First-principles calculation of bonding and hydrogen trapping mechanism of Fe3C/α-Fe interface

The Fe3C/α-Fe interface in pearlite is the main hydrogen trapping site. The first-principles calculation method based on density functional theory was employed to investigate the bonding and hydrogen trapping mechanism of the Fe3C/α-Fe interface with three different orientation relationships, specifically the Bagaryatsky orientation, Isaichev orientation, and Pitsch-Petch orientation. The results showed that by calculating the interface energy and separation work, the theoretical bonding strength and stability of the three interfaces presented the following order: Isaichev orientation > Pitsch-Petch orientation > Bagaryatsky orientation. Hydrogen segregation energy revealed that H atoms were more likely to be trapped at the Fe3C/α-Fe interface region and the hydrogen trap ability of three interfaces was in the following order: Isaichev orientation > Pitsch-Petch orientation > Bagaryatsky orientation. The maximum absolute value of segregation energy was found at the interface with Isaichev orientation, which was 0.38 eV. The differential charge density, density of states, and Mulliken bond population calculations revealed that the formation of the interface was related to the covalent bond between C atoms in cementite and Fe atoms in ferrite, and affected by the spatial distribution of C atoms. The C atoms also repelled the H atoms, so the strength of H–Fe bond was identified as the dominant factor of hydrogen trapping behavior. Overall, these insights can potentially aid in improving the design and performance of materials with pearlite structures.