The influence of microstructure on the mechanical properties of some refractory compounds

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date

2011

Author dc:creator

• Hoffman, Mark P.

Contributors dc:contributor

• Will, W.

• microstructure
• electron energy loss
• local atomic structure
• refractory compounds
• amorphous titanium diboride

Statement dc:rights

• 1987 Mark P. Hoffman

Language dc:language

en

Identifier

1856879

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/25225