Equilibrium crystallization and distribution coefficients of alloy components in ternary systems with continuous solid and liquid solutions

Features of equilibrium crystallization of alloys in a ternary system consisting of solid and liquid solutions of components A, B, and C with melting points related as t _C < t _A < t _B are investigated in detail. It is demonstrated that, in alloys of any composition, the distribution coefficients of components B and C are k _B > 1 and k _C < 1, respectively. For the component A, this characteristic, depending on the alloy composition, can be either larger or smaller than unity, and at temperature t _A , k _A = 1.     

Solidification of the eutectic Sn–43 mol % Bi alloy

The processes of melting and solidification of the eutectic Sn–43 mol % Bi alloy are studied by cyclic thermal analysis. It is found that this alloy melts at a temperature T _L = 412 K (which corresponds to the reference melting temperature of the eutectic) upon heating and solidifies isothermally at a temperature T _S = 394 K upon cooling; that is, the temperature difference is ΔT _LS ^? = 18 K. A comparison of temperatures T _L and T _S reveals a temperature hysteresis (TH). The activities and the activity coefficients of tin and bismuth in the eutectic are calculated at temperatures T _L and T _S . The enthalpies of melting at T _L and solidification at TS are measured. The ways of changing the Gibbs energy during TH are determined.     

On the Nonequilibrium Interface Kinetics of Rapid Coupled Eutectic Growth

Nonequilibrium interface kinetics (NEIK) is expected to play an important role in coupled growth of eutectic alloys, when solidification velocity is high and intermetallic compound or topologically complex phases form in the crystallized product. In order to quantitatively evaluate the effect of NEIK on the rapid coupled eutectic growth, in this work, two nonequilibrium interface kinetic effects, i.e., atom attachment and solute trapping at the solid–liquid interface, were incorporated into the analyses of the coupled eutectic growth under the rapid solidification condition. First, a coupled growth model incorporating the preceding two nonequilibrium kinetic effects was derived. On this basis, an expression of kinetic undercooling (?T _k), which is used to characterize the NEIK, was defined. The calculations based on the as-derived couple growth model show good agreement with the reported experimental results achieved in rapidly solidified eutectic Al-Sm alloys consisting of a solid solution phase (α-Al) and an intermetallic compound phase (Al₁₁Sm₃). In terms of the definition of ?T _k defined in this work, the role of NEIK in the coupled growth of the Al-Sm eutectic system was analyzed. The results show that with increasing the coupled growth velocity, ?T _k increases continuously, and its ratio to the total undercooling reaches 0.32 at the maximum growth velocity for coupled eutectic growth. Parametric analyses on two key alloy parameters that influence ?T _k, i.e., interface kinetic parameter (μ _i ) and solute distribution coefficient (k _e ), indicate that both μ _i and k _e influence the NEIK significantly and the decrease of either these two parameters enhances the NEIK effect.     

Diffusion of copper along the grain boundaries in aluminum

The grain boundary diffusion (GBD) of copper in aluminum is investigated in the range t = 300?400°C. Investigations were performed on a scanning electron microscope equipped with an attachment for electron probe X-ray microanalysis. The triple product sδD _gb (where s is the segregation coefficient, δ is the width of the grain boundary, and D _gb is the GBD coefficient) was calculated by the Fisher criterion using two methods (namely, the copper concentration in the grain boundary, depending on the penetration depth, was determined and the angles in the vertex of the concentration profile was measured using an optical microscope). In the first case, sδD _gb was 5.1 × 10^?11 exp(?102/(RT)) m³/s; in the second case it was 1.4 × 10^?11 exp(?94/(RT)) m³/s. The obtained results are compared with innumerous literature data.     

Structure and magnetic properties of the Nd<Subscript>9.5</Subscript>Fe<Subscript>84.5</Subscript>B<Subscript>6</Subscript> alloy subjected to severe plastic deformation and annealing

The effect of severe plastic deformation (SPD) by torsion and subsequent annealing on the structure and magnetic properties of the cast Nd_9.5Fe_84.5B₆ alloy is studied. SPD by torsion is shown to lead to partial amorphization of the Nd₂Fe¹⁴B phase and the precipitation of α-Fe; subsequent annealing results in the crystallization of the amorphous phase and the formation of a nanocomposite Nd₂Fe₁₄B/α-Fe structure. After SPD by torsion at 20 revolutions and annealing at 873 K, the (101) texture is formed; in this case, the coercive force is H _c = 360 kA/m and the maximum energy product is (BH) _max = 166 kJ/m3. The residual magnetization and the squareness ratio of the hysteretic loop of the textured alloy decrease as the ambient temperature decreases.     

Investigation of the End-Point Temperature Control Based on the Critical Temperature of Vanadium Oxidation During the Vanadium Extraction Process in BOF

To solve the problem related to the end-point temperature control during the vanadium extraction, industrial experiments and thermodynamic analyses were implemented to find out and verify the foundation for the new standard. The transition temperatures of carbon-vanadium oxidation (T _tr ) and the molten bath temperature measured on the industrial experiments showed a negative temperature difference after smelting for 3.5 min. However, for about 30 wt% vanadium was removed when the molten bath temperature exceeded T _tr . T _tr was only suitable for achieving the goal of “keeping carbon while extracting vanadium” in the early and medium period. The critical temperature of vanadium oxidation (T _cr ) stood for the thermodynamic equilibrium between the oxidation and reduction of vanadium in the later period. It served as the basis to control the end-point temperature to satisfy the demand of “deep vanadium extraction”. As the molten bath temperature increased above T _cr , the residual vanadium neither decreased further nor increased, but showed an equilibrium state.     

Integral Model for Development of Instant Interface Temperature at Time <Emphasis Type="Italic">τ</Emphasis> = 0<Superscript>+</Superscript> of Cylindrical Solid Additive-Bath System

Closed-form solution derived from the integral model for the instant interface temperature θ _e between the cylindrical-shaped additive and the growing frozen layer of the bath material onto the additive immediately after the immersion of the additive in the bath indicates this temperature dependence on the property ratio B and the Stefan number S _t . Increasing B (0 ≤ B ≤ ∞) or decreasing S _t (∞ ≥ S _t ≥ 0) raises θ _e from the initial temperature of the additive to the freezing temperature of the bath material, and for S _t →0, 0 ≤ B ≤ ∞, it assumes the expression \( {{\theta}}_{e} = \sqrt {6B} /\left( {3 + \sqrt {6B} } \right). \)     

Effect of Recovery and Recrystallization on the Hall–Petch Relation Parameters in Submicrocrystalline Metals: I. Experimental Studies

Yield strength σy, macroelastic limit σ₀, and effective grain-boundary hardening coefficient K_eff in the Hall–Petch relation (\({\sigma _y} = {\sigma _0} + {K_{eff}}/\sqrt d \)) in the submicrocrystalline (SMC) materials produced by equalchannel angular pressing are experimentally studied. It is shown that, as compared to parameter σ₀ and K in the Hall–Petch relation for coarse-grained metals, the SMC metals are characterized by higher values of σ0 and lower values of K_eff. The critical grain size (d₁) at which Keff in the σ_y–d^–1/2 relations of SMC materials changes falls in the range 0.2–0.5 μm. The dependences of macroelastic limit σ₀ and coefficient K_eff on the annealing temperature are found to be determined by recrystallization. If abnormal grain growth develops in annealing of SMC metals, anomalous hardening is detected and a nonmonotonic temperature dependence of coefficient K_eff takes place. In the case of conventional recrystallization at a high annealing temperature, SMC metals exhibit a smooth decrease in σ₀ and an increase in K_eff to the values of K characteristic of coarsegrained materials.     

Influence of the Strengthening Curve on the Axial Stress in Round Rod on Drawing

For the drawing of round rod in conical drawplates, the boundary problem is solved on the basis of the Amontons–Coulomb frictional law for materials in which strengthening corresponds to the equation σ_s/σ_s0 = 1 + m(ln λ)ⁿ. The influence of the parameters m and n of the strengthening curve on the axial stress σ_x in the reducing section of the drawplate is established. The new result is compared with existing solutions. It is found that, if the strengthening law is replaced by approximate functions without taking account of the shape of the strengthening curve at small n, the calculated values of σ_x are too low, by 15–25%.     

Bulk Nanolaminated Nickel: Preparation,Microstructure, Mechanical Property,and Thermal Stability

A bulk nanolaminated (NL) structure with distinctive fractions of low- and high-angle grain boundaries (f _LAGBs and f _HAGBs) is produced in pure nickel, through a two-step process of primary grain refinement by equal-channel angular pressing (ECAP), followed by a secondary geometrical refinement via liquid nitrogen rolling (LNR). The lamellar boundary spacings of 2N and 4N nickel are refined to ~ 40 and ~ 70 nm, respectively, and the yield strength of the NL structure in 2N nickel reaches ~ 1.5 GPa. The impacts of the deformation path, material purity, grain boundary (GB) misorientation, and energy on the microstructure, refinement ability, mechanical strength, and thermal stability are investigated to understand the inherent governing mechanisms. GB migration is the main restoration mechanism limiting the refinement of an NL structure in 4N nickel, while in 2N nickel, shear banding occurs and mediates one-fifth of the total true normal rolling strain at the mesoscale, restricting further refinement. Three typical structures [ultrafine grained (UFG), NL with low f _LAGBs, and NL with high f _LAGBs] obtained through three different combinations of ECAP and LNR were studied by isochronal annealing for 1 hour at temperatures ranging from 433 K to 973 K (160 °C to 700 °C). Higher thermal stability in the NL structure with high f _LAGBs is shown by a 50 K (50 °C) delay in the initiation temperature of recrystallization. Based on calculations and analyses of the stored energies of deformed structures from strain distribution, as characterized by kernel average misorientation (KAM), and from GB misorientations, higher thermal stability is attributed to high f _LAGBs in this type of NL structure. This is confirmed by a slower change in the microstructure, as revealed by characterizing its annealing kinetics using KAM maps.     

Magnetic Hysteretic and Mechanical Properties of a 31Kh20K3M Alloy with an Increased Carbon Content

An Fe–31Cr–20Co–3Mo (31Kh20K3M) alloy containing 0.09 wt % C, which is almost twice as much as its maximum content according to GOST 24897–81, has been studied to verify the influence of the carbon content on the magnetic hysteretic properties of hard magnetic high-chromium Fe–Cr–Co alloys. The optimal heat treatment, including thermomagnetic treatment, results in the average values of residual magnetic induction B_r = 0.96 T and coercive force H_cB = 63 kA/m and the maximum energy product (BH)_max = 29 kJ/m³. Some heat treatment regimes give B_r = 1.03 T, H_cB = 72 kA/m, and (BH)_max = 31 kJ/m³. In addition, for isotropic alloy samples, the following average values are obtained: B_r = 0.71 T, HcB = 56 kA/m, and (BH)_max = 15 kJ/m³. These magnetic hysteretic properties of the 31Kh20K3M alloy with an increased carbon content are similar to those of a powder 30Kh21K3M alloy with the minimum carbon content.     

Influence of heat treatment on the residual magnetization of steel in partial magnetic hysteresis

A formula is derived for the residual magnetization M_r of steel after repeated magnetic hysteresis, on the basis of measurements of the saturation magnetization M_s, the coercive force H_cs, the residual magnetization M_rs for the limiting hysteresis loop, and the maximum magnetizing field strength H_m of the partial hysteresis loop. The influence of variation in the tempering temperature t_te of steel on M_r at different H_m is analyzed. The dependence M_r(t_te) is established for small and large H_m. It is established that the M_r results may effectively be used for nondestructive assessment of the tempering of moderate-carbon alloy steel.     

Effect of heat treatment on the superplasticity of magnesium alloys

A necessary microstructural condition for the manifestation of the effect of superplasticity in alloys is a small grain size (d < 10 μm). The ingots of commercial magnesium alloys have a very coarse cast structure with d > 100 μm. We have studied the regimes of heat treatment of such materials in AZ91, AE42, QE22, and ZRE1 alloys with a purpose of obtaining a fine-grained structure. The optimum temperature of overaging of quenched magnesium alloys lies between 300 and 350°C. After hot pressing of heat-treated alloys, the average grain size is 6.4 (AZ91), 6.2 (AE42), 1.2 (ZRE1), and 0.7 (QE22) μm. The best characteristics of superplasticity are manifested by the ZRE1 and QE22 alloys with a relative elongation of 750% and strain-rate sensitivity m = 0.75 at T = 420°C and strain rate \(\dot \varepsilon \) = 3 × 10^?4 s^?1. Under these conditions, the AZ91 and AE42 alloys have δ ≤ 260% and m = 0.45.     

Aging Temperature Dependence of <Emphasis Type="Italic">α</Emphasis>″-Martensite Decomposition Mechanism in Ti-Al-Fe-Si Alloy

The mechanism by which α″-martensite decomposes in Ti-4Al-4Fe-0.25Si-0.1O alloy is found to change depending on the aging temperature, with Fe-rich α first transforming in twins of α″-martensite. As the aging temperature increases, Fe is segregated at the boundaries between α″ and α. At temperatures >?773 K, the Fe-segregated boundaries provide a nucleation site for B2-structured TiFe intermetallic compounds. This process of α″-martensite decomposition is described as follows: α″?+?α″_Twin?→?α″_Fe-rich?+?α_Fe-rich,V1?→?α_Fe-lean,V2?+?α_Fe-lean,V1?+?TiFe.     

Monitoring the Physicomechanical Properties of 40X Steel on the Basis of the Limiting Magnetic Hysteresis Loop

The mechanical properties (strength σ_u, yield point σ_0.2, relative elongation ψ; and hardness HB and HRC) of 40X steel depend monotonically on the tempering temperature T_te after quenching and are closely correlated. Their relationships are described by linear regression equations. The corresponding correlation coefficients and computational errors are determined. The coercive force H_c of 40X steel is not clearly related to its physicomechanical properties over the whole range of T_te. However, magnetic analysis of the structure of 40X steel may be based on an algorithm that employs Hc and the ratio of the residual magnetization to the saturation magnetization. The results given by this algorithm depend uniquely on T_te over its practical range and are highly sensitive to change in the physicomechanical properties of 40X steel.     

Microstructure and Properties of Graphitized Free-Cutting Steel

This article describes the metallographic studies and the tensile tests of quenched and high-temperature tempered samples of graphitized free-cutting steel and the experience of machining graphitized samples. The experimental results have shown that the microstructure of the graphitized steel is comprised mainly of ferrite and graphite, and graphite particles are distributed both along grain boundaries and inside them. The morphology of graphite is presented by a spherical shape (average diameter of ~10 μm). The ratio of the yield stress to the ultimate strength is 0.59, and the machinability coefficient is k_T = 5.4241. The microstructure of steel samples after quenching and high-temperature tempering is comprised mainly of secondary sorbite. In this case, the ratio of the yield stress to the ultimate strength is 0.82.     

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.     

Determination of the heat-transfer coefficient between the AK7ch (A356) alloy casting and no-bake mold

The heat-transfer coefficient h between a cylindrical cast made of AK7ch (A356) aluminum alloy and a no-bake mold based on a furan binder is determined via minimizing the error function, which reflects the difference between the experimental and calculated temperatures in the mold during pouring, solidification, and cooling. The heat-transfer coefficient is h _L = 900 W/(m² K) above the liquidus temperature (617°C) and h _S = 600 W/(m² K) below the alloy solidus temperature (556°C). The variation in the heat-transfer coefficient in ranges h _L = 900–1200 W/(m² K) (above the alloy liquidus temperature) and h _S = 500–900 W/(m² K) (below the solidus temperature) barely affects the error function, which remains at ~22°C. It is shown that it is admissible to use a simplified approach when constant h = 500 W/(m² K) is specified, which leads to an error of 23.8°C. By the example of cylindrical casting, it is experimentally confirmed that the heat-transfer coefficient varies over the casting height according to the difference in the metallostatic pressure, which affects the casting solid skin during its solidification; this leads to a closer contact of metal and mold at the casting bottom.     

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.     

Technology and properties of porous permeable aluminum-based materials

Results of the investigation of preparation conditions (pressure of powder pressing and time of sintering of compacts) and of the effect of aluminum additions (5–20 wt %) on the properties of a sintered porous material of an aluminum powder and its mixture with an Al₂O₃ powder are given. The possibility is shown of the production of porous (P = 30–35%), highly permeable (k = 2.0 to 2.5 × 10^?13 m²) aluminum-based sintered material with an addition of 20% Al₂O₃ and maximum size of pores equal to 1.3–1.5 μm in the following regime: p = 60 MPa, T = 723–823 K with an isothermal holding for 30–60 min.