A critical assessment has been performed to determine the stacking fault energy (SFE) of the austenite phase in high manganese steels using X-ray diffraction (XRD). It was found that the SFE varies substantially with the chosen elastic constants. This strong dependence induces substantial errors in the estimated values of the SFE of the austenite and, thus, the mechanical behavior of Fe-Mn-Al-C steels. The SFE of three different Fe-Mn-Al-C alloys with varying aluminum (Al) content was determined in order to establish the main plastic deformation mechanism. The aim of this work is to establish a more straightforward and reliable methodology to calculate the SFE by XRD. In this effort, it was determined that uncertainty in the elastic constants can generate errors in up to 37% of the SFE. Moreover, in the studied case, for average of elastic constant values, the predominant deformation mechanism is defined, but when considering one set of constants, these can present uncertainty of 2.7 mJ/m² and 4.4 mJ/m² for alloys of 0% Al and 3% Al, respectively. This would lead them to be within the following plastic deformation mechanism, while for 8% Al the uncertainty is negligible.

This study explores the cyclic elastoplastic deformation behavior of an Fe–Mn–Al–C alloy at room temperature by employing load-controlled nanoindentation with a Berkovich indenter, offering new insights into the competition between plastic and elastic energy. The dynamic nanoindentation tests were conducted with load ratios $$\left(R= {P}_\text{min}/{P}_\text{max}\right)$$ R = P min / P max ranging from 0 to 0.5 for 100 and 200 mN, considering 50, 300 and 500 loading cycles. Results revealed that at the maximum depth, the elastic (E _e) and plastic (E _p) energy remains constant, whereas the ability to absorb E _p decreases by approximately 1.4 and the E _e decreases by approximately 1.5 when R varies from 0 to 0.5. Additionally, the relationship between E _e and E _p is ~ 2 times regardless of the load or number of load cycles. The occurrence of pop-ins at low loads suggests potential interactions between dislocations and twins, given the austenitic nature of the alloy with a low stacking fault energy (SFE). Creep behavior was analyzed at loads ranging from 1 to 10 mN with a holding time of 30 seconds. The creep rate increases with increasing load and holding time, suggesting that at the macroscopic scale, the strain rate affects the strain hardening rate.

The fatigue response by applying cyclic loads on individual grains using monotonic and cyclic nanoindetation to analyze the effect on load or displacement control in an austenitic Fe-20Mn-3Al-09C alloy were analyzed. The material response to the cycles considering the load control and the displacement control to properties such as hardness, elastic's modulus, and contact stiffness, was studied by analyzing the load-unload curves (P-h). The material softening Analysis showed that these properties decrease with increasing cycles due to the activation of deformation mechanisms. The elasticity's Modulus and hardness values for monotonic loads in load control presented values close to those reported in the literature. On the other hand, in displacement control, the values were lower. In load and displacement control mode, the first two cycles presented no overlap between unloading and loading between cycles, due to large irreversible plastic deformation and low elastic recovery after unloading. In the subsequent cycles, overlaps between the hysteresis curves were predominant, due to the activation of the deformation mechanisms.