The development of phase-based property data using the CALPHAD method and infrastructure needs

Abstract

Initially, the CALPHAD (Calculation of Phase Diagrams) method was established as a tool for treating thermodynamics and phase equilibria of multicomponent systems. Since then the method has been successfully applied to diffusion mobilities in multicomponent systems, creating the foundation for simulation of diffusion processes in these systems. Recently, the CALPHAD method has been expanded to other phase-based properties, including molar volumes and elastic constants, and has the potential to treat electrical and thermal conductivity and even two-phase properties, such as interfacial energies. Advances in the CALPHAD method or new information on specific systems frequently require that already assessed systems be re-assessed. Therefore, the next generation of CALPHAD necessitates data repositories so that when new models are developed or new experimental and computational information becomes available the relevant low-order (unary, binary, and ternary) systems can be re-assessed efficiently to develop the new multicomponent descriptions. The present work outlines data and infrastructure needs for efficient CALPHAD assessments and updates, highlighting the requirement for data repositories with flexible data formats that can be accessed by a variety of tools and that can evolve as data needs change. Within these repositories, the data must be stored with the appropriate metadata to enable the evaluation of the confidence of the stored data.Keywords: CALPHAD; Thermodynamics; Diffusion; Property data; Data and file repositories; Materials data infrastructure ReviewThe first efforts using computational methods to describe Gibbs energy functions to represent the phases and describe phase equilibria were made more than 60 years ago as reviewed in [1]. However, only after computers became available did these efforts become systematic. In 1970, Kaufman and Bernstein [2] presented a collection of analytical thermodynamic descriptions of the Gibbs energy of the phases of binary and ternary systems as functions of temperature and concentration. These descriptions could be used for the calculation of phase equilibria and thermochemical properties in a large number of systems. This collection established the CALPHAD method as a valuable tool for the treatment of multicomponent a phase equilibria and spawned the development of several software packages and databases with collections of thermodynamic descriptions of multicomponent systems [1]. However, it soon became

OpenCalphad - a free thermodynamic software

“…The properties that are currently implemented by the CALPHAD software and databases are the Gibbs energy, molar volume, diffusion, and precipitation kinetics. However, there are many other physical properties that are phase based, and the approach used by the CALPHAD method is well suited for modeling them [55]. The description of these properties will be most likely tied to the thermodynamic description of the individual phases and for expanding the CALPHAD code to include these properties; the availability of a source code for the calculation of thermodynamics will greatly benefit the efficiency of the new code.…”

The OpenCalphad thermodynamic software interface

“…For example, to consider the diffusion of elements, their mobilities together with the thermodynamic factor need to be described to provide the diffusion coefficient. In addition, there are also interface energies, interface mobilities, elastic constants and other phase-based properties that may be of interest [24]. …”

The Calphad Method and Its Role in Material and Process Development

“…Gheribi and Chartrand [65] proposed a CALPHAD method to predict the thermal conductivity for dielectric and semiconductor phases. Campbell et al [66] presented an extensive review of the modeling of these and other phase-based properties, and showed that the CALPHAD method can even be applied to interphase properties, such as interfacial energies, surface tension of the liquid phase, nucleation, grain boundary diffusion or thermal migration.…”