Split and Shift of ε-martensite Peak in an X-ray Diffraction Profile during Hydrogen Desorption: A Geometric Effect of Atomic Sequence

Abstract

Cryogenic X-ray diffraction measurements demonstrated a split of the ε-martensite peak at 193 K in a hydrogen-charged austenitic steel. Only the higher angle peak remained after aging at room temperature. This phenomenon can be interpreted by a change in the interstitial hydrogen position. Particularly, the motion of the leading partial involved in ε-martensitic transformation can move interstitial hydrogen from a tetrahedron to an octahedron site, expanding the lattice. Subsequently, the hydrogen can move back to the tetrahedron site, which relatively shrinks the lattice. The two different hydrogen positions cause the peak to split.