Quasi-reversibility of TWIP and TRIP of Fe-17Mn steel during low cycle fatigue

Fatigue life is a critical property of structural materials for ensuring public safety. While the reversibility of deformation mechanisms under cyclic loading can greatly enhance fatigue life, the evolution of this reversibility during continuous fatigue has not received much attention, despite its significant impact. This study used in-situ neutron diffraction to analyze the evolution of multiple deformation mechanisms activated during the early stage of low-cycle fatigue at ±1 % strain amplitudes in fully austenitic Fe-17Mn-0.5C steel. In the steel with near-zero ΔG^γ→ϵ controlled by carbon concentration, the leading partial dislocations move in {111}_γ grains during tension and in {200}_γ grains during compression, creating stacking faults. Under cyclic loading, these mechanisms exhibit reversible stacking faults behavior due to the activation of trailing partial dislocations, ultimately leading to the reversibility of both twinning-induced plasticity and transformation-induced plasticity. As the number of fatigue cycles increases, stacking faults become more prominent, while the contribution from twinning faults diminishes. The pronounced stacking faults cause work hardening at the intersections of newly formed ε-martensite plates and twinned areas, thus accelerating phase transformations that require higher critical resolved shear stresses. However, the negative ΔG^γ→ϵ and increased stability of ε-martensite during fatigue cycles result in a quasi-reversible martensitic transformation behavior with an increase in residual ε-martensite. This work provides insights into enhancing a fundamental understanding of fatigue mechanisms by demonstrating the unusual quasi-reversibility characteristics of high-Mn steel and highlighting its potential as a fatigue-resistant structural material.