The impact of alloying elements on the precipitation stability and kinetics in iron based alloys: An atomistic study

TL;DR

This study uses atomistic simulations to understand how different alloying elements affect the stability and formation of clusters in iron-based alloys, which influence their mechanical properties under irradiation.

Contribution

It provides a detailed atomistic analysis of how specific alloying elements impact cluster stability and precipitation kinetics in Fe-based alloys, using DFT and kinetic Monte Carlo methods.

Findings

Mn and Ni delay precipitation kinetics by an order of magnitude.

Trace P and Si further slow down cluster formation.

Si is crucial for forming mixed MnNiCuSi clusters.

Abstract

Iron based industrial steels typically contain a large number of alloying elements, even so-called low alloyed steels. Under irradiation, these alloying elements form clusters that have a detrimental impact of the mechanical properties of the steel. The stability and formation mechanisms of such clusters are presently not fully understood. Therefore, in this work, we study the thermal stability and formation kinetics of small solute clusters in the bcc Fe matrix. We use density functional theory (DFT) to characterize the binding energy of vacancy/solute clusters containing Cr, Mn, Ni, Cu, Si and P, thereby exploring>700 different configurations. The constructed DFT data base is used to fit a cluster expansion (CE) for the vacancy-FeCrMnNiCuSiP system. In turn, the obtained CE is applied in atomistic kinetic Monte Carlo simulations to study the effect of Mn, Ni, Cr, Si and P on the precipitation formation in the FeCu alloy. We conclude that the addition of Mn and Ni delay the precipitation kinetics by an order of magnitude. The additional alloying with traces of P/Si further delays the kinetics by an additional order of magnitude. We found that Si plays an essential role in the formation of spatially mixed MnNiCuSi cluster.