. In this paper, fully dense single-phase bulk Cu2Se material was prepared by the combination of self-propagating high-temperature synthesis (SHS) with in situ quick pressing (QP) for the first time. This new approach shortens the duration of the synthesis from days to hours compared to conventional preparation methods. SHS-QP technique is an ultra-fast preparation method, which utilizes the heat released by the SHS reaction and an external applied pressure to achieve the synthesis and densification of materials in one-step. The ultra-fast process of the SHS-QP technique enables the fabrication of single-phase Cu2Se bulk materials with relative density of over 98% and with precise control over the stoichiometry owing to the ability to suppress the Se vapor during the reaction. The SHS-QP prepared Cu2Se samples exhibit excellent thermoelectric figure of merit, ZT ∼ 1.5 at 900 K, which is comparable to those of Cu2Se materials prepared by conventional methods. This study opens a new avenue for the ultra-fast and low-cost fabrication of Cu2Se thermoelectric materials.

CoCrFeNi Multi-principal Element Alloy Prepared Via Self-propagating High-Temperature Synthesis Plus Investment Casting Method

A CoCrFeNi multi-principal element alloy was successfully prepared via the combination of self-propagating high-temperature synthesis and investment casting. The phase identification, the as-cast microstructure, and the solidification phenomena were investigated. Unlike the dendrite morphology obtained by arc melting, cellular growth in the as-cast alloy was observed as a consequence of the rapid solidification. The solidification process is discussed with regard to the rate of advance of the liquid–solid interface, the equilibrium melting range, and the interface temperature gradient.

Surface strengthening aluminum alloy by in-situ TiC-TiB2 composite coating

An integration technology was employed to prepare TiC-TiB2 strengthening coating on aluminum alloys, with the combination of Self-propagating high-temperature synthesis (SHS) and Vacuum-expendable pattern casting (VEPC). During the VEPC process, the Ti-C-B4C-TP SHS reaction was ignited by molten Al alloy, resulting in the simultaneous obtainment of TiC-TiB2 SHS coating with the cast Al alloy. Specifically, Teflon (PTFE) as reaction promoter was introduced into the SHS system to guarantee the reaction to be ignited successfully. With 3.8 wt% PTFE addition, homogeneous and dense TiC-TiB2 coating microstructure was obtained. Compared to the matrix, the hardness of the surface coating increased from 80 HB to 284 HB. And, the weight loss decreased from 533 mg to 52 mg at load of 20 N, indicating the significant improvement of wear resistance. In addition, a comprehensive bonding strength of 160 MPa was achieved. The proposed method for preparing hard coating on Al alloys broadens their industry application, where higher hardness and better wear resistance are required.

High-temperature ceramic MoSi2 – MoB – HfB2 obtained by the combination of self-propagating high-temperature synthesis and hot pressing

High-temperature ceramic MoSi2 – MoB – HfB2 obtained by the combination of self-propagating high-temperature synthesis and hot pressing

Ultrafast Synthesis and Thermoelectric Properties of Mn1+xTe Compounds

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

Combination of reaction synthesis and Spark Plasma Sintering in production of Ti-Al-Si alloys

This work is devoted to the preparation of alloys based on intermetallic compounds in Ti-Al-Si system by powder metallurgy using Self-propagating High-temperature Synthesis (SHS). Since samples after SHS are very porous, in order to reduce the porosity, a combination of SHS, milling, and Spark Plasma Sintering (SPS), has been here tested as a complex production technology. Selected mechanical properties of consolidated samples (hardness, fracture toughness) and tribological properties (abrasive wear resistance) were determined. The microstructure of compacted Ti-Al-Si alloys is almost non-porous with the combination of titanium aluminides and titanium silicides. The alloys achieve good mechanical properties except for the fracture toughness.

Comparison of Ni-Ti-Si Alloy Prepared by Various Powder Metallurgy Routes

This work describes three ways of preparation of Ni-Ti-Si shape memory alloy by powder metallurgy methods. The self-propagating high-temperature synthesis, combination of self-propagating high-temperature synthesis, milling and spark plasma sintering and mechanical alloying with following spark plasma sintering were applied to Ni-Ti-Si powder mixture. The differences in microstructure, phase composition, transformation temperatures and mechanical properties were observed and at the same time these properties were compared with other Ni-Ti and Ni-Ti-X alloys.

Development of an in-situ multi-component reinforced Al-based metal matrix composite by direct metal laser sintering technique — Optimization of process parameters

In the present investigation, an in-situ multi-component reinforced aluminum based metal matrix composite was fabricated by the combination of self-propagating high-temperature synthesis and direct metal laser sintering process. The different mixtures of Al, TiO2 and B4C powders were used to initiate and maintain the self-propagating high-temperature synthesis by laser during the sintering process. It was found from the X-ray diffraction analysis and scanning electron microscopy that the reinforcements like Al2O3, TiC, and TiB2 were formed in the composite. The scanning electron microscopy revealed the distribution of the reinforcement phases in the composite and phase identities. The variable parameters such as powder layer thickness, laser power, scanning speed, hatching distance and composition of the powder mixture were optimized for higher density, lower porosity and higher microhardness using Taguchi method. Experimental investigation shows that the density of the specimen mainly depends upon the hatching distance, composition and layer thickness. On the other hand, hatching distance, layer thickness and laser power are the significant parameters which influence the porosity. The composition, laser power and layer thickness are the key influencing parameters for microhardness.

Wear-Resistant Coatings Prepared by Combination of SHS and Lost Foam Casting

With a brief introduction of self-propagating high-temperature synthesis (SHS) and lost foam casting (LFC), there goes an issue about the simultaneous produce of casting and wear-resistant coating by the combination of such two techniques, which has a positive significance for energy conservation and sustainable development. Through the statement of some common hard phases generated by SHS such as TiC, WC and TiB2, it indicated that the hard phases had a good combination with iron, and thus demonstrated the feasibility of the simultaneous produce of casting and wear-resistant coating. In the end, the development and the trend of the future about this issue has been drawn.

Formation of composite coatings based on titanium carbide via electrospark alloying

This work concerns studying the coatings prepared via electrospark alloying. To deposit the coatings, we used STIM-2/30 electrodes derived from a combination of self-propagating high-temperature synthesis (SHS) and extrusion. It was found that the composite coating is formed from titanium carbides and a solid solution of nickel in iron and contains both large (4–5 μm) and small carbides (less than 1 μm); in addition, large grains of titanium carbide are formed in the central portion of the coating, and the grain size decreases to 100 nm while approaching the transition zone. Large grains of titanium carbide in the coating consist of dispersed carbides with sizes less than 1 μm. It is determined that the composition of the substrate has an effect on the size of the transition and diffusion zones. It ranges from 17 μm for steel 9KhSA to 26 μm for steel 20; that is, the higher the degree of alloying, the less the depth of the modified layer.

Cast Intermetallic Alloys by SHS Under High Gravity

Intermetallides are known for their high strength, heat/corrosion resistance, and unique friction properties. Nickel-, cobalt-, and titanium-based intermetallic alloys are being used as superalloys for gas-turbines, aerospace jets, pressure vessels, heat-resistant coatings [1], and multi-purpose catalysts [2, 3]. As is known, a wide variety of refractory materials, including intermetallics, can be fabricated by the methods of so-called SHS metallurgy which is a combination of Self-propagating High-temperature Synthesis (SHS) and metallothermy [4–6]. Since the combustion temperatures are extremely high (2500–3500 K), the combustion products (alloys and oxides) appear in the their liquid state. In this communication we report on the synthesis of some new Ni-, Co-, and Ti-based cast alloys by SHS metallurgy in conditions of normal gravity and in the field of centrifugal forces.

Synthesis and properties of cast carbide alloys

A process for synthesizing materials based on a combination of self-propagating high-temperature synthesis and thermal reduction is developed. Some theoretical aspects of the synthesis and the special features of the combined processes as applied to microheats are considered. New cast carbide alloys (known as carbide steels) are synthesized. The parameters of the yield of cast alloy from a blend are determined experimentally. The microstructure, the chemical composition, and the hardness of the synthesized alloys are determined.

Spark plasma sintering of UHTC powders obtained by self-propagating high-temperature synthesis

Fully dense ZrB2–SiC and HfB2–SiC ultra-high-temperature ceramics (UHTCs) composites are fabricated by first synthesizing via self-propagating high-temperature synthesis (SHS) the composite powders from B4C, Si, and Zr or Hf reactants, and subsequently consolidating the product by spark plasma sintering (SPS) without the addition of any sintering aid. It was found that the SHS technique leads to the complete conversion of reactants to the desired products and the SPS allows for the full consolidation (>99.5% relative density) under the optimal operating conditions of 1800 °C/20 min/20 MPa and 1800 °C/30 min/20 MPa, for the cases of ZrB2–SiC and HfB2–SiC, respectively. Based on the results reported in this work, it can be stated that the combination of SHS and SPS methods represents a particularly rapid and convenient preparation route (lower sintering temperature and processing time) for UHTCs as compared to the techniques available in the literature for the fabrication of analogous products.