High-energy Mechanical Alloying Research Articles

Production of NiTi alloy by direct metal deposition of mechanically alloyed powder mixtures

In this study, the combination of high energy mechanical alloying and micro direct metal deposition techniques is experimented with the aim of assessing the feasibility of synthesizing near single phase NiTi from elemental Nickel and Titanium powders. The effects of mechanical alloying process parameters on phase composition of laser melted products are investigated by using X-ray diffraction and scanning electron microscopy equipped with energy dispersive spectroscopy. The results showed that B2-NiTi phase with small quantity of NiTi2 can be obtained by micro direct metal deposition of mechanically alloyed Ni50.8Ti49.2 powder.

Structure and mechanical properties of Fe–Ni–Zr oxide-dispersion-strengthened (ODS) alloys

A series of bulk nanostructured Fe–Ni–Zr oxide-dispersion-strengthened (ODS) alloys were synthesized using high energy mechanical alloying and consolidated using high temperature equal channel angular extrusion. The resultant microstructures are composed of nano/ultrafine or micrometer-sized grains with larger intermetallic precipitates and small Zr oxide clusters (<10 nm diameter, measured and confirmed by atom probe tomography). The ODS alloys possess elevated compression properties, e.g., 1.2 and 2.4 GPa compressive yield stress at room temperature for samples consolidated at 700 °C and 1000 °C, respectively. This work highlights the relationship between processing, microstructure, and properties for this class of ferritic ODS alloys.

High Performance TiP2O7 Based Intercalation Negative Electrode for Aqueous Lithium-Ion Batteries Via a Facile Synthetic Route

Combining high energy mechanical alloying with intimate carbon coating has proven effective in improving electrochemical performance of polyanion-based materials (1, 2). Ball milling with intimate carbon helps to prepare a homogenous mixture of precursors and reduce particle size during following thermal treatment (3, 4). In addition, this combination can decrease the thermal treatment time needed (5). In this study, we demonstrated TiP2O7/graphite prepared by high energy mechanical alloying combined with intimate carbon coating has superior cycling performance in aqueous lithium-ion electrolyte. The TiP2O7/graphite composite material was prepared by an intensive mechanical mixing solid state synthesis method at 700°C. Physical properties were characterized via powder X-ray diffraction, Rietveld refinement, SEM, BET and TGA. Electrochemical performance was evaluated in both a three electrode test setup and two electrode coin cells via cyclic voltammetry and galvanostatic cycling tests. The TiP2O7/Graphite composite demonstrates excellent cycling performance in 1M Li2SO4 when matched with LiMn2O4 as a positive electrode: when cycled at C/2 for 150 cycles, the capacity retention is over 91% with coulombic efficiencies exceeding 99%. The initial discharge capacity obtained at a C/10 rate is 91mAh/g which was about 75% of theoretical capacity 121mAh/g. Reference: 1. W. Wu, A. Mohamed and J. F. Whitacre, Journal of The Electrochemical Society, 160, A497 (2013). 2. W. Wu, J. Yan, A. Wise, A. Rutt and J. F. Whitacre, Journal of The Electrochemical Society, 161, A561 (2014). 3. J.-K. Kim, G. Cheruvally, J.-W. Choi, J.-U. Kim, J.-H. Ahn, G.-B. Cho, K.-W. Kim and H.-J. Ahn, Journal of Power Sources, 166, 211 (2007). 4. J.-K. Kim, J.-W. Choi, G. Cheruvally, J.-U. Kim, J.-H. Ahn, G.-B. Cho, K.-W. Kim and H.-J. Ahn, Materials Letters, 61, 3822 (2007). 5. L.-X. Yuan, Z.-H. Wang, W.-X. Zhang, X.-L. Hu, J.-T. Chen, Y.-H. Huang and J. B. Goodenough, Energy & Environmental Science, 4, 269 (2011). Figure 1

Synthesis of Nanocrystalline Al2O3 Reinforced Al Nanocomposites by High-Energy Mechanical Alloying: Microstructural Evolution and Mechanical Properties

The scientific importance of nanocomposites is being increased due to their improved properties. In the current paper, the relationship between the reinforcement weight fraction and Tensile properties of Al/Al2O3 (with a reinforcement weight fraction of 0, 2.5, 5 and 10 wt%) synthesized by high energy ball milling is studied. Scanning electron microscopy analysis, X-ray diffraction analysis and transmission electron microscopy are used to characterize the produced powder. The results show that the addition of Alumina particles accelerates the milling process, leading to faster work hardening rate and fracture of the aluminum matrix. Moreover, Al crystallite size become refined during ball milling of Al powder in the presence of Al2O3 particles. Uniform distribution of nano-sized Al2O3 particles in the Al matrix could be achieved with increase in the reinforcement weight fraction. The microhardness of the composite increases with the increase of the reinforcement weight fraction and it reaches 94 HV at 10 wt% Al2O3 composite. The yield strength and ultimate strength of the composite are also increased by increasing the reinforcement weight fraction.

Effect Of Milling Time On Microstructure Of AA6061 Composites Fabricated Via Mechanical Alloying

AbstractThe aim of this work is to determine the effect of manufacturing conditions, especially milling time, on the microstructure and crystallite size of a newly developed nanostructural composite material with the aluminium alloy matrix reinforced with halloysite nanotubes. Halloysite, being a clayey mineral of volcanic origin, is characterized by high porosity and large specific surface area. Thus it can be used as an alternative reinforcement in metal matrix composite materials. In order to obtain this goal, composite powders with fine microstructures were fabricated using high-energy mechanical alloying, cold compacting and hot extrusion techniques. The obtained composite powders of aluminium alloy reinforced with 5, 10 and 15 wt% of halloysite nanotubes were characterized with SEM, TEM and XRD analysis. It has been proven that the use of mechanical alloying leads to a high degree of deformation, which, coupled with a decreased grain size below 100 nm and the dispersion of the refined reinforcing particles–reinforces the material very well.

Defect generation and analysis in mechanically alloyed stoichiometric Fe–Ni alloys

FeNi, with the chemically-ordered L10 tetragonal structure, is a promising material for next-generation rare-earth-free permanent magnets. Due to the extremely low atomic Fe and Ni mobility below the critical chemical order/disorder temperature of 320°C, no conventional metallurgical methods are able to induce its formation. Diffusion rates could be enhanced with the creation of excessive vacancies. High-energy mechanical alloying was employed to produce a nanocrystalline Fe–50at.%Ni alloy. The high energy mechanical milling is expected to change the defect characteristics that would be used to study the effect that mechanical alloying has on the defect concentrations. X-ray diffraction revealed that over the entirety of the milling period, the Fe and Ni powders formed an fcc solid solution. The Williamson–Hall equation and Scherrer equation revealed that reductions in grain sizes were caused during alloying. The initial increase in internal strain, and by extension dislocations, was followed by a decrease in strain with further alloying, which was due to the combination effect of creation of dislocation from mechanical deformation and annihilation of dislocations at increasing grain boundaries. Doppler broadening positron annihilation spectroscopy (DB-PAS) showed that the overall number of open-volume defects decreased with increased milling time. Finally, changes of relative permeability, for the mechanically alloyed FeNi phase, were explained by the pinning effect of dislocations.

Microstructures and properties of W–Cu functionally graded composite coatings on copper substrate via high-energy mechanical alloying method

In the present work, process of gradual addition of powders was proposed to prepare W–Cu functionally graded composite coatings on copper surface via high-energy mechanical alloying method using a planetary ball mill. The microstructures and elemental and phase composition of mechanically alloyed coatings were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS). Fully dense and uniform triple layer W–Cu (W–30wt.% Cu+W–15wt.% Cu+W–7wt.% Cu) functionally graded composite coatings was metallurgically bonded on the pure copper substrate, with an average thickness of ∼92μm. Microhardness test and friction and wear test were carried out to examine the mechanical properties of the coatings. The results showed that the maximum microhardness of the triple layer gradient coatings reached HV0.1 212, showing a threefold improvement upon the pure copper substrate. And the cross-sectional microhardness values of the processed sample changed gradually, which gave a proof for the cushioning and sustaining functions of the W–Cu functionally graded composite coatings. The friction coefficient of the as-fabricated triple layer W–Cu functionally graded composite coatings was 0.5 and the corresponding wear mass loss was only 2.8mg, which was obviously lower than that of the pure copper substrate. A reasonable formation mechanism of W–Cu functionally graded composite coatings prepared by process of gradual addition of powders via high-energy mechanical alloying method was presented.

Equal-Channel Angular Extrusion of a Low-Density High-Entropy Alloy Produced by High-Energy Cryogenic Mechanical Alloying

In this study, we demonstrate the feasibility of forming a bulk consolidated, low-density high-entropy alloy, namely AlFeMgTiZn, which shows reasonable mechanical properties and high hardness. The fabrication of the high-entropy alloy from powdered precursors via high-energy mechanical alloying as a function of milling time is presented. In turn, the evolution of the alloy microstructure with postmilling anneal treatment is elucidated. Last, the severe plastic deformation processing methodology, i.e., equal-channel angular extrusion, chosen for consolidation, is described and shown to result in a bulk product with good results.

Microstructure evolution and thermal stability of nanostructured Fe50Al30(Ni70Zr30)10B10 powders produced by mechanical alloying

The mixtures of Fe, Al, Ni, Zr and B elemental powders with nominal composition Fe50Al30(Ni70Zr30)10B10 were mechanically alloyed in a planetary ball mill. The structural and morphological changes during high energy mechanical alloying were investigated by X-ray diffraction and scanning electron microscopy. The final product of the mechanical alloying process was nanocrystalline iron reach bcc-Fe(Al,Ni,Zr,B) solid solution with a mean crystallite size in the range of a few nanometers. From the Mössbauer spectrometry results, the magnetic hyperfine field was found to decrease with the progressive mixing of the elemental powders at the atomic scale. This decrease emanates mainly from the presence of Al, Zr, Ni and B atomic species as first nearest neighbors of Fe probe. The thermal stability of the as-milled powders was analyzed by differential scanning calorimetry. At early stages of milling, the exothermic peaks observed at higher temperatures correspond to the reaction between the mixed powder elements, while at intermediate stages they are related to the structural transformation associated with the crystallite growth.

Structural, optical and thermal characterization of nanostructured CdSe obtained by mechanical alloying

A CdSe nanostructured alloy was produced by high energy Mechanical Alloying (MA). The existence of three crystalline phases, two CdSe polymorphs and a small fraction of CdO phase, was revealed through X-ray powder diffraction. With continued MA process, the CdO phase was dispersed between the nanostructures of zinc blende (ZB) and wurtzite (WZ). Differential Scanning Calorimetry (DSC) measurements indicated sublimation at 122°C confirmed by thermal treatment. Raman spectroscopy revealed that the sublimated material was composed by a trigonal Se. After the thermal treatment, a partial phase transition from ZB to WZ was observed, which is in agreement with that observed by DSC, as well as by nucleation of the CdSeO3.

Microstructure and mechanical properties of bulk nanostructured Cu–Ta alloys consolidated by equal channel angular extrusion

Nanostructured Cu–Ta alloys have shown promise as high-strength nanocrystalline materials in part due to their limited grain growth at high temperatures. In the present study, Cu–Ta alloy powders, synthesized via high-energy cryogenic mechanical alloying, were consolidated into bulk nanostructured specimens using equal channel angular extrusion (ECAE) at high temperatures. Subsequent microstructure characterization indicated full consolidation, which resulted in an equiaxed grain structure for the Cu matrix along with the formation of fine Ta precipitates, the size distributions of which varied both with composition and processing temperature. Microhardness, compression and shear punch testing indicated, in some cases, an almost threefold increase in mechanical properties above that predicted by Hall–Petch estimates for pure nanocrystalline Cu. Stress relaxation tests substantiated the strain-hardening behavior and grain-size-dependent dislocation activity observed in the nanocrystalline Cu–Ta samples.

Role of Halloysite Nanoparticles and Milling Time on the Synthesis of AA 6061 Aluminium Matrix Composites

The aim of this work is to determine the effect of a reinforcing phase and manufacturing conditions on the structure and properties of newly developed nanostructural powders of composite materials with the aluminium alloy matrix reinforced with natural halloysite nanotubes. Composite materials were manufactured employing as a matrix the air atomized powders of AA 6061 aluminium alloy and as a reinforcement the halloysite nanotubes. Composite powders of aluminium alloy matrix reinforced with 5, 10 and 15 wt.% of halloysite nanotubes were fabricated by high-energy mechanical alloying using a planetary mill. Elaborated composite powders were characterized for their apparent density, microhardness, particle size distribution and microstructure. A structure of newly developed nanostructured composite materials reinforced with halloysite nanotubes prove that a mechanical alloying process allow to improve the arrangement of reinforcing particles in the matrix material. A homogenous structure with uniformly arranged reinforcing particles can be achieved by employing reinforcement with halloysite nanotubes if short time of mechanical alloying is maintained thus eliminating an issue of their agglomeration.

Structural and microstructural properties of nanocrystalline Cu–Fe–Ni powders produced by mechanical alloying

A nanostructured disordered copper–iron–nickel alloy having the (Cu60Fe40)70Ni30 composition was prepared through the mechanical alloying of the elemental powders in a high-energy ball mill under an argon atmosphere. The structural and morphological evolutions during mechanical alloying were investigated by X-ray diffraction and scanning electron microscopy. The patterns obtained were analyzed using the MAUD program. The transformation of the phase depended on the alloying time. The final product of the mechanical alloying process was nanocrystalline double-phase FCC-Cu(Fe,Ni) and BCC-Fe(Ni) solid solutions with a mean crystallite size in the range of few nanometers. The dislocation densities were found to be 6×1015m−2, and the strain hardening caused by high-energy mechanical alloying was consistent with the concept of dislocations.

ERRATUM: PROPERTIES OF BULK Fe-Ni/CNT NANOCOMPOSITES PREPARED BY MECHANICAL MILLING AND SINTERING

The effects of carbon nanotubes (CNTs) on mechanical and tribiological properties of the NiFe/CNT composites prepared by high energy mechanical alloying and hot pressing, were investigated. Bulk samples were prepared by sintering of cold pressed (300 MPa) samples at 1040°C for 1 h. X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and optical microscopy were employed for evaluation of the phase composition, surface morphology and porosities of the samples. The microhardness of as-milled Ni3Fe and NiFe powders reached to 720 and 650 VHN, respectively. The hardness of NiFe and Ni3Fe bulk samples reduced to 190 and 270 Vickers because of the grain growth during sintering and remaining porosity. The hardness of NiFe-CNT and Ni3Fe-CNT bulk samples reached to 360 and 400 Vickers, respectively. The friction and wear properties of the bulk samples were investigated under dry conditions using a pin-on-disk test rig under an applied load of 8 N. The wear rate, mass loss and friction coefficient of the composite samples remarkably reduced in comparison with NiFe and Ni3Fe matrix alloys which demonstrate effects of the CNTs on mechanical and tribiological behavior of the composites resulting from the excellent mechanical properties and unique topological structure of the CNTs.

Electrical resistivity, wear map and modeling of extruded tungsten reinforced copper composite

The present work includes the effect of W addition in improving the properties of Cu with the help of high-energy mechanical alloying. Composite preforms of (5–15W) with copper were fabricated by Powder Metallurgy (P/M) method. The preforms were sintered at 850°C, subsequently the furnace was cooled and again the specimens were hot extruded to get 92% preform density. Four point probe tester, Scanning Electron Microscope, Energy Dispersive Spectrum and pin on-disc system were used to evaluate electrical conductivity, characterization and tribological property of Cu–W composite respectively. The various stages in dominant oxidation and delamination wear mechanism was clearly discussed. The wear rate and coefficient of friction decreased with increase in load and sliding distance. Design expert software was used to develop contour map, mathematical model and useful conclusions were made.

Fabrication of Ti–Cu–Al coatings with amorphous microstructure on Ti–6Al–4 V alloy substrate via high-energy mechanical alloying method

A high-energy planetary ball mill was applied to fabricate Ti–Cu–Al coating on Ti–6Al–4V alloy substrate. The microstructure and elemental and phase composition of coatings were studied. The surface SEM images showed that the rough but densified coating surfaces, the cross-section microstructures as well as the related EDS line scan results illustrated different structures in the coatings, and the XRD results as well as TEM and corresponding SEAD pattern provided evidences of the existence of amorphous phase in the coatings. Mechanical properties including microhardness and friction and wear behavior were tested respectively. The microhardness testing results indicated that the fabricated coatings could largely strengthen the substrate surface. And the friction and wear resistance were tested with a ball-on-block sliding configuration, with the testing results showing decrease in both friction coefficients and wear weight loss after mechanical alloying treatment. The analysis and testing results also showed that a proper increase in the applied milling time favored the improvement in the thickness, surface smoothness, densification level, microstructural and chemical homogeneity as well as amorphization degree of the deposited coating. On the basis of two significant action mechanisms associated with a planetary ball mill, a reasonable mechanism was presented for the formation of amorphous phase contained coatings on Ti–6Al–4V alloy substrate.

Effects of Cu content and mechanical alloying parameters on the preparation of W–Cu composite coatings on copper substrate

Abstract A novel surface coating preparation technique utilizing high-energy mechanical alloying (MA) method was used to deposit tungsten–copper composite coatings on pure copper surface using a planetary ball mill. The microstructures and elemental and phase composition of mechanically alloyed coatings at different process parameters were studied using scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS). The effects of mechanical alloying parameters on the fabricating of tungsten–copper composite coatings had been investigated. Fully dense and uniform tungsten–copper composite coatings were metallurgically bonded on the copper substrate, with an average thickness of ∼65 μm under the optimized mechanical alloying parameters (i.e., rotation speed of 350 rpm, milling time of 9 h and powder ratio of W–30 wt.%Cu). Microhardness tests were carried out to examine the mechanical properties of the coatings. The results showed that the maximum microhardness of the coatings reached HV 0.1 193, showing a great improvement upon pure copper substrate. Mechanical alloying is a complex process and hence involves optimization of a number of variables to achieve the desired results. In this work, effects of the main parameters on the preparation of tungsten–copper composite coatings were properly presented.

Effect of Mo Addition on Structure and Magnetocaloric Effect in γ-FeNi Nanocrystals

Nanocrystalline powders of (Fe70Ni30)100−xMox (x = 1 to 4) were produced by high-energy (SPEX) mechanical alloying. Increasing the Mo content was found to stabilize the face-centered cubic phase in mechanically alloyed nanopowders. To obtain a single γ-phase, a powdered sample was solution annealed in the γ-phase field and water quenched. The Curie temperature, TC, of the alloys was lowered with Mo addition, without decreasing the refrigeration capacity (RC), due to the additional temperature broadening of the magnetic entropy change. Based on previous study on the role of disorder, the additional temperature broadening was attributed to increased positional disorder and changes in the distribution of ferromagnetic exchange bonds introduced by Mo addition into the γ-FeNi system. (Fe70Ni30)97Mo3 and (Fe70Ni30)96Mo4 alloys have RCFWHM values of ∼440 J/kg and ∼432 J/kg at 5 T, comparable to other prominent magnetic refrigerants operating near room temperature. The economic viability of these alloys, along with their competitive magnetocaloric properties and potential for scalable production, make them good candidate magnetic refrigerants without critical rare-earth materials.

MECHANICAL-ACTIVATED PHASE FORMATION OF NiTi IN THE PRESENCE OF NANOPARTICLES

Effect of Al 2 O 3 nanoparticles (80 nm) on the grain structure and phase formation in Ni -50 Ti system during high-energy mechanical alloying (MA) was studied. While the formation of NiTi B2 phase occurs progressively during MA, it is shown that the hard inclusions cause abrupt phase formation at short milling times, particularly at higher nano- Al 2 O 3 contents. High-resolution transmission electron microscopy showed significant grain refinement in the presence of alumina nanoparticles to sizes less than 10 nm, which precedes the formation of semicrystalline structure and reduces the diffusion length and thus accelerates the phase formation. The composite powder reached steady-state MA condition at shorter milling times with finer grain structure and higher hardness.

PROPERTIES OF BULK Fe–Ni/CNT NANOCOMPOSITES PREPARED BY MECHANICAL MILLING AND SINTERING

The effects of carbon nanotubes (CNTs) on mechanical and tribiological properties of the NiFe /CNT composites prepared by high energy mechanical alloying and hot pressing, were investigated. Bulk samples were prepared by sintering of cold pressed (300 MPa) samples at 1040° C for 1 h. X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and optical microscopy were employed for evaluation of the phase composition, surface morphology and porosities of the samples. The microhardness of as-milled Ni 3 Fe and NiFe powders reached to 720 and 650 VHN, respectively. The hardness of NiFe and Ni 3 Fe bulk samples reduced to 190 and 270 Vickers because of the grain growth during sintering and remaining porosity. The hardness of NiFe -CNT and Ni 3 Fe -CNT bulk samples reached to 360 and 400 Vickers, respectively. The friction and wear properties of the bulk samples were investigated under dry conditions using a pin-on-disk test rig under an applied load of 8 N. The wear rate, mass loss and friction coefficient of the composite samples remarkably reduced in comparison with NiFe and Ni 3 Fe matrix alloys which demonstrate effects of the CNTs on mechanical and tribiological behavior of the composites resulting from the excellent mechanical properties and unique topological structure of the CNTs.