STUDY OF HYDROGEN EMBRITTLEMENT MECHANISM IN STEEL USING DENSITY FUNCTIONAL THEORY AND MOLECULAR DYNAMICS SIMULATION

• Main Author: Budiantono, Reva
• Format: Final Project
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/81474
• Institution: Institut Teknologi Bandung

Currently, the most economically beneficial hydrogen storage in industry is compressed hydrogen storage using cylinder made of metal such as steel. The most frequently encountered damage to this cylinder is hydrogen embrittlement. In order to studying the mechanism in details, down to the atomic scale, computational studies have been conducted using density functional theory simulation with VASP and molecular dynamics simulation with LAMMPS. The polycrystalline structure of pure iron is modeled through a Symmetric Tilt Grain Boundary or STGB ?3 (11 ?2 ?). Steel is modeled by doping carbon and manganese elements into the STGB structure. Through the theory of Hydrogen-Enhanced Decohesion Emission or HEDE embrittlement mechanism, hydrogen embrittlement study can be carried out in three stages: hydrogen trapping, hydrogen difussion, and hydrogen accumulation effects. This study found that hydrogen can be stably trapped in the octahedral sites at a distance of 0.6 - 2 Å from the STGB plane. It has been proven that addition of carbon facilitates hydrogen trapping, but not specifically at particular sites. The addition of manganese was also proven to ease hydrogen trapping. Hydrogen can diffuse accros pure iron STGB with an activation energy of 1.20 eV. It has been proven that carbon and manganese facilitates hydrogen difussion with activation energies of 0.09 eV and 1.11 eV, respectively. Once diffused and trapped, hydrogen can accumulate and cause damage. Hydrogen has been proven to reduce the separation work and increase embrittlement potential. Through uniaxial tensile test simulations, it was found that 100 wppm hydrogen can reduce the maximum tensile stress more than 1.1 GPa. This study has investigated hydrogen embrittlement, but more comprehensive methods and simulation models are needed. Keywords: hydrogen trapping, hydrogen diffusion, hydrogen accumulation, steel, density functional theory, molecular dynamics