Spark Plasma Method Research Articles

Effects of Al2O3 micro/nanoparticles on the microstructure and corrosion behavior of W–Ni–Fe matrix through spark plasma sintering process

The purpose of this research is to examine the effect of Al2O3 micro/nanoparticles on the properties of the W–Ni–Fe matrix. The study involved analyzing the microstructure, hardness, density, and corrosion behavior of the W-4.9Ni-2.1Fe matrix with varying percentages of Al2O3 micro/nanoparticles (0.5, 1, and 1.5 wt%) that were sintered using the spark plasma method. The corrosion properties of different composites were studied using electrochemical impedance spectroscopy, Tafel polarization, and weight loss measurements. Furthermore, microstructural evaluations were carried out on samples before and after corrosion tests using optical and field emission scanning electron microscopy. The results indicated that a 1% increase in the percentage of Al2O3 nanoparticles led to approximately a 16% increase in the matrix hardness. This increase was attributed to the reduction in grain size and the distribution of pores in the nanocomposites. Tafel polarization measurements also showed that adding 1% Al2O3 nanoparticles resulted in an 83% improvement in the corrosion resistance of the W–Ni–Fe matrix in a 3.5 wt% NaCl solution. The improved corrosion resistance of the fabricated nanocomposites was attributed to the uniform distribution of Al2O3 nanoparticles in the matrix and reduction in the cathodic region. However, it was found that the formation of galvanic microcells was a critical cause of corrosion in micro-composites, leading to a reduction in corrosion resistance compared to the W–Ni–Fe matrix. Raman spectroscopy patterns indicated that Fe3O4, Fe(OH)2, NiO, and Ni(OH)2 were the main corrosion products.

Microstructure and Raman spectroscopy analysis of LiNiZn ferrite ceramics sintered by spark plasma method

In this study, the effects of different parameters (sintering temperature and holding time) of spark plasma sintering (SPS) on the microstructure and magnetic properties of LiNiZn ferrite ceramics were systematically investigated, and the samples sintered by SPS (SPS samples) were compared with the samples sintered by traditional sintering (TS samples). X-ray diffraction analysis confirmed that all the samples were ferrites with spinel structure. The microstructure of the samples was analyzed by scanning electron microscopy. Compared with TS samples, SPS samples exhibited finer and more uniform grains and denser structure. At the sintering temperature of 1000 °C, SPS samples exhibited higher saturation magnetization (Ms, 79.7 emu⋅g−1) and lower ferromagnetic resonance linewidth (ΔH, 231 Oe) than TS samples (Ms: 69.3 emu⋅g−1, ΔH: 298 Oe). The phase structure and cation distribution of the samples were analyzed by Raman spectroscopy. Herein, it was speculated that the instantaneous high temperature generated by spark plasma redistributed the cations in the crystal, and the distribution mode was stabilized by rapid cooling. Based on the change of magnetic moment of ferrite molecules caused by cation distribution, a method of judging the specific Ms by fitting analysis of Lorentz curve of A1g Raman signal of ferrite ceramics was proposed. The SPS samples showed more compact and uniform microstructure and more reasonable cation distribution than TS samples, and these characteristics were mainly responsible for the remarkable improvement of magnetic properties. The results indicate that SPS method can effectively alleviate the contradiction between Ms and ΔH, and provide an alternative pathway to prepare high-performance soft magnetic ferrite.

Investigation of density, phase, fracture toughness, thermal conductivity, and friction coefficient of Cf/SiC composite produced by the spark plasma sintering method

This research aimed to prepare a carbon fiber/silicon carbide composite via the spark plasma (SPS) method. For this purpose, first, a slurry of β-silicon carbide nanoparticles with carbon fiber and nano-alumina sintering aid was prepared. Then, the bulk composite was formed by the SPS method at 1900 °C and 50 MPa. Next, the effect of sintering time was investigated on the density, friction coefficient, fracture toughness, and microhardness of the samples. The results indicated that with an increase in the sintering time from 10 to 20 min, the density rose from 78 to 95% of the theoretical density, and the hardness of the samples increased from 1150 Vickers to 2580 Vickers. Finally, the friction coefficient was elevated from 0.13 to 0.5.

Influence of Alumina Nanofibers Sintered by the Spark Plasma Method on Nickel Mechanical Properties

The article presents the study of alumina nanoparticles’ (nanofibers) concentration effect on the strength properties of pure nickel. The samples were obtained by spark plasma sintering of previously mechanically activated metal powders. The dependence of the grain size and the relative density of compacts on the number of nanofibers was investigated. It was found that with an increase in the concentration of nanofibers, the average size of the matrix particles decreased. The effects of the nanoparticle concentration (0.01–0.1 wt.%) on the elastic modulus and tensile strength were determined for materials at 25 °C, 400 °C, and 750 °C. It was shown that with an increase in the concentration of nanofibers, a 10–40% increase in the elastic modulus and ultimate tensile strength occurred. A comparison of the mechanical properties of nickel in a wide range of temperatures, obtained in this work with materials made by various technologies, is carried out. A description of nanofibers’ mechanisms of influence on the structure and mechanical properties of nickel is given. The possible impact of impurity phases on the properties of nickel is estimated. The tendency of changes in the mechanical properties of nickel, depending on the concentration of nanofibers, is shown.

Sintering of Ge-Sb-Se Chalcogenide Glass Powder by Tube Furnace and Spark Plasma Methods

In this research, density and infrared transmittance of chalcogenide glass sintered by two methods; tube furnace sintering (TBS) and spark plasma sintering (SPS), were studied and characterized. In TBS, the effects of sintering dwell temperature, dwell time, and heating rate on final density and transmittance were investigated. The TBS test showed that the transmittance was seriously deteriorated above the sintering temperature of 380 °C, resulted from the crystallization, Se evaporation, and pore expansion. To overcome the limitation of TBS, SPS was employed by adjusting the sintering condition. The results of a comparative study indicated that sintering temperature is a dominant factor affecting the transmittance and density of sintered glasses, closely related to pore fraction.

Plasma-Spark Sintering of Oxide–Non-Oxide Components with the Addition of a TiC–ZrC Solid Solution and Various Metal Powder Mixtures

The effects of powder mixtures of W–Mo and Zr–Ti combined with sintered solid solution TiC–ZrC during spark plasma sintering of compositions at a pressing load of 60 MPa in the range 1200 – 1600°C on the phase composition, microstructure, grain sizes of crystalline phases, relative density, linear shrinkage, physical-mechanical properties, and linear correlation of elasticity modulus and fracture toughness of mullite–β-Si3N4–c-BN samples are shown in the present work. Synthesized powders of β-Si3N4 and c-BN are characterized by extensive crystallization of β-Si3N4 and c-BN. Solid solution TiC–ZrC sintered by a spark-plasma method at 1800°C shows roughly equal crystallization of (Zr,Ti)C and (Ti, Zr)C and a nonuniform and incompletely sintered crystalline microstructure. Samples with W–Mo and Zr–Ti mixtures sintered in the range 1200 – 1600°C show extensive mullitization; active crystallization of β-Si3N4, (Ti,Zr)C, solid solutions Mo, Wand W, Mo, and β-Zr,Ti; and lower crystallization of c-BN, (Zr,Ti)C, and β-Ti,Zr. The W–Mo mixture in the range 1400 – 1600°C favors the formation of a more uniformly and densely sintered microstructure of the ceramic phase; roughly round-shaped particles of solid solutions Mo, W and W, Mo in the metallic phase; more reinforced boundary areas of ceramic-metallic and metallic phases; and polydisperse grain compositions of crystalline phases. As a result, the composition with the W–Mo mixture sinters more uniformly and gradually in the range 1200 – 1600°C with the corresponding sample showing greater values of physical-mechanical properties, higher cracking resistance, and a greater linear correlation of the elasticity modulus and fracture toughness.

Magnetic properties of BaNixFe12–xO19 (x=0.0–1.0) hexaferrites, synthesized by citrate–gel auto-combustion and sintered by conventional and spark plasma methods

The influence of nickel substitutions on the local structure, dielectric and magnetic properties of Ba hexaferrites is investigated in this study for use as rare earth free permanent magnets and microwave devices, especially. For this purpose, BaNixFe12–xO19 (x = 0.0, 0.2, 0.5, 0.8 and 1.0) powders were prepared by auto–combustion of their citrate–nitrate gels precursor whilst spark plasma sintering and conventional sintering techniques were used in order to prepare BaNixFe12–xO19 sintered ceramics samples. Structure, microstructure, dielectric and magnetic properties of BaNixFe12–xO19 materials were investigated by X-ray diffraction, scanning electron microscopy (SEM), dielectric measurements, Mössbauer spectroscopy and SQUID magnetometry. X-ray diffraction analyses indicated that BaNixFe12–xO19, x = 0.0–1.0crystallized on the hexagonal BaFe12O19 structure and, the lattice parameters a and c, decrease as the Ni content increases. Raman spectroscopy analysis confirmed the formation of the BaFe12O19 phase. The presence of Fe in the +3 oxidation state (Fe3+) and of Ni2+ is confirmed by X-ray photoelectron spectroscopy (XPS). The SEM investigations on BaNixFe12–xO19 powders showed the change of the morphology from a granular-like structure to a platelet-like structure with increasing the nickel content which influences the dielectric and magnetic properties of these materials. Dielectric measurements performed on BaFe12−xNixO19 ceramics showed consistent differences between the two sintering methods. Impedance analysis shows a contribution of grains and grain boundaries in all samples. The Mössbauer spectroscopy results evidenced the five Wyckoff crystallographic iron positions and their site occupancy with respect to Ni substitutions content. The permanent magnet characteristics of the hexaferrites were confirmed by the high values of coercive field (up to ∼ 1.7 kOe) and remanence (∼28 emu/g), while the saturation magnetization values are found up to 95 emu/g at low temperatures and 70 emu/g at room temperature (for x = 0.8). The coercive field, remanence and maximum energy product decrease with nickel content, while the saturation magnetization behaves unmonotonically due to the specific variation of the site occupancy. More insight into the link between local structure and magnetic properties of Ni substituted Ba hexaferrite was given.

Strengthening oxide-oxide-free materials by incorporation of TiC‒ZrC solid solutions into their structure during plasma-spark sintering of initial powder mixtures under high compression load

The effect of sintered TiC‒ZrC solid solutions during spark plasma sintering of com-positions at pressing loading of 60 MPa in the range 1200‒1600 о С on the phase composition, microstructure, relative density, open porosity, linear shrinkage, physical-mechanical properties and linear correlation of modulus of elasticity and fracture toughness of mullite‒WC‒TiC‒ZrC and mullite‒c-BN‒TiC‒ZrC samples is shown. Synthesised powders of WC, c -BN and sintered at 1800 о C TiC‒ZrC solid solutions by spark plasma method are characterisized by intensive crystallization of WC, c -BN and (Ti, Zr)C with uniformly, densely sintered, crystalline microstructures, respectively. Sintered samples, containing solid solutions with ratios of TiC and ZrC, equal to 80/20 and 90/10 mol. %, show intensive development of mullite and (Ti, Zr)C, graduall growing of c -BN and (Zr, Ti)C as well as decrease the intensity of WC phase in the range 1200‒1600 о C. Microstruc-tures of samples with c -BN and TiC‒ZrC solid solutions in different ratios more uniformly and densely sintered, crystalline, finegrained with insignificant quantity of pores, more reinforced at the boundaries areas of oxide and nonoxide crystalline phases. As a result, such samples show higher values of relative density, linear shrinkage and physical-mechanical properties in the range 1200‒1600 о С, higher resistance to the cracking at 1500 о C and larger linear correlation of modulus of elasticity and fracture toughness in the range 1200‒1600 о C.

Investigation into the Influence of the Structure Dispersion and Homogeneity on the Properties of Powder Metastable Austenitic Carbide Steels and Diamond Tools

Diffusion and homogenization in “iron (5 μm–nickel (5 μm or 50 nm)” powder systems of various degrees of dispersion during sintering (900 and 1000°C), as well as spark plasma sintering, are investigated using the Matano–Boltzmann method. Calculated diffusivities in pairs of micron powders sintering without applying pressure (900°C, 6 h) and by the spark plasma method (900°C, 5 min) in these systems are equal to 7 × 10–10 cm2/s. It is shown that the use of nanodispersed nickel powder in diffusion pairs based on finely dispersed iron powder promotes a twofold increase in diffusivity at 900°C in contrast to the pair with the microdispersed nickel powder. Constants in the Ivensen sintering kinetics equation are calculated for the “iron–nickel” powder systems, by which the factors activating sintering of these systems are established. The dependences of the structural phase composition and physicomechanical properties of carbide steels of the Fe(base)–14 wt % Ni–8 wt % TiC system on the sintering temperature in range t = 900–1200°C and structure dispersity and homogeneity are determined. The dependences of the grain size, porosity, hardness, microhardness, fracture toughness, and bending ultimate strength on the sintering temperature are shown. Dependences of tribotechnical properties on the degree of homogeneity of the solid solution and volume of the phase transformation of metastable austenite into deformation martensite during abrasive friction turn out similar for carbide steels and diamond tools based on carbide steel. Optimal values of the variation coefficient of the nickel concentration in austenite and carbide steels of the same chemical composition but with different degrees of dispersity, which provide the maximal volume of the austenite decomposition and high values of the diamond-tool grinding coefficient, turn out equal to 5 in both systems, but the sintering parameters are different. It is shown that the physicomechanical properties of the studied systems depend on the structure porosity and dispersity, while tribotechnical properties depend on the structural homogeneity of steels.

Sintering a Mixture of Powders in the Al2O3–SiO2–β-SiAlON–TiC–Dy2O3 System by the Spark-Plasma Method with High Compaction Loading

The effect of the addition of 2 and 5 mol.% Dy2O3 during spark-plasma sintering at a compaction loading of 60 MPa in the range of 1200 – 1600°C on phase composition, microstructure, relative density, open porosity, linear shrinkage, physicomechanical properties, and linear correlation of the elastic modulus and fracture toughness of mullite–sialon–TiC samples is shown. The synthesized powders of sialon and TiC are characterized by corresponding intensive crystallization. The increase in the content of Dy2O3 from 2 to 5 mol.% in the sintered composition to produce β-SiAlON/TiC = 70/30 mol.% promotes intensive mullitization, active growth of sialon and less intensive growth of TiC in the range of 1200–1600°CC, and also leads to the formation of less densely sintered crystalline microstructures in the sample, containing round crystalline TiO2 particles, pores and glassy phase at the boundaries of the regions in mullite–sialon–TiC solid solution composites at 1500°CC. Asample containing 5 mol.% Dy2O3 has lower values of relative density, linear shrinkage, physical and mechanical properties in the range of 1200 – 1600°CC, lower crack resistance with the formation of microcracks at 1500°CC and a slightly larger linear correlation of the elastic modulus and impact toughness in the range of 1200 – 1600°C.

Study of the effect of dispersion and homogeneity of the structure on the properties of powder metastable austenitic carbide steels and diamond tools

Diffusion and homogenization in powder systems of varying degrees of dispersion «iron (5 μm) – nickel (5 μm or 50 nm)» during sintering (900 and 1000 °C), as well as spark plasma sintering using the Matano-Boltzmann method were studied. In these systems, the calculated diffusion coefficients in pairs of micron powders, sintered without application of pressure (900 °C, 6 h) and the spark plasma method (900 °C, 5 min), were equal to 7·10–10 cm2/s. It is shown that in diffusion pairs based on microdispersed iron powder, the use of nanodispersed nickel powder instead of microdispersed one contributes to an increase in the diffusion coefficient at a temperature of 900 °C by a factor of 2. The constants in the sintering kinetics equation of V.A. Ivensen are calculated for iron–nickel powder systems. Through them the factors activating the sintering of these systems were established. The dependences of the structure-phase composition and physicomechanical properties of carbides of the Fe (base) system — 14 wt.% Ni – 8 wt.% TiC system on the sintering temperature in the interval t = 900÷1200 °C, dispersion and homogeneity of the structure were determined. The dependences of grain size, porosity, hardness, microhardness, toughness, bending strength on sintering temperature are shown. The established dependences of the tribotechnical properties on the degree of homogeneity of the solid solution and the volume of the phase transformation of the metastable austenite to deformation martensite during friction on the abrasive were similar for carbide steels and diamond tools based on carbide steels. The optimal values of the coefficient of variation of nickel concentration in austenite in carbidostils of the same chemical composition, but different dispersion, providing the maximum amount of austenite decomposition and high values of the diamond tool grinding coefficient were 5 in both systems, but the sintering parameters differed. It is shown that the physicomechanical properties of the studied systems depend on the porosity and dispersion of the structure, and the tribotechnical properties are subjected to the homogeneity of the structure of the steel.

Microstructure and properties of the mullite‒ZrO<sub>2</sub>(Y<sub>2</sub>O<sub>3</sub>)‒Si<sub>3</sub>N<sub>4</sub>-composite ceramics sintered in different ways

The research objective was to investigate the packing degree, phase composition, microstructure and some other properties of the mullite‒ZrO2composite ceramics with the Si3N4addition sintered in different ways, such as: by the conventional method, by the spark-plasma method, and both in the microwave and solar ovens. The comparative analysis was carried out for the strength properties (these were the ultimate compressing strength and the elasticity modulus) for the ceramic samples which had been sintered by means of the conventional and of the spark-plasma methods. Some reasons for the defect formation in the samples after their sintering in the microwave and solar ovens were mentioned.Ill.8. Ref. 10. Tab. 2.

Preparation of Mullite–TiC–TiN Materials by a Spark Plasma Method with High Compaction Loading and Their Properties

The phase composition of synthesized TiC and TiN materials and also the properties of mullite–TiC–TiN specimens with a different ratio of TiC and TiN, sintered by a spark plasma method in the range 1200 – 1600°C with a compaction load of 75 MPa are studied. Specimens with a different ratio of TiC and TiN are characterized by intense mullitization in the range from 1200 to 1600°C. an increase in TiC concentration, and correspondingly a reduction in TiN concentration in sintered powder mixtures facilitates formation at 1500°C of a densely sintered crystallized structure consisting of numerous mullite crystals, TiC and partly TiN, formed from melts. In the range 1400 – 1600°C the relative density and linear shrinkage of specimens gradually increases with a reduction in open porosity, but specimen elasticity modulus, Vickers hardness, and ultimate strength in compression increase.

Spark-plasma method with the high-load pressing for the mullite‒TiC‒TiN materials preparation and the material's properties

The phase composition of the synthesized TiC and TiN powders and the properties of the mullite‒TiC‒TiN samples with different TiC and TiN ratio were investigated. The samples have been sintered by means of the spark-plasma method within 1200‒1600 оС under the pressing load of 75 MPa. In the range within 1200 and 1600 °C the intense mullitization was observed in the samples with the different TiC and TiN ratio. The TiC concentration growth in the sintered samples and respectively the TiN concentration reducing at 1500 °C give rise to the dense-sintered crystal structure consisting of numerous mullite crystals, TiC and partially TiN, forming out of the solutions. Within 1400‒1600 °С the samples' relative density and the linear shrinkage gradually grow the open porosity decreasing, at the same time the samples' elasticity modulus, Vickers hardness number and ultimate compression strength increase under compression. Ill. 6. Ref. 10. Tab. 1.

Preparation of superionic ceramics by spark plasma method

The principle of spark plasma ceramics sintering method is presented, its advantages and disadvantages are discussed. Li+ ionic conductor Li3xLa2/3–xTiO3 (x = 0.1) and oxygen ionic conductor CeO2-20 mol% Sm2O3 nanoceramics have been prepared using this method. Electrical properties of the obtained ceramics were measured in the broad frequency range of 10 Hz to 3 GHz and temperature interval from 300 K up to 800 K. Ionic conductivities inside grains and in the grain boundaries have been separated from impedance spectra.DOI: http://dx.doi.org/10.5755/j01.ms.19.3.2403

Microwaved assisted fast synthesis of n and p-doped Mg2Si

Magnesium silicide based alloys fast syntheses have been carried out using microwave heating. Precursors were first ball milled powders together under inert gas. Resulting powders were then placed into a glassy carbon crucible before being heated by microwave irradiation. Sintering of the powder was performed by spark plasma method. XRD and SEM/EDS were used to investigate composition, structure and morphology. Thermoelectric performances of the samples were measured in the temperature range of 320–775 K. The doping effect of several elements such as silver, tin, antimony, cobalt and bismuth has been studied. n-Type and p-type Mg{sub 2}Si based materials have been successfully synthesized, with maximum ZT value up to 0.7 and 0.35 at 770 K for a n-type and a p-type sample, respectively. We demonstrate here that the use of microwave irradiation to prepare doped Mg{sub 2}Si is possible, and we discuss here the thermoelectric properties of such samples. - Schematic representation of microwave hybrid heating. - Highlights: • A promising method for fast production of Mg{sub 2}Si in the frame of heat harvesting applications is presented. • A novel technological approaches towards nanostructured materials is proposed. • Thermoelectric properties of Mg{sub 2}Si doped materials prepared under microwave irradiation are discussed.

Microstructure and mechanical properties of Al–Si–Ni–Ce alloys prepared by gas-atomization spark plasma sintering and hot-extrusion

Al–Si–Ni–Ce alloys with the composition of Al 78.5Si 19Ni 2Ce 0.5, Al 76Si 19Ni 4Ce 1 and Al 73Si 19Ni 7Ce 1 were atomized and then sintered by using spark plasma method. The microstructure of the as-atomized powders, sintered and hot-extruded samples was analyzed. The influences of granularity and sintering parameters including time and temperature on the density of sintered alloy were also discussed. It is shown that the atomized powders are composed of Si, Al 11Ce 3, Al 3Ni and alpha Al. Tiny Al 3Ni particles precipitate from supersaturated matrix near the powder boundaries during SPS. Hot-extrusion process leads to the layer structure and more homogeneous distribution of precipitates. These alloys exhibit high comprehensive mechanical properties with combination of high Vicker's micro-hardness, moderate tensile properties and elongation, which provide a novel kind of promising engineering materials.

Thermoelectric Properties of Spark Plasma-Sintered In4Se3-In4Te3

We report the thermoelectric properties of spark plasma-sintered In4Se3-In4Te3 materials. For comparison, pure In4Se3 and In4Se3 (80 wt.%)/In4Te3 (20 wt.%) mixture samples were prepared. In4Se3 and In4Te3 powders were synthesized by a conventional melting process in evacuated quartz ampoules, and a spark plasma method was used for the sintering of the pure In4Se3 and mixture samples. Thermoelectric and structural characterizations were carried out, and the mixing effect of In4Se3 and In4Te3 on the thermoelectric properties was investigated.

Microstructures and Thermoelectric Properties of Spark Plasma Sintered In4Se3

We report microstructures and thermoelectric properties of In4Se3 thermoelectric materials. In4Se3 powder was synthesized by conventional melting process in evacuated quartz ampoules and sintering of In4Se3 was performed by spark plasma method at various sintering temperature. The microstructure and density of the sintered body of In4Se3 were strongly dependent on the sintering temperature. Thermoelectric properties, such as electrical conductivity, Seebeck coefficient and thermal conductivity, were also characterized and the effects of the sintering condition on the thermoelectric properties were investigated.

Mechanical properties of binder-free single-walled carbon nanotube solids

Abstract Single-walled carbon nanotubes (SWCNTs) were successfully solidified without any additives using a spark plasma method. Purification of raw soot was crucially important in order to improve the mechanical properties of the SWCNT solid, which exhibited a significant nonlinear deformation response in contrast with brittle fracture of an unpurified SWCNT solid.