Binary Fe-B Research Articles

Nanocrystal evolution during ultra-fast heating in an amorphous Fe85B15 alloy

During the crystallization of Fe-based metallic glasses the precipitation of the BCC-Fe nanocrystals smaller than the exchange length (30–40 nm) has been reported as an effective strategy for a reduced coercivity and an increased saturation magnetization. In binary Fe-B alloys it has been shown that nanocrystals well below the exchange length can be obtained by rapid heating above 100 K/s. In order to determine if the fast heating process can yield a further refinement in nanocrystal size, the influence of different heating rates (0.17–5000 K/s) on the crystallization behavior of an amorphous Fe85B15 alloy was investigated using Flash DSC and TEM. Above a critical heating rate (500 K/s), the number density and diameters of BCC-Fe nanocrystals become saturated due to diffusion-field impingement that enriches the amorphous matrix with B that leads to the precipitation of Fe3B nanocrystals that deteriorate the magnetic properties.

Investigation of the Stability Mechanisms of Eight-Atom Binary Metal Clusters Using DFT Calculations and k-means Clustering Algorithm.

Here, we report density functional theory calculations combined with the k-means clustering algorithm and the Spearman rank correlation analysis to investigate the stability mechanisms of eight-atom binary metal AB clusters, where A and B are Fe, Co, Ni, Cu, Ga, Al, and Zn (7 unary and 21 binary clusters). Based on the excess energy analysis, the six most stable binary clusters are NiAl, NiGa, CoAl, FeNi, NiZn, and FeAl, and except for FeNi, their highest energetic stabilities can be explained by the hybridization of the d- and sp-states, which is maximized at the 50% composition, i.e., A4B4. Based on the Spearman correlation analysis, the energetic stability of the binary clusters increases with an increase in the highest occupied molecule orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy separation, which can be considered as a global descriptor. Furthermore, reducing the total magnetic moment values increases the stability for binary clusters without the Fe, Co, and Ni species, while the binary FeB, CoB, and NiB clusters increase their energetic stability with a decrease in the cluster radius, respectively, i.e., an energetic preference for compact structures.

Nanostructural formation kinetics in an Fe86B14 soft magnetic alloy investigated by in situ transport measurements under isothermal conditions

The soft magnetic properties in iron-based nanocrystalline alloys have generally been achieved through the addition of nonmagnetic additives, but this has the unwanted effect of reducing the saturation magnetization. In a recent advance, it was shown that magnetically soft nanostructured alloys could be prepared from a simple, binary Fe-B amorphous precursor by ultrarapid annealing (URA). These materials had a saturation magnetization comparable to that of silicon steel, while a refined grain structure resulted in considerably lower core losses through the exchange averaging effect of the magnetic anisotropy. As yet, the formation mechanism of the soft magnetic nanostructure in this simple binary system has not been identified. We investigated the crystallization process of amorphous ${\mathrm{Fe}}_{86}{\mathrm{B}}_{14}$ using in situ transport measurements. The relationship between the resistivity and the volume fraction of bcc-Fe crystallites was calibrated by $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy. In this paper, we show that the isothermal crystallization behavior of these Fe-B amorphous alloys is well described by the Johnson-Mehl-Avrami-Kolmogorov kinetic model and that the the Avrami exponent ($n$) shows a tendency to increase with increasing annealing temperature (${T}_{\mathrm{a}}$); the exponent $n$ is approximately 1.5 at ${T}_{\mathrm{a}}<700\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ while $n>2$ at ${T}_{\mathrm{a}}=729\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. This suggests that below 700 K the nucleation rate is governed solely by a limited number of quenched-in nuclei whereas at higher temperatures, homogeneous nucleation starts to dominate. Since the onset of crystallization is increased dramatically by rapid heating, the formation of the refined nanostructure induced by URA can be well understood by an increase in the number density of nuclei due to homogeneous nucleation. The increased homogeneous nucleation at higher annealing temperatures can be linked to enhanced atomic transport due to viscous flow.

Liquidus Surface and Spinodal of Fe-B-C Alloys

In this work the study is performed for the specimens of Fe-B-C alloys with boron content of 0.005–7.0 wt. % and carbon content of 0.4–6.67 wt. %, the rest is iron. According to the findings of microstructure analysis, XRD and differential thermal analyses, the primary phases and the temperatures of their formation are determined. Depending on boron content (in the range of 1.5–8.80 wt. %) and carbon content (0.5–6.67 wt. %) in the Fe-B-C alloys, the primary phases in the process of crystallization are γ-Fe, boron cementite Fe3(CB) and boride Fe2В. The outcomes of the experiment carried out in this work determine the phase composition and phase transformations occurring in the alloys and the liquidus surface is constructed. The findings show that the liquidus temperature for Fe-B-C system alloys is low compared to binary Fe-B and Fe-C alloys. At the liquidus surface of the Fe-B-C alloys, there is a point at boron content of 2.9 wt. % and carbon content of 1.3 wt. % with the lowest temperature of 1375 K and it is the point of intersection of monovariant eutectics. This fact is in a good agreement with the results of other authors. The microstructure of alloys located at the curves of monovariant eutectics is represented by the γ–Fe+Fe2B and γ–Fe+Fe3(CB) eutectics and the primary crystals of Fe2B iron boride in the shell of Fe3(BC) boron cementite. In this paper it is shown experimentally the existence of a quasi-binary section and the coordinates of the peritectic point are fixed: the boron content is 5.0 wt. %, carbon content is 3.0 wt. % and the temperature is 1515 K. The free energy of the Fe-B-C melt is calculated for the first time by the quasi-chemical method and the surface of thermodynamic stability of the Fe-B-C melt is plotted, depending on temperature and boron and carbon content in the alloy. The results obtained in the paper show that in order to obtain a homogeneous Fe-B-C melt, which does not contain any microheterogeneous structure in the form of short-order microregions, it is necessary to perform the overheating more than to 180 K for the region where the primary phase is iron, and no less than to 200 K for the regions with boron cementite and boride.

Experimental study and thermodynamic re-modelling of the constituent binaries and ternary B–Fe–Ti system

In the present paper, the complete ternary B–Fe–Ti system is thermodynamically modelled based on our own experimental results and information reported in literature. Series of key experiments were performed for the binary Fe-B, Fe-Ti and the ternary B-Fe-Ti systems in order to obtain parameters of invariant reactions. For this, 19 alloys were prepared and analysed in the as-cast and annealed conditions by means of SEM/EDS, SEM/EBSD, XRD and DTA/DSC techniques. A new ternary boride Ti2FeB2 with the crystal structure of Mo2FeB2 (an ordered derivative of U3Si2 crystal structure type) was revealed to exist at temperatures from 1273 K to solidus. The elaborated thermodynamic description was applied to calculate selected phase equilibria as to provide a comparison between calculated and experimental results. The calculations are shown to reproduce available experimental data entirely well.

Investigation of the Liquidus Line on the Fe-B State Diagram

In this paper we determine the crystallization temperature of a melt of the Fe-B system depending on the boron content and. The thermodynamic properties of the boron-bearing phases are studied. The investigation was performed for alloys with the boron content of 2.0-4.2.0% (wt.), the rest is iron. The smelting of Fe-B system alloy was carried out in a furnace in alundum saggers in the argon atmosphere. The cooling rate of as-cast alloys was 10 K/s. To ascertain the structural condition of alloys we used the microstructure analysis, the differential thermal and the X-ray structural analyses. In the paper, based on experimental data for the Fe-B alloys, we determined the crystallization temperatures of alloys under consideration, depending on the content of boron in the alloy. In addition, we revealed that the γ-Fe+Fe2B eutectic transformation occurs at the temperature of 1441 K and at the boron content of 3.8% (wt.). To determine the thermodynamic functions of the phases we used the quasi-chemical method. With accounting for the contribution of the first degree approximation of the high-temperature expansion for the thermodynamic potential we derived expressions for the free energy of the melt of the binary Fe-B alloy, the boron-doped austenite and the Fe2B boride. The expressions obtained for the free energy potential and the chemical potential of the melt of the binary Fe-B alloy, the austenite and the Fe2B boride enable to obtain the Fe-В phase diagram liquidus boundaries. The calculations performed in this paper made it possible to obtain the numerical values of the crystallization temperature of the alloy, depending on the boron content, and to determine the temperature of the γ-Fe+Fe2B eutectic transformation and the boron content, at which this transformation takes place in the alloy. Such an approach allows describing most completely from the thermodynamic point of view the crystallization process and the eutectic transformation. The results of the calculations obtained in this paper are in good agreement with the experimental data.

Hydrogenation caused reversible structural changes in FeCrB type metallic glasses monitored by magnetization parameters

The reversible structural changes caused by alloying with hydrogen help us to understand the relation between amorphous structure and magnetic properties. One binary FeB and three FeCrB type metallic glasses were selected for this study. The significant increase in coercivity after sample hydrogenation and its subsequent decrease during dehydrogenation are explained by changes in magnetostrictive anisotropy. Applying the Kondorsky model, the dimensional changes in stress centers caused by hydrogenation and dehydrogenation processes were determined from experimentally determined coercivity and effective anisotropy.

Computer simulation of the crystal morphology and growth rate during ultrarapid cooling of an Fe-B Melt

The solidification of a binary Fe-B melt is studied by computer simulation with regard for the temperature dependence of the diffusion coefficient and the possibility of nonequilibrium alloying-component entrapment (i.e., the dependence of the distribution coefficient on the ratio of the solidification rate V to the diffusion rate VD). The effect of high cooling rates of the melt on the dendritic morphology is analyzed. The dependence of the dendrite-tip growth rate on the melt supercooling is obtained. At large supercoolings, a morphological transition is shown to occur; it is related to the change from a diffusion to a diffusionless dendrite growth mode.

Reaction sintering of metal powders: B.Kieback et al. (Technological University of Dresden, Dresden, Germany.)

The influence of a few per cent rare earth additives to iron-boron amorphous alloy was investigated. Compared with binary Fe-B, changes in Curie temperature, magnetization, coercive force and amorphous-crystalline transition were observed. The role of the atomic size effect and the chemical properties of rare earth in these changes are discussed.

Densification of particles under isostatic compaction: A.Eksi, S.Saritas. (Gazi University, Turkey.)

The influence of a few per cent rare earth additives to iron-boron amorphous alloy was investigated. Compared with binary Fe-B, changes in Curie temperature, magnetization, coercive force and amorphous-crystalline transition were observed. The role of the atomic size effect and the chemical properties of rare earth in these changes are discussed.

Determination of reversible Curie point relaxation spectra in Fe-B metallic glasses

Reversible Curie point ( T C) and energy relaxation were investigated in Fe-B metallic glasses as a function of B content ( x = 13.2 and 14.7 at%). The effect of the substitution of a small amount (5 at%) Fe by Ni on the energy relaxation of Fe 86.8B 13.4 was also investigated. The calculation of the relaxation spectra of these alloys with relatively high T C values is not straightforward and it is made only possible by taking into account the exact annealing procedure. It is concluded that in Fe-B metallic glasses the relaxation spectrum of the Curie point decreases with the B content, together with that of the energy, indicating that boron inhibits the atomic movements during relaxation. This points to reversible topological atomic rearrangements (TSRO) as the source of relaxation in binary Fe-B alloys. The increase of the energy spectrum upon substitution of 5 at% Fe by Ni suggests that chemical ordering of metal atoms (CSRO) is the dominant process of the reversible relaxation in ternary Fe-Ni-B alloys.

Plasma carburized PM low alloy steel with high fatigue strength: K. Ishii et al (Hitachi Powdered Metals Ltd, Tokyo, Japan)

The influence of a few per cent rare earth additives to iron-boron amorphous alloy was investigated. Compared with binary Fe-B, changes in Curie temperature, magnetization, coercive force and amorphous-crystalline transition were observed. The role of the atomic size effect and the chemical properties of rare earth in these changes are discussed.

Activities of boron in the binary Fe-B, Co-B, and Cu-B melts

Activities of boron in the binary Fe-B, Co-B, and Cu-B melts have been directly determined by the electromotive force (emf) measurement. Boron-saturated liquid Cu-B alloy was used as the reference electrode and a ternary 28 wt pct Al2O3-29 wt pct B2O3-43 wt pct CaO oxide melt was used as the electrolyte. Deviations of the boron activities from Raoult's law have been found largely negative for the Fe-B and Co-B systems but largely positive for the Cu-B system. Boron activities calculated from the literature data have not been in good agreement with the measured data. Activities of iron, cobalt, and copper have been calculated from the obtained boron activities by means of the Gibbs-Duhem equation. Some modifications to the liquidus curves on the Fe-B and Co-B phase diagrams have been presented.

Magnetic property of liquid state in amorphous Fe-B and Ni-B alloys

The magnetic properties of the liquid state in binary Fe-B and Ni-B alloys have been measured at temperatures up to 1600 K. In Fe-B alloys, the susceptibility χ of the liquid state is in accordance with the Curie-Weiss law but the paramagnetic Curie point exhibits a drastic change in the composition dependence at about 21 at% B-Fe, suggesting a structural change in the liquid state. Spin paramagnetism was observed in Ni-B alloys; the values of χ at 1600 K and ∂(1/χ)/∂ T vary from 1 to 4 × 10 -6 emu/g Oe and from 60 to -400 g Oe/emu K, respectively, depending on B content. These results are discussed in connection with the magnetism in the amorphous state.

Magnetic properties of Fe-B amorphous alloys containing rare earth additives

The influence of a few per cent rare earth additives to iron-boron amorphous alloy was investigated. Compared with binary Fe-B, changes in Curie temperature, magnetization, coercive force and amorphous-crystalline transition were observed. The role of the atomic size effect and the chemical properties of rare earth in these changes are discussed.

Magnetic and stress annealing of Fe 80T 3B 17 amorphous alloys

The influence of transition metal additives to eutectic Fe-B on the magnetic and stress induced anisotropy was investigated. The results are compared with the same properties of binary Fe-B amorphous alloys and treated by taking into account the chemical and physical properties of the transition metal in question.

Investigation of magnetic properties and thermal stability of Fe-TM-B metallic glasses

The influence of transition metal (TM) additives on the Curie temperature ( T c), saturation magnetization ( M s) and thermal stability of binary Fe-B metallic glasses was investigated. Parallel changes were found in M s and T c, showing typical group number effects. Nearly linear correlation has been observed between the initial temperature and activation energy of crystallization.

Mössbauer Spectroscopy of Amorphous Fe-B Alloys

Binary Fe-B amorphous alloys containing 12–25 at%B were studied by 57Fe Mössbauer spectroscopy. The spectra were examined by Fourier analysis and near-neighbor configuration analysis. The characteristic concentration dependence of the internal field distribution was explained by the interactions between iron and boron atoms in different ways depending on the boron content and the microstructure of the amorphous matrix. Alloys with boron content below 20 at% exhibited well-developed short range order with the bcc-like near-neighbor configuration, while Fe-25 at%B and slowly-quenched Fe-12 and 13 at%B alloys showed a considerable fraction of chemical order of the Fe3B type. The existence of chemical clusters in Fe-25 at%B suppressed the nucleation of Fe2B precipitates, and this alloy was therefore the most thermally-stable.

Formation and magnetic properties of Fe-B-Si amorphous alloys

The magnetic properties and crystallization temperatures of alloys in the ternary Fe-B-Si system are reported. The Curie temperature increases slightly on replacement of boron by silicon. This results in a sharp ridge of relatively constant room-temperature saturation magnetization extending from Fe 80 B 20 to Fe 82 B 12 Si 6 . The coercivity exhibits a broad minimum, both before and after stress relief annealing, in the region around Fe 81 B 15 Si 4 and extending at least to Fe 77 B 13 Si 10 . The crystallization temperature increases with increasing silicon and with decreasing iron and boron. The alloys with silicon are generally easier to prepare in the amorphous state than the binary Fe-B alloys. Thus for the highest saturation magnetization alloy combined with ease of preparation, stability, and lowest losses, the alloys between Fe 81 B 17 Si 2 and Fe 82 B 12 Si 6 are preferred.