Monotectic Reaction Research Articles

Phase Diagrams and Thermodynamic Properties of the FeO–SiO2–V2O3 Systems

The phase diagrams of FeO–SiO2–V2O3 systems as the main components of vanadium slag are assessed on the basis of the existing literature models and experimental studies to modify partial parameters by FactSage thermodynamic software. The results show that the eutectic and peritectic reactions for the FeO–V2O3 system happen at about 1626 and 1985 K, respectively. The eutectic and monotectic reactions for the V2O3–SiO2 system happen at about 1935 and 1963 K, respectively. According to the actual blowing temperature of the vanadium‐extraction converter, the isothermal section at 1573, 1623, and 1672 K of the FeO–SiO2–V2O3 ternary system is calculated, and the isothermal section at 1573 and 1623 K has seven phase regions, which are the liquid + spinel + tridymite, liquid + wustite + spinel, spinel + tridymite + karelianite, liquid + tridymite, liquid + spinel, liquid + wustite, and liquid, respectively. But liquid + wustite and liquid + wustite + spinel regions disappear at 1673 K. Meanwhile, two ternary eutectic points are determined to be at 1470 and 1476 K, respectively. Peritectic reaction of phase wustite, karelianite, and silica (tridymite and cristobalite) occurs at 1702 and 1750 K, respectively.

Effect of Si and Cu additions on the phase composition, microstructure and properties of Al-Sn alloys

The phase transformations in Al-Cu-Si-Sn alloys were studied using both thermodynamic calculations and experimental methods. The calculated isothermal and vertical sections confirm the presence of fields of liquid phase immiscibility and monotectic reactions. It is shown that annealing at 500 °C, followed by quenching, significantly modifies the morphology of the Sn phase, with the particles acquiring a globular shape due to local melting. The influence of Si and Cu on hardness, density, specific electrical conductivity and manufacturability of the base model alloys, Al-20 wt% Sn and Al-6 wt% Sn, is investigated. It is shown that the Al6Sn4Cu5Si alloy is not inferior to antifriction bronze Cu4Sn4Zn17Pb in terms of tribological characteristics and it significantly exceeds it with regard to density, hardness and thermal conductivity.

Analysis of the Microstructural Evolution during the Transient Upward, Downward and Horizontal Directional Solidification of the Al-1.2wt%Pb Monotectic Alloy

Monotectic alloys are of great industrial importance because of their favorable tribological behavior. Many studies in order to better understand the morphologies obtained by monotectic reaction have been developed. To better understand the morphologies obtained by monotectic Al-1.2wt%Pb alloy reaction, especially in relation to induced convective flow, this paper aims to compare the microstructural evolution of the alloy obteind by directional solidification in transient heat-flow conditions in upward, downwand and horizontal solidification devices. It was observed a morphology transition from particles to fibers on upward and downward cases and a morphology of only particles on the horizontal case. The classical relationship used for eutectic growth, λ2v = C, which was considered applicable to monotectic reactions, didn’t seemed to be valid in the interphase spacing evolution for the downward device, however power functions (λ = C.va) were found in all cases.

Liquid–liquid phase equilibrium in ternary immiscible Al–Bi–Sn melts

ABSTRACTIn this paper, the liquid-phase separation of ternary immiscible Al–Bi–Sn melts was studied with resistivity and thermal analysis methods at different temperatures. The resistivity–temperature curves appear anomalous and abrupt change as rising temperature, corresponding to the distinctive and low peak of melting process in the differential scanning calorimetry (DSC) curves, indicative of the occurrence of the liquid-phase separation. The anomalous behaviour of the resistivity temperature dependence is attributable to concentration–concentration fluctuations. The microheterogeneity–microhomogeneity transformation causes large fluctuations in concentration, which make the randomness and chaos of the atoms larger, leading to the greater impediment to electron movement and the sharp rise of resistivity. The addition of tin to the Al–Bi immiscible alloys decreases the monotectic reaction. It is concluded that concentration–concentration fluctuations are responsible for the anomalous behaviour of resistivity and DSC methods.

Phase Equilibria of the Ternary Sn-Pb-Co System at 250°C and Interfacial Reactions of Co with Sn-Pb Alloys

The isothermal section of the ternary Sn-Pb-Co system at 250°C was experimentally determined through a series of the equilibrated Sn-Pb-Co alloys of various compositions. The equilibrium phases were identified on the basis of compositional analysis. For the Sn-Co intermetallic compounds (IMCs), CoSn3, CoSn2, CoSn and Co3Sn2, the Pb solubility was very limited. There exist five tie-triangle regions. The Co-Pb system involves one monotectic reaction, so the phase separation of liquid alloys near the Co-Pb side occurred prior to solidification. The immiscibility field was also determined. Additionally, interfacial reactions between Co and Sn-Pb alloys were conducted. The reaction phase for the Sn-48 at.%Pb and Sn-58 at.%Pb at 250°C was CoSn3 and CoSn2, respectively. Both of them were simultaneously formed in the Sn-53 at.%Pb/Co. The formed IMCs were closely associated to the phase equilibria relationship of the liquid-CoSn3-CoSn2 tie-triangle. Furthermore, with increasing temperatures, the phase formed in equilibrium with Sn-37 wt.%Pb was found to transit from CoSn3 to CoSn2 at 275°C. We propose a simple method of examining the phase transition temperature in the interfacial reactions to determine the boundaries of the liquid-CoSn3-CoSn2 tie-triangles at different temperatures.

Zinc–Bismuth and Aluminum–Indium Monotectic Alloy-Based Fixed-Point Cells with Double Phase Transition for In Situ Calibration of Thermocouples

Re-calibration of a thermocouple after it has been installed in a process is often not practical. In situ monitoring of performance is desirable and can be done with built-in reference standards based on melting or freezing phase transitions. Binary alloys with a monotectic reaction frequently have two invariant melt/freeze phase transitions taking place in the same material over a range of compositions. This makes them potentially well suited to be in situ temperature calibration artifacts, enabling correction for thermocouple drift without the need to disturb the thermocouple. A zinc–bismuth fixed-point cell was constructed and has been shown to be stable with two well-defined melting plateaus at nominally 255 $$^\circ \hbox {C}$$ and 415 $$^\circ \hbox {C}$$ . Two miniature fixed-point cells (each designed to be permanently installed with a thermocouple) based on zinc–bismuth and aluminum–indium alloys were made. Measurements have shown that the phase transitions can be identified despite the small quantity of metals used and that the alloys were sufficiently stable to have the potential to provide improved long-term confidence in process control and monitoring.

Effects of cooling rate and Al on MnS formation in medium-carbon non-quenched and tempered steels

Abstract The effect of Al on the morphology of MnS in medium-carbon non-quenched and tempered steel was investigated at three different cooling rates of 0.24, 0.43, and 200°C·s-1. The formation mechanisms of three types of MnS were elucidated based on phase diagram information combined with crystal growth models. The morphology of MnS is governed by the precipitation mode and the growth conditions. A monotectic reaction and subsequent fast solidification lead to globular Type I MnS. Type II MnS inclusions with different morphological characteristics form as a result of a eutectic reaction followed by the growth in the Fe matrix. Type III MnS presents a divorced eutectic morphology. At the cooling rate of 0.24°C·s−1, the precipitation of dispersed Type III MnS is significantly enhanced by the addition of 0.044wt% acid-soluble Al (Als), while Type II MnS clusters prefer to form in steels with either 0.034wt% or 0.052wt% Als. At the relatively higher cooling rates of 200°C·s−1 and 0.43°C·s−1, the formation of Type I and Type II MnS inclusions is promoted, and the influence of Al is negligible. The results of this work are expected to be employed in practice to improve the mechanical properties of non-quenched and tempered steels.

Stability phase diagram of GdBa2Cu3O7−δ in low oxygen pressures

We report the stability phase diagram of GdBa2Cu3O7−δ (GdBCO) in the low oxygen pressure (PO2) regime of 1–100mTorr. For this study, amorphous precursor films were deposited on the LaAlO3 (LAO) (001) substrates at 200°C by pulsed laser deposition (PLD), annealed at various high temperatures in low PO2, and then quenched using a reel-to-reel tube furnace. By analyzing the phases and microstructures of the as-quenched films, the stability phase diagram of GdBCO could be accurately constructed. In the PO2 regime of 20–100mTorr, the GdBCO stability line on the log PO2 versus 1/T (K−1) diagram can be expressed by the equation of log PO2 (Torr)=10.85 – 13880/T (K), and unlike the well-known peritectic reaction of GdBCO↔Gd2BaCuO5 (Gd211)+Liquid (L) in high PO2, a pseudobinary peritectic reaction of GdBCO↔Gd2O3+Liquid (L1) occurs at the stability line of GdBCO. In the PO2 regime of 1–10mTorr, the GdBCO stability line can be expressed by the equation of log PO2 (Torr)=9.263 – 12150/T (K), and a ternary peritectic reaction of GdBCO↔Gd2O3+GdBa6Cu3Oy (Gd163)+L2 occurs at the stability line of GdBCO. In addition, a monotectic reaction of L1↔L2+Gd163 occurs at the phase boundary between Gd2O3+L1 and Gd2O3+Gd163+L2.

Stable and Metastable Equilibria in the Pb-Cd System

Thermodynamic and phase diagram data in the Pb-Cd system are reevaluated. A substitutional solution model is used for the liquid and fcc and hcp phases. The stable and metastable equilibria of this system are calculated using the thermodynamic equations derived from equilibrium data. Besides the well-established eutectic reaction at 521 K (248 °C), one stable monotectic reaction at 548 K (275 °C) is found due to the existence of a stable liquid miscibility gap. The stable monotectic reaction has been missed in all previous evaluations. Experimental verifications of the stable and metastable phase equilibria are provided using droplet samples and undercooled liquid alloys. A differential thermal analysis (DTA) method is applied to determine the phase reaction temperatures using both traditional heating and cooling processes and a specially designed cycling process. Additional microstructural evidence is used to elucidate the nature of the phase reactions. The refined thermodynamic descriptions are based upon both the thermochemical and phase diagram stable and metastable data. The agreement between the calculated and experimental data is good. All experimental stable and metastable results are well explained by the new Pb-Cd phase diagram calculations within the experimental accuracy limits. Combined experimental and thermodynamic modeling procedures developed for determining the stable and metastable phase equilibria yield a highly reliable overall phase diagram assessment and a quantitative basis for the interpretation of non-equilibrium solidification processing.

A bridge from monotectic alloys to liquid-phase-separated bulk metallic glasses: Design, microstructure and phase evolution

The Zr–Ce–La system is characterized by a miscibility gap and a monotectic reaction. It separates into Zr-rich and CeLa-rich liquids upon cooling through the gap. Based on this system, a new Zr–Ce–La–Al–Co monotectic system was created to synthesize liquid-phase-separated bulk metallic glasses (LPS-BMGs) by copper mold casting. A systematical investigation was performed for the effects of the relative atomic ratios of Zr:CeLa, Co:Al and Ce:La on the microstructure features and chemical compositions of the two coexistent phases. Dual atom pairs with positive heat of mixing (Zr–Ce: +12kJmol−1 and Zr–La: +13kJmol−1) are originally adopted to develop such LPS-BMGs. A series of in situ formed LPS-BMGs with a critical thickness of 2.5mm has been successfully synthesized. By combining the kinetics of liquid–liquid phase separation with the formation of metallic glasses, the mechanisms of phase formation and the microstructure evolution in the rapidly cooled alloys are discussed in detail. Furthermore, a thermodynamic model is proposed for LPS-BMG design, attempting to build a bridge from monotectic/immiscible (M/I) alloys to LPS-BMGs. This work not only provides opportunities for new insights into the synthesis of LPS-BMGs and their properties but also opens new perspectives for processing and research of M/I alloys.

Solid-liquid phase equilibria on the GdBa2Cu3O7-δstability phase diagram in low oxygen pressures (1 - 100 mTorr)

We report the solid-liquid phase equilibria on the (GdBCO) stability phase diagram in low oxygen pressures () ranging from 1 to 100 mTorr. On the basis of the GdBCO stability phase diagram experimentally determined in low oxygen pressures, the isothermal sections of three different phase fields on log vs. 1/T diagram were schematically constructed within the ternary system, and the solid-liquid phase equilibria in each phase field were described. The invariant points on the phase boundaries include the following three reactions; a pseudobinary peritectic reaction of + liquid (), a ternary peritectic reaction of + liquid (), and a monotectic reaction of . A conspicuous feature of the solid-liquid phase equilibria in low regime (1 - 100 mTorr) is that the GdBCO phase is decomposed into or rather than well-known in high like air.

Thermal and microstructural characterization and crystallization kinetic studies in the TeO2−B2O3 system

Thermal, phase and microstructural characterization of the (1−x)TeO2−xB2O3 system, where 0.05 ≤ x ≤ 0.40 in molar ratio, was realized by applying differential thermal analysis, differential scanning calorimetry, X-ray diffraction and scanning electron microscopy/energy dispersive X-ray spectrometer techniques to investigate the glass forming region, phase equilibria, microstructural characterization of the TeO2−B2O3 system and to study the crystallization kinetics of the boro-tellurite glasses. Samples were prepared using a conventional melt quenching technique at 750 °C. Glass forming range of the system was determined as 5–25 mol% B2O3 and thermal behavior of the glasses were examined by running thermal analysis. In order to obtain the thermal equilibrium, as-cast samples were heat-treated above all crystallization reaction temperatures at 520 °C and the phase equilibria investigations were realized with the heat-treated samples. Monotectic reaction of the binary system: liquid1 → liquid2 + TeO2, was detected at 666 ± 2 °C. A stable phase separation region where the samples show two different phases, white colored opaque and light yellow transparent, was investigated in terms of the phase equilibria and the morphology. Non-isothermal investigation of crystallization kinetics of the boro-tellurite glasses were realized in terms of the crystallization mechanism and the activation energy by using the Ozawa and the modified Kissinger techniques, respectively. The activation energy of the crystallization reaction was calculated as around 300 kJ mol−1.

Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg2Ni, and Al3Ni2 intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg2Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.

Al-Bi-Sn (Aluminum-Bismuth-Tin)

The Al-Bi phase diagram depicts a liquid miscibility gap with the critical temperature at 1037 C. A monotectic reaction occurs at 658 C, where an Al-rich liquid L1 decomposes to (Al) and a Bi-rich liquid L2. The final solidification is at the Bi-end through the eutectic reaction at 270 C: L2 M (Al) + (Bi). The Al-Sn phase diagram is of the simple eutectic type, with the eutectic reaction at 228 C and 97.6 at.% Sn. The shape of the liquidus curve suggests the presence of a metastable liquid miscibility gap in the AlSn system. The Bi-Sn system is of the simple eutectic type, with the eutectic reaction at 139 C and 43 at.% Bi. See [Massalski2] for the above phase diagrams.

Spinodal decomposition and droplets entrapment in monotectic solidification

In this article, we present two models to simulate solidification morphologies in monotectic alloys. With the first model, we investigate the morphological evolution under the influence of spinodal decomposition. The model requires that a gradient energy contribution for the concentration field should be incorporated, in order to stabilize phase separation when the liquid concentration is inside the region of miscibility gap. The free energy of the system in this model is derived from direct interpolation of the bulk energy densities. This, however, results in simulation regions in nanometer scale due to contributions from the chemical free energy of the system to the total surface excess. With the second model, our purpose is to develop a phase-field model to simulate scales that are larger than nanometer, where the departures from equilibrium are very small resulting in phase concentrations outside the spinodal region. In view of this, we exclude the concentration gradient contribution to the grand chemical potential functional, and develop a model based on [M. Plapp, Phys. Rev. E 84, 031601 (2011); A. Choudhury and B. Nestler, Phys. Rev. E 85, 021602 (2012)]. The advantage is that the free energy excess across the interface at equilibrium disappears, and hence it is easier to derive the required surface energies with higher interface widths. Due to this benefit, we employ the method to simulate the dynamic entrapment process in the monotectic reaction and study the influence of liquid(1) - liquid(2) surface energy and undercooling on the entrapment process.

Influence of Alloying Elements on Sulfide Formation in Lead Free Bronze Castings with Dispersed Sulfide Particles

The influence of the zinc sulfide ratio in the sulfide particle in the lead free bronze castings on the machinability is studied. Also, the influence of alloying elements of the zinc sulfide ratio of the sulfide particle is studied for understanding the mechanism of the zinc sulfide formation during the solidification. The zinc sulfide ratio is evaluated with the analysis of the microstructure in the lead free bronze prepared by the sand mold casting. The condition in which the zinc sulfide stably exists during the solidification is estimated with thermodynamic calculation. The machinability is improved with the decrement of the zinc sulfide ratio. The sulfide is formed as the copper sulfide and the zinc sulfide through eutectic reaction, and also appears as the liquid phase through monotectic reaction. The zinc sulfide is formed with the copper sulfide at the temperature, at which the zinc sulfide was predicted to be unstable by the thermodynamic calculation. The ratio of the zinc sulfide increases with increasing zinc content. Tin does not affect the zinc sulfide ratio when the tin content is less than about 4mass%. There is no effect of nickel on the zinc sulfide ratio. [doi:10.2320/matertrans.F-M2011835]

Experimental determination and thermodynamic modeling of phase equilibria in the Cu–Cr system

Liquidus temperatures in the Cu–Cr system at compositions of 10.0–72.7 at.% Cr were determined using electromagnetic levitation melting. The present data agree with the prediction of a recent thermodynamic study of the system for compositions up to 20.0 at.% Cr. However, they show large and positive deviations for other compositions. Microscopic studies reveal that compositions between 10.0 and 50.5 at.% Cr solidified into a dendritic microstructure, whereas those between 55.9 and 72.7 at.% Cr solidified into a droplet-shaped microstructure. The microstructure of the latter type provides direct evidence for the existence of a stable miscibility gap over Cr-rich compositions. Phase equilibria in the Cu–Cr system were calculated using the CALPHAD method. A novel phase diagram was proposed for the Cu–Cr system, which shows a monotectic reaction between compositions of 50.8 and 83.2 at.% Cr at an invariant temperature of 2020 ± 22 K. The novel phase diagram has reduced the discrepancies between the literature data.

One-Step Fabrication of Al/Sn-Bi Core–Shell Spheres via Phase Separation

Al/Sn-Bi core–shell spheres, which have potential for use in advanced electronic packaging, were fabricated in one step via phase separation by spraying liquid (Al0.345Bi0.655)67.8Sn32.2 alloy into silicone oil. The core–shell spheres changed morphology from three-layer to concentric or eccentric dual-layer type with decreasing melt superheat and increasing oil temperature. The spheres are Al-rich in the core, covered with a Sn-Bi-rich periphery, showing a two-stage melting behavior suitable for electronic packaging. The (Al0.345 Bi0.655)67.8Sn32.2 alloy was identified through thermal analysis to undergo liquid-phase separation, monotectic reaction, and eutectic reaction one after another during cooling. Finally, the solidification path of (Al0.345Bi0.655)67.8 Sn32.2 alloy was analyzed and was schematically illustrated.

AlNiYCo Amorphous Matrix Composites Induced by Bismuth and Lead Additions

(Al85Ni5Y8Co2)98Bi2 and (Al85Ni5Y8Co2)98(Bi50Pb50)2 alloys are rapidly solidified using the single-roller melt-spinning method. Al85Ni5Y8Co2 amorphous matrix composites containing faceted BiY particles are synthesized by the liquid-solid reaction between added bismuth and constituents of the molten Al-Ni-Y-Co glass-forming alloy. The microstructure of the rapidly quenched (Al85Ni5Y8Co2)98(Bi50Pb50)2 multiphase composites consists of Al-based amorphous matrix and crystalline Pb-rich and BiY particles. The Pb-rich particles stem from liquid-liquid and monotectic reactions induced by lead addition. The phase constitution and microstructure are investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The reaction-induced crystalline BiY and Pb-rich particles are uniformly distributed in the amorphous matrix. The microstructure formation of the rapidly quenched alloys was discussed.

ChemInform Abstract: Experimental Phase-Diagram Study and Thermodynamic Optimization of the Silver-Strontium-Copper-Oxygen (Ag-Sr-Cu-O) and Silver-Calcium-Copper-Oxygen (Ag-Ca-Cu-O) Systems.

The phase relations in the silver-strontium-copper-oxygen (Ag-Sr-Cu-O) and silver-calcium-copper-oxygen (Ag-Ca-Cu-O) systems were studied in oxygen, air, and nitrogen environments, using differential thermal analysis and energy-dispersive X-ray spectrometry. The presence of silver reduces the melting temperature of the oxide liquid to a monotectic in the strontium- and calcium-containing systems by 62 and 82 K, respectively (to 1222 and 1244 K, respectively) in oxygen. The oxide liquid dissolves silver (up to a metallic ratio of 0.17) in the Ag-Sr-Cu-O system in oxygen at a temperature slightly higher than that required for monotectic reaction. In the Ag-Ca-Cu-O system, the silver content has been measured to be 0.29 (metallic ratio). The oxide systems have been optimized using the experimental data from monotectics and those from lower-order systems that have been published previously. This work is part of a project to evaluate the phase relations within the silver-bismuth-strontium-calcium-copper-oxygen (Ag-Bi-Sr-Ca-Cu-O) system and, in particular, to focus on the influence of silver on the phase equilibria around the superconducting phases during partial-melt processing.