High-energy Ball Milling Time Research Articles

Effect of Milling Time and Reinforcement Volume Fraction on Microstructure and Mechanical Properties of SiCp-Reinforced AA2017 Composite Powder Produced by High-Energy Ball Milling.

The influence of milling time and volume fraction of reinforcement on the morphology, microstructure, and mechanical behaviors of SiCp-reinforced AA2017 composite powder produced by high-energy ball milling (HEBM) was investigated. AA2017 + SiCp composite powder with different amounts of SiC particles (5, 10, and 15 vol%) was successfully prepared from gas-atomized AA2017 aluminum alloy powder with a particle size of <100 μm and silicon carbide (SiC) powder particles with an average particle size of <1 μm. An optical microscope (OM), X-ray diffraction (XRD), and scanning electron microscope (SEM) were utilized to characterize the microstructure of the milled composite powder at different milling periods. The results indicated that the SiC particles were homogeneously distributed in the AA2017 matrix after 5 h of HEBM time. The morphology of the particles transformed from a laminar to a nearly spherical shape, and the size of the milled powder particles reduced with increasing the content of SiC particles. The XRD analysis was carried out to characterize the phase constituents, crystallite size, and lattice strain of the composite powders at different milling periods. It was found that with increasing milling time and SiC volume fraction, the crystallite size of the aluminum alloy matrix decreased while the lattice strain increased. The average crystallite sizes were reduced from >300 nm to 68 nm, 64 nm, and 64 nm after 5 h of milling, corresponding to SiC contents of 5, 10, and 15 vol%, respectively. As a result, the lattice strain increased from 0.15% to 0.5%, which is due to significant plastic deformation during the ball milling process. XRD results showed a rapid decrease in crystallite size during the early milling phase, and the minimum grain size was achieved at a higher volume fraction of SiC particles. Microhardness tests revealed that the milling time has a greater influence on the hardness than the amount of SiC reinforcements. Therefore, the composite powder milled for 5 h showed an average microhardness three times higher than that of the unmilled powder particles.

Photocatalytic activity enhancement of g-C3N4 nanosheets through simultaneous inter- and intra-layer charge separation using a facile mechano-thermal method

Herein, a novel mechano-thermal approach has been proposed to tune the electronic structure and enhance the photocatalytic performance of g-C3N4 nanosheets. According to the results, the high-energy ball-milling method modified the role of the ammonium chloride from the blowing agent to the doping agent, leading to the introduction of the interstitial and substitutional Chlorine (Cl) atoms into the nanosheet structure. Such a modification not only promoted electron-hole separation through the inter- and intra-layer of the g-C3N4 nanosheets, but it also led to the band gap energy reduction and higher oxidation capability of the photogenerated holes. These key improvements have been reflected in the optimized sample with a high-energy ball-milling time of 15 min (g-C3N4–15). Compared to the sample without the ball-milling process, g-C3N4–15 exhibited simultaneous intra- and inter-layer charge separation, reduction in the band gap energy from 2.82 to 2.76 eV, and positive shift in the valence band. Furthermore, these modifications in the electronic structure of the nanosheets contributed to the outstanding photocatalytic performance of the g-C3N4–15 towards methylene blue (MB) photodegradation. Among the samples with different ball-milling times, g-C3N4–15 demonstrated the highest MB photodegradation rate constant (0.0125 min−1), approximately 9 times greater than the sample without the ball-milling process. Additionally, the proposed photodegradation pathway suggested that the positive shift in the valence band of g-C3N4–15 could activate hydroxyl radicals (.OH) and promote demethylation and ring-opening of MB dyes.

Effect of High-Energy Ball Milling Time on the Density and Mechanical Properties of W-7%Ni-3%Fe Alloy

The present work was aimed at the investigation of the effect of high-energy ball milling (HEBM) time on the sintering kinetics, structure, and properties of the heavy tungsten alloy (HTA) W-7%Ni-3%Fe. The HTA samples were obtained from nanopowders (20–80 nm) using conventional liquid-phase sintering (LPS) in hydrogen and using spark plasma sintering (SPS) in vacuum. The HTA density was shown to depend non-monotonously on the HEBM time that originates from the formation of nonequilibrium solid solutions in the W-Ni-Fe systems during HEBM. The SPS kinetics of the HTA nanopowders was shown to have a two-stage character, the intensity of which depends on the Coble diffusion creep rate and on the intensity of diffusion of the tungsten atoms in the crystal lattice of the γ-phase. The kinetics of sintering of the initial submicron powders has a single-stage character originating from the intensity of the grain boundary diffusion in the γ-phase. The dependencies of the hardness and of the yield strength on the grain sizes were found to obey the Hall–Petch relation. The hardness, strength, and dynamic strength in the compression tests of the fine-grained tungsten alloys obtained using SPS and LPS were studied.

Unraveling the dispersion mechanism of carbon nanotubes in aluminum powder particles during high energy ball milling by FIB-TEM study

For the development of high-performance aluminum (Al) matrix composites reinforced with carbon nanotubes (CNTs), high energy ball milling (HEBM) is the most prevalent method to disperse CNTs in Al powder. However, the dispersion mechanism of CNTs in Al powder is still unclear, mainly because it is difficult to characterize CNTs when they are buried inside Al powder particles. Herein, focused-ion-beam-assisted transmission electron microscopy observation of CNTs in Al powder via HEBM with various milling times was conducted. Results showed that with increasing HEBM time, CNTs clusters were firstly broken up to be dispersed shorter-lengthed CNTs on the surface of Al flakes with gradually reduced thickness. Afterward, cold-welding of Al flakes was the predominant phenomenon, which resulted in re-spheroidization of Al powders and homogeneously dispersed CNTs. This study may provide guidance for controlling and optimizing the HEBM process to disperse CNTs in Al matrix towards the development of high-performance CNTs/Al composites.

Effects of titanium high energy ball milling on the solid-phase reaction Ti+C

The effect of high energy ball milling (HEBM) of titanium on the stoichiometry of TiCx under reaction diffusion in the Ti + C system was studied. It was found that under annealing simultaneous competing processes of carbon diffusion and recovery with further recrystallization stabilize nonstoichiometric products of Ti + C reaction. The process of TiC0.8-1.0 formation proceeds at a short HEBM time of Ti = 1 min. Nonstoichiometric carbides TiC0.4-0.5 are formed at HEBM times of Ti ≥ 3 min. The fraction of unreacted titanium depends on the size of the Ti grain.

Multiphase materials based on the Fe73.9Si15.5Cu1Nb3B6.6 alloy obtained by dry and wet high-energy ball milling processes

Novel hybrid materials based on the soft nanocrystalline Fe73.9Si15.5Cu1Nb3B6.6 alloy are designed in this work with the purpose of reducing its particle size and developing different compositional, structural, and magnetic properties depending on the high-energy ball milling time and route employed. Innovative processes combining mixer, vibratory and planetary motions at the same time are carried out under a dry and a wet route, obtaining reduced sub-micron particle size distributions after 2 h of milling. The established approach takes advantage of the nature of amorphous materials to promote the formation of different hybrid compounds and it is supported by the high virulence of the milling process performed at 2000 rpm. On the one hand, the results obtained by the dry route show a structural and magnetic evolution dominated by the presence of ferromagnetic α-Fe3Si nanocrystals. On the other hand, the wet approach that is supported by glycerol evidences the destruction of the α-Fe3Si with the milling time in favor of the non-magnetic β-FeSi2 phase, obtaining a new functionality for the Fe73.9Si15.5Cu1Nb3B6.6 alloy. Their properties as soft magnetic alloys are evaluated and compared depending on the followed route, opening up a new physicochemical method in the development of multiphase compounds with potential applications. With this work, a controlled formation of different hybrid compounds is achieved, revealing an effective mechanism to introduce functional materials with different properties embedded in an amorphous ferromagnetic matrix.

Particle size dependent anisotropic thermoelectric properties of N-type Bi2(Te,Se)3 alloys on hot deformation

The anisotropy of thermoelectric properties and microstructures in Bi2Te2.7Se0.3 fabricated by repressing (hot deformation) is investigated. The initial particle and grain size decreased with high-energy ball milling time, which affected the degree of grain orientation during the hot deformation process. To achieve high-performance thermoelectric properties, the anisotropic TE properties are optimized with the control of the degree of grain orientation, carrier concentration and temperature-dependent transport properties. By optimizing synthesis processes, we achieved a highly anisotropic figure of merit (ZT), with peak ZT values of 0.7 and 1.05 at 423 K, in the out of plane and in-plane directions, respectively. The in-plane ZT of the hot deformation sample was enhanced by 24% compared with that of the as-pressed sample (ZT = 0.85) due to reduced electrical resistivity and thermal conductivity, which was attributed to the significant anisotropy in grain orientation.

Studies on the Effect of Processing Parameters on Microstructure and Properties of Magnesium Compacts Prepared via Powder Metallurgy

The present study involves the investigation on the effect of processing parameters of powder metallurgy on the microstructure and hardness characteristics of the green as well as sintered specimens of magnesium. The processing parameters include the high-energy ball milling time, compaction pressure, and sintering temperature. From SEM images of 1, 3, and 5 h ball-milled powders, it is revealed that the sequence of change of morphology and size of particles is: flattening (formation of lamellas), fracturing (cracking of lamellas), and dynamic balance (adherence of a small particle with other particles and fracturing), respectively. The average particle size decreases with increasing ball milling time. 0, 1, 3, and 5 h ball-milled powders are compacted at different pressures. It is found that green density of the compacts of ball-milled powders depends on the morphology of powder particles, particle size, and compaction pressure. The selected samples were sintered at 500, 550, and 600 °C for 1 h. SEM characterization indicates that grain growth occurs with increasing sintering temperature. With constant mass, the sintering theory indicates that grain growth of larger particles takes place at the expense of smaller particles due to the difference of surface curvature. The density and hardness of sintered samples were calculated by using Archimedes principle and Vickers hardness tester, respectively.

Effect of particle size and high-energy ball milling time on microstructure and mechanical properties of WC-10Co cemented carbides with plate-like WC grains

The effect of particle size and high-energy ball milling time on microstructure and mechanical properties of WC-10Co cemented carbides with plate-like WC grains were studied using a scanning electron microscope, x-ray diffraction and mechanical properties tests. The results show that coarsening W particle size seemed to be beneficial for the increase of the plate-like WC content due to the easy acquirement of the thin W flake with high-density defects. Additionally, increasing the ball milling time could first increase the content of plate-like WC grains, and then decrease with 96 h ball milling. The high amount of defects and activity of fine W particles from fracturing with long ball milling time could enhance the formation of plate-like WC grains. However, the oxygen content could be increased with the excess ball milling time, which reduced the content of liquid Co and thus impeded the formation of plate-like WC grains. As the content of plate-like WC grains increased, the intergranular fracture gradually transformed into the main fracture mode. Additionally, crack bridging and crack path deflection could be seen in the alloy with plate-like WC grains. The high fracture surface area and energy required for crack propagation could improve the strength of WC-10Co cemented carbides with plate-like WC.

Structure and Mechanical Properties of the New Ti30Ta20Nb Biomedical Alloy.

In order to better understand the relationship between parameters of a mechanical alloying process and microstructure, especially the structure of porosity, some research and studies were carried out. The current study investigates the possibility to prepare the porous materials by mechanical alloying and annealing. A high-energy ball-milling process in the planetary ball mill Fritch PULVERISETTE 7 premium line was used for the solid-state synthesis of the single phase powders for titanium based biomedical alloy. The influence of the high-energy ball-milling time on the structure and morphology of the synthesized precursors after annealing was investigated. Additionally, the effect of the variable time of the ball-milling on the structural characteristics, pore morphology and mechanical properties of a biomedical Ti30Ta20Nb (wt.%) was investigated as well. This study confirms the predominance of the titanium β phase and also the presence of the titanium α phase. The analysis of the diffraction patters obtained using the Rietveld method showed that when the milling time increases, the lattice parameters for the tested samples become reduced. Summing up, it should be pointed out that the areas of pure unreacted titanium still exist in the material. These areas were correlated to the results of an X-ray diffraction analysis. This research starts the process of converting mechanical alloying into a production method which could become an alternative to the space holder technique for the new titanium alloys used for medical applications.

Optimization of High-Energy Ball-Milling Time for Fe1.1Se0.5Te0.5 Polycrystalline Superconductors

The Fe 1.1 Se 0.5 Te 0.5 polycrystalline superconductors were prepared by a high-energy ball-milling (HEBM) technique. Ball-milling times of 0, 2, 4, 6, and 8 h were adopted to optimize this technique. The influences of ball-milling time on the phase distributions of milled powders and sintered bulks, the morphology of ball-milled powders, and superconducting properties of final sintered bulks were systematically studied. It was found that with increasing ball-milling time, the ball-milled powders changed from a crystal to a noncrystalline and then to an alloy. At the same time, the main phases in ball-milled powders changed from original mixed powders of Fe, Se, and Te to (Se, Te) solid solution, and then to the two phases of β-Fe(Se, Te) and δ -Fe(Se, Te), accordingly. Due to the reduction in diffusion length, it was more likely for HEBM powders to form FeSeTe ternary alloys. Thus, the obtained Fe(Se, Te) bulk with HEBM time of 4 h exhibited the highest T c of 14.3 K and the largest content of superconducting phase. However, in the samples achieved by longer HEBM time, phase segregation and oxidation were observed. Therefore, the HEBM time of 4 h is the most suitable for the fabrication of high-quality precursor powders according to these experiments.

The influence of high-energy ball milling on the heterogeneous reaction kinetics in the Ti-Si system

The high-temperature (1300–1600 K) kinetics for the Ti-Si reactive system were investigated using electro-thermal analysis. The influence of short-term (1–3 min) high-energy ball milling (HEBM) of Ti+0.6Si heterogeneous powder mixtures on the kinetic parameters was also studied. It was shown that HEBM leads to a significant decrease of the apparent activation energy (Ea) of the solid-state reaction between silicon and titanium. For the non-milled mixture, Ea is 339 ± 63 kJ/mol, while after 3 min of HEBM it drops more than twice to 148 ± 12 kJ/mol. The reaction initiation temperature also decreases with an increase of HEBM time: from 1467 ± 62 K for the pristine mixture to 1110 ± 42 K after 3 min of mechanical treatment. The conclusion was made that a decrease of crystalline size and an increase of the crystal lattice defect concentration, which in combination enhance the grain boundary diffusion, can be responsible for the high reactivity of the mechanically activated mixtures.

Phase composition and microstructure of new Ti–Ta–Nb–Zr biomedical alloys prepared by mechanical alloying method

The study presents the results of the influence of high-energy ball-milling time on the structure of the new β-type Ti–Ta–Nb–Zr alloys for biomedical applications. Initial elemental powders were mechanically alloyed in a planetary high-energy ball mill at different milling times (from 10 to 90 h). Observation of the powder morphology after various stages of milling leads to the conclusion that with the increase of the milling time the size of the powder particles as well as the degree of aggregation change. Clear tendency of crystalline size reduction at every stage of the grinding process is clearly observed. The X-ray diffraction results confirmed the formation of β phase during high-energy ball milling of the precursor mixture of Ti, Ta, Nb, and Zr. The Rietveld refinement method has shown that both the production method and the atomic radii of the elements used in the mechanical synthesis have influence on the structure. Furthermore, it was found that a broadening of the diffraction peaks with increase of the milling time results from an increase in the crystallites dispersion and an enlargement in the lattice distortion. The results indicate that this technique is a powerful and high productive process for preparing new β-titanium alloys with nanocrystalline structure and appropriate morphology.

Fabrication of lanthanum-doped thorium dioxide by high-energy ball milling and spark plasma sintering

AbstractHigh-energy ball milling was used to synthesize Th1-xLaxO2-0.5x (x = 0.09, 0.23) solid solutions, as well as improve the sinterability of ThO2 powders. Dense La-doped ThO2 pellets with theoretical density above 94% were consolidated by spark plasma sintering at temperatures above 1400 °C for 20 min, and the densification behavior and the non-equilibrium effects on phase and structure were investigated. A lattice contraction of the SPS-densified pellets occurred with increasing ball milling duration, and a secondary phase with increased La-content was observed in La-doped pellets. A dependence on the La-content and sintering duration for the onset of localized phase segregation has been proposed. The effects of high-energy ball milling, La-content, and phase formation on the thermal diffusivity were also studied for La-doped ThO2 pellets by laser flash measurement. Increasing La-content and high energy ball milling time decreases thermal diffusivity; while the sintering peak temperature and holding time beyond 1600 °C dramatically altered the temperature dependence of the thermal diffusivity beyond 600 °C.

Mechanical behaviour of dual nanoparticle-reinforced aluminium alloy matrix composite materials depending on milling time

Aluminium 6061 alloy matrix composite materials reinforced with carbon nanotubes (CNTs) and silicon carbide nanoparticles (nSiCs) were prepared by high-energy ball milling and hot pressing. In addition to inducing fine particle strengthening, nSiCs were also used as a solid mixing agent to improve the dispersion of the CNTs in the Al matrix powder. The dependence of the densification and mechanical strength of the composites reinforced with the dual nanoparticles on the milling time is discussed. The crystallite sizes of Al in the composites were also investigated. Moreover, the relative defect ratios of the CNTs in the composites were calculated from the intensities of the D and G peaks of the Raman spectra. With this new approach to composite fabrication, a hardness and tensile strength of 334 HV and 293 MPa, respectively, were achieved. The high-energy ball milling time significantly affected the microstructure and mechanical properties of the composites; however, the dual nanoparticle reinforcement can potentially be used in a variety of industrial component materials with precisely controlled material properties.

Preparation of Mg/Nano‐HA Composites by Spark Plasma Sintering Method and Evaluation of Different Milling Time Effects on Their Microhardness, Corrosion Resistance, and Biocompatibility

Herein, Mg/nano‐HA composites (10 wt% nano‐HA) are prepared by spark plasma sintering (SPS) technique. Indeed, hydroxyapatite (HA) is used as reinforcement material in order to maintain biocompatibility and bioactivity. The influence of high energy ball milling time are considered by different methods. The study finds that an appropriate time (5 h) during high energy ball milling process effectively can eliminate the prior particle boundary (PPB). Furthermore, the Mg/nano‐HA composites milled for 5 h has appropriate microhardness, stable corrosion resistant, and excellent biocompatibility, which can act as a potential candidate for orthopedic implants.

Microstructural effects on the sliding-wear resistance of ZrC–MoSi2 triboceramics fabricated by spark-plasma sintering

The effects were individually investigated of ZrC grain size and MoSi2 content on the lubricated sliding-wear resistance of ZrC–MoSi2 triboceramics densified by spark-plasma sintering (SPS). Microstructures with different average grain sizes were obtained by varying the high-energy ball-milling time of the ZrC–MoSi2 powder mixtures and their SPS temperature, while the microstructures with different secondary phase contents were obtained by varying the relative concentrations of ZrC and MoSi2 in the powder batches. Experimentally, it was found that the ZrC–MoSi2 triboceramics are all highly wear resistant, but also that wear resistance decreases as the ZrC grain size and MoSi2 content increase. The dominant wear mode was identified as abrasion, and the prevailing wear mechanism was plastic deformation accompanied by localized fracture. Accordingly, the wear trends are explained in terms of the hardness of the ZrC–MoSi2 triboceramics. Finally, the implications are discussed of providing the electrically-conductive ZrC–MoSi2 triboceramics with greater wear resistance via controlled processing.

Effects of High-Energy Ball Milling Time on the Sintering Process of FeSe Superconductors

FeSe superconducting bulks were prepared with high energy ball milling (HEBM) aided sintering process, within which process, tetragonal β-FeSe superconducting phase could be formed directly with one step sintering process, and the formation of hexagonal δ-FeSe non-superconducting phase was effectively avoided. The influences of HEBM time on the sintering process of FeSe bulks were systematically investigated. With different HEBM time, the phase composition and morphology of precursor powders changed correspondingly, which thus influenced the final phase composition and superconducting properties of FeSe superconducting bulks. Due to the formation of FeSe bulks with larger tetragonal phase content and higher superconducting transition temperature, HEBM time of 6.0 h was recognized as the optimal parameter. Shorter HEBM time could lead to the insufficient decrease of particle size and low density. While longer HEBM time caused the formation of amorphous hexagonal δ-FeSe, which crystallized during sintering process. Thus no more tetragonal FeSe could be obtained. The FeSe superconducting bulk with the critical temperature Tc(onset) of 8.0 K was obtained with the HEBM time of 6 h, and sintering temperature of 700 oC for 12 h.

Optimization of FeSe superconductors with the high-energy ball milling aided sintering process

FeSe Superconducting bulks with high superconducting phase ratio were prepared with high energy ball milling (HEBM) aided sintering process. During the HEBM process, the solid solution of Fe–Se (Fe(Se)SS) can be successfully obtained, which not only assured the atomic uniformity of precursor powders, but greatly shortened the diffusion distance between Fe and Se atoms. Therefore tetragonal β-FeSe superconducting phase can be formed directly with one step sintering process and the formation of hexagonal δ-FeSe non-superconducting phase can be avoided. The influences of Fe/Se ratio and sintering temperature on the phase transition process and the superconducting properties were systematically studied. The change of Fe/Se ratio showed great influences on both the superconducting volume and critical temperature of final bulks. By increasing the sintering temperature to 700 °C, FeSe bulk with higher texture, better crystallization and optimized chemical composition was achieved. The FeSe superconducting bulk with the critical temperature Tc(onset) of 9.0 K was obtained with the Fe/Se ratio of 1.20, HEBM time of 6 h, and sintering temperature of 700 °C.

Phase transformation of the CuAl2 intermetallic alloy during high-energy ball-milling

In the present investigation, we have studied the phase transformation of the CuAl2 intermetallic alloy with tetragonal structure by high-energy ball-milling. The structural changes with milling time were followed by X-ray diffraction, differential scanning calorimetry and electron microscopy. It is found that CuAl2-phase transforms to body centered cubic structure after a long periods of high-energy ball-milling time. According to SEM results, the milling powders change their mechanical behavior from brittle to ductile during the phase transformation. Rietveld analysis showed that around 29% of unit cells in the metastable cubic structure are occupied by Cu suggesting Al segregation in the material and explaining the change in the mechanical behavior of the alloy.