Low-cycle and extremely-low-cycle fatigue behaviors of high-Mn austenitic TRIP/TWIP alloys: Property evaluation, damage mechanisms and life prediction

Abstract The cyclic deformation and damage behaviors of the Fe–Mn and Fe–Mn–C TRIP/TWIP steels are comprehensively studied in a wide range of strain amplitude (from 0.3% to 8.0%). It is found that with increasing C content, the dislocation structures change from wavy slip to planar slip after cyclic deformation. In order to evaluate the low-cycle and extremely-low-cycle fatigue (LCF and ELCF) properties, a fatigue life prediction model, N f = ( W a / W 0 ) β , with a hysteresis energy-based criterion is used and developed. The model reveals that the LCF and ELCF damage mechanisms can be controlled by the material's damage capacity (the intrinsic fatigue toughness W 0 ) and its ability of transforming mechanical work into effective damage (the damage transition exponent β ). From a macroscopic point of view, W 0 is related to the match of strength and ductility (approximately the static toughness U ), and β mainly has a negative correlation with the cyclic strain hardening exponent n ′. On the micro-scale level, W 0 represents the defect-accommodated ability of the materials, and β is determined by the uniformity and reversibility of plastic deformation. For the current Fe–Mn(–C) TRIP/TWIP steels with increasing C content, the cooperation between an increasing damage capacity and an incremental damage accumulation rate leads to a higher ELCF property and a lower LCF property.