Structural evolution of an Al–Te mixture during ball milling

An Al–Te mixture was mechanically alloyed with a planetary ball mill, and the structural evolution of the Al–Te mixture during ball milling was characterized by X-ray diffractiometry (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and thermodynamic computation. Although crystalline α-Al₂Te₃ was synthesized in the initial stage of milling, but the final product is a metastable Al₂Te_3 ? δ (Space group: Fm 3¯m) with lattice parameter a = 5.925 Å. The metastable Al₂Te_3 ? δ decomposes into Al and Te at about 140 °C.     

Formation kinetics of Ni–15% Fe–5% Mo during ball milling

Systematic study on Ni–15% Fe–5% Mo by high energy ball milling of elemental Mo powder and pre-alloyed intermetallic FeNi₃ has been done to understand the formation kinetics during ball milling. X-ray powder diffraction (XRPD) has been employed to study the structure evolution. Mo atoms were found to dissolve into FeNi₃ within 40 h of milling. The speed of the diffusion of Mo atoms into FeNi₃ alloy was very slow as analyzed using the Johnson–Mehl–Avrami (JMA) equation. The substitution process destroyed the long-range FeNi₃ and NiMo bonds were formed. This change caused a decrease in magnetization.     

Microstructural evolution of Al–Fe powder mixtures during high-energy ball milling

High-energy ball milling has been performed on FexAl1-x powder mixtures with x=0.75, 0.50, 0.25 and 0.20. X-ray diffraction, Mossbauer spectroscopy and electron microscopy have been used to characterize the samples milled for different times and annealed in a differential scanning calorimeter. It is found that, during milling, there is diffusion of both elements into each other, with a prevalence of iron diffusion into aluminium, at least in the early stages of the process. This behaviour is more pronounced in the aluminium-rich samples. The growth of the Fe(Al) and Al(Fe) solid solutions has been observed for x0.5, different from the lower iron concentrations where the Fe(Al) phase has not been detected. The annealing of pre-milled samples favours the formation, depending on the sample composition and on the annealing temperature, of intermetallic phases such as Fe3Al, FeAl, Fe2Al5 and FeAl3. © 1998 Chapman & Hall     

Correlation between structural parameters and magnetic properties of ball milled nano-crystalline Fe–Co–Si powders

The main aim of this research is to fabricate the nano-crystalline Fe–Co–Si alloy with superior magnetic properties to be used in producing soft magnetic composites. The alloy powders were prepared by using a planetary ball mill. Morphological, structural and magnetic evolutions during milling were analyzed by scanning electron microscopy coupled with Energy-dispersive X-ray microanalyzer, X-ray diffractometer and vibrating sample magnetometer. The results confirm the production of the Fe(Co) and Fe(Co, Si) solid solutions after milling. Increasing the milling time did lead to smaller crystallite sizes and lattice parameters, but larger amounts of micro-strain and dislocation density. The magnetic measurements indicate that higher amounts of Si lead to lower values of saturation magnetization. The variations of coercivity could be attributed to the introduction of dislocations and reduction of crystallite size as a function of milling time.     

The effect of ball milling on the melting behavior of Sn–Cu–Ag eutectic alloy

Sn–Ag–Cu (SAC) solder alloys are the best Pb free alternative for electronic industry. Since their introduction, efforts are made to improve their efficacies by tuning the processing and composition to achieve lower melting point and better wettability. Nanostructured alloys with large boundary content are known to depress the melting points of metals and alloys. In this article we explore this possibility by processing prealloyed SAC alloys close to SAC305 composition (Sn-3wt%Ag-0.5wt%Cu) by mechanical milling which results in the formation of nanostructured alloys. Pulverisette ball mill (P7) and Vibratory ball mills are used to carry out the milling of the powders at room temperature and at lower temperatures (−104 °C), respectively. We report a relatively smaller depression of melting point ranging up to 5 °C with respect to original alloys. The minimum grain sizes achieved and the depression of melting point are similar for both room temperature and low-temperature processed samples. An attempt has been made to rationalize the observations in terms of the basic processes occurring during the milling.     

Disclination dipoles observation and nanocrystallization mechanism in ball milled Cu–Nb powders

The object of this work is to investigate the structure of disclination dipoles and the nanocrystallization mechanism in ball-milled Cu–Nb powders. The structure of the partial disclination dipole in the nano-sized, face-centered cubic Cu crystals is directly revealed to be constituted by individual dislocations. It is found that such disclination defects can produce large lattice rotations at the nanometer scale in crystals during milling. The observation of microstructural evolution and analysis of the nanocrystallization mechanism indicate that the grain refinement induced by severe plastic deformation dose not only depend on the actions of dislocations and twins, but also on the disclination defects, especially for the further refinement of nano-size crystals.     

Formation of fcc titanium during heating high energy ball milled Al–Ti powders

Phase transformation during high energy milling Al–25 at.% Ti and Ti–25 at.% Al powders and during heating the ball milled powders of the same compositions was studied. It was found that a small amount of Ti underwent an allotropic transformation from hcp Ti to fcc Ti during milling. This transformation also occurred during heating the properly milled Al–25 at.% Ti and Ti–25 at.% Al powders. The transformation was endothermic, and the onset temperature of this transformation was 321 °C. It is likely that only thin Ti layers which have a nanometer scale thickness and are embedded in Al matrix can undergo this transformation.     

Effect of ball milling on the physical and mechanical properties of the nanostructured Co–Cr–Mo powders

In the present study, Co-based machining chips (P1) and Co-based atomized alloy (P2) has been processed through planetary ball mill in order to obtain nanostructured materials and also to comprise some their physical and mechanical properties. The processed powders were investigated by X-ray diffraction technique in order to determine several microstructure parameters including phase fractions, the crystallite size and dislocation density. In addition, hardness and morphological changes of the powders were investigated by scanning electron microscopy and microhardness measurements. The results revealed that with increasing milling time, the FCC phase peaks gradually disappeared indicating the FCC to HCP phase transformation. The P1 powder has a lower value of the crystallite size and higher degree of dislocation density and microhardness than that of the P2 powder. The morphological and particle size investigation showed the role of initial HCP phase and chemical composition on the final processed powders. In addition results showed that in the first step of milling the crystallite size for two powders reach to a nanometer size and after 12 h of milling the crystallite size decreases to approximately 27 and 33 nm for P1 and P2 powders, respectively.     

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.     

Synthesis and microwave absorbing properties of Mn–Zn nanoferrite produced by microwave assisted ball milling

In this paper, well dispersed spinel Mn_xZn_1?xFe₂O₄ (x = 0.3,0.5 and 0.7) were obtained by microwave assisted ball milling at 2.45 GHz through only one step. The synthesized products were characterized by X-ray diffraction, high resolution transmission electron microscope, vibration sample magnetometer, and vector network analysis. Synthesized Mn–Zn nanoferrite showed the saturation magnetization reached 84.91emu/g when the x was 0.7 and the largest magnetic loss tangent at the frequency of 2.45 GHz. Microwave absorbing properties of these composites were studied at the frequency range of 2–18 GHz. Two microwave reflection loss peaks appeared for all the spinel ferrite. When x was 0.5, the minimum reflection loss appeared at the highest frequency. When x was 0.7, these two minimum reflection loss peaks, ?17.36 and ?48.13 dB, were calculated with the ?10 dB bandwidth at the frequency ranges of 2.24–5.04 and 13.28–14.88 GHz, respectively. Resonance reflection loss peaks shifted to lower frequencies when the matching thickness increased.     

Numerical study of solid–liquid two-phase flow and erosion in ball valves with different openings

In the coal chemical industry, petrochemical industry, and other industries, ball valve is a common and important valve due to its reliable structure. The conveying medium has particles that affect the valve surface under the drive of water flow, thereby making the ball valve face the risk of erosion and damage. In this study, the CFD-DEM method was adopted to study the influence of different openings and particle diameters on the two-phase flow and erosion characteristics inside the ball valve. The two-phase flow and particle distribution of the ball valve were analyzed, and the main erosion wall surfaces were determined. The erosion distribution of these walls was obtained. The variation rule of particle number with erosion rate was analyzed, which shows that particle number played a dominant role in erosion degree. Result also showed that in the case of small opening, the erosion decreased with the increase in particle diameter.     

Studies on the mechanism of the structural evolution in Cu–Al–Ni elemental powder mixture during high energy ball milling

The present work is focused on the understanding of the phase and microstructural evolution during mechanical alloying of 82Cu–14Al–4Ni powder mixture. Morphology and phase evolution in the milled powder at different stages of milling were studied and a physical modeling of the mechanical alloying has been proposed. It has been demonstrated that milling process mainly consisted of four stages, i.e., flattening and cold welding of powder particles to form a porous aggregate followed by its fragmentation, plastic deformation of small aggregates to form layered particles, severe plastic deformation of layered particles to form elongated flaky particles, and fragmentation of elongated particles into smaller size flaky powder particles. It was also found that the initial period of milling resulted in rapid grain refining, whereas alloying was accomplished during the later period of milling. TEM study of the 48 h milled powder revealed that the microstructure was equiaxed nanocrystalline in nature. It was found that the grains were either randomly distributed or arranged as banded type. A possible explanation for such a behavior has been presented.     

Evaluation of mechanical properties using spherical ball indentation and coupled finite element–element-free galerkin approach

In the present work, the mechanical properties of pressure tube material (Zr-Nb2.5) are evaluated using the coupled finite element–element-free Galerkin approach. Penalty approach is used to impose contact constraints and non-penetration condition at the interface. An efficient node-to-segment algorithm is employed to model the contact behavior. An updated Lagrangian approach is used to model the large deformation. Loading and unloading response of the indentation process is analyzed using von-Mises and Gurson-Tvergaard-Needleman (GTN) plasticity models. In multiple indentations, the indentation depth is progressively increased up to a maximum specified limit with partial unloading. Load-indentation depth curves are used to extract the flow properties of the material.     

Effect of cup and ball types on alumina–tungsten carbide nanocomposite powder synthesized by mechanical alloying

Alumina-based nanocomposite powders with tungsten carbides particulates were synthesized by ball milling WO₃, Al and graphite powders. X-ray Diffraction (XRD) was used to characterize the milled and annealed powders. Microstructures of milled powders were studied by Transmission Electron Microscopy (TEM). Results showed that Al₂O₃–W₂C composite formed after 5 h of milling with major amount of un-reacted W in stainless steel cup. The remained W was decreased to minor amount by increasing carbon content up to 10 wt.%. When milled with ZrO₂ cup and balls, Al₂O₃–W₂C composite was completely synthesized after 20 h of milling with the major impurity of ZrO₂. In the case of stainless steel cup and balls with 10 wt.% carbon, Fe impurity after 5 h of milling (maximum 0.09 wt.%) was removed from the powder by leaching in 3HCl·HNO₃ solution. The mean grain size of the powder milled for 5 h was less than 60 nm. The powder preserved its nanocrystalline nature after annealing at 800 °C.     

Development of ADEM–CFD model for analyzing dynamic and breakage behavior of aggregates in wet ball milling

A new simulation method was developed for analyzing the grinding mechanisms of aggregates in wet ball milling. The calculation of the following five behaviors is needed in this case: dynamics and breakage behaviors of aggregates, collisions of aggregates, a motion of fluid including aggregates, ball-fluid interaction forces and aggregate-fluid interaction forces. The dynamic and breakage behaviors of aggregates were calculated by advanced discrete element method (ADEM). The collisions of aggregates were represented by DEM. The motion of fluid including aggregates was solved by spatially-averaged equations of the fluid with finite difference method (FDM). The ball-fluid interaction forces were calculated by immersed boundary method (IBM). The model for the aggregate-fluid interaction forces has not been established, so that a new simulation model for estimating them was developed and named ADEM-computational fluid dynamics (ADEM-CFD) model. The ADEM-CFD model was verified by comparing the fluid drag coefficients obtained by White’s equation. The new simulation method considering the five behaviors was validated by comparing with an experiment about dynamic and breakage behaviors of aggregates around a falling ball in liquid. It is found that the new simulation method proposed could analyze the dynamic and breakage behaviors of aggregates in wet ball milling.     

Effect of high energy ball milling on solid state reactions in Al–25 at.-%Ni powders

Abstract

The effect of high energy ball milling on the solid state reactions between aluminium and nickel in Al–25 at.-%Ni powders has been investigated using scanning electron microscopy, thermal analysis techniques, and X-ray diffractometry. It has been observed that the microstructure of the powder particles evolves in three stages: stage I is the formation of entrapped nickel particles in the aluminium matrix structure; stage II is the formation of an Al–Ni multilayered structure; and stage III is the formation of Al₃Ni single phase. The temperature required to activate the reaction between aluminium and nickel during heating decreases by more than 200 K as the powder particle microstructure evolves from the entrapped particle structure to the multilayered structure, and then it decreases gradually with decreasing nickel layer thickness. The nucleation and lateral growth of Al₃Ni phase at the Al/Ni interfaces occurs at much lower temperatures than those required for the transverse growth of Al₃Ni. The fraction of Al₃Ni formed through nucleation and lateral growth at the interface is almost linearly proportional to the interfacial area. The activation energy for nucleation and lateral growth of Al₃Ni at the Al/Ni interfaces is independent of nickel layer thickness, but the activation energy for transverse growth of Al₃Ni decreases substantially with decreasing nickel layer thickness. The latter is attributed to the observation that the nickel layers are thinned by plastic deformation and thus contain an increasingly higher density of dislocations.     

Effects of ball milling intensity on structural changes in mixed 50Ni–50Ti powders during mechanical alloying process

Abstract

Mixed 50Ni–50Ti powders were milled in an attritor high energy ball mill and the structural evolution of the milled powders characterised by X-ray diffraction analysis. The microstrain, crystallite size, and lattice parameters of the nickel and titanium crystals were measured. The results show that increases in the rotational velocity and the total ball volume/tank volume ratio leads to a decrease in the crystallite size and rapid changes in the microstrain and lattice parameters, which enhance the amorphisation rate, thereby reducing the time required to obtain afully amorphous phase.

MST/2079     

Intermetallic compound layer formation between Sn–3.5 mass %Ag BGA solder ball and (Cu, immersion Au/electroless Ni–P/Cu) substrate

The growth kinetics of intermetallic compound layers formed between eutectic Sn–3.5Ag BGA (ball grid array) solder and (Cu, immersion Au/electroless Ni–P/Cu) substrate by solid-state isothermal aging were examined at temperatures between 343 and 443 K for 0–100 days. In the solder joints between the Sn–Ag eutectic solder ball and Cu pads, the intermetallic compound layer was composed of two phases: Cu₆Sn₅ (-phase) adjacent to the solder and Cu₃Sn (-phase) adjacent to the copper. The layer of intermetallic on the immersion Au/electroless Ni–P/Cu substrate was composed of Ni₃Sn₄. As a whole, because the values of the time exponent (n) are approximately 0.5, the layer growth of the intermetallic compound was mainly controlled by a diffusion-controlled mechanism over the temperature range studied. The growth rate of Ni₃Sn₄ intermetallic compound was slower than that of the total Cu–Sn(Cu₆Sn₅+Cn₃Sn). The apparent activation energy for growth of total Cu–Sn(Cu₆Sn₅+Cu₃Sn) and Ni₃Sn₄ intermetallic compound were 64.82 and 72.54 kJ mol^–1, respectively.