Neutron diffraction pole figure measurements on iron meteorites

Abstract

Neutron diffraction pole figures were measured on three iron-nickel meteorite samples, the hexahedrites Coahuila and Walker County, both belonging to group IIA, and the octahedrite Gibeon, group IVA. As expected, pole figure peaks of the hexahedrites can be assigned to reflections from a single crystal or to reflections due to twinning on {221}. Macroscopically visible fractures in Walker County sample can be recognized in the pole figures by peak splitting and broadening. Schreibersite pole figures of the Coahuila meteorite corroborate the orientation relationship between prismatic rhabdites and kamacite {110} Rh ' {210} α, <001> Rh ' <100> α). For the octahedritic specimen, taenite pole figures reveal that taenite rims have the orientation of the parent γ-phase crystal. By the kamacite pole figures we deduce the orientation between kamacite lamellae and taenite rims to be close to Nishiyama-Wassermann relationship ({110} α ' {111} γ, <001> α ' <1̄10> γ). Variant selection occurs with the kamacite crystals, and suggests the presence of strain during kamacite growth.