Self-propagating High-temperature Synthesis Products Research Articles

Correlation of reactant particle size on residual stresses of nanostructured NiAl generated by self-propagating high-temperature synthesis

This investigation analyzed the effect of reactant particle size on the stress development characteristics of NiAl synthesized through self-propagating high temperature synthesis. Four sample combinations of NiAl were synthesized based on initial particle diameters of the reactants: (i) 10 μm Al and 10 μm Ni (S1), (ii) 10 μm Al and 100 nm Ni (S2), (iii) 50 nm Al and 10 μm Ni (S3), and (iv) 50 nm Al and 100 nm Ni (S4). Characterization of NiAl was performed by parallel comparison of the distribution of residual stresses of the samples prior to and after the reaction. Residual stresses were quantified using x-ray diffraction. Upon characterization it was found that combinations S1, S2, and S3 exhibited tensile residual stresses, while combination S4 exhibited compressive residual stresses. Statistical analysis confirmed that self-propagating high temperature synthesis products derived from nanoparticle reactant sizes exhibited compressive residual stresses offering improved fatigue resistance in composite production.

In Situ Synthesis of Heat Resistant Gradient Composite on Steel Surface

A heat resistant gradient composite was synthesized in situ on steel with the self-propagating high temperature synthesis (SHS) reaction of 3Ni-Al-Ti-C system during casting. The phases, microstructure, and composition of the composite were analyzed by using an X-ray diffractometer (XRD), and a scanning electron microscope (SEM) coupled with an energy-dispersive X-ray spectroscope (EDS). The formation mechanism of the composite is also discussed. TiC/Ni 3 Al/steel gradient composite is achieved by forming the gradient distributions of Fe, Ni, and Al, accompanied with the gradient variation of the microstructure from TiC/Ni 3 Al, to TiC/Ni 3 Al/steel, and to steel. The composite is in situ synthesized through whole reaction of 3Ni-Al-Ti-C system in liquid steel and densification procedure, and the liquid steel infiltrates into pores in the SHS product and forces liquid Ni 3Al to form self-compaction further.

Development of a hard nano-structured multi-component ceramic coating by laser cladding

The present paper reports laser-assisted synthesis of a multi-component ceramic composite coating consisting of aluminum oxide, titanium di-boride and titanium carbide (Al 2O 3–TiB 2–TiC). A pre-placed powder mixture of aluminum (Al), titanium oxide (TiO 2) and boron carbide (B 4C) was made to undergo self-propagating high-temperature synthesis (SHS) by laser triggering. Laser subsequently effected cladding of the products of SHS on the substrate. The effect of laser scanning speed on the hardness, microstructure and phase composition of the composite coating was investigated. The coating exhibited an increase in hardness and a decrease in grain size with increase in laser scanning speed. A maximum micro-hardness of 2500 HV 0.025 was obtained. X-ray diffraction (XRD) of the top surface of the coating revealed the presence of aluminum oxide (Al 2O 3), titanium di-boride (TiB 2) and titanium carbide (TiC) along with some non-stoichiometric products of the Ti–Al–B–C–O system. Field emission gun scanning electron microscopy (FESEM) and high-resolution transmission electron microscopic (HRTEM) analysis revealed some nano-structured TiB 2 and Al 2O 3, which are discussed in detail.

Study of the synthesis mechanism and magnetic properties of quasi-nano-sized Ba–Mg ferrite powders formed by self-propagating high-temperature synthesis

Abstract Quasi-nano-sized BaxMg1−xFe2O4 ferrite powders were prepared by using self-propagating high-temperature synthesis (SHS) combined with mechanical milling. The combustion temperature and the propagating rate of the SHS reaction were in the range of 930–1115 K and about 4.5–6.4 mm/s, respectively. X-ray and neutron-beam analysis showed that the SHS products were Ba0.38Mg0.62Fe2O4 and Ba0.42Mg0.58Fe2O4, respectively. The final ferrite powder size after mechanical milling was less than about 150 nm. The maximum magnetization (Ms), the residual magnetization (Mr) and the coercive force (iHc) of quasi-nano-sized BaxMg1−xFe2O4 significantly depend on the initial molar ratio of BaO to MgO of the reactant powder mixture and the oxygen partial pressure during the SHS reaction. The complex permeability decreased with the increase of the frequency, and its real value ( μ r ′ ) reached the peak value at about 0.6 GHz. The SHS mechanism includes the competitive reduction reaction between barium and magnesium oxides, which influences the non-stoichiometric numbers and the magnetic properties of the ferrites.

Influence of Al addition on the products of self-propagating high-temperature synthesis of Al–Ti–Si system

Influence of Al addition on the products of self-propagating high-temperature synthesis (SHS) reaction in Al–Ti–Si system is investigated. When Al content is 0 wt.%, the product only consists of Ti 5Si 3. When the Al addition is varied over the range of 5–15 wt.%, the TiAl 3 phase appears along with the Ti 5Si 3 phase. Besides Ti 5Si 3 and TiAl 3, the transient phase Ti 5Si 4 is also detected in the final products when Al content increases over the range of 20–40 wt.%. However, both the Ti 5Si 3 and Ti 5Si 4 phases disappear completely when Al content further increases to 50 wt.%; only TiAl 3 phase and trace of Al exist in the final products. Moreover, increase in Al content causes a decrease in Ti 5Si 3 and an increase in TiAl 3 amount, which indicates that Al not only serves as a diluent but also participates in the SHS reaction process. Furthermore, the solubility of Si in TiAl 3 increases significantly with Al addition increasing, while that of Al in Ti 5Si 3 mainly depends on the Al content in the Al–Ti–Si system. In addition, the Al incorporation has a great effect on the microstructure formation and evolution of the SHS reaction products. When Al content is less than 15 wt.%, the final product mainly consists of Ti 5Si 3; however, which changes into Ti 5(Si,Al) 3 as Al content increases to 20–25 wt.%, and then turns into another solid solution Ti(Al,Si) 3 when Al content further increases to 30–50 wt.%. Consequently, the microstructure evolution may be summarized as follows: Ti 5Si 3 → Ti 5(Si,Al) 3 → Ti(Al,Si) 3.

Self-propagating high-temperature synthesis with post-heat treatment of La1−xSrxFeO3 (x=0–1) perovskite as catalyst for soot combustion

Abstract La1−xSrxFeO3 (x = 0–1) perovskite, Sr-substituted LaFeO3, was prepared by Self-propagating high-temperature synthesis (SHS) and its catalytic activity for soot combustion was experimentally examined in comparison with that of a conventional Pt/Al2O3 catalyst. The products were also characterized by XRD, FE-SEM, and BET specific surface area. The XRD analysis revealed that all the products had a perovskite phase as the major compound, together with intermediate phases with higher x values (x = 0.7–1). The BET specific surface area of the products increased with x. Moreover, the catalytic activity for soot combustion also increased with x, wherein the BET specific surface area appeared an appropriate index for explaining the observed activity. The sample with x = 0.8 exhibited the highest activity for soot combustion among all the SHS products. The soot combustion temperature of this product was as much as 100 °C lower than that of non-catalytic soot combustion. In other words, it had the same activity as that at only 20 °C higher, in comparison to conventional Pt/Al2O3 catalyst. More significantly, average apparent activation energy of sample with x = 0.8 calculated by Friedman method using TG/DTA was approximately 15 kJ/mol lower than that of Pt/Al2O3 catalyst. This result suggested that La1−xSrxFeO3 has the possibility to be an alternative catalyst to Pt/Al2O3 catalyst.

Influence of reactant particle size on products of self-propagating high-temperature synthesis in 30wt.% Cr–Ti–B4C system

Abstract Influence of reactant (Cr, Ti and B 4 C) particle size on the SHS reaction products in 30 wt.% Cr–Ti–B 4 C system has been investigated. Particle size of Cr powder has a significant effect on the phase compositions and microstructures of SHS reaction products. The SHS reaction in Cr–Ti–B 4 C system with nano-size Cr goes more complete and occurs more easily than that in the system with micron-size Cr. Increase in particle size of B 4 C powder has a little effect on the phase compositions of SHS reaction products, which consist of TiB 2 , TiC and Cr phases as well as transient phase Cr 5 B 3 and a trace of C, but results in the increase of the amount of Cr 5 B 3 . Furthermore, the average sizes of TiB 2 and TiC increase from ∼0.5 and ∼1 μm to ∼2 and ∼3 μm, respectively, as the B 4 C particle size increases from ∼3.5 to 40 μm. Increase in particle size of Ti powder (∼38, ∼48 and ∼74 μm) has little influence on the phase compositions of the products, as well as average sizes and morphologies of TiB 2 and TiC.

Ceramic nanolaminates—Processing and application

The self-propagating high-temperature synthesis (SHS) has been used in authors’ works for preparation of ceramic nanolaminates, namely Ti 3SiC 2, Ti 3AlC 2 and Ti 2AlN. The possibility of obtaining near-single-phase materials, processing of SHS products into sinterable powders and densification of the powders by sintering and hot-pressing are discussed. Finally, polycrystalline nanolaminate materials with controlled phase composition and microstructure have been obtained. The materials have been investigated as structure materials by testing their mechanical properties. The possibility of using of prepared powders to obtain ceramic composites, ceramic bonds and FGM materials, as well as their potential application are discussed.

Hardening of metal surface via self-propagating high-temperature synthesis in thin films

The technique of metal surface hardening via self-propagating high-temperature synthesis (SHS) in thin films followed by fusion penetration of the metal surface by means of solar radiation is described. It has been established that SHS leads to the formation of the δ phase of an Al-Ni system in the three-layer film structure Ni-Al-Ni and that the SHS reaction in the film coating proceeds via four stages. It has been shown that, after fusion penetration, hardening products of SHS are concentrated in the surface layer at a depth of 1–2 μm and the microhardness of the as-treated stainless steel samples increases by a factor of 1.7.

Production of silicon nitride by the acid enrichment of products of combustion of ferrosilicon in nitrogen

Production of silicon nitride by acid enrichment of products of interaction between ferrosilicon and gaseous nitrogen under conditions of self-propagating high-temperature synthesis (SHS) is studied. The effect of the nature of acid, its concentration, agitation of solution, and process temperature is determined. The reaction of the Si3N4 + Fe composite powder and the hydrochloric acid solution is found to have a stage behavior. The apparent activation energy of iron passing into the solution is determined. The purity of the produced Si3N4 powder is demonstrated to depend on a degree of nitration of SHS products. The chemical and phase composition of the powder and its specific surface are determined.

Mechanical alloying and self-propagating high-temperature synthesis of stable icosahedral quasicrystals

Abstract The phase evolution of the mechanically alloyed ternary 63%Al + 25%Cu + 12%Fe and 65%Al + 20%Cu + 15%Fe powder mixtures with milling time has been studied by X-ray diffraction method. It was found that an icosahedral quasicrystalline phase was formed directly during high-energy ball milling of the Al–Cu–Fe mixtures. The X-ray and scanning electron microscopic investigations demonstrated the possibility to use self-propagating high-temperature synthesis (SHS) in combination with preliminary mechanical activation for the synthesis of stable icosahedral quasicrystals. The typical morphology of the Al 63 Cu 25 Fe 12 icosahedral quasicrystals formed in the SHS process is a pentagonal dodecahedron with a size of 3–5 mm. The phase composition of the SHS products depends on the time of preliminary mechanical activation. The content of cubic intermetallic phase in SHS products increases with the time of preliminary mechanical activation of the 63%Al + 25%Cu + 12%Fe powder mixtures.

Determination of Non-Stoichiometry of Tubular Titanium Carbide Formed by Self-Propagating High Temperature Synthesis

Titinium carbide (TiCx) was produced by self-propagating high temperature synthesis (SHS) method. The morphology and non-stoichiometric number of the SHS product were observed by scanning electron microscopy and neutron diffractometry, respectively. Tubular titanium carbide with hole inside was formed with different non-stoichiometric number (x), which value increased with combustion temperature.

Combustion synthesis of porous biomaterials

This article discusses the unique material manufacturing process of self-propagating high temperature synthesis (SHS) as applied to the making of porous biomaterials. Porous materials have long been considered as the first step toward in-vivo bone tissue engineering and the creation of patient life-time implants. The authors have approached this challenge by utilizing combustion synthesis, to create novel materials such as NiTi + TiC as well as porous forms of materials that are commonly accepted for biomedical applications such as tricalcium phosphate and hydroxyapatite. In the SHS product, physico-chemical properties are controlled by, but not limited to, reactant stoichiometry; green density; particle size of the reactant mix; use or presence of a gasifying agent; heating rate of the reactants and gravity. By balancing these parameters, the energy of the reaction is controlled to create the desired product stoichiometry, porosity, and mechanical properties. SHS provides a means to rapidly manufacture materials, saving time and production costs as well as enabling the synthesis of custom devices through the use of individual molds. Mold materials can range from graphite to paper or paper machete. Combustion synthesis offers a method for the rapid manufacture of affordable, individual biomedical devices that will reduce patient recovery time.

Self-propagating high-temperature synthesis of barium titanate and subsequent densification by spark plasma sintering (SPS)

This paper describes the self-propagating high-temperature synthesis (SHS) of perovskitic oxides, specifically BaTiO 3, and their subsequent densification by spark plasma sintering. With the final goal of obtaining dense nanostructured materials, SHS products were mechanically treated at different milling time conditions, before densification. It was found that the grain size of ball milled powders decreases with increasing milling time, this effect being more evident at early stages of milling. Depending upon the ball milling (BM) conditions adopted, crystallite size in the range 15–70 nm was obtained. After milling for 5 h, the resulting powders (20–30 nm) were sintered by SPS, at 700 A, for different periods of time. By properly varying sintering time in the interval 70–140 s, it is possible to obtain products with relative density in the range 66–99%, respectively. In particular, grain growth during sintering was found to be limited (below 50 nm) if the electric current is applied for time intervals equal to or less than 100 s. The observed dielectric properties are typical of a nanocrystalline BaTiO 3 ceramic.

Effect of HCl concentration on TiB 2 separation from a self-propagating high-temperature synthesis (SHS) product

This paper presents a synthesis of TiB 2 powder via self-propagating high-temperature synthesis (SHS) method using a mixture of TiO 2, B 2O 3 and Mg followed by acid leaching. In the acid leaching step, the MgO content in the SHS product was leached in different HCl concentrations. X-ray diffraction (XRD) analysis showed that when 9.3 M HCl was used, the leached SHS product was found similar to that of the commercial TiB 2 powder. However, scanning electron microscopy (SEM) and BET surface area analysis revealed that the leached product was agglomerated and exhibited very high surface area.

Processing of nano-structured barium hexaferrite by self-propagating high temperature synthesis (SHS) using nitrate precursor

Barium hexaferrite magnetic powder was produced by self propagating high temperature synthesis (SHS) route through putting a hot filament on top of the compact mixture of iron, iron oxide and barium nitrate powders with a Fe (total)/Ba molar ratio of 12. Morphology, particle size distribution, thermal behavior, phase evolution, chemical analysis and magnetic properties of the products were investigated by SEM, LPSA, DTA/TGA, XRD, EDS and VSM techniques, respectively. EDS analysis confirmed the presence of barium hexaferrite in as-SHS sample. An exothermic peak appeared at 814 °C in DTA/TGA traces seems to be due to the formation of barium hexaferrite. Single-phase barium hexaferrite was formed after annealing of SHS product at 1150 °C for 2 h. SEM micrograph of the sample annealed at 1150 °C for 2 h showed plate-like hexagonal particles of barium hexaferrite with mean size of 2 μm. Saturation magnetization (Ms) and coercivity (Hc) for sample annealed at 1150 °C for 2 h were obtained 66 emu/g and 192 kA/m, respectively. The microstructure of as-SHS sample after it was pressed and then sintered at 1250 °C for 3 h exhibited nano-grains of barium hexaferrite with mean diameter of 200 nm.

Preparation of ZrB2 ceramics by self-propagating high-temperature synthesis and hot pressing sintering

ZrB2 ceramics were prepared by self-propagating high-temperature synthesis (SHS) and were sintered by hot pressing (HP). The effects of the granularities and doses of raw materials in Zr−B2O3−Mg on SHS process and product were investigated. XRD and combustion temperature curves prove that the ideal SHS reactants of Zr−B2O3−Mg are 50 μm Zr powder, 75 μm B2O3 powder and 400 μm Mg powder with 45% excessive. The particle sizes of SHS product, acid-leached product, sintered product are 2–5 μm, 0.5–2 μm, 2–10 μm respectively. Chemical analysis indicates that the acid-leached product consists of ZrB2 (94.59%), ZrO2 (3.87%) and H3BO3 (1.54%). The sintered product has a relative density of 95.4%.

Effect of Shell Dimensions on Compaction and Shape Change during SHS-Pressing

The finite-element method is used to study the effect of sand shell size on compaction and shape change during compaction of billets formed from the hot products of self-propagating high-temperature synthesis. The extreme nature of the change in billet density in relation to shell thickness that governs its reserve of compressibility is established. In order to make high-density billets it is necessary that shell compressibility reserve is higher than that of the synthesis products. With decrease in shell radial dimensions there is distortion of billet shape due to a nonuniform stress-strained state close to the side surface of the tool with external friction.

Self-Propagating High-Temperature Synthesis of Aluminum Nitride and its Characterization

Aluminum nitride was synthesized by self-propagating high-temperature synthesis (SHS) with flaky aluminum powder in various conditions such as particle size, nitrogen pressure (PN 2), dilution factor f( Dil</sub), packing density, and bulk sample size. AlN content in the SHS product increases with an increase of fDil, and it eventually reaches about 95 % at fDil=0.6. Generally, reaction front velocity is significantly affected by PN2 and packing density, but not by fDil. The degree of AlN conversion reduces more or less with an increase of bulk sample size, but that could be improved by using the SHS pre-prepared product as a diluent.

Equilibrium of Products of Self-Propagating High-Temperature Synthesis

Equilibrium of Products of Self-Propagating High-Temperature Synthesis