Jan-Olof Andersson

The Thermo-Calc databank system☆

Abstract A description is given of Thermo-Calc, a databank for thermochemistry and metallurgy developed at the division of Physical Metallurgy of the Royal Institute of Technology (KTH) in Stockholm. Using the facilities of Thermo-Calc one can tabulate thermodynamic data, calculate the heat change of chemical reactions and their driving force, evaluate equilibria for chemical systems and phase transformations and calculate various types of multicomponent phase diagrams by an automatic mapping procedure. The databank is quite general and can be applied to all systems where data assessed by a model implemented in the databank are available. The assessment procedure necessary to develop and extend the the databank is discussed. A brief description of the modules of Thermo-Calc is given and two examples are included which demonstrate how flexibly the calculations can be made. These examples will also show that the system is quite easy to use and that there are extensive on-line help facilities.

THERMO-CALC & DICTRA, computational tools for materials science

Software for calculation of phase diagrams and thermodynamic properties have been developed since the 1970s. Software and computers have now developed to a level where such calculations can be used as tools for material and process development. In the present paper some of the latest software developments at Thermo-Calc Software are presented together with application examples. It is shown how advanced thermodynamic calculations have become more accessible since: - A more user-friendly windows version of Thermo-Calc, TCW, has been developed. - There is an increasing amount of thermodynamic databases for different materials available. - Thermo-Calc can be accessed from user-written software through several different programming interfaces are available which enables access to the thermodynamic software from a user-written software. Accurate data for thermodynamic properties and phase equilibria can then easily be incorporated into software written in e.g. C++, Matlab and FORTRAN. Thermo-Calc Software also produces DICTRA, a software for simulation of diffusion controlled phase transformations. Using DICTRA it is possible to simulate processes such as homogenization, carburising, microsegregation and coarsening in multicomponent alloys. The different models in the DICTRA software are briefly presented in the present paper together with some application examples.

Models for numerical treatment of multicomponent diffusion in simple phases

A general formalism for multicomponent diffusion in simple phases is presented in some detail. The formalism is mainly based on previous work by various authors. The purpose of the present work is to develop the formalism to such an extent that it is suitable for implementation on a computer. Expressions for the multicomponent diffusion‐coefficient matrix is given. The concentration dependence of the kinetic coefficients is discussed in terms of simple models.

Thermodynamic properties of the CrFe system

Abstract A revised thermodynamic assessment of the CrFe system is presented. Some of the major improvements are: Altered composition dependence of the Curie temperature, improved description of the bcc/sigma phase equilibrium and thermodynamic properties of bcc and a lower minimum of the gamma loop. A set of parameters describing the Gibbs energy in each phase is given.

A compound-energy model of ordering in a phase with sites of different coordination numbers

Abstract When applied to a phase where all the sites do not have the same coordination number, the bond-energy model gives a term in u AA − u BB , which cannot be assigned a numerical value because the energy of different elements cannot be compared. As an alternative a compound-energy model is now developed from the well-known model for reciprocal systems. It gives a similar result but the u AA − u BB term does not appear. In addition, the new model takes into account two kinds of factors resulting in ordering, those which make different elements prefer different kinds of lattice sites and those which give a preference for unlike neighbors. The ordering in the sigma phase is considered in some detail.

Computer simulation of multicomponent diffusional transformations in steel

ABSTRACT The thermodynamic and kinetic basis for simulation of multicomponent diffusional transformations is reviewed. The concepts underlying a new program package called DICTRA are described. The new software utilizes a new numerical procedure for solving a system of coupled diffusion equations and is interfaced with the THERMO-CALC system for calculation of local equilibrium at a moving phase interface.

A thermodynamic evaluation of the FeMoC system

Abstract A new evaluation of the Fe-Mo-C system has been made using a sublattice model and including the magnetic effect. A set of parameter values describing the Gibbs energy of each individual phase was determined with a computerized optimization technique. It gives satisfactory agreement with the experimental information over a wide temperature range. Several diagrams and tables concerning phase equilibria are presented.

A NEW METHOD OF DESCRIBING LATTICE STABILITIES

Abstract The lattice stability is defined as the Gibbs energy of an element in a certain structure relative to its value in another structure. It is often assumed to vary linearly with temperature, an assumption which is either limited to a narrow range of temperature or implies that C p of the two phases are the same. A better method would be to use the information available for C p and derive a more realistic extrapolation. However, it is demonstrated that even the best assessment available today may give absurd results for the stability of a liquid phase relative to a solid. SGTE has recommended another method which makes use of the experimental difference in C p at the melting point. It is a simple method and guarantees that the results will be reasonable. The method should not be considered as ideal but it provides a workable framework until reliable physical models are available to represent thermodynamic data for phases outside their range of stability.

Thermodynamic properties of Cr-C

Revue des proprietes thermodynamiques: energie de Gibbs et solubilite du systeme Cr−C a haute temperature. Revue, a partir de ces resultats, du diagramme C−Cr

Thermodynamic properties of MoC

Abstract An evaluation of the Mo-C system has been made using a sublattice model. A set of parameter values describing the Gibbs energy of each individual phase was determined with a computerized optimization technique. It gives satisfactory agreement with the experimental information over a wide temperature range. Several diagrams and tables concerning phase equilibria are presented.