Fe-Mo Systems Research Articles

Thermodynamic re-modeling of the binary Al–Mo and ternary Al–Fe–Mo systems based on novel experimental data

Thermodynamic re-modeling of the binary Al–Mo and ternary Al–Fe–Mo systems based on novel experimental data

Electrotransport in binary iron-based metal melts

The mobility of ions in binary iron-based liquid metal systems is calculated for the first time, based on studies on the specific resistance and self-diffusion coefficient in a wide range of concentrations. It is established that iron ions move toward the anode in Fe–V and Fe–Mo systems, and toward the cathode in Fe–W and Fe–Pt systems; i.e., there is inversion of electrotransport for iron ions. When the concentration of a component is reduced, the mobility of its ions grows in modulus.

Ab initio study of energetics and magnetism of sigma phase in Co–Mo and Fe–Mo systems

We analyse, from first-principles, the energetics and magnetic ordering of sigma phases in Co–Mo and Fe–Mo systems. Total energy differences between the sigma phase and Standard Element Reference (SER) structures are calculated in the whole concentration range at equilibrium volumes by means of the linear muffin-tin orbitals method in the atomic-sphere approximation (LMTO-ASA), the full-potential linearised augmented-plane waves (FLAPW) method and the pseudopotential approach. They are compared with the enthalpy of formation of sigma phase obtained from the phase equilibria calculations at higher temperature based on the semiempirical CALPHAD (CALculation of PHAse Diagram) method. It turns out that the binary sigma phases are more stable than the weighted average of the sigma phase of elemental constituents and that this stability for Fe–Mo is higher than for Co–Mo. On the other hand it was found that the binary sigma phases do not exhibit any stability with respect to the weighted average of the SER structures. The magnetic configurations in all systems are investigated and the stabilizing effect of magnetic order in sigma phase at 0 K is presented. It turns out that the atomic magnetic moment strongly depends on the type of occupied sublattice and total composition of the alloy.

Oxomolybdenum monodithiolene complexes linked with sulfur bridged iron: antiferromagnetically coupled Fe(iii)Mo(v) systems

Mo-Fe heterometallic complexes with Fe(X)(2) (X = Cl, SPh) moiety attached to monodithiolene oxomolybdenum via sulfur bridge, viz., [Ph(4)P](2)[Cl(2)FeS(2)MoOS(2)(DMED)] (2) (DMED, dimethylethylenedicarboxylate), [Ph(4)P](2)[Cl(2)FeS(2)MoO(tdt)] (3) (tdt, toluenedithiolate) and [Ph(4)P](2)[(SPh)(2)FeS(2)MoO(tdt)] (4) are reported. Mossbauer spectroscopy, magnetism, EPR, electrochemistry and electronic structure based on DFT and TD-DFT calculation show the transfer of electron from iron to molybdenum centre resulting antiferromagnetically coupled Fe(III)Mo(V) unit from the starting Fe(II) and Mo(VI) compounds. A net spin of S = 2 ground state arising from antiferromagnetically coupled Fe(III) and Mo(V) shows a rare X-band EPR in normal mode at g ~ 12 in the solid state. In addition, Mossbauer studies show that electron drifting is more pronounced upon substitution of the chloride ligand by thiophenolate. The changes in dithiolene periphery electronically affect the charge distribution between Mo-Fe in {OMo(μS)(2)Fe} core. DFT calculations indicate that the increasing stability of dative Fe → Mo hetero metal-metal bond in these complexes from 3 to 2 to 4 is related to the extent of electron transfer from the iron to molybdenum centre.

Application of ab initio electronic structure calculations for prediction of phase equilibria in superaustenitic steels

Our recent results of the application of ab initio electronic structure calculations to the modeling of phase equilibria in binary and ternary transition-metal systems containing complex intermetallic phases (Laves phase, sigma phase) are summarized. As examples, the application of total energy differences calculated by ab initio methods for the sigma phase included in the CALPHAD treatment of the Cr–Mo and Cr–Fe–Mo systems is presented. The description of the sigma phase, based on the above-mentioned total energy differences, for the systems Cr–Fe, Cr–Ni, Fe–Ni, Fe–Mo, Cr–Mo, and for Cr–Fe–Ni and Cr–Fe–Mo systems has been included in the thermodynamic database for the calculation of phase equilibria in steels, developed earlier by some of the authors. Theoretical results obtained by using the new and older models are compared with new experimental data for superaustenitic (high-nickel–chromium) steels.

Phase diagram calculations in the Co–Mo and Fe–Mo systems using first-principles results for the sigma phase

We calculate the phase diagrams of Co–Mo and Fe–Mo systems by means of a combination of ab initio electronic structure calculations and the CALPHAD approach. Ab initio calculations of the total energy differences between the sigma phase and standard element reference (SER) structures for pure constituents are accomplished by means of the full-potential linearized augmented plane wave (FLAPW) method in the generalized gradient approximation (GGA). During these calculations the structure relaxation is performed. The results obtained are employed as a part of the Gibbs energy describing the thermodynamics of the sigma phase. Subsequently, the thermodynamic data sets describing the sigma phases in the Co–Mo and Fe–Mo systems are optimized using the CALPHAD approach by employing both the experimental and thermodynamic data extended by ab initio calculations. Description of all other phases is taken from the literature.

Effect of the elastic strain energy on the nucleation of Laves phases in α-iron base alloys

The elastic strain energy of coherent clusters in Fe-Mo, Fe-Ti, Fc-Nb and Fe-Ta systems has been calculated as a function of their shapes and orientations using the Eshelby’s method for anisotropic crystalline materials. The result is consistent with the formation of plate-shaped Laves phases in Fe-Nb, Fe-Ta and Fe-Ti systems and with that of spherical clusters, in Fe-Mo system, prior to the formation of plate-shaped Laves phase. The latter is believed to be formed due to the elastic interaction with the dislocations. The result also accurately predicts the {111}α habit plane of the Fe2Nb and the {001}α of the Fe2Ta Laves phases. The habit plane {011}α of the Fe2Ti Laves phase is not consistent with the calculation result for pure β Ti clusters. However, a strong segregation of Fe atoms into β Ti clusters can favor the formation of {011}α instead of {001}α habit planes.

Magnetic Anomaly and Icosahedral Phase Formation in Fe-Cu and Fe-Mo Systems

ABSTRACTThe first observation of a new class of icosahedral phase associated with a magnetic transition in Fe-Cu and Fe-Mo systems are reported. It is found that the icosahedral order can be re-established when the destabilized Fe60Cu40 icosahedral phase subject to a magnetic transition at high annealing temperature. The Fe70Mo30 amorphous films obtained by sputtering exhibit a similar behavior at high magnetic transition temperature. A brief discussion of the observed phenomena is addressed.

Different behaviours of amorphization induced by ion mixing

Ion mixing of multiple metal layers was conducted at 77 K in five selected binary metal systems, i.e. the Ag-Cr, Co-Cu, Cu-Fe, Fe-Mo and Fe-Nd systems, which all have a nearly zero or positive heat of formation (Δ H For ). TEM examination showed a common microscopic feature of localized amorphization after high dose ion irradiation, i.e. the amorphous phase was frequently interspersed in a crystalline matrix. EDS analysis was therefore carried out to determine the actual compositions of the phases formed. It revealed that all local amorphous regions resided within rather narrow composition ranges. The narrow range found here for amorphization is probably the reason that amorphous alloy formation was difficult in these systems. After comparing these observations with those reported earlier for the some 30 systems so far studied, it is found that the behaviour of ion mixing induced amorphization, and hence the binary metal systems, can be classified into two categories. The first category contains the readily amorphous phase forming systems and usually features very limited terminal solid solubilities along with large negative heat of formation. Typical examples are the Au-Ti, Ni-Mo, Ni-Nb and Ru-Zr systems. In these systems amorphization can be achieved over a wide composition range once a minimum dose is reached. For systems in the second category, amorphization is only allowed in a rather narrow composition range, as in the systems studied here. This is also the case when a system has a large solid solubility, even though its Δ H For is rather negative, e.g. the Mo-Ru and Au-V systems. In such situations, the results of phase formation may be sensitive to the composition as well as to the ion irradiation dose. The possible mechanism responsible for the different behaviors of phase formation by ion mixing are also discussed.

Permanent magnet materials based on the rare earth-iron-boron tetragonal compounds

Structural and metallographic studies were carried out on the Nd-Fe-B alloy system as well as the Nd-Fe-B tetragonal compound on which record high energy magnets have been developed using a powder metallurgical technique. The study on the new magnet has also been extended to other R-Fe-B componds containing various rare earths (R) and to R-Fe-Co-B alloys. The results are as follows; (1) The sintered Nd-Fe-B magnet is composed of mainly three phases, the Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B matrix phase plus Nd-rich phase and B-rich phase ∼ Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> ) as minor phases. (2) Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B has the space group of P4 <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> /mnm. The crystal structure of this phase can be described as a layer structure with alternate stacking sequence of a Nd-rich layer and a sheet formed only by Fe atoms. The sheet of Fe atoms has a structure similar to the σ-phase found in Fe-Cr and Fe-Mo systems. (3) The Nd-rich phase containing more than 95 at.% Nd, 3∼5 at.% Fe and a trace of B has fcc structure with a=0.52 nm. This phase is formed around grain boundaries of the matrix phase. Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</inf> phase has an one-dimentional incommensurate structure with a=a <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c\simeq8</tex> C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> , based on a tetragonal structure with a <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> =0.716 nm and c <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</inf> =0.391 nm. (4) In the as sintered Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">77</inf> B <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</inf> alloy periodic strain contrasts are observed along grain boundaries, which disappear after annealing at 870K. This may be related to the enhancement of the intrinsic coercivity of the sintered magnet by post sintering heat treatment. (5) Stable R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B phases are formed by various rare earths except La. Of all the R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B compounds, Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B has the maximum saturation magnetization as high as 1.57 T. Dy and Tb form R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B phases with the highest anisotropies. Small additions of these elements greatly enhance the coercive force of the Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B base magnet. (6) Partial replacement of Fe by Co raises the Curie temperature of the Nd <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</inf> B compound, which improves the temperature coefficient of the remanence of the magnet. But the intrinsic coercive force is decreased by the Co addition.