Long-term corrosion behavior of HVOF sprayed FeCrSiBMn amorphous/nanocrystalline coating

A FeCrSiBMn amorphous/nanocrystalline coating with 700 μm in thickness and 0.65% in porosity, was prepared by high velocity oxygen fuel(HVOF) spraying process. The long-term corrosion behavior of the FeCrSiBMn coating was evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy(EIS) tests in a 3.5% NaCl solution with a hard chromium coating as a reference. The FeCrSiBMn coating exhibited higher corrosion potential and lower corrosion current density than the hard chromium coating. The pore resistance(Rp) and charge transfer resistance(Rct) of FeCrSiBMn coating were higher than those of the hard chromium coating. In addition, after immersion in the Na Cl solution for 28 d, only small pores in the FeCrSiBMn coating were observed. All the results indicated that the FeCrSiBMn coating held superior corrosion resistance to the hard chromium coating. This could be attributed to the dense structure, low porosity and amorphous/nanocrystalline phases of the FeCrSiBMn coating.

Quasi-plastic deformation mechanisms and inverse Hall-Petch relationship in nanocrystalline boron carbide under compression

Grain boundaries(GBs)play a significant role in the deformation behaviors of nanocrystalline ceramics.Here,we investigate the compression behaviors of nanocrystalline boron carbide(nB_(4)C)with varying grain sizes using molecular dynamics simulations with a machine-learning force field.The results reveal quasi-plastic deformation mechanisms in nB_(4)C:GB sliding,intergranular amorphization and intragranular amorphization.GB sliding arises from the presence of soft GBs,leading to intergranular amorphization.Intragranular amorphization arises from the interaction between grains with unfavorable orientations and the softened amorphous GBs,and finally causes structural failure.Furthermore,nB_(4)C models with varying grain sizes from 4.07 nm to 10.86 nm display an inverse Hall-Petch relationship due to the GB sliding mechanism.A higher strain rate in nB_(4)C often leads to a higher yield strength,following a 2/3 power relationship.These deformation mechanisms are critical for the design of ceramics with superior mechanical properties.

Growth characteristics of amorphous-layer-free nanocrystalline silicon films fabricated by very high frequency PECVD at 250 ℃

Amorphous-layer-free nanocrystalline silicon films were prepared by a very high frequency plasma enhanced chem-ical vapor deposition （PECVD） technique using hydrogen-diluted Sill4 at 250 ℃. The dependence of the crystallinity of the film on the hydrogen dilution ratio and the film thickness was investigated. Raman spectra show that the thickness of the initial amorphous incubation layer on silicon oxide gradually decreases with increasing hydrogen dilution ratio. High-resolution transmission electron microscopy reveals that the initial amorphous incubation layer can be completely eliminated at a hydrogen dilution ratio of 98%, which is lower than that needed for the growth of amorphous-layer-free nanocrystalline silicon using an excitation frequency of 13.56 MHz. More studies on the microstructure evolution of the initial amorphous incubation layer with hydrogen dilution ratios were performed using Fourier-transform infrared spectroscopy. It is suggested that the high hydrogen dilution, as well as the higher plasma excitation frequency, plays an important role in the formation of amorphous-layer-free nanocrystalline silicon films.

Molybdenum based amorphous and nanocrystalline coatings prepared by high velocity oxy-fuel spraying

The high velocity oxy-fuel(HVOF) based thermal spray process has developed as a potential advantageous approach for fabricating various kinds of functional coatings.In this article,the coatings of Mo-based alloy were synthesized using the HVOF process.The microstructure and the mechanical properties of the HVOF-processed coatings were investigated using SEM,TEM,XRD,and hardness and wear tests.Annealing treatment was applied to the as-sprayed coatings to develop the microstructure and its effect on the microstructure and mechanical properties of the coatings was examined.It is found that the HVOF-processed Mo-based alloy coatings are comprised of an amorphous splat matrix embedded with nano-sized crystalline particles.Annealing at temperatures over 950 ℃ results into crystallization of the amorphous matrix.The mechanical properties of the as-sprayed coatings are enhanced with annealing temperature up to 750 ℃ and from 950 to 1050 ℃,keeps constant between 750 and 950 ℃,and reduce over 1050 ℃.The change of the mechanical property with the microstructure was illustrated in the study.

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.

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.

Effect of melt spinning on gaseous hydrogen storage characteristics of nanocrystalline and amorphous Nd-added Mg_2Ni-type alloys

Nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of(Mg_(24)Ni_(10)Cu_2)_(100-x)Nd_x(x=0, 5, 10, 15, 20) were prepared by melt spinning technology and their structures as well as gaseous hydrogen storage characteristics were investigated. The XRD, TEM and SEM linked with EDS detections reveal that the as-spun Nd-free alloy holds an entire nanocrystalline structure but a nanocrystalline and amorphous structure for the as-spun Nd-added alloy, implying that the addition of Nd facilitates the glass forming in the Mg_2Ni-type alloy. Furthermore, the degree of amorphization of the as-spun Nd-added alloy and thermal stability of the amorphous structure clearly increase with the spinning rate rising. The melt spinning ameliorates the hydriding and dehydriding kinetics of the alloys dramatically. Specially, the rising of the spinning rate from 0(the as-cast was defined as the spinning rate of 0 m/s) to 40 m/s brings on the hydrogen absorption saturation ratio(R_5~a)(a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity) increasing from 36.9% to 91.5% and the hydrogen desorption ratio(R_(1 0)~d)(a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity) rising from 16.4% to 47.7% for the(x=10) alloy, respectively.

Magnetothermal Analysis of Nanocrystallization of Amorphous and Relaxations of Nanocrystalline Materials

For a few years it has been realized that nanocrystalline phases can be formed during crystallization of amorphous alloys annealed isothermally below the crystallization temperature of usual heating experiments. Data of this transformation monitored by the measurement of magnetic susceptibility are presented. A method using a magnetic balance with electronic stabilisation and combined computer facilities is applied. Constant heating and cooling rates as well as isothermal heat treatments are used. Magnetic measurements are able to detect the onset of the transformation of amorphous NI-P alloys much earlier than was possible with differential scanning calorimetry. The transformation kinetics can be analyzed by means of the Avrami plot based on the Johnson-Mehl-Avrami equation. The kinetics of solid state reactions in the nanostructured material can be investigated similarly. Formation of a Ni-phase in a nanostructured Hf-Ni alloy could be detected in a very early stage, where calorimetric methods are not sensitive. Segregation phenomena could be detected from the experiments even after long time. The sensitivity of the applied method is not dependent on the heating rate as the sensitivity of scanning calorimetry is.

Highly Improved Electrochemical Performances of the Nanocrystalline and Amorphous Mg_2Ni-type Alloys by Substituting Ni with M (M=Cu,Co,Mn)

The element Ni in the Mg2Ni alloy is partially substituted by M（M = Cu, Co, Mn） in order to ameliorate the electrochemical hydrogen storage performances of Mg2Ni-type electrode alloys. The nanocrystalline and amorphous Mg20Ni10-xMx（M = None, Cu, Co, Mn; x = 0-4） alloys were prepared by melt spinning. The effects of the M（M = Cu, Co, Mn） content on the structures and electrochemical hydrogen storage characteristics of the as-cast and spun alloys were comparatively studied. The analyses by XRD, SEM and HRTEM reveal that all the as-cast alloys have a major phase of Mg2Ni but the M（M = Co, Mn） substitution brings on the formation of some secondary phases, MgCo2 and Mg for the（M = Co） alloy, and Mn Ni and Mg for the（M = Mn） alloy. Besides, the as-spun（M = None, Cu） alloys display an entirely nanocrystalline structure, whereas the as-spun（M = Co, Mn） alloys hold a nanocrystalline/amorphous structure, suggesting that the substitution of M（M = Co, Mn） for Ni facilitates the glass formation in the Mg2Ni-type alloys. The electrochemical measurements indicate that the variation of M（M = Cu, Co, Mn） content engenders an obvious effect on the electrochemical performances of the as-cast and spun alloys. To be specific, the cyclic stabilities of the alloys augment monotonously with increasing M（M = Cu, Co, Mn） content, and the capacity retaining rate（S20） is in an order of（M = Cu） 〉（M = Co） 〉（M = Mn） 〉（M = None） for x≤1 but changes to（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None） for x≥2. The discharge capacities of the as-cast and spun alloys always grow with the rising of M（M = Co, Mn） content but first mount up and then go down with increasing M（M = Cu） content. Whatever the M content is, the discharge capacities are in sequence：（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None）. The high rate discharge abilities（HRDs） of all the alloys grow clearly with rising M（M = Cu, Co） content except for（M = Mn） alloy, whose HRD has a maximum value with varying M（M = Mn） content. Furthermore, for the as-cast alloys, the HRD is in order of（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None）, while for the as-spun（20 m·s^-1） alloys, it changes from（M = Co） 〉（M = Mn） 〉（M = Cu） 〉（M = None） for x = 1 to（M = Cu） 〉（M = Co） 〉（M = None） 〉（M = Mn） for x = 4.

Preparation and Properties of FeZrB Amorphous-Nanocrystalline Soft Magnetic Alloy

Fe68Zr20B12 amorphous alloy was prepared by mechanical alloying（MA） method and annealed at different temperatures. Microstructures and magnetic properties of Fe68Zr20B12 alloys as-milled and annealed at 693, 843, 943 and 993 K were studied. The raw powders（Fe, Zr, B） formed b. c. c. α-Fe solid solution at early stages of MA and then transformed into amorphous alloy. Grain size（D） of Fe68Zr20B12 alloys increases with increasing annealing temperature and keeps at nanometer level. The specific saturation magnetization（σs） increases with increasing annealing temperature from 300 K to 943 K, and then decreases with annealing temperature at 993 K because of the precipitation of Fe3B.

Amorphous-Nanocrystalline Transition in Silicon Thin Films Obtained by Argon Diluted Silane PECVD

The Plasma-Enhanced Chemical Vapor Deposition (PECVD) method is widely used compared to other methods to deposit hydrogenated silicon Si:H. In this work, a systematic variation of deposition parameters was done to study the sensitivities and the effects of these parameters on the intrinsic layer material properties. Samples were deposited with 13.56 MHZ PECVD through decomposition of silane diluted with argon. Undoped samples depositions were made in this experiment in order to obtain the transition from the amorphous to nanocrystalline phase materials. The substrate temperature was fixed at 200oC. The influence of depositions parameters on the optical proprieties of the thin films was studied by UV-Vis-NIR spectroscopy. The structural evolution was also studied by Raman spectroscopy and X-ray diffraction (XRD). The structural evolution studies show that beyond 200 W radio frequency power value, we observed an amorphous-nanocrystalline transition, with an increase in crystalline fraction by increasing RF power and working pressure. The deposition rates are found in the range 6 - 10 /s. A correlation between structural and optical properties has been found and discussed.

Magnetic properties and promising cryogenic magneto-caloric performances of Gd_(20)Ho_(20)Tm_(20)Cu_(20)Ni_(20) amorphous ribbons

The magnetic cooling utilizing magneto-caloric effect is recognized as promising energy efficiency and environmentally friendly technology.Here we report a systematical study on the microstructures,magnetic properties and cryogenic magneto-caloric performances of the Gd_(20)Ho_(20)Tm_(20)Cu_(20)Ni_(20) amorphous ribbons.It is found that the ribbons reveal a second-order phase transition and are accompanied by a table-shaped magneto-caloric effect.The calculated magneticentropy-change maximum |ΔSM|,temperature averaged entropy change(i.e.,TEC(10)),and refrigerant capacity reach 13.9 J/kg·K,13.84 J/kg-K and 740 J/kg with magnetic field change of 0-7 T,respectively,indicating that the present Gd_(20)Ho_(20)Tm_(20)Cu_(20)Ni_(20) amorphous ribbons are good candidates for magnetic cooling.

Giant Magneto-Impedance Effect in Fe_(96-x)B_4 (x=7 or 10) Nanocrystalline Ribbons

The total ribbon voltage of as-quenched and annealed Fe96-xZr_xB_4 (x=7 or 10) ribbons has been measured as a function of applied dc field and drive current frequency. The experimental results show that both samples exist the optimum annealing temperature and optimum frequency at which the relative change in ribbon voltage is strongest, and the sensitivity of the magnetic response of the annealed Fe_89Zr_7B_4 ribbon is two order of magnitude larger than that of the annealed Fe_86Zr_10 B4 ribbon. The effect of magnetic properties and structural characteristics on giant magneto-impedance was discussed.

Giant magnetoimpedance effect in Fe-Zr-Nb-Cu-B nanocrystalline ribbons

The giant magnetoimpedance effect of the nanocrystalline ribbonFe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) (atom fraction in %) was investigated. There is an optimumannealing temperature (T_A≈ 998 K) for obtaining the largest GMI (giant magneto-impedance) effectin the ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11). The ribbon with longer ribbon length has strongerGMI effect, which may be connected with the demagnetization effect of samples. The frequencyf_(max), where the maximum magnetoimpedance GMI(Z)_(max) = [(Z(H) - Z(0))/Z(0)]_(max) occurs, isnear the intersecting frequency f_i of the curves of GMI(R), GMI(X), and GMI(Z) versus frequency.The magnetoreactance GMI(X) decreases monotonically with increasing frequency, which may be due tothe decrease of permeability. In contrast, with the AC (alternating current) frequency increasing,the inagnetore-sistance GMI(R) increases at first, undergoes a peak, and under then drops. Theincrease of the magnetoresistance may result from the enhancement of the skin effect with frequency.The maximum magnetoimpedance value GMI(Z)_(max) under H = 7.2 kA/m is about -56.18% at f= 0.3 MHzfor the nanocrystalline ribbon Fe_(84)Zr_(2.08)Nb_(1.92)Cu_1B_(11) with the annealing temperatureT_A= 998 K and the ribbon length L = 6 cm.

Giant Stress-impedance Effect in Amorphous and Current Annealed Fe_(73.5)Cu_1Nb_3Si_(13.5)B_9 Ribbons

The giant stress-impedance (GSI) effect in amorphous and current annealed Fe73.5Cu1Nb3Si13.5B9 ribbons has been investigated. The results showed that the GSI effect changed drastically with annealing techniques and the maximum stress impedance ratio of 350% was obtained after optimal conditions of current annealing. The behaviors of the stress impedance vary with densities of annealing current and the stress longitudinally applied during current annealing. The maximum change of stress impedance existed in the sample annealed by high-current-density electropulsing under applied stress of 100 MPa.

Nanoscale Morphology in Tensile Fracture of a Brittle Amorphous Ribbon

The paper reports on the observation of nanoscale morphology on the tensile fracture surface of a brittle amorphous Fe-based ribbon. The formation of nanoscale damage cavity structure is a main characteristic morphology on the fracture surfaces. Approaching the ribbon boundary, these damage cavities assemble and form the nanoscale periodic corrugations, which are neither Wallner lines nor crack front waves. The periodic corrugations result from the interactions between the reflected elastic waves by the boundaries of amorphous ribbon and the stress fields of the crack tip.

Giant Magnetoimpedance Effect of As-Spun Nanocrystalline Ribbon of FeZrBCu Alloy

The melt-spun nanocrystalline ribbons of Fe86.5Zr7B4Cu2.5 alloy were prepared by single wheel technique with wheel surface velocity of 37 m/s.It is found that there appears a lot ofα-Fe nanoparticles with sizes of 5-10 nm in as-spun nanocystalline ribbons which exhibit giant magnetoimpedance(GMI)effect.The GMI ratio up to 33.69% at frequency f=1MHz under a DC field of 5 172A/m can be obtained.

The Effect of Surface Etching and Dation on the Permeability Spectrum of Nanocrystalline Fe_(85-x)Co_xNb_7B_8 Ribbon

Etching and oxidation were adopted to improve the frequency dependence of permeability of nanocrystalline Fe85-xCoxNb7B8 ribbons. The effect of etching and oxidation on the permeability spectrum of nanocrystalline Fe85-CoxNb7B8 ribbons was investigated. The relaxation frequency shifted to higher frequency end after etching and oxidation while the amplitude of μ1 was reduced at the same time. As a whole, μf0 rises and reflects the increasing of resistivity after etching and oxidation.

Magnetic Properties of Fe- and FeNi-based Amorphous Composite Ribbons

Ms-T curves and hysteresis loops were investigated for amorphous Fe78Si9B13, (FeNi)78(CrSiB)22, their lap-wound-cores, and their composite ribbons made by two-chamber-crucible technique. The properties of the lap-wound cores of the two kinds of ribbons are similar. For the composite ribbons, the intrinsic properties are the average of the two alloys. Their technological properties, i.e., hysteresis loops, however, are no longer the average of the two alloys. Instead, they show some dramatic changes compared to the lap-wound-cores. Especially, the shape of the hysteresis loop of the composite ribbon cores is largely different from that of lap-wound-cores. The reason for the difference is supposed to be internal stress induced from cooling after annealing.

Effect of Laser Annealing on Permeability Spectra in Co-based Amorphous Ribbon

We investigated the variation of permeability spectra and relaxation frequency in Co-based amorphous ribbon annealed by pulsed Nd:YAG laser at various annealing energy Ea. The complex permeability spectra varies sensitively with the annealing energy, where the spectra could be decomposed into two contributions from domain wall motion,μdw(f) and rotational magnetization μrot(f) by analyzing the measured spectra as a function of driving ac field amplitude. The magnitude of μdw(f) and μrot(f) in dc limit shows maximum at Ea = 176 mJ. The maximum relaxation frequency for rotational magnetization, determined by μ'(f) curve, is about 700 kHz at Ea=62 mJ but that for wall motion is about 26 kHz at 230 mJ. These variations reflect the increase of magnetic softness and microstructural change by the annealing.