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Evolution of secondary phases in 0.17C-16Cr-11Mn-0.43N austenitic stainless steel at 800 and 850°C: Thermodynamic modeling of phase equilibria and experimental kinetic studies  [PDF]
?i?ka R.,Bakajová J.,?tefániková M.,Dománková M.
Journal of Mining and Metallurgy, Section B : Metallurgy , 2012, DOI: 10.2298/jmmb120702051c
Abstract: The precipitation of secondary phases was investigated in the 0.17C-16Cr-11Mn-0.43N austenitic stainless steel during annealing at 800 and 850°C for times between 5 min and 100 h. Light microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, scanning electron microscopy, and differential thermal analysis were used in experiments. Thermodynamic calculations were done by the ThermoCalc database software package. Cr2N and M23C6 were considered to be stable phases at the annealing temperatures. Cells consisting of alternating Cr2N and austenite lamellae were observed in the steel microstructure after sufficiently long annealing. The metastable chi phase was also found in all the annealed samples. After 100 h of annealing the equilibrium sigma started to precipitate. The thermodynamically predicted M6C was not confirmed experimentally in any of the annealed samples. DTA analysis showed the initial precipitation stage was followed by the phase dissolution. For the investigated steel the computational thermodynamics can be used only for qualitative interpretation of the experimental results as the measured endothermal peaks were found to be shifted of about 50 ÷ 70°C related to the computed results.
New Thermodynamic Paradigm of Chemical Equilibria  [PDF]
B. Zilbergleyt
Physics , 2011,
Abstract: The paper presents new thermodynamic paradigm of chemical equilibrium, setting forth comprehensive basics of Discrete Thermodynamics of Chemical Equilibria (DTd). Along with previous results by the author during the last decade, this work contains also some new developments of DTd. Based on the Onsager's constitutive equations, reformulated by the author thermodynamic affinity and reaction extent, and Le Chatelier's principle, DTd brings forward a notion of chemical equilibrium as a balance of internal and external thermodynamic forces (TdF), acting against a chemical system. Basic expression of DTd is the chemical system logistic map of thermodynamic states that ties together energetic characteristics of chemical reaction, occurring in the system, the system shift from "true" thermodynamic equilibrium (TdE), and causing that shift external thermodynamic forces. Solutions to the basic map are pitchfork bifurcation diagrams in coordinates "shift from TdE - growth factor (or TdF)"; points, corresponding to the system thermodynamic states, are dwelling on its branches. The diagrams feature three typical areas: true thermodynamic equilibrium and open equilibrium along the thermodynamic branch before the threshold of its stability, i.e. bifurcation point, and bifurcation area with bistability and chaotic oscillations after the point. The set of solutions makes up the chemical system domain of states. The new paradigm complies with the correspondence principle: in isolated chemical system external TdF vanish, and the basic map turns into traditional expression of chemical equilibrium via thermodynamic affinity. The theory binds together classical and contemporary thermodynamics of chemical equilibria on a unique conceptual basis. The paper is essentially reworked and refocused version of the earlier preprint on the DTd basics, supplemented with new results.
Thermodynamic calculation of phase equilibria in stainless steels  [PDF]
Klan?nik G.,Petrovi? Steiner D.,Medved J.
Journal of Mining and Metallurgy, Section B : Metallurgy , 2012, DOI: 10.2298/jmmb121119048k
Abstract: In this paper two examples of thermodynamic investigation of stainless steels using both, experimental and modeling approach are described. The ferritic-austenitic duplex stainless steel and austenitic stainless steel were investigated using thermal analysis. The complex melting behavior was evident for both alloy systems. Experimentally obtained data were compared with the results of the thermodynamic calculations using the CALPHAD method. The equilibrium thermal events were also described by the calculated heat capacity. In spite of the complexity of both selected real alloy systems a relative good agreement was obtained between the thermodynamic calculations and experimental results.
Phase equilibria in the In–Sb–Bi system at 300 oC
DUSKO MINIC,DRAGAN MANASIJEVIC,DRAGANA ZIVKOVIC,ZIVKOVIC
Journal of the Serbian Chemical Society , 2006,
Abstract: Binary thermodynamic data, successfully used for phase diagram calculations of the binary systems In–Sb, Bi–Sb and In–Bi, were used fort the prediction of phase equilibria in the ternary system In–Sb–Bi at 300 oC. The predicted equilibria were compared with the results of SEM–EDX analysis.
STRUCTURAL STABILITY OF HIGH NITROGEN AUSTENITIC STAINLESS STEELS
Jana Bakajová,Mária Dománková,Peter Gogola
Materials Engineering , 2011,
Abstract: This paper deals with the structural stability of an austenitic stainless steel with high nitrogen content. The investigated steel was heat treated at 800°C using different annealing times. Investigation was carried out using light microscopy, transmission electron microscopy and thermodynamic calculations. Three phases were identified by electron diffraction: Cr2N, sigma – phase and M23C6. The thermodynamic prediction is in good agreement with the experimental result. The only is the M23C6 carbide phase which is not thermodynamically predicted. Cr2N is the majority secondary phase and occurs in the form of discrete particles or cells (lamellas of Cr2N and austenite).
Thermodynamic analysis and phase equilibria investigation in Pb Zn Ag system  [PDF]
Mitovski Aleksandra M.,?ivkovi? Dragana T.,Manasijevi? Dragan M.,Mini? Du?ko M.
Hemijska Industrija , 2010, DOI: 10.2298/hemind100115007m
Abstract: Physico-chemical processes that take place during the refining process in the extractive metallurgy of lead, are connected with ternary Pb Zn Ag system, which is necessary to study from the theoretical practical and aspects. Such investigation is important from production point of view, because of the phenomena that occur during desilvering of lead which is one of the important stages during lead refining process. Process of lead desilvering binds to ternary system Pb Zn Ag, which was the reason for numerous investigations, both from thermodynamic point of view and in terms of testing and determining the phase diagram, bearing in mind the theoretical, and practical importance of knowledge about the processes which are going in investigated system. The paper presents the results of thermodynamic analysis and investigation of phase equilibria of the Pb Zn Ag ternary system using the method of thermodynamic predictions and phase diagrams calculations, respectively, and the experimental results of metalography obtained by optical microscopy. Phase diagram of the vertical section Pb Zn80Ag20 is presented, obtained by CALPHAD calculation methodology, and using PANDAT thermodynamic software, compared to experimental results obtained by DTA analysis. The results show a pronounced break in solubility, which is characteristic for the whole ternary Pb Zn Ag system. Also, it can be noticed that the thermodynamic properties follow the behavior of this system, which is expressed through positive deviation of Raoult’s law, pointing to the lack of lead affinity compared to the other two components in the system. The optical microscopy results of the investigated system show the following: - Sample L1 (weight% Pb = 98): the structure of the observed section shows double eutectic (Pbsol+Zn Agsol) which lies in the base of the primary crystals of lead (Pbsol) - Samples L2 L5: the structure consists of a dual eutectic (Pbsol+Zn Agsol) and primary crystals Zn Agsol Also, it can be noticed certain structural inhomogenity, as a consequence of stratification that occurs in the ternary Pb Zn Ag system. However the metalography investigation results confirm the results obtained by defining the phase diagram and mutually agree relatively well in accordance with existing literature data.
Thermodynamic Models for Vapor-Liquid Equilibria of Nitrogen+Oxygen+Carbon Dioxide at Low Temperatures  [PDF]
J. Vrabec,G. K. Kedia,U. Buchhauser,R. Meyer-Pittroff,H. Hasse
Physics , 2009, DOI: 10.1016/j.cryogenics.2008.11.002
Abstract: For the design and optimization of CO2 recovery from alcoholic fermentation processes by distillation, models for vapor-liquid equilibria (VLE) are needed. Two such thermodynamic models, the Peng-Robinson equation of state (EOS) and a model based on Henry's law constants, are proposed for the ternary mixture N2+O2+CO2. Pure substance parameters of the Peng-Robinson EOS are taken from the literature, whereas the binary parameters of the Van der Waals one-fluid mixing rule are adjusted to experimental binary VLE data. The Peng-Robinson EOS describes both binary and ternary experimental data well, except at high pressures approaching the critical region. A molecular model is validated by simulation using binary and ternary experimental VLE data. On the basis of this model, the Henry's law constants of N2 and O2 in CO2 are predicted by molecular simulation. An easy-to-use thermodynamic model, based on those Henry's law constants, is developed to reliably describe the VLE in the CO2-rich region.
Computer-based simulation of high-temperature corrosion phenomena
Trindade, Vicente Braz;Krupp, Ulrich;Christ, Hans-Jürgen;
Journal of the Brazilian Chemical Society , 2008, DOI: 10.1590/S0103-50532008000100022
Abstract: the aim of this paper is to introduce a computer simulation tool, which is designed for prediction of service-life of components operating under corrosive conditions such as carburization, oxidation and nitridation at high-temperature. different classes of materials (low-cr ferritic steels, austenitic steels and ni-base superalloys) were exposed at temperatures between 550 oc and 1000 oc to different corrosive atmospheres (carburizing, oxidizing and nitriding). the tool for the prediction of internal/inwards corrosion processes at high-temperatures makes use of the numerical finite-difference technique to treat diffusional kinetics on the one hand and the concept of local equilibrium thermodynamics on the other hand. for this purpose, a link has been established between the numerical environment of matlab and the thermodynamic library chemapp. using this new tool, the kinetics of nitridation, oxidation and carburization processes were predicted numerically taking the material?s microstructure into consideration by distinguishing between precipitation along the grain boundaries and within the grain interior. excellent agreement between experimental observations and simulation results revealed the high potential of the computer modeling for application to complex corrosion processes.
A comparative study of the corrosion resistance of incoloy MA 956 and PM 2000 superalloys
Terada, Maysa;Marques, Rogério Albuquerque;Magnani, Marina;Padilha, Angelo Fernando;Costa, Isolda;
Materials Research , 2010, DOI: 10.1590/S1516-14392010000400002
Abstract: austenitic stainless steels, titanium and cobalt alloys are widely used as biomaterials. however, new medical devices require innovative materials with specific properties, depending on their application. the magnetic properties are among the properties of interest for some biomedical applications. however, due to the interaction of magnetic materials with magnetic resonance image equipments they might used only as not fixed implants or for medical devices. the ferromagnetic superalloys, incoloy ma 956 and pm 2000, produced by mechanical alloying, have similar chemical composition, high corrosion resistance and are used in high temperature applications. in this study, the corrosion resistance of these two ferritic superalloys was compared in a phosphate buffer solution. the electrochemical results showed that both superalloys are passive in this solution and the pm 2000 present a more protective passive film on it associated to higher impedances than the ma 956.
Calorimetric examination of mixtures for modification of nickel and cobalt superalloys  [PDF]
F. Binczyk,J. Sleziona,R. Przeliorz
Archives of Foundry Engineering , 2009,
Abstract: The study presents the results of thermodynamic calculations and calorimetric examination of thermal reactions taking place at hightemperatures between the nanoparticle inoculants and metallic constituents of nickel and cobalt superalloys. The calculations andmeasurements were made for different compositions, containing cobalt aluminate CoAl2O4, cobalt oxide CoO*Co2O3, zircon flourZrSi2O4, powdered and metallic Al, powdered Ti, and IN-713C alloy. The obtained results have indicated the possibility of using certainmixtures as potential inoculating additives for the volume modification of nickel and cobalt superalloys. A characteristic feature of these alloys is the formation of a detrimental structure containing very large columnar crystal, present even in castings of a very high solidification rate. It has been proved that the inoculant most effective in the formation of the structure of equiaxial grains is the inoculant based on cobalt aluminate, colloidal silica and powdered aluminium.
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