Wet Mechanical Alloying Research Articles

Obtaining and characterisation of thermoelectric Mg2Si compound via wet and dry mechanical alloying and spark plasma sintering

Mg2Si thermoelectric compound was obtained by dry and wet (isohexane and benzene) mechanical alloying route. The Mg2Si compound was characterised by X-ray diffraction, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), laser particle size analysis and thermoelectric measurements. After 14 h of milling, the complete reaction of the elements is achieved by both routes. The powders particle size distribution obtained after 14 h of dry or wet milling (using benzene) reveals a bimodal curve. The wet milling moves the particle size distribution towards smaller particle sizes. The SEM analysis confirms the results of particles size analysis. DSC analyses performed for samples milled up to 14 h present stress relief and recrystallisation thermal events. For the benzene wet-milled sample, the DSC curve shows an additional thermal event at 350 °C, associated with benzene removal. Thermoelectric properties were determined on spark plasma sintered compacts. The milling process with benzene leads to a higher value of Seebeck coefficient (≈580 μV/K). The electrical conductivity is low at room temperature and increases exponentially with temperature.

Soft Magnetic Nanocrystalline Ni-Fe-X-Y and MeFe2O4 Powders Obtained by Mechanosynthesis

"The soft magnetic nanocrystalline powders, alloys (Ni3Fe, 79Ni16Fe5Mo, 77Ni14Fe5Cu4Mo, wt. %) and zinc ferrite, were obtained by dry and wet mechanical alloying and reactive milling, followed by different heat treatments. The powders were characterised by X-ray diffraction, scanning electron microscopy, X-ray microanalysis, differential scanning calorimetry, thermomagnetic and magnetic measurements. The X-ray diffraction shown the progressive new phases formation. The crystallite size is between 18-7 nm depending on materials and milling conditions. The particle size is smaller for wet-mechanical alloying comparing with dry-milling. The thermomagnetic measurement shown the Curie temperature of the alloys. The spontaneous magnetisation of the wet-milled and annealed samples is higher than of the molten alloys. Keywords: mechanical alloying; Ni-Fe-X-Y alloys; soft ferrite; magnetisation; XRD; DSC. "

Ternary Ag2Se1-xTex: A Near-Room-Temperature Thermoelectric Material with a Potentially High Figure of Merit.

Discovering high-performance near-room-temperature thermoelectric materials is extremely imperative to widen the practical application in thermoelectric power generation and refrigeration. Here, ternary Ag2Se1-xTex (x = 0.1, 0.2, 0.3, 0.4, and 0.5) materials are prepared via the wet-mechanical alloying and spark plasma sintering process to investigate their near-room-temperature thermoelectric properties. From density functional theory calculation and single-parabolic-band modeling study, we found that the reduced contribution of Se 4p orbitals to the total density of states decreases the carrier effective mass with increasing Te content, which should enhance the theoretically maximum zT. These calculation results are also verified by the experimental results. Meanwhile, complex microstructures including dislocations, nanograins, high-density boundaries, TeSe substitution, lattice distortions, and localized strain have been observed in ternary Ag2Se1-xTex. These complex microstructures strengthen phonon scattering and in turn lead to ultralow lattice thermal conductivity in the range of 0.21-0.31 W m-1 K-1 in ternary Ag2Se1-xTex at 300 K. Although the increased deformation potential suppresses the carrier mobility, benefiting from the engineered band structures and ultralow lattice thermal conductivity, a high zT of >1 can be potentially obtained in the ternary Ag2Se1-xTex with appropriate carrier concentration. This study indicates that ternary Ag2Se1-xTex is a promising candidate for near-room-temperature thermoelectric applications.

Synthesis and characterisation of amorphous Fe38.5Co38.5Nb7B15Cu1 powders via mechanosynthesis using industrial raw materials

This work presents a comparative study on the HITPERM type alloy prepared by wet and dry mechanical alloying. The chosen composition for this study was Fe38.5Co38.5Nb7B15Cu1. The powders were obtained via mechanical alloying starting from elemental Fe, Co, Cu powders and the ferroalloys of Nb and B. Mechanical alloying experiments were done using a high energy planetary ball mill Pulverizette 6 under Ar atmosphere. It was observed that for the powder milled in wet milling conditions, using benzene as process control agent, the alloy amorphisation occurs after 40 h of milling. X-ray diffraction patterns highlighted the alloy amorphisation. In the dry milled powder case, the amorphisation did not occur even after 100 h of milling. The thermal stability and the crystallisation kinetics of the amorphous powders were investigated via differential scanning calorimetry and in-situ high-temperature X-ray diffraction. The powders morphology and chemical homogeneity were studied by scanning electron microscopy and X-ray microanalysis. The saturation magnetisation also reveals a difference between wet and dry milled powders versus milling time. The obtained results concerning the alloy amorphisation and its thermal stability are compared with available data of the literature.

Structural Evolution in Wet Mechanically Alloyed Co-Fe-(Ta,W)-B Alloys

In the present study, the effect of wet mechanical alloying (MA) on the glass-forming ability (GFA) of Co43Fe20X5.5B31.5 (X = Ta, W) alloys was studied. The structural evolution during MA was investigated using high-energy X-ray diffraction, X-ray absorption spectroscopy, high-resolution transmission electron microscopy and magnetic measurements. Pair distribution function and extended X-ray absorption fine structure spectroscopy were used to characterize local atomic structure at various stages of MA. Besides structural changes, the magnetic properties of both compositions were investigated employing a vibrating sample magnetometer and thermomagnetic measurements. It was shown that using hexane as a process control agent during wet MA resulted in the formation of fully amorphous Co-Fe-Ta-B powder material at a shorter milling time (100 h) as compared to dry MA. It has also been shown that substituting Ta with W effectively suppresses GFA. After 100 h of MA of Co-Fe-W-B mixture, a nanocomposite material consisting of amorphous and nanocrystalline bcc-W phase was synthesized.

Phase composition and wear resistance of compacts and coatings based on carbides fabricated in W-Fe-C system by wet mechanical alloying

The paper reports on phase composition, microhardness and wear resistance of compacts and coatings based on η-carbides (Fe,W)6C and (Fe,W)12C produced by mechanical alloying of tungsten and iron powders in petroleum ether. The compacts have been prepared by magnetic-pulse compacting, and the coatings being formed on iron substrate by the selective laser sintering. The compacts exhibit microhardness up to 9.6 GPa and high abrasive wear resistance. Friction coefficients are 0.27-0.6 and 0.33-0.53 in frictional pairs with a steel disc and a ball made of WC-Co alloy, respectively, and wear not exceeding 10 µm in the tribo-pairs. The coatings have a microhardness of 16 GPa and friction coefficients of 0.28 and 0.2 for friction with balls made of steel and WC-Co, respectively, with no wear being practically observed in tribo-pairs. Combining the mechanosynthesis and selective laser sintering is shown to be very efficient to fabricate coatings based on η-carbides (Fe,W)6C and (Fe,W)12C possessing high values of hardness and wear resistance.

Hierarchical Structures Advance Thermoelectric Properties of Porous n-type β-Ag2Se.

Owing to the intrinsically good near-room-temperature thermoelectric performance, β-Ag2Se has been considered as a promising alternative to n-type Bi2Te3 thermoelectric materials. Herein, we develop an energy- and time-efficient wet mechanical alloying and spark plasma sintering method to prepare porous β-Ag2Se with hierarchical structures including high-density pores, a metastable phase, nanosized grains, semi-coherent grain boundaries, high-density dislocations, and localized strains, leading to an ultralow lattice thermal conductivity of ∼0.35 W m-1 K-1 at 300 K. A relatively high carrier mobility is obtained by adjusting the sintering temperature to obtain pores with an average size of ∼260 nm, therefore resulting in a figure of merit, zT, of ∼0.7 at 300 K and ∼0.9 at 390 K. The single parabolic band model predicts that zT of such porous β-Ag2Se can reach ∼1.1 at 300 K if the carrier concentration can be tuned to ∼1 × 1018 cm-3, suggesting that β-Ag2Se can be a competitive candidate for room-temperature thermoelectric applications.

Structure and properties of mechanosynthesized W-Fe-C carbides

A novel approach has been developed for the synthesis of (Fe,W)6C and (Fe,W)12C carbides from iron and tungsten powders via their wet mechanical alloying followed by compaction and annealing at 900 °C. It has been found that the compacted samples show the density of up to 12.5 g·cm−3, microhardness of up to 10GPa, and high wear resistance under abrasive wear and dry sliding friction against a steel disk. As for the level of the catalytic activity with respect to the hydrogen evolution reaction in sulfuric acid solution, the obtained carbides are between Fe3C and WC-6Co alloy.

Nanostructured monoclinic Cu2Se as a near-room-temperature thermoelectric material.

Searching for new-type, eco-friendly, and Earth-abundant thermoelectric materials, which can be used as an alternative to the high-cost bismuth telluride, is important for near-room-temperature applications. In this work, nanostructured monoclinic Cu2Se with a low carrier concentration has been synthesized by a wet mechanical alloying process combined with spark plasma sintering. Such a low carrier concentration, which originates from the effectively suppressed Cu deficiencies during the fabrication process, induces a relatively low electrical conductivity and carrier thermal conductivity. Besides, the nanostructured grains combined with point defects and phonon resonance enhance the phonon scattering to induce a low lattice thermal conductivity without sacrificing the electrical transport properties. As a result, our nanostructured monoclinic Cu2Se obtains a figure of merit of 0.72 at 380 K with good thermal stability. This work indicates that nanostructured monoclinic Cu2Se is a promising near-room-temperature thermoelectric material.

Nanostructured AgCu system at repeated melting

The thermal behavior of the eutectic powder particles mixture Ag-28% Cu (mass) represents the aim of this research. This comportment is studied from the point of view of the structural changes induced to the powder mixture processing by the wet mechanical alloying (WMA) technique. After 80 h of WMA in ethylene glycol aqueous solution and argon atmosphere, the initial powder mixture becomes nanostructured composite particles with bimetallic AgCu matrix reinforced by in situ processed Cu2O. The particle size distribution, depicted by laser diffraction technique, reveals the nanometric range of the composite particles between 60 and 80 nm. The phase identification, quantitative analysis as well as crystallite size measurements by XRD confirm the nanostructured feature of the bimetallic matrix, acknowledged by SEM with EDX and FIB, as well as the reinforcing components synthesis during the WMA process. Two successive melting processes have been developed to point out the increased melting point in the range of 928.00–946.10 °C. The thermal analysis, developed in argon atmosphere, highlights the thermal effects of AgCu/Cu2O nanoparticles generated by argon adsorption/desorption from the powders surface.

Hydrogen absorption/desorption characteristics of Mg-V-Ni hydrogen storage alloys

In this study, Mg+5at%V+5at%Ni alloys are prepared by wet mechanical alloying (MA) in an organic solvent under a purified argon atmosphere. The hydrogen absorption capacities of the samples are evaluated at 473 K at an initial hydrogen pressure of 0.2 MPa in a Sieverts apparatus. First, to obtain the ideal hydrogen absorption and desorption characteristics, organic solvents for milling are changed. Among the alloy samples milled with different organic solvents, the maximum hydrogen absorption capacity is obtained for the alloy prepared with benzene. After determining the organic solvent, the milling time was varied from 3 to 8 h. The maximum hydrogen absorption capacity of 5.15 mass% can be achieved in 7 h-milling. Furthermore, the apparent hydrogen diffusion coefficients are obtained by fitting the temporal change of the hydrogen absorption capacity with a theoretical curve. The theoretical curves are calculated, assuming that the particle shape is a sphere and the size of the sample is 40 μm.

Mechanochemically synthesized NiCo2O4/Vulcan/PANI nanocomposite and investigation of its electrochemical behavior as a supercapacitor

Wet-mechanical alloying was used to synthesize NiCo2O4 (Ni-Co) nanoparticles. XRD results showed that single phase nanoparticles were formed after 1 h of milling and a minimum crystallite size of ~ 3 nm was obtained for 3 h-milled sample. The 3-h-milled sample was mechanically alloyed with Vulcan (Vu) to fabricate NiCo2O4/Vulcan (Ni-Co/Vu). The Ni-Co/Vu sample was thoroughly mixed with aniline (ANI), and the mixture was then polymerized to polyaniline (PANI). The microscopic evaluations showed the change in shape of Ni-Co particles from spherical to worm-liked after the polymerization process. Their structure was evaluated using FT-IR and Raman spectroscopies. The electrochemical studies through cyclic voltammetry (CV) and chronopotentiometry (CP) showed the highest capacitance for the 3-h-milled Ni-Co, in comparison with other milled samples. The capacitance of 341 F g−1 of the 3-h-milled sample, was enhanced to 455 and 644 F g−1, upon introducing Vu and Vu/ PANI, respectively.

A comparative study of the Fe-based amorphous alloy prepared by mechanical alloying and rapid quenching

This paper presents a comparative study regarding the preparation of Fe-based amorphous alloys via mechanical alloying (MA) and rapid quenching (RQ). The obtained samples (powders and ribbons) were characterised by X-ray diffraction (XRD), in-situ high-temperature X-ray diffraction (HT-XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) and vibrating sample magnetometry (VSM). By using elemental powders of Fe, Si and B, it was found that amorphisation cannot be achieved by dry MA or RQ. Wet MA using benzene as process control agent (PCA) led to the alloy amorphisation after 20 h of milling. It was proved that the amorphisation via wet MA is possible due to the extra amount of C atoms provided by the PCA decomposition. Using powders obtained by wet MA or a mixture of Fe, Si, B and C elemental powder, amorphous ribbons were obtained by RQ. During the amorphous samples crystallisation, a mixture of α-Fe(Si) and Fe borides is formed. The magnetic measurements showed that the magnetic characteristics of the samples are strongly influenced by the technique used for their preparation.

Amorphisation of Fe-based alloy via wet mechanical alloying assisted by PCA decomposition

Amorphisation of Fe75Si20B5 (at.%) alloy has been attempted both by wet and dry mechanical alloying starting from a mixture of elemental powders. Powder amorphisation was not achieved even after 140 hours of dry mechanical alloying. Using the same milling parameters, when wet mechanical alloying was used, the powder amorphisation was achieved after 40 h of milling. Our assumption regarding the powder amorphisation capability enhancement by contamination with carbon was proved by X-ray Photoelectron Spectroscopy (XPS) measurements which revealed the presence of carbon in the chemical composition of the wet mechanically alloyed sample. Using shorter milling times and several process control agents (PCA) (ethanol, oleic acid and benzene) with different carbon content it was proved that the milling duration required for powder amorphisation is linked to the carbon content of the PCA. Differential Scanning Calorimetry (DSC), thermomagnetic (TG) and X-ray Diffraction (XRD) measurements performed to the heated samples revealed the fact that, the crystallisation occurs at 488 °C, thus leading to the formation of Fe3Si and Fe2B. Thermogravimetry measurements performed under H2 atmosphere, showed the same amount of contamination with C, which is about 2.3 wt%, for the amorphous samples regardless of the type of PCA. Saturation magnetisation of the wet milled samples decreases upon increasing milling time. In the case of the amorphous samples wet milled with benzene up to 20 h and with oleic acid up to 30 h, the saturation magnetisation has roughly the same value, indicating the same degree of contamination. The XRD performed on the samples milled using the same parameters, revealed that powder amorphisation can be achieved even via dry milling, just by adding the equivalent amount of elemental C calculated from the TG plots. This proves that in this system by considering the atomic species which can contaminate the powder, they can be used as microalloying elements which could provide the required extra amount of metalloids.

Preparation and characterisation of Co–Fe–Ni–M-Si–B (M = Zr, Ti) amorphous powders by wet mechanical alloying

Co-based amorphous alloys were prepared via wet mechanical alloying process starting from elemental powders. The reference alloy Co70Fe4Ni2Si15B9 (at. %) as well as the alloys derived from this composition by the substitution of 5 at.% of Zr or Ti for Si or B (Co70Fe4Ni2Si15B4Zr5, Co70Fe4Ni2Si15B4Ti5, Co70Fe4Ni2Si10B9Zr5 and Co70Fe4Ni2Si10B9Ti5) are obtained in amorphous state, according to X-ray diffraction (XRD) investigation, after 40 h of milling. The calculated amount of amorphous fraction reaches 99% after 40 h of milling. The largest increase of the crystallisation temperature was induced by the substitution of Zr or Ti for Si while, regardless of the type of substitution, an important increase of the Curie temperature of the alloy was obtained. A Co-based solid solution, with Co2Si and Co2B phases, result after crystallisation of the amorphous alloys as proved by XRD investigations. Saturation magnetisation of the alloys decreases upon increasing milling time, however it remains larger than the saturation magnetisation of the reference alloy. This was discussed in correlation with the specificity of the wet mechanical alloying process and the influence of the chemical bonding between Co and metalloids atoms over the magnetic moment of Co.

Synthesis of amorphous Fe75Si20−xMxB5 (M = Ti, Ta, Zr) via wet mechanical alloying and its structural, thermal and magnetic characterisation

Amorphous Fe75Si15B5M5 powders with M=Ti, Ta and Zr, were synthesized by mechanical alloying and their thermal stability, crystalline state, particles morphology and magnetic properties were investigated in this study. It is found that the time to achieve amorphisation during milling increases by the substitution of any of the above transition metals 5% for silicon. The particle size distribution is dependent on the mechanical properties of the transitional metals used. Crystallisation temperature of the alloys was enhanced with up to 24% compared to the reference ternary alloy Fe75Si20B5. Magnetic measurements revealed a higher saturation magnetisation in the case of the amorphous alloy containing titanium than for the reference amorphous alloy. XRD patterns for the samples heated up to 900°C reveal the presence of carbides as a result of powder contamination by the process control agent (PCA).

Effect of Process Control Agents on the FeSiB Powder Amorphisation by Wet Mechanical Alloying

Result of research concerning the influence of milling conditions on the amorphisation of the Fe75Si20B5 (at.%) alloy is presented. Amorphous powder of Fe75Si20B5 (at.%) was prepared by dry and wet mechanical alloying (MA) route starting from a mixture of Fe, Si and B elemental powders. The mixture was wet/dry milled up to 50 hours. Benzene, oleic acid and ethanol were used as process control agents (PCA) in order to investigate the influence of their chemical composition on the powder amorphisation. The evolution of the powder crystalline structure, thermal stability and magnetic properties were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetry (TG) as well as magnetic measurements versus temperature and field. It is proved that the chemical composition of the PCA (especially the carbon content) plays an important role in the amorphisation process induced by wet MA.

Synthesis of Fe<sub>75</sub>Si<sub>20-x</sub>B<sub>5</sub>M<sub>x</sub> (M=Ti, Ta or Zr) Powders by Wet Mechanical Milling

Amorphous Fe75Si20-xB5Mxpowders with M= Ti, Ta or Zr andx= 0 and 5 were synthesized by wet mechanical alloying, using benzene as a surfactant. The thermal stability of the Fe-Si-B alloy increases by introducing transition metals. The replacement of 5% Si with Ti, Ta or Zr leads to an increase of the crystallization temperature. It was found that the replacement of 5% Si with Zr increases the crystallization temperature with 115 °C, and also reveals a glass transition temperature around 580 °C.

Structural, magnetic and thermal characterization of amorphous FINEMET powders prepared by wet mechanical alloying

Abstract Fe73.5Cu1Nb3Si13.5B9 (at.%) amorphous alloy has been prepared from elemental powder mixture by wet mechanical alloying route, using benzene as process control agent (PCA). The powder has been investigated from the structural, thermal and magnetic point of views. After 15 h of wet mechanical milling, the alloy is obtained in nanocrystalline state, further increase of milling time leading to the progressive amorphization of the alloy. Full amorphization of the alloy is reached after 80 h of wet mechanical alloying. A significant decrease of the particle size is observed during alloy formation, the further increase of the milling time leading only to minor changes of the particles size. By DSC investigation, the primary crystallization of amorphous powder was found to take place at around 570 °C leading to the formation of Fe–Si alloy and iron borides. The Curie temperature of the amorphous material is 280 °C. The XRD investigations of the fully crystallized alloy (heated up to 900 °C) reveal the presence of the NbC phase into the alloy microstructure as a result of powder contamination with carbon. The decrease of the saturation magnetization of the powder upon increasing milling time was observed and is discussed in the light of the structural and chemical changes induced by milling process. A post milling annealing at 300 °C leads to the enhancement of the saturation magnetization due to the stress release and the removal of the benzene adsorbed on the powder surface.

Structural and magnetic characteristics of Co-based amorphous powders prepared by wet mechanical alloying

Amorphous soft magnetic powder of Co70Fe4Ni2Si15B9 (at.%) was obtained by wet mechanical alloying starting from elemental powders using benzene as process control agent (PCA). After 40h of milling, full amorphisation of the powder was achieved as proved by XRD investigations. The evolution of the mean particle size and specific surface of the particles versus milling time was explained in the light of the phases evolutions and their specific properties. A decrease of the powder magnetisation was observed during its progressive amorphisation as a result of changes of the magnetic moments environment and the presence of benzene in the samples. According to DSC studies the amorphous powder present a two steps crystallisation leading to the formation of Co-fcc, Co2Si and Co2B phases. Annealing of the powder at 300°C for 1, 2 and 3h leads to a substantial increase of the saturation magnetisation.