Deformation and fracture behavior during annealing of residually stressed polycrystalline aluminum oxide

Three types of polycrystalline aluminum oxide, with varying amounts of impurities, were tempered and then annealed to study the behavior of residual stress relaxation. Results from microprobe analysis, thermal expansion analysis, annealed strength measurements, and scanning electron fractography clearly indicate stress relaxation at annealing temperatures occurred by elastic creep through crack nucleation and growth in regions under tensile stresses. From the scanning electron fractographs, it was found that intergranular glassy phase played an important role in the crack formation and propagation. At elevated temperature, viscous intergranular glassy phase behaved as an adhesive layer and when under tensile stresses caused de-adhesion of grain-boundaries or the formation of cracks. Fine-grained aluminas, with little or no glassy phase, exhibited both sub-critical and critical crack propagation. Since cracks decrease the load-carrying ability of the aluminas, it was concluded that by minimizing the glassy phase, porosity, grain size and residual stresses one can suppress crack formation.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Materials Engineering

Department dc:contributor.department

Materials Engineering

Grantor dc:publisher

Virginia Polytechnic Institute and State University

Year dc:date.issued

1982

Author dc:creator

• Tree, Yenho Kuo

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en_US

Handle dc:identifier.uri

http://hdl.handle.net/10919/87147

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/87147