Papers by Keyword: Phase Equilibrium

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Authors: Yu Dong Zhang, Chang Shu He, X. Zhao, Yan Dong Wang, Liang Zuo, Claude Esling
Abstract: The Weiss model is extended by substituting the molecular field coefficient lwith a short-range-ordering coefficient g valid around and above Tc. The temperature variations of susceptibility of fcc Fe are calculated with a band model. Based on the above models, the phase equilibrium diagram of Fe-C binary system under a magnetic field is calculated.
Authors: Bao Kui Chen, Feng Zhong Sun
Abstract: Inadequacy was discussed of using acid dew point temperature (ADT) as safe low limitation of exhaust gas temperature on the background of waste heat deep utilization of flue gases. Concept of limited corrosion dew point (LCT) was presented based on corrosion property of ordinary carbon steel and binary phase equilibrium of H2SO4-H2O system,. Calculation formula of LCT was solved by establishing fugacity equation of H2O with a fixed concentration and constant pressure. The results show that LCT lies during 68-84°C when volume percentage of H2O vapor varies from 6-12% which is in line with that of exhaust gas of boiler. The maximum relative error of the calculated data is 1.43% in contrast to reported data. Ordinary carbon steel in contact with flue gas with its surface temperature above LCT will not occur obvious corrosion and wet soot deposition through observation of experiment on site. It is available for exhaust gas temperature to decline below ADT but above LCT in process of deep utilization of waste heat of flue gas.
Authors: O.M. Barabash, Yu.V. Milman, N.P. Korzhova, T.N. Legkaya, Yu.N. Podrezov
Authors: Qiang Chen, Chang Ling Liu, Yu Guang Ye
Abstract: In this paper, we focused on the determination of phase equilibrium conditions of hydrates formed in the pore water and porous media from South China Sea. High pressure differential scanning calorimetry (HP DSC), a relatively new thermo-analytical technique was applied to this research. During the study, nitrogen hydrates and methane hydrates phase equilibrium conditions were determined in thewater-hydrates- gas (W-H-G) system. Then a series of experiments were carried on using core sample drilled from South China Sea to determine the phase equilibrium properties in pore water and porous media systems. It show that the hydrates phase equilibrium point is about 2K lower than in pure water from pressure range 10 to 30 MPa, due to the thermodynamic inhibition effect of brine solution.
Authors: Le Zhou, Yong Ho Sohn
Abstract: Heusler NiMnGa alloys are often categorized as ferromagnetic shape memory alloys or magnetocaloric materials, which are important for both practical applications and fundamental research. The NiMnGa alloys undergo a series of diffusion and diffusionless transformation from high temperature to low temperature. Among these transformation, martensitic transformation from austenitic phase to martensitic phase is critical in determining the properties of the alloys. Although martensitic transformation is considered diffusionless, diffusion also has important applications in the research of NiMnGa alloysDiffusion couples along with equilibrium alloys have been used to determine the ternary phase diagrams in NiMnGa alloys. Phase diagrams are important in selecting NiMnGa alloys, in particular two-phase NiMnGa alloys for practical applications. Furthermore, the diffusion couples effectively assist in the determination of compositions that exhibit martensitic transformation temperature near room temperature. Diffusion coefficients have been assessed for NiMnGa alloys. Tracer diffusivity of Ni, Mn and Ga was reported in a wide temperature range and followed Arrhenius behavior. Two different activation energies were obtained, corresponding to B2 and L21 crystal structure, respectively. Interdiffusion coefficients for NiMnGa alloys with B2 crystal structure are measured, which showed that Ni diffuses the fastest, followed by Mn then Ga. The diffusion coefficients provide useful information for fabricating NiMnGa alloys through diffusional process.A combinatorial approach involving diffusion couples and advance characterization has been developed to investigate the mechanical properties, microstructure and crystallography of NiMnGa alloys rapidly and systematically over a large compositional range. The composition-dependent modulus and hardness for NiMnGa alloys was extracted from the diffusion couples with the help of nanoindentation. Martensitic phases with non-modulated and various modulated crystal structures, and austenitic phase were identified in the interdiffusion zones by transmission electron microscopy. The results demonstrate the capability of using diffusion couples to speed up the discovery of new NiMnGa alloys or other similar alloys showing martensitic transformation.
Authors: Yu Dong Zhang, Claude Esling, Xiang Zhao, Liang Zuo
Abstract: The new phase equilibrium of Fe-C diagram under magnetic field has been theoretically calculated. Results show that the magnetic field mainly shifts the γ⁄α+γ equilibrium line and the eutectoid point to the high carbon and high temperature sides. Based on this result, an experimental setup has been launched to investigate the effect of magnetic field on austenite decomposition in medium carbon and high carbon steels. The thermodynamic and kinetic effects of the high magnetic field on proeutectoid transformation at different cooling rates have been studied. It was found that for medium carbon steels, the magnetic field increases the amount of proeutectoid ferrite and accelerates the diffusional decomposition of austenite at medium and relatively fast cooling rates (10°C/min and 46°C/min). But there is no special grain growth along the field direction. The results led to a proposal of a new rapid annealing under a high magnetic field. However, when cooling is slow (2°C/min), the magnetic field shows a strong tendency to promote the proeutectoid ferrite grains to grow along the field direction through the magnetic dipolar interaction, which leads to the formation of an elongated grain structure. Moreover, the magnetic field also exhibits influence on the austenite decomposition in hypereutectoid steel by changing the amount of secondary cementite and lamellar spacing of pearlite.
Authors: Tae Kwon Ha, Kyu Dong Lee, Jin Hwa Song, Hyo Tae Jeong
Abstract: Strengthening method for the Fe-36Ni based Invar alloy for power transmission wire was investigated in this study. High strength of 1300 MPa could be obtained in this alloy through solution hardening, precipitation hardening and strain hardening by cold working. Phase equilibrium of the Invar alloy was calculated using FactSage®, revealing that thermodynamically stable phases are Mo2C, MoC, M23C6-type FeCrMo carbide, and M6C-type FeMo carbides. Aging treatments were carried out at temperatures ranging from 400 to 900oC for time intervals from 3 min to 30 hrs. Peak aging condition was obtained as 400oC and 1 hr. With temperature increased, peak hardness was decreased abruptly. Microstructure observation was conducted by optical microscopy, scanning electron microscopy, and transmission electron microscopy. By using the result from aging treatment, high strength above 1300MPa was obtained in the cold rolled Invar alloy plate.
Authors: Ju Hyun Won, Seok Hong Min, Tae Kwon Ha
Abstract: Effect of B addition on the microstructure and mechanical properties of AZ84 Mg alloy was investigated in this study. Through calculation of phase equilibria of AZ84 Mg alloy, carried out by using FactSage® and FTLite database, solution treatment temperature was decided as temperature of 330oC, where supersaturated solid solution can be obtained. Solid solution treatment of AZ84 Mg alloy was successfully conducted at 330oC and supersaturated microstructure with all almost all phases resolved into matrix was obtained. After solution treatment, hot rolling was successfully conducted by reduction of 60%. Compression and tension tests were carried out at room temperature on the samples in as-cast, solution treated, hot-rolled and subsequently recrystallized states. After solid solution treatment, each alloy was soaked at temperatures of 180 and 200oC for time intervals from 1 min to 48 hrs and hardness of each condition was measured by micro-Vickers method. Peak aging conditions were deduced as at the temperature of 200 oC for 10 hrs for ZA84 Mg alloy. By addition of boron, aging kinetics was expedited and strength was enhanced.
Authors: Tae Kwon Ha, Seok Hong Min
Abstract: Thermodynamic equilibrium of Fe-36Ni-base Invar alloy containing C contents from 0.25 to 0.38 weight per cent during solidification has been investigated in this study. From the thermodynamic simulation using ThermoCalc®, it has been revealed that equilibrium phases which can be formed are two kinds of MC-type precipitates, i.e. (Nb, Mo, V)C and MoC, and M2C carbides. The MoC carbide was expected to be formed at relatively lower temperature below 770oC. Microstructure observation revealed the coarse precipitates in the as-cast ingots, which was Mo-rich non-equilibrium phase and could be resolved by the successive heat treatment. With increasing C contents from 0.25 to 0.38 wt.%, tensile strength of Invar alloy increased from 950 to 1100MPa after hot rolling and thermal expansion coefficient showed a trivial increase. Hot-rolled Invar alloy was successfully drawn at room temperature from 6 to 4 mm in diameter, which dramatically decreased thermal expansion coefficient.
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