Single-phase Field Research Articles

Phase equilibria of CaO–Al2O3–CaO·TiO2 system at 1500 °C in hydrogen atmosphere

The phase diagram of CaO–Al2O3-TiOx system is of great importance in guiding the design of metallurgical slag systems for Al–Ti alloy steel, controlling Ti-bearing inclusions in molten steel, and regulating the mineral phase of vanadium-titanium magnetite. In the present work, the high temperature equilibration-quench technique was adopted, and the types and compositions of equilibrium phases were identified by Electron Probe Micro Analysis (EPMA) and X-ray diffraction (XRD). The isothermal section of CaO–Al2O3–CaO·TiO2 system at 1500 °C in H2 atmosphere was constructed for the first time. There are 7 three-phase fields, 10 two-phase fields, and a single liquid phase field. On this basis, according to the theoretical analysis of the crystal structure, the formation energy analysis based on first-principles calculations, and the related theories of defect chemistry, the formation mechanisms of CaTiO3 and Ca3Ti2O7 solid solution with were determined, respectively. Additionally, the experimental phase diagram was utilized to discuss the dissolution type and the equilibrium solubility of typical inclusions (Al2O3, Ti3O5, and CaO·TiO2) in Al–Ti alloy steel.

Control effect on the divergent and convergent riblets in particle-laden turbulent boundary layer

Particle image velocimetry was employed to investigate the impact of convergent–divergent riblets on turbulent boundary layers in both clear water and liquid–solid two-phase flow fields containing 155 μm polystyrene particles. The turbulence statistics such as turbulence intensity and Reynolds stress were investigated. The spatial topology of spanwise vortex head and the development and evolution process of hairpin vortices were explored from Euler and Lagrange perspectives, respectively. Additionally, the particle distribution, concentration, and dispersion within the turbulent boundary layer were statistically analyzed. The results indicated that the boundary layer thickness, friction resistance, integrated turbulence intensity, and Reynolds stress were significantly lower on divergent riblet walls compared to convergent riblet walls. Notably, divergent riblets with a yaw angle of 30° exhibited the best drag reduction effect in both single-phase and two-phase flow fields. The addition of particles resulted in an increase in boundary layer thickness but effectively reduced turbulent fluctuations in the logarithmic region, enhancing drag reduction. This extended the drag reduction range of divergent riblets to a yaw angle of 45°, increasing the maximum drag reduction rate to 26.18%. Through spatial multi-scale local average structure function and finite-time Lyapunov exponent field analysis, it was found that the 30° divergent riblet wall significantly inhibited the development of vortex structures and reduced momentum exchange within the boundary layer. Conversely, the 30° convergent riblet wall had the opposite effect, while the particle phase inhibited the development of all wall turbulent structures. Analysis of particle concentration variations within different regions of the turbulent boundary layer revealed that as the normal height of the boundary layer increased, particle concentration gradually increased, and particle dispersion decreased accordingly. The analysis further showed that particle dispersion was mainly influenced by flow structures, whereas concentration was significantly affected by turbulence intensity. These findings elucidate the effect of the flow field on the particle phase and provide insights into the interaction mechanism between the flow field and particles.

Dynamic recrystallization in a near β titanium alloy under different deformation modes – Transition and correlation

During the thermoforming of TC18 titanium alloy multi-cavity components, different deformation modes always exist and change, such as uniaxial compression (UC), shear-compression deformation (SCD), uniaxial tension (UT) and shear-tension deformation (STD). Dynamic recrystallization (DRX) of β grains occurs during the single-phase field deformation and has a great influence on the performance of components. In this study, the types and mechanisms of DRX in TC18 titanium alloy as well as transition and correlation under different deformation modes are investigated. It is found that discontinuous dynamic recrystallization (DDRX) initiates through grain boundary bulging at a low strain and dominates in different modes of deformation. Continuous dynamic recrystallization (CDRX) initiates at different strains depending on deformation modes, and the mechanisms vary, subgrain rotation within grains and lattice rotation near GBs under UC and STD, while only subgrain rotation under UT, in addition to these two mechanisms, grain fragmentation is also involved under SCD. Secondary dynamic recrystallization (SDRX) only occurs at a high strain under SCD and STD. Deformation modes lead to differences in orientation, slip and rotation of grains, further result in different dislocation density, distribution and accumulation, which contribute to the occurrence and transition of different types of DRX. Meanwhile deformation modes result in differences in the difficulty of GB migration and lattice rotation, ultimately in the initiation and degree of DDRX and CDRX. The shear stress in SCD and STD promotes the occurrence of CDRX. The present results can provide a guidance for obtaining good performance of the titanium alloy components.

Electrical-thermal-mechanical coupled modeling and simulation on deformation behaviors of Ti6554 alloy in electrically-assisted micro-tension

The electrically assisted forming (EAF) technology can reduce the load & stress and improve the formability of difficult-to-deform alloys due to its coupled thermal and athermal effects. To decouple the two effects and to elucidate each mechanism for deeply understanding and optimizing the EAF processing, we developed an electrothermalmechanical (ETM) macro-meso multiscale model by combing a modified Johnson-Cook (JC) constitutive model with the dislocation density based crystal plasticity finite element (DD-CPFE). The modified JC was used to describe the macroscopic electro-assisted deformation, while the meso-scale DD-CPFE was used to deal with the thermal and athermal effects on the slip rate. Statistically stored dislocations (SSDs) were introduced into the Orowan rate equation to explain the thermal effect part, and the athermal part was reflected through the effect of free energy change on the dislocation motion in the rate equation, due to the collision between free electrons and metallic ions. The simulated results show that the equivalent stress, strain, and dislocation densities are distributed heterogeneously in a meso-scale and sensitive to the current density. Local thermal effect due to geometrically necessary dislocations (GND) exerts no effect on the temperature gradient because of rapid heat conduction between grains. The thermal effect is dominated by the thermal expansion obviously reducing the flow stress in the single-phase and two-phase fields (0 to 70 A/mm2), while the athermal effect is effective in the two-phase field (corresponding to the current density range of 0 to 20 A/mm2) in reducing the flow stress, which is reasonably explained by the change of bonding strength in defect zones, such as grain boundaries, of the HCP structure via the first principle calculations.

Formation mechanism of Cube texture components ({001}) associated with dynamic recrystallization during compression in the single BCC phase region of Ti-22Al-25Nb alloy

The present study, employing EBSD as the primary method, investigates the formation mechanism of Cube texture components in Ti-22Al-25Nb alloy during uniaxial compression at high-temperature single-phase field. The research reveals that the formation of Cube components is closely related to texture evolution and dynamic recrystallization (DRX) behavior. Firstly, the formation of <001> and <111> dual fiber texture structures is a prerequisite for the development of Cube component, which mainly forms under large strains. Subsequently, continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) play distinct roles in the formation of Cube component. CDRX and DDRX occur in grains belonging to <001> and <111> fiber textures, respectively, exhibiting significant orientation dependence. <001> grains, characterized by a lower Taylor factor, undergo CDRX, causing sub-grains near the grain boundaries in <001> grains to rotate towards the Cube orientation. In contrast, <111> grains with a higher Taylor factor undergo DDRX, leading to the accumulation of high stored energy near the grain boundaries in <111> grains. When the two types of grains are adjacent, the significant orientation difference between them facilitates the rapid growth of Cube-oriented sub-grains through grain boundary migration. This results in a conspicuous Cube texture component on a macroscopic scale.

PHASE EQUILIBRIUM STATES IN A TWO-COMPONENT DIPHENYL-n-NONADECANE SYSTEM

The melting curves of the diphenyl-n-nonadecane system were calculated using the Schroeder equation and using the UNIFAC and UNIFAC Dortmund methods. The calculation results showed that the diphenyl-n-nonadecane system is eutectic. The compositions experimentally studied by the method of differential thermal analysis and calculated by the indicated methods are not eutectic. Individual substances and 9 compositions within the studied system were experimentally studied using a differential scanning calorimeter. Based on the data obtained, a phase diagram was constructed, including one single-phase field above the liquidus curve and 4 two-phase fields – α-n-C19H40+(Ph)2, β-n-C19H40+(Ph)2, L+n-C19H40, L+(Ph)2. The predominant branch of the liquidus curve belongs to the more refractory component, diphenyl. In the solidus at a temperature of 18.7 °C, a polymorphic transformation α-n-C19H40 ⇆ β-n-C19H40 is noted, which coincides with the literature temperature data. The heating DTA curve of the eutectic alloy showed two endoeffects corresponding to the polymorphic transition of n-nonadecane and the melting of the eutectic. The calculation of the eutectic coordinates by the UNIFAC Dortmund method showed the smallest deviation in the composition of the eutectic alloy from the experimental data. For an alloy of eutectic composition, the specific enthalpy of melting, the molar values of the entropy and enthalpy of melting, the volumetric specific enthalpy of melting, and the density for standard conditions are determined. This two-component system was studied by low-temperature differential thermal analysis. The eutectic melt can be used in industry as a heat carrier. Also, the eutectic composition of the diphenyl-n-nonadecane system under study can be used as a working fluid of a heat accumulator. For citation: Kazakova A.I., Yakovlev I.G., Garkushin I.K. Phase equilibrium states in a two-component diphenyl-n-nonadecane system. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 46-53. DOI: 10.6060/ivkkt.20236606.6733.

Phase diagram of CaO–Al2O3-CeOx slag system at 1600 °C in reducing atmosphere and air atmosphere

CaO–Al2O3-CeOx slag system is of great significance for designing a new type of metallurgical slag system suitable for rare earth steel. In this paper, the phase equilibria of CaO–Al2O3-CeOx system were experimentally studied. Isothermal sections of CaO–Al2O3–Ce2O3 system and CaO–Al2O3–CeO2 system at 1600 °C were constructed, respectively. 4 three-phase fields, 5 two-phase fields and a single liquid phase field in CaO–Al2O3–Ce2O3 system were determined; 2 three-phase fields, 3 two-phase fields and a single liquid phase field in CaO–Al2O3–CeO2 system were determined. On this basis, the dissolution process of three typical inclusions (viz. Al2O3, CeAl11O18 and CeAlO3) in CaO–Al2O3–Ce2O3 slag system was discussed.

Special deformation mechanisms dominated by grain boundary sliding of extrusion–refined Ti–22Al–25Nb alloy during compression in single BCC phase field

The deformation behavior of Ti–22Al–25Nb alloys with refined initial grain size was investigated under isothermal uniaxial compression in the BCC (B2) single-phase field, where a high-temperature extrusion process was used to produce the test materials with finer initial grains. As compressed at low to moderate strain rates, the present material exhibits significant continuous flow softening. To study the deformation and softening mechanisms during the compression, the samples' microstructures were examined using EBSD. The analysis shows that this alloy has a considerable grain boundary sliding (GBS) mechanism in addition to the conventional mechanisms of dynamic recovery (DRV), dynamic recrystallization (DRX), and texture softening. For the first time, this study offers direct evidence of the presence of GBS in current alloys. And the dominant role of GBS in high-temperature deformation and softening of current alloys was identified by comparing the impacts of various mechanisms on the dislocation density distribution. Besides, the impact of GBS on texture evolution was also discussed.

Synthesis and physico-chemical studies of alloys of the As2Se3–CuCr2Te4 system and properties of the obtained composite materials

Alloys of the As2Se3–CuCr2Te4 system were synthesized in a wide range of concentrations, and their physico-chemical properties were studied by differential thermal analysis (DTA), X-ray diffraction (XRD), microstructural (MSA) analysis, as well as by determining the microhardness and density, and its [Formula: see text]–[Formula: see text] phase diagram was constructed. It has been established that the phase diagram of the As2Se3–CuCr2Te4 system is quasi-binary of the eutectic type. The system has small single-phase fields based on the original components. In the As2Se3–CuCr2Te4 system, the area of the solid solution based on the As2Se3 compound at room-temperature is 2 mol%, and the area of the solid solution based on the CuCr2Te4 compound is 6 mol%. Joint crystallization of As2Se3 and CuCr2Te4 ends at the double eutectic point with a composition of 15 mol% CuCr2Te4. With slow cooling in the As2Se3–CuCr2Te4 system based on As2Se3, the glass formation region reaches 10 mol% CuCr2Te4. The magnetic properties of the obtained solid solutions (CuCr2Te[Formula: see text](As2Se[Formula: see text] ([Formula: see text]–0.03; 0.05) were studied.

SYNTHESIS AND INVESTIGATION OF PHOTO- AND ELECTRICAL PROPERTIES OF GLASSY ALLOYS OF THE As3Se3-NdSe SYSTEM

Alloys of the As2Se3-NdSe system were synthesized in a wide range of concentrations. The As2Se3-NdSe system was studied by differential thermal (DTA), X-ray diffraction (XRD), microstructural (MSA) analysis, as well as by measuring microhardness and density. The system has small single-phase fields based on primary components. In the As2Se3-NdSe system, the area of the solid solution based on the As2Se3 compound at room temperature is 1.5 mol. %, and the area of the solid solution based on the NdSe compound is 2.0 mol. %. Upon slow cooling in the As2Se3-NdSe system based on As2Se3, the glass formation region reaches 17 mol % NdSe. The photo- and electrical conductivity of glassy alloys of the As2Se3-NdSe system containing (As3Se3)1-x(NdSe)x (x = 0.03; 0.05; 0.07; 0.10) has been studied

A Revision of the Sb-Te Binary Phase Diagram and Crystal Structure of the Modulated γ-Phase Field

A new experimental study of Sb-Te, based on long term annealed samples homogenized by intermediate powdering and re-annealing of the pressed powder pellets was performed. More than 25 samples were prepared, covering the entire composition range between 0 and 60 at.% Te. This part of the phase diagram was disputed for many years, as the number of phases and their crystal structures were uncertain. Samples were characterized by optical microscopy, SEM/EDX, powder XRD and DTA. Our results show the existence of a continuous single phase field (γ) ranging from 11.4 to 56.9 at.% Te at 520 °C. A comparison of all obtained diffraction patterns showed clear evidence for a continuously modulated crystal structure. It was possible to refine all powder patterns by applying a structural model in the (3 + 1)-dimensional super-space group R­3m(0,0,γ). Lattice parameters of the basic cell as well as the modulation vector are varying continuously throughout the phase field and the γq-component ({mathbf{q}} = gamma_{q} cdot {mathbf{c}}^{user2{*}}) of the incommensurate q-vector shows a linear extrapolation to pure Sb (γq = 3/2) and Sb2Te3 (γq = 6/5). In agreement with previous authors, the single-phase field γ was found to have a melting point minimum (30 at.% Te, 535 °C). Furthermore, two peritectic reactions were observed and the course of liquidus lines was determined in the whole investigated composition range. The new phase diagram differs considerably from all previous versions, and, for the first time, gives a complete rationalization of the crystal structures observed in the debated composition area.

A pseudo-spectral based efficient volume penalization scheme for Cahn–Hilliard equation in complex geometries

In this paper, we have developed an efficient volume penalization based diffuse-filtering scheme to solve variable mobility based Cahn–Hilliard equation in complex geometries. The main novelty of the work is that a dealiased pseudo-spectral scheme with immersed interface method (IIM) is proposed for solving any generalized concentration-dependent mobility function-based Cahn–Hilliard (CH) equation in complicated computational domains. An indicator function based mobility parameter is introduced to perform simulation of binary spinodal decomposition problem at a lower computational expense in complex geometries by solving a single phase field equation. Due to the smooth removal of high frequency Fourier components, the solution of the present RK4 based diffuse-filtering scheme does not display spurious currents when suitable low-pass filtering strategy and adequately resolved mobility indicator are incorporated. The traditional and memory optimized zero padding schemes are also implemented to show the comparative performance of different dealiasing schemes for the variable mobility based Cahn–Hilliard equation. It is found that the diffuse-filtering scheme displays reasonable accuracy similar to the zero padding based schemes but its average CPU time is significantly lower, which indicates better computational performance of the scheme for the variable mobility Cahn–Hilliard equation. Time variation of the characteristic length scale during spinodal decomposition of a binary mixture agrees well with the analytical prediction. The optimal three stage SSPRK3 temporal scheme is employed and it is found that time step size can be increased approximately 1.4 times than the classical RK4 scheme reducing total CPU time. Oscillation free numerical solution and conservation of order parameter are obtained for the complex geometry based spinodal decomposition problem. A radially-averaged structure factor is introduced to quantify resolution issues of the dealiasing schemes for the spinodal decomposition problem in different complex geometries.

Laplacian Echo-State Networks for production analysis and forecasting in unconventional reservoirs

Production data analysis for low permeability shale reservoirs is crucial in characterizing flow regimes and reservoir properties, and the forecasting of production is essential for portfolio and reservoir management. However, traditional methods have failed due to incorrect physics or complicated convolution from the well control history. In this research, we provide a physics-assisted analytics workflow using Laplacian Eigenmaps Coupled Echo-State Network (LEESN) to facilitate and accelerate the analysis of noisy historical production data. Pressure-rate deconvolution is an ill-posed, complex time-series problem. When using the traditional Echo-State Network (ESN), the number of training sets is less than the number of neurons. To solve this problem, we apply LEESN to first deconvolve noisy variable-pressure variable-rate histories into smooth constant-pressure rate responses. The physics-based training features and training algorithm provide additional benefits in addition to the analytic approach by honoring transient flow physics. After training, the constant-pressure rate response can be predicted and used for reservoir characterization, and the trained model could be further used for production and EUR forecasting through long-term rate predictions to the economic limit. The proposed workflow was first validated by synthetic cases where the production data were obtained through simulation. The short-term flow rate history was obtained by specifying highly variable controlling pressures. We also added artificial white Gaussian noise to mimic measured signals collected in the field and input this information into LEESN for deconvolution. The constant-pressure rate response was generated after training to determine flow regimes and properties such as permeability using a traditional transient testing specialized plot. All outcomes from the analytics approach were validated by comparison against the input data of the synthetic simulation model. The advantages of the analytics approach were maintained with a moderate variation of noisy pressure-rate signals. For production forecasting, both the trained analytics model and simulator were used to predict for an extended period, and the results indicated good agreement between the response predictions. We performed a further sensitivity analysis on important parameters such as the training scale as well as the capability of Laplacian Eigenmaps handling moderate noise in training data. The comparison between the model predictions and simulation data showed significantly increased accuracy in production estimates. The efficacy was further demonstrated from additional single-phase and multiphase synthetic and field cases. This study shows that the LEESN approach is a powerful alternative to interpret pressure-rate-time information from production data. The discussion and comparison of LEESN with other traditional production analysis and forecast methods are included as well. Deconvolved pressure-rate data greatly enhances traditional rate-transient analysis (RTA) used to characterize reservoir parameters, and the trained model enables engineers to predict future production even with noisy, highly-variable production histories. The robustness of the proposed analytics methodology is strengthened by coupling the training features with transient flow physics and provides a unique approach for production analysis and forecasting for unconventional reservoirs.

Proton irradiation induced chemical ordering in an Al0.3CoFeNi high entropy alloy

The radiation resistance of single-phase high entropy alloys has been reported to be superior to conventional alloys, due to their high lattice distortion and sluggish diffusion kinetics. The current study combines the beneficial effects of a concentrated multi-component solid solution and chemical ordering on the parent lattice of a candidate alloy, Al0.3CoFeNi, to enhance proton radiation resistance. The strong ordering tendency in this alloy results in the formation of Ni-Al-rich short-range ordered (SRO) domains when it is annealed in a single FCC phase field and water quenched. The irradiation of these microstructures with high-fluence MeV-energetic protons aids the transformation of the prior metastable single FCC solid-solution with SRO domains toward a more stable condition with L12 long-range ordered (LRO) domains embedded within the FCC solid solution matrix. Potentially, the creation of radiation-induced vacancy cascades within the FCC solid-solution enhances local diffusivity aiding the transition from SRO domains to LRO L12 domains. Therefore, this can be considered as a recovery mechanism, since the radiation-induced damage is not allowed to accumulate and is minimized via nanometer-scale precipitation of the ordered intermetallic phase. Additionally, preferential Co segregation to defect clusters or dislocation loops was also observed. In comparison, purely thermal activation via annealing at 500 °C for 30 min induces a similar transformation from SRO to LRO in this alloy, driving the system closer to equilibrium.

Phase relations in the Fe-Fe3C-Fe3N system at 7.8 GPa and 1150°C: implications for C and N hosts in metal-saturated mantle

ABSTRACT The isothermal section of the Fe-Fe3C-Fe3N phase diagram at 7.8 GPa and 1150°С comprises a three-phase field of γ-Fe + Fe3C + ϵ-Fe3(С/N) in the central part and three two-phase fields (γ-Fe + Fe3C, γ-Fe + ϵ-Fe3 (С/N) and Fe3C + ϵ-Fe3(С/N)) bounded by three single-phase fields of γ-Fe, Fe3C and ϵ-Fe3(С/N) solid solutions along the triangle sides. Thus, native iron can host carbon and nitrogen in the γ-Fe + Fe3C or γ-Fe phases in the mantle depleted in volatiles (20 ppm C and 1 ppm N) at temperatures corresponding to the ∼35 mW/m2 heat flux, and in the Fe3C or ϵ-Fe3(С/N) phases if the contents of volatiles in the mantle reach 250 ppm C and 100 ppm N. Iron carbonitride has quite a large stability field even at low nitrogen concentrations in the system simulating native iron.

Hot pack rolling of spark-plasma-sintered pre-alloyed powders to fabricate Ti2AlNb sheets

In this work, spark-plasma-sintered Ti-20.3Al-24.7Nb (at.-%) compact was pack rolled in different phase fields to fabricate Ti2AlNb sheets with high strength and ductility without post-heat treatment. The nano O phases in the B2 matrix contributed to the high tensile strength and ductility in a single B2 phase field. In the O + B2 phase field, the O phases remarkably increased in size and resulted in high tensile strength of 1407.1 MPa. Maintaining the O phases to nano sizes and cooperation with micro-sized α 2 phases resulted in extremely high elongation of 13.91% in the α 2+O + B2 phase field. The , , , and strengthening effects of the α 2 and O phases under different conditions were analysed in detail. Highlights Spark-plasma-sintered pre-alloyed powders are used as the raw compact before hot pack rolled Ti2AlNb sheet. Ti2AlNb sheets with good mechanical properties are obtained without any post-heat treatment. This ‘SPS pre-alloyed powder + hot pack rolling’ method has great potential in breaking the limit in sheet properties. The strengthening effects of different factors are analysed.

An Investigation of the Miscibility Gap Controlling Phase Formation in Refractory Metal High Entropy Superalloys via the Ti-Nb-Zr Constituent System

Refractory metal high entropy superalloys (RSAs) have been heralded as potential new high temperature structural materials. They have nanoscale cuboidal bcc+B2 microstructures that are thought to form on quenching through a spinodal decomposition process driven by the Ta-Zr or Nb-Zr miscibility gaps, followed by ordering of one of the bcc phases. However, it is difficult to isolate the role of different elemental interactions within compositionally complex RSAs. Therefore, in this work the microstructures produced by the Nb-Zr miscibility gap within the compositionally simpler Ti-Nb-Zr constituent system were investigated. A systematic series of alloys with compositions of Ti5NbxZr95−x (x = 25–85 at.%) was studied following quenching from solution heat treatment and long duration thermal exposures at 1000, 900 and 700 °C for 1000 h. During exposures at 900 °C and above the alloys resided in a single bcc phase field. At 700 °C, alloys with 40–75 at.% Nb resided within a three phase bcc + bcc + hcp phase field and a large misfit, 4.7–5%, was present between the two bcc phases. Evidence of nanoscale cuboidal microstructures was not observed, even in slow cooled samples. Whilst it was not possible to conclusively determine whether a spinodal decomposition occurs within this ternary system, these insights suggest that Nb-Zr interactions may not play a significant role in the formation of the nanoscale cuboidal RSA microstructures during cooling.

SYNTHESIS OF ALLOYS OF THE Sb2Se3-CuCr2Te4 SYSTEM AND PHYSICO-CHEMICAL PROPERTIES

The interaction in the quasi-ternary system Sb2Se3-CuTe-Cr2Te3 along the Sb2Se3-CuCr2Te4 section was studied by methods of physicochemical analysis: differential thermal (DTA), X-ray phase (XRD), microstructure (MSA), as well as by measuring the density and its microhardness and plotted. The phase diagram of the system is quasi-binary, eutectic type. The composition of the double eutectic formed in the system is 20 mol % CuCr2Te4 and a temperature of 490°C. As a result of the analysis of the microstructure, it was determined that there are single-phase fields based on the original components. It was found that at room temperature, solid solutions based on Sb2Se3 extend to 5 mol % CuCr2Te4, and on the basis of CuCr2Te4 solid solutions reach 13 mol % Sb2Se3.

Thermomechanical and thermodynamic behavior of deformed austenite in four different steel grades

In this work, the deformation behavior and thermodynamic aspect of four different steel grades were analyzed. This group of alloys includes a plain C–Mn, and three Nb-microalloyed steels grades. Two of the microalloyed steels are pipeline grades: a modified X-70 grade, and a typical X-80 steel. These materials were previously identified to produce dynamically transformed ferrite (combined with recrystallized grains) during physical simulation of hot rolling in the single austenite phase field of their phase diagrams. For C–Mn and microalloyed steels, hot deformation at a stain of 0.4 and strain rate of 1 s−1 generates 15 and 25 vol% of ferrite, respectively. In addition, the X-70 and X-80 steels yield 19 and 8 vol% of ferrite, respectively, after deformation strains of 0.4 and 0.2, and strain rate of 1 s−1. All the deformation was applied at least 53 °C above their respective Ae3 temperatures. The concept of transformation softening was applied to explain the occurrence of dynamic transformation during hot torsion tests. Here the driving force to dynamic transformation (DT) was taken by measuring the difference between the critical stress to DT in the austenite phase, and the yield stress of the ferrite that takes its place. The obstacle energy consists of the free energy between the parent and product phases and the shear accommodation and lattice dilatation work associated with phase transformation of austenite to ferrite. It is shown here that, for all the selected materials, the calculated driving force is higher than the energy obstacles, which thermodynamically explains the occurrence of DT.

INTERACTION IN THE SYSTEMS Tl2Se–Ga(In)2Se3–SnSe2

Quasi-ternary systems Tl2Se–Ga(In)2Se3–SnSe2 were investigated by physico-chemical analysis methods (differential thermal, X-ray phase, X-ray structural analysis), and their isothermal sections at 520 K in the entire concentration range were plotted. On the section of TlGaSe2–SnSe2 the existence of three compounds Tl2Ga2SnSe6, TlGaSnSe4, and TlGaSn2Se6, was found. The quaternary compounds form in the peritectic reactions L+α↔Tl2Ga2SnSе6 at 956 K, L+Tl3Ga3SnSе8↔Tl- GaSnSе4 at 851 K, and L+SnSе2↔TlGaSn2Sе6 at 833 K. The crystal structure of Tl2Ga2SnSe6 was determined in the tetragonal symmetry, S.G. I4/mcm; а=08095(1), c=0.402(1) nm), TlGaSn2Se6 has trigonal structure (S.G. R3; a=1.03289, c=0.94340 nm). The isothermal section of the Tl2Se–Ga2Se3–SnSe2 system at 520 K contains 9 single-phase fields and 14 regions of two-phase equilibria which separate the concentration triangle into 10 fields of three-phase equilibria. The largest solid solutions ranges are those of the TlGaSе2 and Ga2Se3 compounds. The location of 5 three-phase fields and 11 two-phase equilibria between binary and ternary compounds were identified at the section of the Tl2Se–In2Se3–SnSe2 system at 520 K. Phase diagram of the TlInSe2–SnSe2 section of the eutectic type. The solid solubility range of TlInSe2 along this section reaches 28 mol.%. Single crystals of the solid solutions Tl1‑xGa1‑xSnxSe2 (x=0.05–0.1) and Tl1‑xIn1‑xSnxSе2 (x=0–0.25) that form in the TlGa(In)Se2–SnSe2 systems were grown by the Bridgman-Stockbarger method. According to X-ray diffraction analysis results, it was determined that the grown Tl1-xGa1-xSnxSe2 crystals have monoclinic structure (S.G. C2/c), and the Tl1‑xIn1-xSnx- Sе2 crystals are tetragonal (S.G. I4/mсm).