Unveiling the Mechanism of Cyclic Indentation in a Fe–Mn–Al–C Alloy

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 (R= Pₘin/Pₘax) 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.