Fe Grains Research Articles

In situ studies on superior thermal stability of bulk FeZr nanocomposites

Nanostructured metals received significant attention due to their high mechanical strength. However, their poor thermal stability hinders their applications at high temperature. Here we show extraordinary thermal stability of FeZr nanocomposites with micron-sized Fe grains well distributed in the nanostructured Fe/Fe2Zr eutectic laminates. The hardness of annealed FeZr nanocomposites remained unchanged up to 700°C. Grain growth at higher annealing temperatures leads to hardness drop. Moreover, in situ annealing inside a transmission electron microscope revealed an unexpected coarsening mechanism of α-Fe grain: thermal stress arising from thermal expansion mismatch between Fe and Fe2Zr led to plastic yielding of large α-Fe grains. Debonding between α-Fe grain and Fe2Zr along phase boundary introduced nanometer thick gaps, which were subsequently filled by Fe from eutectic laminates, manifested as grain coarsening of α-Fe grains.

Atomistic tensile deformation mechanisms of Fe with gradient nano-grained structure

Large-scale molecular dynamics (MD) simulations have been performed to investigate the tensile properties and the related atomistic deformation mechanisms of the gradient nano-grained (GNG) structure of bcc Fe (gradient grains with d from 25 nm to 105 nm), and comparisons were made with the uniform nano-grained (NG) structure of bcc Fe (grains with d = 25 nm). The grain size gradient in the nano-scale converts the applied uniaxial stress to multi-axial stresses and promotes the dislocation behaviors in the GNG structure, which results in extra hardening and flow strength. Thus, the GNG structure shows slightly higher flow stress at the early plastic deformation stage when compared to the uniform NG structure (even with smaller grain size). In the GNG structure, the dominant deformation mechanisms are closely related to the grain sizes. For grains with d = 25 nm, the deformation mechanisms are dominated by GB migration, grain rotation and grain coalescence although a few dislocations are observed. For grains with d = 54 nm, dislocation nucleation, propagation and formation of dislocation wall near GBs are observed. Moreover, formation of dislocation wall and dislocation pile-up near GBs are observed for grains with d = 105 nm, which is the first observation by MD simulations to our best knowledge. The strain compatibility among different layers with various grain sizes in the GNG structure should promote the dislocation behaviors and the flow stress of the whole structure, and the present results should provide insights to design the microstructures for developing strong-and-ductile metals.

NEAR-INFRARED EXTINCTION DUE TO COOL SUPERNOVA DUST IN CASSIOPEIA A

We present the results of extinction measurements toward the main ejecta shell of the Cassiopeia A supernova (SN) remnant using the flux ratios between the two near-infrared (NIR) [Fe II] lines at 1.26 and 1.64 $\mu {\rm m}$. We find a clear correlation between the NIR extinction ($E(J-H)$) and the radial velocity of ejecta knots, showing that redshifted knots are systematically more obscured than blueshifted ones. This internal "self-extinction" strongly indicates that a large amount of SN dust resides inside and around the main ejecta shell. At one location in the southern part of the shell, we measure $E(J-H)$ by the SN dust of 0.23$\pm$0.05 mag. By analyzing the spectral energy distribution of thermal dust emission at that location, we show that there are warm ($\sim$100 K) and cool ($\sim$40 K) SN dust components and that the latter is responsible for the observed $E(J-H)$. We investigate the possible grain species and size of each component and find that the warm SN dust needs to be silicate grains such as MgSiO$_{3}$, Mg$_{2}$SiO$_{4}$, and SiO$_{2}$, whereas the cool dust could be either small ($\leq$0.01 $\mu {\rm m}$) Fe or large ($\geq$0.1 $\mu {\rm m}$) Si grains. We suggest that the warm and cool dust components in Cassiopeia A represent grain species produced in diffuse SN ejecta and in dense ejecta clumps, respectively.

Irradiation tolerance of amorphous SiOC/crystalline Fe composite

We examined the radiation tolerance of amorphous silicon oxycarbide (SiOC) and crystalline Fe composite by using ion irradiation and transmission electron microscopy (TEM). The Fe/SiOC multilayer thin films were grown via magnetron sputtering with controlled length scale on a surface oxidized Si (100) substrate. These alloys were irradiated by 120keV He+ ions to a damage level of ~1.3 displacements per atom (dpa) at room temperature. TEM characterization shows neither sign of point defect clusters in Fe layer, nor an indication of crystallization or new phase formation in SiOC layer. Our findings suggest that the crystalline/amorphous interface and Fe grain boundary can help to annihilate point defects generated during irradiation, and therefore enhance radiation tolerance properties.

Diffusion and solid state reactions in Fe/Ag/Pt and FePt/Ag thin-film systems

Depth profiles of tri-layered Fe(15 nm)/Ag(10 nm)/Pt(15 nm)/SiO2(100 nm)/Si(1 0 0) and bi-layered Fe50Pt50(15 nm)/Ag(7.5 nm)/SiO2(100 nm)/Si(1 0 0) thin films after different heat treatments were investigated by secondary neutral mass spectrometry. Isotherm annealing of the tri-layered samples was carried out between 245 and 390 °C up to several hours, while isochrone thermal annealing was performed between 600 and 900 °C for 30 s. Composition profiles, obtained after isotherm heat treatment, show that initially there was a strong intermixing between Ag and Pt, resulting most likely in the formation of an AgxPt1−x reaction layer. Furthermore, the intermixing process was much faster in the Ag layer accompanied by the segregation of Ag to the substrate/Pt interface. Later on the Pt, which diffused through the Ag layer, started to penetrate into the Fe grain boundaries. This process led to the formation of the FePt reaction product. At the same time as the Pt diffused into the Fe layer, reducing the amount of Pt in the AgxPt1−x layer, the Ag appeared to ‘move’ towards the substrate. Finally, an almost fully homogeneous FePt alloy layer formed with some FePt present in the grain boundaries of the remaining Ag. This behavior was compared to both types of samples subjected to isochrone thermal annealing. High temperature treatments resulted in similar results and eventually in the formation of a homogeneous L10 ordered FePt alloy with randomly distributed Ag in the grain boundaries and at the free surface.

Synthesis of aluminum oxide dispersed α-Fe with nano sized grains by simple milling

Aluminum oxide (with 4volume% of Al2O3) dispersed α-Fe (BCC) with nano-sized grain was synthesized by reactive-cryogenic milling with a mixture of the elemental Fe, Al and Fe3O4 (Magnetite) powders as a reactant. Prior to the Hot Isostatic Press (HIP) for further densification of the materials, the milled powders were hot pressed (HPed) at the elevated temperature. The microstructure of the consolidated materials was characterized by standard metallographic techniques such as TEM (Transmission Electron Microscopy), STEM–EDS (Energy Dispersive Spectroscopy), and XRD (X-ray Diffractometer). Mechanical properties of the materials were determined by compressive yield test and micro Vickers hardness test at room temperature. The grain size estimation was attempted for the materials by XRD, using the Scherrer formula and TEM pictures. The microstructure of the materials was comprised with a mixture of a homogeneous distribution of Fe and Al2O3 nano grains. The 0.2% off-set yield strength and micro Vickers hardness of the materials were as high as 824±39MPa and 3.70±0.1GPa, respectively.

Effects of NaBF4 + NaF on the Tensile and Impact Properties of Al-Si-Mg-Fe Alloys

NaBF4 + NaF were found to play three roles, i.e., Fe-eliminator, grain refiner, and eutectic modifier, in treating A356 alloy with a high Fe content. The joint effects led to significant improvement in both tensile and impact properties of thus treated alloy. The multiple reactions between the NaBF4 + NaF and Al-Si-Mg-Fe system are suggested to form Fe2B, AlB2, and Na in the melt, as per thermodynamic analysis. The three are responsible for Fe removal, grain refinement, and eutectic modification, respectively. When NaBF4 and NaF are mixed in weight ratio of 1:1, an optimum addition rate is in the range between 1.0 and 2.0 wt pct for treating AlSi7Mg0.3Fe0.65 alloy, based on the results of tensile and impact tests. Excessive addition of the salt may deteriorate the mechanical properties of the alloy, basically owing to overmodification of Si and contamination of salt inclusions.

SULFURIZATION OF IRON IN THE DYNAMIC SOLAR NEBULA AND IMPLICATIONS FOR PLANETARY COMPOSITIONS

One explanation for the enhanced ratio of volatiles to hydrogen in Jupiter's atmosphere compared to a a gas of solar composition is that the planet accreted volatile-bearing clathrates during its formation. Models, however, suggest that S would be over abundant if clathrates were the primary carrier of Jupiter's volatiles. This led to the suggestion that S was depleted in the outer nebula due to the formation troilite (FeS). Here, this depletion is quantitatively explored by modeling the coupled dynamical and chemical evolution of Fe grains in the solar nebula. It is found that disks that undergo rapid radial expansion from an initially compact state may allow sufficient production of FeS and carry H2S-depleted gas outward where ices would form, providing the conditions needed for S-depleted clathrates to form. However, this expansion would also carry FeS grains to this region, which could also be incorporated into planetesimals. Thus for clathrates to be a viable source of volatiles, models must account for the presence of both H2S in FeS in the outer solar nebula.

Post-irradiation plastic deformation in bcc Fe grains investigated by means of 3D dislocation dynamics simulations

Post-irradiation tensile straining is investigated by means of three-dimensional dislocation dynamics simulations adapted to body centred cubic Fe. Namely, 1μm Fe grains are strained at various temperatures in the 100–300K range, in absence and in presence of radiation-induced defect dispersions. The defect-induced hardening is consistent with the disperse barrier effect up to 5×1021m-3 loops and is weakly dependent on the straining temperature. The dislocation-loops interaction rate augments with the accumulated plastic strain, loop density and strength; while it is mainly independent of the number of active slip systems and thermally activated screw dislocation mobility. An additional, radiation-induced hardening mechanism known as dislocation “decoration” is also implemented and tested for comparison. Those results show that the plastic flow localisation transition depends on the total yield point rise rather than on the lone, dispersed loop density. The simulation results are then rationalized through an original micro-mechanical model relating the grain-scale stress–strain behaviour to dislocation sub-structure formation and spreading. That model combines strain dependent and strain independent hardening mechanisms, which both contribute to the associated stress–strain response and plastic flow spreading.

Analysis of phase transformations in Fe–(Co)–B–Si–(P)

The phase transformations in ferromagnetic nano-structured (Fe85−xCoxB10Si5)100−yPy (where x=4; 8; 12 and y=0; 3) systems were investigated. The multi-component amorphous alloys were prepared by planar flow casting into the form of thin ribbons and then isothermally crystallized at selected temperatures determined from the heating experiments.The subsequent crystallization stages of bcc-Fe and borides were determined by the electrical resistivity, differential scanning calorimetry and thermogravimetry measurements, the important temperature parameters and intervals of stability and phase transformations were estimated. The phase analysis performed by TEM and XRD diffraction identified different crystallization products formed in the course of transition from the amorphous state. Morphology of nano-sized Fe grains in amorphous matrix and the transformation of remaining matrix into boride phases were observed we compared the effects of different additives onto the transformations curves and on the resulting structure.

Effect of substrate temperature on structure and magnetic properties of Fe/C granular multilayers

[Fe (3 nm)/C (3 nm)]10 granular multilayers were synthesized by alternately depositing iron and carbon at different substrate temperatures using magnetic sputtering. The effects of substrate temperature on the microstructure, surface morphology and magnetic properties were investigated using X-ray diffraction, Raman spectroscopy, atomic force microscopy, transmission electron microscopy, magnetic force microscopy and superconducting quantum interference device magnetometer. Results show that the Fe/C granular multilayers films exhibit amorphous-like structure and the crystalline Fe particles are dispersed in an amorphous C matrix, namely, the Fe/C granular multilayers consisting of successive planes of nanosized Fe grains are separated by amorphous C along the growth direction. With the increase of substrate temperature from room temperature to 350 °C, Fe grain sizes increase from ~8.42 to ~9.59 nm, and Fe and C phases are separated completely at 350 °C. Magnetic measurements reveal that the coercivity and saturation magnetization of the Fe/C granular multilayers are strongly dependent on substrate temperature. The coercivity increases with the increase of substrate temperature, while the saturation magnetization decreases. It suggests that the enhanced coercivity can be attributed to the weakened inter-grain interaction because of the phase segregation and the increase in grain size, and the reduction of saturation magnetization is due to the diffusion of the C atoms to the surfaces of Fe particles. The magnetic domain percolation behavior cannot be observed in Fe/C granular multilayers since the Fe volume fraction is less than percolation threshold in our experiment.

Properties of He clustering in α-Fe grain boundaries

Classical molecular dynamics and density functional theory calculations are performed to study the impact of two distinct Fe grain boundaries (GBs) on the clustering properties of helium (He) and the possible He effect on GB decohesion. Several He concentrations are considered. Common properties of He clustering are found for the both GBs, which are visibly different from the bcc bulk. In particular, He clusters in the GBs are always elongated in the directions parallel to the interface and contracted in the direction normal to the GB plane, while they are isotropic in the bcc bulk. When the He number in the clusters is sufficiently large, the strong local pressure promotes the occurrence of loop punching, which is easier to trigger in the GBs than in the bulk, resulting in a lower He-to-vacancy ratio in the GB clusters. The emitted self-interstitial atoms (SIAs) can more easily dissociate from the clusters in the GBs than in the bulk, leading to relatively lower local pressures around the clusters in the GBs, and facilitating the clusters growth. He is found to decrease GB cohesion, and the embrittling effect of He increases with its concentration. But interestingly, this effect decreases with He clustering. The present findings are fully compatible with existing experimental evidence, for instance, for a stronger GB embrittlement due to He at rather low temperatures than at higher temperatures.

Production and Properties of Soft Magnetic Cores Made From Fe-Rich FeSiBPCu Powders

Fe-rich Fe83.3Si4B8P4Cu0.7 powders with the particle sizes below 150 $\mu $ m were prepared by spinning water atomization process. As-prepared powders were structurally amorphous. The powders with small and large particle size were insulated with the phenol resin and compacted to a toroidal shaped core (outer diameter $\sim 13$ , inner diameter $\sim 8$ , and height $\sim 5$ –6 mm) by cold-pressing at the pressure of $\sim 0.5$ –1.5 GPa. Core loss decreases, and magnetic permeability increases after annealing treatment at 350 °C for 20 min. The powder particles in the annealed core consist of nanocrystalline $\alpha $ -Fe grains in the amorphous matrix. Cores exhibit a constant initial permeability ( $\mu _{i})$ up to the frequency range of $\sim 30$ MHz. Core loss is shown to be dependent on particle size. Cores made from smaller powder particles have low core loss at high frequencies. Our powder cores exhibit lower core loss than the Somaloy500 powder cores measured under the magnetic induction of 0.5 T, and are promising for filling the gaps in high frequency and high induction application of ferrite materials.

Development of Nanostructure Formation of Fe<sub>73.5</sub>Cu<sub>1</sub>Nb<sub>3</sub>Si<sub>13.5</sub>B<sub>9</sub> Alloy from Amorphous State on Heat Treatment

Iron-based amorphous alloys have attracted technological and scientific interests due to their excellent soft magnetic properties. The typical nanocrystalline alloy with the composition of Fe73.5Cu1Nb3Si13.5B9 known as FINEMENT has been studied for structural properties analysis. Recently, it is found that after proper annealing the amorphous alloy like Fe73.5Cu1Nb3Si13.5B9 has a transition to the nanocrystalline state, thus exhibiting good magnetic properties. The alloy in the form of ribbon of 10 mm width and 25mm thickness with the composition of Fe73.5Cu1Nb3Si13.5B9 was prepared by rapid quenching method. The prepared ribbon sample has been annealed for 30 min in a controlled way in the temperature range 490℃ - 680℃. By analyzing X-ray diffraction (XRD) patterns, various structural parameters such as lattice parameters, grain size and silicon content of the nanocrystalline Fe(Si) grains, crystallization behavior and nanocrystalline phase formation have been investigated. In the nanocrystalline state, Cu helps the nucleation of α-Fe(Si) grains while Nb controls their growth, Si and B has been used as glass forming materials. Thus on the residual amorphous, the nanometric Fe(Si) grains develops. From broadening of fundamental peaks, the optimum grain size has been determined in the range of 7 - 23 nm.

20107 表面観察による溶融鉛フリーはんだ中の炭素鋼の初期腐食解析

The purpose of this study is to investigate the corrosion behavior of pure iron and low-carbon steel in molten lead-free solder. Pure iron, S10C, and S45C were used as corrosion test specimens. Sn-3.0mass%Ag -0.5mass%Cu was used as the molten lead-free solder for the corrosion test. Corrosion test was carried out at 773 K for up to 300 minutes in the electronic furnace. The experimental results showed that corrosion incubation period of iron and steel are dependent on the carbon content. The more carbon concentration steel contains, the longer incubation period, hi the initiation of corrosion of iron and steel, it was supposed that some IMCs (FeSn_2) had nucleated at the Fe grains or primary ferrite grains. These corrosion nucleation sites in this study has not been clarified in this study.

First-principles Study of Hydrogen-induced Embrittlement in Fe Grain Boundary with Cr Segregation

First-principles Study of Hydrogen-induced Embrittlement in Fe Grain Boundary with Cr Segregation

024 分子動力学シミュレーションによるFe対応粒界の破壊強度解析

024 分子動力学シミュレーションによるFe対応粒界の破壊強度解析

Epitaxial Fe/Y2O3 interfaces as a model system for oxide-dispersion-strengthened ferritic alloys

The fundamental mechanisms underlying the superior radiation tolerance properties of oxide-dispersion-strengthened ferritic steels and nanostructured ferritic alloys are poorly understood. Thin film heterostructures of Fe/Y2O3 can serve as a model system for fundamental studies of radiation damage. Epitaxial thin films of Y2O3 were deposited by pulsed laser deposition on 8% Y:ZrO2 (YSZ) substrates with (100), (110), and (111) orientation. Metallic Fe was subsequently deposited by molecular beam epitaxy. Characterization by X-ray diffraction and Rutherford backscattering spectrometry in the channeling geometry revealed a degree of epitaxial or axiotaxial orientation for Fe(211) deposited on Y2O3(110)/YSZ(110). In contrast, Fe on Y2O3(111)/YSZ(111) was fully polycrystalline, and Fe on Y2O3(100)/YSZ(100) exhibited out-of-plane texture in the [110] direction with little or no preferential in-plane orientation. Scanning transmission electron microscopy imaging of Fe(211)/Y2O3(110)/YSZ(110) revealed a strongly islanded morphology for the Fe film, with no epitaxial grains visible in the cross-sectional sample. Well-ordered Fe grains with no orientation to the underlying Y2O3 were observed. Well-ordered crystallites of Fe with both epitaxial and non-epitaxial orientations on Y2O3 are a promising model system for fundamental studies of radiation damage phenomena. This is illustrated with preliminary results of He bubble formation following implantation with a helium ion microscope. He bubble formation is shown to preferentially occur at the Fe/Y2O3 interface.

Effect of pre-reduction on the performance of Fe2O3/Al2O3 catalysts in dehydrogenation of propane

The effect of carbon monoxide and hydrogen pre-reduction on the performance of 10FeAl catalyst in propane dehydrogenation was studied. The optimal results, 20wt% propylene yield at an overall propane conversion of 24wt% was obtained over the sample pre-reduced by hydrogen at 600°C for 10h at 560°C. Based on XRD, XPS and IR results, it is proposed that the carbon and FexC species formed from propylene cracking under the activation of surface adsorbed oxygen species are the active sites for the formation of abundant methane over untreated 10FeAl catalyst. Pre-reduction treatment leads to the consumption of surface adsorbed oxygen species and the formation of Fe and Fe2+ species, which are active for propane dehydrogenation. For one thing, propane hydrogenolysis is strongly inhibited due to the large size (around 30nm) of Fe grains. For another, propylene cracking and the generation of carbon and FexC species are largely suppressed in the absence of surface electronegative oxygen species, hence inhibiting propane cracking and hydrogenolysis reactions, resulting in greatly improved dehydrogenation performance.

Fe-Rich Fe–Si–B–P–Cu Powder Cores for High-Frequency Power Electronic Applications

The Fe-rich Fe 83.3 Si 4 B 8 P 4 Cu 0.7 magnetic powder with the particle size below 150 μm was obtained by spinning water atomization process. The as-prepared powder shows almost amorphous structure. The toroidal cores with outer diameter 13 mm and inner diameter 8 mm with height ~4-6 mm were compacted and sintered at different temperature by spark plasma sintering technique under the maximum load of ~800 MPa. High relative density (with respect to nanocrystalline ribbons of the same composition) up to ~89% was obtained. The powder particles in the sintered core consist of nanocrystalline α Fe grains in the amorphous matrix. A constant initial permeability (μ i ) more than 50 was obtained up to the frequency range of 50 MHz. As expected, the permeability was found to increase with the increase in density of the core (maximum initial permeability of 364). Low magnetic coercivity (H c ) can be obtained in these cores, closed to ~80 A/m. Lowcore loss (W) is due to reduced eddy-current loss (at high frequencies), resulting from the electrical insulation of the powder particles by resin. Our soft magnetic powder cores (PCs) exhibit lower core loss than the Somaloy PCs measured under a relatively high magnetic induction, e.g., 0.5 and 1 T, which may fill the gaps in high-frequency high induction application of ferrite materials.