Characterization of MCrAlY/nano-Al_(2)O_(3) nanocomposite powder produced by high-energy mechanical milling as feedstock for high-velocity oxygen fuel spraying deposition

Al_(2)O_(3) nanoparticles and MCrAlY/nano-Al_(2)O_(3) nanocomposite powder(M=Ni,Co,or NiCo)were produced using high-energy ball milling.The MCrAlY/nano-Al_(2)O_(3) coating was deposited by selecting an optimum nanocomposite powder as feedstock for high-velocity oxy-gen fuel thermal spraying.The morphological and microstructural examinations of the Al_(2)O_(3) nanoparticles and the commercial MCrAlY and MCrAlY/nano-Al_(2)O_(3) nanocomposite powders were investigated using X-ray diffraction analysis,field-emission scanning electron microscopy coupled with electron dispersed spectroscopy,and transmission electron microscopy.The structural investigations and Williamson-Hall res-ults demonstrated that the ball-milled Al_(2)O_(3) powder after 48 h has the smallest crystallite size and the highest amount of lattice strain among the as-received and ball-milled Al_(2)O_(3) owing to its optimal nanocrystalline structure.In the case of developing MCrAlY/nano-Al_(2)O_(3) nanocompos-ite powder,the particle size of the nanocomposite powders decreased with increasing mechanical-milling duration of the powder mixture.

Reactive Milling and Mechanical Properties of NiAl Composite with HfC Dispersoids

A NiAI-based composite with HfB2 dispersed particles has been synthesized by mechanical alloying of Ni, Al, Hf and C powders. The formation mechanism of NiAI-HfC during milling can be attributed to two chemical reactions: Ni+AI→NiAI+△H; Hf+C→HfC+△H, induced by mechanical collision in a certain period of time, which results in an abrupt exothemic reaction. Hot pressing (HP) and hot isostatic pressing (HIP) have been used to make the NiAI-10HfC compacts near fully dense. Compressive testing from room temperature to 1000℃ indicated that the yield stress of NiAI-10HfC composite is 3-4 times higher than that of cast NiAl and correspond to the MA NiAI-10TiB2 composite. In the meantime, yield strength at high temperature is dependent on strain rate, and deformation is controlled by diffusion mechanism.

Hydrogen storage behavior of nanocrystalline and amorphous La-Mg-Ni-based LaMg_(12)-type alloys synthesized by mechanical milling

Nanocrystalline and amorphous LaMg11Ni+x%Ni(x=100,200,mass fraction)alloys were synthesized by mechanicalmilling.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 scanningcalorimeter(DSC)connected with a H2detector.The results indicated that increasing Ni content significantly improves the gaseousand electrochemical hydrogen storage performances of the as-milled alloys.The gaseous hydrogen absorption capacities andabsorption rates of the as-milled alloys have the maximum values with the variation of the milling time.But the hydrogen desorptionkinetics of the alloys always increases with the extending of milling time.In addition,the electrochemical discharge capacity andhigh rate discharge(HRD)ability of the as-milled alloys both increase first and then decrease with milling time prolonging.

Mechanical and wear properties of Al-Al_3Mg_2 nanocomposites prepared by mechanical milling and hot pressing

β-A13Mg2 intermetallic was used as a reinforcing agent to improve the mechanical properties of an aluminum matrix. Different amounts of A13Mg2 nanoparticles （ranging from 0wt% to 20wt%） were milled with aluminum powders in a planetary ball mill for 10 h. Consolidation was conducted by uniaxial pressing at 400β under a pressure of 600 MPa for 2 h. Microstructural characterization confirms the uniform distribution of A13Mg2 nanoparticles within the matrix. The effects of nano-sized A13Mg2 content on the wear and mechanical properties of the composites were also investigated. The results show that as the A13Mg2 content increases to higher levels, the hardness, compressive strength, and wear resistance of the nanocomposites increase significantly, whereas the relative density and ductility decrease. Scanning electron microscopy （SEM） analysis of worn surfaces reveals that a transition in wear mechanisms occurs from delamination to abrasive wear by the addition of A13Mg2 nanoparticles to the matrix.

Structural characterization of AA 2024-MoSi_2 nanocomposite powders produced by mechanical milling

Nano-sized MoSi2 powder was produced successfully from commercially available MoSi2 by a mechanical milling process carried out for 100 h, and mechanical alloying was employed to synthesize AA 2024-MoSi2 nanocomposites, The effects of MoSi2 reinforcement and mechanical milling on the structure, morphology, and iron contamination of the produced materials were investigated using X-ray diffraction, scanning electron microscopy, and atomic absorption spectrometry. It is revealed that the morphology of the aluminum alloy changes continuously during milling from spherical to plate-like, irregular, and finally equiaxed. The presence of MoSi2 reinforcement accelerates the milling process and results in a smaller average particle size. The Williamson-Hall method determined that the crystallite size of the aluminum alloy in the composite powder is smaller than that of the unreinforced alloy at the same milling time and this size reaches 45 nm after 16 h milling time. The Fe contamination content is higher for the nanocomposite in comparison with the unreinforced alloy because of the wearing role of MoSi2 hard particles.

METASTABLE STATE TRANSFOR MATIONS OF Al_3Ti BASE ALLOYS DURING MECHANICAL MILLING AND SUBSEQUENT ANNEALING

Developing multi phase alloy is an effective approach for the strengthening and toughening of the L1 2 Al 3Ti alloy. A Nb modified Al 3Ti base alloy which has a L1 2 matrix and the precipitated second phase has been developed. Since the effect of second phase is strongly influenced by its size and distribution, high energy ball milling was employed to fabricate the alloy in comparison with the conventional casting process. It was found that structure evolution during mechanical milling is different for DO 22 , L1 2 and L1 2+DO 22 two phase alloys. The DO 22 Al 3Ti transformed only to a FCC structure even after long time milling. The ordering of L1 2 Al 67 Ti 25 Mn 8 decreased quickly and changed into a FCC structure after short time milling, subsequent milling led to the amorphous transition. The DO 22 phase in Al 3Ti Mn Nb alloys dissolved into the L1 2 matrix quickly in the early stage of milling and the matrix changed into a FCC supersaturated solid solution after 10 h milling, further milling led to the amorphous transition. Reordering of the metastable structures occurred during the annealing process. The consolidated materials consisting of fine equiaxed grains with dispersed particles exhibited remarkable improvement of strength and promising ductility.

Influence of Mechanical Milling on Photocatalytic Activity of g-C_3N_4 Prepared by Heating Melamine

Using X-ray diffraction,transmission electron microscopy,Brunauer-Emmett-Teller surface area measurement,ultraviolet-visible diffuse reflection spectra,and photoluminescence spectroscopy,the effect of mechanical milling on the photocatalytic activity of g-C3N4 photocatalyst was investigated.The rhodamine B,as a photodegrading goal,was used to evaluate the photocatalytic activity of g-C3N4.The experimental results indicate that the milling treatment is an effective method to improve the photocatalytic activity of g-C3N4.The enhanced photocatalytic activity was attributed to the improvement in catalyst＇s surface area and dye adsorption on catalyst surface.Moreover,checking the luminescence properties of g-C3N4,it is found that the photocatalytic active sites on g-C3N4 are likely the same as luminescence sites.

Study on Nano-structured WC-Co Composite Powders Made by Mechanical Milling

Nano structured WC Co composite powders were prepared by high energy mechanical milling. The microstructure of as milled WC Co composite powders (including grain size, lattice strain, Co distribution and lattice defects) was investigated by X ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and energy dispersive X ray spectroscopy (EDS). Nano structured WC co vered and separated by cobalt thin layers with average grain size less than 10 nm was obtained by high energy mechanical milling. The morphology of WC grains is almost spherical. High energy mechanical milling could also bring about a large number of lattice defects in WC grains.

Influence of chloride salts on hydrogen generation via hydrolysis of MgH_2 prepared by hydriding combustion synthesis and mechanical milling

The effects of chloride salts(NaCl,MgCl2and NH4Cl)on the hydrolysis kinetics of MgH2prepared by hydridingcombustion synthesis and mechanical milling(HCS+MM)were discussed.X-ray diffraction(XRD)analyses show that high-purityMgH2was successfully prepared by HCS.Hydrolysis performance test results indicate that the chloride salt added during the millingprocess is favorable to the initial reaction rate and hydrogen generation yield within60min.A MgH2?10%NH4Cl composite exhibitsthe best performance with the hydrogen generation yield of1311mL/g and a conversion rate of85.69%in60min at roomtemperature.It is suggested that the chloride salts not only play as grinding aids in the milling process,but also create fresh surface ofreactive materials,favoring the hydrolysis reaction.

Effects of the deep rolling process on the surface roughness and properties of an Al-3vol%SiC nanoparticle nanocomposite fabricated by mechanical milling and hot extrusion

Deep rolling is one of the most widely used surface mechanical treatments among several methods used to generate compressive residual stress. This process is usually used for axisymmetric components and can lead to improvements of the surface quality, dimensional accuracy, and mechanical properties. In this study, we deduced the appropriate deep rolling parameters for Al-3vol%Si C nanocomposite samples using roughness and microhardness measurements. The nanocomposite samples were fabricated using a combination of mechanical milling, cold pressing, and hot extrusion techniques. Density measurements indicated acceptable densification of the samples, with no porosity. The results of tensile tests showed that the samples are sufficiently strong for the deep rolling process and also indicated near 50% improvement of tensile strength after incorporating Si C nanoparticle reinforcements. The effects of some important rolling parameters, including the penetration depth, rotation speed, feed rate, and the number of passes, on the surface quality and microhardness were also investigated. The results demonstrated that decreasing the feed rate and increasing the number of passes can lead to greater surface hardness and lower surface roughness.

EFFECT OF MILLING INTENSITY ON STRUCTURAL CHANGES OF MIXED Al－Fe－Ni POWDERS IN MECHANICAL ALLOYING PROCESS

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Microstructure and Mechanical Property of 2024 Aluminium Alloy Prepared by Rapid Solidification and Mechanical Milling

Rapidly solidified 2024 aluminium alloy powders were mechanically milled, then consolidated to bulk form. The microstructural changes of the powders in mechanical milling (MM) and consolidation process were characterized by X-ray diffraction analyses and transmission electron microscopy observations. The results showed that mechanical milling reduced the grain size to nanometer, dissolved the Al2Cu intermetallic compound into the aluminium matrix and produced an aluminium supersaturated solid solution. During consolidation process. the grain size increased to submicrometer, and the Al2Cu and Al2(Cu, Mg, Si, Fe, Mn) compounds precipitated owing to heating. Increasing consolidation temperature and time results in obvious grain growth and coarsening of second phase particles. The tensile yield strength of the consolidated alloy with submicrometer size grains increases with decreasing grain size, and it follows the famous HallPetch relation

Electrochemical Hydrogen Storage Performance of the Nanocrystalline and Amorphous Pr-Mg-Ni-based Alloys Synthesized by Mechanical Milling

The PrMg12-type composite alloy of PrMg_(11)Ni + x wt% Ni (x=100,200) with an amorphous and nanocrystalline microstructure were synthesized through the mechanical milling.Effects of milling duration and Ni content on the microstructures and electrochemical hydrogen storage performances of the ball-milled alloys were methodically studied.The ball-milled alloys obtain the optimum discharge capacities at the first cycle.Increasing Ni content dramatically enhances the electrochemical property of alloys.Milling time varying may obviously impact the electrochemical performance of these alloys.The discharge capacities show a significant upward trend with milling duration prolonging,but milling for a longer time more than 40 h induces a slight decrease in the discharge capacity of the x=200 alloy.As milling duration increases,the cycle stability clearly lowers,while it first declines and then augments under the same condition for the x=200 alloy.The high-rate discharge abilities of the ball-milled alloys show the optimum values with milling time varying.

Gaseous hydrogen storage thermodynamics and kinetics of RE-Mg-Ni-based alloys prepared by mechanical milling

Nanocrystalline/amorphous La Mg11Ni+x Ni(x=100%, 200%, mass fraction) composite hydrogen storage alloys were synthesized by ball milling technology. The effects of Ni content and milling time on the gaseous hydrogen storage thermodynamics and dynamics of the alloys were systematically investigated. The hydrogen desorption properties were studied by Sievert's apparatus and a differential scanning calorimeter(DSC) connected with a H2 detector. The thermodynamic parameters(ΔH and ΔS) for the hydrogen absorption and desorption of the alloys were calculated by Van't Hoff equation. The hydrogen desorption activation energy of the alloy hydride was estimated using Arrhenius and Kissinger methods. The results indicate that a variation in the Ni content has a slight effect on the thermodynamic properties of the alloys, but it significantly improves their absorption and desorption kinetics performances. Furthermore, varying milling time clearly affects the hydrogen storage properties of the alloys. All the as-milled alloys show so fast hydrogen absorption rate that the absorbed amount in 10 min reaches to at least more than 95% of the saturated hydrogen absorption capacity. Moreover, the improvement of the gaseous hydrogen storage kinetics of the alloys is found to be ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and prolong milling time.

An Investigation on Hydrogen Storage Kinetics of the Nanocrystalline and Amorphous LaMg12-type Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous LaMg_（12）-type LaMg_（11）Ni ＋ x wt% Ni（x = 100, 200） alloys were synthesized by mechanical milling. Effects of Ni content and milling time on the gaseous and electrochemical hydrogen storage kinetics of as-milled alloys were investigated systematically. The electrochemical hydrogen storage properties of the as-milled alloys were tested by an automatic galvanostatic system. And the gaseous hydrogen storage properties were investigated by Sievert apparatus and a differential scanning calorimeter（DSC） connected with a H_2 detector. Hydrogen desorption activation energy of alloy hydrides was estimated by using Arrhenius and Kissinger methods. It is found that the increase of Ni content significantly improves the gaseous and electrochemical hydrogen storage kinetic performances of as-milled alloys. Furthermore, as ball milling time changes, the maximum of both high rate discharge ability（HRD） and the gaseous hydriding rate of as-milled alloys can be obtained. But the hydrogen desorption kinetics of alloys always increases with the extending of milling time. Moreover, the improved gaseous hydrogen storage kinetics of alloys are ascribed to a decrease in the hydrogen desorption activation energy caused by increasing Ni content and milling time.

Multirange Fractals in Materials: Applications to Fracture and Mechanical Alloying under Ball Milling

A new model of multirange fractals is proposed to explain the experimental results observed on the fractal dimensions of the fractured surfaces in materials. A new explanation to the Williford's multifractal curve on the relationship of fractal dimension with fracture properties in materials has been given. It shows the importance of fractorizing out the effect of fractal structure from other physical causes and separating the appropriate range of scale from multirange fractals. Mechanical alloying process under ball milling as a non-equilibrium dynamical system has been also analyzed.

Mechanical wet-milling and subsequent consolidation of ultra-fine Al_2O_3-(ZrO_2+3%Y_2O_3) bioceramics by using high-frequency induction heat sintering

Alumina/zirconia composites were synthesized by wet-milling technique and rapid consolidation with high frequency induction heat sintering(HFIHS). The starting materials were a mixture of alumina micro-powder (80%, volume fraction) and 3YSZ nano-powders (20%). The mixtures were optimized for good sintering behaviors and mechanical properties. Nano-crystalline grains are obtained after 24 h milling. The nano-structured powder compacts are then processed to full density at different temperatures by HFIHS. Effects of temperature on the mechanical and microstructure properties were studied. Al2O3-3YSZ composites with higher mechanical properties and small grain size are successfully developed at relatively low temperatures through this technique.

Structures,properties and responses to heat treatment of deformation processed Cu-15%Cr composite powders prepared by mechanical milling

Cu-15%Cr composite powders were produced from elemental powders by mechanical milling technique. The structures, properties and thermal stability of the composite powders were characterized by scanning and transmission electron microscopy (SEM and TEM, respectively), electron probe microanalysis(EPMA), X-ray diffractometry and microhardness testing. The results show that powders are first flattened into thin discs at the initial stage of milling and then evolved into spheroid on further milling. Lamellar structure in powders is produced after intermediate milling. The Cr laminas degenerate into particles uniformizing in Cu matrix with excessive milling. The microhardness values and internal strain sharply increase with increasing milling time. Nano-sized Cu grains were found by TEM analysis. The microstructural observations suggested that the composite powders have high thermal stability and both spherodisation and thermal grooving contribute to the instability of Cr

HA/Ti composite for biomedical application by mechanical milling

In order to overcome the poor mechanical properties of HA and the low bioactivity of Ti, HA/Ti composites with various compositions were prepared by mechanical milling. The effects of milling condition and the composition on the microstructure, the density and the hardness of the composites were studied. The results show that during the ball milling process, Ti particles are refined and the homogeneity of the HA/Ti mixtures is improved; HA will partially decompose due to the existence of Ti and high sintering temperature. The microstructure of HA/Ti composites is highly dependent on the milling condition and the composition. In the microstructure, Ti phase connects to be a continuous network, and HA/Ti mixtures disperse in the network. The longer the milling time, the finer the network will be. The density of HA/Ti composites decreases with the content of HA increasing and the milling time prolonging, because HA deteriorates the sinterability of Ti.The hardness of HA/Ti composites increases firstly with the content of HA increasing, and then drops when the content of HA exceeds 30%. Addition of HA will strengthen the HA/Ti composite but will decrease the density of the composite, which accounts for the effect of HA on the hardness of the composites.

Mechanically activated disproportionation of NdFeB alloy by ball milling in hydrogen

Mechanically activated disproportionation of Nd 12 Fe 82 B 6 alloy by ball milling in hydrogen atmosphere was experimentally investigated. The aspects of thermodynamics and kinetics for the mechanically activated disproportionation of the NdFeB alloy were discussed. Both the evolution of the disproportionation reaction and the corresponding microstructure change of the alloy during milling were characterized by X ray diffraction (XRD) analysis. The results show that the matrix phase Nd 2Fe 14 B of the as cast Nd 12 Fe 82 B 6 alloy can be disproportionated into a mixture of Nd hydride (H 5Nd 2), FeB/Fe 2B, and α Fe, by ball milling under hydrogen pressure of 0.2 MPa. The as disproportionated phases are of the size about 20 nm, suggesting that ball milling in hydrogen is an effective route for low temperature disproportionation processing of the NdFeB alloy to ensure a full nano structured as disproportionated microstructure. This is the basis for synthesizing Nd 2Fe 14 B/ α Fe nano composites with magnetic exchange coupling effect by subsequent desorption recombination processing.