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In situ Solute and Grain Character Mapping of Nanocrystalline Alloys at Elevated Temperatures using Sub-Second Heating Capability

Descriptive Note:

[Technical Report, Final Report]

Corporate Author:

University of Alabama - Tuscaloosa

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Two nanocrystalline alloys of Fe-4Cr and Fe-16Cr were sputter deposited and formed a solid solution A2 phase. Each alloy was then in situ annealed up to 800 deg C with the phase and microstructure quantified by transmission electron microscopy TEM. The low partial pressure of oxygen in the TEM column 2.6 10expn -6Pa oxidized both films at temperatures at and above 700 deg C. However, the oxide morphologies were quite different. The Fe-4Cr revealed nanosphere Cr oxide clusters within the grains which has been explained by the thermodynamic preference for Cr to be in solution. The Fe-16Cr precipitated distinct Cr2O3 grains which has been described by Cr phase separation at the grain boundaries. Iron oxide was not observed and demonstrating Crs strong preference for oxygen, even in very low oxygen environments. Using precession electron diffraction PED, the grain characters of these boundaries were determined revealing a significant effect of high angle grain boundaries on the growth and precipitation behavior of the oxides. The collective results reveal the initial stages of oxidation evolution in nanocrystalline grains, the role of Cr content on such behavior.

Subject Categories:

  • Properties of Metals and Alloys
  • Crystallography
  • Thermodynamics

Distribution Statement:

[A, Approved For Public Release]