Influence that nanosecond electromagnetic pulses have on the acquisition of tin and the properties of its alloys

It is established experimentally that the influence that nanosecond electromagnetic pulses (NEMPs) have on the charge melt during the carbothermic reduction of cassiterite in the Na₂CO₃-NaNO₃ medium (1: 0.3) at t = 900–950°C accelerates the formation of the metal phase by a factor of ∼2 and affects its composition. As the duration of irradiation increases to 30 min, the tin content in the crude alloy increases to ∼95%. The influence that the NEMP treatment of the bronze melt has on its physicomechanical properties is revealed. It is shown that the influence of pulses for 10–15-min increases the alloy density to 8.92 g/cm³, hardness by a factor of 1.24, and thermal conductivity by a factor of 2.     

A new method to dynamically measure the surface tension,viscosity, and density of melts

A new formulation has been developed to describe the fluid dynamics of a liquid draining through an orifice under the influence of gravity. The model relates experimental quantities of head and flow rate, with surface tension, viscosity, and density, facilitating the calculation of all three properties. Experiments performed with molten aluminum at temperatures from 937 to 1173 K indicate that surface tension (N/m) and density (kg/m³) are [0.871 − 0.155 × 10⁻³ (T − T _liq)] and [2390 − 0.15 (T − T _liq)], which is within 6.5 and 2.5 pct, respectively, of values reported in the literature. The viscosity has been determined to be 5.2 × 10⁻⁴ Nsm⁻², which is significantly less than data reported from other sources. The method is unique because the measurements are performed under highly dynamic conditions.     

Steel dissolution in quiescent and gas stirred Fe/C melts

The dissolution rates of commercial black iron rods in iron/carbon melts under isothermal conditions were measured. The effect of melt carbon content, temperature, natural convection, and gas stirred forced convection conditions were investigated. The experimental data under natural convection conditions (no external stirring) were fitted with a dimensionless correlation for vertical cylinders: Sh = 0.13(Gr . Sc)^0.34, representing mass transport control dominated by turbulent natural convection. Under bottom injection gas stirring conditions, it was found that the kinetic power input had little effect on the rod dissolution rates which were controlled by the total gas flow rate. Derived mass transport coefficients under gas stirring conditions were found to have the following dependence on the gas injection rates:k _m ∝Q ^0.21, wherek _m = mass transport coefficient andQ = gas flow rate. A comparison of the experimental results with previously measured mass transfer coefficients under forced convection conditions gave a plume velocity flow rate dependence ofU ∝Q ^0.3. A general discussion of gas stirring fluid dynamics and resulting mass transport effects is presented.     

Subgrain strengthening of aluminum conductor wires

The influence of wire processing variables on the formation of subgrain structures and strengthening in three aluminum conductor materials is described. Electrical conductor grade aluminum, an Al-Fe-Mg alloy and an Al-Fe-Co alloy each develop subgrain structures with mean linear intercepts (•L) in the range of 0.4 to 1.5 μm with several sequences of wiredrawing and partial annealing. The yield strengths of these wires were found to obey a a = σ₀ +k(•L) ^m relationship, with an exponentm = -1 independent of the processing sequence used to arrive at the structure. The role of precipitate particles in the alloys is to raisek above that for EC-A1 while Mg in solid solution increases σ₀. The precipitates also affect the development of the substructure during the wiredrawing and annealing.     

The Effect of Fluid Flow on the Eutectic Lamellar Spacing

The effect of fluid flow on the lamellar spacing of unidirectionally solidified Al-CuAl₂ eutectic alloy has been investigated experimentally. It was found that the practical condition for the modification of lamellar spacing can conveniently be given byPe > 1(Pe = Uλ/2D, whereU: flow rate, λ : lamellar spacing,D : solute diffusion coefficient in the melt), when the value ofU at the characteristic distance λ/8 ahead of the solid-liquid interface is used. The theoretical prediction of the relation between λ andv, given by Quenisset and Naslain, λ²v = A/(1 − BG_uλ²/D) where G_u is the flow velocity gradient at the solid-liquid interface and v is the solidification rate, was confirmed to be valid. The numerical constantsA andB are determined to be 8.46 x 10^-17 m³ per second and 1.56 × 10^-2, respectively. Associate Professor, on leave from the Department of Metallic Materials and Technology, Dalian Institute of Technology, Dalian, China.     

Viscosity of a CaO-MgO-Al2O3-SiO2 melt containing spinel particles at 1646K

This article reports an experimental investigation into the effect of solid suspension on the viscosity of molten slags. Up to about 20 vol pct of spinel (MgAl₂O₄) particles of three size ranges (fine: 0.10 to 0.21 mm; medium: 0.21 to 0.44 mm; and coarse: 0.44 to 0.99 mm) were added to a CaO-MgO-Al₂O₃-SiO₂ melt at 1646 (±10)K. A Brookfield DVII+ viscometer was used. The viscosity determined for the solid-free melts was in good agreement with the results of published work. The viscosity for the solid-containing melt was found to increase with the addition of the particles. With more than 10 vol pct solid particles, particularly the fine and the coarse ones, the melt showed an apparent “Bingham” behavior, i.e., the shear stress increased linearly with the shear rate but had a residual shear stress (up to 3 Pa depending on the amount and size of solid added) at zero shear rate. The viscosity of the solid-containing slag, η, was found to fit an Einstein-Roscoe type equation, η=η ₀ (1−af)⁻ⁿ, where η ₀ is the viscosity of the solid-free melt, f is the volume fraction of solid particles in the melt, and a and n are parameters taking the value of 4.24, 3.29, and 3.56 and 1.28, 2.36, and 2.24 for the fine, medium, and coarse particles, respectively, for best fit.     

Modeling of porosity during spray forming: Part I. Effects of processing parameters

In this article, a porosity model is developed based on particle packing theory, fluid mechanics, and particle thermal and dynamic behavior during spray forming. According to this model, the amount of porosity in as-deposited materials can be estimated on the basis of the average fraction of solid in the incident spray and the solid particle packing density. A porosity coefficient Φ is introduced. By using this model, the effects of deposition distance, atomization gas pressure, melt flow rate, and melt superheat on porosity are investigated. The amount of porosity demonstrates distinct V-shaped variations with the processing parameters. Finally, the optimal processing parameters for achieving low porosity are discussed on the basis of the calculated results.     

A mathematical model for metal flow and heat transfer in centrifuge melt spinning

Centrifuge melt spinning (CMS) is a technique used for the production of rapidly solidified metallic ribbons, in which the liquid metal is ejected centrifugally from a rotating crucible onto a quenching copper rim which rotates in the direction opposite the crucible. A numerical model has been developed to describe the hydraulic features of the alloy melt stream, together with the heat flow in the solidifying melt. The model takes into account, among other things, the dragging mechanism caused by the counter-rotation of the casting crucible and the quenching rim, the additional spreading velocity imparted to the melt by centrifugal forces developing on the rotating rim, the increase of heat transfer in the melt due to convection, and the changes of the viscosity of the melt with temperature. Comparison of the mathematical model with experimental results obtained for an Al-12 at. pct Ge alloy indicates that CMS is characterized by heat-transfer coefficients ranging from 3 to 11 * 10⁶ W m⁻² K⁻¹ depending mainly on the velocities of the casting crucible and the rim. The effect of various process parameters, such as crucible and rim velocities, on the dimensions of the obtained ribbons and the effect of the enhanced heat flow in the melt on the reduction of thermal gradients in the ribbon are presented.     

Deformation of semi-solid Sn-15 Pct Pb alloy

The rheological behavior of semisolid Sn-15 pct Pb alloy was studied using a parallel-plate viscometer. Small nondendritic and dendritic semisolid samples of the alloy were deformed under a constant load at initial pressures up to 232 kPa (33.6 psi) and at fractions solid from 0.15 to 0.60. Strain-time data for the nondendritic material obey the non-Newtonian, two-parameter, Ostwald-de-Waele, power-law model,i.e. μ = mγ ⁿ⁻¹, where μ is viscosity γ shear rate andm andn are constants. For fractions solid above about 0.30, the following empirical equation relates viscosity, shear rate and fraction solidμ = a exp (bf_s) γ^(cf _s ^+d) 0.3 <f _s < 0.60 wheref _s is fraction solid anda, b, c, d are constants. The nondendritic alloy deformed homogeneously without cracking to very large strains (up to 80 pct). Dendritic alloys required much higher loads and cracked easily. For the nondendritic alloys the forging pressures to obtain 50 pct compression were of the order of 7 to 70 kPa (1 to 10 psi) for fractions solid under 0.55 and 172.5 to 207 kPa (25 to 30 psi) for fraction solid of about 0.60. For the dendritic alloys, the forging pressure required to achieve 10 pct compression is about 85 kPa at a fraction solid of 0.35 and increases rapidly with increasing fraction solid.     

The kinetics of S35 exchange between SO2/CO/CO2 gas mixtures and copper sulfide melts at 1523 K

The kinetics and mechanisms of oxidation of copper sulfide melts have been investigated using a radioisotope exchange technique. Copper sulfide melts were doped with S³⁵. The transfer of the radioisotope between the melt and SO₂/CO/CO₂ gas mixtures in chemical equilibrium with the melt was monitored by analyzing the changes in radioactivity of the gas. Analysis of the results indicates that the rate-limiting chemical reaction involves the formation of an activated complex SO, and the rate of exchange of the sulfur isotope at 1523 K is described by the relationshipR = 6.4(±2) (P _CO /P _CO2 )P _SO2 g atom S m⁻² s⁻¹. formerly Research Assistant, University of Queensland formerly Postdoctoral Fellow, University of Queensland     

Some observations of diffusional flow in a superplastic alloy

A metallographic study has been made of the denuded zones from diffusional flow in a hydrided alloy of magnesium with 6 wt pct Zn and 0.5 wt pct Zr (ZK 60). At the deformation temperature of 450°C, with an initial grain size of 18 um, the alloy was superplastic. Its maximum strain-rate sensitivity,m = (d log σ)/(d log ∈), was ⊥0.6 at fe –⁴ 10~⁴ sec–¹. A diffusional strain, ed = ΔL_d/L_d, was calculated from measurements of zone thickness, ΔL_d, and interzone distance,L _d. This was a reasonably constant fraction of the total strain,e, up to the limiting strain of ⊥220 pct. Over a strain-rate range of 3.3 x 10–³ sec–¹ to 3.3 x 10⊥⁵ sec–¹,e _d /e increased from about 0.05 to 0.30.     

Stabilization mechanisms of retained austenite in transformation-induced plasticity steel

Three stabilization mechanisms—the shortage of nuclei, the partitioning of alloying elements, and the fine grain size—of the remaining metastable austenite in transformation-induced plasticity (TRIP) steels have been studied by choosing a model alloy Fe-0.2C-1.5Mn-1.5Si. An examination of the nucleus density required for an athermal nucleation mechanism indicates that such a mechanism needs a nucleus density as large as 2.5 · 10¹⁷ m⁻³ when the dispersed austenite grain size is down to 1 μm. Whether the random nucleation on various heterogeneities is likely to dominate the reaction kinetics depends on the heterogeneous embryo density. Chemical stabilization due to the enrichment of carbon in the retained austenite is the most important operational mechanism for the austenite retention. Based on the analysis of 57 engineering steels and some systematic experimental results, an exponential equation describing the influence of carbon concentration on the martensite start (M _s) temperature has been determined to be M _s (K)=273+545.8 · e ^−1.362w _c(mass pct). A function describing the M _s temperature and the energy change of the system has been found, which has been used to study the influence of the grain size on the M _s temperature. The decrease in the grain size of the dispersed residual austenite gives rise to a significant decrease in the M _s temperature when the grain size is as small as 0.1 μm. It is concluded that the influence of the grain size of the retained austenite can become an important factor in decreasing the M _s temperature with respect to the TRIP steels.     

Mixing time and correlation for ladles stirred with dual porous plugs

Bulk mixing times up to a degree of 95 pct were measured in three different, cylindrical-shaped water model ladles (D=0.60 m, 0.45 m, and 0.30 m, respectively) in which, water was agitated by air introduced through two tuyeres/nozzles placed diametrically opposite at the base of the vessels at ±1/2 R positions. To this end, the electrical conductivity measurement technique was applied. A range of gas flow rates and liquid depths were investigated (viz. 0.7≤L/D≤1.2 and 0.002≤ɛ _m (watt/kg)≤0.01) and these were so chosen to conform to the practical ladle refining conditions. In the beginning, extensive experimental trials were carried out to assess the reliability of the measurement technique. In addition, some experiments were carried out to determine the location of the probe in the vessel such that measured mixing times could be interpreted as the bulk mixing times. It was observed that for smaller gas flow rates (or specific energy input rates), 95 pct bulk mixing times tend to decrease appreciably with increasing gas flow rates (e.g., τ _mix∞Q ^−0.58. However, for relatively higher flow rates, the dependence was found to be less pronounced, mixing times decreasing nearly in proportion to a third power of gas flow rates. Similarly, it was found that there exists a critical gas flow rate for any given vessel beyond which mixing times in dual plug stirred configuration are somewhat shorter than those in equivalent axi-symmetrical systems. A dimensional analysis followed by multiple regression of the experimental data (for ɛ _m ≥0.07 W/kg) indicated that mixing times in ladles fitted with dual plugs located diametrically opposite at ±R/2 locations could be reasonably described via τ _{mix, 95 pct}=15Q ^−0.38 L ^−0.56 R ^2.0 in which L is the depth of liquid (m), R is the vessel radius (m), and Q is the ambient flow rate (referenced to mean height and temperature of the liquid). Finally, the adequacy and appropriateness of the correlation was demonstrated with reference to the experimental data derived from a 0.20 scale, tapered cylindrical-shaped water model of a 140 T industrial ladle as well as scaling equations and modeling criteria reported in the literature.     

Mixing and solid-liquid mass-transfer rates in a creusot-loire uddeholm vessel: A water model case study

The process of mixing and solid-liquid mass transfer in a one-fifth scale water model of a 100-ton Creusot-Loire Uddeholm (CLU) converter was investigated. The modified Froude number was used to relate gas flow rates between the model and its protoype. The influences of gas flow rate between 0.010 and 0.018 m³/s and bath height from 0.50 to 0.70 m on mixing time were examined. The results indicated that mixing time decreased with increasing gas flow rate and increased with increasing bath height. The mixing time results were evaluated in terms of specific energy input and the following correlation was proposed for estimating mixing times in the model CLU converter: T _mix=1.08Q ^−1.05 W ^0.35, where Q (m³/s) is the gas flow rate and W (tons) is the model bath weight. Solid-liquid mass-transfer rates from benzoic acid specimens immersed in the gas-agitated liquid phase were assessed by a weight loss measurement technique. The calculated mass-transfer coefficients were highest at the bath surface reaching a value of 6.40 × 10⁻⁵ m/s in the sprout region. Mass-transfer coefficients and turbulence parameters decreased with depth, reaching minimum values at the bottom of the vessel.     

Strain aging and strain rate sensitivity of oxygen-enriched (α + β) Zircaloy-2

The flow behavior of oxygen-enriched Zircaloy-2, with oxygen concentrations ranging from 1260 to 12360 ppm, was investigated over the (α +β) phase field and parts of the adjacent α andβ phase regions. The flow curves were determined in compression at constant true strain rates in the range 10^-4 to 10^-1 s^-1, and the strain aging response was evaluated from the relative yield drops observed in interrupted tests. Unlike those of the single phase materials, the flow curves of the (α +β) alloys were characterized by large yield drops. These were strongly dependent on temperature, strain rate, prestrain, and phase proportion, and attained a peak value at temperatures corresponding to aβ fraction of 0.5 to 0.8. The activation energy for strain aging increased from 220 to 340 kJ/mol with an increase in oxygen concentration from 4180 to 12360 ppm. The strain aging effect is attributed to the solutes Fe and Cr, which concentrate in theβ phase and probably form ordered zones of Zr(Fe,Cr)₂ on the hot work substructure. The strain rate sensitivitym increased with temperature for both the fullya and fullyβ alloys, withm _gb = 2 m_α. In the (α +β) range, a slight maximum inm was observed in the lowβ fraction (i. e., 0.2 to 0.4β) region and a minimum in the largeβ fraction (J. e., 0.6 to 0.8β) region. The maximum is ascribed to the softβ film which forms around thea grains, whereas the minimum is attributed to the occurrence of strain aging in this range.     

Electrosintering of iron powder compacts

The influence of a nominal external electric field E=3 to 10 kV/cm on the sintering of iron powder compacts for 30 minutes at 1140 °C in a vacuum of ∼10⁻⁶ torr was investigated. It was found that the field reduced the porosity by as much as 29 to 73 pct compared to sintering without a field, the magnitude depending on the procedure employed to measure the density of the specimen. Optical microscopy revealed that the specimen electrosintered with E=10 kV/cm had a skin of ∼0.2 mm in thickness, where the porosity was significantly less than in the interior. This was also the depth of carburization that was obtained upon carburizing the electrosintered specimens. It is proposed that the decrease in porosity produced by the field results from a decrease in the chemical potential of vacancies at or just below the charged external surface. Vacancy flux equations employed to calculate the porosity as a function of distance below the external surface showed that the porosity becomes approximately zero at a distance of x _c=0.4 to 0.5 mm below the surface, which is in reasonable accord with the microscopy measurements. Similar values of x _c were obtained by assuming that the entire porosity decrease given by the density measurements occurred in a ring of thickness of x _c below the external surface. The difference in the density measured by two Archimedes-principle procedures and microscopy observations suggests that the cavities open to the external surface of the electrosintered specimens are smaller or narrower than those for specimens sintered without a field.     

Relationship between austenite dislocation density introduced during thermal cycling and M s temperature in an Fe-17 wt pct Mn alloy

The reason why thermal cycling decreases the martensite start (M _s ) temperature of an Fe-17 wt pct Mn alloy was quantitatively investigated, based on the nucleation model of ε martensite and a thermodynamic model for a martensitic transformation. The M _s temperature decreased by about 22 K after nine cycles between 303 and 573 K, due to the increase in shear-strain energy (ΔG _sh ) required to advance the transformation dislocations through dislocation forests formed in austenite during thermal cycling. The ΔG _sh value increased from 19.3 to 28.8 MJ/m³ due to the increase in austenite dislocation density from 1.5 × 10¹² to 3.8 × 10¹³/m² with the number of thermal cycles (in this case, up to nine cycles). The austenite dislocation density increased rapidly for up to five thermal cycles and then increased gradually with further thermal cycles, showing a good agreement with the increase in austenite hardness with the number of thermal cycles.     

On the stress exponent and the rate-controlling mechanism of high-temperature creep in some solid solutions

The internal stress, σ_i, and the effective-stress exponent of the dislocation velocity,m*, have been determined during creep of Fe-3.5 at. pct Mo alloy at 1123 K under 10.8 to 39.2 MN/m² and of Ni-10.3 at. pct W alloy at 1173 K under 19.6 to 88.2 MN/m². Both alloys have been classified among class I alloys under a certain condition including the present one, because the applied-stress exponent of the steady-state creep rates,n, is almost 3. Values of σ_i obtained by stress-transient dip test were small and almost independent of the applied stress, σ_c, in Fe-3.5 Mo alloy. On the other hand, in Ni-10.3 W alloy σ_i increased with increasing σ_c as in the case of many pure metals. The value ofm* obtained by analyzing stress-relaxation curves immediately after creep deformation was unity in Fe-3.5 Mo alloy, whereas in Ni-10.3 W alloy it was about 2.5. These results indicate that the rate-controlling mechanisms in creep are different from each other in these two alloys and that the classification according ton-value does not always coincide with the classification according to the rate-controlling mechanisms. It is concluded that the fact thatn ≃ 3 is not a sufficient evidence supporting that creep is controlled by one of microcreep mechanisms.     

Predicted volume change behavior accompanying the solidification of binary alloys

For the volume changes accompanying solidification, distinctions are made between the volume changeβ _Mfor the whole freezing process, the volume changeβ _mfor liquid entrapped within the freezing zone, and the localized volume changeβ _Taccompanying the liquid-solid phase transformation at a given temperature. The first volume change is important in mold design, while the latter two are important factors in the formation of casting defects such as shrinkage pores, solidification cracks, and inverse segregation. Values ofβ _M, β_M, andβ _mare deduced for equilibrium conditions in the representative alloy systems Al-Cu, Bi-Sb, Fe-C and Pb-Sn. While the volume changeβ _Mmay vary only moderately with alloy composition,β _mis a strong function of composition and of the temperature of enclosure. The isothermal volume change,β _T, equal to the relative density difference between solid and liquid, varies during the freezing process and is strongly dependent upon composition. Isothermal volume changes and hence density differences as large as 20 pct are deduced for some Bi-Sb and Pb-Sn alloys.