Effect of Cr Segregation on Grain Growth in Nanocrystalline {\alpha}-Fe Alloy: A Multiscale Modelling Approach

TL;DR

This study develops a multiscale modeling framework combining DFT and phase-field methods to investigate how Cr segregation influences grain growth in nanocrystalline { extalpha}-Fe, revealing temperature-dependent deviations from classical growth laws.

Contribution

It introduces a novel multiscale approach integrating DFT and phase-field modeling to analyze Cr segregation effects on grain growth in nanocrystalline { extalpha}-Fe.

Findings

Cr segregation causes deviations from linear grain growth at high temperatures.

The threshold grain size decreases with increasing temperature.

Analytical predictions based on Cahn solute drag align with simulation results.

Abstract

We present a multiscale modelling framework that integrates density functional theory (DFT) with a phase-field model (PFM) to explore the intricate dynamics of grain growth in nanocrystalline {\alpha}-Fe single-phase alloy in the presence of chromium (Cr) segregation. We begin our study by validating our simulation results for equilibrium segregation in stationary GB with Mclean isotherm. Polycrystal simulations featuring nanocrystalline grains at different temperatures reveal that the grain growth kinetics depends on the ratio of Cr diffusivity to intrinsic GB mobility. In the absence of segregation, the relationship between the square of average grain size (d 2 ) and time (t) demonstrates a linear correlation. We observe that the d 2 vs. t plot exhibits a consistent linear trend up to a threshold grain size, independent of Cr segregation at GB. However, when Cr is segregated at GB, a deviation from this linear trend with a decreasing slope is evident within the temperature range of 700K to 900K beyond the threshold size. This threshold grain size decreases with increasing temperature. Notably, at 1000K, the deviation from the linear trend is observed from the initial stages of grain growth with segregation, albeit with a linear trend exhibiting a smaller slope. We also present an analytical formulation based on Cahn solute drag theory to predict grain growth behaviour in the presence of solute segregation and our simulation results well aligned this analytical formulation.