Changes in the oxygen content,morphology, and microstructure of Mo-10Nb composite powders during mechanical alloying

The prefabrication of Mo-Nb composite powders is an effective way of improving the homogeneity of Mo-10Nb targets, which have broad application prospects in the photoelectric sensor industry. However, this aspect has been rarely addressed so far. Therefore, we prepared Mo-10Nb composite powders by mechanical alloying (MA), and investigated the effects of the experimental parameters such as the milling speed and duration on the particle morphology, size distribution, compositional homogeneity, crystallite size, inner strain, and oxygen content. High-quality Mo-10Nb composite powders with 3-μm spherical particles of narrow size distribution, homogeneous elemental distribution, and nanometric crystalline structure were obtained by implementing optimum MA parameters, viz., a milling speed of 250 rpm and duration of 36 h using an MITR QM-QX-4L omnidirectional ball mill. The mechanically alloyed Mo-10Nb composite powders were prone to oxidation when exposed to air, which led to a sharp increase in the oxygen content to ~5400 ppm. X-ray photoelectron spectroscopic analysis revealed the presence of Nb₂O₅, MoO₂, and MoO₃ on the surface of the Mo-10Nb particle. We believe that this study demonstrates an interesting strategy for the fabrication of high-quality Mo-10Nb targets.     

Nanocrystalline AlCoFeNiTiZn high entropy Alloy: Microstructural,Magnetic, and thermodynamic properties

AlCoFeNiTiZn high entropy alloy was successfully produced in powder form by the mechanical alloying process. The ball-milled alloyed product was characterized by X-ray diffractometry, scanning electron microscopy, energy dispersive spectroscopy, and transmission electron microscopy techniques, which indicated that after 120 h of milling, the solid solution was formed as predicted by thermodynamic calculations. Mechanical alloying began to form the BCC phase almost at 30 h and the FCC phase after about 30 h. Nucleation and growth were the processes involved in the formation of these phases, as shown by the Johnson-Mehl-Avrami kinetic model. Sintering was then used to fabricate the alloy in bulk metallic form. The powders were cold pressed and sintered after 120 h of mechanical alloying using a tube furnace with a controlled atmosphere at 500 °C. A similar FCC + BCC phase mixture was present after sintering. The sintered sample also contained minor amounts of Gahnite (ZnAl₂O₄) spinel material. DSC analysis revealed that recrystallization occurred at 280 °C. The as-milled and as-sintered alloys exhibit semi-hard magnetic properties measured by vibrating sample magnetometer (VSM), with saturation magnetization values of 39.14 and 65.78 emu/g, respectively.     

Mechanical alloying of biocompatible Co–28Cr–6Mo alloy

We report on an alternative route for the synthesis of crystalline Co–28Cr–6Mo alloy, which could be used for surgical implants. Co, Cr and Mo elemental powders, mixed in an adequate weight relation according to ISO Standard 58342-4 (ISO, 1996), were used for the mechanical alloying (MA) of nano-structured Co-alloy. The process was carried out at room temperature in a shaker mixer mill using hardened steel balls and vials as milling media, with a 1:8 ball:powder weight ratio. Crystalline structure characterization of milled powders was carried out by X-ray diffraction in order to analyze the phase transformations as a function of milling time. The aim of this work was to evaluate the alloying mechanism involved in the mechanical alloying of Co–28Cr–6Mo alloy. The evolution of the phase transformations with milling time is reported for each mixture. Results showed that the resultant alloy is a Co-alpha solid solution, successfully obtained by mechanical alloying after a total of 10 h of milling time: first Cr and Mo are mechanically prealloyed for 7 h, and then Co is mixed in for 3 h. In addition, different methods of premixing were studied. The particle size of the powders is reduced with increasing milling time, reaching about 5 μm at 10 h; a longer time promotes the formation of aggregates. The morphology and crystal structure of milled powders as a function of milling time were analyzed by scanning electron microscopy and XR diffraction.     

Magnetic and structural properties of amorphous/nanocrystalline Fe42Ni28Zr8Ta2B10C10 soft magnetic alloy produced by mechanical alloying

Magnetic behavior, microstructural evolution, and amorphization studies of Fe₄₂Ni₂₈Zr₈Ta₂B₁₀C₁₀ alloy, synthetized by mechanical alloying, were investigated. The non-equilibrium microstructure originated from a grain size reduction to about 2.5 nm indicated by X-ray diffraction and the introduction of internal strain up to 3.8%. The results showed that as the milling time increased the amorphous phase became dominant and reached about 92 wt.% at 176 h. The magnetic measurements which were obtained by vibrating sample magnetometer, showed an increase in saturation magnetization up to 12 h and then a decrease until 66 h followed by a slow increase. Simultaneously, the coercivity increased, decreased and finally reached a constant level of about 24 Oe. The value of coercivity obtained in the present study is less than the values reported for the widely investigated mechanically alloyed Fe–Ni–Zr–B alloys, which shows this alloy is a very good soft magnet.     

Nanocrystalline Al/Al12(Fe,V)3Si alloy prepared by mechanical alloying: Synthesis and thermodynamic analysis

Al–Al₁₂(Fe,V)₃Si nanocrystalline alloy was fabricated by mechanical alloying (MA) of Al–11.6Fe–1.3V–2.3Si (wt.%) powder mixture followed by a suitable subsequent annealing process. Structural changes of powder particles during the MA were investigated by X-ray diffraction (XRD). Microstructure of powder particles were characterized using scanning electron microscopy (SEM). Differential scanning calorimeter (DSC) was used to study thermal behavior of the as-milled product. A thermodynamic analysis of the process was performed using the extended Miedema model. This analysis showed that in the Al–11.6Fe–1.3V–2.3Si powder mixture, the thermodynamic driving force for solid solution formation is greater than that for amorphous phase formation. XRD results showed that no intermetallic phase is formed by MA alone. Microstructure of the powder after 60 h of MA consisted of a nanostructured Al-based solid solution, with a crystallite size of 19 nm. After annealing of the as-milled powder at 550 °C for 30 min, the Al₁₂(Fe,V)₃Si intermetallic phase precipitated in the Al matrix. The final alloy obtained by MA and subsequent annealing had a crystallite size of 49 nm and showed a high microhardness value of 249 HV which is higher than that reported for similar alloy obtained by melt spinning and subsequent milling.     

Microstructures of mechanically alloyed Fe60Ni40 studied by XAFS and XRD

The structures of the mechanically alloyed Fe₆₀Ni₄₀ powders are investigated by X-ray absorption fine structure (XAFS) and X-ray diffraction (XRD). For the Fe₆₀Ni₄₀ mixture milled for longer than 10 h, the XRD patterns indicate that the bcc phase of α-Fe almost disappears and only the fcc phase remains. The XAFS results further demonstrate that the local structure of Fe atoms is similar to that of Ni atoms for the MA Fe₆₀Ni₄₀ (10 h) alloy. With the milling time going to 40 h, the first-shell bond length R₁ = 2.48 Å, coordination number N₁ = 11.9 and Debye–Waller factor σ = 0.117 Å around Fe atoms are nearly equal to those (R₁ = 2.49 Å, N₁ = 12.0 and σ = 0.117 Å) around Ni atoms and the magnitude peaks of the higher shells disappear. These results imply that the local structure of Fe atoms is identical with that around Ni atoms in the MA Fe₆₀Ni₄₀ (40 h) alloy, where a homogenous solid solution with a large lattice distortion is produced as a final product of MA.     

Rapid formation of lead magnesium niobate-based ferroelectric ceramics via a high-energy ball milling process

Pyrochlore-free nano-sized 0.90Pb(Mg_1/3Nb_2/3)O₃(PMN)-0.10PbTiO₃(PT) and 0.65PMN-0.35PT powders were synthesized from oxides via a high-energy ball milling process. Single perovskite phase PMN-PT were readily formed from the oxide mixture after milling for only 2 h. The grain size calculated from X-ray diffraction (XRD) patterns of all samples is about 20 nm, which is in agreement with the observation from scanning electron microscopy (SEM) (20-50 nm). PMN-PT ceramics were obtained by sintering the milled powders at temperature from 1000 to 1100°C for 2 h. The dielectric, ferroelectric properties of the PMN-PT ceramics derived from the synthesized powders were comparable with the reported results in the literature.     

Structural,Thermal and Magnetic Properties of Nanocrystalline Co<Subscript>80</Subscript>Ni<Subscript>20</Subscript> Alloy Prepared by Mechanical Alloying

Co₈₀Ni₂₀ powder mixture was mechanically alloyed by high-energy planetary ball milling, starting from elemental Co and Ni metal powders. The morphological, microstructural, thermal and magnetic properties of the milled powders were characterised respectively by scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and vibratory sample magnetometry. In addition to a highly disordered phase, two face-centred cubic (FCC) and hexagonal close-packed (HCP), solid solutions, FCC Co(Ni), FCC Ni(Co) and HCP Co(Ni), are observed after 3 h of milling. Their grain sizes decrease with increase in milling time attaining, at 48 h of milling, 12 nm, 25 nm and 10 nm, respectively. Beyond a certain milling time, no further refinement of the microstructure occurs and the morphological equilibrium is usually given by a bimodal particle size distribution. Magnetic measurements of the milled Co₈₀Ni₂₀ alloy powder exhibit a soft ferromagnetic character where the magnetic parameters are sensitive to the milling time mainly due to the particle size refinement as well as the formation of Co(Ni) and Ni(Co) solid solutions. Both the saturation magnetisation ( M _s) and coercivity ( H _c) were found to decrease with milling time, attaining the values of M _s = 126 emu/g and H _c = 60 Oe after 48 h of milling.     

Effect of rotation speed and milling time to attain Nb-10Hf-1Ti alloy powders on morphology and microstructure of Nb-10Hf-1Ti powder

The mechanical alloying process was employed to produce C103 alloy with Nb-10% Hf-1% Ti (wt.%) composition using Nb, Hf and Ti powders. The mechanical alloying process was performed in an argon atmosphere in the chamber and bullets of tungsten carbide with a ball-to-powder weight ratio (BPR) of 20:1 at rotation speed of 200, 300 and 400 rpm for 2, 5 and 8 h. At rotation speeds of 200 and 300 rpm particle size decreased and became more spherical during MA. While increasing milling time at 400 rpm caused agglomeration of particles. XRD results showed that increasing milling time at a constant rotation speed has no considerable effect on reduction of crystallite size, but the lattice strain is strongly affected by it and increased obviously with further rotation speed. The results showed that the optimum milling time and rotation speed to attain Nb-10Hf-1Ti alloy powders with the least amount of contamination and appropriate morphology are 5 h and 300 rpm, respectively.     

Synthesis of Mo5SiB2 based nanocomposites by mechanical alloying and subsequent heat treatment

In this study, systematic investigations were conducted on the synthesis of Mo₅SiB₂-based alloy by mechanical alloying and subsequent heat treatment. In this regard, Mo-12.5 mol% Si-25 mol% B powder mixture was milled for different times. Then, the mechanically alloyed powders were heat treated at 1373 K for 1 h. The phase transitions and microstructural evolutions of powder particles during mechanical alloying and heat treatment were studied by X-ray diffractometry and scanning electron microscopy. The results showed that the phase evolutions during mechanical alloying and subsequent heat treatment are strongly dependent on milling time. After 10 h of milling, a Mo solid solution was formed, but, no intermetallic phases were detected at this stage. However, an α-Mo-Mo₅SiB₂ nanocomposite was formed after 20 h of milling. After heat treatment of 5 h mechanically alloyed powders, small amounts of MoB and Mo₂B were detected and α-Mo-MoB-Mo₂B composite was produced. On the other hand, heat treatment of 10 h and 20 h mechanically alloyed powders led to the formation of an α-Mo-Mo₅SiB₂-MoSi₂-Mo₃Si composite. At this point, there is a critical milling time (10 h) for the formation of Mo₅SiB₂ phase after heat treatment wherein below that time, boride phase and after that time, Mo₅SiB₂ phase are formed. In the case of 20 h mechanically alloyed powders, by increasing heat treatment time, not only the quantity of α-Mo was reduced and the quantity of Mo₅SiB₂ was increased, but also new boride phases were formed. Finally, after 5 h heat treatment, the Mo phase completely disappeared and a Mo₅SiB₂-based composite was completely formed.     

Ultrafast synthesis of the nanostructured Al59Cu25.5Fe12.5B3 quasicrystalline and crystalline phases by high-energy ball milling: Microhardness,electrical resistivity,and solar cell absorptance studies

In this study, the Al₅₉Cu_25.5Fe_12.5B₃ nanoquasicrystalline alloy and related crystalline phases were synthesized through mechanical alloying using a high-energy ball milling and consolidated by a cold isostatic pressing apparatus. This paper focuses on the synthesis, structural and microstructural evolutions, thermal stability, microhardness, and electrical and optical properties of the Al₅₉Cu_25.5Fe_12.5B₃ nanoquasicrystalline alloy for solar selective absorber usages. The structural evolutions of the mechanically alloyed and heat-treated AlCuFeB powders were investigated by X-ray diffractometry. Accordingly, the effect of milling time and heat treatment on the formation of quasicrystalline and related crystalline phases were studied in the AlCuFeB alloy system. The microstructure, morphology, and chemical microanalysis of the un-milled and as-milled powders were examined by field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy. The composition of the as-milled AlCuFeB powders was estimated employing inductively coupled plasma-atomic emission spectroscopy. The thermal stability of the AlCuFeB powders was recorded by differential thermal analysis, and the weight gain of the particles during annealing was investigated through thermogravimetric analysis. The nanostructured Al₅₉Cu_25.5Fe_12.5B₃ stable quasicrystalline phase and crystalline Al(Cu,Fe) solid-solution were synthesized by the ultrafast milling procedure in 1 h. The rationale behind using the term ultrafast synthesis is to synthesize the QC i-phase only by the high-energy ball milling procedure in short-term ball milling without subsequent annealing treatment. However, the single quasicrystalline phase could not be obtained even after the annealing treatment. The quasicrystalline size was calculated by the Williamson–Hall method and optimized by the Rietveld refinement procedure, and it was found that the size is varied between 53 and 61 nm. Furthermore, the particle size distribution of the as-milled AlCuFeB powders was measured using laser static light scattering, which ranges from 0.1 to 50 μm. The microhardness of the consolidated as-milled and heat-treated samples was estimated utilizing the Vickers microhardness indenter. At the same time, their electrical resistivity was assessed by the four-point probe method at room temperature. The spectral analyses of absorption on the consolidated as-milled samples were carried out in the ultraviolet, visible, and near-infrared regions. It was found that the presence of the quasicrystalline phase in the AlCuFeB alloy prominently improves the microhardness, electrical resistivity, and particularly sunlight absorptance.     

Solid state amorphization transformation in the mechanically alloyed Fe27.9Nb2.2B69.9 powders

Mössbauer spectrometry and Rietveld analysis of X-ray diffraction patterns were used to follow the solid state amorphization transformation during the milling process of the Fe_27.9Nb_2.2B_69.9 powders. The reaction between elemental Fe, Nb and B powders leads to the formation of the Nb(B) and Fe(B) solid solutions after 1 and 10 h of milling, respectively. A mixture of α-Fe, Nb(B) and highly disordered Fe(Nb, B) solid solution is found after 25 h of milling. An amorphous structure is obtained on further milling time (100 h). From the Mössbauer spectrometry results, it is observed that the total mixing of the elemental powders, at the atomic level, is achieved after 50 h of milling and a stationary state corresponding to a full paramagnetic amorphous phase is reached after 100 h of milling. The amorphization process can be described by an Avrami parameter close to n = 1.     

The preparation,formation mechanism and magnetic properties of a Fe-Cr-Mn-N amorphous alloy

In this paper, the amorphous phase formation process, formation mechanism and magnetic properties, during the mechanical alloying (MA), have been investigated in Fe₆₀Cr₁₅Mn₁₀N₁₅ alloy, respectively. The results obviously indicate that amorphous Fe₆₀Cr₁₅Mn₁₀N₁₅ with a wide supercooled liquid region (SCLR, 82?K) can be obtained via 40?h MA process. With the milling time increasing gradually, the microstructures evolve from the initial crystalline powder, to completely amorphous phase, and eventually to amorphous phase with embedded Cr₂N. By calculation, the mixing chemical enthalpy ΔH^chem and amorphous formation enthalpy ΔH^form have been obtained as ?0.24?kJ/mol and ?6.610?kJ/mol, respectively, implying the existence of thermodynamic advantage for the amorphous phase formation. In addition, the effect of 7 at% B and 7 at% Mo addition on the amorphous phase formation have also been studied, however, the diffraction peaks corresponding to Mo (Cr₂N) still appear after 120?h milling. Meanwhile, isothermal annealing experiments were conducted at different temperatures, obtaining the microstructure evolution as: amorphous?→?amorphous alloy?+?Cr₂N?→?α-Fe?+?Cr₂N?→?α-Fe?+?CrN?+?Cr₂N. And the hysteresis loops in amorphous Fe₆₀Cr₁₅Mn₁₀N₁₅ undergoing both the MA process and isothermal annealing procedure provide us with the evidence that this alloy system can exhibit excellent soft magnetic properties.     

Magnetic properties of iron-base b.c.c. alloys produced by mechanical alloying

The structure and magnetic properties of Fe-M (M = Zr, Hf, Co or Si) alloy powders produced by mechanical alloying (MA) of elemental powders or a mixture of elemental powders and alloy powders have been examined. The MA Fe-Zr and Fe-Hf powders have a non-equilibrium b.c.c. phase in the composition range above 90 at% Fe. The coercivity of the MA Fe-Zr and Fe-Hf powders exhibits a minimum value (1300 A m⁻¹) combined with a high magnetization of 2.2×10⁻⁴ Wb m kg⁻¹ at 95 at % Fe, which corresponds to the concentration of zero magnetostriction. Although the compacts made from the MA b.c.c. Fe-Zr powders do not exhibit good soft magnetic properties, the permeability of the compacts made from the MA Fe-Co powders annealed at 1173 K for 18 ks in H₂ is nearly the same as that of the alloy ingot produced by conventional casting followed by the same annealing treatment. On leave from ALPS Electric Co. Ltd, Nagaoka 940, Japan.     

Soft mechanochemical synthesis of MgFe2O4 nanoparticles from the mixture of α-Fe2O3 with Mg(OH)2 and Fe(OH)3 with Mg(OH)2

Abstract

The influence of long term soft milling of a mixture of (1) Mg(OH)₂ and α-Fe₂O₃ and (2) Mg(OH)₂ and Fe(OH)₃ powders in a planetary ball mill on the reaction synthesis of nanosized MgFe₂O₄ ferrites was studied. Soft mechanochemical reaction leading to formation of the MgFe₂O₄ spinel phase was followed by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and magnetisation measurements. The spinel phase formation was first observed after 5 h of milling and its formation was completed after 15 h in case (2). The synthesised MgFe₂O₄ ferrite had a nanocrystalline structure with a crystallite size of about 10 and 15 nm respectively for cases (1) and (2). Measurements after 15 h of milling show magnetisation values of 15·23 and 10·14 J T^–1 kg^–1 respectively for cases (1) and (2).     

Effect of starting composition on formation of MoSi2–SiC nanocomposite powder via ball milling

MoSi₂?CSiC nanocomposite powders were successfully synthesized by ball milling Mo, Si and graphite elemental powders. Effects of milling time and annealing temperature were also investigated. The composite formation and phase transformation were monitored by X-ray diffraction. The microstructure of milled powders was studied by SEM, TEM and XRD peak profile analysis. Formation of this composite was completed after 10 and 20?h of milling for 25%SiC and 50%SiC, respectively. High temperature polymorph (HTP) of MoSi₂ was obtained at the end of milling (20?h). On the other hand, annealing led to transformation of HTP to low temperature polymorph (LTP) of MoSi₂. Mo₅Si₃ was formed during annealing as a product of a reaction between MoSi₂ and excess graphite. Mean grain size <50?nm was obtained for 20?h milled sample on the basis of peak profile analysis and TEM images.     

Mechanochemical synthesis and characterization of nanocrystalline 0.4Bi(Zn1/2Ti1/2)O3-0.6PbTiO3 powders

Perovskite 0.4Bi(Zn_1/2Ti_1/2)O₃-0.6PbTiO₃ (BZT-PT) powders were successfully synthesized from precursor oxides using a high-energy planetary ball milling. The phase development of the powders during milling was studied by means of X-ray diffraction and Raman scattering techniques. The microstructure of the powders was characterized using transmission electron microscopy, and the thermal behavior was studied as well. The results reveal that after 15 h of milling the formation of BZT-PT phase can be completed and submicron agglomerates of small crystallite sized ~ 12 nm are present in the powders. However, further prolonging the milling time to 25 h leads to the amorphization of the BZT-PT phase.     

Simultaneous carbothermic reduction of iron and titanium oxides to produce an iron-based composite by mechanically activated sintering method

In this research, for the first time, Fe–TiC nano-crystalline composite was produced via simultaneous reduction of iron and titanium oxides by petrocoke. Powder mixture of Fe₂O₃/TiO₂/petrocoke was mechanically activated in a high-energy ball mill at different times. X-ray diffraction method (XRD) and Scanning Electron Microscopy (SEM) were used to characterize the milled powders. The results showed that new phases were not formed during milling, even after 20 h of milling. However, crystallite size and lattice strain of hematite were remarkably decreased and increased, respectively. Thermogravimetry and Differential Thermal Analysis (TG–DTA) were done on 0, 10 and 20 h mechanically activated powders. These experiments showed a substantial decrease in reduction temperature of iron and titanium oxides as a result of mechanical activation. Then, the powders were cold compacted and sintered at 1200 °C in argon atmosphere for 1 h. XRD results of 20 h milled samples demonstrated that, in this condition, iron oxide was completely reduced to nano-crystalline iron and titanium dioxide was reduced to nano-crystalline titanium carbide and Fe–TiC nano-crystalline composite was successfully formed.     

Electrocatalytic properties of mechanically alloyed Co-20wt%Ni-10wt%Mo and Co-70wt%Ni-10wt%Mo alloy powders

Mechanically alloyed Co-20wt%Ni-10wt%Mo and Co-70wt%Ni-10wt%Mo (nominal compositions) alloy powders were produced by milling of pure elemental powders. Mechanically alloyed powders were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. MA powder specimens were tested electrollitically in a 30% KOH aqueous solution at 298 K. X-ray diffraction analysis and transmission electron microscopy of milled powders showed the presence of two phases, an fcc solid solution and intermetallic compounds of Ni or Co with Mo. These phases showed a nanometric size. The linear sweep voltammograms confirmed also the presence of two phases in both mechanically alloyed alloy powders. The Co-20wt%Ni-10wt%Mo alloy powders showed the best electrocatalytic activity for hydrogen evolution reaction.     

Effect of the ball mass to sample mass relation in the magnetic and structural properties of Fe0.6Mn0.1Al0.3 alloys prepared by mechanical alloying

Fe_0.6Mn_0.1Al_0.3 samples were prepared by mechanical alloying (MA) using the 6:1, 9:1 and 12:1 ratios between the ball mass and powder mass (BM/PM) and milling times of 3, 6, 9 and 12 h. Balls of 10 and 20 mm diameter were used. X-ray diffraction (XRD) studies showed that the 6:1 and 9:1 samples present, for all milling times and balls of 20 mm, the three elements, and in some cases (9:1 and 12:1 relations) the formation of a bcc disordered Fe-Mn-Al phase. The 12:1 samples with 12 h milling present only the bcc disordered phase. Mössbauer spectra (MS) of the 6:1 samples were fitted with a narrow hyperfine field distribution (HFD) with ≈32.6 T mean field (typical for pure Fe). The 9:1 spectra were fitted with a HFD and an increasing paramagnetic site which, according to X-ray results, correspond to impure Fe and the paramagnetic alloy, respectively. For the 12:1 samples, the spectra were fitted in a similar way but, for 12 h, the HFD is broad. In this case the alloy is totally consolidated and presents ferromagnetic and paramagnetic sites. When balls of 10 mm diameter were used the bcc formation is accelerated.