Reversible twinning and detwinning in TWIP steel under cyclic tensile loading: In situ synchrotron X-ray diffraction

Twinning-induced plasticity (TWIP) steels exhibit exceptional combinations of strength and ductility due to the activation of deformation twinning in the FCC austenite matrix. While the formation of deformation twins during monotonic deformation has been widely studied, the reversibility of twin-related defects during cyclic tensile loading and its influence on cyclic stability remain insufficiently understood. In this study, a high-Mn twinning-induced plasticity (TWIP) steel is investigated using in situ high-energy synchrotron X-ray diffraction during continuous cyclic tensile loading under two strain amplitudes over a wide temperature range (173–523 K). Time-resolved single-shot diffraction measurements enable quantitative tracking of stacking fault energy, twin fault probability, dislocation density and texture during deformation. The results reveal partially reversible evolution of faulted microstructures during cyclic tensile loading, indicating repeated activation of twinning and detwinning processes mediated by Shockley partial dislocations. Cyclic variations in stacking and twin fault probabilities demonstrate that twin boundary migration occurs dynamically during tensile cycling even in the absence of compressive load reversal. The degree of reversibility is strongly influenced by cyclic strain amplitude and temperature, which govern the relative contributions of dislocation slip, mechanical twinning, and limited FCC-to-HCP transformation. Enhanced twinning activity at lower temperature or higher cyclic strain leads to pronounced cyclic fluctuations in defect density and texture evolution. The present time-resolved diffraction approach provides new experimental insight into the micromechanical origins of cyclic stability in low stacking fault energy austenitic alloys and highlights the role of reversible twinning and detwinning processes in governing their deformation behaviour.