High-energy Ball-milled Powders Research Articles

FeCoNiCu Alloys Obtained by Detonation Spraying and Spark Plasma Sintering of High-Energy Ball-Milled Powders

FeCoNiCu Alloys Obtained by Detonation Spraying and Spark Plasma Sintering of High-Energy Ball-Milled Powders

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.

Dynamic stress-strain response of high-energy ball milled aluminium powder compacts

Ball milling is a bulk powder manufacturing process used in the creation of dispersion strengthened and nanostructured materials. Fundamentally, these powders have not been dynamically characterized in a green state prior to hot consolidation. The understanding of high strain-rate compaction on void collapse and particle interaction for such systems can help the development of predictive models for impact events of porous metallic structures that may be employed as energy absorbers, reactive structures, and intermetallic materials. This study investigates high strain-rate impact of porous green compacts of as-received and high-energy ball milled (HEBM) aluminium powders characterized under dynamic compression using a split-Hopkinson pressure bar (SHPB) in a passive confinement configuration. The plastic deformation of the powder compacts and crush up were shown to be strain-rate insensitive within the strain rate range of 1000–2100 s−1 and as a result, were modelled adequately with a second order P-α model. The as-received aluminium and HEBM aluminium powders appear to have the same strain-hardening coefficient and strength index as solid aluminium after yielding. The respective stress-strain responses of green compacts follow the same trend but differ only in strength as result of porosity and pre-strain experienced prior to dynamic compression. The HEBM powder was found to be twice as strong as the untreated as-received aluminium powder.

Fabrication of a high strength and ductility Ti‒22Al‒25Nb alloy from high energy ball-milled powder by spark plasma sintering

A high strength and ductility Ti‒22Al‒25Nb alloy was fabricated from high energy ball-milled powder by spark plasma sintering. The pre-alloyed powder with a normal composition (at %) of 53 Ti, 22 Al and 25 Nb was firstly ball-milled for different milling times, and subsequently consolidated by spark plasma sintering. The effects of ball-milling time on the microstructure and mechanical properties of the ball-milled powder and sintered compact were investigated. The Ti‒22Al‒25Nb alloy sintered by SPS at 950 °C for 10 min under a pressure of 50 MPa from the ball-milled powder showed the microstructure with a large amount of ultrafine/nano O-phase. The best balance of tensile properties was exhibited in the Ti‒22Al‒25Nb alloy sintered from the ball-milled powder for 20 h; the yield strength, the tensile strength and the elongation to failure were 1092 MPa, 1105 MPa and 9.4% at room temperature respectively, exceeding other coarse grain Ti‒22Al‒25Nb alloys fabricated by other powder metallurgy methods in the comprehensive tensile property. The precipitation of secondary phase, the grain refinement and the change of residual dislocation density in the sintered alloy directly affected the tensile properties of the sintered alloy.

The role of fracture in the impact initiation of Ni-Al intermetallic composite reactives during dynamic loading

Mechanical initiation of reactions in powder systems involve complex interactions that can yield unexpected results. Two materials that exhibit similar thermal responses can behave very differently under the same loading conditions due to differences in their mechanical properties. Reactive composite powders with small characteristic dimensions can exhibit short ignition delays and reduced thermal ignition thresholds; however, a full understanding of the response of these powders to rapid mechanical loading is still unclear. This work seeks to clarify the role of mechanical properties in impact induced ignition by considering the response of nanolaminate (NL) powders and high energy ball milled (HEBM) Ni-Al powders subjected to impact loading. The selected materials have nearly identical thermal ignition temperatures, but contrast a relatively complex microstructure (HEBM) with a simple ordered microstructure (NL) while maintaining comparable length scales (approximately 50–100 nm diffusion distances). The powders were placed into a windowed enclosure and mechanically loaded using a light gas gun, which allowed the resulting reactions to be observed using high-speed imaging. Even though the thermal ignition temperatures for the two powders are within 30 °C of each other, it was observed that the NL powders reacted on the microsecond timescale, immediately following the compaction wave for a short distance before decoupling from the compaction front. In contrast, the HEBM powders reacted after a several millisecond delay and clearly propagated as a deflagration front. Microindentation showed that the HEBM powders are much more ductile than those of NL. This suggests that the primary difference between the behavior of these materials on impact results from the ability and degree of the material to fracture, illustrating that the mechanical properties of a reactive material can have a dramatic effect on ignition during impact loading.

Composition-dependent charge transport and temperature-dependent density of state effective mass interpreted by temperature-normalized Pisarenko plot in Bi2−xSbxTe3 compounds

Abstract

Structure and Properties of Nano-Scale Oxide-Dispersed Iron

Bulk samples of pure iron and yttria dispersed iron with and without titanium (i.e., Fe, Fe-Y2O3, and Fe-Y2O3-Ti) were prepared by hot extrusion of high-energy ball-milled powders. An examination of the microstructure using TEM revealed that the addition of titanium resulted in the reduction of the dispersoid size with a concomitant increase in the volume fraction of the dispersoids. As a result, Fe-Y2O3-Ti exhibited a substantial increase in hardness and tensile properties as compared to Fe and Fe-Y2O3. The higher hardness and strength of Fe-Y2O3-Ti is shown to be due to the presence of finer and higher number density of Y-Ti-O complex oxides. Dynamic strain aging in the temperature range of 423 K to 573 K (150 °C to 300 °C) was observed in all the compositions studied.

Effect of ball milling time on the thermoelectric properties of p-type (Bi,Sb)2Te3

P-type (Bi,Sb)2Te3 compounds were fabricated with high energy ball-milled powder and their thermoelectric properties were investigated as a function of the ball milling time. The fine grain sizes were confirmed with the X-ray analysis and the microscopy images in the samples fabricated with powders from long ball milling time. The values of the lattice thermal conductivity of the samples at high temperature show smaller values for long milling time (>24h) than those for short time, resulted from the finer grain sizes of the samples. As well as the microstructural change, the Seebeck coefficient and the electrical resistivity of the compounds were significantly altered with the ball milling time. The carrier concentration was dramatically increased in the samples after 24h milling, which was attributed to the formation of the antisite defects introduced by the accumulated thermal energy. The formation of antisite defects may be also promoted by the unintentional Fe doping from jars and balls. The highest value of ZT=1.14 was achieved at 323K for the samples with 10h. The temperature where the value of ZT was maximized and the values of ZT was varied with the ball milling time, which implies that the ball milling time should be carefully optimized for the suitable application of this compounds.

Development of ZrC in the tungsten matrix composite containing Zr<SUB align="right">2Cu and MWCNTs during liquid-reactive sintering

Formation of ZrC during liquid-reactive sintering of the high energy ball-milled powder mixture of tungsten, Zr2Cu and multi-walled carbon nanotubes (MWCNTs) was investigated. The composite powder was compacted and sintered at 1400°C up to 12 h. During sintering, carbon atoms from the well-dispersed MWCNTs diffuse to the tungsten matrix to form WC, and Zr2Cu liquid phase flows into fine capillaries between the tungsten particles. Carbon atoms from WC in the tungsten matrix diffuse into Zr2Cu liquid phase and form ZrC because Gibbs free energy of ZrC formation is lower than that of WC formation. Formation of WC and ZrC was observed by the SEM microstructures of the sintered composites. The formation of carbides in the sintered composite was confirmed by FT-IR spectra and XRD analysis. The density of the sintered composite increases from 80% to 91% theoretical density, after 6 h of sintering. The hardness of the sintered composite (720 Hv) increased up to ~230% more than monolithic tungsten (310 Hv), due to the formation of ZrC and the densification of the sintered composite.

Mechanical Properties of β–Ti-35Nb-2.5Sn Alloy Synthesized by Mechanical Alloying and Pulsed Current Activated Sintering

A developed Ti-35 pct Nb-2.5 pct Sn (wt pct) alloy was synthesized by mechanical alloying using high-energy ball-milled powders, and the powder consolidation was done by pulsed current activated sintering (PCAS). The starting powder materials were mixed for 24 hours and then milled by high-energy ball milling (HEBM) for 1, 4, and 12 hours. The bulk solid samples were fabricated by PCAS at 1073 K to 1373 K (800 °C to 1100 °C) for a short time, followed by rapid cooling to 773 K (500 °C). The relative density of the sintered samples was about 93 pct. The Ti was completely transformed from α to β-Ti phase after milling for 12 hours in powder state, and the specimen sintered at 1546 K (1273 °C) was almost transformed to β-Ti phase. The homogeneity of the sintered specimen increased with increasing milling time and sintering temperature, as did its hardness, reaching 400 HV after 12 hours of milling. The Young’s modulus was almost constant for all sintered Ti-35 pct Nb-2.5 pct Sn specimens at different milling times. The Young’s modulus was low (63.55 to 65.3 GPa) compared to that of the standard alloy of Ti-6Al-4V (100 GPa). The wear resistance of the sintered specimen increased with increasing milling time. The 12-hour milled powder exhibited the best wear resistance.

Fabrication of Al-Based Matrix Composite Reinforced with WAl<sub>12</sub> Intermetallic Particles by Press-Forming Process Using High-Energy Ball-Milled Powders

The 22wt%WAl12intermetallic particulate reinforced Al-based matrix composite was successfully fabricated by press-forming technology using high-energy ball-milled powders. X-ray diffraction analysis shows that WAl12reinforcement phase has been obtained after in situ reaction of Al matrix with W14Al86alloy at 620°C. The mechanical properties of the composite material were studied at room temperature. The Young’s modulus, microhardness and the maximum ultimate tensile strength of this composite material can reach 75GPa, 1.51GPa and 471MPa, respectively. The results show that there is a good interfacial bonding between the Al matrix and WAl12particles. However, the composite cannot be applied in high temperature environment because of its fairly low strength residual ratio.

Properties of High-Energy Ball-Milled Fe–Se Based Superconductors

We have synthesized FeSe0.5Te0.5 superconductors by high-energy ball-milling and subsequent annealing. High-energy ball-milling of elemental powder mixtures resulted in the formation of metastable and/or nanocrystalline phases. Both XRD and DSC results show that the ball-milled powers were completely transformed to FeSe0.5Te0.5 with the grain size of a few nanometers during sintering at low temperatures. The resulting materials exhibited superconducting transition at 14 K. The enhancement of critical current density was observed for the high-energy ball-milled powder, compared with the un-milled powders.

An investigation on flowability and compressibility of AA 6061 100 − x- x wt.% TiO 2 micro and nanocomposite powder prepared by blending and mechanical alloying

This work investigates the relationships between the components of powders, namely, the powder surface morphology, the flow characteristics and the compressibility of low-energy (microcomposite) and high-energy (nanocomposite) ball milled powders of Al 6061 alloy reinforced with TiO 2 particles. The morphology of the above powder as the function of reinforcement and the milling time was studied by using the scanning electron microscope (SEM). The changes in powder characteristics such as the apparent density, tap density, true density and flow rate were examined by the percentage of reinforcement and milling time. The cohesive nature of the powder was also investigated in terms of Hausner ratio and Kawakita plot. Further, the particle/agglomerate size of low-energy and high-energy ball milled powders was explained by the laser particle size analyzer. X-ray peak broadening analysis was used to determine structural properties of mechanically alloyed powders. The compressibility behavior was examined by the compaction equation proposed by Panelli and Ambrosio Filho to investigate the deformation capacity of the powder. The compressibility behavior, namely, the densification parameter ( A) of the microcomposite powder (irregular morphology) was decreased significantly with increasing TiO 2 content due to the disintegration of TiO 2 particles and the cluster formation followed by its agglomeration. The compressibility behavior, namely, the densification parameter ( A) of the nanocomposite powder (equiaxed and almost spherical) was decreased slowly with increasing TiO 2 content due to work hardening on the matrix powder. With increased milling time, the compressibility behavior of AA 6061-10 wt.% TiO 2 composite powders increased up to 30 h of milling due to embedding of TiO 2 particles with matrix and changes in powder morphology and finally decreased after 40 h due to work hardening effect.

Synthesis, structure and sinterability of 6061 AA100−x–xwt.% TiO2 composites prepared by high-energy ball milling

Abstract Manufacturing of 6061 Al alloy reinforced with different weight percentages of TiO2 metal matrix composite powder through low-energy and high-energy ball milling for microcomposites and nanocomposites respectively followed by cold uniaxial compaction and sintering was investigated. The milled powder was characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and differential thermal analyzer. No intermetallic compounds were observed during high-energy ball milling by wet method, but petite iron contamination was present due to vial media after 40 h milling. The crystallite size of about 46 nm was obtained in the case of high reinforcement content. Powder surface morphology, crystallite size as a function of chemical composition and milling time, and lattice parameter of the high-energy ball-milled powder were examined. The effect of matrix-to-reinforcement particle size ratio on the green compressive strength for both composites was also investigated. The green pellets were degassed at 350 °C for 60 min, and then sintered in the temperature steps of 475, 550 and 625 °C under reducing atmosphere for 120 min. The effects of reinforcement content on densification as percentage theoretical density, sinterability and Vickers hardness of the composites were also studied. The results revealed that the sinterability improved as the percentage of reinforcement increased for nanocomposites whereas it worsened for microcomposites. The nanocomposites exhibited a high Vickers hardness of 1126 MPa, which was around 3–4 times higher than that of microcomposites.

Magnetocaloric effect in high-energy ball-milled Gd 5Si 2Ge 2 and Gd 5Si 2Ge 2/Fe nanopowders

Evolution of structure and magnetocaloric properties in ball-milled Gd 5Si 2Ge 2 and Gd 5Si 2Ge 2/0.1 wt% Fe nanostructured powders were investigated. The high-energy ball-milled powders were composed of very fine grains (70–80 nm). Magnetization decreased with milling time due to decrease in the grain size and randomization of the magnetic moments at the surface. The magnetic entropy change (Δ S M) was calculated from the isothermal magnetization curves and a maximum value of 0.45 J/kg K was obtained for 32 h milled Gd 5Si 2Ge 2 alloy powder for a magnetic field change of 2 T while it was still low in Fe-contained alloy powders. The thermo-magnetic measurements revealed that the milled powders display distribution of magnetic transitions, which is desirable for practical magnetic refrigerant to cover a wide temperature span.

Fabrication of Al alloy matrix composite reinforced with subsive-sized Al 2O 3 particles by the in situ displacement reaction using high-energy ball-milled powder

High-energy mechanical milling (HEMM) and sintering were employed to fabricate an Al alloy matrix composite reinforced with subsive-sized Al 2O 3 particles. Al–(Mg, Cu, Si)–SiO 2, composite powders were prepared by HEMM. Nano-sized SiO 2 particles embedded in Al–(Mg, Cu, Si) matrix particles were obtained by HEMM. Al-based metal matrix composite reinforced with subsive-sized Al 2O 3 particles was fabricated successfully by sintering at 650 and 750 °C for 2 h using milled powder. Subsive-sized Al 2O 3 particles and eutectic Si were formed by in situ displacement reaction between Al and SiO 2 during sintering, and homogeneously distributed in the Al–Si–(Mg, Cu) matrix. The flexural strength of the sintered specimen (1.2 GPa) using 8 h milled powder was about four times as the sintered specimen using as-mixed powder.

Effect of different processing on the microstructure and mechanical properties of Al 67Mn 8Ti 24Nb 1 alloy

The microstructures and mechanical properties of a Nb-modified multiphase Al 3Ti-based alloy prepared by different techniques such as-cast, spray forming and mechanical milling have been investigated. The dendrites in the as-cast Al 67Mn 8Ti 24Nb 1 experienced considerable fragmentation in the spray forming or ball milling process. The microstructure with an equiaxed L1 2 matrix and homogeneous distributed second phase was obtained in almost all part of the spray formed deposit and its porosity was low. Al 67Ti 24Mn 8Nb 1 alloy consolidated from high energy ball-milled powders shows higher strength and better fracture toughness than as-cast or sprayed alloy, which result in fine grain size about 1 μm and the secondary phase particles were refined to the order of hundred nanometers in the ball-milled powder consolidated alloy.