Ball Milling Of Powder Mixtures Research Articles

Effect of green body annealing on microstructure and optical properties of Y2O3:Yb3+ ceramics

Influence of annealing temperature in the Т = 600–1200°С range on a mesostructure of Y2O3:Yb3+ green bodies and properties of obtained ceramics were studied. It was shown that annealing of green bodies should be carried out at the maximum possible temperatures when sintering occurs without approaching of particle centers. It was established that green bodies annealed at T = 800°C are characterized by optimal mesostructure in terms of densification efficiency during subsequent vacuum sintering. Y2O3:Yb3+ ceramics prepared from green bodies which were previously annealed at 800°C possess the highest optical quality and in-line optical transmittance of 72% at λ = 1100 nm wavelength. Annealing at lower temperatures does not remove all the defects introduced by ball-milling of powder mixture, that hinders formation of pore-free ceramics. Green bodies annealing above T = 800°C leads to partial compact densification that is accompanied with a decrease in sinterability during vacuum sintering.

Effect of TiB2 particles on microstructure and mechanical properties of B4C–TiB2 ceramics prepared by hot pressing

B4C-20 wt% TiB2 ceramics were fabricated by hot pressing B4C and ball-milled TiB2 powder mixtures. The effects of the TiB2 particle size on the microstructure and mechanical properties were investigated. The results showed that the TiB2 particle size played an important role in the mechanical properties of the B4C–TiB2 ceramics. In addition, SiO2 introduced by ball milling was beneficial for densification but detrimental to the mechanical properties of the B4C–TiB2 ceramics. The typical values of relative density, hardness, flexural strength, and fracture toughness of the ceramics were 99.20%, 35.22 GPa, 765 MPa, and 7.69 MPa m1/2, respectively. The toughening mechanisms of the B4C–TiB2 ceramics were explained by crack deflection and crack branching. In this study, the effects of high pressure and temperature caused liquefying SiO2 to migrate to the surface of B4C–TiB2 and react with diffused carbon source in the graphite foil to form a 30 μm thick SiC layered structure, which improved the high-temperature oxidation resistance of the material. The unique SiC layered structure overcame the insufficient oxidation resistance of B4C and TiB2, thereby improving the oxidation resistance of the ceramics under high-temperature service conditions.

Properties of Cold Sprayed Coatings Produced from Boron-Based Ball-milled Powder Mixture

Properties of Cold Sprayed Coatings Produced from Boron-Based Ball-milled Powder Mixture

Effect of cubic and hexagonal boron nitride additions on the microstructure and properties of bulk MgB2 superconductors

MgB2 is a promising material for intermediate temperature applications where conventional low temperature superconductors cannot be used, especially if the range of magnetic fields over which is has acceptable current carrying performance can be expanded. However, its applicability is limited by poor properties at elevated magnetic fields. Carbon-based dopants can be used to dramatically improve the high-field performance of MgB2, but at the cost of a reduction in the superconducting transition temperature (T c) that limits the operation temperature to 20 K or below. Here we report an enhancement of superconducting performance of MgB2 with the addition of cubic and hexagonal boron nitride (BN), without any significant reduction in T c. Ex-situ bulk samples of MgB2 with two forms of BN addition were manufactured by the field assisted sintering technique after high energy ball milling of powder mixtures. We find that hexagonal BN (hBN) nanoparticles mixed homogenously with MgB2 powder react much more easily to produce Mg–N–B impurities than larger cubic BN (cBN) particles (∼10 µm) under the same processing conditions. The addition of 1 wt% hBN or 5 wt% cBN combined with 6 h of milling has been demonstrated to improve the critical current density (J c) of MgB2 over the entire magnetic field range. It is proposed that the nano-sized Mg–N–B impurities, that typically reside at MgB2 grain boundaries, increase pinning strength by introducing additional flux pinning centres. In addition, excess Mg may benefit the low-field performance by improving the connectivity. This work shows the significance of microstructural characterization on inhomogeneous superconducting materials to analyse their performance.

Dependence of magnetic properties with structural/microstructural parameters of ball-milled Fe15Co2P3 powder mixture

This research work aims to investigate the mechanical alloying of Fe15Co2P3 powder mixture in terms of phases’ formation, microstructural parameters, and magnetic properties as function of milling time. Parametric Rietveld refinement method, of the obtained X-ray patterns, was performed for qualitative and quantitative phase analysis alongside the determination of structural, microstructural, and mechanical properties. The ball-milled powder mixture crystallized within the face-centered cubic α-Fe(P) solid solution in equilibrium with Co75Fe25 phase. The crystallite size decreases reaching 100 and 200 nm respectively after 3 h of milling. The highest values of the dislocation density, microstrain, and stored energy are registered for the α-Fe(P) solid solution. The studied mechanical properties manifest the brittle nature of the α-Fe(P) solid solution compared to the Co75Fe25 phase. The squareness ratio Mr/Ms and the coercivity values of the milled powders increase with increasing milling time and reach steady state after 2 h. The hysteresis loss energy and maximum permeability reach minimal values of 45 × 10−4 W/m3 and 49 × 10−3 H/m respectively, after 1 h of milling at the opposite of the switching field distribution. The obtained results demonstrate the formation of nanostructured Fe15Co2P3 ternary alloy with optimum characteristics as promising candidate for diverse applications primarily in the biomedical field for diagnostics and therapeutics such as magnetic hyperthermia and vector probes for future imaging technologies.

Evolution of microstructure and wear-friction behavior of W-30 wt.% Cu nanocomposite produced via a mechanochemical synthesis route

Abstract W-30 wt.% Cu nanocomposites were prepared by chemical reduction of a ball-milled WO3-CuO powder mixture under a hydrogen atmosphere. The prepared samples were analyzed by means of X-ray diffraction, transition electron microscopy, scanning electron microscopy and energy dispersed spectroscopy. Microstructural studies revealed higher density of the composite sintered at 1300 °C compared to 1 050 °C and 1 150 °C due to activated liquid phase sintering as well as the solution-reprecipitation mechanism at 1300 °C. Density and hardness of the W-Cu composite samples measured in the range of 87.5- 97.3 g cm-3 and 22 - 63 Rockwell A, respectively. It was also found that the wear mechanism of the composite includes the following steps: chipping of tungsten particles, plastic deformation of copper phase and formation of some Cu-free pores and micro-cracks, pulling out of tungsten particles and plastic strain and deformation of tungsten particles and formation of a mechanically mixed layer on the surface.

Evolution of microstructure and wear-friction behavior of W-30 wt.% Cu nanocomposite produced via a mechanochemical synthesis route

Abstract W-30 wt.% Cu nanocomposites were prepared by chemical reduction of a ball-milled WO3-CuO powder mixture under a hydrogen atmosphere. The prepared samples were analyzed by means of X-ray diffraction, transition electron microscopy, scanning electron microscopy and energy dispersed spectroscopy. Microstructural studies revealed higher density of the composite sintered at 1300 °C compared to 1 050 °C and 1 150 °C due to activated liquid phase sintering as well as the solution-reprecipitation mechanism at 1300 °C. Density and hardness of the W-Cu composite samples measured in the range of 87.5- 97.3 g cm-3 and 22 - 63 Rockwell A, respectively. It was also found that the wear mechanism of the composite includes the following steps: chipping of tungsten particles, plastic deformation of copper phase and formation of some Cu-free pores and micro-cracks, pulling out of tungsten particles and plastic strain and deformation of tungsten particles and formation of a mechanically mixed layer on the surface.

Enhanced photocatalysis performance of mechano-synthesized V2O5–TiO2 nanocomposite for wastewater treatment: Correlation of structure with photocatalytic performance

The harmful chemical organic dyes used in textile industries and wastewater posses a great threat to human beings due to huge toxicity and enormous health hazards. Consequently, the conversion of these harmful chemicals into harmless substances becomes utmost essential for sustainable development in wastewater research. High-energy ball-milling of orthorhombic V2O5-anatase (a) TiO2 mixture (1:1 M ratio) at room temperature results in the formation of nanocrystalline V2O5–TiO2 solid solution phase. A series of V2O5–TiO2 solid solution is synthesized by varying the milling time from 5min to 20h. The Rietveld X-ray powder structure refinement methodology has been adopted for microstructure characterization of unmilled and all ball-milled nanocomposite samples, in terms of lattice imperfections. From Rietveld analysis, lattice parameters, relative phase abundance of individual phases, crystallite size and r.m.s. lattice strain values are estimated. At the early stage of milling of 30min, a-TiO2 transforms to polymorphic rutile (r)-TiO2 due to high energy impact of mechanical alloying. The final ball-milled powder mixture is composed of V2O5–TiO2 solid solution with a trace amount of r-TiO2 phase. Photocatalytic study through the degradation of Rhodamine B (RhB) in presence of visible light reveals enhanced degradation (~94%) of RhB with 3h ball-milled V2O5–TiO2 nanocomposite, compared to ~74% with 15h milled nanocomposite reported earlier. Optical bandgaps of ball-milled V2O5–TiO2 nanocomposites are within the semiconducting range. FESEM study of ball-milled powder mixture reveals the pineapple flower-like morphology of nanoparticles of V2O5–TiO2 nanocomposites. An enormous number of the leaf (V2O5)/flower (TiO2) semiconducting heterojunctions with small crystallite size and higher surface area are believed to excel the photocatalytic performance of the nanocomposite through electron-hole pair production and easy electron transport mechanism between valance and conduction bands due to low bandgap energy of TiO2 with the addition of V2O5. TEM study further reveals the particle size distribution and confirms the presence of crystalline phases in the ball-milled nanocomposite. FTIR spectrum of 3h ball-milled V2O5–TiO2 in RhB solution corroborates the photocatalytic property of the prepared nanocomposite. Finally, an attempt has been made to establish a correlation between structure/microstructure and photocatalytic performance of the nanocomposites.

Magnesium-based composites reinforced with graphene nanoplatelets as biodegradable implant materials

Magnesium (Mg) and its alloys are considered promising biodegradable implant materials because of their strength and ability to degrade naturally in the body. However, pure Mg degrades rapidly in the physiological environment which adversely affects its mechanical integrity before sufficient bone healing. In this study, a high energy ball mill was used to disperse 0.5 wt% zirconium (Zr) and 0.1 wt% GNPs in Mg powders. Ball milled powder mixtures were then cold pressed under 760 MPa into green compacts and sintered in an argon atmosphere at 610 °C for 2 h. Results indicated that the addition of Zr and GNPs to the Mg matrix significantly enhanced its compressive yield strength by 91% and reduced the corrosion rate by 48% and 68% in electrochemical polarization test and hydrogen evolution test, respectively, compared to pure Mg. The contributions of various strengthening mechanisms to the compressive yield strength of MMNCs were quantitatively predicted in conjunction with validation via experimental results. This study demonstrates the potential of GNPs as effective reinforcement in fabrication of MMNCs with improved mechanical and corrosion properties.

Structure and Phase Composition of a W-Ta-Mo-Nb-V-Cr-Zr-Ti Alloy Obtained by Ball Milling and Spark Plasma Sintering.

In this paper, the structural characteristics of a W-Ta-Mo-Nb-V-Cr-Zr-Ti non-equiatomic refractory metal alloy obtained by spark plasma sintering (SPS) of a high-energy ball-milled powder mixture are reported. High-energy ball milling resulted in the formation of particle agglomerates ranging from several tens to several hundreds of micrometers. These agglomerates were composed of micrometer and submicrometer particles. It was found that, during ball milling, a solid solution of A2 structure formed. The grains of the sintered material ranged from fractions of a micrometer to several micrometers. During SPS, the phase transformations in the alloy led to the formation of a Laves phase of C15 structure and ZrO and ZrO2 nanoparticles. The microhardness of the ball-milled alloy and sintered material was found to be 9.28 GPa ± 1.31 GPa and 8.95 GPa ± 0.42 GPa, respectively. The influence of the processing conditions on the structure, phase composition, and microhardness of the alloy is discussed.

Effect of Increasing the Strength of Aluminum Matrix Nanocomposites Reinforced with Microadditions of Multiwalled Carbon Nanotubes Coated with TiC Nanoparticles.

Aluminum matrix composites reinforced with multiwalled carbon nanotubes (MWCNTs) are promising materials for applications in various high-tech industries. Control over the processes of interfacial interaction in Al/MWCNT composites is important to achieve a high level of mechanical properties. The present study describes the effects of coating MWCNTs with titanium carbide nanoparticles on the formation of mechanical properties and the evolution of the reinforcement structure in bulk aluminum matrix nanocomposites with low concentrations of MWCNTs under conditions of solid-phase consolidation of ball-milled powder mixtures. Using high-energy ball milling and uniaxial hot pressing, two types of bulk nanocomposites based on aluminum alloy AA5049 that were reinforced with microadditions of MWCNTs and MWCNTs coated with TiC nanoparticles were successfully produced. The microstructural and mechanical properties of the Al/MWCNT composites were investigated. The results showed that, on the one hand, the TiC nanoparticles on the surface of the MWCNT hybrid reinforcement reduced the damage of reinforcement under the intense exposure of milling bodies, and on the other hand, they reduced the contact area of the MWCNTs with the matrix material (acting as a barrier interface), which also locally inhibited the reaction between the matrix and the MWCNTs.

The role of Fe particle size and oxide distribution on the hydrogenation properties of ball-milled nano-crystalline powder mixtures of Fe and Mg

In the aim of evidencing the relationship between Mg2FeH6 synthesis and the size of Fe particles, several specimens have been prepared by applying various milling energies (milling time) on a 2.1 Mg and 1Fe powder mixture doped with a small fraction of Unsaturated Fatty Amine (UFA). The resulting nano-crystalline composite structures display a broad Fe particle size distribution as a function of milling time. The hydrogenation of those complex powders has been conducted at temperatures lower than 400 °C under 60 bar of hydrogen pressure. As expected, the Fe particle size significantly influenced the hydrogenation kinetics. Also, the inevitable distribution of a minor fraction of oxides occurring during the milling process affected greatly the hydrogen storage capacity.Under the low pressure and temperature conditions selected in the frame of this study, lower than 100 bar and 500 °C conventionally used for synthesis of high purity Mg2FeH6, the hydrogenation reaction was demonstrated to be almost completed within 6 h, confirming the fast hydrogen absorption capability of the prepared materials. Plus, nearly 84 wt% of Mg2FeH6 was achieved under the afore mentioned moderate conditions and a minor fraction of unreacted Fe still remained due to diffusion constraints existing at low temperatures.

Nonlinear Electrical Properties of ZnO-V2O5 Based Rare Earth (Er2O3) Added Varistors

The densification, microstructure and nonlinear electrical properties of ZnO-V2O5-MnO2-Nb2O5 varistor ceramics have been investigated with different amounts (0–2 mol.%) of Er2O3 addition. The ball milled powder mixtures have been sintered at 900°C, 1100°C and 1300°C for 1 h. The microstructure shows the presence of ZnO grains as the primary phase with secondary phases like Zn3(VO4)2, ErVO4, Zn4V2O9, Er- and Mn-rich in the intergranular layers. Generation of ErVO4 and Er-rich secondary phases at triple points and grain boundaries is found to inhibit grain growth resulting in the significant reduction of ZnO grain size, although this slightly diminishes the densification process. At a particular sintering temperature, the size of ZnO grains gets reduced over ten times when Er2O3 addition is increased from 0 mol.% to 2 mol.%. The nonlinear electrical property of the varistors improves with Er2O3 addition up to 0.5 mol.% and further addition (1–2 mol.%) does not appear to be beneficial in the chosen sintering temperatures. For varistors sintered at 1100°C, average ZnO grain size reduces from 10.8 μm in Er2O3 free sample to 7.2 μm in 0.5 mol.% Er2O3 added sample; this, in turn, significantly improves nonlinear electrical properties. The breakdown field increases from 1588 V cm−1 to 2585 V cm−1 with concurrent enhancement of nonlinear exponent value from 16 to 26 when Er2O3 concentration is raised from 0 mol.% to 0.5 mol.%.

Carbide formation in electric-discharge-sintered Ti3Al compact caused by steric acid in ball-milled Ti and Al powder mixture

Elemental Ti and Al powders with a composition of Ti-25 at% Al, with and without 2 wt% steric acid as a process control agent, were ball-milled at 1000 rpm for 1 h using a Spex mill/mixer. The prepared powder mixture was then consolidated using an electric discharge sintering (EDS) with a 450 μF capacitor at an input voltage of 1.5–1.7 kV. The ball-milling process did not alter the original phase and composition of the elemental Ti and Al powders regardless of the addition of steric acid. However, the EDS of the ball-milled powder mixture with the steric acid formed nano-scaled Ti3AlC2 particles, which were embedded in the grains of the Ti3Al. The resulting compressive yield strength of the Ti3Al-Ti3AlC2 composite compact was about 1935 MPa, which is over twice the amount of the EDS compact obtained using the ball-milled powder mixture without the steric acid. In this paper, the fabrication method of the Ti3Al-Ti3AlC2 composite compact using an EDS process is reported for the first time, and the formation sequence and the strengthening mechanisms are discussed.

Low temperature sintered magneto-dielectric ferrite ceramics with near net-shape derived from high-energy milled powders

Nanosized Ni0.70Zn0.25Co0.05Fe1.90Mn0.02O4 ferrite ceramics were fabricated from high-energy ball milled powder mixtures with various ratios of Fe2O3/Fe as starting materials, in order to achieve magneto-dielectric materials with near net shape behavior for practical applications. The ferrite ceramics were obtained by sintering the milled powder compacts at 800 °C for 4 h, with a linear expansion of less than 4% as compared to the green pellets. The ceramics had an average grain size of less than 200 nm. The real part of relative permittivity decreases with increasing percentage of Fe2O3 used in the starting mixtures. The sample from the powder mixture with 50% Fe2O3 exhibits promising magneto-dielectric properties at frequencies of up to 90 MHz, which can be used for miniaturization of antennas at very high frequency (VHF) band.

Synthesis of nickel boride by thermal explosion in ball-milled powder mixtures

In this work, a synthesis route of Ni3B, an attractive material for making heating elements and a promising component for catalysts, was developed using high-energy ball milling of nickel and boron powder mixtures. The milling duration was varied from 1 to 15 min. Ball milling led to partial dissolution of boron in the crystalline lattice of nickel and crystallite size refinement of nickel. Heating of the ball-milled mixtures at a constant rate led to thermal explosion, the indications of which were a rapid temperature rise and the formation of boride phases. The duration of ball milling was shown to influence the phase composition of the products of thermal explosion. The time of milling ensuring the formation of single-phase Ni3B was determined to be 7 min. The ignition temperature of thermal explosion decreased with the milling time: a decrease by more than 300 °C was observed for the mixture milled for 15 min relative to the non-milled mixture. The maximum temperature developed during thermal explosion increased in the mixture milled for 1 min relative to the non-milled mixture and then decreased with the milling time reaching the level of the non-milled mixture after 15 min of milling. The observed dependence of the maximum temperature on the milling time is related to the net effect of mixing uniformity improvement between the reactants and a partial transformation of the reaction mixtures into Ni(B) solid solutions and Ni3B during milling. The proposed synthesis route of a single-phase Ni3B powder has advantages of short processing time and low-energy consumption.

The Effect of Powder Ball Milling on the Microstructure and Mechanical Properties of Sintered Fe-Cr-Mo-Mn-(Cu) Steel

Abstract The effect of ball milling powder mixtures of Höganäs pre-alloyed iron Astaloy CrM, low-carbon ferromanganese Elkem, elemental electrolytic Cu and C-UF graphite on the sintered structure and mechanical properties was evaluated. The mixing was conducted using Turbula mixer for 30 minutes and CDI-EM60 frequency inverter for 1 and 2 hours. Milling was performed on 150 g mixtures with (in weight %) CrM + 1% Mn, CrM + 2% Mn, CrM + 1% Mn + 1% Cu and CrM + 2% Mn + 1% Cu, all with 0.6%C. The green compacts were single pressed at 660 MPa according to PN-EN ISO 2740. Sintering was carried out in a laboratory horizontal furnace Carbolite STF 15/450 at 1250°C for 60 minutes in 5%H2 – 95%N2 atmosphere with a heating rate of 75°C/min, followed by sintering hardening at 60°C/min cooling rate. All the steels were characterized by martensitic structures. Mechanical testing revealed that steels based on milled powders have slightly higher mechanical properties compared to those only mixed and sintered. The best combination of mechanical properties, for ball milled CrM + 1% Mn + 1% Cu was UTS 1046 MPa, TRS 1336 MPa and A 1.94%.

Characteristics of WO3-CuO Powder Mixture Prepared by High-Energy Ball Milling in a Bead Mill for the Synthesis of W-Cu Nanocomposite Powder

A Nanosized WO3 and CuO powder mixture is prepared using novel high-energy ball milling in a bead mill to obtain a W-Cu nanocomposite powder, and the effect of milling time on the structural characteristics of WO3-CuO powder mixtures is investigated. The results show that the ball-milled WO3-CuO powder mixture reaches at steady state after 10 h milling, characterized by the uniform and narrow particle size distribution with primary crystalline sizes below 50 nm, a specific surface area of 37 m2/g, and powder mean particle size (D50) of 0.57 μm. The WO3-CuO powder mixtures milled for 10 h are heat-treated at different temperatures in H2 atmosphere to produce W-Cu powder. The XRD results shows that both the WO3 and CuO phases can be reduced to W and Cu phases at temperatures over 700oC. The reduced W-Cu nanocomposite powder exhibits excellent sinterability, and the ultrafine W-Cu composite can be obtained by the Cu liquid phase sintering process.

Fabrication of Tungsten Powder Mixtures with Nano and Micro Size by Reduction of Tungsten Oxides

An optimum route to fabricate a hybrid-structured W powder composed of nano and micro size powders was investigated. The mixture of nano and micro W powders was prepared by a ball milling and hydrogen reduction process for WO3 and W powders. Microstructural observation for the ball-milled powder mixtures revealed that the nano-sized WO3 particles were homogeneously distributed on the surface of large W powders. The reduction behavior of WO3 powder was analyzed by a temperature programmed reduction method with different heating rates in Ar-10% H2 atmosphere. The activation energies for the reduction of WO3, estimated by the slope of the Kissinger plot from the amount of reaction peak shift with heating rates, were measured as 117.4 kJ/mol and 94.6 kJ/mol depending on reduction steps from WO3 to WO2 and from WO2 to W, respectively. SEM and XRD analysis for the hydrogen-reduced powder mixture showed that the nano-sized W particles were well distributed on the surface of the micro-sized W powders.

Low temperature formation of Mg2FeH6 by hydrogenation of ball-milled nano-crystalline powder mixture of Mg and Fe

Low temperature formation of Mg2FeH6 is demonstrated by hydrogenation of Mg-Fe elemental powder mixture at a temperature as low as 350°C which is lower than the conventional process temperature, 500°C. To enable the low temperature synthesis, the powder mixture of Mg and Fe has been prepared by high energy ball milling using different process control agents (PCAs). A systematic study on the ball milling and hydrogenation conditions has been carried out to maximize the yield of the ternary line compound. The hydrogenation conditions together with the particle size of the starting materials turn out to play a significant role in the hydrogenation kinetics of the system. An optimized condition has demonstrated a significant hydrogenation as well as a robust cycling ability at low temperature which suggests the strong potential of the process for practical applications.