The Nature of Ferrite in Iron-Nickel Meteorites

Open Access
Author:
Dasgupta, Prateek
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 27, 2011
Committee Members:
  • Paul Raymond Howell, Thesis Advisor
Keywords:
  • Iron-Nickel Meteorites
  • Three Dimensional Reconstructions
  • Ferrite
Abstract:
Iron-Nickel meteorites formed billions of years ago, and have undergone near- equilibrium phase transformations due to their extremely slow cooling rate (- ̃1°C per million years). This presents an interesting case study for a metallurgist since no terrestrial alloy can replicate this cooling rate. In this thesis, for the first time a definite link between iron-nickel meteorites and their terrestrial counterparts, steels have been forged in terms of crystallography , morphology and nucleation of ferrite found in both. Various microstructural features found in the Cape York meteorite are discussed, concentrating on the various forms of ferrite. Three dimensional reconstructions of ferrite have permitted us to make important conclusions on its morphology and crystallography, which forms the backbone of this thesis. Various forms of ferrite observed in iron-nickel meteorites are distinguished on the basis of their hardness values. Finally, the nucleation of various forms of ferrite in the Cape York and Odessa meteorites, with particular importance to the role of ceramic inclusions found in both; is investigated. While investigating the role of inclusions in the nucleation of ferrite, a link between steels and meteorites is once again forged as we try to ascertain the similarities in the ferrite found in each. Energy dispersive spectroscopy was used to investigate the inclusion chemistry in order to evaluate their role in the nucleation of ferrite. Finally, a model for the formation of Widmanstatten ferrite is presented.