Preparation of ultra-fine fibrous Fe-Ni alloy powder by coordinated co-precipitation-direct reduction process

The precursor prepared by coordinated co-precipitation was direct reduced by hydrogen to ultra-fine fibrous Fe-Ni alloy powder. The effects of concentrations of reactants, pH value, reaction temperature and additive on the preparation of precursor were systematically investigated. The structures, thermal decomposition processes and morphologies of the precursors were characterized by X-ray diffraction (XRD), thermal gravity-differential thermal analysis (TG-DTA) and scanning electron microscoy (SEM). The results show that using 2% polyvinylpyrrolidone (PVP) (in mass fraction) as additive, a well-dispersed precursor with a uniform morphology can be obtained in a solution with Fe2+ and Ni2+ total concentration (1:1) of 0.8 mol/L, pH value of 6.2 at 60 °C, and a pure and well dispersed fibrous iron-nickel powder can be prepared by direct reduction of this precursor in a mixed atmosphere of nitrogen and hydrogen at the temperature of 420 °C.

Non-isothermal reduction kinetics of Fe_2O_3-NiO composites for formation of Fe-Ni alloy using carbon monoxide

The non-isothermal reduction kinetics and mechanism of Fe2O3-NiO composites with different Fe2O3-NiO compacts using carbon monoxide as reductant were investigated. The results show that the reduction degree increases rapidly with increasing the content of NiO, and the presence of NiO also improves the reduction rate of iron oxides. It is found that NiO is preferentially reduced at the beginning of the reactions, and then the metallic Ni acts as a catalyst promoting the reduction rate of iron oxides. It is also observed that the increase of the Ni O content enhances the formation of awaruite(FeNi3) but decreases the percentage of kamacite(Fe,Ni) and taenite(Fe,Ni). The particle size of the materials tends to be uniform during the reduction process due to the presence of metallic nickel, metallic iron and the formation of Fe-Ni alloy. The concentration of CO in the product gas is greater than that of CO2 at the beginning of the reaction and then slows down. The fastest reduction rate of Fe2O3-NiO composites with CO appears at 400-500 °C, and nucleation growth model can be used to elucidate the reduction mechanism. Nucleation growth process is found to be the rate controlling step when the temperature is lower than 1000 °C.

Effect of solid-solution temperature on the microstructure of Fe-Ni based high strength low thermal expansion (HSLTE) alloy

The influence of solid-solution temperature on the dissolution of carbide precipitates, the average grain size and the microhardness of the austenite matrix in an Fe-Ni based high strength low thermal expansion （HSLTE） alloy was investigated to obtain the proper temperature range of the solid-solution process. The XRD analysis, microstructure observations, and the theoretical calculations showed that the Mo-rich M2C-type precipitates in the Fe-Ni based HSLTE alloy dissolve completely at about 1100℃. The average grain size of the studied alloys increases from 14 to 46 μm in the temperature range of 1050 to 1200℃. The microhardness of the matrix decreases gust for the sake of solid-solution treatment, but then increases later with increasing solution temperature because of the solution strengthening effect.

Manufacture of μ-PIM gear mold by electroforming of Fe-Ni and Fe-Ni W alloys

The micro gear mold for powder injection molding was made by electroforming process of Fe-Ni and Fe-Ni-W alloys using UV-lithography process. Kinetics and activation energies in electroplating of both alloys were investigated to determine the best process conditions. Fe content within electrodeposited Fe-Ni alloys increased with the increase of rotating disk speed and the decrease of temperature and it is considered from the calculated activation energy of iron content that the rate determining step is controlled by mass transfer. Iron content in Fe-Ni electrodeposit varied from 58.33% to 70.45% by increasing current density from 2 to 6 A/drn2. Also, iron content in Fe-Ni-W electrodeposit increased from 59.32% to 70.15%, nickel content decreased from 27.86% to 17.07% and the content of tungsten was almost consistent in the range of 12.78%-12.82% although the current density increases from 1.5 to 5 A/dm^2. For the electroforming of micro gear mold, SU-8 mandrel with 550 μm in diameter and 400 μm in height was prepared by UV-lithography processing. Subsequently, Fe-36Ni and Fe-20Ni-13W alloys micro gear molds were electroformed successfully. Surface hardness values of the electroformed micro molds were measured to be HV490 and HV645, respectively.

Textures of high-strength and low-expansion Fe-Ni alloy wires during cold-drawing processes

Textures of high-strength and low-expansion Fe-Ni alloy wires during cold-drawing processes were investigated using X-ray diffraction （XRD） and electron back scatter diffraction （EBSD） techniques. The experimental results show that the 〈111〉 and 〈100〉 fibre textures are the main texture components, and crystalline grains in the surface are more fine and uniform than those in the center of Fe-Ni alloy wires during cold-drawing processes. It is found that the volume fraction of the 〈111〉 fibre texture component determined by quantitative regression calculation of the Gaussian distribution function reaches more than 60% and the strong 〈111〉 fibre texture component favors the torsional property of Fe-Ni alloy wires.

First-principles calculation of phase equilibria and phase separation of the Fe-Ni alloy system

Theoretical investigation of the phase equilibria of the Fe-Ni alloy has been performed by combining the FLAPW total energy calculations and the Cluster Variation Method through the Cluster Expansion Method. The calculations have proved the stabilization of the LIE phase at 1：3 stoichiometry, which is in agreement with the experimental result, and predicted the existence of L1 0 as a stable phase below 550 K; this L1 0 phase has been missing in the conventional phase diagram. The calculations are extended to the Fe-rich region that is characterized by a wide range phase separation and has drawn considerable attention because of the intriguing Invar property associated with a Fe concentration of 65%. To reveal the origin of the phase separation, a P-V curve in an entire concentration range is derived by the second derivative of free energy functional of the disordered phase with respect to the volume. The calculation confirmed that the phase separation is caused by the breakdown of the mechanical-stability criterion. The newly calculated phase separation line combined with the L1 0 and L12Eorder-disordered phase boundaries provides phase equilibria in the wider concentration range of the system. Furthermore, a coefficient of thermal expansion （CTE） is attempted by incorporating the thermal vibration effect through harmonic approximation of the Debye-Gruneisen model. The Invar behavior has been reproduced, and the origin of this anomalous volume change has been discussed.

ANOMALOUS EFFECT OF PRESSURE ON THE CURIE TEMPERATURE IN MECHANICALLY ALLOYED Fe-Ni INVAR

Measurements of magnetic susceptibility in mechanically alloyed Fe-Ni Invar alloys were taken under pressures up to 7.5GPa. The rate of decrease in the Curie temperature for 700℃ annealed specimen was larger than that annealed at 1000℃. This result can be explained by considering the fact that the width of the concentration fluctuation becomes larger in the specimen annealed at lower temperature.

Synthesis and Characterization of Nanostructured Fe-Ni Alloy Whisker

The nanocrystalline γ-(Fe,Ni) alloy whiskers have been prepared by chemical reduction of Fe2+ and Ni2+ ions with potassium borohydride under the function of a dispersant agent PE followed by heat treatment at 600℃ under the protection of nitrogen.Conditions, such as quantity of NaOH, concentration of salts, and species of surfactants, of preparation of Fe-Ni alloy have been discussed. X-ray diffraction(XRD), transmission electron microscopy(TEM) and vibrating sample magnetometer(VSM) characterized the synthesized Fe-Ni alloy. Character, capability and use of the materials have been summarized.

Electrodeposition of Fe-Ni alloy coating on ferritic stainless steel

Fe-Ni alloy coatings were electrodeposited on ferritic stainless steel(FSS)in solutions containing FeSO4 and NiSO4.The effects of pH,[Fe2 +]/[Ni 2+](molar ratio)of electroplating solutions and cathode current density on deposition rate and surface appearances of the coatings were investigated.The results indicated that the deposition rate of the coating in solution with [Fe 2+ ]/[Ni 2+ ]of 0.4 slightly increased with increasing pH from 2.5 to 3.5 under the current density of 5.5 mA/cm 2 ,and then the deposition rate of the coating in solution with pH 4.0 began to decrease.The deposition rate also slightly increased with pH up to 3.5 under higher cathode current densities of 13.5 and 27 mA/cm2.Under 13.5 mA/cm 2,however,the coating deposited in solution with pH 4 was prone to crack or flake.The deposition rate increased and the surface of coatings became less smooth with increasing cathode current density.The effect of the ratio of[Fe2 +]to[Ni 2+]on deposition rate was not obvious.With increasing the ratio of [Fe2 +]to[Ni 2+]in plating solution,the content of Fe in the coatings increased;while the Ni content in the coatings decreased with the increase in the ratio of[Fe 2+ ]to[Ni 2+ ].The deposited coating consisted of Fe-Ni alloy phase.

Research on surface defects and continuous casting process of Fe-Ni alloy

Over the last decade,various Fe-Ni alloys have been developed at Baosteel using the EAF-AOD-LFVD-CC route. This paper first reveals the main cause of defects in Fe-Ni alloys,including surface edge cracks on hot-rolling strips and slivers on cold-rolling strips of Fe-36% Ni alloy. Then,the material properties and in-situ solidification behavior w ere experimentally investigated. The gas content and average diameter of the inclusions in Fe-36% Ni alloy that occur along the EAF-AOD-LF-VD-CC route w ere also investigated via potentiostatic electrolysis using a non-aqueous organic electrolytic. Furthermore,the heat transfer and solidification in a continuous casting mold w ere predicted based on an inverse heat transfer model using the measured mold temperature. Experimental results show that the gas content,w hich is < 0. 001 5% in a continuous casting slab,and the average diameter of the inclusions both decrease during the metallurgical EAF-AOD-LF-VD-CC process. The average diameter of the inclusions in a continuous casting slab is ～ 18 μm,w hich tends to induce slivers during subsequent cold-rolling process. Experimental in-situ solidification results show that the mushy zone betw een the liquidus and solidus of Fe-Ni alloy is much narrow er than that of plain carbon steel. Stresses are generated during continuous casting,primarily due to the thermal contraction of a few percentage points,and any strain applied to the steel w ithin this temperature region w ill cause cracks to propagate outw ard from the solidification front betw een the dendrites. Numerical simulation results illustrate that heat flux and shell thickness are uneven across the w idth of the mold,particularly the shell thickness close to the edge of the slab surface in the fixed face is 6-mm thinner than that at the slab center. Based on these results,the incidence of surface defects in Fe-Ni alloy can be greatly reduced by the adjustment and optimization of its refining and continuous casting process.

Effect of Melt Quenching on Martensite Transformation in Fe-Ni Alloy

The main features of martensite transformation in melt-quenched Fe-31.4% Ni alloy on cooling below room temperature have been studied. It is found that the ribbon 50～60 μm thick, prepared by spinning technique, is a natural composite in which isothermal and surface martensite are not formed, while athermal martensite forms at lower temperature, all factors being the same, as compared to the alloy of the same composition and grain size, prepared by recrystallization.

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.

Mossbauer Spectroscopy of Fe-Ni-Nb-B Alloy in Weak Magnetic Field

Amorphous and nanocrystalline (Fe1–xNix)81Nb7B12 (x = 0, 0.25, 0.5, 0.75) alloys were measured by M?ssbauer spectrometry in the weak external magnetic field of 0.5 T. From structural analyses, ferromagnetic bcc-FeNi and fcc-FeNi and paramagnetic (Fe-Ni)23B6 phases were identified in the annealed samples. It was shown that in the external magnetic field the intensities of the 2nd and the 5th lines (A23 parameter) are the most sensitive M?ssbauer parameters. Rather small changes were observed in the values of internal magnetic field. Our results showed that the amorphous precursor is more sensitive to the influence of external magnetic field than the nanocrystalline alloy. All spectra of amorphous precursor showed the increase of A23 parameter and decrease of internal magnetic field values of about 1 T (±0.5 T) under influence of external magnetic field. In the case of nanocrystalline samples the tendency for the values of internal magnetic field is similar but the effect is not so pronounced. The measurements confirmed that even weak external magnetic field affected orientation of the net magnetic moments. Our results indicate that effect of the external magnetic field is stronger in the case of amorphous samples due to their disordered structure.

STRUCTURE FORMATION OF UNDERCOOLED Fe-30Ni ALLOY

Bulk Fe-30Ni alloy melt was nudercooled up to 337K by combining the glass fluxing technique with superheating-cooling cycle. Grain refinement at low undercoolings was observed in the experiment in addition to that at high undercoolings. The current grain refinement mechanisms were examined, and it is concluded that the refined gains are all developed from dendrites, however the grain refinement at low undercoolings is due to chemical superheating, while that at high undercoolings due to rapid solidification contruction.

Influence of electroplating conditions on magnetic properties of Fe-36wt.% Ni alloy film

A Fe-Ni soft magnetic film was prepared in sulphate solution by electroplating.The influences of the molar ratio of n[Fe^(2+)]/n[Ni^(2+)],current density,bath temperature,pH and L-ascorbic acid concentration on magnetic properties of Fe-Ni alloy film were investigated.The results show that the saturated flux density(BS)of the film increases initially and decreases after it reaches the specific value with the increase of n[Fe^(2+)]/n[Ni^(2+)]molar ratio,current density,bath temperature and pH.However,the relationship between L-ascorbic acid concentration and BS keeps linear.It is observed that the coercive force(H_(c))is enhanced with the increase of n[Fe^(2+)]/n[Ni^(2+)]molar ratio,current density and pH.By comparison,when the bath temperature increases,Hc always decreases.With the increase of L-ascorbic acid concentration,the coercive force increases initially and then decreases.

Solidification characteristics of Fe-Ni peritectic al oy thin strips under a near-rapid solidification condition

This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of δ-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe-7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the microsegregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.

Syntheses of Fe-Ni Magnetic Nanoparticles and Their Applications on Biologic Labeling

In this study,we compared FeNi alloy magnetic nanoparticles(MNPs) prepared by either combustion or chemical precipitation methods.We found that the FeNi MNPs generated by combustion method have a rather high saturation magnetization Ms of ～180 emu/g and a coercivity field Hc of near zero.However,the alloy nanoparticles are easily aggregated and are not well dispersive such that size distribution of the nanoparticle clusters is wide and clusters are rather big(around 50～700 nm).To prepare a better quality and well dispersed Fe-Ni MNPs,we also developed a thermal reflux chemical precipitation method to synthesize FeNi3 alloy MNPs.The precursor chemicals of Fe(acac)3 and Ni(acac)2 in a molecular ratio of 1:3 reacted in octyl ether solvent at the boiling point of solvent(～300 ℃) by the thermal reflux process.The 1,2-hexadecandiol and tri-n-octylphosphine oxide(TOPO) were used as reducer and surfactant,respectively.The chemically precipitated FeNi3 MNPs are well dispersed and have well-controlled particle sizes around 10～20 nm with a very narrow size distribution(±1.2 nm).The highly monodispersive FeNi3 MNPs present good uniformity in particle shape and crystallinity on particle surfaces.The MNPs exhibit well soft magnetism with saturation magnetization of ～61 emu/g and Hc～0.The biomedically compatible FeNi MNPs which were coated with biocompatible polyethyleneimine(PEI) polymer were also synthesized.We demonstrated that the PEI coated FeNi MNPs can enter the mammalian cells in vitro and can be used as a magnetic resonance imagine(MRI) contrast agent.The results demonstrated that FeNi MNPs potentially could be applied in the biomedical field.The functionalized magnetic beads with biocompatible polymer coated on MNPs are also completed for biomedical applications.

Morphology and Magnetic Properties of Electrodeposited Iron and Nickel Based Alloy Foils

An alternative to conventional process for the preparation of soft magnetic metal foils of Fe,Fe-Ni,Fe-Co and Fe-Ni-Co by electroforming was described.The microstructure and magnetic properties were observed.The results showed that the crystal size of the iron-based alloy foil is less than 10μm,while that of nickel-based alloy foil is about 2μm.Moreover,the electroformed Fe-Ni foil has better magnetic properties than the conventional milled permalloy 1J79 foil.

Microstructure and Magnetic Properties of Fe-Ni Alloy Fabricated by Selective Laser Melting Fe/Ni Mixed Powders

Fe-Ni alloy, as a widely applied ferromagnetic material, is synthesized using selective laser melting （SLM）. The chemical compositions and microstructure of the SLM Fe-Ni alloy are characterized by X-ray diffraction （XRD）, energy dispersive X-ray spectroscopy and scanning electron microscopy. It was found that the samples exhibited fine grains with homogenous distribution when a low laser scanning velocity was used. Moreover, the magnetic properties of the samples with different laser parameters are also measured. It shows that the SLM Fe-30%Ni alloy possesses a low coercivity and high saturation magnetization. It also can be obtained that SLM is an alternative faster method to prepare soft magnetic material with complex shapes. Moreover, the magnetic properties can be influenced by the laser parameters.

δ/γtransformation in non-equilibrium solidified peritectic Fe-Ni alloy

Through phase transformation kinetic analysis and experimental observation,the δ/γtransformation occurring in the non-equilibrium peritectic Fe-4.33at.%Ni alloys was systematically investigated.According to JMA solid-state transformation ki-netic theory,the Time-Temperature-Transformation(TTT)curves of the δ/γtrans-formation in peritectic Fe-Ni alloy were calculated.On this basis,the physical cor-relation between the δ/γtransformation and the initial undercooling of melt(T)was elucidated.The results indicate that the change of T can alter not only the overall δ/γtransformation pathways but also the transformation fraction with re-spect to each transformation mechanism.