Synthesis by ball milling and characterization of Al-Zn alloys

Mechanical ball milling is a useful technique for systems with positive enthalpy of mixing. With this technique solubility of a solute in a solid solution can be enhanced. Al-Zn system has positive heat of mixing. High energy ball milling has been employed to produce four alloys of Al with 2.5 to 10 wt% Zn. Powders of Al (1–125 m) and Zn (0.7–5.0 m) were mixed together in the desired proportion and milled with a powder to ball weight ratio of 1:20. The size and shape of the particles of as-received and alloy powders were examined in a scanning electron microscope (SEM) while their microanalysis was performed by energy dispersive system (EDS) attached with SEM. It has been observed that 120 h of milling of the powders produced homogeneous alloys. X-ray diffraction (XRD) patterns confirm complete solubility up to 10 wt% Zn in Al. Using the quasi-chemical theory of binary solid solutions, the enthalpy of mixing of 10 wt% Zn in Al has been determined to be 276 cals/mol. It is shown that stress exerted by very high density of dislocations, generated by mechanical milling, plays a major role in the enhancement of solubility. Hardness has been measured and it increases with increasing solute content.     

Synthesis of Cu-W nanocomposite by high-energy ball milling

The Cu-W bulk nanocomposites of different compositions were successfully synthesized by high-energy ball milling of elemental powders. The nanocrystalline nature of the Cu-W composite powder is confirmed by X-ray diffraction analysis, transmission electron microscopy, and atomic force microscopy. The Cu-W nanocomposite powder could be sintered at 300-400 degrees C below the sintering temperature of the un-milled Cu-W powders. The Cu-W nanocomposites showed superior densification and hardness than that of un-milled Cu-W composites. The nanocomposites also have three times higher hardness to resistivity ratio in comparison to Oxygen free high conductivity copper.     

Synthesis of titanium oxynitride by mechanical milling

The synthesis of a titanium oxynitride phase by mechanically milling elemental titanium powder in air at ambient temperature has been studied. X-ray powder diffraction, transmission electron microscopy and chemical analysis showed that milling resulted in the formation of a nanocrystalline f c c oxynitride phase having the composition TiNO_0.5. The effects of milling time and subsequent heat treatment on the structure and lattice parameters are reported. The results indicate that mechanical milling significantly increases the reactivity of titanium with nitrogen.     

Synthesis of hydrophobic Ni-VN alloy powder by ball milling

This is the first report discussing the synthesis of hydrophobic alloy powders consisting of Ni and transition metal nitride (vanadium nitride (VN)) at different proportions through mechanical alloying. The milled alloy powder showed very good resistance to wetting when it was placed in a beaker containing water. The maximum contact angle of 150° with water was recorded for the alloy composition of Ni-75 (wt.%) VN when the powder was loosely sprayed on a glass slide. Few working examples also elucidated the hydrophobic nature of the as-prepared alloy powder. The optimised alloyed powder composition and its phase and morphology as well as the time of milling for maximum hydrophobicity were established with the help of X-ray diffraction (XRD) and field emission scanning electron microscope (FE-SEM) for phase and morphology analysis, respectively. The unique chemistry of toluene with elemental Ni and transition metal nitride VN as characterized by X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy led to the development of hydrophobicity in the ball milled powder.     

Synthesis and structural evolution of tungsten carbide prepared by ball milling

Tungsten carbide has been synthesized directly by ball-milling tungsten powder and activated carbon in vacuum. The structural development of the WC phase with milling times up to 310 h has been followed using X-ray, neutron diffraction and scanning electron microscopy. Subsequent annealing (at 1000 °C for 1 and 20 h) of material milled for 90 h or longer, results in samples comprising almost entirely crystalline WC. The production of WC itself during milling results in enhanced iron contamination from the steel mill and balls on extended milling which were monitored by energy-dispersive X-ray and Mossbauer spectroscopies. This revised version was published online in November 2006 with corrections to the Cover Date.     

Synthesis of BF–PT perovskite powders by high-energy ball milling

0.7BiFeO₃–0.3PbTiO₃ (BF–PT) powders were synthesized from a mixture of the oxides Bi₂O₃, Fe₂O₃, PbO and TiO₂ using a Fritsch P4™ vario-planetary ball milling system. The perovskite structure of the BF–PT powder can be obtained well and the crystallite size of the powders was greatly reduced to 20–35 nm after milling for 8 h. The pre-calcined course shows a rhombohedral–tetragonal phase transition with the increasing temperature and shows the structure transition near the Curie temperature T_c.     

球磨反应合成镁基复相储氢合金的研究

采用x射线衍射（XRD）、差热分析（TG，DSC）等方法研究了Mg和预处理Al粉（主要成分为A1和Ni）在高纯氢气气氛下的反应合成过程，分析了球磨反应合成对反应产物的相组成及放氢性能的影响。结果表明：Mg粉和预处理铝粉在氢气气氛作用下可直接氢化生成纳米尺寸的MgH2、Mg（AlH4）2等镁基复相储氢合金，该合金在较低的温度下即可放氢，并探讨了放氢机理。     

Nanocrystals by high energy ball milling

It has been shown that nanometer-size grains can be induced in even brittl e intermetallic compounds by high energy ball milling. The large grain boundary area provided by these nanocrystallites can help provide, along with the disordering energy, the driving free energy for the crystalline-to-amorphous transformation. Examples were given for Nb₃Sn (complete amorphization), Ni₃Al (partial amorphization), and Ni₃Si (no amorphization).     

Fabrication of commercial pure Ti by selective laser melting using hydride-dehydride titanium powders treated by ball milling

Micro-fine sphericalpowders are recommended for selective laser melting(SLM). However, they are mostly expensive due to the complex manufacturing technique and low yield. In this paper, using lowcost treated hydride-dehydride(HDH) Ti powders, commercial pure Ti(CP-Ti) was successfully fabricated by SLM. After 4-h milling, the resulting powders become near-spherical with no obvious angularity, and have optimal flowability with the apparent density of 1.64 ± 0.02 g/cm~3, tap density of 2.10 ± 0.04 g/cm~3,angle of repose 40.11?±0.09?, and Carr's index of 77.74 ± 0.15. The microstructure was determined with full acicular martensitic β phase. The CP-Ti can achieve superior mechanical properties with the ultimate tensile strength of 876.1 ± 20.5 MPa and elongation of(14.7 ± 0.5)%, which exhibit distinctly competitive compared to the as-cast CP-Ti or Ti-6 Al-4 V. Excellent mechanical properties together with its low-cost make SLM-fabricated CP-Ti from modified HDH Ti powders show promising applications.     

Synthesis of boron nitride nanotubes from boron oxide by ball milling and annealing process

Boron nitride nanotubes were synthesized from boron oxide by high-energy ball milling and annealing method. The diameter of the nanotubes is in the range of 20-200 nm. The nanotubes show a bamboo-like structure and cylindrical-like structure under low magnification. The shorter bamboo nodes with distinct knots were observed for the bamboo-like nanotubes with larger diameters and the knots can also occasionally be observed in the cylindrical-like BN nanotubes with smaller diameters under high magnification. Al and Si were found to be catalytic materials responsible for the formation of BN nanotubes besides the metallic particles containing Fe, Ni and Cr.     

球磨合成Fe3Al金属间化合物及其固相反应机理

Fe3Al金属间化合物是一种新型耐高温材料,并因其电热和磁性能受到重视。本文研究由铁、铝元素混合粉末利用高能球磨工艺合成Fe3Al。通过对冷焊现象的分析,用适量的有机物有效地控制了机械合金化过程。利用X射线衍射研究了反应物在球磨过程中的结构演变。通过对Fe／Al固相反应热力学的分析,认为Fe／Al原子比相等成分附近,固相反应最容易进行。     

Crystallite size study of nanocrystalline hydroxyapatite and ceramic system with titanium oxide obtained by dry ball milling

High energy dry ball milling has been used to produce nanocrystallite powders of Hydroxyapatite (HAP) using the starting materials Ca(H₂PO₄)₂ and Ca(OH)₂. The calcium phosphate system with titanium (CaP-Ti) were prepared with the raw materials Ca(H₂PO₄)₂ and TiO₂. The HAP was obtained after a couple of hours of milling (5, 10 and 15 h) and in the reaction with CaP-Ti was obtained after 5 h of milling. The HAP and the ceramic calcium phosphate with titanium (CaP-Ti) were studied by X-Ray powder Diffraction and Scanning Electron Microscopy (SEM). The grain size analysis through XRD shows that the particle size of HAP increase of the milling time and the size of CaTi₄P₆O₂₄ decrease with the increase of the milling time.     

Synthesis and catalytic performance of antimony trioxide nanoparticles by ultrasonic-assisted solid-liquid reaction ball milling

In this study, the cubic antimony trioxide (Sb₂O₃) nanoparticles were successfully synthesized by ultrasonic-assisted solid-liquid reaction ball milling technique. And the synthetic process, using Sb powder as raw material, was conducted with an atmosphere of acetic acid aqueous solution at low temperature (?100 °C). Some controlled trials, including without the assistance of ultrasonic wave, different reaction solutions and diverse ultrasonic frequencies, were performed. The products were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that the Sb₂O₃ nanoparticles with uniform and ultrafine particle size were obtained within short reaction time under the coaction of both ultrasonic wave and ball milling. Furthermore, the catalytic capacity of the Sb₂O₃ nanoparticles for decomposition of H₂O₂ was measured during the oxidative decomposition of methylene blue (MB). The test exhibited rapid and efficient color removal in the degradation of MB.     

Carburising behaviour of low carbon steel with nanocrystalline surface layer induced by ball milling

Abstract

Ball milling, as a surface nanocrystallisation method, was employed to investigate the influence of severe plastic deformation on the carburisation treatment performed on low carbon steel. The results indicated an enhancement in the carburisation efficiency as a result of surface milling. This enhancement was attributed to the formation of a nanocrystalline layer in the surface of the treated samples. It was found that the main reasons for the accelerated kinetics of the carburisation process would be the considerable amounts of non-equilibrium defects and the finer austenite grains in the early and later stages of the treatment respectively, which facilitate the carbon diffusion.     

Synthesis of Ag-ZnO composites via ball milling and hot pressing processes

Ag — 8 wt. % ZnO composites were synthesized by ball milling, heat treating and hot pressing of silver and zinc oxide powder mixtures. The crystalline size and microstrain of the milled powders before and after heat treatment were determined by Debye-Scherrer andWilliamson-Hall methods. It was shown that heat treatment resulted in decrease of microstrain and increase in the crystallite size of the milled powders. The effect of uniaxial pressure magnitude and duration of hot pressing at 550 °C on the final density of the powder compacts were investigated. The results showed that both plastic flow and atomic diffusion mechanisms affected densification of the composite powders during the hot pressing process. However, the latter one had more effective role on the density of the hot-pressed samples. The synthesized composites showed homogenous microstructure with relatively high density and hardness.     

Synthesis and piezoelectric properties of nanocrystalline PZT-based ceramics prepared by high energy ball milling process

Nanocrystalline powders of a soft FeNbLi-doped PZT material have been prepared by a novel mechanochemical process consisting of mixing the stoichiometric oxides in a planetary ball mill for prolonged times up to 80 h. The constituent oxides were reacted in a tungsten carbide vial with balls of 5, 10 and 20 mm in diameter and a ball/powder ratio of 15/1. The chemical reaction between the component oxides was triggered after 20 h of energetic milling and was completed after 80 h. The XRD of the reacted nanopowder showed the well known perovskite structure. Compacted samples of this powder were sintered between 800-1300°C for 3 h and the main piezoelectric properties were determined. The density of the sintered samples reached nearly 99% of the theoretical density at 1100°C and showed good piezoelectric characteristics: planar coupling factor of 0.66, dielectric displacement constant d ₃₃ of 550 pm/V, mechanical quality factor of 85, and relative dielectric constant of 3800. The possible mechanisms for solid state reaction of mechanically activated nanopowders such as local heating and pressure at collision as well as defects diffusion are discussed.     

Microstructural characteristics and mechanical properties of carbon nanotube reinforced aluminum alloy composites produced by ball milling

The influence of milling time on the structure, morphology and thermal stability of multi-walled carbon nanotubes (MWCNTs) reinforced EN AW6082 aluminum alloy powders has been studied. After structural and microstructural characterization of the mechanically milled powders micro- and nano-hardness of the composite powder particles were evaluated. The morphological and X-ray diffraction studies on the milled powders revealed that the carbon nanotubes (CNTs) were uniformly distributed and embedded within the aluminum matrix. No reaction products were detected even after long milling up to 50 h. Nanotubes became shorter in length as they fractured under the impact and shearing action during the milling process. A high hardness of about 436 ± 52 HV is achieved for the milled powders, due to the addition of MWCNTs, after milling for 50 h. The increased elastic modulus and nanohardness can be attributed to the finer grain size evolved during high energy ball milling and to the uniform distribution of hard CNTs in the Al-alloy matrix. The hardness values of the composite as well as the matrix alloy compares well with that predicted by the Hall–Petch relationship.     

Synthesis of Fe-Si-B-Mn-based nanocrystalline magnetic alloys with large coercivity by high energy ball milling

Alloys of Fe-Si-B with varying compositions of Mn were prepared using high energy planetary ball mill for maximum duration of 120 h. X-ray diffraction (XRD) analysis suggests that Si gets mostly dissolved into Fe after 80 h of milling for all compositions. The residual Si was found to form an intermetallic Fe₃Si. The dissolution was further confirmed from the field emission scanning electron microscopy/energy dispersive X-ray analysis (FE-SEM/EDX). With increased milling time, the lattice parameter and lattice strain are found to increase. However, the crystallite size decreases from micrometer (75–95 μm) to nanometer (10–20 nm). Mössbauer spectra analysis suggests the presence of essentially ferromagnetic phases with small percentage of super paramagnetic phase in the system. The saturation magnetization (M _s), remanance (M _r) and coercivity (H _c) values for Fe-0Mn sample after 120 h of milling were 96.4 Am²/kg, 11.5 Am²/kg and 12.42 k Am^?1, respectively. However, for Fe-10Mn-5Cu sample the M _s, H _c and M _r values were found to be 101.9 Am²/kg, 10.98 kA/m and 12.4 Am²/kg, respectively. The higher value of magnetization could be attributed to the favourable coupling between Mn and Cu.