αFe Phase Research Articles

Effect of TaC content on microstructure and wear behavior of PRMMC Fe-TaC coating manufactured by electrospark deposition on AISI304 stainless steel

The Fe-TaC coatings on stainless steel by electrospark granule deposition in an anode mixture of iron granules and tantalum carbide powder were first obtained. The material deposition rate on the substrate increased with the TaC powder concentration growth in the anode mixture, facilitating the initiation of electrical discharges. X-ray analysis of deposited coatings shows the presence of the TaC, γFe, and αFe phases. The tantalum carbide concentration grows with an increase in the content of TaC powder in the anode mixture, from 2.4 to 14.8 vol%. The dependence of the wear rate of coatings on the concentration of tantalum carbide in the anode mixture had a parabola form, with a minimum of 5 vol%. However, with a further increase in the TaC concentration in the anode mixture, the wear rate of the coatings monotonically increased due to spalling of TaC grains due to a deficiency of the metal binder.

Experimental determination and thermodynamic evaluation of low-temperature phase equilibria in the Fe–Ni binary system

Phase equilibria between αFe and γ(Fe,Ni) in the Fe–Ni binary system at low temperatures above 400 °C were determined experimentally, and thermodynamic descriptions to calculate the Gibbs energy of involved phases were revised with taking into account the interaction effect between the chemical and magnetic orderings. Heat-treatment for equilibration of gas-atomized powder of Fe–Ni alloys without deformation resulted in the formation of a microstructure consisting of directional γ precipitates in α' martensite matrix. Converge-milling processing, a kind of mechanical alloying technique, in advance of heat-treatment, was applied to introduce a large number of lattice defects into powder particles, which enhanced α + γ recrystallization to form an equiaxed dual-phase polycrystalline microstructure. Equilibrium compositions of the equiaxed grains of the α and γ phases were measured by an FE-EPMA, the spatial resolution of quantitative analysis of which is 0.5 μm in diameter with accelerating voltage of 6 kV. Equilibrium compositions of the γ phase coincided with the phase diagram assessed in accordance with experimental results in the literature. On the other hand, the solubility of Ni in the α phase exhibited considerable deviation from “retrograde solubility” determined according to previous data. Thermodynamic analysis with revised parameters suggests that the underestimated solubility of Ni in the αFe phase is caused by the additional Gibbs energy due to lattice defects in the α’ martensitic structure.

Microstructural evolution and magnetic property of a rapidly solidified ternary Fe37.5Cu37.5Sn25 peritectic-type alloy

The liquid Fe37.5Cu37.5Sn25 peritectic-type alloy was rapidly solidified by glass fluxing, drop tube, and melt spinning techniques. The solidification structures consisted of three phases, including the αFe solid solution and the Cu3Sn and Cu6Sn5 intermetallic compounds under different conditions. In this work, the bulk undercoding ΔT equals the liquidus temperature TL minus the nucleation temperature TN of the primary solid phase. During the bulk undercooling process, a maximum liquid undercooling of 272 K (0.18TL) was achieved. Metastable liquid phase separation was induced if the undercooling exceeded 177 K. Within a moderate undercooling range from 8 to 177 K, the solidified structures showed coarse dendrites, and the dendritic growth velocity increased to 41.5 mm/s following a power relation. As the drop tube technique provided a containerless state, a maximum surface cooling rate of 3.5 × 104 K/s was achieved. The alloy droplets displayed metastable liquid phase separation even at the largest droplet diameter of 944 μm. The cooling rate and thermal Marangoni migration were found to greatly influence the phase-separated patterns of the alloy droplets. Under the melt spinning condition, the microstructures of the Fe37.5Cu37.5Sn25 alloy ribbons were significantly refined and displayed soft magnetic characteristics. Furthermore, the experimental results demonstrated that the grain size of the αFe phase affected the coercivity of the alloy ribbons.

Corrosion, Mechanical and Catalytic Properties of Coatings Based on FeNiCrWMoCoCB Metallic Glasses

This work is devoted to the deposition of coatings based on FeNiCrWMoCoCB metallic glasses on a surface made of 35 steel; the deposition is carried out by electrospark machining in a medium of granules of metals and alloys used as electrode materials. X-ray diffraction analysis showed that an amorphous phase is predominant in the composition of coatings. At a temperature of 1100°C, the amorphous phase crystallizes in borocarbide of the M23(C,B)6 type, an intermetallic of iron, nickel, and chromium, and αFe phase. Polarization tests of the coating in the NaCl solution (3.5%) demonstrate a lower corrosion current and a higher polarization resistance compared with the 35 steel. It is found during the study of a heat resistance at 600, 700, and 800°C that the use of the FeNiCrWMoCoCB coating on the 35 steel enhances a resistance of its surface to a high-temperature gas corrosion in 8.7, 6.3, and 3.0 times, respectively (the experiment time was 40 h). The wear resistance of the FeNiCrWMoCoCB coatings in a dry sliding wear mode at loadings of 10 and 25 N was 2.2 and 1.7 times higher than for the 35 steel. The samples with the coatings based on the FeNiCrWMoCoCB metallic glasses show a high catalytic activity for a decomposition of a methylene blue solution as at the presence of hydrogen peroxide, as well as without it.

Structural changes during the formation of diffusion bonded joints between titanium and stainless steel

.In the present investigation, transient liquid-phase bonding was performed between pure titanium (Grade 2) and stainless steel (X5CrNi 18-10) using nickel foil as an intermediate material. The process was carried out at the temperatures of: 950, 975 and 1000 ° C for 60 minutes under the compressive stress of 2 MPa in a vacuum. The microstructure was investigated using light microscopy and scanning electron microscopy equipped EDS. The metallographic examination shows that the diffusion interfaces are free from cracks. However, Kirkendall voids were observed at the borders of materials. Especially large voids were formed in middle section of the joint prepared using the highest bonding temperature. The structure of the joints on the titanium side was composed of the eutectoid mixture αTi+Ti2Ni and layers of intermetallic phases Ti2Ni, TiNi and TiNi3. The nickel interlayer blocked the diffusion of titanium to stainless steel side at 950 °C bonding temperature and prevented from formation of the Fe-Ti intermetallic layers. The layer of a solid solution γFe+Ni between nickel and stainless steel was observed at the 950 °C processing temperature. The mixture of λ+FeTi+Ti, FeTi+Ti, λ+αFe and λ+χ+αFe phases was formed at 975 and 1000 °C at the nickel-stainless steel interlayer.

Homogeneous granular microstructures developed by phase separation and rapid solidification of liquid Fe-Sn immiscible alloy

Liquid Fe41.5Sn58.5 alloy was containerlessly solidified under the free-fall microgravity condition inside drop tube. Conspicuous liquid phase separation took place in the broad miscibility gap of 325 K and formed the dispersed pattern microstructures of Fe-rich phase distributed in the matrix of Sn-rich phase. Although the equilibrium phase constitution includes only FeSn and FeSn2 compounds in the phase diagram, the high cooling rate and large undercooling lead to the formation of four new metastable phases αFe, Fe3Sn, (Sn)1 and (Sn)2 respectively. The granular patterns of Fe3Sn phase dominates the droplet solidification process. Phase field simulation reveals that the granular microstructure experiences three evolution stages during liquid phase separation: the nucleation, aggregation, or coalescence and Ostwald ripening of secondary liquid phase, which agrees well with the experimental results. Meanwhile, two kinds of Marangoni migrations play an important role to develop the homogeneous granular structures. EDS analysis shows that the solute contents of various phases increase with the decrease of alloy droplet diameter, while the primary αFe phase is found to contain as much as 18.07 at.% Sn at droplet diameter 73 μm owing to the significant solute trapping during rapid solidification.

Solute redistribution during phase separation of ternary Fe–Cu–Si alloy

Ternary Fe48Cu48Si4 immiscible alloy was rapidly solidified under the containerless microgravity condition inside a drop tube. Liquid phase separation took place in the alloy melt and led to the formation of various segregated structures. The core–shell structure consisting of Fe-rich and Cu-rich zones and the homogenously dispersed structure were the major structural morphologies. Phase field simulation results revealed that the two-layer core–shell was the final structure of liquid phase separation. The solute redistribution of liquid Fe48Cu48Si4 alloy experienced the macroscopic solute distribution induced by liquid phase separation, the secondary phase separation within the separated liquid phases and the solute trapping during rapid solidification. Energy dispersive spectroscopy analysis showed that the solute Si was enriched in the Fe-rich zone whereas depleted in the Cu-rich zone. In addition, both αFe and (Cu) phases in the Fe-rich zone exhibited a conspicuous solute trapping effect. As compared with (Cu) phase, αFe phase had a stronger affinity with solute Si.

Effects of external magnetic field on the diffusion coefficient and kinetics of phase transformation in pure Fe and Fe–C alloys

The calculation model of the diffusion coefficient under an external magnetic field was presented. The self-diffusion coefficient in the αFe (bcc) phase and the diffusion coefficients of Ni and Co in the αFe phase were calculated. The calculated results indicate that the diffusion coefficient decreases with the decreasing of temperature and increasing of external magnetic field intensity. The kinetics of the γFe (fcc) → α Fe (bcc) phase transformation under an external magnetic field in pure Fe and Fe-1 at. % C alloy were also studied. It is found that grain refinement under an external magnetic field is caused by the increasing of nucleation rate and growth rate as well as the short transformation time.

Fe-Cr-B系硬質ガスアトマイズ粉末の諸特性に及ぼす添加元素の影響

In order to obtain a high hardness shot peening media, the properties of Fe-8%Cr-6.5%B media (Base media) with several additive elements were investigated. Fe-8%Cr-6.5%B-X%M media (X%M=2%Zr, 2%Nb and 2~16%W; Denoted hereafter as X%M media) were produced by gas atomization. Vickers hardness, density and ductility of these media were examined. The properties of Base, 2%Zr, 2%Nb and 2%W media were examined. Vickers hardness of 2%W media was high, but those of 2%Zr and 2%Nb media were low compared to that of Base media. Then, the properties of Base and 2∼16%W media were examined. Vickers hardness of 4%W showed the first peak, then decreased until 8%W. Furthermore, in the range of W addition amount beyond 8% Vickers hardness increased again. 4%W media with the combination of high hardness of 1300 HV, high density of 7.6 Mg/m3 and high ductility exhibited the best performance as shot peening media in this study. From the results of X-ray diffraction, transmission electron microscope (TEM) observations and the evaluations of Vickers hardness after heat treatment at 973 K, it was inferred that 0∼4%W media were strengthened by 250∼300 HV due to supersaturated solid solution of B element with αFe phase. In addition, all media with W addition were strengthened due to solid solution of W element with αFe phase. According to the simulation from the theoretical formula proposed by Ogawa and Asano, it was estimated that the maximum compressive residual stress at carburized steel surface shot peened by 4%W media was approximately 20 MPa higher than that by Base media.

Dendrite growth characteristics within liquid Fe-Sb alloy

Bulk samples and small droplets of liquid Fe-10%Sb alloys are undercooled up to 429 K (0.24T L) and 568 K (0.32T L), respectively, with glass fluxing and free fall techniques. The high undercooling does not change the phase constitution, and only the αFe solid solution is found in the rapidly solidified alloy. The experimental results show that when the undercooling is below 296 K, the growth velocity of αFe dendrite rises exponentially with the increase of undercooling and reaches a maximum value 1.38 m/s. Subsequently, the growth velocity begins to decrease if undercooling further increases. The αFe phase grows into coarse dendrites under small undercooling conditions, whereas it becomes vermicular dendrites in highly undercooled melts. The solute trapping is closely related to the dendrite growth velocity and cooling rate rather than undercooling. Although the solute trapping can be remarkably suppressed by the rapid dendrite growth, the segregationless solidification is not observed in the present experiments due to the large solidification temperature range.

Phase relationships in the Er–Fe–Mn ternary system at 773 K

In order to determine the existence of phases and relationships in the Er–Fe–Mn system at 773 K, we have carried out this work mainly by X-ray powder diffraction with the aid of differential thermal analysis and have obtained the conclusions below. The existence of seven binary compounds ErFe 2, ErFe 3, Er 6Fe 23, Er 2Fe 17, ErMn 12, Er 6Mn 23, ErMn 2 and one intermediate solid solution γ(Fe·Mn) have been confirmed in this system. Er 6Fe 23 and Er 6Mn 23 form continuous solid solution Er 6 (Fe 23− X Mn X ) (0 ≤ X ≤ 23). At 773 K, the maximum solid solubility of Fe in αMn, ErMn 12, ErMn 2 phases and Mn in ErFe 2, Er 2Fe 17, αFe phases are about 31, 69, 13 at% Fe and 47, 28, 8 at% Mn, respectively. The homogeneity range of γ(Fe·Mn) phase extended from about 34 at% Mn to 52 at% Mn. The maximum solid solubility of Er in γ(Fe·Mn) phase is about 2 at% Er. The isothermal section consists of ten single-phase regions, sixteen two-phase regions and seven three-phase regions. No ternary compounds were observed at 773 K in this system.

Magnetic properties of NdFe 11TiN x–αFe two-phase films

Nd(Fe,Ti) 12N x –αFe two-phase films were prepared by DC magnetron sputtering on Si substrate at room temperature to 650°C and subsequent nitriding at 450°C. The evolution of phases and magnetic properties after deposition, annealing and nitriding were studied. The films contained mainly ThMn 12 structure and αFe phase (around 10% by weight). The energy-product is as high as 18.2 MGOe at 300 K, 26.8 MGOe at 200 K, and 34.9 MGOe at 5 K.

Formation of intermetallic compounds during the sintering of zirconium–iron powders compact

The sintering process at 840°C and at 925°C, of Zr-7.2 wt. % Fe was studied by room-temperature Mössbauer spectroscopy, x-ray diffractometry, and scanning electron microscopy. According to phase analysis, most of the αFe phase disappeared after 20 h of sintering at 840°C and after 4 h at 925°C. During the sintering, small quantities of the intermetallic compound ZrFe2 as an intermediate phase were observed clearly by the Mössbauer technique and very weakly by x-ray diffractometry. The relationship among the relative quantities of αFe, ZrFe2, and Zr3Fe phases was determined. The change in density as a function of sintering time was measured, and the results were explained on the basis of the different sintering stages and phase transformations.

7: Critical evaluation of constitution of aluminium-cobalt-iron system

An evaluation of the published experimental information on the system AI-Co-Fe has been carried out, and diagrams are presented for the composition and temperature ranges in which the equilibrium relationships appear well established. Both the AI-Fe and AI-Co systems contain composition ranges corresponding to ordered body-centred cubic (bcc) structures of the CsCl-type, and extensive solid-solution formation between them and, at the appropriate temperatures, the αFe phase in the Co-Fe system characterizes the ternary system. At temperatures below approximately 760°C a volume exists in the ternary model corresponding to separation of the bcc alloys, within a range of compositions and temperatures, into a mixture of disordered β and ordered β2 solid solutions. Effectively nothing is known of the equilibrium relationships between the intermediate phases of complex crystal structure in the systems AI-Fe and AI-Co, but it is established that both Co2Al9 (ϕ) and FeA13 (θ) enter into equilibrium with aluminium containing only very small amounts of Co and Fe in solid solution. The general nature of the system is illustrated with diagrams and tables.

7: Critical evaluation of constitution of aluminium-cobalt-iron system

An evaluation of the published experimental information on the system AI-Co-Fe has been carried out, and diagrams are presented for the composition and temperature ranges in which the equilibrium relationships appear well established. Both the AI-Fe and AI-Co systems contain composition ranges corresponding to ordered body-centred cubic (bcc) structures of the CsCl-type, and extensive solid-solution formation between them and, at the appropriate temperatures, the αFe phase in the Co-Fe system characterizes the ternary system. At temperatures below approximately 760°C a volume exists in the ternary model corresponding to separation of the bcc alloys, within a range of compositions and temperatures, into a mixture of disordered β and ordered β2 solid solutions. Effectively nothing is known of the equilibrium relationships between the intermediate phases of complex crystal structure in the systems AI-Fe and AI-Co, but it is established that both Co2Al9 (ϕ) and FeA13 (θ) enter into equilibrium with aluminium containing only very small amounts of Co and Fe in solid solution. The general nature of the system is illustrated with diagrams and tables.

α鉄の磁気変態にもとづく固溶度線の異常に対するコバルトの効果

The solubility of Be, P, Mo and W in αFe in the Fe-X-Co ternary system was determined by X-ray diffraction and microprobe analysis. It was detected that the anomaly in solubility of these elements due to the magnetic transition was enlarged with the addition of Co. This result agrees well with an anticipation from the fact that the ferromagnetic character of αFe is generally emphasized by alloying of Co. Using an improved method of Zener and Hillert et al., these solubility data were analyzed thermodynamically by separating the free energy of αFe phase into the magnetic and non-magnetic components. The metastable miscibility gap in αFe-Mo-Co system was also estimated, and it was concluded that the miscibility gap in the αFe-Mo binary system expanded with the addition of Co.

Study of the sintering of a Ti-9 pct Fe system by Mössbauer spectroscopy

The first stages in the sintering of Ti-9 pet Fe were studied with the aid of room temperature Mossbauer spectroscopy and X-ray diffractometry. At a sintering temperature of 800°C most of the aFe disappeared after ten hours, at 1000°C—after less than 10 minutes. The first stages of the densification process are controlled by the disappearance of the aFe phase, which causes a decrease in density. Density increases again only after that phase has completely disappeared. Small quantities of TiFe intermetallic as an intermediate phase were observed to form, which subsequently converted to sTi. These small quantities of the intermetallic as well as the αFe phase were discernible only by Mossbauer spectroscopy, not by X-ray diffractometry. A model is presented to describe the formation of transient intermediate phases characteristic of the sintering process.