ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

The influence of light elements on precipitates of complex phases in steel

Refractory elements are necessary additions in powder metallurgy steels because they contribute to the enhancement of their creep and wear resistance at elevated temperatures. These elements exist either in solid solution phase or form carbides, which altogether account for their remarkable effect. At high enough concentrations of refractory elements, topologically close-packed (TCP) phases phases may form in the material during service. These phases are generally brittle and so their presence compromises the integrity of the steel. In addition, the formation of TCP phases leads to the depletion of refractory elements in the matrix resulting in reduced strengthening effect. These undesirable characteristics raise the need for a fundamental understanding of these complex phases to be able to predict their behavior in various systems.

C14 Laves structure showing one of the Frank-Kasper polyhedra characterizing topologically close-packed phases.

Simulation of complex phases is a challenging task to perform at the electronic structure level given the large number of atoms required even for the simplest configurations. On one hand, empirical potentials which find extensive use in large-scale molecular dynamics simulations lack the accuracy and transferability needed to tackle the problem of complex phases. In this project, we take a multi-scale modelling approach to gain an understanding of the impact of topologically close-packed phases in steel and the subsequent effect of light elements. This starts by probing the electronic structure at the level of density functional theory, the results of which will serve as the basis for the development of bond-order potentials (BOPs). BOPs are a simplified description of the electronic structure and a compromise between the computational demand and accurate electronic structure calculations and the limited transferability of simple empirical potentials. This allows us to simulate large systems that approach realistic microstructure.

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