High-energy Milled Research Articles

Innovative, low-cost eco-composite boards produced from high-energy milled wood, plastic waste, and bio-polymer

Currently, there is a big issue with waste, its processing and subsequent use. While there are many initiatives to replace materials that are poorly biodegradable, it is necessary to process and ideally use the waste that is already produced. In this study, the properties of composite boards made of waste materials and biodegradable polymer were investigated. The composite boards were made from wood and plastic waste using high-energy milling technology. This technology for material preparation is promising, as it includes controlling the morphology of particles, homogenizing the mixture, and drying the material during the milling process. The results showed higher flexural strength of high-density fiberboard (HDF) boards compared with tested composites with one exception. Wood/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] composite exhibited 30% higher modulus of elasticity (MOE) than HDF due to the higher modulus of PHBV. The lowest thickness swelling (3%) and water absorption (12%) were measured for wood/recycled high density polythene (rHDPE) composite. The HDF boards recorded the lowest dimensional stability. The highest water absorption of tested composites was measured for wood/PHBV composite. The resistance to wood-rotting fungi was greatest for wood/PHBV composite containing marble powder, which corresponded to the results of scanning electron microscopy.

Influence of Pre-Milling of Cr3C2-25 NiCr Spray Powder on the Fatigue Life of HVOF-Sprayed Coating on ASTM A516 Steel Substrate

The aim of the present investigation is to evaluate the influence of the powder size of Cr3C2-25NiCr spraying powder on the fatigue behavior of HVOF-sprayed coating on the ASTM A516 steel substrate. Conventional commercial Cr3C2-25NiCr spraying powder was previously treated through high-energy milling. The crystallite sizes of milled powders were measured by X-ray diffraction and transmission electronic microscopy. Three different powder formats of the same Cr3C2-25NiCr composite were subjected to HVOF spraying to produce (i) a Milled-Coating (from high-energy milled spray powder), (ii) an Original-Coating (from conventional commercial spray powder), and (iii) a 50%-50% mixture of both (Milled + Original-Coating). The same spraying conditions were adopted for all the assessed cases. The sprayed coatings were investigated through the Knoop hardness test and SEM-EDS analysis. In addition, 3-point bending fatigue tests were conducted at different stress levels up to 107 cycles. The coating morphology and roughness effects on fatigue behavior were analyzed. The Cr3C2-25NiCr milled coating presented a lower fatigue life above the fatigue limit and a higher fatigue limit than other coatings; this outcome could be attributed to its lower surface roughness and finer grain size microstructure.

Improving plasticity of kaolins by high-energy milling for use in porcelain tile compositions

The production of porcelain tiles is increasing in Brazil besides the production of grés tiles and monoporosa is decreasing since COVID 19. Plastic clays are used in the composition of porcelain tiles to give plasticity to the pastes in the forming step. However, there is a shortage of plastic clays in south Brazil, the largest producer of porcelain tiles. Therefore, the aim of this work was to improve the plasticity of two commercially available kaolins by high-energy milling (HEM). Both kaolins were characterized before and after milling by X-ray diffraction, particle size, plasticity, and cation exchange capacity techniques. After high-energy milling, the processed kaolins were used in the composition of a commercial porcelain tile paste. The performance of the paste before and after use of the processed kaolins was determined regarding its firing shrinkage and sintering temperature. The porcelain tile compositions with the high-energy milled kaolins showed less densification during pressing and greater shrinkage after firing, but the tiles presented dimendional stability, improving the quality of the tiles.

Submicron Ti(C,N)-based cermets with improved microstructure using high-energy milled and subsequent heat-treated ultrafine Ti(C,N) powders

Ti(C,N)-based cermets with ultrafine or submicron black core-rim grains are attracting candidates for high-quality tools and dies, due to their high hardness and strength. However, high chemical activity of ultrafine Ti(C,N) powders lead to the increased instability and difficulty to control the sintering process, since the denitrification and interface diffusion are accelerated during the solid-state reaction. Based on this, owing to the unrealized commercial ultrafine-grade powders, ultrafine Ti(C,N) powders with an average grain size around 150 nm, low oxygen content and few dislocations are fabricated via the high-energy ball milling and subsequent heat treatment of commercial micron Ti(C,N) powders. Related morphology evolution, microstructure and composition of the ultrafine Ti(C,N) powders are investigated. Dense submicron Ti(C,N)-based cermets with grain size of 0.62 μm and uniform core-rim phases are successfully prepared by using the as-fabricated ultrafine Ti(C,N) powders. Compared to cermets via the conventional high-energy milling route, submicron Ti(C,N)-based cermets exhibit higher hardness of 1750 ± 40 N/mm2, bending strength of 1960 ± 135 MPa, and satisfactory fracture toughness of 9.2 MPa m1/2, owing to smaller grain size, uniform microstructure and partial black core-rim grains.

Use of XRD technique to investigate the stability of quasicrystalline phase in high-energy milled Al/AlCuFe powders

Quasicrystalline alloys have excellent potential for being used in composites. They have high hardness, low friction coefficient and, in particular for AlCuFe, the components have high availability. The quasicrystal of the AlCuFe alloy can especially work well as reinforcements in aluminium matrix composites, contributing to increasing hardness, when compared to pure aluminium. Depending on the method used to obtain the composite, high-energy milling is necessary to mix the powders of the matrix and the reinforcement. Therefore, this work aimed to investigate the stability of quasicrystalline phase in Al/AlCuFe powders milled using XRD technique. For this, Al/AlCuFe powders were milled in high energy planetary ball mill in proportions of 10 and 20%vol. of AlCuFe. XRD analysis were then carried in the samples. The results showed that, for the parameters used, there was no phase transformation during milling.

Development of dense Al2O3–TiO2 ceramic composites by the glass-infiltration of porous substrates prepared from mechanical alloyed powders

In this work bio-composites were obtained by infiltrating porous alumina–titania (Al2O3–TiO2) substrates with a lanthania-rich (La2O3) glass. Al2O3–TiO2 substrates were fabricated using high-energy milled powder mixtures of two different compositions with molar ratios of 3:1 and 1:1, uniaxial compaction under 100 MPa and sintering at 1300 °C - 2 h or 1400 °C - 2 h. The high energy milling process of the powders resulted in homogeneous, extremely fine mixtures. For comparison, as-received Al2O3 and TiO2 powders were also mixed at a proportion of 3:1 and sintered at 1600 °C - 2 h. The sintered substrates presented α-Al2O3 and β-Al2TiO5 (aluminium titanate) as crystal phases and relative densities ranging between 65.5 ± 2% and 69.4 ± 1.2% of the theoretical density. These porous substrates were infiltrated with a lanthania containing glass at a temperature of 1140°C-2h. The resulting ceramic composites exhibited high density, varying between 94 to 99% of the theoretical density, Vickers hardness ranging between 895 ± 14 HV and 1036 ± 33 HV, fracture strength ranging between 218 ± 28 MPa and 254 ± 18 MPa and a fracture toughness (KC) higher than 2.6 MPam1/2. Phase analysis of the infiltrated substrates by X-ray diffraction indicated the decomposition of aluminium titanate into alumina and titania besides the formation of lanthanum borosilicate, LaBSiO5. In addition, all compositions studied presented non-cytotoxic behaviour and low chemical solubility, inferior to 75 μg/cm2.

Investigation of the electrochemical corrosion properties of high-energy milled Ti6Al4V alloy in simulated body fluid environment

ABSTRACTIn this study, the electrochemical corrosion properties of high-energy milled Ti6Al4V alloy are investigated. The Ti6Al4V alloy is produced by high-energy milling at different milling times in mechanical milling device as 15–120 min. Produced alloy powders are cold-pressed under 620 MPa pressure and sintered at 1300°C temperature and characterised by scanning electron microscopy (SEM), X-ray diffraction, hardness and density measurements. Corrosion tests are conducted in simulated body fluid at 37°C body temperature. Results showed that the average particle size of the powder is reduced, and the hardness of the alloy is increased with the increasing milling time. It is determined that the corrosion properties of the alloys change by the high-energy milling time, and the corrosion rate increases by the decreasing particle size of the powder. SEM examination of the corroded surfaces after potentiodynamic polarisation tests revealed that pitting formation tendency of the alloys on the alloy surface increases by the increasing high-energy milling time.

Refractory metal alloying: A new method for improving mechanical properties of tungsten heavy alloys

Abstract Influence of mechanically alloyed tungsten-rhenium powders on the microstructure and mechanical properties of liquid phase sintered 89W-7Ni-3Fe-1Re heavy alloy was studied. Heat treatment and swaging were conducted on alloys prepared using both conventionally blended and mechanically milled powders. The results indicated the formation of bcc solid solution by high energy milling of tungsten and rhenium powders. The corresponding particle and the crystallite size decreased after high energy milling. Grain size and contiguity of the milled alloy were significantly lower than those of conventional counterpart. The alloy prepared using high energy milled W-Re powder exhibited relatively superior balance of strength, ductility and impact toughness. These findings suggest that refractory powder mechanical alloying prior to sintering is beneficial for improving the mechanical properties of tungsten heavy alloys.

Structural and thermodynamic properties of nanocrystalline Cr3C2–25(Ni20Cr) composite powders produced by high-energy ball milling

Nanostructured coatings have been used to protect components exposed to severe service conditions. High energy milling is widely used to produce nanocrystalline feedstock of coating materials such as chromium carbide and tungsten carbide. This paper presents the structural and thermodynamic properties of Cr3C2–25(Ni20Cr) powders that were high energy milled for different times. During the high energy milling of Cr3C2–25(Ni20Cr) powder, severe plastic deformation takes place. A small part of the energy spent in this process is stored in the crystal lattice as deformation energy. The crystallite size and microstrain in nanocrystalline Cr3C2–25(Ni20Cr) powders milled for different times were determined by X-ray diffraction measurements. Differential scanning calorimetric (DSC) studies of the milled powders revealed a broad transformation, characteristic of a large exothermic reaction in the nanostructured powder. The enthalpy variation measured by DSC permitted determination of the deformation energy stored in the Cr3C2–25(Ni20Cr) powders milled for different times. These measurements also enabled calculation of the specific heat variation of the milled powders.

Improved field emission stability and uniformity of printed carbon nanotubes prepared using high energy-milled glass frit

Stable and uniform electron field emitters were fabricated by the screen-printing of a carbon nanotube (CNT) paste. The CNT paste was prepared by mixing thin multi-walled CNTs, organic binder and glass frits in terpineol followed by three-roll milling. The paste was screen-printed onto an indium tin oxide (ITO)-coated glass substrate and exposed to firing. The emitters formed by the adhesive tape treatment of the printed pastes generally showed non-uniform heights of emitting tips due to the large-sized glass frit distributed in the paste. On the other hand, small glass frits with a uniform particle size distribution could be obtained by high energy milling. In addition, the CNT paste prepared using the high energy-milled glass frits showed very uniform tip heights. The uniform CNT tip height was found to play an important role in acquiring the long-term emission stability and uniformity of field emitters.

고에너지 밀링을 통한 Ni-BaCe0.9Y0.1O3-δ서멧 멤브레인의 미세구조 균질성 향상

Hybridization of dense ceramic membranes for hydrogen separation with an electronically conductive metallic phase is normally utilized to enhance the hydrogen permeation flux and thereby to increase the production efficiency of hydrogen. In this study, we developed a nickel and proton conducting oxide (BaCe 0.9 Y 0.1 O 3-δ : BCY) based cermet (ceramic-metal composites) membrane. Focused on the general criteria in that the hydrogen permeation properties of a cermet membrane depend on its microstructural features, such as the grain size and the homogeneity of the mix, we tried to optimize the microstructure of Ni-BCY cermets by controlling the fabrication condition. The Ni-BCY composite powder was synthesized via a solid-state reaction using 2NiCO₃·3Ni(OH)₂·4H₂O, BaCeO₃, CeO₂ and Y₂O₃ as a starting material. To optimize the mixing scale and homogeneity of the composite powder, we employed a high-energy milling process. With this high-energy milled composite powder, we could fabricate a fine-grained dense membrane with an excellent level of mixing homogeneity. This controlled Ni-BCY cermet membrane showed higher hydrogen permeability compared to uncontrolled Ni-BCY cermets created with a conventionally ball-milled composite powder.

Topological investigation of electronic silicon nanoparticulate aggregates using ultra-small-angle X-ray scattering

The network topology of two types of silicon nanoparticles, produced by high energy milling and pyrolysis of silane, in layers deposited from inks on permeable and impermeable substrates has been quantitatively characterized using ultra-small-angle X-ray scattering, supported by scanning electron microscopy observations. The milled particles with a highly polydisperse size distribution form agglomerates, which in turn cluster to form larger aggregates with a very high degree of aggregation. Smaller nanoparticles with less polydisperse size distribution synthesized by thermal catalytic pyrolysis of silane form small open clusters. The Sauter mean diameters of the primary particles of the two types of nanoparticles were obtained from USAXS particle volume to surface ratio, with values of ~41 and ~21 nm obtained for the high energy milled and pyrolysis samples, respectively. Assuming a log-normal distribution of the particles, the geometric standard deviation of the particles was calculated to be ~1.48 for all the samples, using parameters derived from the unified fit to the USAXS data. The flow properties of the inks and substrate combination lead to quantitative changes in the mean particle separation, with slowly curing systems with good capillary flow resulting in denser networks with smaller aggregates and better contact between particles.

High Energy Milled Ex Situ MgB2 as Precursor for Superconducting Tapes Without Critical Current Anisotropy

One lane of the present MgB2 research is focused on scale-up of the conductor preparation for magnet applications. One limitation is the deformation of long length powder in tube conductors since the composite structure leads to a couple of complications. Therefore, a combination of various methods is commonly used: swaging, drawing, and flat rolling. In dense tapes deformed via distinct routes, a critical current anisotropy with respect to an external magnetic field is observed. The in situ method (unreacted Mg+B) is preferably used for conductor preparation, with the advantage offering more doping possibilities for the precursors to create flux pinning centers and to enhance the upper critical field and supporting a dense filament. In this work, we show in concurrence to the commonly preferred route, the possibility and potential of ex situ conductor preparation schemes, with the option of carbon doping, using high energy milling. Long multifilament tapes with 20 hours milled powder without carbon and with 5 wt% C were successfully deformed to wires and tapes. Tapes with 21 cores show critical current densities with Jc=104 A/cm2 at B=8.8 T without any current anisotropy in different field-direction different to the case of the in situ conductors.

Fabrication of TiAl Alloy Powders by High-Energy Ball Milling and Low Temperature Sintering

Ti/Al(Ti-50at.%Al) composite powders were prepared by high-energy ball milling followed by reaction sintering heat treatment at 550°C ~ 650°C for 2 hours. Mechanical alloying of TiAl had been performed in a high energy plant ball after different milling times and pre-sintered at different temperatures. The particle sizes of Ti/Al powders were analyzed by scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis was performed for microstructural characterization. The results show that microstructural and morphological changes of high energy milled powder are studied as a function of milling time. Over 600°C TiAl powders are completely alloyed by being sintered at different temperatures. The powders are mainly composed of γ-TiAl as well as a small amount of AlTi3. The TiAl alloy powders of high energy ball mill/2h and sintered at 650°C/2h get plasma spheroidization. Spheroidizing powders with fine texture, γ-TiAl and AlTi3phase, particle size of 10~40μm are obtained.

Microstructure Evolution of a Fine Grain Al-50wt%Si Alloy Fabricated by High Energy Milling

Microstructure evolution of high energy milled Al-50wt%Si alloy during heat treatment at different temperature was studied. Scanning electron microscope (SEM) and X-ray diffraction (XRD) results show that the size of the alloy powders decreased with increasing milling time. The observable coarsening of Si particles was not seen below 730°C in the high energy milled alloy, whereas, for the alloy prepared by mixed Al and Si powders, the grain growth occurred at 660°C. The activation energy for the grain growth of Si particles in the high energy milled alloy was determined as about 244 kJ/mol by the differential scanning calorimetry (DSC) data analysis. The size of Si particles in the hot pressed Al-50wt%Si alloy prepared by high energy milled powders was 5-30 m at 700°C, which was significantly reduced compared to that of the original Si powders. Thermal diffusivity of the hot pressed Al-50wt%Si alloy was 55 mm2/s at room temperature which was obtained by laser method.

Synthesis of Layered Ti<sub>2</sub>Al(N<sub>0.5</sub>C<sub>0.5</sub>) by a Combination of High Energy Milling and Hot Press Sintering

Elemental mixture of Ti, Al and C was high energy milled in a planetary ball mill under high-purity nitrogen gas protection and then hot pressed. The fully dense bulk layered ternary Ti2AlN0.5C0.5 with sub-micron grain size was successfully obtained. The phase formation and transformation in high energy milling and subsequently hot press sintering were studied in detail by using X-ray diffraction (XRD). Scanning electron microscopy (SEM) linked with energy dispersive spectroscopy (EDS) was used for the structural and compositional analysis. The formation mechanism was also discussed.

Effect of milling intensity on the formation of LiMgN from the dehydrogenation of LiNH 2–MgH 2 (1:1) mixture

Metal–N–H systems have recently attracted considerable attention as alternative hydrogen storage materials to traditional metal hydrides. In this work, the reactions of the mixture LiNH 2–MgH 2 (1:1) during different mechanical milling processes and the subsequent dehydrogenation reaction were investigated by using TGA, XRD and FT-IR in order to determine an optimal condition for the formation of pure LiMgN. High-energy milling (SPEX mill) and low-energy milling (rolling jar) techniques were used in this work. The results demonstrated that monolithic LiMgN can be produced using the low-energy ball milling technique. The hydrogenation properties of the as-prepared LiMgN were investigated by a Sieverts’ type instrument. In contrast, multiple reactions including the metathesis reaction between LiNH 2 and MgH 2 and release of H 2 and/or NH 3 took place during high-energy milling using the SPEX mill, which resulted in complicated and unexpected reactions during the subsequent dehydrogenation experiments. Consequently, the dehydrogenated products from the high-energy milled samples consisted of multi-phase mixtures.

Synthesis of Mg 15Fe materials for hydrogen storage applying ball milling procedures

The effects of different synthesis procedures on the microstructure and hydrogen uptake characteristics of the Mg 15Fe materials were studied. The applied processes of synthesis consisted basically on ball milling in argon atmosphere followed by a hydriding reaction. Two mill devices with distinct milling modes were employed, i.e. a low energy mill (LEM) (Magneto Uni-Ball-Mill II) and a high energy mill (HEM) (Fritsch Planetary Mill, P6). The HEM sample showed better Mg–Fe mixing degree than the sample obtained from the LEM process due to the small particles of Fe resulting from the larger amount of mechanical energy transferred to the materials by the HEM device. The better Mg–Fe contacting was responsible for the higher hydrogen capacity and faster hydrogen uptake rate of the high energy milled material. Therefore, the HEM procedure was more effective than the LEM. The hydrogen uptake properties of the HEM synthesized material were compared with other Mg-based materials obtained via inert and reactive ball milling without a subsequent activation step. This study showed that Mg 15Fe mixture of powders synthesized via reactive ball milling in hydrogen (RBM–LEM) has higher hydrogen capacity (5.5 wt% H) and faster kinetics than samples with the same composition milled in argon (LEM – 1.65 wt% H and HEM 1.87 wt% H). Nevertheless, a superior hydrogen capacity (6.5 wt% H) were obtained by adding LiBH 4 to Mg 15Fe via HEM in argon atmosphere.

TEM analysis and sorption properties of high-energy milled MgH 2 powders

The main focus of this work was the use of cryo-stage transmission electron microscopy (TEM) to elucidate features of the milled MgH 2 powder microstructure not accessible via “conventional” hydride characterization techniques such as X-ray analysis. We chose a classic problem in hydride research: the effect of high energy milling on the microstructure and the desorption properties of magnesium hydride (MgH 2) powder. High-energy mechanical milling provided for marked hydrogen desorption enhancement, while subsequent annealing reduced and ultimately eliminated it. Milling created a significant amount of microstrain in the α-MgH 2. It also reduced the particle size and changed the size distribution to be multi-modal. Milling reduced α-MgH 2 grain size by a factor of two, which can be considered a fairly minor effect. Post-milling anneals completely eliminated the microstrain, increased the grain size to a similar value as the as-received powder, and smoothed the particle size distribution. Using TEM we were able to image the individual hydride grains within the powder particles. TEM analysis of the milled microstructure identified a high density of nano-scale twins within the hydride grains. Annealing reduced the twin density and coarsened their size. Elasticity analysis indicates that the energy stored by the accumulated dislocations as the result of the milling is negligible compared to the heat of the hydride formation.

Pressureless reactive sintering of ZrB 2 ceramic

Pressureless reactive sintering was investigated to fabricate ZrB 2 from a mixture of elemental Zr and B powders. Both hand mixing and high-energy milling were used to blend the powders. The sintering experiments were carried out at 1800, 2000 and 2200 °C. The samples made from the high-energy milled powders had relative densities varying between 66 and 79%, while the relative densities of the hand mixed powders varied between 58 and 70%. The average grain size of the sintered ceramic was independent of the mixing procedure and increased with the sintering temperature (from 8.5 to 23.5 μm for the hand mixed samples and from 4.6 to 34.9 μm for the milled samples).