Initial Stage Of Mechanical Alloying Research Articles

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.

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.

Morphology and structure evolution of Y2O3 nanoparticles in ODS steel powders during mechanical alloying and annealing

Oxide dispersion strengthened (ODS) steels are the most fascinating candidate materials for high temperature nuclear applications. ODS steel with nominal composition of Fe–14Cr–2W–0.2V–0.07Ta–10Y2O3 was prepared by mechanical alloying (MA). The morphology and structure evolution of the alloy powders and Y2O3 nanoparticles during MA and following annealing were studied in this work. Results show that the Y2O3 nanoparticles changed into flake polygons and rods from the nearly spherical shape after MA. The lattice structure of Y2O3 was damaged at the initial stage of MA, and amorphous areas appeared during this process. In the subsequent annealing procedure, the flake polygon structure of Y2O3 was gradually transformed into long strips, and then separated to form a nearly spherical shape. Y2O3 particles presented a more stable structure and the crystallization procedure of Y2O3 particles were completed more thoroughly at higher annealing temperature.

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.

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.

Mössbauer probe spectroscopy of the initial stage of mechanical alloying in a binary Mg-Fe system in comparison to Al-Fe and Si-Fe systems

This work compares the results from investigating a Mg-57Fe binary system with a 99: 1 atomic ratio to previously obtained data for systems based on Al and Si. It is shown that the necessary conditions of the process are the formation of a nanostructure state and the penetration of Fe atoms into the boundaries of the grains of the basic elements. Substantial differences are observed in the kinetics of nanostructure state formation and the consumption of Fe in the Mg → Al → Si series, due to the determining role of the chemical interaction of Mg (Al, Si) with Fe.

Deformation-induced structural transformations in Si and the initial stage of mechanical alloying of Si and Fe

The methods of X-ray diffraction, Mossbauer spectroscopy, IR spectroscopy, and laser diffractometry are employed to study the changes in the structure and phase transformations that accompany mechanical alloying of Si and 57Fe used in an atomic ratio of 99: 1. It is established that the process comprises the development of a nanocrystalline state of Si with crystallite sizes smaller than 10 nm; the formation of an amorphous phase of Si at particle surfaces and in near-boundary distorted zones of interfaces in Si nanostructure; the penetration of 57Fe atoms along grain boundaries; and the formation of Si-Fe clusters, the local environment of Fe atoms in which is typical of a deformed α-FeSi2 phase, with these clusters being located in the interfaces.

Mössbauer probe spectroscopy studies of initial stage of Al-Fe mechanical alloying

The initial stage of mechanical alloying (MA) in a binary mixture of powdered Al and 57Fe in an atomic ratio of 99: 1 has been studied using X-ray diffraction and 57Fe Mossbauer probe spectroscopy. The proposed microscopic model of MA includes the formation of a nanostructured state (∼15 nm) in FCC Al, the penetration of Fe atoms across Al grain boundaries, and the formation of isolated Fe atoms and Fe-Al clusters in boundary distorted zones of Al matrix interface similar to the local atomic environment in deformed Al6Fe and Al9Fe2 phases. Based on the published data, it is assumed that with increasing Fe concentration in the initial mixture, and, correspondingly, increasing amount of clusters, distorted FCC interface regions are transformed into amorphous phase.

Characterization of Mechanically Alloyed Powders for High-Cr Oxide Dispersion Strengthened Ferritic Steel

High-Cr oxide dispersion strengthened (ODS) ferritic steel powders with the nominal composition of Fe–16Cr–4Al–0.1Ti–0.35Y2O3 in wt% were produced by milling of elemental powders and Y2O3 particles in argon atmosphere to investigate changes in the particle properties during mechanical alloying (MA). SEM observation and PSD analysis revealed that the MA powders milled for different times were composed of agglomerated particles having multimodal distributions with substantial size variation ranging from several μm to 350 μm. The mean size of particles rapidly increased at the initial stage of MA, then gradually decreased to 22 μm with increasing milling time up to 48 h, and kept constant thereafter. During milling of the Fe–16Cr–4Al–0.1Ti–0.35Y2O3 powder, MA within 6 h had mainly taken place between Fe and Al to form a bcc-Fe(Al) solid solution. The lattice constant of bcc-Fe steadily increased with a drastic increase in the solute concentrations of Cr, Al, and Ti in Fe. Alloying between Fe and alloying elements is almost fulfilled after milling for 48 h. The MA powder milled in air was much smaller than that milled in gaseous argon under the same conditions. Milling in an air atmosphere is effective to reduce the particle size of the ODS ferritic steel powder, although the pickup of oxygen from environment causes too high excess oxygen content.

Synthesis of nanocrystalline Zr(B1−xNx) by mechanical alloying

Abstract Investigation on the structural evolution of the mixture of Zr and hexagonal BN (h-BN) powders during mechanical alloying (MA) was performed by means of X-ray diffractometry, Fourier transform infrared spectroscopy and scanning electron microscopy. The grain size of h-BN decreases rapidly with increasing milling time, which makes the diffraction peaks disappear at the initial stage of MA. And then most of the N and B atoms diffuse into Zr grains to form a (Zr, B, N) solid solution. An fcc phase Zr(B1−xNx) was found in the sample milled for about 40 h, and all the sample transformed into nanocrystalline Zr(B1−xNx) when the mixture was ball milled for longer than 48 h. The (Zr, B, N) solid solution may transform into Zr(B1−xNx) during annealing at about 900 °C, which confirmed that the formation of Zr(B1−xNx) is a diffusion process.

Mechanochemical synthesis of B82phases by ball-milling of Fe60 - xCoxGe40mixtures

Powders of Fe, Co and Ge blended in mixtures of Fe60Ge40, Co60Ge40, Fe30Co30Ge40 (at.%) were synthesized into alloys by milling in a high energy ball-mill. Only β-phases with hexagonal structure B82 are formed in all alloys after 2 h of mechanical alloying (MA). In Fe60Ge40 and Fe30Co30Ge40 chemical interaction occurred with simultaneous formation of β-Fe5Ge3 and FeGe2. In the system of Fe-Ge the FeGe2 phase is characterized by the highest negative enthalpy of formation in comparison with other phases, therefore it is preferably formed at the initial stage of MA. In the Co60Ge40 alloy the β-Co5Ge3-phase is formed without intermediate reaction products. The obtained β-phases have a nanocrystalline structure (13-18 nm) and are characterized by considerable local chemical heterogeneity. Structural transformations during heating to 720°C of metastable β-Fe5Ge3 result in a stable B82 phase and consist of micro deformation relaxation and elimination of chemical heterogeneity. The heating of chemically heterogeneous β-Co5Ge3 results in its stratification and formation of metastable Co2Ge with orthorhombic structure. At T ≥ 630°C, Co2Ge redissolves in hexagonal β-Co5Ge3 and after heating to 720°C the β-phase becomes chemically homogeneous.

Initial Stage of Mechanical Alloying in Fe(80)X(20) (X = Nb, Ta) Systems

The kinetics of an initial stage of mechanical alloying in Fe/Nb and Fe/Ta systems (80 : 20 at. %) was studied using X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. At the initial stage of mechanical treatment, these systems undergo a transition to a nanostructured state, the content of X phase (Nb, Ta) decreases almost linearly with the dose of supplied energy and a non-uniform α-Fe(X) solid solution is formed. The transfer of Fe into the solid solution occurs gradually, and the phase of pure iron is retained in the system for a long time. At an energy dose of 12 kJ/g, an amorphous phase of non-uniform composition starts to form in both systems. Upon mechanical alloying, the composition of the amorphous phase changes and, at an energy dose of 20–25 kJ/g, it corresponds, on the average, to Fe70X30. The X component is transferred into the solid solution and amorphous phase with no delay at the grain boundaries. The post-treatment annealing of the systems results in their decay into pure initial components and an intermetallic compound Fe2X with the increased Fe content.

Initial stage of mechanical alloying in the Fe–C system

Mössbauer spectroscopy (MS), X-ray diffraction, transmission electron microscopy (TEM), Auger spectroscopy, magnetic measurements and differential thermal analysis (DTA) were used to study the initial stages of mechanical alloying in the Fe–C system. The mechanical alloying of Fe and C powder mixtures with the atomic ratio 85:15 in a planetary ball mill was taken as an example. It has been shown that the initial stage involves the formation of nanostructure in the α-Fe particles, penetration and segregation of carbon along the α-Fe grain boundaries, formation of the amorphous Fe–C phase in the interface regions consisting of the boundary and close-to-boundary distorted zone. The carbon concentration in the amorphous Fe–C phase is estimated at 25 at.%. The amount of the amorphous phase reaches 67 at.% (67% of all the Fe and C atoms are in this phase).

Kinetics of the Initial Stage of Mechanical Alloying in the Fe(80)Zr(20) System

The kinetics of the initial stage of mechanical alloying in the Fe/Zr system (80 : 20 at. %) was studied using X-ray diffraction, Mossbauer spectroscopy, and magnetic measurements. The stage of structural disordering of the mixture is shown to proceed quickly and end by a dose of 9 kJ g–1. Further, intense formation of the amorphous phase takes place; as the dose of 16 kJ g–1 is reached, all zirconium contained in the initial mixture passes into this phase, and its amount does not grow any more. The composition of the amorphous phase corresponds to Fe73Zr27 and remains constant throughout the mechanical processing up to a dose of 25 kJ g–1. Annealing of the reaction mixture at 700°C results in decomposition of the amorphous phase and formation of an intermetallic with the composition and structure corresponding to Fe23Zr6. No contamination of the mixture by the material of the balls and vessel during mechanical treatment was detected.

Amorphization in an immiscible CuTa system by mechanical alloying

The amorphization of Cu 30Ta 70 powders by mechanical alloying has been studied. The structural changes in this material during mechanical alloying were monitored by X-ray diffraction and transmission electron microscopy. It was found that a nanocrystalline supersaturated solid solution of tantalum was formed in the initial stage of mechanical alloying. Amorphous transformation of alloyed powders began to take place when the milling time exceed 30 h and a single phase of an amorphous product was obtained after 100 h of milling. The crystallization reaction of the formed amorphous phase was studied by differential thermal analysis and the kinetics of the reaction has been examined as well. The present results suggest that the enhancement of the free energy due to the supersaturation of copper in tantalum and the introduction of a high density of defects by ball milling comprise the driving force for the amorphization of the Cu-Ta system.