Amorphous solidification of pure metals in submicron spheres

Submicron droplets of high purity elemental metals have been sprayed in high vacuum by electrohydrodynamic atomization. It is found that under these extreme conditions of high cooling rate and very small liquid volume, some pure metals solidify from the melt as an amorphous phase. A systematic study has been conducted for 15 metals plus silicon and germanium of the distribution of the amorphous phase with droplet size, f.c.c., b.c.c. and h.c.p. metals have been studied and it is found that the b.c.c. metals form an amorphous phase much more readily. The observed maximum diameter of amorphous spheres is less than 100 nm in all cases and is used as experimental input to an analytical simulation to determine the glass transition temperatures of the metals in each case. In general, amorphous phases are found in metals that have a reduced glass transition temperature of greater than 0.44. The dependence of glass transition temperature on other physical properties such as enthalpy of fusion and enthalpy of vaporization is also presented.     

Solidification structures in rapidly quenched Cu-Ti-Zr alloys

The melt-spinning and pulsed laser-quenching techniques were used to generate fast cooling rates necessary to form metallic glass in ternary Cu-Ti-Zr alloys. Even though the cooling rates generated during melt-spinning were much lower than those generated during pulse laser-quenching, the amount of glass obtained in the melt spun alloys was much larger than in the laser-quenched alloys. The microstructure of the laser-quenched alloys consisted of metallic glass and a fine microcrystalline fcc phase, whereas the melt-spun ribbons of the same compositions were completely amorphous. Glass transition temperature trends in the ternary system were determined from alloys of composition traversing linearly from the binary Cu-Ti side to the Cu-Zr side. These trends showed a nearly linear change of T_g with composition.     

Solubility of oxygen in niobium-bearing iron-nickel melts

The solubility of oxygen in niobium-bearing iron-nickel melts is studied experimentally, for the example of Fe-40% Ni alloy at 1823 K. Niobium reduces the solubility of oxygen in this melt. Values are determined for the equilibrium constant of the reaction between niobium and oxygen dissolved in the given melt (logK _{(1)(Fe-40% Ni)} = ?4.619), the Gibbs energy (ΔG _{(1)(Fe-40%Ni)} ^o = 161210 J/mol), and the interaction parameters (e _{Nb(Fe-40% Ni)} ^O = ?0.630; e _{O(Fe-40% Ni)} ^Nb = ?0.105; e _{Nb(Fe-40% Ni)} ^Nb = 0.010). Over a wide range of concentrations, the Gibbs energy of the reaction between niobium and oxygen dissolved in Fe-Ni melts, the equilibrium constants, and the interaction parameters at 1823 K are determined. The solubility of oxygen in Fe-Ni melts of different composition containing niobium is determined at 1823 K. With increase in nickel content in the Fe-Ni melts, the oxygen affinity of niobium increases significantly, on account of the decrease in oxygen binding forces with increase in nickel content in the melt (γ _O(Fe) ^° = 0.0084, γ _O(Ni) ^° = 0.297).     

Experimental observations of dendritic growth

A new technique has been developed which allows independent control of the temperature gradient and growth velocity during unidirectional solidification. This technique employs a heat source and sink which remain stationary with the solid-liquid interface as a crystal is translated to allow freezing. When the method is applied to the growth of simple binary Pb-Sb alloys, it is found that the term “dendrite spacing” does not uniquely describe our observations; and we observe that the primaries and secondaries respond differently to variations in the temperature gradient, growth velocity and concentration. The observations are discussed in terms of previous measurement of dendrite arm spacings.     

Solubility of iron-nickel alloys in liquid aluminum

Translated from Poroshkovaya Metallurgiya, No. 7(355), pp. 58–62, July, 1992.     

转炉LT粉尘碳酸化固结实验研究

碳酸化球团-转炉工艺将含铁粉尘与CO2资源化利用相结合,是含铁粉尘再资源化的“绿色”工艺.本文研究了不同CaO配比、反应温度、CO2分压等工艺参数对碳酸化反应转化率及球团质量的影响规律.研究表明:随碳酸化反应温度及CO2气体浓度升高,氧化钙转化率增加,碳酸化球团的抗压强度提高.制备碳酸化球团的最佳工艺参数为:反应温度600℃,气体流速1.5cm/s,CO2浓度100％,反应时间20 min.     

Thermal-Microstructural Analysis of Anodic and Electrolytic Copper Solidification: Simulation and Experimental Validation

This work analyzes the solidification process of anodic and electrolytic copper. The aim of this study is to perform an experimental validation of numerical results computed using a proposed thermal formulation including microstructural evolution. To this end, a set of experiments is carried out testing primary and eutectic phase formation in copper. To evaluate the formation of different microstructural phases, anodic copper (99.80 pct purity, approximately) and electrolytic copper (99.99 pct purity, approximately) are used. Primary and eutectic phases evolve in anodic copper; meanwhile, only a primary phase is obtained in electrolytic copper. The effect of heat extraction conditions is evaluated using sand, graphite, and steel molds to promote different cooling rates. The proposed microstructural model takes into account nucleation and grain growth laws based on thermal undercooling together with microstructural evolution. The primary copper evolution model is based on solute diffusion at the grain scale and on the dendrite top-growing kinetic; meanwhile, the eutectic evolution is assumed proportional to the copper initial composition and eutectic undercooling. The corresponding numerical formulation is solved in the framework of the finite-element method. Finally, the computed temperature histories and final values for the grain density and radius, including primary or dendritic phase and eutectic solid volumetric fractions, are all compared and validated with the experimental measurements.     

Experimental acute hepatic vein occlusion: histological observations in the rat

The histological consequences of hepatic venous outflow obstruction were studied in the rat. Circulatory changes as venous congestion and interstitial fluid accumulation are followed by signs of cellular damage progressing till hemorrhagic infiltration and focal necrosis. These are quite completely reversible in a period of 15 days.     

Thermodynamics of the oxygen solutions in iron-nickel melts

The oxygen solutions in Fe-Ni melts containing chromium, manganese, vanadium, carbon, silicon, titanium, or aluminum are studied thermodynamically. The equilibrium constants of the deoxidation of the melts by these elements are determined, and the activity coefficients for infinite dilution and the interaction parameters in alloys of various compositions are found. The oxygen solubilities in the alloys are calculated as a function of the nickel and deoxidizer contents. The deoxidizer contents at the minima in the oxygen solubility curves for the melts are determined, and the corresponding minimum oxygen concentrations are calculated. As the nickel content in the system increases, the deoxidizing capacities of chromium, manganese, and silicon are shown to increase substantially, and the deoxidizing capacity of carbon increases most strongly. As the nickel content in the melt increases, the deoxidizing capacities of vanadium and titanium first decrease insignificantly and then increase substantially. As the nickel content in the melt increases to 50%, the deoxidizing capacity of aluminum first decreases and then increases; in pure nickel, it is identical to that in pure iron.     

Thermodynamics of the oxygen solutions in zirconium-containing iron-nickel melts

Thermodynamic analysis of the oxygen solutions in zirconium-containing iron-nickel melts is carried out. The equilibrium deoxidation constants of the melts by zirconium, the activity coefficients at infinite dilution, and the interaction parameters in melts of various compositions are determined. The dependences of the oxygen solubility in the melts on the nickel or zirconium content are calculated. Zirconium is shown to possess a very high deoxidizing capacity in iron-nickel alloys. The zirconium contents at the minima in oxygen solubility curves and the corresponding minimum oxygen concentrations are determined. As the nickel content in a melt increases to ∼45%, the deoxidizing capacity of zirconium decreases and, then, increases. The deoxidizing capacity of zirconium in pure nickel is noticeably higher than that in pure iron.     

Evaluation of Formation and Evolution of Microporosity in Anodic Copper Solidification Processes: Simulation and Experimental Validation

The current study analyzes the formation and evolution of microporosity during the solidification of anodic cooper. The aim of this study is to develop a thermofluid-formulation including microstructural evolution and to perform experiments to validate some measured variables with the respective numerical predictions. To this end, a set of experiments is carried out in copper testing primary and eutectic phase formation together with porosity evolution. To evaluate the formation of different microstructural phases and porosity, anodic copper (99.80 pct purity, approximately) is poured into different types of molds. The effect of heat extraction on the thermofluid-microstructural response is evaluated using graphite and steel molds to promote different cooling rates. The microporosity depends on the microstructural formation; hence the microstructure needs to be firstly described. The proposed microstructural model takes into account nucleation and grain growth laws based on thermal undercooling together with microstructural evolution. The primary phase evolution model is based on both solute diffusion at the grain scale and the dendrite tip growth kinetics, while the eutectic evolution is assumed proportional to the copper initial composition and eutectic undercooling. The microporosity model accounts for the partial pressures of gases and the solute distribution in the liquid and solid phases. The corresponding numerical formulation is solved in the framework of the finite element method. Finally, the computed temperature, solid, and liquid volumetric fractions, and pressure histories together with the final values for the radius, density, and pore volumetric fraction, are all compared and validated with the experimental measurements.     

Capillary instabilities in polycrystalline metallic foils: Experimental observations of thermal pitting in nickel

Interference microscopy has been used to measure the surface profile of a thermal pit at the intersection of three grain boundaries on the surface of an annealed nickel foil. The experimentally obtained profile is compared with the predictions of a recently developed model of thermal pitting at grain boundary vertices by surface diffusion. This comparison indicates reasonable agreement between experimental observations and theoretical predictions.     

Prediction of Inclusion Evolution During Refining and Solidification of Steel: Computational Simulation and Experimental Confirmation

Metallurgical and Materials Transactions B - We developed a simulation model to predict inclusion transformation during the solidification of steel by linking the Ohnaka model with the FactSage...