Mikro deformasyon mekanizmalarının yüksek mukavemetli çeliklerin performansına etkilerinin çok ölçekli modelleme ve deneysel yöntemlerle belirlenmesi

The first aim of the work presented herein is to investigate the composition and temperature dependencies of deformation response of high-manganese austenitic steels under high-velocity tensile, compressive and impact loading scenarios with a focus on micro-scale deformation mechanisms. The promotion of twinning deformation under high-velocity loading over the slip-twin interactions usually observed in low-velocity loading conditions was comprehensively examined with optical microscopy, confocal laser scanning microscopy, scanning electron microscopy and transmission electron microscopy. In addition, thermal analysis of plastic deformation was carried out by in-situ thermal imaging. The current findings clearly demonstrate that the formation of nano-twins within the primary twins constitutes a significant contribution to the strain hardening response of high-manganese austenitic steels. Overall, the current results shed light on the complicated work hardening mechanisms prevalent in high-manganese austenitic steels utilizing high-velocity deformation experiments. The investigation of micro-deformation mechanisms in high-manganese austenitic steels was extended by modeling the contributions of dynamic strain aging on the unique hardening response of this class of steels, as well as hydrogen interstitial effects on hydrogen storage materials. For these purposes, a new multi-scale modeling approach was proposed. Specifically, for dynamic strain aging modeling, a unique hardening model was proposed that can compute the shear stress contribution of carbon atom and incorporates it to the classical Voce hardening. The proposed model is capable of predicting the role of dynamic strain aging and resulting negative strain rate sensitivity on the deformation response of Hadfield steel. For modeling the hydrogen interstitial effects on the overall hardening response of hydrogen storage materials, classical crystal plasticity scheme was modified to account for the shear stress imposed on arrested dislocations due to the surrounding hydrogen interstitials. In order to observe the hydrogen effect experimentally and validate the corresponding model, several tensile tests were conducted to hydrogen-induced samples at a moderate strain rate and at room temperature. The combined experimental and unique modeling effort opens a new venue for predicting the alterations in the performance of metallic hydrogen storage materials, where hydrogen embrittlement is unavoidable.