The Formation of Ferrite in Iron-Nickel Meteorites

Open Access
Author:
DeFrain, Raymond Matthew
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
November 11, 2008
Committee Members:
  • Paul Raymond Howell, Thesis Advisor
Keywords:
  • Widmanstatten
  • meteorites
  • iron-nickel
  • ferrite
  • austenite
Abstract:
The iron-nickel meteorites we find on Earth represent cores of planets, which have formed billions of years ago, but more importantly allow the researcher to view a metallographic sample which has cooled like no other terrestrial steel. The cooling rate of meteorites, from their initial liquid metal state to an ambient temperature has occurred on the order of 1 °C per million years. This heat treatment creates an alloy which nears the thermodynamic equilibrium, which our theories predict. Therefore, meteorites are ideal specimens for the researcher and metallurgist to study alike, considering their alien, near-optimal, inherent phase transformations. In this thesis, the Cape York, Henbury, and Brenham meteorites are studied in an attempt to characterize the structures found within each sample. Moreover, many forms of ferrite are described within this report and may act as argument points as to multimodal ferrite nucleation. Finally, nucleation and growth methods of Widmanstätten ferrite are discussed as crystallography and morphology are used as guidelines to base our assumptions. Characterization methods used in this study include light microscopy, scanning electron microscopy, energy dispersive spectroscopy, electron probe micro-analysis, and orientational imaging microscopy.