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Dissertation/Thesis Abstract

The Temperature Dependence of Grain Boundary Complexion Transitions and Their Effect on the Grain Boundary Character and Energy Distributions
by Kelly, Madeleine N., Ph.D., Carnegie Mellon University, 2017, 186; 10604582
Abstract (Summary)

Abrupt changes in grain boundary energy (GBE) and character are associated with a change in GB complexion, GB mobility and exaggerated grain growth. In this thesis, complexion transitions and their effect of relative GBE and GB character distributions (GBCD) are studied for ceramics: europium doped spinel (Eu doped spinel), yttria doped (Y-doped), undoped alumina (Al 2O3), and strontium titanate (SrTiO3).

The population of GB planes (GBPD) of Eu doped spinel was investigated at temperatures before and after a previously identified a complexion transition. The microstructure changed from unimodal (1400 °C) to bimodal (1600 °C) and the relative area of {111} increased. This information was used to understand the GBs involved in the transition.

Atomic force microscopy was used to measure relative GBE from thermal grooves on the surfaces of Al2O3, 100 ppm Y-doped Al 2O3, and 500 ppm Y-doped Al2O3 heated between 1350 °C and 1650 °C. The relative GBE of Al2O 3 decreased slightly with increased temperature. When the doped samples were heated, there was an overall increase in the relative GBE, interrupted by abrupt reductions (increases) in relative GBE (mobility) between 1450 °C and 1550 °C. When the 100 ppm Y-doped sample was cooled, there was an increase in the relative GBE at the same complexion transition temperature, indicating that the transition is reversible.

Relative GBE was measured from thermal grooves on (SrTiO3 in a region of non-Arrhenius grain growth. Between 1350 °C and 1390 °C, an abrupt decrease in relative GBE and exaggerated grain growth indicated that a complexion transition occurred. Solidified liquid eutectic wet the boundaries at 1550 °C so these GB interfaces could not be compared to the lower temperatures.

3D microstructures of samples heated below (1350 °C), within (1390 °C), and above (1425 °C) the non-Arrhenius region in (SrTiO3 were measured. Internal dihedral angles indicated that slowly growing grains have lower GBE than more rapidly growing grains. Low GBE grains increased in fraction with increased temperature until 1425 °C. The GBE distribution and GBCD at 1425 °C indicated a correlated high population and low energy for the {001}, the (111) sigma 3 and (2¯21) sigma 9 GBs.

Indexing (document details)
Advisor: Rohrer, Gregory S.
Commitee: Harmer, Martin P., Holm, Elizabeth A., Rollett, Anthony D.
School: Carnegie Mellon University
Department: Materials Science and Engineering
School Location: United States -- Pennsylvania
Source: DAI-B 79/01(E), Dissertation Abstracts International
Subjects: Materials science
Keywords: Complexion, Grain boundary character, Grain boundary energy, Serial sectioning, Temperature dependence, Thermal groove
Publication Number: 10604582
ISBN: 978-0-355-18658-1
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