Ball Milling Of Elemental Powders Research Articles

A comprehensive experimental and modeling study of the strain rate- and temperature-dependent deformation behavior of bio-degradable Mg-CeO2 nanocomposites

A comprehensive study was undertaken on the temperature-dependent and strain rate-sensitive deformation behavior of near-dense low-volume fraction magnesium-cerium dioxide (Mg-CeO2) nanocomposites synthesized by powder metallurgy technique. The process involved ball milling of elemental powders → cold compaction → sintering in an inert atmosphere, and in-situ hot extrusion. The Mg-CeO2 nanocomposites displayed strain rate and temperature sensitivity, exhibiting higher yield strength, superior compressive characteristics, greater hardness, and improved ductility compared to pure Mg and most commercial Mg alloys. Furthermore, a thorough micro-structural investigation was conducted to characterize the distributions of ceria nanoparticles, grain refinement degree, ceria-magnesium interface, formation of deformation twins and interfacial bonding between the reinforcement and matrix. The present study has proposed two modeling approaches, the Johnson–Cook (J–C) constitutive model and a machine learning-assisted model, to predict the mechanical behavior of monolithic Mg and Mg-CeO2 nanocomposites. The models effectively explained the deformation behavior under various strain rates and temperatures.

Production of a Reinforced Refractory Multielement Alloy via High-Energy Ball Milling and Spark Plasma Sintering

Refractory high entropy alloys have shown potential to be developed as structural materials for elevated temperature applications. In the present research, the multielement alloy Fe2TiVZrW0.5 was produced by high-energy ball milling of elemental powders in the air to promote the formation of reinforcing oxide and nitride particles followed by spark plasma sintering consolidation. The sintering temperature was optimized to achieve a full-density material that was characterized from the microstructural and mechanical points of view. Hardness and KIC were measured in the as-sintered condition as well as after thermal treatment at 1100 °C. TEM observations showed the presence of a fine distribution of ZrO2 and Ti(V)-N in the microstructure mainly constituted by the bcc Fe-V and Fe-V-W phases. The fine distribution of ceramic particles in a metallic multielement matrix is responsible for the consistent hardness and thermal stability of this alloy.

Development of Cu-based shape memory alloy through selective laser melting from elemental powder mixture: Processing and characterization

The Cu-based shape-memory alloy 81Cu-11Al-3Ni-3Mn (wt%) was processed by selective laser melting (SLM) and the parameters were optimized to obtain samples with a high relative density of up to 99 %. The study used ball milling of elemental powders to obtain the feedstock material and the process was developed for building dense SMA structures. The process optimization is performed to obtain dense structures by varying laser power and scan speed. Further, the parameters yielding higher density is selected to study the influence of the different laser power on the overall density, defect distribution, mechanical properties, and grain sizes. Cu-based SMA fabricated at different laser powers were characterized using Scanning electron microscopy (SEM), Differential scanning calorimetry, X-ray diffraction (XRD), tensile test, and microhardness tests. It was observed that the processing technique has a strong influence on the degree of porosity and the distribution of the pores, the grain size as well as the grain morphology. Dense and uniform samples are formed with elemental powder which shows a maximum hardness of 380 HV, and tensile strength of 1550 MPa. The transformation peak became sharp with respect to laser power increment and the transformation temperature increased with an increase in laser power. The study provides a path toward the deployment of SLM for building dense Cu-based SMA from elemental powders.

Investigation on the Thermodynamic Stability of Nanocrystalline W-Based Alloys: A Combined Theoretical and Experimental Approach.

The stability of nanostructured metal alloys is currently being extensively investigated, and several mathematical models have been developed to describe the thermodynamics of these systems. However, model capability in terms of thermal stability predictions strongly relies on grain boundary-related parameters that are difficult to measure or estimate accurately. To overcome this limitation, a novel theoretical approach is proposed and adopted in this work to identify W-based nanocrystalline alloys which are potentially able to show thermodynamic stability. A comparison between model outcomes and experimental findings is reported for two selected alloys, namely W-Ag and W-Al. Experimental results clearly highlight that W-Ag mixtures retain a segregated structure on relatively coarse length scales even after prolonged mechanical treatments. Moreover, annealing at moderate temperatures readily induces demixing of the constituent elements. In contrast, homogeneous nanostructured W-Al solid solutions are obtained by ball milling of elemental powders. These alloys show enhanced thermal stability with respect to pure W even at high homologous temperatures. Experimental evidences agree with model predictions for both the investigated systems.

Amorphization, mechano-crystallization, and crystallization kinetics of mechanically alloyed AlFeCuZnTi high-entropy alloys

Equiatomic and non-equiatomic AlFeCuZnTi high-entropy alloys (HEAs) were prepared by high energy ball milling of elemental powders. For the equiatomic HEA with chemical composition at the boundary of solid solution and amorphous phase regions, an amorphous phase was obtained at moderate milling times, which was mechano-crystallized into a BCC solid solution by continued milling. For the non-equiatomic HEA with chemical composition well within the solid solution region, the same BCC solid solution was obtained during mechanical alloying. The crystallization kinetics of the amorphous HEA was studied by differential scanning calorimetry (DSC) thermal analysis. The crystallization activation energy (calculated based on the Kissinger equation) was correlated to the mean self-diffusion activation energy of the constituting elements, which was related to the multi-component nature of HEAs.

Effective atomic diffusion coefficient dependence on applied pressure during spark plasma sintering

It has been hypothesized that the superimposition of an applied pressure enhances mass transfer during pressure-assisted sintering; however, a pressure-related coefficient DT, representing the contribution of a diffusion flux has never been established heretofore. Here, we aim to establish a theoretical framework to determine the DT by combining the Frenkel and E-S models with an Arrhenius equation. To accomplish this goal, via gas atomization and 30 h ball-milling of elemental powders, Ti40.6Zr9.4Cu37.5Ni9.4Sn3.1 metallic glass powders were both used to validate the framework during spark plasma sintering (SPS). The quantitative results reveal that the densification rate increases as the pressure increases due to the enhanced diffusion flux DT.

Effects of ternary alloy additions on the microstructure of highly immiscible Cu alloys subjected to severe plastic deformation: An evaluation of the effective temperature model

Phase evolution in dilute, strongly immiscible Cu-Mo, Cu-Mo-Ni, and Cu-Mo-Ag alloys during severe plastic deformation at low-temperature has been experimentally investigated. For the Cu95Mo05 alloy, Mo nanoparticles are formed, ∼10 nm in diameter, as part of a steady state microstructure, with less than ∼1 at.% Mo dissolved in the matrix. Addition of 10 or 20 at.% Ni to this binary alloy results in a significant increase in the Mo solubility, whereas comparable additions of Ag has a corresponding little effect. The steady state microstructures of alloys during ball milling of elemental powders are very similar to those during HPT processing of initially homogeneous solutions. The results are discussed in terms of an effective temperature model. Model MD simulations are presented to help relate the predictions of the effective temperature model to atomistic mechanisms.

Structure and nanoindentation mechanical properties of novel porous Ti-Ta material with a core-shell structure using the powder metallurgy method

In this paper, results from microstructural and nanoindentation studies of novel Ti-Ta core–shell structured type materials for potential biomedical applications are presented. The use of Ta as the outer coating of the Ti core allows the creation of a light and porous material with potentially increased resistance to corrosion. Ti–Ta core–shell particles were fabricated using the powder metallurgy method by the ball milling of elemental powders and subsequently sintered at 1000 °C for 24 h. The specimens were examined using scanning and transmission electron microscopy, X-ray diffraction, atomic force microscopy and nanoindentation methods. The compositions of the prepared materials were detected using energy dispersive spectroscopy and X-ray fluorescence methods. The FIB technique in combination with high resolution TEM ensured proper sample preparation and description of the structure of the material. The results indicate that the core–shell particles have inhomogeneous microstructures and compositions. A core-shell structure, consisting of Ti-rich cores and Ta-rich shells formed due to diffusion between the Ti and Ta powders. The outer part of the particles contains an area enriched in tantalum. Moving closer to the core, there is an equilibrium region of Ti and Ta, whereas the core is composed of pure titanium. A sintered two-phased (α + β) Widmanstätten-type microstructure was also observed. The mechanical studies indicated the presence of three main zones, different in terms of the mechanical properties inside of a particle. A formation model for the α, α + β and β phases during material synthesis was proposed.

Effective Atomic Diffusion Coefficient Dependence on Applied Pressure During Spark Plasma Sintering

It has been hypothesized that the superimposition of an applied pressure enhances mass transfer during pressure-assisted sintering; however, a pressure-related coefficient DT, representing the contribution of a diffusion flux has never been established heretofore. Here, we aim to establish a theoretical framework to determine the DT by combining the Frenkel and E-S models with an Arrhenius equation. To accomplish this goal, via gas atomization and 30 h ball-milling of elemental powders, Ti40.6Zr9.4Cu37.5Ni9.4Sn3.1 metallic glass powders were both used to validate the framework during spark plasma sintering (SPS). The quantitative results reveal that the densification rate increases as the pressure increases due to the enhanced diffusion flux DT.

Electrocatalytic Activity of Amorphous Ni-Nb-Y Alloys for the HER in Alkaline Water Electrolysis

Introduction: The recent development of anion exchange membranes (AEM) has renewed interest in alkaline water electrolysis for large-scale production of hydrogen gas. These systems can achieve current densities comparable to PEM-based systems while enabling the use of non-PGMs as catalyst materials. New electrocatalysts are required to interface with such AEMs in advanced alkaline water electrolyser designs. Amorphous alloys have previously been proposed as electrocatalysts due to their unique atomic structure, which results in electrochemical properties particularly suitable for catalysis. These properties include a high density of co-ordinatively unsaturated sites, a much greater solute solubility allowing for highly tunable homogeneous compositions, and a high stability against surface segregation of solute atoms [1-3]. To date, amorphous alloys have been underutilized as catalysts due to the lack of suitable methods to increase their electrochemically active surface area. Mechanical alloying and subsequent dealloying can be used to overcome this issue to yield 3D mesoporous and nanoporous amorphous structures. The present work assesses the role of structure and chemistry on the catalytic activity of Ni-Nb-Y amorphous alloys towards the hydrogen evolution reaction. Ni-based alloys exhibit some of the highest activity among the non-PGM catalysts while yttrium and niobium are excellent glass formers and offer interesting catalytic performance, particularly yttrium which has shown high catalytic activity when alloyed with nickel [4, 5]. Experimental Methods: Cryogenic ball milling of elemental powders was used to synthesize a novel high surface area amorphous Ni79.2Nb12.5Y8.3 alloy. Composite amorphous alloys with minor secondary crystalline phases (Ni5Y and Y2O3) were also synthesized and evaluated. X-ray diffraction and electron microscopy were used to analyze the alloy structures and particle morphology. Working electrodes were prepared by synthesizing catalyst suspensions consisting of the alloyed powder along with Nafion® 117 solution and iso-propanol and drop casting said suspensions on glassy carbon electrodes. Electrochemical characterization was assessed through steady state polarization (Tafel) curves, cyclic voltammetry, and AC impedance spectroscopy. Results and Discussion: The Ni79.2Nb12.5Y8.3 amorphous alloy exhibited improved intrinsic catalytic performance compared to nickel, and the addition of minor secondary crystalline phases, namely Ni5Y, resulted in even greater intrinsic performance. Electrochemical testing revealed this trend to be consistent even when testing amorphous composite materials containing higher (Ni81.3Nb6.3Y12.5) and lower (Ni77.1Nb18.8Y4.2) Y content. Tafel measurements for Ni-Nb-Y alloys can be seen in figure 1 with corresponding data summarized in table 1. These alloys highlight the improved catalytic performance to be a result of the secondary Ni5Y phase as opposed to the total alloying content. These results warrant further electrochemical characterization of multiphase amorphous nickel alloys with finely dispersed crystallinity for catalyst development. Conclusions and Future Work: The mechanical alloying process can be used to produce highly tunable chemical compositions where then the addition of finely dispersed secondary crystalline phases result in improved catalytic activity. The preliminary electrochemical results illustrate that mechanically alloyed Ni-based amorphous materials are promising catalyst precursors for clean electrochemical hydrogen production.

Effects of Ternary Alloy Additions on the Microstructure of Highly Immiscible Cu Alloys Subjected to Severe Plastic Deformation: An Evaluation of the Effective Temperature Model

Phase evolution in dilute, strongly immiscible Cu-Mo, Cu-Mo-Ni, and Cu-Mo-Ag alloys during severe plastic deformation at low-temperature has been experimentally investigated. For the Cu95Mo05 alloy, Mo nanoparticles are formed, ~ 10 nm in diameter, as part of a steady state microstructure, with less than ~ 1 at.% Mo dissolved in the matrix. Addition of 10 or 20 at.% Ni to this binary alloy results in a significant increase in the Mo solubility, whereas comparable additions of Ag has a corresponding little effect. The steady state microstructures of alloys during ball milling of elemental powders are very similar to those during HPT processing of initially homogeneous solutions. The results are discussed in terms of an effective temperature model. Model MD simulations are presented to help relate the predictions of the effective temperature model to atomistic mechanisms.

Nafion Coated Mg50Ni50 and (La,Mg)2Ni7 Negative Electrodes for NiMH Batteries

A study is carried out to develop a surface modified Mg based alloy with an improved discharge capacity that would be durable in alkaline environment. For this purpose, Mg50Ni50 alloy is synthesized via ball milling of elemental powders and tested electrochemically in both bare and nafion coated form. The study shows that the bare electrode yields an acceptable discharge capacity but subject to a fast capacity decay. Nafion coating is effective in reducing the capacity decay where the discharge capacity after 20 cycle is as high as 82% of the initial capacity. The study further shows that there is a substantial increase in the discharge capacity of the electrode with nafion coating. This is also investigated with a more traditional alloy of (La0.70Mg0.30)2(Ni0.85Co0.15)7. The capacities which are 329 and 334 mAh/g in bare electrodes, in the first cycle, are increased to 498 and 448 mAh/g with nafion coating for Mg50Ni50 and La0.70Mg0.30)2(Ni0.85Co0.15)7 respectively. It is proposed that the increase in discharge capacity is due to the increase in local hydrogen pressure at electrode-nafion interface made possible by the nafion envelope resulting in the increased hydrogen storage in the active powders.

Non-equilibrium microscale thermomechanical modeling of bimetallic particulate fractal structures during ball milling fabrication

Nanostructured bimetallic reactive multilayers can be conveniently produced by ball milling of elemental powders. This research explores the non-equilibrium microscale conductive thermal transport in ball-milled particulate fractal structures during fabrication, arising from heat dissipation by bulk plastic deformation and surface friction. Upon impactor collisions, temperature increments are determined at interface joints and domain volumes using Green's functions, mirrored by source images with respect to warped ellipsoid domain boundaries. Heat source efficiency is calibrated via laboratory data to compensate for thermal expansion and impactor inelasticity, and the thermal analysis is coupled to a dynamic mechanics model of the particulate fracture. This thermomechanical model shows good agreement with the fractal dimensions of the observed microstructure from ball milling experiments. The model is intended to provide a comprehensive physical understanding of the fundamental process mechanism. In addition, the model could serve as a real-time thermal observer for closed-loop process control, as well as for interfacial diffusion and reaction analysis during ball milling.

Processing of Cu-Fe and Cu-Fe-SiC nanocomposites by mechanical alloying

The Cu-Fe and Cu-Fe-SiC nanocomposite powders were synthesized by a two step mechanical alloying process. A supersaturated solid-solution of Cu-20wt% Fe was prepared by ball milling of elemental powders up to 5 and 20h and subsequently the SiC powder was added during additional 5h milling. The dissolution of Fe into Cu matrix and the morphology of powder particles were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. It was found that the iron peaks in the XRD patterns vanish at the early stages of mechanical alloying process but the dissolution of Fe needs more milling time. Moreover, the crystallite size of the matrix decreases with increasing milling time and the crystallite size reaches a plateau with continued milling. In this regard, the addition of SiC was found to be beneficial in postponing the saturation in crystallite size refinement. Moreover, the effect of SiC on the particle size was found to be significant only if it is added at the right time. It was also found that the silicon carbide and iron particles are present after consolidation and are on the order of nanometer sizes.

Early stages of phase formation before the ignition peak during mechanically induced self-propagating reactions (MSRs) of titanium and graphite

The mechanism of mechanically induced self-propagating reaction (MSR) of titanium with graphite to produce TiC during reactive ball milling of elemental powders was investigated using high resolution electron microscopy, and Raman and X-ray photoelectron spectroscopies. Prior to the exothermic ignition, off-stoichiometric Ti(1+x)C(1−x) nuclei are formed by reaction at the interface between the severely deformed Ti particles and graphite milling debris. After ignition, both rapid growth of existing nuclei, and nucleation and growth of additional off-stoichiometric Ti(1+x)C(1−x) occurs. Local product morphologies after the ignition varied, depending local restrictions on the rate of diffusion of carbon into the TiC as it grows.

Compact Process for the Preparation of Microfine Spherical High-Niobium-Containing TiAl Alloy Powders

High-Nb-containing TiAl alloys are a new generation of materials for high-temperature structural applications because of their superior high-temperature mechanical properties. The alloy powders can be widely used for additive manufacturing, thermal spraying, and powder metallurgy. Because of the difficulty of making microfine spherical alloy powders in quantity by conventional techniques, a compact method was proposed, which consisted of two-step ball milling of elemental powders and subsequent radio frequency (RF) argon plasma spheroidization. In comparison with conventional mechanical alloying techniques, the two-step milling process can be used to prepare alloy powders with uniform scale in a short milling time with no addition of process control agent. This makes the process effective and less contaminating. After RF argon plasma spheroidization, the powders produced exhibit good sphericity, and the number-average diameter is about 8.2 μm with a symmetric unimodal particle size distribution. The powders perform high composition homogeneity and contain predominately supersaturated α 2-Ti3Al phase. The oxygen and carbon contents of the spheroidized powder are 0.47% and 0.050%, respectively.

Production of Cu-TiC Nanocomposite Using Mechanical Alloying Route

In this study, Cu-TiC nanocomposites were produced by high energy ball milling of elemental powders and in-situ formation of TiC in the copper matrix. Cu-40wt% Ti powder mixture were milled for 60 h, then graphite powder was added, subsequently milling was continued for further 10 h. Based on theoretical calculations, at this composite, the amount of TiC as reinforcement should be 60.25vol% (45.47wt%). The effect of milling time on solution progress of titanium in the copper lattice was studied by X-Ray diffraction analysis (XRD) with CuKα radiation. Considering XRD of Cu-40wt%TiC after 60 h milling data and Williamson-Hall relation, crystallite size and lattice strain of copper were determined 12nm and 1.04% respectively. To ensure the formation of titanium carbide, XRD analysis was performed after pressing at 300MPa and sintering at 900oC for an hour and heating rate of 2.5oC/min. XRD pattern was indicated the formation of TiC,CuTi3and TiO2phases in Cu matrix.

Enhancement in Thermoelectric Figure-of-merit of n-type Si-Ge Alloy Synthesized Employing High Energy Ball Milling and Spark Plasma Sintering

ABSTRACTIn the present study, we report the enhancement in figure-of-merit (ZT) of nanostructured n-type Silicon-Germanium (Si80Ge20) thermoelectric alloy synthesized using high energy ball milling followed by spark plasma sintering (SPS). After 90 h of ball milling of elemental powders of Si, Ge and P (2 at.%), a complete dissolution of Ge in Si matrix has been observed forming the nanostructured n-type Si80Ge20 alloy powder. X-ray diffraction analysis (XRD) confirmed the crystallite size of the host matrix (Si) to be ∼7 nm and also indicated the formation of an additional phase of SiP nano-precipitates after SPS. HR-TEM analysis revealed that the nano-grained network was retained post-sintering with a crystallite size of size of 9 nm and also confirmed the SiP precipitates formation with a size of 4 to 6 nm. As a result, a very low thermal conductivity of ∼2.3W/mK at 900°C has been observed for Si80Ge20 alloy primarily due to scattering of phonons by nanostructured grains and nano-scaled SiP precipitates which further contribute to this scattering mechanism. Electrical conductivity values of SiGe sintered alloy are slightly lower to that of reported values in literature. This was attributed to the formation of SiP which creates a compositional difference between the grain boundary region and the grain region, leading to a chemical potential difference at interface and the grain region. Figure-of-merit (ZT) of n-type Si80Ge20 nanostructured alloy was found to be ≈1.5 at 900°C, which is the highest reported so far at this temperature.

Formation of Nano-Sized Y2O3 Dispersoids in Mechanically Alloyed Ni–(Cr, Y2O3, Y) Alloys During Heat-Treatments

In the present work, the evolution of nanoparticles during annealing and hot-consolidation in mechanically alloyed Ni-22Cr-1.5Y, Ni-22Cr-1.5Y2O3 and Ni-3% Y2O3 was examined. The high-energy ball-milling of elemental powders resulted in the complete dissolution of the constituent Cr, Y, or Y2O3, forming a Ni-based solid solution. During the subsequent annealing, however, oxide particles precipitated from the solid solution. In the case of mechanically alloyed Ni-22Cr-1.5Y2O3, over-grown Cr2O3 precipitated at a temperature as low as above approximately 500 degrees C and ternary YCrO3 particles precipitated at 1100 degrees C. In the case of mechanically alloyed Ni-22Cr-1.5Y, on the other hand, the binary Y2O3 phase precipitated at 1100 degrees C during spark plasma sintering. The presence of Cr in the alloy composition facilitated the formation of Cr2O3 or YCrO3, and the precipitated oxides were highly prone to grain growth during hot-consolidation, sometimes reaching several micrometers. In Cr-exempt Ni-3%Y or Ni-3% Y2O3, however, the growth of nanodispersoids was restrained even at temperatures as high as 1000 degrees C and the resulting dispersoid was only nano-sized Y2O3.

Mg3Cd: A model alloy for studying the destabilization of magnesium hydride

We prepared an ordered Mg3Cd alloy by high energy ball milling of elemental powders. The synthesized alloy exhibited good hydrogenation kinetics and reversibly absorbed about 2.8 wt. % of hydrogen. The temperature dependence of hydrogenation kinetics of the alloy measured in the range of temperatures covering the order-disorder phase transformations in the Mg3Cd and MgCd phases did not exhibit any anomalies and could be fitted with a single Arrhenius line. The measured apparent activation energy (69 ± 2 kJ/mol) hinted that hydrogenation process was controlled by diffusion of Cd in metallic phase. The pressure-composition isotherms exhibited negligible pressure hysteresis and sloping pressure plateau. Based on microstructural evidence obtained with the aid of X-ray diffraction and scanning electron microscopy, we built a thermodynamic model predicting the plateau hydrogen pressure for partially hydrogenated alloy. The predictions of the model were in a good agreement with the experimental data. Finally, we discussed the origins and the growth mechanisms of Cd whiskers observed in the alloys after full hydrogenation cycle.