ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

Influence of central d-band elements: mobility, segregation, and interaction with defects in Ni-base superalloys

Our project focuses on improving the understanding of the role of refractory elements in the context of Ni-based superalloys. The beneficial effect of these alloying additives on the high-temperature alloy properties is well-documented, however not yet thoroughly understood from a microscopic point of view. Gaining further insight into the underlying mechanisms would prove beneficial for future alloy design and fine-tuning.

A proper description of the diffusion and segregation processes across the interface between the γ' precipitates and the γ matrix is a main point of this overarching goal. Our approach is based on a combination of precise density functional theory (DFT) calculations and the kinetic Monte Carlo (kMC) technique for describing time and temperature dependent diffusion and long-term system behaviour.

Schematic of the combined DFT/kMC approach for simulation of diffusion processes. Diffusion barriers calculated by DFT enter the kinetic Monte-Carlo simulations as input parameters. The kMC simulations in turn provide access to macroscopic system properties such as diffusion-coefficients and segregation profiles.

The fundamental building blocks of the kMC approach are the individual diffusion barriers for all relevant processes within the system. These, in their entirety, determine the time evolution of the system. Within our method, the first step consists of creating a systematic catalogue of these environment-dependent barriers using density functional theory in combination with the nudged elastic band (NEB) technique.

Given a complete description of the barriers the kMC algorithm provides access to the time dependent behaviour of the system. Since only the rare diffusion events are taken into account on this simulation level, the accessible time-scales are on the order of seconds. From these simulations macroscopic properties such as diffusion coefficients and segregation profiles can be extracted and compared with experimental findings.

As such, our approach combines the precision of density functional theory with the efficient diffusion description of the Monte Carlo method. With this, we aim at a comprehensive and systematic treatment of the various alloying elements relevant for Ni-based superalloy development and manufacture.

This project is a part of the SFB/Transregio 103 Superalloy Single Crystals.

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