Role of Disclinations and Nanocrystalline State in the Formation of Quasicrystalline Phases on Mechanical Alloying of Cu-Fe Powders

Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of quasicrystalline phases were monitored using X-ray diffraction. Diffusion of Fe into the Cu matrix is proposed as the cause which triggers the instability of crystalline phases and leads to the formation of quasicrystalline phases after 10 h of milling. Milling for 100 h resulted in two different quasicrystalline phases with different lattice constants. Role of the nanocrystalline microstructure as an important criterion for the destabilisation of crystalline phases is explained. It is suggested that the formation of nanocrystalline microstructure and their subsequent transformation into quasicrystalline phases may be associated with a continuous increase in the disclination content of the system, which had formed as a result of continued milling and mechanical deformation.

Effects of Mechanical Alloying Parameters on the Microstructures of Nanocrystalline Cu-5 wt% Cr Alloy

Nanocrystalline Cu-5 wt%Cr alloy powders were fabricated by mechanical alloying （MA）, The effects of MA processing parameters on the crystallite size, solid solubility, and microstructures of the Cu- 5 wt%Cr alloys were investigated including type and size distribution of the grinding medium and ball-topowder weight ratio （BPR）. The results show that the crystallites were refined effectively and solid solubility of Cr in Cu was extended when heavier ball and higher BPR were adopted. The maximum solubility is extended up to 5.6 at% （namely 4.6 wt%） Cr in Cu by use of a combination of large and small size WC-Co balls with BPR of 30：1. A Cn-5 wt%Cr supersaturated solid solution alloy bulk is obtained by spark plasma sintering the as-milled powders at 900 ℃ for 5 min.

Preparation of an Nanocrystalline Ta-Cu Alloy by Mechanical Alloying

Nanocrystalline alloy wlth graln size of about 10～20nm was prepared by mechanlcal alloying of elemen- tal powders in an imnliscible Ta-Cu system, The structure changes of Ta_70Cu_30 during mechanical alloying were monitored by X-ray diffraction. scanning electron microscopy and transmission electron microscopy. High-energy ball milling can efficiently reduce the grain size and considerably increase the Cu solubility in Ta. The significant enhancement of hardness of alloyed powders was also observed.

ELECTRODE CHARACTERISTICS OF NANOCRYSTALLINE LaNi_5 PREPARED BY MECHANICAL ALLOYING

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Structural Characterization of Nanocrystalline Ni_(50-x)Ti₅₀Cu_x(X = 5, 9 wt%) Alloys Produced by Mechanical Alloying

Nanocrystalline Ni(50-x)Ti50Cux(X = 5, 9 wt%) alloys were successfully produced by mechanical alloying. Mechanical activation was performed at different milling times under a high purity argon (99.998 vol%) atmosphere. Phase analysis and structural features of the samples were examined by X-ray diffraction (XRD). Results revealed that NiTiCu (B2) phase was achieved after 600 min of milling. The formation of this phase was mostly related to the critical factors in determining the site replacement of elements in Ni-Ti-Cu ternary system. After 600 min of milling, the average crystallite size and lattice strain of the samples were about 5 - 10 nm and 1.057% - 1.967%, respectively. Evaluation of the full width at half maximum (FWHM) values for all the samples indicated the occurrence of anisotropic line broadening. The determined amounts of crystallinity revealed that the fraction of crystalline phase decreased with increasing weight percentage of copper up to 9% and reached a minimum value after 600 min of milling. The lattice parameters and the unit cell volume of the milled samples were always larger than the standard values. In addition, lattice parameter deviation influenced by the weight percentage of copper. Based on the obtained data, mechanical alloying process can be used for production of nanocrystalline NiTiCu alloys with different structural features.

Synthesis of TiB_2 nanocrystalline powder by mechanical alloying

TiB2 nanocrystalline powder was synthesized by mechanical alloying of Ti-67B elemental powder. X-ray diffraction(XRD) and transmission electron microscopy(TEM) were used to study the structural evolution of the powder during ball milling. The effects of heat treatment on the structural evolution and thermal stability of the mechanically alloyed(MAed) Ti-67B powder were also discussed. During ball milling the Ti-67B powder, a solid solution of B in Ti, Ti(B) is firstly formed. When the powder is milled for 10 h, the amorphous transition of Ti(B) from the crystalline to the amorphous phase occurs. When the powder is milled for 20 h, nanocrystalline TiB2 is formed from the amorphous Ti(B). When the powder is milled for 60 h, only TiB2 is detected with grain size of 10 nm. The formation of TiB2 nanocrystalline is controlled by the gradual diffusion reaction mechanism. During heat-treatment of the MAed Ti-67B powder, the structural changes of TiB2, including grain growth and lattice ordering degree increasing may occur.

Microstructure evolution in nanocrystalline Cu-Nb alloy during mechanical alloying

The microstructural evolution of nanocrystalline Cu-10%Nb(mass fraction) alloy during mechanical alloying(MA) was investigated by using X-ray diffraction,optical microscopy(OM),scanning electron microscopy(SEM) and transmission electron microscopy(TEM) observation. Upon milling of Cu-Nb powders with coarse grains,the grain size is found to decrease gradually with lengthening milling time,and reach the minimum value(about 9 nm) after 100 h milling. The microstrain and the microhardness of the powders increase during the grain refinement. And Cu lattice parameter increases steadily over 100 h milling. The mechanisms of solid solution extension during milling were discussed. The results show that up to 10%Nb can be brought into solid solution by MA. The extension of solid solution is found to relate closely with the formation of nanocrystalline.

Mechanically Driven Alloying and Structural Evolution of Nanocrystalline Fe_(60)Cu_(40) Powder

Highly supersaturated nanocrystalline fcc Fe60Cu40 alloy has been prepared by mechanical alloying of elemental powders. The phase transformation is monitored by X-ray diffraction (XRD),Mossbauer spectroscopy and extended X-ray absorption fine structure (EXAFS). The powder obtained after milling is of single fcc structure with grain size of nanometer order. The Mossbauer spectra of the milled powder can be fitted by two subspectra whose hyperfine magnetic fields are 16 MA/m and 20 MA/m while that of pure Fe disappeared. EXAFS results show that the radial structure function (RSF) of Fe K-edge changed drastically and finally became similar to that of reference Cu K-edge, while that of Cu K-edge nearly keeps unchanged in the process of milling. These imply that bcc Fe really transforms to fcc structure and alloying between Fe and Cu occurs truly on an atomic scale. EXAFS results indicate that iron atoms tend to segregate at the boundaries and Cu atoms are rich in the fcc lattice. Annealing experiments show that the Fe atoms at the interfaces are easy to cluster to α-Fe at a lower temperature, whereas the iron atoms in the lattice will form γ-Fe first at temperature above 350℃, and then transform to bcc Fe

Effect of mechanical alloying and sintering process on microstructure and mechanical properties of Al-Ni-Y-Co-La alloy

Al86Ni7Y4.5Co1La1.5 （mole fraction, %） alloy powder was produced by argon gas atomization process. After high-energy ball milling, the powder was consolidated by vacuum hot press sintering and spark plasma sintering （SPS） under different process conditions. The microstructure and morphology of the powder and consolidated bulk sample were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. It is shown that amorphous phase appears when ball milling time is more than 100 h, and the bulk sample consolidated by SPS can maintain amorphous/ nanocrystalline microstructure but has lower relative density. A compressive strength of 650 MPa of Al86Ni7Y4.5Co1La1.5 nanostructured samples is achieved by vacuum hot extrusion （VHE）.

Investigation of Nanostructured WC-Co Alloy Prepared by Mechanical Alloying

emented carbide of WCCo powder with crystalline size of about 10 nm was directly synthesized from elemental powders by mechanical alloying. Cold compacting was carried out at 800 Mpa using a manual uniaxial press. Sintering of the compacted samples was performed in vacuum in the temperature range of 1040～1350℃. The sintered density, crystallite size and microhardness of sintered samples were measured. The effects of a little VC addition on grain size, density and hardness of WCCo alloy were also presented.

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.

A Study about Fe-Ni Mechanical Alloying Process by Dry and Wet Method

The evolutions of microstructure of Fe0.85Ni0.15 products, which were prepared by mechanical alloying (MA) with and without process control agent (PCA), were studied using X-ray diffraction and scanning electron microscopy respectively. After MA without PCA (dry method) for 30h, Fe0.85Ni0.15 nanocrystalline alloy powders with bcc-Fe(Ni) phase were obtained; however, powders milled with PCA (wet method) from 20 to 90 h, were unalloyed Fe-Ni mixtures with balanced morphology. It seems that dry method works efficiently in nanocrystalline alloying while wet method postpones MA but functionally fines the morphology of materials. Finally, the results were discussed considering the MA kinetics.

Microstructure and Hydrogen Absorption Pro-perties of Mg/MmNi_(5-x) (CoAlMn)_x Composite Prepared by Mechanical Alloying

The microstructure ofthe Mg/MmNi5-x (CoAlMn )x composite hydrogen storage material preparedby the method of mechanical alloyingwas characterized by X-ray diffraction, SEM and particle size distribution analysis. By measuring PCTcurves, the hydrogen absorption properties of the composite was evaluated.The results show that nanocrystallinecomposite structure can be obtainedunder adequate ball milling condition. The reactive activation and hydrogen absorption capacity are improved compared with the sole MmNi5-x(CoAlMn)x alloy. The effect ofmagnesium on the microstructure andhydrogen absorption properties of thecomposite were also evaluated.

Effect of alloying elements on thermal stability of nanocrystalline Al alloys

The effect of incorporating limited-diffusivity elements such as Fe and Ti on thermal stability of the nanocrystalline Al alloy was investigated.Al−10wt.%Fe and Al−10wt.%Fe−5wt.%Ti alloys were fabricated.The initial mixtures of powders were milled for 100 h in vacuum.The bulk samples were fabricated from the milled powders in a high frequency induction heat sintering(HFIHS)system.The milled powders and the bulk sintered samples were characterized by X-ray diffraction(XRD),Vickers microhardness,field emission scanning electron microscopy(FESEM-EDS)and transmission electron microscopy(TEM).The observations indicated that Fe and Ti were completely dispersed in the matrix to form a supersaturated solid solution(SSSS)with Al.Additionally,the inclusion of alloying elements led to an increase in hardness and yield strength of the alloy by 127%and 152%,respectively.The elevated temperature compression tests were carried out to evaluate the thermal stability of the alloys.The Al−10wt.%Fe−5wt.%Ti alloy revealed the optimum thermally stable behavior of the three alloys studied.The incorporation of Fe and Ti improved the thermal stability of the developed alloys through inhibiting the grain growth,hindering dissolution and growth of second phases(such as Al13Fe4 and Al13Ti),and forming a stable solid solution.

Effect of Milling Time on Co<SUB>0.5</SUB>Zn<SUB>0.5</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB>Microstructure and Particles Size Evolution via the Mechanical Alloying Method

Nanocrystalline CoZn-ferrite was fabricated by a high-energy milling method by mixing Fe3O4+CoO+ZnO. The structural properties of the milled powder at different milling times were analysed so to ascertain the diffusion of CoO and ZnO into the tetrahedral and octahedral sites using mechanical alloying method. The effect of mechanical alloying towards particle size was also investigated. The XRD spectra indicated the precursors reacted during milling with the diffusion of ZnO and followed by CoO into their respective crystallographic sites. SEM micrographs showed the agglomeration of powders due to high energy milling and TEM images confirmed that the particles of the materials were of nanosize dimension. In addition, the results show that the grain possesses a single-phase CoZn-ferrite structure in a typical size of ~16–30 nm. The experiment reveals that nanosize CoZn-ferrite can be obtained after the powder is milled for about 8 hours at room temperature. The mechanism and efficiency of the synthesis of the technique are also discussed in this paper.

Structural evolution and stability of mechanically alloyed Fe-Ni nanocrystalline

The structural evolution and stability of Fe100-xNix（x= 10, 20, 35, 50） alloys prepared by mechanical alloying were investigated through X-ray diffraction analysis and transmission electron microscopy. The intrinsic conditions of preparation determining phase stability in nanocrystalline were clarified. After being milled for 120 h, the powders of Fego Ni10 and Fe80 Ni20 consist of a single α（bcc） phase, Fe30 Ni30 powders are a single γ（fcc）, and for Fe65 Ni35 powders there is co-existence of α and γ phases. The as-milled Fe80 Ni20 powders annealed at 680℃ exhibits the stability of high-temperature γ phase at room temperature, which is consistent with the theoretical prediction.

Preparation of Nanocrystalline Metal-carbides by Mechanical Alloying

Nowadays, most of nanocrystalline materials (NM) are fabricated from the gas phase by an evaporation/condensation process. However, this process is difficult to scale up. Recently, mechanical alloying has become an alternative route to produce NM of commercial significance. This method, through low temperature solid state reaction, can produce novel phases and structures of alloys which would not be obtained by any other method, and hence, has attracted great attention.

Structural evolution of Si-50%C powder during mechanical alloying and heat treatment

The nanocrystalline β-SiC powder was successfully synthesized by ball milling the Si-50%C elemental powder. During ball milling, a solid solution of C in Si, Si(C), firstly forms, followed by SiC. The formation of SiC is controlled by the mixing mechanism of the gradual diffusion reaction(GDR) and the mechanically induced self-propagating reaction(MSR). The amount of β-SiC increases with milling time increasing. After 40 h milling, there exists only β-SiC in the milled powder. The grain size of β-SiC is about 6.4 nm after the powder is milled for 60 h. After the 60 h-milled Si-50%C elemental powder is heat treated at 1 100 ℃ for 1 h, the grain size of β-SiC does not change, but the lattice ordering degree of β-SiC increases.

Experimental study of amorphous and nanocrystalline Fe-based alloy

The mechanical alloying of FeNiPB(Cu, Nb) mixed powders was studied by X-ray diffraction (XRD), transition electron microscope (TEM), scanning electron microscopy (SEM) and extended X-ray absorption fine structure (EXAFS). The results show that the FeNiPB(Cu, Nb) mixed powders alloy after milling for 20 h, as the milling time increases to 80h, Fe and Ni atoms are in an amorphous environment, the morphology of FeNiPB(Cu, Nb) mixed powders appears as cotton fiber and its electron diffraction pattern shows a typically diffuse amorphous halo. So FeNiPB(Cu, Nb) mixed powders transform to amorphous state under this condition. After the FeNiPB(Cu, Nb) amorphous alloy was heated at 520℃ for 1 h, the nanocrystalline FeNiPB(Cu, Nb) was produced. So, the Fe-based nanocrystalline alloy can be prepared by partially crystallizing the FeNiPB(Cu, Nb) amorphous alloy.

Effect of milling atmosphere on structural and magnetic properties of Ni-Zn ferrite nanocrystalline

Powder mixtures of Zn, NiO, and Fe2O3 are mechanically alloyed by high energy ball milling to produce Ni-Zn ferrite with a nominal composition of Ni0.36Zn0.64Fe2O4. The effects of milling atmospheres （argon, air, and oxygen）, milling time （from 0 to 30 h） and heat treatment are studied. The products are characterized using x-ray diffractometry, field emission scanning electron microscopy equipped with energy-dispersive x-ray spectroscopy, and transmitted electron microscopy. The results indicate that the desired ferrite is not produced during the milling in the samples milled under either air or oxygen atmospheres. In those samples milled under argon, however, Zn/NiO/Fe2O3 reacts with a solid-state diffusion mode to produce Ni-Zn ferrite nanocrystalline in a size of 8 nm after 30-h-milling. The average crystallite sizes decrease to 9 nm and 10 nm in 30-h-milling samples under air and oxygen atmospheres, respectively. Annealing the 30-h-milling samples at 600℃ for 2 h leads to the formation of a single phase of Ni-Zn ferrite, an increase of crystallite size, and a reduction of internal lattice strain. Finally, the effects of the milling atmosphere and heating temperature on the magnetic properties of the 30-h-milling samples are investigated.