The influence of microstructure on the mechanical properties of some refractory compounds
Hoffman, Mark P.
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https://hdl.handle.net/2142/25225
Description
Title
The influence of microstructure on the mechanical properties of some refractory compounds
Author(s)
Hoffman, Mark P.
Issue Date
1987
Doctoral Committee Chair(s)
Will, W.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
microstructure
electron energy loss
local atomic structure
refractory compounds
amorphous titanium diboride
Language
en
Abstract
A brief review of the basic physics of electron energy
loss spectroscopy and extended x-ray absorption fine structure
spectoscopy is presented in the context of their application
to the study of the microstructure of transition metal
carbides and diborides.
The local atomic structure of amorphous titanium diboride
thin films, prepared by electron beam vaporization of the
crystalline compound onto liquid nitrogen-cooled substrates,
is examined using extended x-ray absorption fine structure
(EXAFS) and extended electron energy loss fine structure
(EXELFS). The extended fine structure spectra of the
amorphous films are compared with corresponding spectra for
crystalline titanium diboride. A relaxation of the
interatomic spacing and a reduction of coordination numbers
for nearest neighbor atoms is observed for the amorphous
state. Local prismatic coordination with random 90° rotations
about prismatic planes is presented as a likely atomic
structure for the amorphous state.
The high-temperature hardness of crystalline tantalum
carbide is linked to the presence of extended stacking faults.
Suzuki hardening limited by bulk carbon diffusion is presented
as the mechanism which distinguishes tantalum carbide from
iv
other carbides with the same structure. Softening is
predicted to occur at temperatures near those observed
experimentally.
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