Microstructural characterization to reveal evidence of shock deformation in a Campo del Cielo meteorite fragment

TL;DR

This study uses electron microscopy to analyze microstructures in a Campo del Cielo meteorite, revealing new evidence of shock deformation mechanisms like Neumann bands and microbands, which enhance understanding of shock effects in iron meteorites.

Contribution

It provides the first detailed microstructural evidence of multilayer twinning and microband formation in a BCC meteorite, linking these features to shock deformation processes.

Findings

High-intensity pattern doubling at twin-twin intersections

Microband formation along {110} planes near Neumann bands

Coexistence of Neumann bands and microbands in a BCC meteorite

Abstract

The study of meteorites and their microstructures is a topic which spans multiple fields of research, such as meteoritics and materials science. For materials scientists and engineers, the extreme and unusual conditions which these microstructures form allow for insight into materials which would exist at the edge of our thermomechanical processing abilities. One such microstructure found in low-shock event iron meteorites is Neumann bands. These bands are an array of lenticular deformation twins that form throughout the Fe-Ni matrix with numerous intersections, resulting in many high stress and strain regions within the material's surface. The existence of these regions and the shocks that formed them encourage atypical strain accommodating mechanisms and structural changes of the material. However, direct investigation of the deformation twin intersections and the microstructural behaviour in and around these regions has been limited. In this work, investigation of these regions in a Campo del Cielo meteorite fragment, with electron backscatter diffraction (EBSD) and forescatter electron (FSE) imaging, revealed two primary findings: high-intensity pattern doubling mirrored across the {110} band at twin-twin intersection and microband formation across the sample surface, which suggest multilayer twinning and constraint of the crystal structure at points of twin-twin intersection. Microbands were found to form along the {110} plane and in regions near Neumann bands. The simultaneous existence of Neumann bands (microtwins) and microbands is presented here for a BCC material, and it is believed the Neumann band and microbands formed during different types and/or shock events. The presence of both Neumann bands and microbands within a BCC iron meteorite is previously unreported and may be valuable in furthering our understanding of shock deformation within iron-based materials.