A comparative study of mechanical alloying and mechanical milling of Nd8Fe88B4

A comparative study was made of structure and magnetic properties of Nd₈Fe₈₈B₄ prepared by mechanical alloying (MA) using elemental powders as starting materials and by mechanical milling (MM) of the alloy. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) combined with transmission electron microscopic (TEM) studies revealed that both milling procedures resulted in a mixture of α-Fe and an amorphous phase. The thermal stability of the as-milled powders produced by MA was comparable to that of the as-milled powders produced by MM. Heat treatment of the milled powders above the crystallization temperature resulted in the formation of a nanocrystalline mixture of Nd₂Fe₁₄B and α-Fe, but annealed MA powders demonstrated a somewhat coarser structure in comparison with annealed MM powders. Therefore, higher remanences and coercivities were obtained by MM.     

Structure and phase transformations in Fe–Ni–Mn alloys nanostructured by mechanical alloying

Ternary Fe₈₆Ni_xMn_14−x alloys, where x = 0, 2, 4, 6, 8, 10, 12, 14, 16 at.%, were prepared by the mechanical alloying (MA) of elemental powders in a high-energy planetary ball mill. X-ray diffraction analysis and Mössbauer spectroscopy were used to investigate the structure and phase composition of samples. Thermo-magnetic measurements were used to study the phase transformation temperatures. The MA results in the formation of bcc α-Fe and fcc γ-Fe based solid solutions, the hcp phase was not observed after MA. As-milled alloys were annealed with further cooling to ambient or liquid nitrogen temperatures. A significant decrease in martensitic points for the MA alloys was observed that was attributed to the nanocrystalline structure formation.     

Co-Cu alloys produced by mechanical alloying of powder precursors characterized by different contact surface and energy excess

Co-Cu alloys were prepared by mechanical alloying using different reaction mixtures (mechanical mixture of Co and Cu powders, composite powders (Co_{(100 ? y)}P_(y))_{100 ? x} /Cu _x with a crystalline core, and composite powders (Co_{(100 ? y)}P_(y))_{100 ? x} /Cu _x with an amorphous core). The use of a complex of structural and magnetostructural methods showed that these alloys are nonuniform nanocomposite materials consisting of two phases, namely, copper- and cobalt-based solid solutions. During the mechanical alloying of the composite powders, parameters that are sensitive to the short-range-order structure of both phases were found to be changed, namely, the lattice parameter in the Cu-based solid solution as determined from X-ray diffraction patterns, and the Bloch constant that is sensitive to the short-range order in the Co-based solid solution change. In the alloys prepared by mechanical alloying of composite powders with an amorphous core, the lattice parameter a and the Bloch constant B reach values corresponding to metastable Co_{100 ? x} Cu _x solid solutions in milling times of 1.5–2.0 h. These times are lower by 1–2 orders of magnitude than the typical times that are necessary for forming metastable Co-Cu solid solutions by standard methods of mechanical alloying from mixtures of powders.     

Microstructural, thermal and magnetic properties of amorphous/nanocrystalline FeCrMnN alloys prepared by mechanical alloying and subsequent heat treatment

Amorphous FeCrMnN alloys were synthesized by mechanical alloying (MA) of the elemental powder mixtures under a nitrogen gas atmosphere. The phase identification and structural properties, morphological evolution, thermal behavior and magnetic properties of the mechanically alloyed powders were evaluated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and vibrating sample magnetometer (VSM), respectively. According to the results, at the low milling times the structure consists of the nanocrystalline ferrite and austenite phases. By progression of the MA process, the quantity and homogeneity of the amorphous phase increase. At sufficiently high milling times (>120 h), the XRD pattern becomes halo, indicating complete amorphization. The results also show that the amorphous powders exhibit a wide supercooled liquid region. The crystallization of the amorphous phase occurs during the heating cycle in the DSC equipment and the amorphous phase is transformed into the crystalline compounds containing ferrite, CrN and Cr₂N. The magnetic studies reveal that the magnetic coercivity increases and then decreases. Also, the saturation magnetization decreases with the milling time and after the completion of the amorphization process (>120 h), the material shows a paramagnetic behavior. Although the magnetic behavior does not considerably change by heating the amorphous powders up to the crystallization temperature via DSC equipment, the material depicts a considerable saturation magnetization after the transformation of the amorphous phase to the nanocrystalline compounds.     

Solid-state reactions upon mechanical alloying of an Fe32Al68 binary mixture

The sequence of solid-state reactions that occur upon mechanical alloying of powder mixtures of Al and Fe taken in an atomic ratio of 68: 32 has been studied by the methods of X-ray diffraction analysis, M?ssbauer spectrometry, and Auger spectrometry. Upon the formation of a nanocrystalline state (<10 nm), there takes place a mutual penetration of Al atoms into Fe and Fe atoms into Al particles. The rate of consumption of the fcc Al is substantially higher than that of the bcc Fe. The process of the mechanical alloying (MA) was found to be two-stage. At the first stage, up to 2 at % Fe is dissolved in the fcc Al, and an amorphous Fe₂₅Al₇₅ phase is formed in the interfaces, whose amount reaches 70 at % at the finish of the initial stage. In the interfaces of the ??-Fe phase, a disordered bcc phase of composition Fe₆₆Al₃₄ is formed, which contains up to 12 at % Al segregates. At the second stage, the amorphous phase crystallizes into an orthorhombic intermetallic compound Fe₂Al₅. The residual ??-Fe, bcc Fe₆₆Al₃₄, and segregated Al form a bcc phase of composition Fe₃₅Al₆₅.     

Hydrogen storage behavior of nanocrystalline and amorphous La–Mg–Ni-based LaMg12-type alloys synthesized by mechanical milling

Nanocrystalline and amorphous LaMg₁₁Ni+x% Ni (x=100, 200, mass fraction) alloys were synthesized by mechanical milling. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. The gaseous hydrogen absorption and desorption properties were investigated by Sievert's apparatus and differential scanning calorimeter (DSC) connected with a H₂ detector. The results indicated that increasing Ni content significantly improves the gaseous and electrochemical hydrogen storage performances of the as-milled alloys. The gaseous hydrogen absorption capacities and absorption rates of the as-milled alloys have the maximum values with the variation of the milling time. But the hydrogen desorption kinetics of the alloys always increases with the extending of milling time. In addition, the electrochemical discharge capacity and high rate discharge (HRD) ability of the as-milled alloys both increase first and then decrease with milling time prolonging.     

The synthesis of nanocrystalline Ni75Nb12B13 alloys by high energy ball milling of elemental components

Ni₇₅Nb₁₂B₁₃ alloys were synthesized by mechanical alloying (MA) of individual Ni, Nb and B components. X-ray investigation showed the formation of Ni (Nb, B) solid solution and amorphous phase at the intermediate stage of milling. Metastable phases formed by MA turned into Ni (Nb), Ni₂₁Nb₂B₆ and Ni₃Nb stable phases during heating up to 720 °C. The exothermal effects on DSC curves were caused with these processes. The disintegration of Ni (Nb, B) solid solution and crystallization of an amorphous phase resulted in the stable phases formation during the milling prolongation as well as after thermal treatment.     

Mg–Y–Cu bulk metallic glass prepared by mechanical alloying and vacuum hot-pressing

We have studied the amorphization behavior of Mg_85−xY₁₅Cu_x (x=20–40) alloy powders synthesized by mechanical alloying technique. The as-milled powders were mainly amorphous after 10 h of milling. The thermal stability of these Mg_85−xY₁₅Cu_x glassy powders was investigated by differential scanning calorimeter (DSC). The ranges of Tg, T_x and ΔT_x are around 430–459, 467–497, and 30–46 K, respectively. The Mg₄₉Y₁₅Cu₃₆ glassy powders exhibit the largest supercooled region of 46 K. The amorphization behavior of Mg₆₁Y₁₅Cu₂₄ was examined in details. Amorphous phases gradually became dominant after 7.5 h of milling and fully amorphous powders formed at the end of milling. The thermal stability of Mg₆₁Y₁₅Cu₂₄ glassy powders was similar to that of melt-spun Mg₆₀Y₁₅Cu₂₅ amorphous alloys. Mg₆₁Y₁₅Cu₂₄ bulk metallic glass with homogeneously embedded nanocrystalline precipitates was successfully prepared by vacuum hot pressing. It was found that the applied pressure during consolidation could enhance the thermal stability and prolong the existence of amorphous phase inside Mg₆₁Y₁₅Cu₂₄ powders.     

Solid State Interaction in Ni-Mo-B System During Mechanical Alloying and Annealing

This work presents the results of a study of Ni_87?x Mo _x B₁₃ alloys (x?=?7, 10 and 14?at.%), which were obtained by mechanical alloying (MA) of elemental powder mixtures in a MAPF-2M high-energy planetary ball mill. The x-ray diffraction analysis and differential scanning calorimetry measurements were used. The single-phase fcc solid solutions of Mo and B in Ni were formed by MA of Ni-Mo-B mixtures of various compositions for 6-8?h. The coherent domain sizes of solid solutions calculated from the x-ray peak widths were 12-14?nm. The exothermic effects on the DSC curves, which corresponded to the phase transformations of supersaturated Ni(Mo,B) solid solutions, were observed during heating of the synthesized alloys. After heating to 700?°C, the alloys contained a fcc Ni(Mo) phase and a metastable hexagonal MoB₄ phase. Thermodynamically stable phase composition of Ni₈₀Mo₇B₁₃ and Ni₇₇Mo₁₀B₁₃ alloys, containing three phases: fcc Ni (Mo), Ni₂₁Mo₂B₆ with cubic lattice and Ni₃B with orthorhombic lattice, was reached after the isothermal annealing at 1000?°C. The ratio between the amounts of these phases in the alloys corresponds to their location in a three-phase area of the Ni-Mo-B equilibrium phase diagram.     

Phase transformations during deformation of Fe-Ni and Fe-Mn alloys produced by mechanical alloying

Compositions of Fe_{(100 ? x)}Mn _x (x = 10 and 12 at. %) and Fe_{(100 ? y)}Ni _y (y = 18 and 20 at. %) were produced by combined mechanical alloying of pure-metal powders and annealed in the austenitic field. After annealing and cooling to room temperature, the alloys had a single-phase austenitic structure. During deformation, the γ phase partially transforms into the α ₂ phase (and/or ? phase in Fe-Mn alloys). The phase composition of the alloys after deformation depends on the amount of alloying elements and the predeformation annealing regime. The amount of martensite in the structure of a bulk alloy obtained by powder compacting grows proportionally to the degree of deformation of the sample.     

Discharge Capacities of Mg1?x Nd x Ni (x?=?0, 0.05, 0.1, 0.2) Alloys Prepared by Mechanical Alloying

In this study, the Mg_1?x Nd _x Ni (x?=?0, 0.05, 0.1, and 0.2) alloys were prepared by mechanical alloying (MA), and their electrochemical properties were measured by simulated battery test. It is observed that the introduction of Nd can accelerate the formation of the amorphous structure of MgNi alloy. With the increasing milling time from 40 to 60?h, the initial discharge capacity of Mg_1?x Nd _x Ni (x?=?0, 0.05, 0.10, and 0.20) alloys increases gradually, while during the milling time from 60 to 70?h, it decreases. The maximum capacity of the Mg_1?x Nd _x Ni alloys is gradually reduced with increasing Nd content x. With the milling time t?=?60?h and x?=?0, the discharge capacity is increased up to 378.2?mAh/g. Experimental results show that partial substitution of Mg with Nd can improve cyclic stability of the amorphous MgNi sample at the expense of a reduction in the initial capacity.     

Composition and non-equilibrium crystallization in partially devitrified co-rich soft magnetic nanocomposite alloys

The body-centered cubic (bcc) phase tends to preferentially nucleate during solidification of highly undercooled liquid droplets of binary alloy systems, including Fe–Co, Fe–Ni and Fe–Cr–Ni. We investigate a similar tendency during the partial devitrification of Co-rich amorphous precursors of composition (Co_1?xFe_x)₈₈Zr₇B₄Cu₁ by identifying the structure and composition of the nanocrystalline grains. The Co:Fe ratio of the bcc nanocrystals varies linearly with the Co:Fe ratio of the amorphous precursor, and can lie well within the single-phase face-centered cubic (fcc) region of the Fe–Co phase diagram at the crystallization temperature. Classical nucleation theory therefore suggests several potential explanations for the preferential nucleation of bcc phase from an amorphous precursor, including: (i) a reduced amorphous/bcc interface energy as compared to the close-packed phases; (ii) a lower strain of precipitation for bcc nuclei as compared to close-packed fcc and hexagonal close-packed nuclei; and (iii) stabilization of the bcc phase by dissolved glass-formers such as Zr and B.     

Alloying behavior and characterization of (CoCrFeNiMn)90M10 (M=Al,Hf) high-entropy materials fabricated by mechanical alloying

The alloying behavior and microstructures of the (CoCrFeNiMn)₉₀M₁₀ (M=Al, Hf) high-entropy alloy (HEA) powders fabricated by mechanical alloying were studied. The CoCrFeNiMn)₉₀Al₁₀ powders have duplex solid-solution structures. In contrast, nanocrystalline HfNi₃ anchoring in amorphous structures is found in the (CoCrFeNiMn)₉₀Hf₁₀ powders. The (CoCrFeNiMn)₉₀Al₁₀ powders show better ferromagnetic behaviors, mainly explained by the facilitated motion of the magnetic domain induced by the coherent interface between duplex phases. Combined with our previous work, the rules of forming solid-solution and amorphous phase in as-milled HEA powders are preliminarily proposed. It is found that, compared with the as-cast HEA reported previously, the variation range of mixing enthalpy with atomic size difference of the solid-solution formed in as-milled HEA powders is broader. Moreover, the variation ranges between mixing enthalpy and entropy with atomic size difference of the amorphous phase in HEA powder become wider than those of high-entropy bulk metallic glass.     

Ti50Cu23Ni20Sn7 bulk metallic glasses prepared by mechanical alloying and spark-plasma sintering

A powder metallurgy technology was developed to prepare Ti₅₀Cu₂₃Ni₂₀Sn₇ bulk metallic glasses (BMGs). Firstly, amorphous powder was prepared by mechanical alloying (MA) method successfully after being milled for 30 h. Phase transformation of the as-milled powder was characterized by X-ray diffraction (XRD). Morphology of the as-milled amorphous powder was observed by scanning electron microscopy (SEM). Onset temperature of glass transformation and onset temperature of crystallization (T_x and T_g) of the as-milled amorphous powder were evaluated by differential scanning calorimeter (DSC). Secondly, the as-milled amorphous powder was then consolidated by spark-plasma sintering (SPS) method into a specimen with the shape of cylindrical stick, with a diameter and height of about 20 and 10 mm, respectively. The SPS experiment was conducted under a pressure of 500 MPa at a heating rate of 40 K/min, sintering and holding for 1 min at the temperature of 763 K. It was confirmed that the as-milled powder is of fully amorphous however the consolidated specimen shows to be an amorphous matrix with partial crystallization. Compressing strength, Young's modulus, micro-hardness, friction and density of the consolidated specimen are about 975 MPa, 121 GPa, 13 GPa, 0.12 and 6599 kg/m³, respectively. Fractograph of the specimen appears to be shear fracture and very few defects can be seen from the picture of SEM.     

Kinetic study of non-isothermal crystallization in Al80Fe10Ti5Ni5 metallic glass

This study investigated the crystallization behavior of a kinetically metastable Al₈₀Fe₁₀Ti₅Ni₅ amorphous phase. The Al₈₀Fe₁₀Ti₅Ni₅ amorphous phase was synthesized via the mechanical alloying of elemental powders of Al, Fe, Ti, and Ni. The microstructures and crystallization kinetics of the as-milled and annealed powders were characterized using X-ray diffraction, transition electron microscopy, and non-isothermal differential thermal analysis techniques. The results demonstrated that an Al₈₀Fe₁₀Ti₅Ni₅ amorphous phase was obtained after 40 h of ball milling. The produced amorphous phase exhibited one-stage crystallization on heating, i.e., the amorphous phase transforms into nanocrystalline Al₁₃(Fe,Ni)₄ (40 nm) and Al₃Ti (10 nm) intermetallic phases. The activation energy for the crystallization of the alloy evaluated from the Kissinger equation was approximately 538±5 kJ/mol using the peak temperature of the exothermic reaction. The Avrami exponent or reaction order n indicates that the nucleation rate decreases with time and the crystallization is governed by a three-dimensional diffusion-controlled growth. These results provide new opportunities for structure control through innovative alloy design and processing techniques.     

Structure and thermal behavior of multicomponent Fe68−xNixZr15Nb5B12 (x = 5, 10, 15, 20) alloys

Multicomponent Fe_68−xNi_xZr₁₅Nb₅B₁₂ (x = 5, 10, 15, 20) alloy powders milled for 60 h were prepared by mechanical alloying (MA). The structure and crystallization behavior were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential thermal analysis (DTA). Ni enhances the amorphisation of alloy powders. Particle size increases with increasing Ni content. Both onset crystallization temperature T_x and the first crystallization peak temperature T_p of the four alloys shift to a higher temperature with increasing heating rate while melting temperature (T_m) is just the opposite. Fe_68−xNi_xZr₁₅Nb₅B₁₂ (x = 5, 10, 15, 20) alloys all have a large supercooled liquid region ΔT_x. The supercooled liquid region ΔT_x increases and the crystallization activation energy E decreases with increasing Ni content.     

纳米晶(Ag-Cu28)-25Sn合金粉末的制备及表征

采用机械合金化法制备纳米晶(Ag-Cu28)-25Sn合金粉末.用X射线衍射(XRD)仪、扫描电镜(SEM)、高分辨透射电镜(HRTEM)和差示扫描量热分析仪(DSC)等分析手段,对合金化过程中物相组成、微观结构及熔化特性进行表征.结果表明:(Ag-Cu28)-25Sn纳米晶合金粉末的物相组成为Cu3Sn和Ag4Sn.球磨 40 h,合金化完全,其熔化温度为548.5 ℃;球磨至60 h,合金明显非晶化,其熔化温度为554.0 ℃,熔程变小且在186.3和399.5 ℃处出现明显放热峰.HRTEM表明,纳米晶的尺寸约为5～10 nm,合金中有非晶态物质出现和晶格缺陷产生.200和400 ℃退火后,合金的平均晶粒尺寸分别为21.3和33.9 nm.     

Thermal behavior and structure of Fe84Nb7B9 nanocrystalline powders

1 Introduction Fe84Nb7B9 nanocrystalline alloy is an excellent type of soft magnetic materials, characterized by its high saturation induction, permeability and good noise degeneration property[1, 2]. It can effectively promote the miniature, light, energ…     

Application of classical nucleation theory to phase selection and composition of nucleated nanocrystals during crystallization of Co-rich (Co,Fe)-based amorphous precursors

Classical steady-state nucleation theory is applied to Co-rich Fe,Co-based alloys to provide a rationale for experimental observations during the nanocrystallization of Co-rich (Co,Fe)₈₉Zr₇B₄ and (Co,Fe)₈₈Zr₇B₄Cu₁ amorphous precursors. The amorphous precursor free energy is estimated using density functional theory. This simple theory suggests: (i) strain or interface energy effects could explain a tendency for a body-centered cubic (bcc) phase to form during crystallization. Dissolved glass formers (Zr,B) in crystalline phases may also contribute; (ii) similar face-centered cubic (fcc) and hexagonal close-packed (hcp) free energies could explain the presence of some hcp phase after crystallization even though fcc is stable at the crystallization temperature; (iii) nanocrystal compositions vary monotonically with the Co:Fe ratio of the amorphous precursor even when multiple phases are nucleating because nucleation is not dictated by the common tangency condition governing bulk phase equilibria; and (iv) Fe-enrichment of the bcc phase can be attributed to a relatively small free energy difference between the amorphous and bcc phases for high Co-containing alloys.     

Effect of Ni on glass-forming ability of Cu-Ti-based amorphous alloys

1 Introduction Recently, a number of bulk metallic glassy alloys have been reported, such as La-Al-Ni[1], Cu-Ti-Zr-Ni [2, 3], Cu-Ti-Zr-Ni-Be[4, 5], Cu-Ti-Zr-Ni-Si[6?8] and Cu-Ti-Zr-Ni-Sn[9]. Because of the exceptional good glass-forming ability, these mu…