Application of Ab Initio Electronic Structure Calculations in Construction of Phase Diagrams of Metallic Systems with Complex Phases

Abstract

Ab initio electronic structure theory has achieved considerable reliability concerning predictions of physical and chemical properties and phenomena. It provides understanding of matter at the atomic and electronic scale with an unprecedented level of details and accuracy. In the present contribution, the electronic structure theory and state-of-the-art ab initio calculation methods in solids are briefly reviewed and the application of the calculated total energy differences between various phases (lattice stabilities) is illustrated on construction of phase diagrams by the CALPHAD (CALculation of PHAse Diagrams) method in systems containing phases with complex structures, as e.g. Laves phases or sigma phase. Particular examples include description of the Laves phases in the Cr-Nb, Cr-Ta and Cr-Zr systems, sigma-phase in the Fe-Cr system and prediction of the phase composition of ternary Fe-Cr-Mo system and super-austenitic steels. It is shown that the utilization of ab initio results introduces a solid basis of the energetics of systems with complex phases, allows to avoid unreliable estimates and extrapolations of Gibbs energies and brings more physics into the CALPHAD method.

Atomistic Modeling‐Based Design of Novel Materials

“…), [31,63,68,159,160,176,179,[210][211][212][213][214][215] and 4) high-throughput search for novel materials [13,[215][216][217][218][219][220][221] using databases such as aflowlib.org, [222] oqmd.org, [223] nomadrepository.eu, aiida.net, [224] or materialsproject.org [225] which can be efficiently accessed by their own online interfaces or Python libraries, for example, pymatgen. [226] For efficient implementation of points 2) and 3) it is envisioned that a multimethod/multiscale approaches, [9,48,162,163,169,[227][228][229][230][231] combining DFT, atomistic, and continuum modeling will be essential. Our group at the Montanuniversitaẗ Leoben together with its collaborating partners has been devoted to contribute substantially to this challenging and exciting research.…”

“…Note that for strongly correlated materials such as CrN, a standard GGA approximation turns out to be insufficient. [142,[169][170][171][172][173] A recently developed TNM alloy, [174,175] which is already in service, proves CALPHAD as a useful design tool for novel advanced structural materials with targeted microstructures. In fact, the GGA þ U predicted temperature is T N ¼ 300K, [37] being close to the experimentally reported value of 280K.…”

“…[168] Latest advances in this direction have been summarized in a series of review papers. [142,[169][170][171][172][173] A recently developed TNM alloy, [174,175] which is already in service, proves CALPHAD as a useful design tool for novel advanced structural materials with targeted microstructures.…”

First-Principles Calculations and CALPHAD Modeling of Thermodynamics

“…For nonstoichiometric compounds with more than one type of Wyckoff positions, lattice stability from first-principles calculations has been used without detailed discussions on the instability issue. [35][36][37][38][39] This paper aims to give an overview on the CALPHAD modeling and first-principles calculations based on our research activities in the past several years. It is organized as following.…”

Application of Ab Initio Results in Modeling Phase Diagrams Containing Complex Phases

“…2 shows two phase diagrams of Fe-Cr system calculated using two different models in the region of existence of the sigma phase. It may be seen that our new two-sublattice model (13) incorporating ab initio results exhibits a better agreement with experimental data (24) than the old three-sublattice approach (not employing ab initio results).…”