Phase Relations in CaO-SiO2-Al2O3-15 mass pct CaF2 System at 1523 K (1250 °C)

CaO-SiO₂-Al₂O₃-CaF₂ is a base system of mold flux for high Al steels. Phase equilibrium in CaO-SiO₂-Al₂O₃-15 mass pct CaF₂ system at 1523 K (1250 °C) was investigated using quenching method followed by X-ray diffraction and Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy. Isothermal section in this system at 1523 K (1250 °C) with Al₂O₃ being less than 25 mass pct and CaO/SiO₂ (mass pct) being between 0.43 and 1.25 was experimentally constructed. The liquidus composition and seven solid-liquid coexistence regions at 1523 K (1250 °C) were determined.     

The Effects of Ni-Plating and Prolonged High Temperature Oxidation at 1423 K (1150 °C) on a CMSX-10 Single-Crystal Ni-Based Super-Alloy and Coating System

A hypothesis was investigated, to assess if Ni-plating a 3rd-generation single-crystal alloy could favorably alter the diffusion profile of critical elements such that brittle, deleterious topologically close-packed (TCP) phases did not form or at least the extent to which they did was reduced. In conjunction with delaying the onset of these phases, it was hoped that more favorable alternatives could be promoted, such as martensite (β′). This study showed that Ni-plating did have some positive effects on the super-alloy/coating system. While the coating produced on the Ni-plated alloy was thinner, it retained a higher Al content than its unplated counterpart when subjected to oxidation. The retention of Al within the coating delayed the phase evolution of the coating from a β or β + β′ to a γ′-dominant coating as the Ni-plated system had a greater driving force for Ni and Al diffusion, which helped to establish the Ni-rich diffusion barrier that entrapped Al in the coating. Unfortunately, Ni-plating does not sufficiently alter the diffusion profiles within the alloy to prevent precipitation of the TCP phases. Four pairs of the CMSX-10 alloy were used for this study. While they were all aluminized, only half of them, one in each pair, were Ni plated prior to aluminizing. Three of the four pairs were then oxidized at 1423 K (1150 °C), while the first pair was kept as a standard. X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy were used to characterize each alloy-coating system in an effort to better understand their performance under high temperature oxidation.     

Evolution of Relationships Between Dislocation Microstructures and Internal Stresses of AISI 316L During Cyclic Loading at 293 K and 573 K (20 °C and 300 °C)

The evolution of dislocation densities and of dislocation microstructures during cyclic loading of AISI 316L is systematically evaluated. In addition, internal stresses are also measured for every cycle and comprehensively analyzed. These observations are made in order to establish relationships between the evolution of dislocation condition and internal stresses, and ultimately to obtain a thorough insight into the complex cyclic response of AISI 316L. Moreover, the dependencies of established relationships on the variation of temperature and strain amplitude are investigated. The back stresses (long-range stresses associated with the presence of collective dislocations over different length scales) are mainly responsible for the cyclic deformation response at high strain amplitudes where dislocations tend to move more quickly in a wavy manner. In contrast, the effective stress, coupling with short-range dislocation interactions, plays an insignificant role on the material cyclic response for wavy slip conditions, but increasingly becomes more important for planar slip conditions. The additionally strong short-range interactions between dislocations and point defects (initially with solute atoms and later in life with corduroy structure) at 573 K (300 °C) cause dislocations to move in more planar ways, resulting in a significant increase in effective stress, leading to their influential role on the material cyclic response.     

Diffusion Behavior of Mn and Si Between Liquid Oxide Inclusions and Solid Iron-Based Alloy at 1473 K

In order to clarify the changes in the composition of oxide inclusions in steel, the effect of the metal and oxide composition on the reaction between solid Fe-based alloys and liquid multi-component oxides was investigated using the diffusion couple method at 1473 K. The measured concentration gradients of Mn and Si in the metal indicated that Mn diffused into the metal from the oxide, while the diffusion of Si occurred in the opposite direction. In addition, the MnO content in the oxide decreased with heat treatment time, while the SiO₂ content increased. The compositional changes in both phases indicated that the Mn content in the metal near the interface increased with heat treatment with decreasing MnO content in the oxide. Assuming local equilibrium at the interface, the calculated [Mn]²/[Si] ratio at the interface in equilibrium with the oxide increased with increases in the MnO/SiO₂ ratio in the oxide. The difference in the [Mn]²/[Si] ratios between the interface and the metal matrix increased, which caused the diffusion of Mn and Si between the multi-component oxide and metal. By measuring the diffusion lengths of Mn and Si in the metal, the chemical diffusion coefficients of Mn and Si were obtained to calculate the composition changes in Mn and Si in the metal. The calculated changes in Mn and Si in the metal agreed with the experimental results.     

The Effect of Nd on the Tension and Compression Deformation Behavior of Extruded Mg-1Mn (wt pct) at Temperatures Between 298 K and 523 K (25 °C and 250 °C)

The tension and compression deformation behavior of extruded magnesium-1 wt pct manganese alloys with nominally 0.3 wt pct (MN10) and 1 wt pct neodymium (MN11) was studied over the temperature range of 298 K to 523 K (25 °C to 250 °C). Nd additions to Mg alloys tend to reduce the strong basal texture exhibited by conventional wrought Mg alloys and this work was intended to study the effect of Nd on the deformation behavior of Mg alloys. In situ tensile and compressive experiments were performed using a scanning electron microscopy, and electron backscatter diffraction was performed both before and after the deformation. A slip trace analysis technique was used to identify the distribution of the deformation systems as a function of strain, and based on this analysis and the texture of the undeformed samples, the critical resolved shear stress ratios between the deformation systems were estimated. In the case of MN11, the deformation behavior under tension at all temperatures was dominated by slip, while in compression, extension twinning was the major deformation mode. In tension at 323 K (50 °C), extension twinning, basal, prismatic 〈a〉, and pyramidal 〈c + a〉 slip were active in MN11. Much less extension twinning was observed at 423 K (150 °C), while basal slip and prismatic 〈a〉 slip were dominant and presented similar relative activities. At 523 K (250 °C), twinning was not observed, and basal slip controlled the deformation. With the reduction of Nd content, less slip deformation and more twinning were observed during the tensile deformation. However, like for MN11, the extent of twinning in MN10 decreased with increasing temperature and basal slip was the primary deformation mode at elevated temperatures. Extension twinning was the major deformation mode under compression for all test temperatures in MN10 and MN11. The tensile strength decreased with increasing temperature for both alloys, where MN10 was slightly stronger than MN11 at 323 K (50 °C), which was expected to be a result of the stronger basal texture exhibited by MN10 due to its lower Nd content. However, MN11 maintained its strength more at elevated temperatures compared with MN10, and this was explained to be a result of the greater Nd content.     

Interfacial Reaction Between High-Al Steel and CaO-Al2O3-Based Mold Fluxes with Different CaO/Al2O3 Ratios at 1773 K (1500 °C)

Metallurgical and Materials Transactions B - The reaction between high-Al steel and CaO-Al2O3-based mold fluxes with different CaO/Al2O3 ratios was investigated at 1773 K (1500 °C). The...     

Interfacial Reaction Between CaO-SiO2-MgO-Al2O3 Flux and Fe-xMn-yAl (x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) Steel at 1873 K (1600 °C)

This study investigated the interfacial reaction kinetics and related phenomena between CaO-SiO₂-MgO-Al₂O₃ flux and Fe-xMn-yAl (x = 10 and 20 mass pct, y = 1, 3, and 6 mass pct) steel, which simulates transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP) steels at 1873 K (1600 °C). It also examines the effect of changes in the composition of the steel and slag phases on the interfacial reaction rate and the reaction mechanisms. The content of Al and Si in the 1 mass pct Al-containing steel was found to change rapidly within the first 15 minutes of the reaction, but then it remained relatively constant. The content of Al and Si in the 3 to 6 mass pct Al-containing steels, in contrast, changed continuously throughout the entire reaction time. In addition, the content of Mn in the 1 mass pct Al-containing steels initially decreased with increasing time, but the content did not change in the 3 to 6 mass pct Al-containing steels. Furthermore, the mass transfer coefficient of Al, k _Al, in the 1 mass pct Al-containing systems was significantly higher than that in other systems; i.e., the k _Al can be arranged such that 1 mass pct Al systems >> 3 mass pct Al systems ≥ 6 mass pct Al systems. The compositions of the final slags were close to the saturation lines of the [Mg,Mn]Al₂O₄ and MgAl₂O₄ spinels when the slags reacted with 1 mass pct Al and 3 to 6 mass pct Al-containing steels, respectively. These results, which show the effect of Al content on the reaction phenomena, can be explained by the significant increase in the apparent viscosity of the slags that reacted with the 3 to 6 mass pct Al-containing steels. This reaction was likely caused by the precipitation of solid compounds such as MgAl₂O₄ spinel and CaAl₄O₇ grossite at locally alumina-enriched areas in the slag phase. This analysis is in good accordance with the combination of Higbie’s surface renewal model and the Eyring equation.     

Distribution of Calcium and Aluminum Between Molten Silicon and Silica-Rich CaO-Al2O3-SiO2 Slags at 1823 K (1550 °C)

Metallurgical and Materials Transactions B - Oxidative refining of silicon after tapping from the furnace is performed to remove calcium and aluminum impurities. Depending on the slag composition,...     

Limestone Dissolution in Converter Slag at 1873 K (1600 °C)

Decomposition and dissolution of limestone in slag at 1873 K (1600 °C) were studied. The limestone samples were in the shape of cubes (11 mm × 11 mm × 11 mm approximately). The decomposition was carried out both in argon and in slag under argon atmosphere. In order to gain an insight into the phenomenon of slow decomposition, the decomposition process of CaCO₃ was simulated using Comsol. The results showed evidently that the decomposition of calcium carbonate was controlled mostly by heat transfer. It was also found that the decomposition product CaO had very dense structure, whether the sample was decomposed in slag or in argon. The slow decomposition and the dense CaO layer would greatly hinder the dissolution of lime in the slag. The present results clearly indicate that the addition of limestone instead of lime would not be beneficial in the converter process.     

The Role of Eta Phase Formation on the Creep Strength and Ductility of INCONEL Alloy 740 at 1023 K (750 °C)

INCONEL alloy 740 is an age-hardenable nickel-based superalloy proposed for advanced ultrasupercritical steam boiler applications operating at high stress and long times above 973 K (700 °C), where creep will be the dominate deformation mode. During high-temperature exposure, the alloy can form eta phase platelets that many have suggested may be detrimental to creep strength and ductility. In this study, creep-rupture tests were conducted on smooth and notched bars of INCONEL alloy 740 at 1023 K (750 °C) for times up to 20,000 hours. Examination of the creep-rupture life, creep ductility, failure modes, and microstructure by quantitative electron microscopy shows that a small amount of eta phase does not diminish the creep performance. Applied stress appears to have a minor effect on the precipitation of the eta phase but not its growth rate. Based on the observation that the microstructure after 20,000 hours of creep exposure has reached equilibrium in comparison to thermodynamic calculations, it is concluded that 20,000 hour creep tests are adequate for prediction of long-term creep performance.     

Solid-State Phase Equilibria of the V-Si-Gd System at 973 K (700 °C)

The solid-state phase equilibria of the V-Si-Gd ternary system at 973 K (700 °C) were experimentally evaluated. The existence of nine binary compounds, namely, V₃Si, V₅Si₃, V₆Si₅, VSi₂, Gd₅Si₃, Gd₅Si₄, GdSi, GdSi_1.67, and GdSi_2?x , was confirmed, and no ternary compound was found at 973 K (700 °C). The homogeneity ranges of V₃Si and GdSi_2?x were investigated. It is worth mentioning that the Gd₃Si₄ compound was discovered through changing the experimental conditions, and its crystal structure was discussed.     

Analysis of the Deformation Behavior in Tension and Tension-Creep of Ti-3Al-2.5V (wt pct) at 296 K and 728 K (23 °C and 455 °C) Using In Situ SEM Experiments

The deformation behavior of a Ti-3Al-2.5V (wt pct) near-α alloy was investigated during in situ deformation inside a scanning electron microscopy (SEM). Two plates with distinct textures were examined. Tensile experiments were performed at 296 K and 728 K (455 °C) (~0.4T _m), while a tensile-creep experiment was performed at 728 K (455 °C) and 180 MPa (σ/σ _ys = 0.72). The active deformation systems were identified in the α phase using electron backscattered diffraction based slip-trace analysis and SEM images of the surface. Prismatic slip deformation was the dominant slip mode observed for all the experiments in both plates, which was supported by a critical resolved shear stress (CRSS) ratio analysis. However, due to the texture of plate 1, which strongly favored the activation of prismatic slip, the percentages of prismatic slip activity for specimens from plate 1 tested at 296 K and 728 K (23 °C and 455 °C) were higher than the specimens from plate 2 under the same testing conditions. T1 twinning was an active deformation mode at both 296 K and 728 K (23 °C and 455 °C), but the extent of twinning activity decreased with increased temperature. T1 twinning was more frequently observed in specimens from plate 2, which exhibited a higher fraction of twinning systems favoring activation at both 296 K and 728 K (23 °C and 455 °C). The tension-creep experiment revealed less slip and more grain boundary sliding than in the higher strain rate tensile experiments. Using a previously demonstrated bootstrapping statistical analysis methodology, the relative CRSS ratios of prismatic, pyramidal 〈a〉, pyramidal 〈c+a〉, and T1 twinning deformation systems compared with basal slip were calculated and discussed in light of similar measurements made on CP Ti and Ti-5Al-2.5Sn (wt pct).     

Low Temperature Sensitization on the Orthogonal Surfaces of Prior Deformed AISI 304LN and Aged at 673 K to 873 K (400 °C to 600 °C)

This study investigates the sensitization behavior of AISI 304LN deformed previously by cold rolling (CR) to 5 pct to 25 pct reduction in thickness and aged at 673 K to 873 K (400 °C to 600 °C). The emphasis was on revealing the degree of sensitization (DOS) resulting from low-temperature sensitization (LTS) on the orthogonal surfaces and correlation thereof with the changes in various metallurgical properties caused by cold rolling. It was found that the DOS differs among the orthogonal surfaces such as the rolling surface (RS), transverse surface (TS), and cross transverse surface (CTS). RS showed lower DOS compared with CTS and TS. The differences in the DOS were attributed to the combined effect of deformation-induced martensite (DIM), grain size, and slip band formation. A deformation of 5 pct was critical to the susceptibility of AISI 304LN to intergranular (IGC) and transgranular corrosion (TGC). The sensitization kinetics was slow or saturated leading to desensitization beyond 5pct deformations at 773 K (500 °C) and 873 K (600 °C). It was, however, uniformly accelerated over 5 to 25 pct deformation when aged at 673 K (400 °C).     

Determination of Gibbs Free Energy of Formation of MnV2O4 Solid Solution at 1823 K (1550 °C)

The Gibbs free energy of formation of MnV₂O₄ solid solution saturated with either MnO or V₂O₃ was experimentally determined at 1823 K (1550 °C) by employing a chemical equilibrium technique. The MnV₂O₄ solid solution mixed with MnO or V₂O₃ was brought to equilibrium with either liquid Fe or liquid Cu to measure equilibrium compositions of the liquid metal. Using the available thermodynamic parameters such as Wagner’s interaction parameter for liquid Fe or Gibbs free energy of liquid solution composed of Cu-Mn-V-O, the Gibbs free energy of formation of the MnV₂O₄ solid solution from constituent oxides (MnO and V₂O₃) was then determined to be: MnO(s) + V₂O₃(s) = MnV₂O₄(MnO-satd.): $\Updelta g^\circ_{{\rm f,MnV}_{2}{\rm O}_{4}}$ = ?31.4 ± 2 (kJ/mol); MnO(s) + V₂O₃(s) = MnV₂O₄(V₂O₃-satd.): $\Updelta g^\circ_{{\rm f,MnV}_{2}{\rm O}_{4}}$ = ?37.8 ± 2 (kJ/mol). The $\Updelta g^\circ_{{\rm f,MnV}_{2}{\rm O}_{4}}$ values were independent of the oxygen partial pressure within the range from 2.0 × 10^?12 to 6.3 × 10^?11, employed in the current study.     

Interactions in the Al2O3 ― ZrO2 ― La2O3 System at 1250 and 1650°C

Triangulation has been determined for the Al₂O₃ ZrO₂ La₂O₃ system, and 1250 and 1650°C isothermal sections of the phase diagram have been constructed. The LaAlO₃ La₂Zr₂O₇ section is quasibinary, while the LaAlO₃ T-ZrO₂ and La₂O₃ ·11Al₂O₃ T-ZrO₂ ones are partially quasibinary. The triangulation of the ternary system is based on ZrO₂ and a phase containing it. No ternary compounds or regions of ternary solid solutions have been identified.     

Activity Coefficient of SiO2 in SiO2-Al2O3-CaO Slags with Low SiO2-Content at 1873 K (1600 °C)

The activity coefficient of SiO₂ in SiO₂-Al₂O₃-CaO slags with limited Al₂O₃ content was measured by equilibrating Fe-C-Si melt and slags at 1873 K (1600 °C). When the Al₂O₃ content was between 48 and 54 wt pct, the results show that $ \gamma_{{{\text{SiO}}_{ 2} }} $ rapidly decreases as the amount of SiO₂ in the slag decreases. The equilibrium amounts of Si and Al in a Fe melt in equilibrium with SiO₂-Al₂O₃-CaO slags were calculated based on the result of this study.     

Thermodynamic Analysis of the Cu-As-S-(O) System Relevant to Sulfuric Acid Baking of Enargite at 473 K (200 °C)

While the growing demand for copper has compelled the industry to adapt new technologies for the treatment of copper-arsenic (enargite) concentrates, the refractory nature of such concentrates combined with the troublesome presence of arsenic has created a major metallurgical and environmental challenge. Preliminary results of the acid bake-leach process at the University of Utah have shown some potential advantages for the treatment of enargite concentrates. While the transformation of enargite to copper sulfate, arsenolite, and elemental sulfur has already been established experimentally, thermodynamic evaluation of the sulfuric acid baking process provides further understanding which should be useful. In this article, the available thermodynamic data for the species involved in the Cu-As-S-O system are compiled. These data were used to calculate the phase stability (Kellogg) diagrams as well as equilibrium compositions at 473 K (200 °C) using the STABCAL and HSC Chemistry^® 5.1 software packages. The equilibrium composition calculations indicate that enargite can transform to copper sulfate either directly or through chalcocite and/or covellite. The major gaseous species during baking were found to be SO₂ and H₂O. The results of the thermodynamic calculations were further compared with two confirmatory baking experiments involving a high-quality enargite sample. The condensed reaction products from sulfuric acid baking based on XRD results include CuSO₄, As₂O₃, CuO·CuSO₄, and S₈ under both neutral and oxidative conditions. While all these compounds were predicted through equilibrium calculations, some of the predicted compounds were not detected in the sulfuric acid-baked enargite. None of the calculations indicated any appreciable amounts of arsenic-bearing gases at the baking temperature of 473 K (200 °C). Consistent with thermodynamic predictions, no H₂S gas was detected during the sulfuric acid baking experiment. Approximately, 80 pct of the baked enargite samples were leached in water.