Fundamental Investigations of the Precipitation Behavior of Fe-25 at%Co-9 at%Mo

Elisabeth Eidenberger

Research output: ThesisDoctoral Thesis

Abstract

The investigated material is an Fe-Co-Mo ternary alloy showing age-hardening behavior similar to hardenable Al-alloys. In this thesis, the precipitation behavior of this alloy as well as the phases accountable for the hardening were studied in detail. Special emphasis was laid on the determination of the mode of decomposition being responsible for the phase separation upon aging. A combination of scattering techniques, calorimetry and direct imaging techniques was employed to thoroughly understand the precipitation reactions in an Fe-25 at%Co-9 at%Mo alloy. Each of the utilized methods has its strengths and weaknesses; their combination and comprehensive comparison yields an optimized output for a copious characterization of the materials microstructure and precipitation behavior. By small-angle neutron scattering (SANS) a macroscopic sample volume is observed to gain information on particle size distribution and volume fraction. In addition, SANS also yields information on the chemistry of precipitates by evaluating the ratio of magnetic to nuclear scattering contrasts. The gained information can be compared to chemistry yielded by, e.g., atom probe (AP) measurements. AP is a powerful method to characterize even early stage phase separations in metallic materials. Additionally, transmission electron microscopy (TEM) and high-resolution TEM illustrate the microstructure of the investigated material and statements on the prevailing crystallography can be made. TEM investigations can also be used to gain knowledge of the chemistry of occurring phases by employing, e.g., energy dispersive X-ray (EDX) analysis. Additional information on the precipitation process is gained by the use of differential scanning calorimetry. It is possible to characterize kinetic parameters and the onset temperature of a phase reaction as well as the temperature of the maximum conversion rate. By introducing, e.g., a Kissinger analysis, the activation energies of the ongoing processes can be found. To complement experimental data, ab-initio calculations based on density functional theory have been used to estimate the magnetic moments of the prevailing intermetallic phases and were applied for the comparison of SANS and AP data.
Translated title of the contributionGrundlegende Untersuchung des Entmischungsverhaltens von Fe-25at%Co-9at%Mo
Original languageEnglish
QualificationDr.mont.
Awarding Institution
  • Montanuniversität
Supervisors/Advisors
  • Dehm, Gerhard, Assessor B (internal)
  • Clemens, Helmut, Assessor A (internal)
Publication statusPublished - 2010

Bibliographical note

embargoed until null

Keywords

  • Small-angle neutron scattering (SANS) Atom probe (AP) Precipitation reactions spinodal decomposition intermetallic phases Fe-Co-Mo alloy

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