Investigation of grain boundary sliding and cavitation during creep of single-phase alumina. Ph.D. Thesis
Using a high-purity alumina with no glassy phase as a model material, both the creep cavitation and grain boundary sliding (GBS) phenomena were studied and their kinetics quantified. The GBS measurements were performed on both tensile and compressive creep specimens with an automated machine-vision-based stereoimaging technique called DISMAP. SEM observations revealed that compressive creep at 70 and 140 MPa resulted in the nucleation of multiple creep cavities primarily on two-grain facets, secondarily at three- and four-grain junctions, and occasionally at triple points. These cavities were generally observed to be of similar size, shape, and spacing on a given grain boundary and their subsequent growth and coalescence led to the formation of facet-sized cavities leading to failure. Cavities were observed to exhibit a variety of irregular, angular shapes, suggesting that their morphologies may be governed by the crystallographic orientation of the grain facet and the corresponding surface energies. Fracture surfaces of tensile specimens tested at 35 MPa revealed creep cavities located primarily at three- and four-grain junctions and triple points, and only occasionally at two-grain facets. Finally, in the 20 MPa tensile specimen, creep cavities were located almost exclusively at grain boundary triple points. GBS measurements showed that during compressive and tensile creep, grain boundaries exhibit mode II GBS, in-plane grain rotation, in-grain shear deformation, mode I grain boundary opening, and out-of-plane GBS. No dependence of grain boundary orientation to the compressive load axis was observed on the magnitude of mode II GBS displacement. During steady-state tensile creep, the cumulative mode II GBS displacements increased linearly with creep strain and showed an increasing trend with creep time. Small-angle neutron scattering (SANS) quantification of creep cavitation revealed that the number of cavities per unit volume increases linearly with creep time.
- Research Organization:
- Univ. of Texas, Austin, TX (United States)
- OSTI ID:
- 237296
- Report Number(s):
- N-96-22484; NIPS-96-08272; TRN: 9622484
- Resource Relation:
- Other Information: TH: Ph.D. Thesis; PBD: Jan 1994
- Country of Publication:
- United States
- Language:
- English
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