Early Stage Of Milling Research Articles

Synthesis, thermodynamic analysis and magnetic study of novel ball- milled Co50Fe25Ta5Si5C15 glassy powders with high thermal stability

In this study, novel glassy Co–Fe–Ta–Si–C alloys were prepared by mechanical alloying, (MA) and the influence of annealing treatment and substitution of Fe for Co on glass-forming ability (GFA), thermal stability and magnetic properties were investigated. Quantitative X-ray diffraction (XRD) analysis by the Rietveld method showed that the new Co50Fe25Ta5Si5C15 powders have an enhanced glass formation rate, especially during the early milling stages compared to the Fe-free Co75Ta5Si5C15 alloy. In good agreement with the XRD measurements, the calculated PHSS thermodynamic parameter revealed that the GFA is notably increased for the new powder. Thermal analysis demonstrated a high thermal stability and a rather wide supercooled liquid region (SLR) of 51 K for the Co75Fe25Ta5Si5C15 glassy alloy. The milling process and subsequent annealing treatment remarkably improved the soft magnetic behavior of the Co75Fe25Ta5Si5C15 powder. The results indicated that the Co75Fe25Ta5Si5C15 glass exhibits a slightly higher coercivity (Hc) and a notably larger saturation magnetization (Ms) than the Co75Ta5Si5C15 alloy in the as-milled state. Furthermore, in the relaxed state, the new alloy possesses a markedly lower Hc of 0.96 kA/m and a higher Ms of 108 Am2/kg than Co75Ta5Si5C15 and large number of ssoft magnetic glasy powders prepared before. The influence of milling time and annealing temperature on the evolution of the magnetic properties were discussed in detail.

Exploring dry grain fractionation as a means to valorize high‐protein malting barley

AbstractBackground and objectivesMalting barley cultivars are potentially the most profitable commodities for producers; however, barley selected for malting purposes has to meet many stringent quality requirements. Barley with excessive grain protein concentration (>13%) is often the reason why it is rejected for malting grade and sold at a lower price on the feed market. The objectives of this study were to explore dry grain fractionation as a means to valorize high‐protein malting barley by producing high fiber/protein fractions for human nutrition and starchy fractions for adjunct brewing.FindingsSeveral malting barley varieties with grain protein concentration above 14% (db) were milled on a Buhler laboratory mill resulting in six flours streams. Coarse and fine shorts were further processed using a Buhler laboratory shorts duster resulting in coarse fiber fractions and two additional flour fractions. The total yield of combined flour fractions ranged from 50.2% to 51.6%, whereas the yield of fiber fractions ranged from 41.5% to 43.7%. The fiber fractions were enriched in β‐glucans (9.3%–11.2%, db), arabinoxylans (9.9%–11.3%, db), and proteins (22%–26%, db) with average 2.2‐, 1.7‐, and 1.5‐fold increase of these constituents, respectively, compared to the whole grain. The content of vitamin E in fiber fractions was higher than in the whole grain, ranging from 82 to 109 ug/g. The fiber fractions also exhibited an improved ratio of tocotrienol to tocopherols. The combined flour fractions were depleted of β‐glucans (0.6%–0.7%, db) and arabinoxylans (0.5%–0.6%, db), contained acceptable levels of proteins (11.5%–13.5%, db) and high levels of starch (79%–82%, db). Mashing experiments with up to 40% replacement of malt with flour fractions showed significant improvements in malt extract without negative influence on malting quality parameters, such as wort beta‐glucans, wort viscosity, and the average degree of polymerization of starch dextrins.ConclusionsThe study demonstrated that covered barley can be milled using milling equipment commonly used in wheat milling without the necessity of prior dehulling of the grain. The milling resulted in two high‐yield fractions (flour and fiber/protein‐rich fractions) with hulls effectively separated during the early stages of milling, making the fractionation process commercially feasible.Significance and noveltyHigh‐protein barley can be valorized by fractionation into fiber/protein‐rich fractions that can be used as valuable food ingredients for the effective and economical control of many food‐related health issues and into starchy flour fractions that can used as adjunct in brewing.

Synthesis and characterization of CuAlS2 nanoparticles by mechanical milling

CuAlS2 chalcopyrite nanocrystalline was successfully synthesized by high energy mechanical milling followed by a homogenization annealing at argon atmosphere. The stoichiometric mixture of elemental Cu, Al, and S powders was mechanically alloyed under argon atmosphere using a high energy ball milling device. The X-ray diffraction patterns indicated that the CuS phase with a hexagonal crystal lattice and interconnected plane morphology forms in the early stage of milling. The Main phase begins at 1 h. With increasing milling time, crystallite size decreased and microstrain increased. The X-ray diffraction patterns of annealed powder at different times and temperatures show increased crystallite size and c/a, and decreased microstrain. The optical direct bandgap values of CuAlS2 nanoparticles were calculated to be about 3.1–3.4 eV. The positive Seebeck coefficient indicates that the dominant carrier holes. The maximum Seebeck coefficient 11.5 μV/K was obtained at 377 ℃.

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.

Structural, Microstructural, and Magnetic Property Dependence of Nanostructured Ti50Ni43Cu7 Powder Prepared by High-Energy Mechanical Alloying

In the current study, Ti-Ni-Cu alloy powders were prepared by mechanical alloying using high-energy planetary ball mill under argon atmosphere. The effects of milling time on the evolution of structure, microstructure, and magnetic properties were analysed. Morphological observations indicated a narrow particle size distribution and homogeneous shape. According to the Rietveld analysis, during early milling stage (1–6 h), the milled powder consists of Ti-based solid solution [HCP-Ti(Ni,Cu)], Ni-based solid solution [FCC-Ni(Ti,Cu)], Cu-based solid solution [FCC-Cu(Ti,Ni)], and amorphous phase (28.52 wt%). For prolonged milling time, the NiTiCu (β19) was achieved from the pre-formed phases. Moreover, microstructural parameters varied considerably with milling time; the crystallite size was found to decrease to the nanoscale range, Ti (41), Ni (21 nm), Cu (16 nm), and β19 (29 nm), while the microstrain 1/2 increased due to the deformations and defects induced during the milling process. Magnetic measurements indicated that all powders exhibited a ferromagnetic behaviour irrespective of milling time whereas the corresponding magnetic parameters were found very sensitive to the milling time. This was associated with particle size refinement in addition to the phase composition and the amount of the amorphous phase; the higher the percentage of the amorphous phase was, the lower the values of Ms and Mr.

Role of particle fineness on engineering properties and microstructure of fly ash derived geopolymer

Fly ash is ball milled for 30 and 90 min duration to obtain two finer fractions. The degree of size reduction is very significant at the early stage of milling, then because of agglomeration effect size reduction becomes sluggish. The effect of particle size on physical, mechanical and microstructural properties of resultant geopolymer is elucidated. The physical properties and mechanical strength improvement with milling time is attributed with formation of higher amount of alkaline alumino-silicate (N-A-S-H) hydrated gel. The weight loss profile in Thermo-gravimetric analysis (TGA) indicates more hydrated gel formation and lower carbonation with finer fraction. Different techniques such as Fourier transforms infrared spectroscopy (FTIR), X-ray diffractometer (XRD), Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) have been used for microstructural evaluation of geopolymers. In FTIR, the asymmetric stretching of Si–O–T (T is Si/Al) has been shifted towards lower frequency due to structural alteration of Al–Si network. The crystalline peak intensity has been decreased because of formation of amorphous gel after geopolymerization, detected by XRD. Under SEM and TEM, finer fraction is characterized with formation of more reaction product. The counts of un-reacted and non-bridge particles are decreased with size reduction.

Structural and magnetic properties of Mn50Al46Cu4C3 flakes obtained by surfactant-assisted ball milling

Mn-Al based hard magnetic magnets have attracted growing attention as low cost hard magnetic materials. Preparation of high performance Mn-Al based anisotropic magnetic powders with high content of magnetic phase is a challenging task due to the poor stability of the ι-MnAl phase. In this work, Mn50Al46Cu4C3 flakes with a micron, submicron and nanosize thickness have been fabricated by surfactant assisted ball milling. Cu and C co-doping in Mn50Al46Cu4C3 can stabilize the ι phase and prevent its decomposition into the nonmagnetic phases even after 15 h milling. The influence of the milling time on the flakes size distribution, morphology and magnetic properties of these Mn50Al46Cu4C3 flakes were investigated systematically. Anisotropic Mn50Al46Cu4C3 flakes first with micron and then with submicron thicknesses were formed via a continuous cleavage along the easy glide (110) planes of the ι-MnAl during the early stage of milling. With further milling, [001] textured polycrystalline nanosize flakes were formed. The coercivity of Mn50Al46Cu4C3 flakes increased initially with the milling time and then it slightly decreased after reaching the maximum value of 2608.1 Oe. However, the coercivities of the flakes also larger than 2500 Oe even for 15 h milling.

Mechanical activation and characterization of micronized cellulose particles from pulp fiber

Ball milling has been widely used for cellulosic fiber pulverization and de-crystallization, but most of the previous milling studies are focused on the micro-structural change and crystallinity reduction of cellulose, few of them have evaluated the systematic influence of milling conditions and the energy efficiency. The objective of the study is to investigate and understand the effect of various ball milling parameters on the pulp fiber grinding performance. Ball mill time, rotational speed, charge ratio, mill ball diameters, and initial moisture content of pulp fiber were studied systematically from planetary ball milling. The pulverized particle size, particle morphology, crystallinity change, bonding disruption, thermal stability, specific surface area, and energy efficiency were evaluated during the milling process. Results revealed that cellulose fiber was mainly pulverized during the early milling stage (˜20 min) and different variables led to changes regarding to the final particle size and shape. After refinement, the crystallinity and the thermal stability of the pulp fiber decreased, from the weakening or disintegration of the inter and intra hydrogen bonds of the cellulose chains. The specific surface area increased by 4˜5 times with the particle size reduction, while the milling energy efficiency decreased after 40 min of milling time.

Processing and Microstructural Characterization of Metallic Powders Produced from Chips of AA2024 Alloy

Accumulated metal waste during machining of aluminum alloys is considered for further recycling to promote environmentally sustainable production. This study aims to characterize the ball-milling process of AA2024 aluminum chips as an alternative to the remelting procedure. The proposed processing modes provide a powder particle size distribution with a d50 of 100–325 μm after 100 min milling. Stearic acid, as a process control agent (PCA), slows down powder refinement if introduced at the early stages of milling. The powder tends to form a flake-shaped morphology owing to the impact of plastic deformation altered by the PCA. Microhardness variation is linked to the joint effect of voids, strengthening phases, mechanically affected zones, and grain structure. Further, the paper reports the crystallite sizes ranging from 25 nm to 45 nm and the lattice strain < 1%. Finally, an outlook on hot-powder compaction and the associated properties of the material are presented.

The effect of metalloid content on glass forming ability, thermal stability and magnetic properties of Fe-Ta-Si-C powders prepared by mechanical alloying

In this study, the structural, thermal and magnetic characteristics of Fe75-xTa5Si10C10+x (x = 0, 5, 10) powders processed by mechanical alloying (MA) were investigated. The X-ray diffraction (XRD) indicated that by increasing the level of carbon, the structural refinement and lattice strain of the nanocrystalline Fe-based solid solution formed in the early stages of milling are enhanced. Furthermore, quantitative XRD analyses demonstrated that the glass forming ability (GFA) is remarkably improved by increasing the amount of carbon, where the percentage of amorphous phase increases from 56% for x = 0 to 98% for x = 10 after 120 h of milling. In addition, thermodynamic calculations, based on the extended Miedema's model, showed that the driving force for the glass formation increases with the concentration of carbon. Also, thermal analyses demonstrated that both the glass transition (Tg) and the onset of the crystallization (Tx) temperatures increase with the content of carbon, suggesting an enhanced thermal stability of the glassy phase. Additionally, the extension of the supercooled liquid region for the alloys with x = 5 and 10 reached a large value of 75 and 78 K, respectively, manifesting a high thermal stability of their supercooled liquid. Magnetic measurements showed that the soft magnetic behavior of the powders milled for 120 h is improved by increasing the level of carbon in terms of a decrease in coercivity (Hc) from 3.7 kA/m for x = 0 to 2.1 kA/m for x = 10. The evolution of the magnetic properties with annealing temperature reflected that the alloy with x = 10 displays a minimum Hc of 1.2 kA/m after annealing at 673 K.

The effect of prolonged milling time on comminution of quartz

The effect of prolonged milling on quartz has been investigated by conventional ball milling. The milling efficiency was enhanced by a proper selection of grinding media (alumina), ball containing fraction, initial particle size and amount of quartz being ground. The milling was carried out in 72 h cycles (total milling time 360 h) under constant operational mill speed of 130 rpm. The effect of milling time on particle size, morphology, purity, and microstructure of quartz was examined. Results indicate that particle size reduced by >96%. It is also found that lattice strain and dislocation density increased while crystallite size decreased substantially as a function of milling time. The change in particle shape from elongated flake to spherical along with relative size determine the shape of particle size distribution curve, uniformity of lattice strain and extent of alumina contamination. The alumina contamination reported for longest milling duration is <3.3% and insignificant during the early stage of milling. The prolonged milling effects on particle size, morphology, purity, and microstructure of quartz enormously under applied milling conditions.

Synthesis and thermal stability of homogeneous nanostructured Fe3C (cementite)

Mechanical alloying (MA) of blended elemental Fe and C powder mixtures corresponding to the stoichiometric composition of Fe3C (cementite) was carried out in a high-energy SPEX 8000 shaker mill. The phase evolution and thermal stability of the phases produced were determined. A supersaturated solid solution of C in Fe (α-Fe) formed in the early stages of milling. The solid solubility increased on continued milling and reached the maximum value of about 0.6 wt% C on milling the powders for 10 h. The Fe3C (cementite) phase started to form on milling the powders for 15 h and a homogeneous Fe3C phase formed on milling the powders for 30 h. Spark plasma sintering (SPS) of the milled powders at 600 °C and 70 MPa for 15 min led to the formation of homogeneous nanocrystalline bulk Fe3C with a very high hardness value of over 900 HV. Annealing of this sample at 900 °C for 1 h resulted in the decomposition of Fe3C to form a mixture of α-Fe and Fe3C and a reduced hardness value. The results confirm that MA of pure Fe and C powders, followed by SPS, can be successfully utilized to synthesize nanocrystalline bulk Fe3C with good mechanical properties and good thermal stability.

Effect of initial composition on phase selection in Ni–Si powder blends processed by mechanical alloying

ABSTRACTThe effect of initial powder blend composition on the synthesis and formation mechanism of nickel silicide phases was investigated by mechanical alloying in Ni-60 and Ni-66.7 at.% Si powder blends. It was noted that the equilibrium NiSi phase started to form in the early stages of milling and that the amount of the NiSi phase in the milled powder increased with increasing milling time. Even though, under equilibrium conditions, a mixture of both the NiSi and NiSi2 phases was expected to be present in the Ni-60 at.% Si composition and the stoichiometric NiSi2 phase in the Ni-66.7 at.% Si composition, the NiSi phase was present in both the compositions investigated. However, while only the NiSi phase was present homogeneously in the Ni-60 at.% Si powder blend, both the NiSi phase and a very small amount of unreacted Si were present in the powder blend of Ni-66.7 at.% Si composition. This unexpected phase constitution in the milled powders was attributed to a partial loss of Si during mechanical alloying of the powder blends, confirmed by energy dispersive X-ray spectrometer analyses, and explained on a thermodynamic basis.

A new approach to fabricate superconducting NbTi alloys

Superconducting NbTi alloys have been successfully fabricated by a simple powder processing route involving ball-milling, pressing and annealing. The microstructure and superconducting properties of the NbTi alloys after each processing step have been characterised and compared to the microstructure and performance of NbTi wire manufactured by a conventional thermomechanical process. At the early stages of milling, a lamellar structure of pure Nb and Ti regions is formed, which is gradually refined by further milling leading to the introduction of a high density of microstructural defects. After 20 h milling, diffusion of Ti into the Nb generates a matrix of β-Nb-50 wt%Ti alloy, with a small grain size (50 nm) and high strain (1.8%), containing an even distribution of thin Ti flakes (10–40 nm). In some regions, these Ti flakes contain a supersaturation of Nb as a result of the energetic ball-milling process. The Tc (8.1 K) and Bc2 (9.8 T at 4.2 K) values of this as-milled material are slightly lower than those reported for Nb-47 wt%Ti due to the impurity content and lattice disorder. Sintering at 400 C leads to well consolidated, high density bulk samples, but annealing at temperatures above 600 C decreases Jc values due to excessive grain growth and strain release. Annealing at lower temperatures results in higher Jc values, a shift of the pinning force density peak towards higher fields and the presence of thermodynamically stable α-Ti precipitates which are effective pinning sites leading to critical current density values comparable with those of commercial NbTi wires.

Synthesis of austenitic stainless steel powder alloys by mechanical alloying

Fe–18Cr–xNi (x = 8, 12, 13, 15, and 20 wt%) blended elemental powders were subjected to mechanical alloying in a high-energy SPEX shaker mill. The milled powders were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive spectroscopy and transmission electron microscopy techniques. It was shown that the sequence of phase formation in the Fe–18Cr–8Ni, Fe–18Cr–12Ni and Fe–18Cr–13Ni compositions was ferrite in the early stages of milling and then formation of austenite, which eventually transformed to stress-induced martensite on continued milling. The time for the formation of the austenite phase was shorter for the 12Ni and 13Ni powder blends than for the 8Ni powder. However, in the Fe–18Cr–15Ni and Fe–18Cr–20Ni compositions, the initial phase to form was ferrite and then a fully austenitic structure had formed on milling the powder for 10 h. No martensitic transformation occurred in this case on continued milling. The phase formation and microstructural features were confirmed by X-ray diffraction and transmission electron microscopy and diffraction techniques. A new metastable phase diagram was proposed outlining the stability of the austenite phase in ternary Fe–Cr–Ni alloys.

Sequence of phase evolution during mechanically induced self-propagating reaction synthesis of TiB and TiB2 via magnetically controlled ball milling of titanium and boron powders

Mechanically induced self-propagating reaction synthesis of titanium boride and diboride was investigated for elemental mixtures of titanium and amorphous boron in starting atomic ratios of Ti50B50 and Ti34B66. Samples were milled for different periods leading up to and after an ignition point which was determined by in-situ monitoring of the mill temperature. Methods of X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy (HRTEM) and Raman spectroscopy were used to determine product evolution.For both compositions, a partial crystallisation of amorphous boron commences during the early stages of milling and progresses through to the ignition point. At later stages and prior to ignition, HRTEM combined with electron diffraction revealed the formation of nanocrystalline titanium diboride, which was confirmed by Raman spectroscopy to be of an off-stoichiometric, boron-lean composition; TiB2-x. This phase is believed to have formed by solid-state reaction at the interface of the heavily deformed Ti and amorphous B via a mechanism which parallels the formation of nanocrystalline off-stoichiometric Ti1+xC1-x prior to the self-propagating synthesis of TiC from Ti and graphite. After ignition, the product for Ti34B66 comprised relatively large facetted grains of TiB2, liquid phase sintered by thin regions of unreacted Ti which had melted due to high heat of reaction. In contrast, the product of Ti50B50 comprised platelike TiB particles, and spheroidal dispersions of TiB2 in unreacted Ti and B. Likely mechanisms for the different product evolution routes for the two compositions are proposed and discussed.

Selective laser melting of TiB2/316L stainless steel composites: The roles of powder preparation and hot isostatic pressing post-treatment

Selective laser melting (SLM), a promising additive manufacturing technology, was used to fabricate TiB2/316L stainless steel composites. An important factor in manufacturing composites via SLM is feedstock powder preparation. In this work, the powders were prepared by either direct mixing or ball milling. The evolution of constituent phases, microstructural features, and size distribution with milling time was investigated. This research determined that powder particles were both coarsened and refined during the early stages of milling (0–6h), depending on the milling time. After 8h of milling, the powders exhibited a wide size distribution and stable spherical morphology, while the average crystallite size of the stainless steel matrix phase significantly decreased to 11.11nm due to severe plastic deformation. The powders obtained after 8h of mixing or milling were processed via SLM, and the microstructures exhibited a continuous ring-like structure of uniformly dispersed TiB2 particles. The hardness of the nanocomposite sample prepared from the ball milled powder exceeded that for samples made with the directly mixed powder, but only for those with the highest content of 15vol.% TiB2 reinforcement particles, due to finer particle sizes and enhancement of the wetting behavior in the molten pool. To increase the final density of these SLM-fabricated components with high hardnesses, a hot isostatic pressing (HIP) post-treatment was applied. The microstructural characteristics of the HIPed samples evolved with HIP holding time from equiaxed grains to segregated regions of coalesced reinforcement particles. In addition, significant drops in hardness and wear resistance values were observed after HIP treatment due to the high-temperature annealing effect.

Energy efficient bead milling of microalgae: Effect of bead size on disintegration and release of proteins and carbohydrates

The disintegration of three industry relevant algae (Chlorella vulgaris, Neochloris oleoabundans and Tetraselmis suecica) was studied in a lab scale bead mill at different bead sizes (0.3–1mm). Cell disintegration, proteins and carbohydrates released into the water phase followed a first order kinetics. The process is selective towards proteins over carbohydrates during early stages of milling. In general, smaller beads led to higher kinetic rates, with a minimum specific energy consumption of ⩽0.47kWhkgDW−1 for 0.3mm beads. After analysis of the stress parameters (stress number and stress intensity), it appears that optimal disintegration and energy usage for all strains occurs in the 0.3–0.4mm range. During the course of bead milling, the native structure of the marker protein Rubisco was retained, confirming the mildness of the disruption process.

Amorphization and nanocrystalline Nb3Al intermetallic formation during mechanical alloying and subsequent annealing

In this paper the formation as well as the stability of Nb3Al intermetallic compounds from pure Nb and Al metallic powders through mechanical alloying (MA) and subsequent annealing were studied. According to this method, the mixture of powders with the proportion of Nb-25at% Al were milled under an argon gas atmosphere in a high-energy planetary ball mill, at 7, 14, 27 and 41h, to fabricate disordered nanocrystalline Nb3Al. The solid solution phase transitions of MA powders before and after annealing were characterized using X-ray diffractometry (XRD). The microstructural analysis was performed using scanning electron microscopy (SEM) as well as transmission electron microscopy (TEM). The results show that in the early stages of milling, Nb(Al) solid solution was formed with a nanocrystalline structure that is transformed into the amorphous structure by further milling times. Amorphization would appear if the milling time was as long as 27h. Partially ordered Nb3Al intermetallic could be synthesized by annealing treatment at 850°C for 7h at lower milling times. The size of the crystallites after subsequent annealing was kept around 45nm.

Effects of ball milling parameters on microstructural evolution and mechanical properties of W-3% Y composites

The W-3 Y composites were successfully prepared by spark plasma sintering of milled W-3 Y powders with different milling times (0 h, 5 h, 15 h, 30 h). X-ray diffraction (XRD), scanning electron microscope (SEM), and laser particle size analysis were used to study the microstructural evolution and morphological change during the milling process. The crystallite sizes exhibited a continuous refinement along with the increased milling time. The median particle sizes, measured by the laser diffraction method, showed a similar change tendency. Due to the existence of Y particles, the W–Y milled powders exhibited spherical-like morphology while pure tungsten milled powders exhibited lamellar morphology at the early milling stage (5–15 h). The microhardness of W-3 Y compacts showed a slight increase with the increase of milling time. The maximum bending strength of 795 MPa was obtained by sintering W-3 Y powders milled for 15 h. As the milling time was prolonged to 30 h, the increased oxygen impurity resulted in a slight decrease of density as well as the degradation of bending strength.