Microstructure evolution and thermal properties in FeMoPCB alloy during mechanical alloying

Fe_79.3Mo_4.5P_8.1C_6.75B_1.35 amorphous alloy composite powder from respective element powders of Fe, Mo, C, B, and Fe–P intermediate compound, was synthesized by mechanical alloying. Microstructure evolution analysis indicates that the synthesized amorphous alloy composite powder after a milling time of 70 h encompasses predominately amorphous matrix embedded by nanocrystalline α-Fe with a grain size of about 5.5 nm. However, unlike other Fe-based amorphous alloys, the synthesized amorphous alloy composite powder exhibits no obvious supercooled liquid region with only crystallization temperature. The corresponding crystallization onset temperature and exothermic enthalpy measured from DSC curves are about 762 K and 15.86 J/g, respectively. The results obtained provide good candidate materials for fabricating bulk metallic glass composites and related bulk nanocrystalline materials.     

Amorphous and quasicrystalline Ti–Ni–Zr powders synthesized by mechanical alloying

The formation of amorphous and quasicrystalline phases in the Ti₄₅Zr₃₈Ni₁₇ system both directly by mechanical alloying and after subsequent annealing was studied. The presence of amorphous, icosahedral quasicrystalline and the Ti₂Ni-type with a fcc structure phases together with the initial metallic components was found in as-milled samples by X-ray diffraction. An increase of the milling time results in an increase of the amorphous phase content. Icosahedral quasicrystalline phases of Ti–Ni–Zr system were produced by mechanical alloying and subsequent annealing. Differential scanning calorimetry studies up to 520 °C showed an extended exothermal effect starting from 300 °C, which corresponds to the crystallization of the as-milled samples. The shape and size of the particles of the alloys were investigated by scanning electron microscopy and argon adsorption. The Specific area surface of the as-milled sample was rather small, in agreement with scanning electron microscopy data. The kinetics of the hydrogenation of the amorphous alloy Ti₄₅Zr₃₈Ni₁₇ at different temperatures was studied.     

Structural and magnetic characterization of composite YCo5/α-Fe (20 wt%) powders prepared by mechanical alloying and subsequent annealing

Powder mixtures of YCo₅ + α-Fe (20 wt%) were prepared by high energy mechanical alloying under Ar using a SPEX 8000 mill and subsequent vacuum annealing. The structural and magnetic properties were investigated by X-ray diffraction, DSC, and magnetic measurements. After 4 h of milling, the alloyed powders were found to be composed of an amorphous Y–Co phase and α-Fe with a mean grain size strongly reduced. The DSC curves exhibited an irreversible broad exothermic peak with a maximum at 555 °C associated with the crystallization process. Subsequent high vacuum annealing in the temperature range 550–750 °C led to the formation of rhombohedral Th₂Zn₁₇-type and α-Fe(Co) phases. Samples were magnetically soft showing low remanence and room temperature coercivity in the range 470–800 Oe. The latter is in agreement with the low magnetocrystalline anisotropy along the basal plane exhibited by the Y₂(Co, Fe)₁₇ phase.     

Phase evolution and magnetic properties of Co/α-Fe2O3 powder mixtures with different molar ratios treated by mechanical alloying

In this work, we report the phase formation and magnetic properties of Co–hematite powder mixtures with two different molar ratios: Co/α-Fe₂O₃: 1/0.7 and 1/1.3 subjected to high-energy mechanical milling using metallic cobalt and hematite powder as the initial raw material in ambient air atmosphere. The samples were activated with a ball to powder weight ratio (BPR) of 10 and the milled powders were collected after 0, 1, 5, 15, 25 and 30 h. Various characterization techniques such as XRD, HRTEM, VSM and Mössbauer spectroscopy were utilized to study the prepared samples. For the samples with Co/α-Fe₂O₃: 1/0.7 milled for 1 and 5 h the formation of cobalt ferrite was confirmed. However, this was not the case for the samples milled above 5 h for whose both Mössbauer and XRD results confirmed the phase decomposition taken place for the previously formed cobalt ferrite phase. Further, the formation of superparamagnetic nanoclusters of iron oxide, a wustite-like Fe_1?XCo_XO phase and the existence of small amounts of metallic Fe/Fe_1?XCo_X phase/s were also detected for these samples. The presence of the latter phase is not believed to be solely related to contamination from the steel vial/balls used. A mechanochemical-reduction process is assumed to be also possibly responsible for the formation of the observed reduced phases. For the powder mixture with Co/α-Fe₂O₃: 1/1.3, however, increased formation of cobalt ferrite phase was observed by increasing the milling time. The highest maximum magnetization (53 e.m.u/g) and coercive field (500 Oe) was obtained for the sample milled for 25 h among various samples of this series of powder mixture. The lower magnetization obtained for this sample compared to that of the bulk is attributed to the size effect. Furthermore, the structural–magnetic properties relationship of the various powders prepared is discussed in detail.     

Structure and properties of nanocrystalline Cu70Fe18Co12 obtained by mechanical alloying

Cu₇₀Fe₁₈Co₁₂ alloy is prepared by mechanical alloying of pure Cu, Fe, Co powder using a high energy ball mill, with increasing milling time ranging from 4 to 8, 24, 36 and 54 h. The variation of the morphology and the elemental distribution were measured at these different stages on various grains of the alloy using a scanning electron microscope with a dispersive energy analyzer. Atomic clusters of iron were observed on some grains after 8 h of milling, confirming the non-homogenisation of the powder at this stage. Beyond 12 h, the homogenisation is ensured over a volume of one cube micron. Microstructural changes during the mechanical alloying have been studied by X-ray diffractometry (XRD) and Mössbauer spectroscopy. X-ray diffraction measurements confirm the dissolution of iron and cobalt phases in the FCC matrix of copper after 24 h of milling with increase of the structural parameter. This same dissolution was also measured by Mössbauer spectroscopy, confirming that after 4 h of milling the CuFe phase begins to form and iron dissolution is incomplete with partial amount of alpha Fe phase surviving after 36 h of milling.     

Amorphization of Co-base alloy by mechanical alloying

Structural transformations and the amorphization of cobalt base alloy particles are possible when a powder mixture of Co and Cr-Mo is subjected to the mechanical alloying (MA) process. Elemental powders mixed in adequate weight ratios were used as precursors. The process was carried out at room temperature in a shaker mixer mill using vials and balls of hardened steel as milling media, with a ball:powder weight ratio of 8:1. The characterization of the crystalline structure of milled powders was carried out by means of X-ray diffraction to analyze the phase transformations as a function of milling time. The aim of this work was to demonstrate that MA can induce the amorphization of Co-Cr-Mo alloy. The evolution of the phase transformation during milling time is reported. The results showed that it is possible to produce a partial solid solution at room temperature of elemental metallic powders Co₇₀Cr₃₀ and Co₉₀Mo₁₀ by mechanical alloying. Using specific experimental conditions, it is also possible to obtain an amorphous phase in a composition Co₆₀Cr₃₀Mo₁₀; first, Cr and Mo were mechanically prealloyed for 9 h to obtain a Cr₈₀Mo₂₀ solid solution, and Co was then added and milled in over 14 h.     

Amorphization induced by mechanical alloying and cold rolling

Solid state amorphous phase change is studied in the Ni---Ti system. It is found that the crystalline to amorphous transition can be obtained by the mechanical alloying, or by annealing of the multilayers produced by mechanical alloying and/or cold rolling. Different products are found after the annealing of the multilayers. The activation energies and interdiffusion coefficients are obtained for the solid state amorphous reaction.     

Preparation of AlRu intermetallic compounds by mechanical alloying

The formation of Al₆Ru intermetallic compounds using high-energy ball milling was investigated. High-purity Al and Ru crystalline powders, in the relative (molar) ratio of 6:1, were milled for periods up to 30 h. Samples of the milled materials were annealed at different times and temperatures. The microstructures of the annealed samples were compared to those of the as-milled samples. It was found that the obtained alloys have compositions that are in accord with the Al–Ru phase diagram. However, the X-ray analysis of a 10 h milled sample, annealed at 873 K for 30 min, showed evidence of the formation of a quasicrystalline icosahedral alloy mixed with the crystalline Al₆Ru. Scanning electron microscopy showed that the microstructures are similar to those obtained by other sample preparation techniques.     

Structural investigation of an amorphous Si24Nb76 alloy produced by mechanical alloying using reverse Monte Carlo simulations

The atomic structure of an amorphous Si₂₄Nb₇₆ alloy produced by mechanical alloying was investigated by using one X-ray total structure factor S(K) as input data for reverse Monte Carlo (RMC) simulations. The partial S_Si–Si(K), S_Si–Nb(K), S_Nb–Nb(K) structure factors and G_Si–Si(r), G_Si–Nb(r), G_Nb–Nb(r) pair probability functions were obtained from the RMC simulations. The structural parameters (interatomic distances and co-ordination numbers) for the first neighbors were extracted and compared with those found in the Nb₃Si compound. It was observed some resemblance between these phases.     

Synthesis of nanocrystalline zinc blende ZnTe by mechanical alloying

Nanocrystalline ZnTe was prepared by mechanical alloying from equiatomic powder mixture. X-ray diffraction and differential scanning calorimetry techniques were used to study the structural and thermal properties of the milled powder. An annealing of the as-milled sample at 600 °C for 6 h was performed to clarify thermal reactions showed in its calorimetry measurement. Minority crystalline phases (Te and ZnO) and residual amorphous ones were observed for both annealed and as-milled samples. The structural parameters, phase fractions, mean crystallite sizes and strains of all crystalline phases were obtained from Rietveld analyses of the X-ray patterns using the program package GSAS.     

Preparation and reactivities of composite nanocrystalline solids prepared by mechanical alloying

The formation of Fe---SiC composite nanocrystalline solids through ball milling is reported. The effects of mechanical deformation, crystallite size and gaseous elements on the solid state reaction between Fe and SiC are also investigated. The formation of Fe₃C after a long milling time is attributed to the kinetics of the reaction between nanocrystalline Fe and SiC.     

Comparison of glass formation by mechanical alloying and solid-state interdiffusion in Ni---Zr composites

The amorphization process in mechanically alloyed Ni---Zr powders has been investigated by optical microscopy, scanning and transmission electron microscopy, X-ray diffraction, differential scanning calorimetry and saturation magnetization measurements. Starting from elemental crystalline Ni and Zr powders, ball milling first produces a characteristically layered microstructure. Further milling leads to an ultrafine composite in which amorphization by solid-state reaction sets in between 4 and 16 h milling time. Longer milling results in fully homogeneous amorphous material. The obtained results corroborate the similarity of the amorphization process during mechanical alloying with the solid-state interdiffusion reaction in artificially modulated multilayer composites. In particular, mechanical alloying prevents intermetallic phase formation during the interdiffusion reaction because of extremely thin starting layers, thus resulting in a wider glass-forming range than obtained by other preparation techniques based on solid-state interdiffusion.     

Structural control and magnetic properties of electrodeposited Co nanowires

Co nanowires with a preferred orientation were fabricated by direct current electrodeposition into the pores of porous anodic alumina membrane, and the structure of Co nanowires was studied by X-ray diffraction and high-resolution transmission electron microscopy with selected-area electron diffraction. It is found that the crystal structure of Co nanowires lies on the deposition potential. When electrodeposition is performed far from equilibrium conditions, i.e., at a high potential, face-centered cubic Co nanowires are deposited, while hexagonal close packing Co nanowires are formed at the low potential. The experimental results indicate that the orientation of the nanowires has effects on the coercivity for both hexagonal close packing (hcp) and face-centered cubic (fcc) Co.     

A comparison of the structures of Ni---Zr amorphous alloys obtained by mechanical alloying and melt spinning

The structures of mechanically alloyed (MA) and melt-spun (MS) Ni_xZr_1-x (x = 0.28, 0.33, 0.40) amorphous alloys were investigated by X-ray diffraction. The interatomic distances, r_NiZr and r_ZrZr, were calculated from the deconvolution of the principal peak of the radial distribution function (RDF) using Gaussian functions. The distances were nearly equal for the amorphous alloys of the same composition prepared by the two methods, i.e., 2.69 and 2.67 Å and 3.28 and 3.22 Å on average for the MA and MS specimens, respectively.     

Appearance of fast ionic conduction in AgI-doped chalcogenide glass powders prepared by mechanical milling

(AgI)_x(As₂Se₃)_1−x glass powders were successfully obtained up to 70 mol% AgI content by the mechanical milling method. Electrical conductivities, which show the exponential increase with addition of AgI, are comparable to the values of the corresponding melt-quenched glasses. The conductivity of 60 mol% AgI-doped glass shows great increase at the early period of the milling. A DSC signal for the β–α phases transition of crystalline AgI becomes weak at the medium stage of the milling, whereas glass transition appears clearly. EXAFS measurements at Ag, I, As, and Se K-edges have been carried out for (AgI)_0.6(As₂Se₃)_0.4 glasses with different period of the milling. The amorphization process of (AgI)_0.6(As₂Se₃)_0.4 system was accompanied by a decrease of the nearest neighboring coordination number of Ag at the medium stage of the milling. These results suggest that the structural disordering of AgI units in the glass matrix would be strongly related to the appearance of fast ionic conduction.     

Structural inhomogeneities and magnetic properties of Co/Cu multilayer films

The polycrystalline Co/Cu multilayer films are prepared by magnetron sputtering onto Si/SiO₂ substrates. The static magnetization and the ferromagnetic resonance (FMR) spectra of these films are investigated. The microscopic cross-sectional structure of the films is examined using transmission electron microscopy. It is demonstrated that the differences in the magnetization curves and the ferromagnetic resonance spectra are associated with the specific structural features governed by the technological parameters of the film sputtering. The possible structural features that arise during the formation of layered structures and are responsible for the appearance of additional lines in the FMR spectra are discussed.     

The influence of atmosphere on the amorphization reaction by mechanical alloying for the Ni---Ti system

A study of the amorphous phase reaction by mechanical alloying (MA) in different atmospheres has been carried out. Structural changes during milling were examined by means of X-ray analysis. The amounts of the gaseous elements absorbed by the powder particles during milling were determined by chemical analysis. It was found that there is almost no influence on the MA process either in an argon or a nitrogen atmosphere. During the milling process in air or an oxygen atmosphere, intermetallic compounds and oxides appeared, accompanying the formation of the amorphous phase. The intermetallic compounds appeared due to the presence of oxygen atoms.     

Structural characterization of Elisabatin B and Elisabatin C

X-ray structures of Elisabatin B (1) and Elisabatin C (2) have been determined. Crystal data for 1: Triclinic, P (No. 2), a = 7.528(2) Å, b = 9.404(2) Å, c = 11.414(2) Å, = 75.363(3)°, = 86.668(4)°, = 89.683(4)°, and Z = 2. Crystal data for 2: Monoclinic, P2₁/c (No. 14), a = 8.242(2) Å, b = 14.870(2) Å, c = 13.060(2) Å, = 101.458(3)°, and Z = 4. Both compounds are highly unsaturated leading to extended aromatic conjugation. They show different intermolecular O–HO hydrogen bonds, via which 1 forms dimers, and 2 zig-zag polymeric chains.     

Ni59Zr20Ti16Sn5 amorphous alloy obtained by melt spinning and mechanical alloying

Amorphous Ni₅₉Zr₂₀Ti₁₆Sn₅ alloys were fabricated by melt spinning and by mechanical alloying (MA) techniques. Additionally the melt spun ribbon was powdered by ball milling. Differential scanning calorimetry (DSC) measurements revealed two or three-steps crystallization of the amorphous alloys. MA powders exhibited the lowest crystallization temperature of the first DSC peak, the melt spun ribbon – the highest one. On the other side, the lowest value of activation energy of crystallization was calculated for ball milled ribbon. Further studies are needed to clarify the differences in thermal stability and crystallization behavior of the alloys.