Speaker
Description
We performed a quantum-mechanical molecular-dynamics (MD) study of Fe$_{3}$Al with and without hydrogen atoms under conditions of uniaxial deformation up to the point of fracture. Addressing a long-lasting problem of hydrogen-induced brittleness of iron-aluminides under ambient conditions, we performed our density-functional-theory (DFT) MD simulations for T = 300 K (room temperature). Our MD calculations include a series of H concentrations ranging from 0.23 to 4 at. % of H and show a clear preference of H atoms for tetrahedral-like interstitial positions within the D0$_{3}$ lattice of Fe$_{3}$Al. In order to shed more light on these findings, we performed a series of static lattice-simulations with the H atoms located in different interstitial sites. The H atoms in two different types of octahedral sites (coordinated by either one Al and five Fe atoms or two Al and four Fe atoms) represent energy maxima. Our structural relaxation of the H atoms in the octahedral sites lead to minimization of the energy when the H atom moved away from this interstitial site into a tetrahedral-like position with four nearest neighbors representing an energy minimum. Our ab initio MD simulations of uniaxial deformation along the ⟨001⟩ crystallographic direction up to the point of fracture reveal that the hydrogen atoms are located at the newly-formed surfaces of fracture planes even for the lowest computed H concentrations. The maximum strain associated with the fracture is then lower than that of H-free Fe$_{3}$Al. We thus show that the hydrogen-related fracture initiation in Fe$_{3}$Al in the case of an elastic type of deformation as an intrinsic property which is active even if all other plasticity mechanism are absent. The newly created fracture surfaces are partly non-planar (not atomically flat) due to thermal motion and, in particular, the H atoms creating locally different environments.
Acknowledgement
The authors acknowledge the Czech Science Foundation for the financial support received under the project No. 20-08130S. Computational resources were provided by the Ministry of Education, Youth, and Sports of the Czech Republic under projects e-INFRA CZ (ID:90140) at the IT4Innovations National Supercomputing Center and e-Infrastruktura CZ (e-INFRA LM2018140) at the MetaCentrum as well as the CERIT-Scientific Cloud (project No. LM2015085), all granted within the program Projects of Large Research, Development, and Innovations Infrastructures. M.F. and M.Š. acknowledge the support provided by the Czech Academy of Sciences (project No. UFM-A-RVO:68081723).
