Starting Powder Mixture Research Articles

Influence of TiH2 addition on the microstructure and mechanical properties of spark plasma sintered TiCx-NiTi/Ni3Ti cermets

TiC0.7-10.7vol% NiTi, TiC0.8-7vol% Ni3Ti and TiC0.9-8vol% Ni3Ti cermets were prepared by spark plasma sintering. The C/Ti atomic ratio of the TiC phase and overall binder composition was modified by adding TiH2 powder into the TiC0.95+Ni49.4Ti50.6 starting powder mixture. The Ti loss from the NiTi starting powder during sintering, converting the metal binder from NiTi into Ni3Ti, could be avoided by the addition of TiH2 with a concomitant change of the TiCx phase stoichiometry. A ductile NiTi binder was obtained in combination with a TiC0.7 phase, while a more brittle Ni3Ti binder was generated in combination with TiC0.8 or TiC0.9. The hardness of the cermets increased with increasing C/Ti ratio of the TiCx phase and decreasing NiTi or Ni3Ti content, whereas the bending strength and fracture toughness of the NiTi binder cermet was significantly higher than for the Ni3Ti binder cermets. The E-modulus of the NiTi binder cermet was substantially lower than for the Ni3Ti binder cermets.

Stainless steel bonded NbC matrix cermets using a submicron NbC starting powder

The microstructure and mechanical properties of 316L and 430L stainless steel bonded NbC cermets were assessed. NbC starting powder mixtures with 15 and 30vol% steel binder were pressureless vacuum sintered for 1h at 1420°C. The liquid forming temperature and shrinkage behaviour of the green powder compacts were investigated by differential scanning calorimetry and dilatometry. Microstructural and compositional analysis were conducted by electron probe microanalysis (EPMA) and XRD to investigate the effect of the steel binder on NbC grain growth and Cr-rich carbide precipitation. Rapid NbC grain growth was observed and the average NbC grain size decreased with increasing binder content. The residual Cr-rich carbide located at NbC grain boundaries can be eliminated by the addition of carbide forming metal precursors such as TiH2 or by a thermal annealing process of the sintered NbC cermets at 1200°C. The hardness and fracture toughness of the NbC-steel cermets was influenced by the steel binder type and content. A maximum hardness of 13.6GPa was measured for the NbC-15vol% 430L cermet, combined with a modest fracture toughness of 7.3MPam1/2.

Influence of a mechano-chemical treatment on the synthesis and characteristics of p-type thermoelectric Ca3Co4O9 ceramics

The influence of a mechano-chemical (MC) treatment on the formation of the Ca349 phase from a stoichiometric mixture of fine-grained CaCO3 and Co3O4 powders, as well as the microstructural and thermoelectric characteristics of the Ca349 ceramics were studied. With an experimentally obtained maximum of 283 mJ/hit the critical ball-impact energy (Eb) required for the formation of the Ca349 compound was not obtained; however, the MC treatment resulted in complete amorphization and an enhanced reactivity of the starting-powder mixture. This enabled the preparation of single-phase Ca349 ceramics with an un-homogeneous microstructure and a density of 50% after only 4 h of calcination at 760 °C, while the untreated mixture required at least 12 h. Additional sintering at 920 °C resulted in a highly homogeneous and fine-grained microstructure for the Ca349 ceramics with a density of 72%, having an approximately two-times higher ZT of 0.10 at 600 °C in comparison to the previously reported values. Our study showed that the mechano-chemical treatment enhances the formation of the Ca349 phase at a low calcination temperature, which enables the preparation of Ca349 ceramics with a microstructure that leads to improved TE characteristics.

(Nbx, Zr1-x)4AlC3 MAX Phase Solid Solutions: Processing, Mechanical Properties, and Density Functional Theory Calculations.

The solubility of zirconium (Zr) in the Nb4AlC3 host lattice was investigated by combining the experimental synthesis of (Nbx, Zr1-x)4AlC3 solid solutions with density functional theory calculations. High-purity solid solutions were prepared by reactive hot pressing of NbH0.89, ZrH2, Al, and C starting powder mixtures. The crystal structure of the produced solid solutions was determined using X-ray and neutron diffraction. The limited Zr solubility (maximum of 18.5% of the Nb content in the host lattice) in Nb4AlC3 observed experimentally is consistent with the calculated minimum in the energy of mixing. The lattice parameters and microstructure were evaluated over the entire solubility range, while the chemical composition of (Nb0.85, Zr0.15)4AlC3 was mapped using atom probe tomography. The hardness, Young's modulus, and fracture toughness at room temperature as well as the high-temperature flexural strength and E-modulus of (Nb0.85, Zr0.15)4AlC3 were investigated and compared to those of pure Nb4AlC3. Quite remarkably, an appreciable increase in fracture toughness was observed from 6.6 ± 0.1 MPa/m(1/2) for pure Nb4AlC3 to 10.1 ± 0.3 MPa/m(1/2) for the (Nb0.85, Zr0.15)4AlC3 solid solution.

Metastable Co3C nanocrystalline powder produced via reactive ball milling: Synthesis and magnetic properties

This study investigates reactive ball milling synthesis of a single phase metastable Co3C compound from starting mixtures of cobalt and graphite powders under argon and nitrogen environments. It reports their phase formations, magnetic, and structural properties. Regardless of the starting powder composition (25.0 or 33.3 at.% C) and milling atmosphere, reactive ball milling leads to the formation of the Co3C compound with an orthorhombic structure. Coercivities of the starting mixtures first increases with milling time as the Co3C compound starts to form and subsequently decreases due to structural defects induced by further milling. Higher graphite containing starting powder mixtures yield higher peak coercivity values and higher transformation rates. The formed Co3C compound exhibits a Curie temperature of 563 K and a decomposition temperature around 710 K. Compared to argon milled powders, reactive milling under a nitrogen atmosphere increases the coercivity and decomposition temperature of the Co3C compound.

Microstructure and thermoelectric characteristics of (ZnO)k×In2O3: Based ceramics (k = 5 and 11)

Oxide thermoelectric ceramics are needed for high-temperature applications that involve harvesting the waste heat by direct transformation into electricity. In the case of n-type materials, the homologous (ZnO)kIn2O3-type phases are very promising for tailoring the TE properties. In this investigation the thermoelectric (ZnO)kIn2O3-based ceramics for k=5 and 11 were prepared using a classic ceramics procedure and sintering at 1500oC. During their preparation, either a fresh powder mixture of ZnO and In2O3 or a mixture of ZnO and In2O3 also containing plate-like grains of the pre-reacted (ZnO)kIn2O3 phases was used to induce possible microstructure texturing. It was demonstrated that the starting composition in terms of k value and the type of starting powder mixture affect the processes, leading to the formation of the equilibrium (ZnO)kIn2O3 homologous phase and, consequently, also the microstructure development. Nevertheless, all the samples had similar final microstructures and no texturing was observed. Regardless of the use of different starting-powder mixtures, the samples with the same composition had a similar ZT: at 627oC it was 0.11 for the samples with k=5 and 0.08 for k=11, which is not so inferior if we take account of the significantly lower content of In2O3 in these samples.

Effect of Powder Particle Shape on the Properties of In Situ Ti–TiB Composite Materials Produced by Selective Laser Melting

This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology (especially the shape) and, consequently, density and compression properties of in situ Ti–TiB composite materials produced by selective laser melting (SLM) technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium (CP-Ti) and 5 wt% titanium diboride (TiB2) powders and subsequently milled for two different times (i.e. 2 h and 4 h). The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti–5 wt% TiB2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti–TiB composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB2 during SLM. The Ti–TiB composite samples prepared from 2 h and 4 h milled Ti–TiB2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those (883 MPa and 5.5%, respectively) for the 95.1% dense sample. The results indicate that once Ti and TiB2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density (i.e. increasing porosity level) of the Ti–TiB composite materials and their mechanical properties.

Characterization of mechano-thermally synthesized Curie temperature-adjusted La0.8Sr0.2MnO3 nanoparticles coated with (3-aminopropyl) triethoxysilane

This research aimed to synthesize nanostructured strontium-doped lanthanum manganite, La0.8Sr0.2MnO3 (LSMO), with its Curie temperature (Tc) adjusted to the therapeutic range, through a mechanothermal route. In order to investigate the effect of heat treatment temperature and duration on the resulting crystallite size, morphology, magnetic behavior and Curie temperature, the starting powder mixture was milled in a planetary ball mill before being subsequently heat treated at distinct temperatures for different time lengths. The composition, morphology, and magnetic behavior were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED) and vibrating sample magnetometer (VSM). In addition, magnetic properties were further investigated using an alternating current (AC) susceptometer and thermo-magnetic analyzer. 20h of milling produced a crystallite size reduction leading to a decrease in the heat treatment temperature of LSMO synthesis to 800°C. Moreover, SEM analysis has shown the morphology of a strong agglomeration of fine nanoparticles. HRTEM showed clear lattice fringes of high crystallinity. The mean crystallite and particle size of 20-hour milled sample heat treated at 1100°C for 10h are relatively 69 and 100nm, respectively. The VSM data at room temperature, indicated a paramagnetic behavior for samples heat treated at 800°C. However, by increasing heat treatment temperature to 1100°C, LSMO indicates a ferromagnetic behavior with well-adjusted Curie temperature of 320K, suitable for hyperthermia applications. Also, reentrant spin glass (RSG) behavior has been found in heat treated samples. The particles are coated with (3-aminopropyl) triethoxysilane (APTES) for biocompatibility purposes; Fourier transform infrared spectroscopy (FTIR) and thermo-gravimetric analysis (TGA) are used for further confirmation of APTES coating.

Development of domestic powder granulate with a polyformaldehyde-based binder for MIM technology

The injection forming technology of polymer melt mixtures with Metal Injection Molding (MIM) metallic powders, which is successfully applied abroad for the serial production of complex-shaped small parts, is presented. Its distribution in Russia is slowed by the lack of production of domestic granules of the starting powder mixture with a polymer binder. The results of the development of compositions and production regimes of fabrication of granulates for laboratory MIM technology using domestic raw materials such as the carbonyl iron powder and binder based on polyformaldehyde with additives of paraffin, stearic acid, and low-pressure and high-pressure polypropylenes are described.

The synthesis of micro-sized silicon carbide whiskers and the application for heat transfer enhancement

This paper presents a simple and cost-effective method for the production of micro-sized silicon carbide whiskers at high yield and the effect on heat transfer enhancement for the whisker laden fluids. For SiC whisker synthesis, the starting powder mixture is obtained by milling short carbon fibers with the white ashes of rice hulls. Calcination in argon, together with the subsequent purification process, results in a high yield of SiC whiskers, which possess a diameter of 200–400 nm and a length of several tens of microns. The formation of the whiskers is discussed according to VS growth mechanism. Convective heat transfer performance in small channel tubes is then studied for fluid systems mixed with those micro-sized SiC whiskers at different concentrations. The heat transfer coefficient of SiC containing fluid can be significantly improved in comparison to the base fluid.

반응소결된 Si3N4-SiO2-BN 복합체의 기계적 강도 및 유전물성에 관한 연구

Silicon nitride (Si₃N₄) is regarded as one of the most promising materials for high temperature structural applications due to its excellent mechanical properties at both room and elevated temperatures. However, one high-temperature Si₃N₄ material intended for use in radomes has a relatively high dielectric constant of 7.9 - 8.2 at 8 - 10 GHz. In order to reduce the dielectric constant of the Si₃N₄, an in-situ reaction process was used to fabricate Si₃N₄-SiO2-BN composites. In the present study, an in-situ reaction between B₂O₄ and Si₃N₄, with or without addition of BN in the starting powder mixture, was used to form the composite. The in-situ reaction process resulted in the uniform distribution of the constituents making up the composite ceramic, and resulted in good flexural strength and dielectric constant. The composite was produced by pressure-less sintering and hot-pressing at 1650℃ in a nitrogen atmosphere. Microstructure, flexural strength, and dielectric properties of the composites were evaluated with respect to their compositions and sintering processes. The highest flexural strength (193 MPa) and lowest dielectric constant (5.4) was obtained for the hot-pressed composites. The strength of these Si₃N₄-SiO₂-BN composites decreased with increasing BN content.

Comparison of Critical Current Density and Pinning Behaviour of Mono-core MgB2 Wires Prepared by Different Methods

Three series of mono-core MgB 2 wires with Nb sheath embedded in Cu subjected to different heat treatments (600 ∘C/300 min, 650 ∘C/30 min and 700 ∘C/30 min) were produced. For each series, three samples with different starting powder mixtures Mg + B (IS), MgH 2 + B (MH) and Mg + B ball milled (ML) were prepared. Hysteresis loops and magnetic relaxations were measured to calculate critical current density (via Bean’s critical state model) and mean effective activation energy (via Anderson’s flux creep theory). Thus, the highest current densities were obtained for IS and the worst superconducting properties were found for MH wires.

Synthesis and characterization of Eu3+ doped CaZrO3-based perovskite type phosphors. part II: PL properties related to the two different dominant Eu3+ substitution sites

Eu3+-doped perovskite type CaZrO3-based phosphors were synthesized by the solid state reaction at 1400°C for 6h in air. To change the short range structure around Eu3+ in the CaZrO3-based compounds, two different cations were selected and co-doped; Sr2+ with a larger ionic radius compared with Ca2+ in the CaZrO3, and Mg2+ having a smaller one. According to the results obtained by our previous study, the chemical composition of the starting powder mixtures was controlled by taking into account of the dominant Eu3+ substitution site as A-site (Ca2+) for Ca1−xSrx−0.05ZrO3:Eu3+0.05 (x=0.2, 0.4), and that as B-site (Zr4+) for Ca1−yMgyZr0.95O3:Eu3+0.05 (y=0, 0.02, 0.04, 0.06, 0.08, 0.1). The results of the X-ray diffraction analysis revealed that Sr2+ mainly occupied the A-site as designed, and the lattice constants of the Ca1−xSrx−0.05ZrO3:Eu3+0.05 increased with increasing amount of the Sr2+-doping up to 35mol% without secondary phase formation. Mg2+ substitution to Ca2+ at the A-site in the CaZr0.95O3:Eu3+0.05 could be also achieved. However, the maximum amount of Mg2+ in the CaZr0.95O3:Eu3+0.05 was found to be low, approximately 6mol%. CaZr0.95O3:Eu3+0.05 showed characteristic emission of the Eu3+ (f–f transition) by CTB excitation. The intensity of the dominant PL emission peak centered at 614nm (5D0 - 7F2) increased consistently with the amount of the Mg2+-doping, and the 6mol% Mg2+-doped sample exhibited the highest emission peak intensity which was approximately 1.4 times higher than that of the Mg2+-free CaZr0.95O3:Eu3+0.05. On the other hand, the emission peak intensity at 614nm decreased with increasing amount of the Sr2+-doping. The relationships between the PL emission properties and the material parameters such as lattice constants of the host CaZrO3-based compounds, dominant Eu3+ substitution site and the site symmetry around Eu3+ in the host lattice were discussed from a viewpoint to improve the PL red emission properties of the Eu3+-doped CaZrO3-based compounds.

Salt-Assisted SHS Synthesis of Aluminium Nitride Powders for Refractory Applications

Powders of aluminum nitride can be prepared by self-sustain high-temperature synthesis (SHS) between aluminum and nitrogen but its high exothermic effect causes melting and evaporation of aluminum and low efficiency of such reaction. A presence of inorganic salt in the starting powder mixture can decrease a heat evolved in the SHS reaction, hinders melting and coalescence of aluminum, and facilitates penetration of nitrogen into interior of a powder bed. Mixtures of alumina powders with different grain sizes and different amounts of aluminum carbonate were subjected to the SHS reaction under 0.05, 0.1 or 1 MPa nitrogen. The powders were composed of aluminum nitride, unreacted aluminum, aluminum oxynitride and in some cases corundum and aluminum oxycarbonate. The finale effects are strongly dependent on the amount of the salt, a grain size of aluminum and a nitrogen pressure.

Characterization and Synthesis of Co(ss)/WSi2-CoWSi Nanocomposite by Mechanical Alloying and Subsequent Sintering

In this study, Co(ss)/WSi2-CoWSi nanocomposite was synthesized via mechanical alloying and heat treatment. In order to fabricate bulk composite, 50-h-milled powders were cold pressed and subsequently sintered at 1150 °C for 4 h in Ar atmosphere. Phase development and structural changes were investigated by x-ray diffraction technique and scanning electron microscopy. After various milling times, the powders were investigated by differential thermal analysis and microhardness measurements. The starting powder mixture has two allotropic structures of Co (fcc and hcp). After 10-h milling, an allotropic transformation takes place in Co (fcc to hcp), and a composite microstructure consisting of cold-welded Co, W, and Si phases is formed. After 20 h, new peaks related to WSi2 appeared in x-ray diffractograms. Increasing milling time to 50 h caused the formation of (Co, W, and Si) solid solution, WSi2, and CoWSi phases. DTA analysis of 30- and 50-h-milled powders confirmed an increase in the degree of ordering. The 50-h-milled powders exhibited high microhardness value of about 1050 HV0.1. XRD result of sintered material demonstrated that only ordered Co(ss)/WSi2-CoWSi nanostructured composite is present. Consolidated sample showed 12% porosity. Nanoindentation results showed that the sintered composite an exhibited a high hardness of 700 HV0.1 with an elastic modulus of 107 GPa.

The Influence of the Microstructure on the Switching Properties of Ag C, Ag-WC-C and Ag-W-C Contact Materials

Abstract The correlation between the microstructure of Ag-C, Ag-WC-C and AgWC composites and their switching properties was investigated. Two methods were used to manufacture the starting powder mixtures, namely classical milling and mechanical alloying . The arc erosion, contact resistance and welding forces of the contact materials obtained by different methods were measured using model devices. This paper presents the results achieved for the tested materials. It was found that weight loss was lower for the contacts produced by high energy milling

Low Temperature Synthesis of Zinc-Titanate Ultra Fine Powders

Development of dielectric materials for microwave frequencies is increasing with rapid progress in mobile and satellite communications systems, where zinc-titanates have found application due to their semi-conducting and dielectric properties. The aim of this work is synthesis of orthotitanate Zn2TiO4 with a spinel structure in low temperature. Starting powder mixtures of ZnO and TiO2, in the molar ratio that is in accordance with the stoichiometry of zinc titanate spinel type Zn2TiO4 and then, Sintered in the range of 1000-1200°C. After that, for production of ultra fine powder the blend was grinded by fast milling (mechanical activation) for 15minutes. Microstructural analysis and morphology were characterized by scanning electron microscopy which equipped with energy dispersive X-ray analyzer (SEM/EDS), also for mineral phases distinguishing was used X-Ray diffraction patterns(XRD) and measurement of particles and their distribution was done by Laser particle size analyzer(LPSA). The results indicated reaction between ZnO and TiO2 started above of 1000°C. According to SEM, XRD and LPSA analysis ultra fine(sub-micron) powder of orthotitanate Zn2TiO4 with spinel structure were obtain.

Formation of Titanium Silicon Carbide (Ti<sub>3</sub>SiC<sub>2</sub>) via Modified Self-Propagating High Temperature Synthesis (SHS) System through Arc Melting

Ti3SiC2 compound was synthesized from the starting powder mixtures of 3Ti/1.2Si/2C/xAl (x=0, 0.1, 0.2, 0.3) by using arc melting method. The effect of Al on the Ti3SiC2 formation was studied. X-ray diffraction and scanning electron microscopy were used to characterize the synthesized materials. It was found that the addition of Al increased the purity of Ti3SiC2. When x=0.2, Ti3SiC2 content in the final product reached 67% after being ball milled for 24 hours. However, excessive Al reduced the content of Ti3SiC2. In addition, the density of the final product decreased with increasing of Al content. It was revealed that addition of Al in the starting powders can increase the final product purity.

Microstructure and wear behavior of spark plasma sintered Ti3SiC2 and Ti3SiC2–TiC composites

Abstract In this paper, processing of Ti 3 SiC 2 and Ti 3 SiC 2 –TiC composites from Ti/Si/TiC/Al powder using spark plasma sintering (SPS) at 1250 °C is reported. The TiC content in the starting powder mixture was optimized such that the resultant Ti 3 SiC 2 –TiC composites retained up to 30 vol% excess TiC as reinforcement. The phase content of TiC reinforcement in the composites, calculated from x-ray diffraction analysis, is compared with TiC content in excess of stoichiometric TiC content needed for the formation of Ti 3 SiC 2 . The results indicate that the composition of the SPS sintered Ti 3 SiC 2 –TiC composites (relative percentages of Ti 3 SiC 2 matrix and TiC reinforcement content) can be effectively tailored by optimum design of the composition of starting powder mixture. The effect of TiC reinforcement content on relative density, phase development, microstructure, hardness, and friction and wear behavior of Ti 3 SiC 2 and Ti 3 SiC 2 –TiC composites are presented.

Microstructure evolution of Mo–Si–Al system during self-propagation high-temperature synthesis

The microstructure and phase constitution of Mo(Si1−x,Alx)2 alloys (x=0.03, 0.1 and 0.4) prepared by self-propagation high-temperature synthesis is first investigated using SEM, EDS and XRD analysis. Then the lattice parameters and adiabatic temperature are calculated. Based on the above experimental and calculated results, the variation mechanism of diffraction peaks and phase transformation subsequence of the Mo–MoO3–Si–Al powders is discussed. Results show that, when the self-propagation reaction is over, there are a homogeneous Mo–Si–Al alloy melt and a fused Al2O3 with lower density at top. Subsequently, MoSi2 or Mo(Si,Al)2 phase nucleates and grows as a primary phase in the Mo–Si–Al alloy melts, and then Al, Si substances are generated from the intergranular residual Al–Si liquid according to Al–Si binary phase diagram. The Al increase in the starting powder mixtures leads to the Al concentration increase in the Mo–Si–Al alloy melt. Consequently, MoSi2 is transformed to Mo(Si,Al)2 to phase in which Si is replaced by Al atoms and Al substance in the intergranular zones increased accordingly.