FCC stacking fault energies from diffraction depend on orientation

Abstract

Stacking fault energy (SFE) critically affects twinning and martensitic transformation in FCC metals. As an intrinsic parameter, it is expected to remain constant under various testing conditions at the same temperature. The widely used Reed-Schramm method estimates SFE from stacking fault probability (SFP) and root mean square (rms) microstrain in deformed metals. In this study, synchrotron high-energy X-ray diffraction was used to evaluate the SFP and rms microstrain in a tensile-deformed TWIP steel. The SFP showed a strong correlation with grain orientation, whereas rms microstrain was relatively orientation-insensitive. These parameters yielded orientation-sensitive measured SFE (mSFE) values ranging from 4 to 30 mJ/m², correlating with the developed [111]//LD (low mSFE) and [100]//LD (high mSFE) texture components. Transmission electron microscopy further revealed microstructural differences, with dense, highly extended stacking faults in [111]//LD grains but few in [100]//LD grains. These findings highlight the limitations of diffraction-based experimental strategies in determining the SFE.