Iron-rich Alloys Research Articles

Three-sublattice model that takes into account the spin density anisotropy, short-range order, and dimensioned factor for the binary Fe-Cr(V, Mo) systems

The diffusion properties of the elements entering into the composition of austenitic and ferritic steels are analyzed as functions of the temperature and the time evolution of induced radioactivity. As compared to austenitic steels, ferritic steels are shown to have better diffusion properties and swelling resistance during operation at temperatures up to 650°C under irradiation conditions and can be used as structural materials in the core of a fast neutron reactor. Experimental and calculated (Calphad method) data on the Fe-Cr phase diagram and the thermodynamic properties and the experimental data on the short-range order in Fe-Cr alloys are analyzed, and it is concluded that they are conflicting and that models taking into account the short-range order should be developed. The results of quantum-mechanical calculations of the average magnetic moment for ferromagnetic (FM) iron as a function of the volume are analyzed and used to introduce a concept of partial magnetic moments of the iron atoms located in the first four coordination spheres (1–4 CS). The values of these moments are calculated. The concept of the partial magnetic moments of iron atoms agrees qualitatively with the experimental data on the spin-density anisotropy of the bcc lattice of pure iron. This concept is used to formulate a three-sublattice model for binary FM alloys of Fe-M systems (M is an alloying paramagnetic element). An extended cell whose sites contain 8 bcc cells and 16 atoms per cell and that is isomorphic to a DO3-type crystal lattice is considered. A functional is constructed for the internal energy on the extended 16-atom cell. The dimensioned factor is taken into account in a self-consistent manner, by the expansion of the interaction energies of atoms of both components located in different CSs in the atom displacement with respect to ideal lattice sites. The dimensioned factor is taken into account in the three-sublattice model to obtain a set of equations of state for bcc FM binary iron-rich alloys in a 1–3 CS approximation. The obtained estimates demonstrate that the anisotropy of the distribution of magnetic moments in the bcc iron lattice is responsible for the appearance of a short-range order in bcc FM iron-rich Fe-Cr (V, Mo) binary alloys.

Textural and morphological studies on zinc–iron alloy electrodeposits

Zinc–iron alloy electrodeposits have industrial significance, since they provide better corrosion resistance and with improved mechanical properties when compared to pure zinc coatings. This is due to the unique phase structure of the alloy formed. But this deposition belongs to anomalous deposition, where the electrochemically less noble zinc deposits more preferentially, than the more noble iron. So the industrial process control over the deposition becomes difficult. So, this study correlates the effect of various deposition parameters over the deposition kinetics and deposited alloy characteristics. Transition and partial current densities were computed. Effect of hydrogen overpotential and surface coverage due to the adsorbed intermediates over anomalous deposition were explored. Plausible deposition mechanism and mathematical model was proposed to predict the anomalous electrodeposition characteristics. Textural, morphological and phase structural characteristics of the alloy was investigated. By the substitution of iron in the hcp lattice, c/a ratio was lowered and the lattice geometry was distorted. Intermetallic compounds of variable composition such as FeZn14, Fe5Zn33, Fe3Zn13 and FeZn3 with ‘η’ and ‘Γ’ phase structures were noted. Electrodeposition parameters were optimized and smooth, adherent, strain-free deposits with required iron content and hardness were obtained. The role of charge and mass transfer control on the texture and morphology of zinc–iron alloy electrodeposition was studied. Zinc-rich alloy with distorted ‘η’ hcp phase was predominant under kinetic limitations, by the iron substitution along ‘c’ axis. The ‘Γ’ phase with relatively iron-rich alloy was formed under diffusion control.

The pros and cons of reductive matte smelting for PGMs

Platinum group metals (PGMs) are traditionally smelted in electric furnaces where the valuable metals are collected in a base-metal sulphide matte. An alternative to this process is the ConRoast process that uses reductive alloy smelting in a DC arc furnace to collect the valuable metals in an iron-rich alloy. Reductive smelting of feed materials containing PGMs, using carbon as a reducing agent, can be used to obtain high PGM and base-metal recoveries and to ensure the solubility of chromium in slags. Based on work carried out in Mintek’s 3 MW DC arc furnace at throughputs of over 1000 tons per month, it was found that PGMs could be collected effectively, and that the chromium problem could be managed. However, if matte is present in the furnace, there remains a significant risk of furnace failure. Furthermore, the PGM ‘lockup’ (inventory inside the furnace) in a process that used reductive matte smelting of UG2 concentrates was much greater than that of reductive alloy smelting. Further differences exist in the better working environment and lower emissions of SO 2 in the case of the ConRoast process.

Recovery of iron from copper flash smelting slags

Copper slag is produced in large amounts in seven copper smelter plants in Chile, and it is estimated that around four million tons of slag are disposed every year, and another 40–45 million tons are historically cumulated. Copper slag contains iron in the range of 42–45%, which can be recovered and recycled along with the contained copper to obtain an iron–copper alloy and a final slag rich in oxides. Therefore, the present work shows the experimental results of the reduction of a flash smelting slag using coke as reductant up to 150% of the stoichiometric carbon required to reduce copper oxide and magnetite. The characterisation and thermodynamic stability of compounds contained in the slag are presented, and the obtained results show the feasibility for recovering an iron rich alloy with iron contents higher than 98% and copper in the range of 0·6–0·8% using a two‐step process.

Dry sliding wear behaviour of hypereutectic Al–Si piston alloys containing iron-rich intermetallics

The effect of iron-rich intermetallics on the wear behaviour of Al–Si hypereutectic alloys has been studied. Dry sliding wear tests have been conducted using a pin-on-disk machine under different normal loads of 18, 51, 74 and 100 N and at a constant sliding speed of 0.3 m/s. The addition of 1.2 wt.% Fe to the LM28 alloy increased the wear rate due to the formation of needle beta intermetallics. Introducing 0.6 wt.% Mn to the iron-rich alloy changed the beta intermetallics into the modified alpha phases, and therefore reduced the detrimental effect of iron. TIG welding method as a surface melting process was applied on the iron and manganese containing alloy and led to a fine microstructure and increased the wear resistance.

Invar effect and noncollinear magnetism in FeCu alloys

The Invar effect has been observed in many Fe rich alloys, most famously Ni Invar. Generally the Invar behavior is associated with the strong coupling between the lattice and magnetic degrees of freedom, and therefore depends on the magnetic ordering in these alloys. Recent experimental works observed an Invar effect in fcc-FeCu solid solutions [Gorria et al., Phys. Rev. B 69, 214421 (2004)]. In the present paper the magnetic states of fcc-FeCu solid solutions for various concentrations are investigated. The first principles calculations employ the locally self-consistent multiple scattering real space method for solving the local-density approximation Kohn–Sham equation to investigate the noncollinear ordering of magnetic moments. The magnetic order for the low iron concentration is found to be noncollinear, spin glasslike, and the ferromagnetic order is not stable, whereas for the iron rich alloys for the ground state equilibrium lattice constants a magnetic order with parallel aligned Fe moments is stable. In this configuration the induced moments at the Cu sites order nontrivially on a cone with an opening of approximately 40° around the Fe moment direction.

Thermodynamic description of the Cu–Fe–Zn system

Thermodynamic description of the ternary Cu–Fe–Zn system is presented. The thermodynamic parameters of the sub-systems, Cu–Fe, Cu–Zn and Fe–Zn, are taken from earlier SGTE-based assessments, and those of the ternary Cu–Fe–Zn system are optimized in this study by using the experimental zinc activity and phase equilibrium data. Due to the lack of experimental data from iron-rich alloys, the validity of the present description is verified only for Cu–Zn-rich alloys.

Phase Relations, Activities and Precious Metal Distribution in the Cu-Fe-S-Sb System Saturated with Carbon at 1200°C

As a fundamental study to develop a new process for eliminating detrimental antimony, recovering precious metals from the antimony-rich matte produced from the copper concentrate, and treating the occasionally generated speiss in nonferrous smelting processes, the phase relations in the Cu-Fe-S-Sb system saturated with carbon and the distribution of some minor elements between the phases in the miscibility gap, where three equilibrated phases of iron-rich alloy, copper-rich alloy and matte coexist, were investigated at 1200°C by using a quenching method. The experimental results were compared with the results for the Cu-Fe-S-As-C system and discussed on the basis of activity coefficient of antimony in the matte phase at different matte grades. By utilizing the obtained data, material balance calculations concerning to the treatment of antimony-rich matte produced in copper smelting by adding the pig-iron was elaborated and also laboratory scale experiments using industrial matte were carried to corroborate the calculations. By using the phase separation, the cleaning of complex matte, the recovery of valuable copper, silver and gold into the copper-rich alloy and matte phases as well as the elimination of iron and an acceptable amount of antimony into the iron-rich alloy phase for discarding as a harmless and smaller deposit might be feasible.

Thermal expansion of iron-rich alloys and implications for the Earth's core.

Understanding the thermal-chemical state of the Earth's core requires knowledge of the thermal expansion of iron-rich alloys at megabar pressures and high temperatures. Our survey of literature revealed a significant lack of such data. We have determined the unit-cell parameters of the iron-sulfur compound Fe(3)S by using synchrotron x-ray diffraction techniques and externally heated diamond-anvil cells at pressures up to 42.5 GPa and temperatures up to 900 K. The zero-pressure thermal expansivity of Fe(3)S is determined in the form alpha = a(1) + a(2)T, where a(1) = 3.0 +/- 1.3 x 10(-5) K(-1) and a(2) = 2.8 +/- 1.5 x 10(-8) K(-2). The temperature dependence of isothermal bulk modulus ((partial differential)K(T,0)/(partial differential)T)(P) is estimated at -3.75 +/- 1.80 x 10(-2) GPa K(-1). Our data at 42.5 GPa and 900 K suggest that approximately 2.1 at. % (1.2 wt. %) sulfur produces 1% density deficit in iron. We have also carried out energy-dispersive x-ray diffraction measurements on pure iron and Fe(0.864)Si(0.136) alloy samples that were placed symmetrically in the same multi-anvil cell assemblies, using the SPring-8 synchrotron facility in Japan. Based on direct comparison of unit cell volumes under presumably identical pressures and temperatures, our data suggest that at most 3.2 at. % (1.6 wt. %) silicon is needed to produce 1% density deficit with respect to pure iron.

Dynamical stability of Fe-H in the Earth's mantle and core regions

The core extends from the depth of 2,900 km to the center of the Earth and is composed mainly of an iron-rich alloy with nickel, with 10% of the mass comprised of lighter elements like hydrogen, but the exact composition is uncertain. We present a quantum mechanical first-principles study of the dynamical stability of FeH phases and their phonon densities of states at high pressure. Our free-energy calculations reveal a phonon-driven stabilization of dhcp FeH at low pressures, thus resolving the present contradiction between experimental observations and theoretical predictions. Calculations reveal a complex phase diagram for FeH under pressure with a dhcp --> hcp --> fcc sequence of structural transitions.

Interdiffusion of solid iron and nickel at high pressure

Interdiffusion rates in solid (fcc) iron–nickel alloys have been measured at pressures between 1 and 23 GPa and temperatures between 1423 and 1973 K. The experiments were performed using piston cylinder and multianvil devices, with diffusion couples comprising pure iron and nickel rods placed end to end. Concentration profiles in quenched samples were measured by electron microprobe, and interdiffusion coefficients were determined using the Boltzmann–Matano method. Over the entire range of pressure and temperature studied, interdiffusion coefficients in the iron-rich alloys are described well by a simple exponential function of the homologous temperature, D=Doexp(−20.4Tm/T), where Tm is the melting temperature of the alloy at the pressure of interest and D0 is a constant equal to 2.7×10−4 m2/s. These data are consistent, within an order of magnitude, with data for other close-packed (fcc and hcp) metals at the same homologous temperatures. At the conditions of Earth's inner core, diffusion coefficients are predicted to be too small for bulk diffusive exchange between the inner and outer core to be significant. It is thus reasonable to model the chemical evolution of the outer core under the assumption that crystallization of the inner core is a perfect fractional process.

Activities of liquid Fe-As and Fe-Sb alloys saturated with carbon

A solid iron base alloy of the so-called furnace residue is often formed as a by-product in reduction smelting of lead sinter and scraps with high contents of arsenic and antimony. The use of phase separation into a liquid iron-rich alloy and a liquid lead-rich alloy in lead-iron-arsenic and lead-iron-antimony systems saturated with carbon at relatively low temperatures of about 1200°C was proposed in a new process for treating the furnace residue to recover valuable elements into the lead-rich alloy and fix toxic arsenic into the iron-rich alloy. As a fundamental study for the proposed process, the activity coefficients and interaction parameters of the Fe-As and Fe-Sb systems saturated with carbon at 1200°C were derived in this study, based on the determined phase relations in the Fe-Pb-As and Fe-Pb-Sb systems saturated with carbon.

Non-equilibrium solidification of concentrated Fe–Ge alloys

The solidification of concentrated alloys containing ordered compounds is less well understood. These alloys often exhibit complex phase change like peritectic reaction during liquid to solid transformation. The Fe-rich part of Fe–Ge binary alloy system consists of several critical points and ordered–disorder transitions and can be used as a model system to study the effect of departure from equilibrium on the solidification microstructure. In order to understand the phase selection and morphological transitions, undercooling and recalescence behaviour; growth rate of the solidifying phases and microstructure need to be explored. In the present paper, we summarise the results obtained in several iron rich alloy compositions (Fe–(14–25) at.% Ge) using techniques of melt quenching, levitation and laser resolidification. These results provide insight to the current theories of dendritic growth and reveals possibility of a new pathway for phase evolution in peritectic alloys at high undercooling involving a massive transformation.

Ferromagnetism of [formula omitted] alloys

The magnetic properties of disordered Fe 86 Mn 14 - y Cu y alloys were investigated with several experimental techniques. The results of X-ray diffraction showed that these alloys are single phase with the A2 (BCC) structure. These are ferromagnetic alloys at room temperature, and the Curie temperature decreases with the increase of the Cu content. An abrupt loss of magnetization was observed below T C at a temperature which increases with the reduction of the Mn content in the alloys. The addition of manganese enhances the solubility of copper in iron matrix and retains the BCC structure in iron-rich alloys. The behavior of the magnetization with temperature and its composition dependence indicate that an antiferromagnetic coupling is expected between the Fe and Mn atoms. The magnetic moments of both Fe and Mn atoms are expected to vary strongly with composition in these alloys.

Phase Relations, Activities and Minor Element Distribution in Cu-Fe-S and Cu-Fe-S-As Systems Saturated with Carbon at 1473 K

As a fundamental study to develop a new process for eliminating detrimental arsenic, recovering precious elements from the arsenic-rich matte produced from the copper concentrate, and treating the occasionally generated speiss in nonferrous smelting processes, the phase relations in the Cu-Fe-S and Cu-Fe-S-As systems saturated with carbon and the distribution of some minor elements between the phases in the miscibility gap, where three equilibrated phases of iron-rich alloy, copper-rich alloy and matte coexist, were investigated at 1473 K by using a quenching method. The experimental results were discussed on the basis of activity coefficient of arsenic in the matte phase at different matte grades. By utilizing the obtained data, material balance calculations concerning to the treatment of arsenic-rich matte produced in copper smelting by adding the pig-iron was elaborated and also laboratory scale experiments using industrial matte were carried to corroborate the calculations. By using the phase separation, the recovery of valuable copper, silver and gold into the copper-rich alloy and matte phases as well as the elimination of iron and arsenic into the iron-rich alloy phase for discarding as a harmless and smaller deposit might be feasible. [doi:10.2320/matertrans.47.2963]

Influence of structure on coercivity in nanocrystalline (Fe 1−xCo x) 86Hf 7B 6Cu 1 alloys

The relationship between coercivity and structure in nanocrystalline (Fe 1− x Co x ) 86Hf 7B 6Cu 1 ( x = 0 – 1 ) alloys was surveyed. It was found that the increase of Co content in the alloys studied was accompanied by the increase of coercivity. However, we suggest that the factors influencing the coercivity change with the concentration of cobalt in these nanocrystalline alloys. In the iron-rich alloys, the average grain size and magnetostriction play predominant roles in the coercivity. On the other hand, in the case of cobalt-rich alloys, the coercivity mostly originates from the FCC-Co phase with large magnetocrystalline anisotropy and the weak exchange coupling between BCC-Fe(Co) and FCC-Co(Fe).

Phase Relations, Activities and Minor Elements Distribution in Fe–Pb–As and Fe–Pb–Sb Systems Saturated with Carbon at 1473 K

As a fundamental study to develop a new process for treating iron-lead base alloys, speiss, with a considerably high content of arsenic or antimony, which are produced in smelting lead ores or secondary materials of lead under a strongly reductive condition, the phase relations and the minor elements distribution of copper, silver, gold and platinum in the Fe-Pb-As and Fe-Pb-Sb systems saturated with carbon were determined at 1473 K by a quenching method. It was found that a miscibility gap composed of an iron-rich alloy phase with a very small content of lead and a lead-rich alloy phase with very few contents of iron and carbon extended over the wide concentration range. Arsenic was mostly distributed in the iron-rich alloy phase, while antimony almost evenly in both phases. For the distribution of precious metals, it was found that silver was mostly enriched in the lead-rich alloy phase, platinum in the iron-rich alloy phase, while gold and copper almost evenly in both phases. Based on the obtained data of the phase separation and using thermodynamic data for the Pb-As and Pb-Sb binary systems, the activity coefficients of arsenic and antimony in the Fe-As and Fe-Sb systems saturated with carbon at 1473 K were derived and expressed by a formula with the interaction parameters.

Mössbauer effect studies of disordered Fe–Ru alloys

AbstractThe bcc and hcp phases of disordered Fe100–xRux alloys are investigated with several experimental techniques to study the composition dependence of the magnetic properties in these structures. With an appropriate annealing the prepared samples are single phase. The iron rich alloys are ferromagnetic at room temperature with the bcc structure. However, an antiferromagnetic coupling is introduced with the addition of ruthenium. Above 30 at% Ru a paramagnetic behavior is observed at 300 K and 77 K, where the alloys have the hcp structure. In the ferromagnetic phase the Curie temperature decreases steadly with the increase of the ruthenium concentration. In the paramagnetic hcp phase the mean volume per atom is al‐most triplicated as compared to the bcc phase, which brings out the breakdown of the magnetization and the collapse of the hyperfine field at the iron sites simultaneously with the crystallographic phase transition. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The behaviour of sulphur in metal?silicate core segregation experiments under reducing conditions

Reactions between molten alloys and solid silicates were investigated under reducing conditions, down to four log units below the IW buffer, at 20–25 GPa and 2000 °C in the Mg–Si–Fe–O–S system. The iron-rich alloys formed in the Fe–Si–S ternary system were single phased at high-pressure and temperature, suggesting closure of the liquid immiscibility gap at these conditions. At the metal/silicate interface, the reduction of Fe2+ was coupled to oxidation of Si in metal, a reaction also observed in similar sulphur-free systems. Silicon and sulphur were observed to coexist simultaneously in the metal phase in contact with silicates and magnesium sulphide, MgS, was observed in the experiments. This latter phase would not segregate to the planetary cores, thus providing a reservoir of sulphur in the silicate and surficial planetary envelopes.

First-principles study of the interplay between magnetism and phase equilibria in Fe?Co alloys

The effect of magnetism on the ground state structures has been investigated by means of first-principles, density-functional calculations. In addition to the experimentally observed CsCl-type ground-state structure for FeCo stoichiometric alloys, our spin-polarized calculations predict several new ordered structures for iron-rich alloys. In particular, our results show that Fe3Co alloys are energetically stable for a number of ordered structures.