Microstructure and performance of electrodeposited nanocrystalline Ni-W alloys

The electro-deposition method was used for preparation of nanocrystalline Ni-W alloys coating. The formation, microstructure and performance of the nanocrystalline were investigated. X-ray diffraction results show that Ni-W alloys are crystallized in scale of 1730nm. Changing with the depositional time, the coating varies with different surface morphology. The observation on the formation of the coating implies that, the alloys preferentially deposit and grow on the scratch and corrosion pit edges. The hardness of the alloy coatings is related to the solution composition, pH value and current density, and the pH value and current density are mainly concerned. The corrosion resistance of Ni-W alloy coating is excellent compared with that of Cr and Ni coatings.

Fabrication and characterization of electrodeposited nanocrystalline Ni-Fe alloys for NiFe_2O_4 spinel coatings

Nanocrystalline Ni-Fe FCC alloy coatings with Fe content of 1.3%-39%（mass fraction） were fabricated on the nickel substrates using a DC electrodeposition technique. The crystal structure, lattice strain, grain size and lattice constant of the Ni-Fe alloy coatings were studied by X-ray diffraction technique. The chemical composition and surface morphology of the FCC Ni-Fe alloy coatings were investigated with the energy dispersive X-ray spectroscopy（EDS） and atomic force microscopy（AFM）. The results show that the Fe content of the Ni-Fe alloy coatings has a great influence on the preferred orientation, grain size, lattice constant and lattice strain. FCC Ni-Fe alloy coatings exhibit preferred orientations of（200） or（200）（111）. With an increase of Fe content, the preferred growth orientation of（200） plane is weakened gradually, while the preferred growth orientation of（111） increases. An increase of the Fe content in the range of 1.3%-25%（mass fraction） results in a significant grain refinement of the coatings. Increasing the Fe content beyond 25% does not decrease the grain size of FCC Ni-Fe alloys further. The lattice strain increases with increasing the Fe content in the FCC Ni-Fe alloys. Since the alloys with Fe content not less than 25% has similar grain size（~11 nm）, the increase in the lattice strain with the increase of Fe content cannot be attributed to the change in the grain size.

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.

Study on Nanocrystalline Rare Earth Mg-Based System Hydrogen Storage Alloys with AB_3-Type

A sort of rare earth Mg-based system hydrogen storage alloys with AB3-type was prepared by double-roller rapid quenching method. The alloys were nanocrystalline multi-phase structures composed of LaNi3 phase and LaNi5 phase by X-ray diffraction and scanning electron microscopy analyses, and the suitable absorption/desorption plateau was revealed by the measurement of P-C-I curve. Electrochemical studies indicate that the alloys exhibit good electrochemical properties such as high capacity and stable cycle life, and the discharge capacity is 369 mAh·g-1 at 0.2 C (72 mA·g-1). after 460 cycles, the capacity decay was only 19.4% at 2 C (720 mA·g-1).

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.

Synthesis of nanocrystalline NiCrC alloy feedstock powders for thermal spraying by cryogenic ball milling

Nanocrystalline NiCrC alloy powders with a qualified particle size distribution for thermal spraying were synthesized using the cryogenic ball milling （cryomilling） method. The morphology, microstructure, size distribution, and phase transformation of the powders were characterized by scanning electron microscopy （SEM）, laser scattering for particle size analysis, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. After cryomilling for 20 h, the average grain size of the as-milled powders approached a constant value of 30 nm by XRD measurement. The average particle size slightly increased from 17.5 to 20.3 μm during the 20-h milling. About 90vol% of the powders satisfied the requirement for thermal spraying with the particle dimension of 10-50 μm, and most of the powders exhibited spherical morphology, which were expected to have good fluidity during thermal spraying. The Cr2O3 phase formed during the cryornilling process as revealed in the XRD spectra, which was expected to enhance the thermal stability of the as-milled powders during the followed thermal spraying or other heat treatment.

Nanocrystalline Mg and Mg alloy powders by hydriding-dehydriding processing

The process of mechanically assisted hydriding and subsequent thermal dehydriding was proposed to produce nanocrystalline Mg and Mg alloy powders using pure Mg and Mg-5.5%Zn-0.6%Zr(mass fraction)(ZK60 Mg) alloy as the starting materal.The hydriding was achieved by room-temperature reaction milling in hydrogen.The dehydriding was carried out by vacuum annealing of the as-milled powders.The microstructure and morphology of both the as-milled and subsequently dehydrided powders were characterized by X-ray diffraction analysis(XRD) ,transmission electron microscopy(TEM) ,and scanning electron microscopy(SEM) ,respectively.The results show that,by reaction milling in hydrogen,both Mg and ZK60 Mg alloy can be fully hydrided to form nanocrystalline MgH2 with an average grain size of 10 nm.After subsequent thermal dehydriding at 300℃,the MgH2 can be turned into Mg again,and the newly formed Mg grains are nanocrystallines,with an average grain size of 25 nm.

Superelastic properties of nanocrystalline NiTi shape memory alloy produced by thermomechanical processing

Effects of thermomechanical treatment of cold rolling followed by annealing on microstructure and superelastic behavior of the Ni50Ti50 shape memory alloy were studied.Several specimens were produced by copper boat vacuum induction melting.The homogenized specimens were hot rolled and annealed at 900°C.Thereafter,annealed specimens were subjected to cold rolling with different thickness reductions up to 70%.Transmission electron microscopy revealed that the severe cold rolling led to the formation of a mixed microstructure consisting of nanocrystalline and amorphous phases in Ni50Ti50 alloy.After annealing at 400°C for 1 h,the amorphous phase formed in the cold-rolled specimens was crystallized and a nanocrystalline structure formed.Results showed that with increasing thickness reduction during cold rolling,the recoverable strain of Ni50Ti50 alloy was increased during superelastic experiments such that the 70%cold rolled-annealed specimen exhibited about 12%of recoverable strain.Moreover,with increasing thickness reduction,the critical stress for stress-induced martensitic transformation was increased.It is noteworthy that in the 70%cold rolled-annealed specimen,the damping capacity was measured to be 28 J/cm3 that is significantly higher than that of commercial NiTi alloys.

Investigation of the effects of misch metal in RS Al-Fe-V-Si-Mm nanocrystalline alloys by PAT

The positron lifetime spectra of severalAl_(93.3-x)Fe_(4.3)V_(0.7)Si_(1.7)Mm_x (x = 0.5%, 1.0%, 3.0%, atom fraction) alloys with differentcontent of misch metal prepared by rapid solidification were measured, and the variations on theinterfacial defects with the content of misch metal were revealed by an analysis of the lifetimeresults. The interface characteristics derived from the lifetime results could be used to give asatisfactory interpretation of the dependence of mechanical properties on the content of mischmetal.

Interfacial Characteristics of Nanocrystalline FeMoSiB Alloys

By using X-ray diffraction (XRD), transmission electronic microscopy (TEM) and transmission Mssbauer spectroseopy (TMES), the formation, structure and properties including microhardness and electrical resistivity of nanocrystalline FeMoSiB alloys have been investigated. By annealing the as-quenched FeMoSiB sample at 833-1023K for 1 h, nanocrystalline materials with grain sizes of 15 to 200 nm were obtained. Mssbauer spectroscopy results reveal a quasi-continuous distribution feature of P(H)-H curves for 15 nm-and 20 nm-grained samples. Also, it was found that resistivity and microhardness of nanocrystalline Fe-Mo-Si-B alloys exhibit strong grain size effect.

THERMAL STABILITY OF THE MECHANICALLY ALLOYED Al－10Ti NANOCRYSTALLINE ALLOY DURING CONSOLIDATION PROCESS

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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.

Thermal stability of nanocrystalline Al-10Fe-5Cr bulk alloy

Thermal stability of nanocrystalline Al-10wt.%Fe-5wt.%Cr bulk alloy was investigated.The initial micro-grained mixture of powders was processed for 100 h using mechanical alloying(MA)to produce nano-grained alloy.The processed powders were sintered using high frequency induction heat sintering(HFIHS).The microstructures of the processed alloy in the form of powders and bulk samples were investigated using XRD,FESEM and HRTEM.Microhardness and compression tests were conducted on the bulk samples for evaluating their mechanical properties.To evaluate the thermal stability of the bulk samples,they were experimented at 573,623,673 and 723 K under compression load at strain rates of 1×10^-1 and 1×10^-2 s^-1.The annealed samples exhibited a significant increase in their microhardness value of 2.65 GPa when being annealed at 723 K,as compared to 2.25 GPa of the as-sintered alloy.The bulk alloy revealed compressive strengths of 520 MPa and 450 MPa at 300 K and 723 K,respectively,when applying a strain rate of 1×10^-1 s^-1.The microstructural stability of the bulk alloy was ascribed to the formation of iron and chromium containing phases with Al such as Al6Fe,Al13Fe4 and Al13Cr2,in addition to the supersaturated solid solution(SSSS)of Cr and Fe in Al matrix.

Utilization of surface nanocrystalline to improve the bendability of AZ31 Mg alloy sheet

A surface nanocrystalline was fabricated by ultrasonic shot peening(USSP)treatment at AZ31 Mg alloy.The effect of nanocrystalline thickness and its placed side(external or internal)on the bendability was studied by a V-bending test.Three durations,5,10,and 15 min,were applied to form the surface nanocrystalline with thicknesses of 51,79,and 145μm,respectively.Two-side treatment led to a similar bendability as that of as-received.One-side internal treatment for 5 min resulted in an improved bendability while the improvement was limited and degenerated for longer treatment.The improvement was related to the drawing back of the neutral axis.The one-side external treatment also improved the bendability,and the improvement was due to the redistribution of strain and stress during bending.With nanocrystalline at external side,it resulted in a larger stress but a smaller strain at the convex,which prevented the happening of crack during bending.

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

Anisotropic Magnetoresistance Effect in Amorphous and Nanocrystalline Fe(Cu,Nb)-Si-B Alloys

The magnetoresistance effect and magnetic properties in amorphous and nanocrystalline Fe(Cu, Nb)-Si-B ribbons have been investigated, it was observed that the anisotropic magnetoresistance (AMR) of nanocrystalline alloy is much smaller than that of amorphous alloy, Indicating that the anisotropy of nanocrystalline alloy becomes smaller after crystallizing, and the smallest AMR is coincident with the excellent soft magnetic characteristics. It is believed that the smaller magnetic crystalline anisotropy is the origin of the excellent soft magnetic characteristics of nanocrystalline alloy.

Behavior of Medium-frequency Core Loss in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency have been investigated in the ranges of 100 Hz<= f<=25000 Hz and 0.1 T< =Bm <=1.0 T for three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys. The measured and calculated results showed that the total power loss per cycle clearly exhibited a nonlinear behavior in the range below 3 kHz～5 kHz depending on both the magnetic state and the value of Dm, whereas it showed a quasi-linear behavior above this range. The total loss was decomposed into hysteresis loss, classical eddy current loss and excess loss, the obvious nonlinear behavior has been confirmed to be completely determined by the dependence of the excess loss on frequency. It has been indicated that the change rate of the excess loss per cycle with respect to frequency sharp decreases with increasing frequency in the range below about 3 kHz～5 kHz, wherease the rate of change slowly varies above this range, thus leading to the quasilinear behavior of the total loss per cycle. In this paper, some linear expressions of the total loss per cycle has been given in a wider medium-frequency segment, which can be used for roughly estimating the total loss.

General Properties of Low-frequency Power Losses in Fe-based Nanocrystalline Soft Magnetic Alloys

The dependences of the power loss per cycle on frequency f and amplitude flux density Bm have been investigated for the three main original magnetic states in five sorts of Fe-based nanocrystalline soft magnetic alloys in the ranges of 10 Hz<=f<=1000 Hz and 0.4 T<= Bm <=1.0 T. The total loss P is decomposed into the sum of the hysteresis loss Physt, the classical eddy current loss Pel and the excess loss Pexc. Physt has been found to be proportional to Bm^2 and f. The behavior of Pexc/f vs f being equivalent to P/f vs f clearly exhibits nonlinearity in the range not more than about 120 Hz, whereas the behavior of P/f vs f roughly shows linearity in the range far above 100 Hz and not more than 1000 Hz. In the range up to 1000 Hz, Physt is dominant in the original high permeability state and the state of low residual flux density, whereas Pexc in the state of high residual flux density is dominant in the wider range above about 100 Hz. The framework of the statistical theory of power loss has been used for representing the behavior of Pexc/f vs f. It has been found that the number n of the simultaneously active 'Magnetic Objects' linearly varies as n = n0 + Hexc/H0 as a function of the dynamic field Hexc in the range below about 120 Hz, whereas n approximately follows a law of the form n = n0 + (Hexc/H0)^m with 1 < m < 2 in the range far above 100 Hz and not more than 1000 Hz. The values of the field HO in principle related to the microstructure and the domain structure have been calculated for the three states.

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.