Diffusion Of Fe Atoms Research Articles

Nucleation and growth of Fe-rich phases in Al-5Ti-1B modified Al-Fe alloys investigated using synchrotron X-ray imaging and electron microscopy

Plate-like Fe-rich intermetallic phases directly influence the mechanical properties of recycled Al alloys; thus, many attempts have been made to modify the morphology of these phases. Through synchrotron X-ray imaging and electron microscopy, the underlying nucleation and growth mechanisms of Fe-rich phases during the solidification of Al-5Ti-1B-modified Al-2Fe alloys were revealed in this study. The results showed that the Al-5Ti-1B grain refiner as well as the applied pressure both resulted in reduction of the size and number of primary Al3Fe phases and promoted the formation of eutectic Al6Fe phases. The tomography results demonstrated that Al-5Ti-1B changed the three-dimensional (3D) morphology of primary Fe-rich phases from rod-like to branched plate-like, while a reduction in their thickness and size was also observed. This was attributed to the fact that Ti-containing solutes in the melts inhibit the diffusion of Fe atoms and the Al3Fe twins produce re-entrant corner on the twin boundaries along the growth direction. Moreover, the TiB2 provides possible nucleation sites for Al6Fe phases. The nucleation mechanism of Fe-rich phases is discussed in terms of experimental observations and crystallography calculations. The decrease in the lattice mismatch between TiB2 and Al6Fe phases was suggested, which promoted the transformation of Al3Fe to Al6Fe phases.

Nucleation and Growth of Fe-Rich Phases in Al-5Ti-1B Modified Al-Fe Alloys Using Synchrotron X-Ray Imaging and Electron Microscopy

The plate-like Fe-rich intermetallic phases directly influence the mechanical properties of recycled Al alloys, thus many attempts have been made to modify their morphology. Here, through synchrotron X-ray imaging and electron microscopy, we reveal the underlying nucleation and growth mechanism of Fe-rich phases during the solidification of Al-5Ti-1B inoculated Al-2Fe alloys. The experiment results shown that Al-5Ti-1B grain refiner and applied pressure both reduce the sizes and number of primary Al 3Fe phases, and promote the formation of eutectic Al6Fe phases. The tomography results shown that Al-5Ti-1B change the 3D morphology of primary Fe-rich phases from rod-like to branched plate-like and reduced their thickness and size. This is attributed to the Ti-containing solutes in the melts retard the diffusion of Fe atoms and the TiB2 provide possible nucleation sites for Al6Fe phases. The nucleation mechanism of Fe-rich phases is discussed in terms of experimental observation and E2EM model. It is suggested that the V segregated at the TiB2/Al6Fe interface and lower their mismatch and promote the transformation from Al3Fe to Al6Fe phases.

Influence of chemical composition and structural heterogeneity of 06ХН28МДТ alloy on mechanisms of its pits formation in return waters

Purpose of the work. Determine the influence of chemical composition and structure of 06ХН28МДТ alloy on mechanisms of its pits formation in model return waters with pH = 4... 8 and chloride concentration 180 mg/l.Research methods. X-ray spectral analysis on СРМ-25 spectrometer, metallographic analysis on optical micro­scope МРР-2Р. Corrosion losses of metals in pittings were determined by photometric analysis of model chloride-containing recycled waters after holding samples therein. Straight-line regression relationships between corrosion losses of metals in pittings ΔCr, ΔNi, ΔFe and alloy parameters were determined by regression analysis by least squares method. In order to determine the influence of alloy parameters on the mechanisms of its pitting formation, previously established characteristic features of selective dissolution of metals in pittings were used.Results obtained. It has been found that in model return waters with pH = 4–6.8 06ХН28МДТ alloy pits to form stable, and with pH = 7 and chloride concentration 180 mg/l – metastable pittings. In stable pittings Cr contributes to the increase of ΔFe from them, and in metastable – vice versa. This is due to the direction of solid-phase diffusion of Fe atoms from the alloy volume to the surface of stable pittings and from the surface of metastable in its volume. Therefore, the increase in Cr content in the alloy contributes to the growth of stable pittings and the repassification of metastable ones due to the decrease in their growth intensity. However, it has been found that the smaller the sizes of titanium nitrides near which pittings are formed, the lower the ΔFe in metastable and stable pittings. This is due to the lower degree of defect of the structure of the alloy austenite solid solution about small titanium nitrides.Scientific novelty. Cr promotes the growth of solid phase diffusion of Fe atoms to the surface of stable and from the surface of metastable pittings into the volume of the 06ХН28МДТ alloy. This promotes the repassification of metasta-ble and, accordingly, the growth of stable pittings. Increasing the size of titanium nitrides in the alloy contributes to increasing the number of austenite structure defects near them and to the growth of stable and metastable pittings.Practical value. Manufacturers of heat exchangers are advised to use 06ХН28МДТ alloy smelts with minimum Cr content, as well as those having titanium nitrides size of not more than 5 mcm.

Formation of Cu2O Solid Solution via High-Frequency Electromagnetic Field-Assisted Ball Milling: The Reaction Mechanism.

The contamination of environmental water with organic pollutants poses significant challenges for society, and much effort has been directed toward the development of catalysts and methods that can decompose these pollutants. While effort has been directed toward the fabrication of Cu2O catalysts by ball milling, this technique can involve long preparation times and provide low yields. In this study, we synthesized a solid solution of Cu2O in 22 h by high-frequency electric-field-assisted ball milling below 40 °C in only one step under aqueous conditions. We investigated the catalytic activities of the produced Cu2O solid solution in the microwave-assisted degradation of dyes, namely rhodamine B, phenol red and methyl orange. The prepared Cu2O solid solution was very catalytically active and completely degraded the above-mentioned dyes within 2 min. The one-dimensional diffusion model and the phase boundary (planar) model were found to describe the kinetics well. Synergism between ball milling and the high-frequency electromagnetic field plays a key role in the preparation of Cu2O solid solution nanoparticles. Ball milling facilitates the relaxation of the Cu2O lattice and high-frequency electromagnetic radiation accelerates the diffusion of Fe atoms into the Cu2O crystal along the (111) crystal plane, quickly leading to the formation of a Cu2O solid solution.

Effect of Deposition Time on Thickness and Corrosion Behavior of Zn-Fe Coating

Zn-Fe coatings on Q235 steel are prepared by pack cementation process at 390 ◦C for 2, 4, 6, 8 and 10 h to investigate the effects of the deposition time on the thickness and corrosion behavior of the Zn-Fe coatings. The thickness of the coating increases with the increase of the deposition time. The coating is composed of a thick outer layer and a thin inner layer. The formation of the coating depends on the inward diffusion of Zn atoms and the outward diffusion of Fe atoms. The outer layer is composed of Fe11Zn40 and FeZn10 phases. The corrosion behavior of the Zn-Fe coatings is evaluated by immersion test and polarization test. The results show that the Zn-Fe coatings can effectively prevent the Q235 steel from corrosion. The corrosion resistance of the coating is proportional to the deposition time.

Mechanistic understanding on the evolution of nanosized Al3Fe phase in Al–Fe alloy during heat treatment and its effect on mechanical properties

Al–1Fe (wt%) alloy containing nanosized Al3Fe phase was processed by continuous rheo-extrusion, and subjected to heat treatment at different temperatures. During heat treatment, due to the diffusion of Fe atoms, the nanosized Al3Fe phase was blunted and fragmented along the width direction, and the bluntness and fragmentation resulted in the spheroidization of Al3Fe phase. However, with the extension of heat treatment time, the spheroidized Al3Fe phase became coarse and grew along a particular plane. Then, the morphology of Al3Fe phase transformed into small plate-like. While, the plate-like Al3Fe phase with an average length of 30 µm in the as-cast Al–1Fe (wt%) alloy indicated good thermal stability during heat treatment. The different thermal stability of Al3Fe phases was attributed to their size. The large surface curvature of nanosized Al3Fe phase significantly accelerated the diffusion of Fe atoms. When the heat treatment temperature was 200 ℃ and 300 ℃, the tensile strength and elongation of the rheo-extruded Al–Fe alloy marginally decreased. The decrease of tensile strength and the decrease of elongation increased when the heat treatment temperature was greater than 400 ℃. The tensile strength and elongation of as-cast Al–1Fe (wt%) alloy were insignificantly altered. Though the loss of tensile strength of Al–Fe alloy containing nanosized Al3Fe phase was much greater, its tensile strength was always higher than the tensile strength of the as-cast Al–Fe alloy in the entire heat treatment.

Effect of titanium grain orientation on the growth of compounds at diffusion bonded titanium/steel interfaces

Commercial pure titanium plates with different grain orientations were successfully bonded to carbon steel plates by diffusion bonding. The Ti/steel interfaces were carefully characterized by scanning electron microscopy, energy-dispersive spectroscopy, electron backscattered diffraction, and X-ray diffraction. The results revealed that TiC was generated at the Ti/steel interface during the diffusion bonding process. The thickness of the TiC layer increased with increasing diffusion temperature and holding time. Furthermore, the orientation of the Ti grains influenced the activation energy for the growth of TiC and affected the thickness of the TiC layer at the Ti/steel interface. The anisotropic growth of the TiC layer was explained by the interstitial diffusion mechanism of C atom in α-Ti. Moreover, the TiC layer acted as a barrier layer at Ti/steel interface, inhibiting the diffusion of Fe atoms into α-Ti. An increased diffusion temperature reduced this barrier effect, leading to the formation of FeTi and Fe2Ti at TiC/Ti interface.

Molecular Dynamics Simulation of Diffusion of Fe in HCP Ti Lattice

Diffusion of a single Fe atom in a defect free hcp Ti lattice was studied using molecular dynamics (MD) simulation. Modified Embedded Atom Method potentials derived by Sa et al. (Scripta Mater 59:595, 2008) were used for carrying out the MD simulations. These potentials were verified by estimating the physical properties of the Fe–Ti system such as cohesive energy, bulk modulus and the shear constants. Fe atom trajectory in Ti lattice was traced in the temperature range of 500–900 °C. Diffusivity of Fe ( $$ D_{Fe} $$ ) atom in Ti lattice was obtained from the estimation of mean square displacement for total time of simulation at each temperature. $$ D_{Fe} $$ at 900 °C was obtained as 7.784 × 10−15 m2/s. From the Arrhenius analysis of $$ \ln D_{Fe} $$ versus temperature, the activation energy required for the diffusion of Fe atom in hcp Ti lattice was obtained as 117 kJ/mol.

Effect of Si on the Formation and Growth of Intermetallic Compounds at Roll-Bonded Aluminum–Steel (Al-St) Interface

The formation and growth of intermetallic compounds (IMC) were investigated using the Al-St clad materials with additional different Si content to aluminum and steel substrate by differential scanning calorimetry, scanning electron microscopy and energy-dispersive x-ray spectroscopy, x-ray diffraction and transmission electron microscopy. The addition of Si to Al (Al-0.8Si/St) can drastically delay the formation of IMC and accelerate the growth of IMC layer. The Si (Al-0.8Si/St) segregates at the interface and inhibits the diffusion of Al atom to steel before the IMC forms, which further decreases the diffusion depth of Al in the steel layer. By contrast, the addition of Si to St (Al/St-0.8Si) has limited impact on delaying the formation and decelerating the growth of IMC layer. The Si (Al/St-0.8Si) hardly affects the diffusion of Fe atom to the aluminum layer. Among the four clad materials, the major IMC layer (η-Fe2Al5) always exhibits the parabolic growth phenomenon. The addition of Si cannot influence the phase compositions of IMC at the interface between the η-Fe2Al5 layer and the aluminum. However, we observe an extra Fe-rich phase β1-Fe3Al at the interface between the Fe2Al5 layer and steel substrate in the Al-0.8Si/St clad material.

Microstructure and Mechanical Properties of Electron Beam‐Welded Joints of Titanium TC4 (Ti‐6Al‐4V) and Kovar (Fe‐29Ni‐17Co) Alloys with Cu/Nb Multi‐Interlayer

Electron beam welding of a titanium alloy (Ti‐6Al‐4V) and a kovar alloy (Fe‐29Ni‐17Co) was performed by using a Cu/Nb multi‐interlayer between them. Microstructure and composition of welded joints were analyzed by means of optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and X‐ray diffraction. Mechanical properties of welded joints were evaluated by microhardness and tensile strength tests. Results indicated that in case of 0.22 mm thickness of Nb foil, microstructure of the titanium alloy side was mainly composed of Ti solid solution and some intermetallic compounds such as FeTi and CuTi2, whereas in case of 0.40 mm thickness of Nb foil, the appearance of weld was more uniform and hardness of the weld zone decreased sharply. However, tensile strength of welded joints was increased from 88.1 MPa for the 0.22 mm Nb foil to 150 MPa for the 0.40 mm Nb foil. It was found that thicker Nb foil could inhibit diffusion of Fe atoms towards the titanium alloy side, thus promoting the formation of Ti solid solution and a small amount of CuTi2 and eliminating FeTi. In addition, in both cases, Cu0.5Fe0.5Ti was found in the fusion zone of the titanium alloy side, which had an adverse effect on mechanical properties of welded joints.

Exhibition of veiled features in diffusion bonding of titanium alloy and stainless steel via copper

An investigation was carried out to know the extent of influence of bonding-time on the interface structure and mechanical properties of diffusion bonding (DB) of TiA|Cu|SS. DB of Ti6Al4V (TiA) and 304 stainless steel (SS) using pure copper (Cu) of 200-μm thickness were processed in vacuum using 4-MPa bonding-pressure at 1123 K from 15 to 120 min in steps of 15 min. Preparation of DB was not possible when bonding-time was less than 60 min as the bonding at Cu|SS interface was unsuccessful in spite of effective bonding at TiA|Cu interface; however, successful DB were produced when the bonding-time was 60 min and beyond. DB processed for 60 and 75 min (classified as shorter bonding-time interval) showed distinctive characteristics (structural, mechanical, and fractural) as compared to the DB processed for 90, 105, and 120 min (classified as longer bonding-time interval). DB processed for 60 and 75 min exhibited layer-wise Cu–Ti-based intermetallics at TiA|Cu interface, whereas Cu|SS interface was completely free from reaction products. The layer-wise structure of Cu–Ti-based intermetallics were not observed at TiA|Cu interface in the DB processed for longer bonding-time; however, the Cu|SS interface had layer-wise ternary intermetallic compounds (T1, T2, and T3) of Cu–Fe–Ti-based along with σ phase depending upon the bonding-time chosen. Diffusivity of Ti-atoms in Cu-layer (DTi in Cu-layer) was much greater than the diffusivity of Fe-atoms in Cu-layer (DFe in Cu-layer). Ti-atoms reached Cu|SS interface but Fe-atoms were unable to reach TiA|Cu interface. It was observed that DB fractured at Cu|SS interface when processed for shorter bonding-time interval, whereas the DB processed for longer bonding-time interval fractured apparently at the middle of Cu-foil region predominantly due to the existence of brittle Cu–Fe–Ti-based intermetallics.

Evolution of implanted Fe ions in SiO2/Si wafer into uniformly sized catalyst particles for carbon nanotube forest growth

We report the synthesis of carbon nanotube (CNT) forests with a narrow diameter distribution based on Fe ion implantation method. By annealing the Fe-implanted SiO2/Si wafer in an Ar atmosphere at 800 °C for 15 min, the Fe particles on the surface of SiO2 layer are successfully formed by the diffusion of Fe atoms from the SiO2 layer. Interestingly, the size distribution of Fe catalyst particles for Fe-implanted SiO2/Si wafers does not change with the prolonged annealing durations of up to 12 h. Using secondary ion mass spectroscopy and transmission electron microscopy (TEM), we confirmed that the implanted Fe atoms diffuse out of the SiO2 layer and form Fe particles on both the SiO2 surface and the interface between SiO2 and Si. The cross-sectional TEM images indicate that the Fe catalyst particles are anchored in the SiO2 layer, which limits the particles' mobility and results in an invariant catalyst size distribution for prolonged annealing durations. Therefore, we anticipate that implantation can be an efficient alternative catalyst preparation method for CNT forest growth which can solve various growth issues that are inherently caused by conventional physical vapor deposition method.

In-situ synthesis of Al76.8Fe24 complex metallic alloy phase in Al-based hybrid composite

The complex metallic alloy (CMA), Al76.8Fe24, was in-situ synthesized in the Al-based hybrid composite by powder metallurgy technique. The structural analysis by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the Al76.8Fe24 CMA phase was formed by diffusion of Fe atoms into the Al matrix during the sintering stage. The formation of the CMA phase was mainly determined by the sintering temperature which was just above the eutectic temperature of Al–Fe. Moreover, the fully dense Al-based hybrid composite was obtained and exhibited ultrahigh strength ∼1100MPa, indicating that this method is expected to be effective in producing CMA particle reinforced Al-based hybrid composite.

Roles of Solute C and Grain Boundary in Strain Aging Behaviour of Fine-grained Ultra-low Carbon Steel Sheets

The roles of solute C and the grain boundary in the strain aging phenomenon of polycrystalline ferritic steel were investigated using Nb-bearing ULC steel sheets with a relatively low solute C content of 1–3 ppm and ferrite grain sizes of 9.5 µm and 183 µm at aging temperatures from 70 to 400°C. The steels exhibited two definite hardening stages. The 1st hardening stage appeared in both fine- and coarse-grained specimens, in which the increase in YP (ΔYP) became saturated at around 30 MPa. From the apparent activation energy and hardening kinetics, the hardening mechanism was assumed to be dislocation pinning by solute C atoms. The 2nd hardening stage, significantly appeared in fine-grained specimens accompanying a large increase in the Hall-Petch coefficient; ΔYP was quite large, reaching 90 MPa. Fine precipitates were not detected in aged specimens observed by TEM and 3DAP. Segregation of solute C to the grain boundaries and diffusion of Fe atoms in the grain boundaries were proposed as possible mechanisms of this 2nd hardening. Grain-boundary hardening was assumed to be one of the hardening mechanisms in the strain aging in polycrystalline ferritic steel.

Perpendicular magnetic tunnel junction (p-MTJ) spin-valves designed with a top Co2Fe6B2 free layer and a nanoscale-thick tungsten bridging and capping layer

Recently, p-MTJ spin-valves with top Co2Fe6B2 free layers have been widely studied. They potentially experience crystallinity degradation in the face-centered-cubic (fcc) structure of the MgO tunneling barrier as a result of the diffusion of Ta atoms and a significant amount of Fe atoms from the Co2Fe6B2 free and pinned layers. A new design of the p-MTJ spin-valve using a nanoscale-thick W bridging and capping layer demonstrated the absence of significant crystallinity degradation in the fcc structure and showed a limited diffusion of Fe atoms, thus achieving a TMR ratio of ~143% at an ex-situ annealing temperature of 400 °C. Coating quantum tunneling devices with thin metallic bridges may lead to magnetic memory cells smaller than 20 nanometres. Dynamic-random-access memory (DRAM) devices are popular because of their simple one-transistor, one-capacitor construction, but they are tricky to produce at nanoscale dimensions. A promising way to construct alternative DRAM devices based on perpendicular magnetic tunnel junctions (p-MTJ) has now been outlined by Jea-Gun Park and colleagues from Hanyang University in South Korea. Their device, which sandwiches a magnesium oxide tunnel barrier between layers of magnetic cobalt—iron—boron films, uses external magnetic fields to switch between on and off memory states. Normally, such p-MTJ devices suffer from degraded magnesium oxide crystallinity and deleterious diffusion of iron atoms. However, the team found that nanoscale-thin layers of tungsten placed under and above the magnetic films prevented premature device breakdown. New design of the p-MTJ spin-valve using W bridging and capping layer demonstrated no significant crystallinity degradation and no considerable Fe atoms diffusion, thus achieving the TMR ratio of ~143% at an ex-situ annealing temperature of 400 oC. A better crystallinity of the MgO layer for W case than Ta case would be related to less diffusion amount of metal atoms and lattice strain in MgO layer. In addition, higher Fe and Co atom concentrations of Co2Fe6B2 free and pinned layers for W case than Ta case would be associated with less solubilities in W layers than Ta layers.

Copper indium gallium selenide (CIGS) solar cell devices on steel substrates coated with thick SiO2-based insulating material

Flexible copper indium gallium selenide (CIGS)-based solar cells were developed on stainless steel (STS) substrates covered with an insulating layer. The properties of the CIGS films fabricated on STS foils coated with SiO2-based soluble material (“sol-SiO2”) were compared with those on plasma enhanced chemical vapor-deposited silicon oxide (“PE-SiO2”)/MoNa/STS and SLG substrates. The decrease in compensating donor due to sufficient Na doping from the insulating layer was attributed to higher open-circuit voltage and fill factor. Furthermore, the double graded Ga composition in the CIGS films grown on the STS substrates was preserved, and the open-circuit voltage was enhanced with a minor decrease in the short-circuit current. As a result, solar cells with 14% efficiency were produced on sol-SiO2/STS samples with a Fe atom diffusion barrier and external Na incorporation. This was far higher than the 9.5% and 12.8% obtained from the solar cells on PE-SiO2/MoNa/STS and SLG, respectively.

(Invited) New Design of Double MgO-Based p-Mtj Spin-Valves with Top Co2Fe6B2 Free Layer Performain Highly Increased TMR Ratio and Thermal Stability

Perpendicular spin-transfer-torque magnetic-random-access-memory (p-STT MRAM) has intensively been researched as a promising memory cell to overcome a physical scaling limit of less than 20 nm in current dynamic-random-access-memory (DRAM) because of its fast write time (~10 ns), non-volatile memory operation, and extremely low power consumption. For realizing terra-bit-level integration of p-STT-MRAM cells fabricated with a selective transistor and a perpendicular-magnetic-tunnel-junction (p-MTJ) spin-valve, the p-MTJ spin-valves with a bottom CoFeB free layer using a Ta bridging and capping layer have been generally and widely researched. They need to achieve a high tunneling-magneto-resistance (TMR) ratio (>150%), thermal stability (Δ) (>74), and switching current (Jc) (~1x102 MA/cm2) at the back end of line (BEOL) temperature of 400oC. It has been reported that a Ta bridging and capping layer would be a good absorption layer for Boron (B) to enhance i-PMA characteristic but Ta atoms easily diffuse into the MgO tunneling barrier during ex- situ annealing temperature (or a thermal budget at BEOL)1,2. Thus, the p-MTJ spin-valves with a bottom CoFeB free layer using a tantalum (Ta: body-centered-cubic structure) bridging and capping layer have extreme difficulty achieving the TMR ratio of > 100% at the BEOL of 400 oC since the TMR ratio decreases rapidly as ex- situ annealing temperature (or a BEOL temperature) increases. Recently, the p-MTJ spin-valves with a top CoFeB free layer using a Ta bridging and capping layer have been intensively studied to obtain a higher TMR ratio at a higher ex- situ annealing temperature (or a BEOL temperature) since it would minimize the diffusion of platinum (Pt) atoms into the MgO tunneling barrier3-5. However, they confront a significant diffusion of Ta atoms into the MgO tunneling barrier at ex- situ annealing (or BEOL) of 400oC, so the b.c.c crystallinity of the MgO tunneling barrier is abruptly degraded, thereby rapidly decreasing the TMR ratio of the p-MTJ spin-valves. An innovative solution proposed in this paper is a new design of a p-MTJ spin-valve with a top Co2Fe6B2 free layer using a W bridging with sub-nanoscale thickness (~0.24 nm) and a tungsten (W: body-centered-cubic structure) capping layer with nanoscale thickness (~4.0 nm). The proposed design demonstrated no diffusion of Ta atoms into the MgO tunneling barrier and minimized the diffusion of Fe atoms at both Co2Fe6B2 free and pinned layer at an ex-situ annealing of 400oC. Therefore, b.c.c crystallinity degradation of the MgO tunneling barrier could be prevented, and high PMA magnetic moments at both Co2Fe6B2 free and pinned layers could be achieved. Thus, the p-MTJ spin-valve with a Co2Fe6B2 free layer using a W bridging and capping layer with nanoscale thickness (~4.0 nm) achieved the TMR ratio of ~143% at ex- situ annealing of 400oC, as shown Fig. 1. Furthermore, as a way to achieve a TMR ratio of >150% at 400°C, in this paper, we present the design of a new double MgO-based p-MTJ spin-valve with a top Co2Fe6B2 free layer by inserting a nanoscale Fe diffusion barrier (~0.30 nm: only two Fe atomic layers thick) between the W capping layer (~ 4.0 nm in thickness) and MgO capping layer (~1.0 nm in thickness). This new p-MTJ spin-valve had a TMR ratio of ~154% and Δ of 90 in ex-situ magnetic annealing at 400°C, as shown Fig. 2. * This work was supported by a Basic Science Research Program grant from the National Research Foundation of Korea (NRF) funded by the Korean government (MSIP) (No. 2014R1A2A1A01006474) and the Brain Korea 21 PLUS Program in 2014. Reference [1] J. Appl. Phys. 2009, 106, 023920 [2] Acta Materialia 2015, 87, 259 [3] IEDM 2015, pp. 26. 2 [4] IEDM 2015, pp. 26. 3 [5] IEDM 2015, pp. 26. 4 Fig. 1. (a) p-MTJ spin-valve structure using a Ta bridging and capping layer, (b) p-MTJ spin-valve structure using a W bridging and capping layer, and (c) dependency of the TMR ratio on bridging and capping layer thickness for both p-MTJ spin-valves using Ta and W bridging and capping layers. Fig. 2. Dependence of TMR ratio on nanoscale thickness of Fe diffusion barrier for double MgO-based p-MTJ spin-valves with a top Co2Fe6B2 free layer. Figure 1

The influence of HIP process on critical parameters of MgB2/Fe wires with big boron grains and without barriers

We show transport results of the critical temperature (Tc), irreversible magnetic field (Birr), upper critical field (Bc2), critical current density (Jc) and the pinning force (Fp) for undoped MgB2 wires without barriers. The results of SEM show that the hot isostatic pressure process increases the density and uniformity of MgB2 materials. Hot isostatic pressure allows for obtaining small grains and increasing the number of connections between the grains, accelerated reaction rate and limits the diffusion of Fe atoms into MgB2 material from the adjacent sheath. The pressure of 1.1 GPa increases Tc quite significantly in high magnetic field range of 6–12 T, improves the Birr and Bc2 and increase the Jc at 4.2 K and 20 K of about three times. Our results may be important for this field since many MgB2 wires are made from big grains of boron greater than 1 μm. Moreover, our research can be important for the production of MgB2 wires for the International Thermonuclear Experimental Reactor with boron 11B.

Relationship Between Iron Whisker Growth and Doping Amount of Oxide During Fe2O3 Reduction

Iron whisker growth during Fe2O3 doped with oxide reduced by CO was investigated by using in situ observation and scanning electron microscopy. The results indicated that the minimum doping amount (MDA) of various oxides, hindering the iron whisker growth, was different. The MDA of Al2O3, Li2O, Na2O, and K2O was 0.5, 0.4, 4, and 12 pct, respectively. From the reduction rate, it was found that Li2O, MgO, and Al2O3 had some suppressive effects on the Fe2O3 reduction process, thus, confining the growth of iron whisker. However, other oxides had some catalytic effects on the Fe2O3 reduction process (Fe2O3-Fe3O4-FeO-Fe), such as CaO, SrO, BaO, Na2O, and K2O. As long as their doping amount was enough, these oxides could inhibit the diffusion of the Fe atom. When the metal ionic radius in doped oxide was bigger than that of Fe3+, such as Ca2+, Sr2+, Ba2+, Na+, and K+, there were lots of spaces left in Fe2O3 doped with oxide after reduction, improving Fe atom diffusion. Consequently, their MDA was more than that of small radius to restrain the growth of iron whisker. Finally, the relationship between corresponding metal ionic radius, electron layer number, valence electron number, and MDA of oxide was expressed by using data fitting as follows: $$ N_{{{\text{A}}_{y} {\text{O}}_{x} }} = 1.3 \times 10^{ - 5} \times \frac{{r_{{{\text{A}}^{x + } }}^{2} \times \sqrt {n_{{{\text{A}}^{x + } }} } }}{{f_{q} }} $$

Effect of Ti on the growth of the Fe–Al layer in a hot dipped Zn–6Al–3Mg coating

This present study discusses the effect of Ti addition to a Zn–6Al–3Mg galvanizing bath on the growth of an Fe–Al alloy layer. When the Ti content in a Zn–6Al–3Mg bath is less than 0.052wt.%, a subsequent increase of Ti in the bath causes a reduction in the average thickness of the resulting FeAl3Znx layer and the Fe2Al5Znx layer. The restraining effect of Ti on the growth of the Fe2Al5Znx layer is attributed to the occupation of Ti atoms in vacancies within the Fe2Al5Znx phase. The average thickness of the FeAl3Znx and Fe2Al5Znx layers increases significantly when the Ti content exceeds 0.052wt.%. The linear growth of the FeAl3Znx layer suggests that an interfacial reaction controls the growth process. The growth curve of the Fe2Al5Znx layer is parabolic, implying that its growth is controlled by the diffusion of Fe atoms. The effect of Ti on the growth of the Fe–Al alloy layer in the Zn–6Al–3Mg bath with different amounts of Ti has been explained based on different mechanisms.