Solid-state transformation in nanocrystalline Ti induced by ball milling

In the current study, we report for the first time a new Ti rhombohedral (trigonal) structure induced by HEBM and subsequent sintering. During ball milling of Ti powder, solid-state transformation does not only depend on the grain refinement but also on the successful deformation of the nano-sized crystallites due to high energy ball impacts. Thermal stability of Ti-nanocrystalline in FCC allotrope was investigated. Upon sintering, the unstable FCC restored back to the rhombohedral phase rather than to HCP. The appearance of HCP Ti after sintering could suggest that prolonged milling leads to dispersion of hard particles (HCP) into more ductile particles belonging to allotropic phases, and hence possibility of resurfacing on sintering.     

Effect of ball size on milling efficiency of zinc oxide dispersions

Zinc oxide (ZnO) was wet milled using inert Al₂O₃-ceramic balls having different diameter at different milling intervals and the milling efficiency of the resultant dispersion was followed through particle size analysis and zeta potential measurements. The results indicated that small-sized balls improved the milling efficiency. The highest share (%) of lower-size particles was obtained after 24?h of ball milling.     

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).     

Solid-state reactions in the Al-Fe system induced by ball milling of elemental powders

Elemental aluminium and iron powders have been mechanically alloyed in the atomic AlFe ratios of 11 and 13. The structural evolution of the samples was followed by X-ray diffraction and differential calorimetry. Extended milling caused the formation of an almost completely disordered b c c solid solution instead of the equilibrium B2 and DO₃ compounds. Upon heating to 700 °C the formation of the B2 phase was observed in the equiatomic samples and no significant variation of the long-range state of order in the iron-rich samples. Upon heating of samples pre-milled for short or intermediate times, at about 400 °C, the nucleation and growth of Al₅Fe₂ was observed which, upon further heating to 700 °C, transformed to the B2 phase or to the b c c solid solution, depending on the sample composition. These results suggest that the solid-state reactions proceed through diffusion of iron atoms in the aluminium layers, and that for an iron concentration in these layers below about 50 at%, the Al(Fe) solid solution could be in a metastable phase.     

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.     

Studies on copper-yttria nanocomposites: high-energy ball milling versus chemical reduction method

Oxide dispersion-strengthened copper-base composites are widely used for applications demanding high tensile strength, high hardness along with good electrical and thermal conductivity. Oxides of metals like aluminium, cerium, yttrium and zirconium are often used for this purpose as fine and uniformly distributed dispersoid particles in soft and ductile copper matrix. Such composites find applications as electrical contacts, resistance-welding tips, lead wires, continuous casting moulds, etc. In this investigation an attempt has been made to produce copper-yttria nanocomposites using two different morphologies of copper powder and two different processing routes namely, high-energy milling and in-situ chemical reduction. The synthesized powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) for their phase identification and morphological study. The nanocomposite powders in each case were subsequently processed to obtain bulk solids by classical powder metallurgy route of press-sinter-repress. The resultant bulk solid compacts were subjected to property evaluation. The study revealed that the properties of Cu-Y2O3 nanocomposites depend on the processing route used and in turn on the resultant powder morphology.     

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.     

Microstructural evolution during combustion reaction between CuO and Al induced by high energy ball milling

The product of the combustion reaction between CuO and Al induced by high energy ball milling has been characterised by using X-ray diffractometry and scanning electron microscopy. It has been observed that the combustion reaction can be ignited very easily by the ball milling. The reaction product consists of polycrystalline Cu in bulk and particle forms and a large number of nanometer sized spherical Al2O3 particles attached to the surface of the Cu. It has been demonstrated that this microstructure is evolved through rapid solidification of Cu and Al2O3 melts and rapid condensation of Cu vapour. Cu and Al2O3 phases are separated in the reaction product. The reason for this is mainly attributed to the large difference in their density and the shaking force of the ball mill.     

Carbothermic reduction of zinc sulfide in the presence of calcium oxide

The carbothermic reduction of zinc sulfide in the presence of calcium oxide has been studied using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and surface area measurements. The results of XRD indicated that zinc sulfide was first transformed from β type to α type, then reacted to give an intermediate product of zinc oxide before being reduced finally to zinc vapor. The sulfur of zinc sulfide was scavenged as calcium sulfide which remained in the solid, and carbon black formed carbon monoxide. SEM showed that the zinc containing particles and carbon grains shrank gradually; the calcium containing grains swelled and sintered during the reaction. The surface area of the solid sample decreased drastically in the initial stage and then increased with reaction time; the pore volume of the solid sample was also reduced much faster initially and then increased slowly. The average pore diameter, however, increased remarkably in the initial stage, decreased and then leveled off. These results were explained by considering the phase transformation of zinc sulfide, escape of zinc vapor, gasification of carbon and expansion and sintering of calcium sulfide. A reaction mechanism and model are proposed to explain the variations in chemical composition and physical properties of the solid sample during the reaction.     

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.     

球磨法制备高活性铝粉

为提高含铝炸药爆热性能,探索高活性金属铝粉的制备方法,采用立式球磨机对球形铝粉进行处理,研究球磨机的搅拌转速、球磨时间、助磨剂的配比对活性铝粉粒径、形貌、热性能的影响;利用扫描电子显微镜、激光粒度测试仪和同步热分析仪检测活性铝粉形貌、粒径及热分解特性;采用热分析参数法测定活性铝含量。结果表明:制备活性铝粉的最佳条件为搅拌转速1 100 r/min,研磨时间4 h,助磨剂占铝粉质量比4%;制备的活性铝粉粒径d_(50)为1.108μm,片状,活性铝质量分数由90.42%增加到98.42%;用于含铝炸药中,爆热值由6 805 kJ/kg增加到7 642 kJ/kg。     

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.