In Situ Bulk Observations and Ab Initio Calculations Revealing the Temperature Dependence of Stacking Fault Energy in Fe\u2013Cr\u2013Ni Alloys

Abstract

The dependence of stacking fault energy ({gamma }_{text{SFE}}) on temperature in austenitic Fe–Cr–Ni alloy powders was investigated by in situ high energy synchrotron X-ray diffraction and ab initio calculations in the temperature range from − 45 °C to 450 °C. The X-ray diffraction peak positions were used to determine the stacking fault probability and subsequently the temperature dependence of γSFE. The effect of temperature on the diffraction peak positions was found to be mainly reversible; however, recovery of dislocations occurred above about 200 °C, which also gave an irreversible contribution. Two different ab initio-based models were evaluated with respect to the experimental data. The different predictions of the models can be explained by their respective treatment of the magnetic moments for Cr and Ni, which is critical for the alloy compositions investigated. Ab initio calculations, taking longitudinal spin fluctuations (LSF) into consideration within the quasi-classical phenomenological model, predict a temperature dependence of {gamma }_{rm SFE} in good agreement with the experimentally evaluated trend of increasing γSFE with increasing temperature: left|Updelta {gamma }_{rm SFE}/Updelta Tright|=0.05 {text{mJ}} {text{m}}^{-2}/{text{K}}. The temperature effect on γSFE is similar for all three investigated alloys: Fe–18Cr–15Ni, Fe–18Cr–17Ni, Fe–21Cr–16Ni (wt pct), while their room temperature {gamma }_{rm SFE} are evaluated to be 22, 25, 20 mJ m−2, respectively.