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.
Highlights
The active deformation mechanism in the austenite phase critically controls the deformation properties of many advanced steels with the martensitic transformation being responsible for the transformation-induced plasticity (TRIP) effect, while twinning is responsible for the twinning-induced plasticity (TWIP)
The variation of the stacking fault probability was measured in a temperature range from À 45 °C to 450 °C, and directly correlated to the temperature dependence of cSFE: All three studied Fe–Cr–Ni alloy compositions show a similar temperature behavior
A linear increase of cSFE with increasing temperature of jDcSFE=DTj 1⁄4 0:05 mJmÀ2=K was observed between À 45 °C and 250 °C, whereas above 250 °C an irreversibility effect was observed
Summary
PLASTIC deformation of materials with the face-centered cubic (fcc) structure occurs by one of three possible mechanisms: deformation-induced martensitic transformation, twinning or dislocation glide.[1,2,3] The active deformation mechanism in the austenite phase critically controls the deformation properties of many advanced steels with the martensitic transformation being responsible for the transformation-induced plasticity (TRIP) effect, while twinning is responsible for the twinning-induced plasticity (TWIP)Manuscript submitted May 31, 2021; accepted September 26, 2021. It is known that the stacking fault energy (cSFE), basically determining the width of stacking faults in fcc materials and the ease of cross-slip, etc., is a key parameter to control the deformation mechanism of austenite. Since the magnitude of cSFE depends among others, on the chemical composition of the alloy, deformation behavior can be tuned by adjusting the chemical composition. This indicates that it is highly desirable to understand the effect of alloying elements (individual and collective effects) on cSFE. Another important effect on cSFE is the temperature effect. This becomes important in forming operation and in service at elevated temperatures, which could potentially change the active deformation mechanism
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