Stage Of Mechanical Alloying Research Articles

Високоентропійний NiFeCrWMo сплав, отриманий в процесі механічного легування

In this work, the evolution of the structure and phase composition of the multicomponent Ni-Fe-Cr-W-Mo system during mechanical alloying (MA) of an equiatomic mixture of elemental metal powders in a planetary mill is investigated. The formation of the phase composition and structure of the powdered equiatomic high-entropy NiFeCrWMo alloy at different stages of mechanical alloying was determined by scanning electron microscopy, X-ray diffraction and X-ray spectral analysis. It was found that during 10 hours of МА, a single-phase high-entropy alloy with the structure of a BCC solid solution in the nanostructural state with a crystallite size of 22 nm and a lattice strain (microstress) of 0.61 % was formed. It was shown that the metal components were completely dissolved in the solid state during mechanical alloying, in contrast to their limited solubility under equilibrium conditions. Moreover, despite the different features of the formation of solid solutions in high-entropy alloys and traditional materials, the order of dissolution of element atoms in the lattice of a solid solution follows general principles and occurs depending on the melting point in the following sequence: Ni→Fe→Cr→Mo→W. The average particle size of the produced powdered NiFeCrWMo high-entropy alloy is 3.8 μm, and their shape is predominantly spherical or close to spherical. The microstructure of the particles of the powdered NiFeCrWMo high-entropy alloy at the early stage (1.5 hours) of mechanical alloying is a layered structure formed in the process of grinding, deformation, and cold welding of particles of elemental metal powders. After 10 hours of МА, the microstructure of the alloy particles becomes homogeneous and contains a small amount of WC inclusions as a result of milling due to wear of grinding bodies in the MА process. The obtained NiFeCrWMo high-entropy alloy can be used in the future as a component/binder for other composite materials, for example, hard alloys based on WC to replace Co. Keywords: high-entropy alloy, mechanical alloying, structure, phase composition, solid solution, nanostructure

Microstructural and mechanical properties of NiCoCrAlSi high entropy alloy fabricated by mechanical alloying and spark plasma sintering

In this study, the microstructural and mechanical properties of NiCoCrAlSi high entropy alloy (HEA) fabricated by mechanical alloying and spark plasma sintering (SPS) method was studied. Initially, the starting powders with the composition of Ni28Co26Cr26Al10Si10 were subjected to mechanical milling at different times of 5, 10, 15, 20 and 40 h. The 40 h milled powder was then sintered by SPS method at 1170 °C. The microstructural characterization, phase analysis and mechanical properties of this sample were evaluated by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Rietveld analysis and tensile test. XRD results showed that by increasing the milling time the size of crystallites reduced and lattice strain increased. In addition, formation of FCC1 (F1) phase at final stages of mechanical alloying was observed. However, the peak of some of the remaining elements was still observed after 40 h of milling. After sintering, formation of FCC2 (F2) phase alongside F1 was observed. According to quantitative analysis, F1 phase with fraction of 89.3 wt% and F2 phase with fraction of 10.7 wt% is formed after SPS process. For this sample, a tensile strength of 1365 ± 141 MPa was obtained.

Investigation of Mechanical Alloying for Powder Materials Based on Mo–Ti–Zr–C and Mo–Hf–C Systems

Powders of composite materials based on Mo–Ti–Zr–C and Mo–Hf–C systems are prepared by a mechanical alloying method. Evolution of the grain size composition of powders based on the Mo–Ti–Zr–C and Mo–Hf–C systems is considered at various stages of mechanical alloying. Alloying element distribution and microstructure of composite powders based on the Mo–Ti–Zr–C and Mo–Hf–C systems are investigated. The contents of oxygen and zirconium that appeared in the powders during mechanical alloying are determined.

Attributes of Spark Plasma Sintering on Developing Oxide Dispersion Strengthened Ferritic Steels and Understanding Structure–Property Relation

Ferritic alloys strengthened by oxide dispersoids having a composition of Fe–16Cr–2W–0.3Ti–0.5Y2O3 and Fe–16Cr–2W–0.3Ti–0.75Y2O3 were developed through mechanical alloying followed by spark plasma sintering process. The densification behaviour of ferritic steel was understood while sintering at a temperature of 900 °C with soaking for 5 min, at the applied pressure of 50 MPa. X-ray diffraction analysis was done on milled powders and sintered bulk samples to confirm the alloying and crystallographic changes. Field emission scanning electron microscopy (FESEM) was carried out to study the morphology and FESEM-EDS to ascertain the composition of alloyed powders. Transmission electron microscopy study conceded the evolution of nanocrystalline ferritic steel during MA. Distinctive stages of mechanical alloying were observed. System with 0.5 Y2O3 displayed better densification behaviour and possessed higher mechanical properties.

Deformation-Induced Structural-Phase Transformations during Mechanosynthesis of Fe–Fullerite in Toluene

Abstract—X-ray diffraction, Mossbauer and Raman spectroscopy have been used to study structural phase transformations during mechanosynthesis of Fe–С60/70 in toluene with 20 and 25 at % С60/70 fullerite. The quantitative carbon content determines the phase composition of mechanocomposites. (Fe3C)D forms at 20 at % С60/70, whereas Fe7C3 and a paramagnetic phase form at 25 at % С60/70 at the initial stage of mechanical alloying. Free carbon is in an amorphous state in the sample. The formation mechanism of carbides and a paramagnetic component is discussed.

A mapping approach to pattern formation in the early stages of mechanical alloying

ABSTRACTThe present work focuses on the refinement of the lamellar structure in composite Ag-Cu particles during the early stages of mechanical processing. We combine the statistical description of the kinetics of processes activated by ball milling with the mathematical description of advection cycles induced by plastic deformation. The model curve satisfactorily best fits the experimental data obtained by suitably designed experiments.

Microstructure and thermodynamic analysis of nanostructured Cu-13.2%Al-4%Ni ternary system synthesized by mechanical alloying

Thermodynamic analysis of nanostructured Cu-13.2%Al-4%Ni synthesized by mechanical alloying was studied through Miedema’s semi-empirical model. The variations of lattice strain, crystallite size and microstructural evolution at various milling times were also measured using X-ray diffraction and scanning electron microscope. The results showed an increase in lattice strain and reduction in crystallite size due to an increase in density of structural defects as a result of high-energy collisions during mechanical alloying. The calculated thermodynamic data suggested that in all binary Cu-Al, Al-Ni and Ni-Cu systems, there is a driving force for solid solution formation over all compositions due to negative Gibbs free energy changes in those compositions, while this value is positive for the formation of amorphous phase over some compositions which can be attributed to the absence of driving force. Additionally, thermodynamic data were in agreement with XRD results which showed solid solution was formed at middle stages of mechanical alloying. Moreover, it is concluded that the formation of solid solution is easier at three corners of ternary diagram, where the concentration of one element is major, whilst amorphous phase formation is more desirable in other compositions.

Synthesis of Intermetallics in Fe-Al-Si System by Mechanical Alloying

Fe-Al-Si alloys have been recently developed in order to obtain excellent high-temperature mechanical properties and oxidation resistance. However, their production by conventional metallurgical processes is problematic. In this work, an innovative processing method, based on ultra-high energy mechanical alloying, has been tested for the preparation of these alloys. It has been found that the powders of low-silicon alloys (up to 10 wt. %) consist of FeAl phase supersaturated by Si after mechanical alloying. Fe2Al5 phase forms as a transient phase at the initial stage of mechanical alloying. The alloy containing 20 wt. % of Si and 20 wt. % of Al is composed mostly of iron silicides (Fe3Si and FeSi) and FeAl ordered phase. Thermal stability of the mechanically alloyed powders was studied in order to predict the sintering behavior during possible compaction via spark plasma sintering or other methods. The formation of Fe2Al5 phase and Fe3Si or Fe2Al3Si3 phases was detected after annealing depending on the alloy composition. It implies that the powders after mechanical alloying are in a metastable state; therefore, chemical reactions can be expected in the powders during sintering.

Stages of Mechanical Alloying in Systems with Different Solubility Cu–Zn and Au–Co in the Case of Cold and Low-Temperature Deformation by Torsion Under Pressure

Methods of X-ray structural analysis and durometry, as well as electron microscopy were used to identify the stages of mechanical alloying in the case of torsion under high quasi-hydrostatic pressure on Bridgman anvils in the Cu–Zn and Au–Co systems that have different mutual solubility and enthalpy of mixing. It was established that decrease in temperature of mechanical alloying from room temperature (cold deformation) to the boiling temperature of liquid nitrogen (80 К, low-temperature deformation) has a considerable impact on mechanical alloying at different processing stages and on characteristics of an alloy synthesized by deformation. In the Cu–Zn system, when the ratio of powder components corresponds to the solid solution of α-brass in equilibrium state, as deformation increased, one observed consecutive change of evolution stages of the powder mix to the state of copper-based solid solution. At the same time, when processing temperature decreases, larger deformation is required to achieve analogous structural changes. In the Au–Co system characterized by absence of solubility at room and lower temperatures, one also observes the stages of powder mix evolution with the increase in deformation. However, complete dissolution occurs in the case of processing at 80 К, while larger deformation is required in the case of increase in mechanical alloying temperature. The paper examines possible mechanisms of solid solution formation in the system of components that are mutually insoluble under equilibrium conditions.

Analysis of the Cu-Al Milling Stages Through the Microstructure Evolution Studied by TEM and SEM

Fil: Giordana, Maria Florencia. Consejo Nacional de Investigaciones Cientificas y Tecnicas; Argentina. Comision Nacional de Energia Atomica. Centro Atomico Bariloche; Argentina

Structural and phase transformations during copper and iron mechanical alloying in liquid medium studied by Mössbauer spectroscopy

Mossbauer spectroscopy and X-ray diffraction have been used to study the kinetics of structural and phase transformations in Cu + 2 at% 57Fe during mechanical activation in liquid media (heptane, distilled water) and subsequent heat treatment (600 and 700 °С). The initial stages of mechanical alloying are associated with the transition of components to the nanostructural state. Iron atom groups form near the grain boundaries, and isolated iron atoms penetrate from the boundaries into the grains. Oxidation of groups of iron atoms that form highly dispersed phases of ternary oxide and magnetite occur in the initial stages of mechanical alloying of Cu + 2 at% 57Fe in water. The formation of the solid solution in the form of isolated iron atoms in the lattice of copper proceeds, regardless of the milling media used. Samples prepared in heptane contain carbon and oxygen, and upon heat treatment, carbide and oxide phases are formed.

Formation of carbide phases upon the mechanosynthesis of the (Fe0.93Cr0.07)75C25 alloy compared with other carbide-forming processes

Methods of X-ray diffraction, differential thermal analysis, and measurements of the dynamic magnetic susceptibility have been used to investigate the sequence of phase transformations upon the mechanical alloying of a mixture of powders of the initial components of the composition (Fe0.93Cr.07)75C25. It has been shown that, at later stages of mechanical alloying, the phase composition is determined by the conditions of the dynamic equilibrium between the crystalline and amorphous phases. A change in the conditions of mechanical alloying leads to a shift in this equilibrium and to a change in the phase composition of the alloy. A comparison of carbide formation in the Fe–C system upon the mechanosynthesis, tempering of martensite, the saturation of iron with carbon from the gaseous medium, the quenching of the melt, and the sputtering deposition of films has been performed. Some general regularities have been established, from which it follows that an important role in phase formation upon the mechanosynthesis, just as in other abovementioned processes, is played by the thermally activated phenomena.

The mechanism and kinetics of initial stage of mechanical alloying in Si(Al, Mg, Cr)99 57Fe1 binary systems

X-ray diffraction and Mossbauer probe spectroscopy data on mechanically alloyed binary systems of the Si(Al, Mg, Cr)99 57Fe1 composition have been analyzed within the framework of the energetic approach. It has been established that the initial stage of mechanical alloying is preceded by a “preparatory” period, during which grains of a main component (element) reach critical size L cr, followed by the alloying process per se. It has been shown that, the maximum of derivative dN/d(logD) (N is the yield of reaction products, and D is the mechanical energy dose), with the maximum corresponding to grain size L max = 17 nm irrespective of the type of the main component, is a universal characteristic when considering the kinetics of the initial stage of alloying. The chemical interaction of a main component with Fe has been found to play the decisive role in the kinetics of mechanical alloying, with the significance of this role increasing in a series Mg, Al, Si, and Cr. A phenomenological explanation has been given to the linear N(D) dependence at the linear dependence of the specific surface area of grain boundaries on the mechanical energy dose.

The initial stage of mechanical alloying in Cr-Fe binary systems

The initial stage of mechanical alloying in Cr-Fe binary systems with atomic ratios of 80: 20 and 99: 1 (57Fe) has been studied by Auger spectroscopy, X-ray diffraction, and Mossbauer spectroscopy. Cr(Fe) x O y oxide clusters are formed at the sites of the contact between Cr and 57Fe particles at the earliest stages of mechanical treatment of the Cr(99)/57Fe(1) mixture. As the treatment duration is increased and a nanostructured state develops, oxide clusters are destroyed and O dissolves in the Cr matrix to increase the lattice parameter of Cr. As the nanostructure is formed in Cr, Fe atoms penetrate through the grain boundaries into the close-to-boundary distorted zones and then into the grain bulk. The process is characterized by a nonuniform concentration distribution of Fe atoms in Cr. The yield of reaction products and specific surface area of grain boundaries have been established to linearly depend on the mechanical energy dose at the initial stage of mechanical alloying.

Phase evolution during early stages of mechanical alloying of Cu–13 wt.% Al powder mixtures in a high-energy ball mill

We report the phase and microstructure evolution of the Cu–13wt.% Al mixture during treatment in a high-energy planetary ball mill with a particular focus on the early stages of mechanical alloying. Several characterization techniques, including X-ray diffraction phase analysis, nuclear magnetic resonance spectroscopy, differential dissolution, thermal analysis, and electron microscopy/elemental analysis, have been combined to study the evolution of the phase composition of the mechanically alloyed powders and describe the microstructure of the multi-phase products of mechanical alloying at different length scales. The following reaction sequence has been confirmed: Cu+Al→CuAl2(+Сu)→Cu9Al4+(Cu)→Cu(Al). The phase evolution was accompanied by the microstructure changes, the layered structure of the powder agglomerates disappearing with milling time. This scheme is further complicated by the processes of copper oxidation, reduction of copper oxides by metallic aluminum, and by variation of the stoichiometry of Cu(Al) solid solutions with milling time. Substantial amounts of X-ray amorphous phases were detected as well. Differential dissolution technique has revealed that a high content of aluminum in the Cu(Al) solid solution-based powders is due to the presence of Al-rich phases distributed between the Cu(Al) crystallites.

Characterization of severely deformed new composites fabricated by powder metallurgy including a stage of mechanical alloying

Mechanical properties of new composites having a binary matrix of Al–4Cu reinforced with TiO2 nano particles were investigated. The composites which consisted of 2wt% and 8wt% of TiO2 reinforcement particles, were fabricated using mechanical alloying and a powder metallurgy route. Morphology, phases and compounds formed during ball milling and densification of samples were studied. With increasing percentages of the reinforcement particles, mechanical properties of the composites were enhanced. Microstructural evolution and mechanical properties changes of the composites after application of twist extrusion (TE), as a severe plastic deformation (SPD) process, were also investigated. It was revealed that the more TE passes the higher hardness and yield strength obtained. In addition, increasing TE passes, led to occurrence of a more homogeneous distribution of the reinforcement particles within the structure, and development of an ultrafine-grained nano-structure. The maximum allowable number of TE passes was found to be four, above which the materials failed.

Investigation the Structural and Magnetic Properties of FINEMET Type Alloy Produced by Mechanical Alloying

In this research, FINEMET alloy with composition of Fe73.5Si13.5B9Nb3Cu1was produced by mechanical alloying from elemental powders. The effect of milling time on the magnetic and structural properties of alloy has been investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometery. The results showed that milling for 53 hr leads to the formation of Fe supersaturated solid solution which includes Si, B and Nb atoms with mean crystallite size of ~30 nm. The shift of the main peak of Fe to the higher angles indicated that Si and B atoms dissolve in the Fe solid solution, at primary stage of mechanical alloying, up to the 42 hr while Nb atoms dissolve at final stages. The magnetization of milled powder for 53 hr was 173.7 emu/g, almost the same as that of the melt-spun ribbon. In addition; the coercivity reached to 15.5 Oe after 53 hr of milling. The higher value of coercivity in mechanically alloyed samples is attributed to strains induce to the structure during milling and the lack of amorphous phase and exchange interaction between nanograins.

Mesostructural refinement in the early stages of mechanical alloying

This study focuses on the early stages of the mechanical alloying of 22 different binary mixtures. In each case, the number of alloyed particles increases linearly with the number of collisions, and the volume of powder effectively processed during a single collision is ∼9.0 × 10−3 mm3. The alloyed particles exhibit a heterogeneous mesostructure with characteristic lengths decreasing exponentially with the number of collisions. The rate of mesostructural refinement is inversely proportional to the difference between the hardnesses of the individual metals.

Preparation and characterization of Fe50Co50 nanostructured alloy

Nanostructured Fe50Co50 alloy was prepared by mechanical alloying of Fe and Co powders in a planetary high energy ball milling. The microstructure and structural evolution of the alloy have been investigated as a function of milling time (0 h, 8 h, 20 h and 35 h) by scanning electron microscopy (SEM) and X-Ray diffraction (XRD) characterization techniques. SEM micrographs showed different powder particles morphologies during the mechanical alloying stages. By XRD analysis it could be identified the structural phases of the alloy and the crystallite size was calculated as a function of the milling time.

Initial stage of mechanical alloying in a binary system with composition Si70Fe30

Mossbauer spectroscopy and X-ray diffraction have been used to study the sequence of solidstate reactions that occur upon the mechanical alloying of mixtures of Si and Fe powders taken in an atomic ratio of 70: 30 in a planetary ball mill. In the course of the formation of a nanocrystalline state, the interpenetration of Si atoms into Fe particles and of Fe atoms into Si particles occurs. In the Si particles, clusters with a local neighborhood of Fe atoms that is characteristic of the deformed α-FeSi2 phase are formed. In the Fe particles, clusters of the ɛ-FeSi and the β-FeSi2 type arise. With increasing time of mechanical treatment, second phases of α-FeSi2 in Si particles and of ɛ-FeSi and β-FeSi2 in Fe particle are formed. In the latter case, a reaction ɛ-FeSi + Si → β-FeSi2 occurs up to the complete disappearance of the ɛ-FeSi phase if the mixture under study is not contaminated by the material of the vessel (Fe) and balls.