Mechanical Alloying Treatment Research Articles

Revealing strengthening contribution of grain refinement and phase precipitation in CrMnFeCoNi high-entropy alloy prepared from different powders

Equiatomic CrMnFeCoNi high-entropy alloys (HEAs) were prepared by vacuum hot-pressing sintering with single phase precursor powders made from mechanical alloying (MA) or spray-drying (SD), respectively. MA process was found beneficial for the following precipitation and formation of secondary phases during sintering, after which multiphase bulk HEAs were formed consisting of FCC, M23C6, and precipitated nanoscale σ phases. The tensile and compressive yield strengths of bulk HEAs fabricated from MA powders reached 1150 and 1200 MPa, respectively, which were about three times than SD powders. The excellent mechanical properties of the former were found due to the precipitation of nanoscale σ phase and M23C6 intermetallic resulted from the MA treatment and sintering processing. Nanoscale σ and M23C6 phase can effectively strengthen the alloy not only by self-reinforcement but also through the grain boundaries of the refined grains induced by the precipitation.

Nanocrystalline Formation and Magnetic Properties in Fe₂O₃-C System by Mechanical Alloying.

The effect of mechanical alloying (MA) on the solid state reaction of hematite and graphite system with a positive reaction heat was investigated using a mixture of elemental Fe₂O₃-C powders. The solid state reduction of hematite to Fe₃O₄ has been obviously observed after 3 hours of MA by a vibrating ball mill. A two-phase mixture of Fe₃O₄ and remaining Fe₂O₃ is obtained after 5 hours of MA. Saturation magnetization gradually increases with MA time due to the formation of Fe₃O4 and then reaches 23 emu/g after 5 hours of MA. In addition, a Fe₃O₄ single phase is obtained by MA after 3 hours and subsequently heat treated up to 700°C. X-ray diffraction result shows that the average grain size of Fe₃O₄ prepared by MA for 5 hours and heat treatment to be in the range of 92 nm. The saturation magnetization of Fe₃O₄ prepared by MA and heat treatment reaches a maximum value of 56 emu/g for 5 hours MA sample. It is also observed that the coercivity of 5 hours MA sample annealed at 700 °C is still high value of 113 Oe, suggesting that the grain growth of magnetite phase during annealing process tends to be suppressed.

Electrochemical Performance of Nickel Silicide Electrodes for Lithium-Ion Batteries in an Ionic-Liquid Electrolyte

Developing lithium-ion batteries (LIBs) with a high energy density, long cycle, and high safety is essential for establishing a sustainable society because LIBs are used as electric vehicle batteries and stationary batteries for utilizing renewables. Silicon (Si) has great potential as an anode active material for next-generation LIBs due to its high theoretical capacity (3580 mA h g- 1 for Li15Si4). However, Si electrodes show poor cycle stability, which is mainly caused by a large volume change in Si during the lithiation (charge) and delithiation (discharge) reactions. Additionally, Si has other disadvantages, such as high electrical resistivity and a low Li+ diffusion coefficient. We have previously investigated the lithiation and delithiation properties of pure binary silicide (M ySiz, M : transition metal) electrodes. Some electrodes maintained a high reversible capacity in an ionic-liquid electrolyte, whereas they showed a poor cycling performance in a conventional organic-liquid electrolyte. In contrast, the effect of difference in crystal phase of silicides composed of the same elements on the lithiation and delithiation properties has not yet been clarified. Herein, we synthesized various pure nickel silicide (Ni-Si) powders. and investigated their lithiation and delithiation properties in an ionic-liquid electrolyte. Ni-Si powders (NiSi2, NiSi, Ni2Si, and Ni3Si) were synthesized by a mechanical alloying (MA) method. The obtained powders were characterized by X-ray diffraction (XRD) and Raman spectroscopy. XRD patterns were identified compared with patterns in the Inorganic Crystal Structure Database (ICSD). Each silicide electrode was prepared by a gas deposition (GD) method, which does not require a binder or conductive agent. We assembled 2032-type coin cells, which consisted of the silicide electrode as the working electrode, Li metal foil as the counter electrode and a glass fiber filter as the separator. 1 mol dm- 3 (M) lithium bis(fluorosulfonyl)amide (LiFSA) in N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)amide (Py13-FSA) was used as an ionic-liquid electrolyte. A galvanostatic charge-discharge test was carried out in the potential range between 0.005 and 2.000 V vs. Li+/Li at 303 K. The current density was set at 50 mA g- 1. To discuss the charge density of each element in Li x Ni y Si z , a first-principle calculation based on density functional theory (DFT) was performed using the projector augmented wave (PAW) method as implemented in the plane wave code of the Vienna Ab initio Simulation Package (VASP). A generalized gradient approximation (GGA) was used as the term exchange correlation with a kinetic cutoff of 350 eV. Brillouin zone sampling was performed with an 8×8×8 k point mesh within a Gamma point centered mesh scheme. We synthesized various Ni-Si powders by a MA method. Comparing the XRD pattern of the prepared samples and the corresponding ICSD pattern, all peaks were assigned to pure Ni-Si phase. Additionally, there were no peaks arising from the raw materials (Ni and Si). In Raman spectra, peaks assigned to crystalline Si (c-Si) and amorphous Si (a-Si) appear at approximately 520 and 490 cm- 1, respectively. Each silicide also gives no Raman peaks of c-Si and/or a-Si which indicates that neither c-Si nor a-Si is included in the synthesized powders. Therefore, the MA treatment successfully produced a pure Ni-Si phase. Fig.1 shows the dependence of the gravimetric discharge capacity of various nickel silicide electrodes on the cycle number in 1 M LiFSA/Py13-FSA.The NiSi2 electrode exhibited the highest initial capacity of approximately 800 mA h g- 1, and the Ni3Si electrode showed the second highest capacity. The results demonstrated that there was no correlation between initial capacity and silicon content in Ni-Si. To reveal the difference in the initial capacity, we determined the charge density of each element in Li x Ni y Si z based on computational chemistry. Li and Si have positive charges in all silicides, whereas Ni has a negative charge in Li x Ni y Si z . These results indicate that Li has a high affinity with Ni in Li x Ni y Si z . In addition, it is suggested that the higher the affinity of Ni with Li is, the higher the initial capacity is. Furthermore, we investigated the distance between Li and close atoms (Ni or Si) in Li x Ni y Si z . The initial capacity increased with an increase in the distance. Therefore, both the affinity of Ni with Li and the distance between Li and neighboring atom should influence on the initial capacity. Figure 1

Preparation and Structural Observation of Co₂MnSi Heusler Alloys by Mechanical Alloying.

A Co₂MnSi Heusler alloy has been prepared by mechanical alloying (MA) method successfully using a mixture of elemental Co50Mn25Si25 powders. A two-phase mixture of amorphous phase and remaining Mn were obtained after 5 hours of MA without any evidence for the formation of Co₂MnSi alloys. The saturation magnetization of MA powders decreased with MA time due to the magnetic dilution by alloying with nonmagnetic Mn and Si elements to 48 emu/g after 5 hours of MA. On the other hand, a Co₂MnSi single phase was obtained by MA after 3 hours and subsequently heat treated up to 650 °C. X-ray diffraction result showed that the average grain size of Co₂MnSi Heusler alloys prepared by MA for 5 hours and heat treatment to be in the range of 85 nm. The saturation magnetization of Co₂MnSi Heusler alloys prepared by MA and heat treatment reached a maximum value of 112 emu/g for 5 hours MA sample. It was also observed that the coercivity of 5 hours MA sample annealed at 650 °C was fairly low value of 27 Oe.

Effects of Zr and chopped C fiber on microstructure and mechanical properties of SiBCN ceramics

To further improve the thermal shock resistance and ablation resistance of SiBCN system ceramics targeted much harsh environment, both ultra-high temperature ceramic phases and carbon fibers are expected to be incorporated simultaneously as the reinforcements. However, tough problems like difficulty in densification as well as degradation of C fibers (Cf) due to interfacial reaction usually cannot be avoided. Thus, in this study, Zr as well as chopped Cf with BN coating were introduced into SiBCN ceramics by mechanical alloying and after hot-pressing sintering to prepare C/SiBCNZr composites. The structure and phase component development have been characterized in detail by XRD, SEM, TEM and XPS etc., and mechanical properties, fracture behavior and toughening mechanisms were also investigated. Zr-B and Zr-O bonds are detected besides Si-C, N-B and N-B-C bonds when pre-alloyed ZrB2 amorphous powder was incorporated into SiBCN system by further mechanical-alloying treatment. After hot-pressing, the ultra-high temperature phases of ZrB2 and ZrN were formed as expected besides the original matrix phases of BN(C) and SiC. Excellent mechanical properties can be obtained for SiBCNZr ceramic. The BN coating on carbon fibers successfully avoids the severe fiber degradation and makes it possible for moderating strong interface bonding, which ensuring the debonding, crack deflection, fiber pulling-out and bridging during the fracture. As a result, the C/SiBCNZr composites retain good mechanical properties and fractures in a pseudoplastic fracture manner, showing better potential applications in harsh environments. Optimization of the BN coating on Cf and Zr incorporation by pre-mechanical alloying can be a good route to achieve Cf/SiBCNZr composites with a better balance between thermal shock resistance, ablation resistance and mechanical properties.

Preparation of Cl doped SnO powder with excellent photocatalytic property by mechanical alloying

Cl-doped SnO photocatalysts were synthesized by mechanical alloying (MA) from SnCl2 and NH4HCO3. The effects of MA time on the structural characterization and photocatalytic activity of SnO powders were studied. Cl-doped SnO nanoparticles can be obtained by MA treatment after 1 h, but MA time considerably affected the crystalline size, microstrain, and photocatalytic properties of the samples. The crystalline size and specific surface area of the SnO samples gradually decreased and their microstrain increased with prolonged MA time. The peak intensity of the photoluminescence spectra of the Cl-doped SnO samples remarkably increased with prolonged MA time. Moreover, the MA samples had good photocatalytic properties. The photodegradation rate of methyl orange dye in 30 min over Cl-doped SnO nanoparticles obtained by MA for 2, 4, and 8 h was approximately 99%. Aging treatment of the SnO samples remarkably affected their phase composition, which can enhance the transformation of SnO to SnO2. The SnO2 transformation degree significantly increased with prolonged MA time through aging treatment, which also slightly deteriorated the degradation efficiency of the samples.

TiO2 coating prepared by mechanical alloying treatment for photocatalytic degradation

ABSTRACTIn this study, a nanostructured TiO2 coating was successfully prepared on a large-scale titanium plate by a simple one-step surface mechanical alloying (SMA) treatment. The coating was characterised to determine the morphological and composition changes with SMA. The coating was ∼60 μm thick and composed of 5 nm diameter rutile TiO2 particles. The photocatalytic activity of the nanostructured TiO2 coating was studied via the ultraviolet–visible (UV–vis) decolorisation of aqueous rhodamine-B. The results showed that the photocatalytic degradation effect in 5 h of the φ30 mm nanostructured TiO2 coating was comparable to that of 20 mg raw TiO2 under similar UV–visible light irradiation. One-step SMA was demonstrated as an appropriate method to produce a high-performance photocatalytic plate.

Experimental Verification of the Decomposition of Y2O3 in Fe-Based ODS Alloys During Mechanical Alloying Process

In this study, we investigated the state of Y2O3, as a major additive element in Fe-based ODS alloys, during mechanical alloying (MA) processes by thermodynamic approaches and experimental verification. For this purpose, we introduced Ti2O3 that formed different reaction products depending on the state of Y2O3 into the Fe-based ODS alloys. In addition, the reaction products of Ti2O3, Y, and Y2O3 powders were predicted approximately based on their formation enthalpy. The experimental results relating to the formation of Y-based complex oxides revealed that YTiO3 and Y2Ti2O7 were formed when Ti2O3 reacted with Y; in contrast, only Y2Ti2O7 was detected during the reaction between Ti2O3 and Y2O3. In the alloy of Fe–Cr–Y2O3 with Ti2O3, YTiO3 (formed by the reaction of Ti2O3 with Y) was detected after the MA and heat treatment processes were complete, even though Y2O3 was present in the system. Using these results, it was proved that Y2O3 decomposed into monoatomic Y and O during the MA process.

Rapid production of Iron Disilicide thermoelectric material by Hot Press Sintering Route

In present research work, a method has been established through powder metallurgical route to produce β-FeSi2 thermoelectric material without giving long time mechanical alloying treatment to the elemental powders and long duration heat treatment cycle. The elemental powders of iron (98.9% purity, 200 mesh) and silicon (98.5% purity, 400 mesh) have been mechanically alloyed for 6h using high-energy Attritor ball-mill and was subjected to Hot Press Sintering (HPS). Effect of HPS parameters on density of compacts was studied. The compacts with higher densities (82–92% relative density) were later on subjected to the thermal cycling treatment. The density as well as the amount of β-FeSi2 phase formation got enhanced due to thermal cycling treatment.

Lithium Storage Property of MoS<sub>2</sub> with Mechanical Alloying Treatment

MoS2 is a candidate for new generation lithium ion battery anode. In this paper, two groups of materials, pure MoS2 and MoS2/graphite composite, were treated by mechanical alloying (MA). The results showed that MA treatment did not change the phase structure of MoS2, but MA will reduce the particle size of MoS2. For MoS2/graphite composite, MA makes graphite distributing homogeneous on the surface of MoS2. After MA, MoS2 keeps the character of 100% columbic efficiency during charging and discharging process. With the increase in cycle number, capacity of MoS2 decays. MA treatment on MoS2 accelerates the decay of capacity. The addition of graphite in MoS2 reduces the harmful effect of MA treatment on cycling property.

Fabrication of Ti–Cu–Al coatings with amorphous microstructure on Ti–6Al–4 V alloy substrate via high-energy mechanical alloying method

A high-energy planetary ball mill was applied to fabricate Ti–Cu–Al coating on Ti–6Al–4V alloy substrate. The microstructure and elemental and phase composition of coatings were studied. The surface SEM images showed that the rough but densified coating surfaces, the cross-section microstructures as well as the related EDS line scan results illustrated different structures in the coatings, and the XRD results as well as TEM and corresponding SEAD pattern provided evidences of the existence of amorphous phase in the coatings. Mechanical properties including microhardness and friction and wear behavior were tested respectively. The microhardness testing results indicated that the fabricated coatings could largely strengthen the substrate surface. And the friction and wear resistance were tested with a ball-on-block sliding configuration, with the testing results showing decrease in both friction coefficients and wear weight loss after mechanical alloying treatment. The analysis and testing results also showed that a proper increase in the applied milling time favored the improvement in the thickness, surface smoothness, densification level, microstructural and chemical homogeneity as well as amorphization degree of the deposited coating. On the basis of two significant action mechanisms associated with a planetary ball mill, a reasonable mechanism was presented for the formation of amorphous phase contained coatings on Ti–6Al–4V alloy substrate.

Formation of Intermetallic Ni-Al Coatings by Mechanical Alloying with Different Intensities

Intermetallic Ni-Al coatings on the Ni substrate were prepared by the mechanical alloying (MA) method in mechanical activators of vibratory and planetary type. It was found that coatings that were fabricated in a high-energy (planetary) activator in comparison with those fabricated in a low-energy (vibratory) activator are more homogeneous, have higher density, and experience better adhesion to the substrate. It was shown that different intermetallic phases (NiAl, NiAl3, and Ni2Al3) can form directly during the MA treatment in the planetary activator.

Structural evolutions of the Fe–40Al–5Cr powders during mechanical alloying and subsequent heat treatment

Nanocrystalline Fe–40Al–5Cr powders were synthesized by mechanical alloying (MA) of the Fe, Al elemental powders and the Fe–20Cr prealloyed powders. Structural evolutions, morphologies, composition homogenization and ordering transformation of the Fe–40Al–5Cr powders during MA and subsequently heat treatment were studied. In the early stage of MA (<15 h), solid solutions of Fe(Al) and Fe–Cr(Al) form through Al diffusing into Fe and Fe–20Cr, respectively. Layered Fe(Al)/Fe–Cr(Al) laminae are the typical structure of the milled powders. On prolonging the milling time from 15 to 70 h, the layered laminae disappear, and the milled powders turn to be dense, fine and spherical. Meanwhile, the composition homogenization of the milled powders is also gradually accomplished. After the Fe–40Al–5Cr powders milled for 70 h, nanocrystalline Fe(Al, Cr) powders form with a homogeneous composition. During heating the milled powders from room temperature to 600 °C, the ordering transformation from Fe(Al, Cr) to B2-FeAl(Cr) occurs. The Cr content in the Fe–40Al–5Cr powders was found to hinder the composition homogenization and ordering transformation of the powders during MA and subsequent heat treatment.

Fabrication of Ultra-Fine Grained Hot Work Tool Steels by Powder Metallurgy Process through Mechanical Alloying Treatment

Hot work tool steels generally consist of the tempered martensitic structure and they are high strength materials using all strengthening mechanisms, such as strain strengthening, grain refinement strengthening, solid solution strengthening and precipitation strengthening. It is necessary to use the grain refinement strengthening that can bring both higher strength at high temperature and toughness than those of conventional steels. In this study, hot work tool steels with ultra-fine grained structure were fabricated by the mechanical alloying treatment. The powder mixture of atomized AISI H13 steel powders and Y2O3 powders was mechanically alloyed by a planetary ball mill for 360ks. The mechanically alloyed powders were packed in a stainless steel tube in a vacuum and then consolidated by hot rolling for full densification. The consolidated material was austenitized at 1293K, which was general austenitizing temperature of H13 steel, and then oil-quenched. Through this process, an ultra-fine grained H13 steel with equiaxed grains of about 0.3 microns in diameter could be obtained. A quenched hardness of the developed steel was comparable to that of an AISI M2 high speed steel produced by melting and hot-working process. Furthermore, although tempered hardness of the M2 steel decreases with increasing tempering temperature of 848K or higher, that of the developed steel does not decrease so much. Therefore the hardness of the developed steel exceeds that of the M2 steel at tempering temperatures over 923K.

기계적 합금화법에 의한 실리콘계 복합물질의 전지전극특성

A Si-CuO-graphite composite was prepared by a mechanical alloying (MA) method. The Si-CuO composite has a mixture structure, where CuO is homogeneously dispersed in Si. Also, and phases were formed during MA and heat treatment. Graphite with the Si-CuO composite was mixed in the same mill for 30 minutes with weight ratio of Si-CuO composite and graphite as 1:1. The Si-CuO composite was homogeneously covered with graphite. SiC phase was not formed. Electrochemical tests of the composite have been investigated, and the first charge and discharge capacities of the material were about 870mAh/g and 660mAh/g, respectively. Those values are about 76% of the first cycle efficiency. The cycle life of the composite showed that the initial discharge capacity of 660 mAh/g could be maintained up to 92% after 20 cycles.

Effect of alloying time on fabrication of Ti3Si(Al)C2 by spark plasma sintering

3Ti–Si–2C–0·2Al mixture powders were used to fabricate high purity Ti3SiC2 ceramic through mechanical alloying (MA) and spark plasma sintering (SPS). The effect of ball milling time on the fabrication of Ti3SiC2 by SPS was also investigated. The results showed that the mixed powders were obviously refined after the MA of 5 h. After milling of 10 h, the mixed powders containing TiC, Ti3SiC2 were synthesised by a mechanically induced self-propagating reaction. After further milling to 20 h, the yield powders were refined. Ball milling time had a remarkable effect on SPS fabrication of Ti3SiC2. A shorter milling time of 5 h only helped to increase the Ti3SiC2 content in the sintered bulk. The samples subjected to the MA treatment of 20 h had a fine and dense organisation. Ball milling of 10 h was most beneficial for fabricating dense and high purity Ti3SiC2. Ti3SiC2 bulk with a purity of 96 wt-% was obtained by MA for 10 h and subsequent SPS at 850°C. When sintered at 1100°C, Ti3SiC2 bulk with a purity of 99·3 wt-% and a relative density of 98·9% was obtained.

Formation of Hydroxyapatite Coating by Mechanical Alloying Method

Hydroxyapatite [Ca10(PO4)6(OH)2 − HA] material has been clinically applied in many areas of dentistry and orthopaedics. Presented work describes the effect of mechanical alloying treatment, as a non-conventional solid-state process, on the microstructure of hydroxylapatite powder and Ti-alloy substrate. The relationship between the crystallinity, crystallite size and strain of the HA with milling factors was investigated. Milled HA powders and Ti-substrate were characterized by X-Ray Diffraction (XRD) and/or scanning probe microscope (SPM) using atomic force microscopy (AFM). Increasing the ratio of the weight of the ball to the powder (Wb:Wp) ratio and milling time accelerates the broadening and intensity reduction of XRD peaks. There was no evidence that milling time up to 2 hrs or Wb:Wp can change chemical composition of the HA. Decomposition of HA phase or secondary phases such as α and/or β-tri-calcium phosphate (α, β − TCP), and calcium oxide (CaO) was not observed throughout the milling process. The average grain size and the internal strain are calculated from the XRD by Scherrer's formula and Hall–Williamson method. The Ti doped HA samples shows a notable broadening and intensity reduction comparing with HA powders before and after milling.

Microstructure of fine-grained β-type titanium alloy produced by mechanical alloying and consolidation process

The mechanical alloying (MA) treatment was applied to the mixed powder of titanium and iron with average composition of Ti–15 mass%Fe. Heptane was also used for the MA treatment as a source of carbon. The MA treatment resulted in the production of alloyed powder in which all constituents were fully dissolved in the solid solution. By the consolidation of the MA-treated powder (hot rolling at 1073 K), a bulk material of β-type titanium alloy with fine-grained structure was successfully obtained. As a result of TEM observation, it was found that the TiC particles with a size of 200 nm were dispersed within the β-Ti matrix structure. The mean grain size of β-Ti was measured at around 1–2 μm. Although the fine-grained β-type titanium alloy produced by the MA treatment and consolidation process has very high hardness, it was also found that a significant amount of metastable coarse metallic compounds, Ti 2Fe, existed in the material, leading to the deterioration of ductility of the consolidated material.

Al-4at.%Zr합금의 기계적합금화 공정과 열처리과정에서 발생하는 상변화거동

Four different mechanical alloying(MA) processes were employed to fabricate very fine intermetallic compound <TEX>$Al_3Zr$</TEX> particles dispersed Al composite materials(MMC) with Al-4at.%Zr composition. Phase transformations including phase stability during MA and heat treatment processes were investigated. Part of Zr atoms were dissolved into Al matrix and part of them reacted with hydrogen produced by decomposition of PCA(methanol) to form hydride <TEX>$ZrH_2$</TEX> during first MA process. These <TEX>$ZrH_2$</TEX> hydrides disappeared when alloy powders were heat treated at <TEX>$500^{\circC}$</TEX>. Stable <TEX>$Al_3Zr$</TEX> dispersoids with <TEX>$DO_23$</TEX> structure were formed by heat treating the mechanically alloyed powders at <TEX>$400^{\circC}$</TEX>. On the other hand, metastable <TEX>$Al_3Zr$</TEX>dispersoids with <TEX>$L1_2$</TEX> structure were formed during first MA of powers with Al-25at.%Zr composition. These metastable <TEX>$Al_3Zr$</TEX> dispersoids transformed to stable <TEX>$Al_3Zr$</TEX> with <TEX>$DO_23$</TEX> structure when heat treated above <TEX>$450^{\circC}$</TEX>.

メカニカルアローイング法による高窒素添加ステンレス鋼の作製と局部腐食特性評価

High nitrogen containing stainless steel was prepared by mechanical alloying (MA) method from SUS 447 powder. The SUS 447 powder was ball-milled at N2 atmosphere and then HIP treatment was carried out. The obtained stainless steels were examined by X-ray diffraction (XRD) and scanning electron microscope (SEM). With the increase in the time of MA treatment, dissolved nitrogen content of the stainless steel was increased, and ferrite phase changed into austenite phase. The evaluation of corrosion behavior was carried out by the electrochemical corrosion test. For the stainless steel with MA treatment without nitrogen, it was found that the pitting potential in sulfuric acid solution including the chloride was very noble. And clear pitting corrosion was not observed for the stainless steel with MA treatment with nitrogen. The results of electrochemical corrosion test indicated that localized corrosion was suppressed by the MA treatment.