Effect of gadolinium on the properties of Pr–Dy–Fe–Co–B materials

Sintered (Pr_1–x–y Dy _x Gd _y )_13–14(Fe_1–z Co _z )_balB_6–7 materials (x = 0.18–0.58, y = 0.05–0.33, z = 0.2–0.36) have been studied. The magnetic moments of gadolinium ions and those of the sublattice formed by Fe and Co ions are shown to be ordered antiferromagnetically. It is noted that an increase in the content of gadolinium, which substitutes for dysprosium, leads to an increase in residual induction B _r , a decrease in coercive force H _cJ , and an increase in the absolute value of the temperature coefficient of induction. The opposite effect takes place in the case of substitution of gadolinium for praseodymium in materials with a fixed dysprosium content.     

Formation of Inclusions in Ti-Stabilized 17Cr Austenitic Stainless Steel

The behavior and formation mechanisms of inclusions in Ti-stabilized, 17Cr Austenitic Stainless Steel produced by the ingot casting route were investigated through systematic sampling of liquid steel and rolled products. Analysis methods included total oxygen and nitrogen contents, optical microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The results indicate that the composition of inclusions was strongly dependent on the types of added alloying agents. During the AOD refining process, after the addition of ferrosilicon alloy and electrolytic manganese, followed by aluminum, the composition of inclusions changed from manganese silicate-rich inclusions to alumina-rich inclusions. After tapping and titanium wire feeding, pure TiN particles and complex inclusions with Al₂O₃-MgO-TiO _x cores containing TiN were found to be the dominant inclusions when [pct Ti] was 0.307 mass pct in the molten steel. These findings were confirmed by thermodynamic calculations which indicated that there was a driving force for TiN inclusions to be formed in the liquid phase due to the high contents of [Ti] and [N] in the molten steel. From the start of casting through to the rolled bar, there was no further change in the composition of inclusions compared to the titanium addition stage. Stringer-shaped TiN inclusions were observed in the rolled bar. These inclusions were elongated along the rolling direction with lengths varying from 17 to 84 µm and could have a detrimental impact on the corrosion resistance as well as the mechanical properties of the stainless steel products.     

Separation of Fine Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Inclusion from Liquid Steel with Super Gravity

An innovative approach of super gravity was proposed to separate fine Al₂O₃ inclusions from liquid steel in this study. To investigate the removal behaviors of inclusions, the effects of different gravity coefficients and time on separating the inclusions were studied. The results show that a large amount of Al₂O₃ inclusions gathered at the top of the sample obtained by super gravity, whereas there were almost no inclusions appearing at the bottom. The volume fraction and number density of inclusions presented a gradient distribution along the direction of the super gravity, which became steeper with increasing gravity coefficient and separating time. As a result of the collision between inclusions, a large amount of inclusions aggregated and grew during the moving process, which further decreased the removal time. The experimental required removal time of inclusions is close to the theoretical values calculated by Stokes law under gravity coefficient G ≤ 80, t ≤ 15 minutes, and the small deviation may be because the inclusion particles are not truly spherical. Under the condition of gravity coefficient G = 80, t = 15 minutes, the total oxygen content at the bottom of the sample (position of 5 cm) is only 8.4 ppm, and the removal rate is up to 95.6 pct compared with that under normal gravity.     

Phase Stability and Transformations in the Zr<Subscript>2</Subscript>Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> Amorphous System

Since Ni and Cu differ by only one valence electron, yet have nearly identical atomic sizes (1.27 vs 1.28 Å for Cu and Ni, respectively), the amorphous Zr₂Ni _x Cu_1?x system is ideal for isolating the effects of electronic structure on short- and medium-range order and the concomitant influence of both the structure and order on devitrification pathways. Thermal analysis, time-resolved high-energy X-ray diffraction (HEXRD), and transmission electron microscopy (TEM) were used to follow metastable and stable crystalline phase formation during devitrification. Using HEXRD, we observed that the first devitrification product in the Zr₂Ni system is the C16 structure, if oxygen is kept sufficiently low, while the Zr₂Cu system forms the C11b structure. For x = 0.25, the initial devitrification involves forming coexisting C11b and C16 phases. When Ni is increased to x ≥ 0.50, the initial devitrification only involves the C16 structure. These results are in complete accord with electronic structure calculations showing that the enthalpy of formation for the C11b phase is favored for x = 0, while enthalpies for C11b and C16 are nearly identical for x = 0.25; the C16 phase has the most negative enthalpy for all compositions in which x > 0.25.     

LaCoO<Subscript>3 – δ</Subscript> as the Material of an Oxygen Electrode for a Molten Carbonate Fuel Cell: I. Electrophysical Properties of Lithiated LaCoO<Subscript>3 – δ</Subscript>

Oxides LaCoO_{3 – δ} + (z/2) Li₂O (0 ≤ z ≤ 0.15) are synthesized to determine the boundaries of changing the electrophysical properties of LaCoO_{3 – δ} due to its in situ lithiation in the (Li_0.62K_0.38)₂CO₃ eutectic melt. A perovskite-like solid solution (La_{1 – x}Li _x )(Li _x Co_{1 – x})O_{3 – δ}, where x = z/(z + 2), is found to form as a result of Li doping. The region of existence of the solution does not exceed 2x = 0.072. At a higher concentration of Li, LiCoO₂ forms along with the perovskite-like phase. At the operating temperature of the carbonate fuel cell (T = 920 K), the single-phase samples have metallic conduction and positive thermopower. The electrical conductivity of the Li-doped samples decreases as compared to that of LaCoO_{3 – δ} by no more than 1.5 times and varies from 3.2 × 10⁴ to 3.8 × 10⁴ S/m.     

Synthesis and Non-isothermal Carbothermic Reduction of FeTiO<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> Solid Solution Systems

To investigate the carbothermic reduction behaviors of xFeTiO₃·(1 ? x)Fe₂O₃ solid solutions, the solid solutions with different x values were synthesized and used in the corresponding reactions. With an increase in x, the temperature pertaining to the onset of carbothermic reduction increased, while the rate of reduction of the solid solutions, α, decreased. The lattice parameters calculated from XRD patterns indicated that the solid solution with a higher x led to a larger lattice distortion. The non-isothermal kinetics were calculated, and an average activation energy E value of 3.0 × 10² kJ/mol was obtained.     

Kinetics study on non-isothermal crystallization of Cu<Subscript>50</Subscript>Zr<Subscript>50</Subscript> metallic glass

In this paper, the crystallization kinetics of melt-spun Cu₅₀Zr₅₀ amorphous alloy ribbons has been investigated using differential scanning calorimetry. Moreover, the Kissinger, Ozawa and isoconversional approaches have been used to obtain the crystallization kinetic parameters. As shown in the results, the onset crystallization activation energy E _x is less than crystallization peak activation energy E _p. The local activation energy E _α increases at the crystallized volume fraction α < 0.2 and decreases at the rest, which suggests that crystallization process is increasingly hard (α < 0.2) at first, after which it become increasingly easy (α > 0.2). The nucleation activation energy E _nucleation is greater than grain growth activation energy E _growth, indicating that the nucleation is harder than growth. In terms of the local Avrami exponent n(α), it lies between 1.27 and 8, which means that crystallization mechanism in the non-isothermal crystallization is interface-controlled one- two- or three-dimensional growth with different nucleation rates.     

Enthalpy of mixing of liquid Cu-Ti-Zr alloys

The enthalpy of mixing of liquid Cu-Ti-Zr ternary alloys is studied by high-temperature isoperibolic calorimetry at 1873 K along three ray sections characterized by the ratios x _Zr: x _Cu = 3: 7, x _Ti: x _Cu = 3: 7, and x _Zr: x _Ti = 1 at x _Cu = 1?0.4. The isotherm of the integral enthalpy of mixing of these melts is described in terms of the Redlich-Kister-Muggianu model. Along with the substantial contributions of binary copper-titanium and copper-zirconium interactions, the contribution of a ternary interaction to the enthalpy of mixing of liquid Cu-Ti-Zr alloys also exists. The first partial enthalpies of mixing of Ni, Al, Si, Sn, and Y with the melts are studied to determine the character of the interaction between the ternary Cu-Ti-Zr melts and metal additions that facilitate amorphization upon melt quenching. The introduction of these metals into the ternary melts is shown to increase their thermodynamic stability.     

Monte Carlo Simulation Study of Diffuse Scattering in PZT,Pb(Zr,Ti)O<Subscript>3</Subscript>

Transverse polarized diffuse streaks have been observed in diffraction patterns of Pb(Zr_1?x Ti _x )O₃ (PZT) ceramics for compositions ranging from x = 0.3 (rhombohedral phase) to x = 0.7 (tetragonal phase) including the important morphotropic phase boundary (MPB) region (x = 0.48). The streaks correspond to diffuse planes of scattering in three dimensions, and these are oriented normal to the (cubic) \( \langle 111\rangle_{c} \) directions. A Monte Carlo (MC) model has been developed that convincingly reproduces the observed diffraction patterns. In this model, the displacements of Pb ions running in chains along each of the \( \langle 111\rangle_{c} \) directions are directed along the chain and are strongly correlated from cell to cell. There is no evidence of lateral correlation. Neighboring chains are essentially independent. At this stage, it is not clear what role the local order revealed by the scattering might play in governing the exceptional piezo-electric properties of the material, but its presence requires the currently accepted models for the average structure to be reassessed.     

Electrical properties of the LaLi<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>Co<Subscript>1 – <Emphasis Type="Italic">y</Emphasis></Subscript>O<Subscript>3 – δ</Subscript> (0 ≤ <Emphasis Type="Italic">y</Emphasis> ≤ 0.10) oxides

The effect of the Li ion concentration on the phase composition, the electrical conductivity, and the thermoelectric power of the LaLi _y Co_1–yO_3–δ (0 ≤ y ≤ 0.1) oxides synthesized by cocrystallization has been studied. It is found that the region of the perovskite-like solid solution LaLi _y Co_1–yO_3–δ is no higher than y = 0.037. In the temperature range 300–1020 K, lithium alloying leads to an increase in the electrical conductivity and a decrease in the positive thermoelectric power of the single-phase samples compared to LaCoO_3–δ. The results are discussed using the density of states model proposed by Senarus Rodriguez and Goodenough for LaCoO_3–δ and La_1–xSr _x CoO_3–δ and using the Mott theory of noncrystalline substances.     

Microstructure and Properties of Fe<Subscript>3</Subscript>Al-Fe<Subscript>3</Subscript>AlC<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Composite Prepared by Reactive Liquid Processing

A Fe₃Al-Fe₃AlC _x composite was prepared using reactive liquid processing (RLP) through controlled mixture of carbon steel and aluminum in the liquid state. The microstructure and phases of the composite were assessed using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, optical microscopy, and differential scanning calorimetry. In addition, the density, hardness, microhardness, and elastic modulus were evaluated. The Fe₃Al-Fe₃AlC _x composite consisted of 65 vol pct Fe₃Al and 35 vol pct Fe₃AlC _x (κ). The κ phase contained 10.62 at. pct C, resulting in the stoichiometry Fe₃AlC_0.475. The elastic modulus of the Fe₃Al-Fe₃AlC_0.475 composite followed the rule of mixtures. The RLP technique was shown to be capable of producing Fe₃Al-Fe₃AlC_0.475 with a microstructure and properties similar to those achieved using other processing techniques reported in the literature.     

Effect of Deoxidation Process on Inclusion and Fatigue Performance of Spring Steel for Automobile Suspension

55SiCrA spring steel was smelted in a vacuum induction levitation furnace. The liquid steel was treated by Si deoxidation, Al modification with Ca treatment and Al modification, and the steel samples were obtained with deformable Al₂O₃-SiO₂-CaO-MgO inclusions closely contacted with steel matrix, Al₂O₃-CaO-CaS-SiO₂-MgO inclusions surrounded by small voids or Al₂O₃(> 80 pct)-SiO₂-CaO-MgO inclusions surrounded by big voids, respectively. Effect of three types of inclusions on steel fatigue cracks was studied. The perpendicular and transverse fatigue cracks around the three types of inclusions leading to fracture were found to vary in behavior. Under the applied stress amplitude of 775 MPa, the fatigue lives of the three spring steels decreased from 4.0 × 10⁷ to 3.8 × 10⁷, and to 3.1 × 10⁷ cycles. For the applied stress amplitude of 750 MPa, the fatigue lives of the three spring steels decreased from 5.2 × 10⁷ to 4.1 × 10⁷, and to 3.4 × 10⁷ cycles. Based on the voids around inclusions, the equivalent size of initial fatigue crack has been newly defined as \( \sqrt {\frac{{{\text{area}}_{\text{inclusion}} }}{{(1 - {\text{CC}})}}} \), where the contraction coefficient CC of inclusion was introduced. A reliable forecast model of the critical size of inclusion leading to fracture was established by the incorporation of actual width b_inclusion or diameter d_inclusion of internal inclusion; the model prediction was found to be in agreement with experimental results.     

Elasticity of Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>W<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript> (<Emphasis Type="Italic">x</Emphasis> ≤ 0.1875) Alloys from First Principles Calculations

The elastic properties of Ni _x W_1?x alloys up to x = 0.1875 have been determined from first principles calculations. We have used stress–strain relationships to calculate the C _ij elastic coefficients and the Voigt–Reuss–Hill approximations to determine the bulk and shear moduli of polycrystals. The W alloying increases the compression modulus while the shear modulus remains almost constant. Furthermore, the W alloying has a minor effect on the elastic anisotropy and, therefore, on its contribution to the indentation modulus.     

A Thermodynamic Model to Estimate the Formation of Complex Nitrides of Al<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript>(1–<Emphasis Type="Italic">x</Emphasis>)</Subscript>N in Silicon Steel

A complex nitride of Al _x Mg_(1?x)N was observed in silicon steels. A thermodynamic model was developed to predict the ferrite/nitride equilibrium in the Fe-Al-Mg-N alloy system, using published binary solubility products for stoichiometric phases. The model was used to estimate the solubility product of nitride compound, equilibrium ferrite, and nitride compositions, and the amounts of each phase, as a function of steel composition and temperature. In the current model, the molar ratio Al/(Al?+?Mg) in the complex nitride was great due to the low dissolved magnesium in steel. For a steel containing 0.52 wt pct Al_s, 10 ppm T.Mg., and 20 ppm T.N. at 1100 K (827 °C), the complex nitride was expressed by Al_0.99496Mg_0.00504N and the solubility product of this complex nitride was 2.95?×?10^?7. In addition, the solution temperature of the complex nitride increased with increasing the nitrogen and aluminum in steel. The good agreement between the prediction and the detected precipitate compositions validated the current model.     

<Emphasis Type="Italic">In situ</Emphasis> Observation of Calcium Oxide Treatment of Inclusions in Molten Steel by Confocal Microscopy

Calcium treatment of aluminum killed steel was observed in situ using high-temperature confocal scanning laser microscope (HT-CSLM). This technique along with a novel experimental design enables continuous observation of clustering behavior of inclusions before and after the calcium treatment. Results show that the increase in average inclusion size in non-calcium-treated condition was much faster compared to calcium-treated condition. Results also show that the magnitude of attractive capillary force between inclusion particles in non-treated condition was about 10^?15 N for larger particles (10 µm) and 10^?16 N for smaller particles (5 µm) and acting length of force was about 30 µm. In the case of calcium-treated condition, the magnitude and acting length of force was reduced to 10^?16 N and 10 µm, respectively, for particles of all sizes. This change in attractive capillary attractive force is due to change in inclusion morphology from solid alumina disks to liquid lens particles during calcium treatment.     

Calculation of the structural and thermodynamic constants of normal chromium spinels

The interstructural distances and crystal lattice parameters of complex chromium spinels of variable composition having five different cations are determined according to the earlier developed procedure taking into account their crystal lattices and calculated effective ionic radii. Using these structural characteristics, the enthalpy of the crystal lattice and the enthalpy of spinel formation are calculated. The composition-lattice parameter and composition-enthalpy of the formation diagrams are constructed for (Mg _i ²⁺ Fe _j ²⁺ )O · (Fe _x ³⁺ Al _y ³⁺ Cr _z ³⁺ )₂O₃ spinels. They make it possible to determine the lattice parameter and the enthalpy of oxide formation for any spinel composition.     

Microstructure of amorphous electrodeposited Co-Ni-W films

The phase composition of electrodeposited films of (Co_{100 ? x} -Ni _x )_{100 ? y} W _y alloys (x = 0–100 at % Ni, y = 0–30 at % W), the microstructures of amorphous films of this system on the submicrometer and nanometer scales, and the mechanism of their nucleation and growth are studied. X-ray diffraction analysis demonstrates that, as the tungsten concentration increases, the transition from a crystalline into an amorphous state in the films based on Co-W alloys occurs through a supersaturated hcp solid solution, whereas this transition in the films based on Ni-W alloys occurs through an fcc structure. Heterophase states consisting of a mixture of hcp and fcc structures are observed in the composition range x = 30–80 at % Ni, and, at concentrations higher than 12–14 at % W, an amorphous phase is also observed. A homogeneous amorphous phase forms at a refractory-metal content of 19–20 at % or more. Transmission and scanning electron microscopies show that the amorphous Co-W, Ni-W, and Co-Ni-W films have a network structure. The laws of the variation of the network microstructure with the chemical composition of the amorphous films are established and explained in the framework of the island model of thin film nucleation and growth.     

Crystal and Electronic Study of Neodymium-Substituted CuFeO<Subscript>2</Subscript> Oxide

Neodymium-substituted CuFeO₂ samples were investigated according to their crystal and electronic properties via the general formula Nd _x Cu_1?x FeO₂. The crystal structure analysis results revealed polycrystalline formations in the sample and a change in crystalline sizes with the substituted heavy fermion “Nd.” Increasing the Nd amount in the sample was determined to cause a disturbance on the Cu-Fe planes that supports the formation of crystal structures with low crystal symmetries such as monoclinic or triclinic geometries. To obtain the background mechanisms of the crystal properties, the X-ray absorption fine structure spectroscopy technique was used to study the electronic properties of the samples. Prominent changes in the crystal structures due to 4f electrons’ contributions from the substituted Nd atoms as the main “role player” in the phase transitions were determined. The Nd atoms were observed as the key element guiding the entire phenomenon as a result of their large size and narrow 4f levels. Also, magnetic properties of the samples were tested at room temperature and without an applied magnetic field by X-ray magnetic circular dichroism study due to previous studies that reported the parent oxide CuFeO₂ to have magnetic ordering at T _N = 11 K (?262 °C). Except the sample for x = 1.0 (NdFeO₃), no magnetic ordering was observed at room temperature; i.e., all of the samples showed paramagnetic behaviors.     

Microstructure and High Temperature Impression Creep Properties of Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) Alloys

The current study has investigated the influence of zirconium (Zr) addition to Mg–3Ca–xZr (x = 0.3, 0.6, 0.9 wt%) alloys prepared using argon arc melting on the microstructure and impression properties at 448–498 K under constant stress of 380 MPa. Microstructural analysis of as-cast Mg–3Ca–xZr alloys showed grain refinement with Zr addition. The observed grain refinement was attributed to the growth restriction effect of Zr in hypoperitectic Mg–3Ca–0.3 wt% Zr alloys. Heterogeneous nucleation of α-Mg in properitectic Zr during solidification resulted in grain refinement of hyperperitectic Mg–3Ca–0.6 wt% Zr and Mg–3Ca–0.9 wt% Zr alloys. The hardness of Mg–3Ca–xZr alloys increased as the amount of Zr increased due to grain refinement and solid solution strengthening of α-Mg by Zr. Creep resistance of Mg–3Ca–xZr alloys increased with the addition of Zr due to solid solution strengthening of α-Mg by Zr. The calculated activation energy (Q_a) for Mg–3Ca samples (131.49 kJ/mol) was the highest among all alloy compositions. The Q_a values for 0.3, 0.6 and 0.9 wt% Zr containing Mg–3Ca alloys were 107.22, 118.18 and 115.24 kJ/mol, respectively.     

Thermodynamic description of the interaction processes in the Cu–Ce–O system in the temperature range 1100–1300°C

A thermodynamic simulation and an experimental study of the interaction between cerium and oxygen in liquid copper have been performed. The thermodynamic analysis of the interaction processes in the Cu–Ce–O system is carried out using the technique of constructing the surface of solubility of components in a metal in the temperature range 1100–1300°C. As a result of simulation, data on changes in the Gibbs energy ΔG _T ° and the equilibrium constants of formation of cerium oxides Ce₂O₃ and CeO₂ from the components of a copper-based metallic melt are obtained. The first-order interaction parameters (according to Wagner) of cerium and oxygen dissolved in liquid copper, namely, e _Ce ^Ce, e _O ^Ce, and e _Ce ^O, are evaluated. Experimental studies of the Cu–Ce–O system have been performed. The morphological features, the size, and the composition of nonmetallic inclusions formed as a result of interaction in the Cu–Ce–O system are studied using scanning electron microscopy and electron-probe microanalysis.