Possibilities of hydrogen atom trapping in steels by ferrite / cementite interfaces. 1. Crystal geometry analysis

A simple crystal geometry analysis of matching of ferrite and cementite lattices at a coherent interface with Bagaryatski type orientation relationship is carried out. The best lattice matching is provided when the interface plane (101) c consists of iron atoms in S type positions. If atom locations in both lattices are supposed to remain unchanged, then some tetrahedral interstitial sites near the interface become distorted, and their radius increases 1.5 times. An assumption is made that such distorted tetrahedral sites may act as trap sites for hydrogen atoms. Surface density of these sites is 6.610 14 cm -2. The structure of the interface and possible trapping sites for hydrogen have to be refined further by ab initio modelling.