Papers by Keyword: Thermo-Calc

Abstract: In semi-solid metal casting processes a slurry, obtained operating in the temperature window between the liquidus and the solidus curve of the phase diagram of the alloy (32.7 °C for AlSi8, 11.3 °C for AlSi11), is injected into the mould. Since the control over the process parameters becomes more complicated as the involved quantities increase, to apply these processes on an industrial scale it is necessary to widen as much as possible this narrow temperature window. This goal can be obtained by tailoring the concentration of elements constituting the alloy. A EN AC-46000 secondary alloy was selected for this study, because of its wide use in foundries. Using a CALPHAD approach, various Al-Si-based pseudo-binary phase diagrams containing main constituents of the alloy (Cu, Zn, Fe, Mg, Mn, Ni, Cr and Ti) were studied, keeping the Si content fixed from 8 to 11 wt.% and the Al content as a complement. The composition limits of acceptability of the commercial alloy EN AC-46000 were used as extremes of the simulation field. The study was then proceeded investigating the pseudo-ternary diagrams, keeping silicon and a second element fixed and a third element variable for all possible combinations. Further constituent elements of the alloy were progressively added, considering all main constituents of the alloy, and evaluating how the concentration of these elements can extend the temperature window. Mg, Fe, Mn and Ti are the most promising candidates for achieving this goal. The results of this study can provide foundries with a prediction tool to define more restrictive ranges of acceptability than those of the commercial alloy, allowing them to estimate through a simple chemical analysis whether scrap of variable composition entering the plant are suitable for the SSM process or they need preliminary corrections of composition.

Abstract: Steel alloys with high Mn and low C, low Cr wt.%, were designed based on the composition system for traditional high toughness, creep resistance, and longevity for high-temperature applications. In terms of energy resource utilization during production and refining, CALPHAD strategical optimization is preferable for all steel alloys. Thermo-Calc software calculates the phase diagrams α-BCC (Ferrite), and M₂₃C₆ (carbide) phases. The vital temperatures which are highlighted in this work are Ac₃ (threshold temperature at which ferrite is fully transformed into austenite (α→γ)), and A₄ (the threshold temperature at which austenite is fully transformed into Delta ferrite (γ→δ)) are essential for phase transformations. JMatPro software is used to predict the mechanical properties of steel alloys. The interfacial energies with regards to alloying elements for M₂₃C₆ are calculated to be between ~0.272 J/m^-2 to ~0.328 J/m^-2 for α-BCC) matrix, while γ-FCC has interfacial energy ranges to be between ~0.132 J/m^-2 to ~0.168 J/m^-2. This paper focuses on investigating the effect of alloying elements on phase transformations, interfacial energy, coarsening rate of carbides, and many other mechanical properties such as toughness at high-temperature applications using CALPHAD strategies.

Abstract: The thermodynamic calculation software Thermo-Calc was used to study the influences of alloy elements Cr, Co, and Mo on the precipitated phases of a S280 ultrahigh strength stainless steel at the temperatures ranging from 400 °C to 1200 °C. The results showed that the precipitated phases in the steel were mainly composed of M₂₃C₆ carbide, M₆C carbide, intermetallic compound of Laves phase and σ phase. The temperature and the content change of alloying elements Cr, Co and Mo have little effect on the precipitation of M₂₃C₆ carbide, while have great effect on the precipitation of Laves phase and σ phase. By lowering the element content and adjusting the heat treatment temperature, the precipitation of σ phase in the alloy can be reduced．According to the results of thermodynamic simulation, after optimizing the chemical composition, the Ф300mm bar was trial-produced. The chemical composition, microstructure and mechanical properties of the alloy were analyzed and tested. The results show that, after tempering at 550 °C, the main precipitated phases in the S280 alloy were M₂₃C₆ carbide and intermetallic compound of Laves phase. The characterized nano-precipitates have good agreement with simulation results. The optimized design of S280 steel reached a tensile strength over 1930 MPa and a fracture toughness of 90 MPa•m^1/2.

Abstract: The thermodynamic modeling of alloy systems consisting of stable and metastable phases e.g. high-alloyed mottled cast iron can be problematic. Thermodynamic databases are rather well-developed for low, medium and high alloyed steels (e.g. HSS) but the application of those databases is not yet very common for high-alloyed (mottled) cast irons. The Thermo-Calc software together with the TCFE7 database is used to calculate isopleth and property diagrams, using the CALPHAD method. Additionally Scheil-Gulliver calculations are performed to simulate the effects of microsegregation during solidification. The results from the thermodynamic calculations are compared with measurements on own samples and with literature values. Those measurements include quantitative light-optical analysis, SEM with BSE detector, EDX measurements for the distribution of the alloying elements as well as XRD and DSC measurements. The investigations show the possibilities which are offered by thermodynamic calculations for high-alloyed mottled cast iron as well as the limitations and the compromises which have to be taken into account when calculating stable and metastable phases existing next to each other.

Abstract: The theoretical prediction of intercritical annealing temperature for DP steels was conducted by thermodynamic calculation, which agreed to the experimental results. When annealed at 800°Caccording to the calculated temperature of 807°C by setting ratios of α:γ in 70:30, the amount of martensite was 13~18% and the mechanical properties achieved DP590 grade. There was at least 10% to 12% austenite transformed to new ferrite and martensite between intercritical annealing and overaging procedure.

Abstract: The solidification path of Al-Cu-Si alloys in the Al-rich corner are investigated. The thermodynamic data needed in the calculation are obtained by direct coupling with the CALPHAD software Thermo-Calc. A paralell experimental investigation is conducted to validate the prediction results. The calculated results show that, the sensitivity of the variations in the solidification paths to the cooling rates are depended on the distance of the initial compositions from the binary eutectic troughs or the ternary eutectic point. Reasonable agreements are observed between the predicted amounts of θ-phase and the measured results.

Abstract: The Thermo-Calc and DICTRA software/database/programming-interface packages, through many successful applications in the fields of Computational Thermodynamics and Kinetics, have tremendously contributed to quantitative conceptual design and processing of various advanced materials. Materials scientists and engineers can efficiently apply such unique and comprehensive tools in calculating material properties, predicting material structures and simulating material processes, which are of wide-ranging industrial and academic importance.

Abstract: Thermodynamic and kinetic data are generally essential for quantitative modeling of materials processing, structure, and property. Thermo-Calc program interfaces, including TQ, TCAPI, and TC MATLAB Toolbox, provides a hierarchy of APIs for application programmers to access thermodynamic and kinetic data via the kernel of Thermo-Calc and DICTRA, the most widely used software and database system for multi-component phase equilibrium and phase transformation calculations. With these program interfaces, variation of thermodynamic and kinetic properties can be directly obtained in real time as the local temperature, pressure, or composition changes. The structure and usage of the Thermo-Calc program interfaces will be introduced in this article. Successful application examples will be illustrated.