Microstructure of Fe-Ni Meteorites

Fe – Ni Meteorites

  • Ni ranges from 4.3 to 34% (few >20%)
  • Cobalt present, 0.4 –1%
  • Sulfur <0.6%
  • P <0.3%
  • C <0.2%
  • Small amounts of other elements

Fe – Ni Meteorites

Three Basic Types:

  • Hexahedrites–Single Crystals, Ni is usually 5.2 –5.8%
  • Octahedrites–Long Ferrite (Kamacite) grains, usually 5 –10% Ni
  • Ataxites–No Gross Macrostructure, usually 15-18% Ni
  • Anomalous types

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Metallography of Iron Meteorites

This article describes the microstructures of the various meteorite types, lists the minerals typically found in them, explains color etching techniques, and describes the metallography of the Odessa and Coahuila meteorites.

Meteorites are grouped into three basic types: stones, stony irons, and irons. Within these groups, the classification of meteorites is a complex subject.
For the iron meteorites, classification is based upon chemical composition, macrostructure, and microstructure. Basically, iron meteorites fall into
three categories – hexahedrites, octahedrites and ataxites. However, some do not fully fit the requirements of these categories and are classified as
anomalous

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Metallographic Techniques for Iron Meteorites

A note on Metallographic Techniques for Iron Meteorites

Meteorites are particularly fascinating subjects for metallographic examination, not merely because of their extraterrestrial origin, but also because of the rich variety of microstructural constituents encountered. While their structure can be assessed use of the familiar nital and picral etchants used extensively for steels, application of selective etchants, including those that produce selective coloration, greatly increases the amount of information
obtained by light microscopy. The article describes efforts to preferentially darken or color microstructural constituents in iron meteorites: kamacite (ferrite), Neumann bands (mechanical twins), taenite (austenite), cohenite (Fe-Ni carbide similar to cementite), martensite and schreibersite/rhabdite (Fe-Ni phosphides). The influence of concentration gradients, deformation, and reheating on the structure can be clearly observed by the use of tint etchants.

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resourcesThe articles and presentations that can be down-loaded from this web site are based upon work done by GFV while employed at Bethlehem Steel (1967-1983), Carpenter Technology (1983-1996), Buehler Ltd. (1996-2009) and Struers (2009-Present) and from the authors consulting work for companies such as, Latrobe Steel, Scot Forge, etc., and from his litigation work. GFV's bylined articles appearing in various issues of the ASM Handbook series have been listed here courtesy of ASM International, Materials Park, Ohio.

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