The effects of in situ Ti0₂ whisker reinforcement on mechanical and thermal properties of glass-ceramics in the Li₂O-Al₂0₃-P₂0₆-Si0₂ system were investigated.
When Ti0₂ whiskers, having an average aspect ratio of 28, are precipitated from the glass-ceramic matrix, (Li<sub>0.4</sub>,Ca<sub>0.05</sub>)AI(Si<sub>0.75</sub>,P<sub>0.5</sub>)<sub>04.5</sub>, flexural strength is improved from 72 to 134 MPa. Fracture toughness, K<sub>Ic</sub>, is increased from the 1.1 to 1.6 MPa·m<sup>1/2</sup> due to crack deflection by the Ti0₂ whiskers. In situ Ti0₂ whisker-reinforced glass-ceramic exhibits rising fracture resistance, K<sub>R</sub>, with increasing crack extension. The fracture resistance, K<sub>R</sub>, is increased from 1.89 to 2.5 MPa·m<sup>1/2</sup> over the crack extension range range of 40 to 200 μm. The composite shows a narrow failure strength distribution compared to the glass-ceramic without Ti0₂ whisker precipitation. The coefficient of thermal expansion (CTE) changes from -2.8x10⁻⁷/"C to -1.7xl0⁻⁷/°C due to the precipitation of Ti0₂ phase which has a positive CTE (7.3xl0⁻⁶/°C).
With the matrix composition, (Li<sub>0.41</sub>,Mg<sub>0.035</sub>)AI(Si<sub>0</sub>0.48</sub>,P<sub>O.52</sub>)O₄, a three-fold increase in flexural strength was observed with a Ti0₂ content of 12 wt%. CTE value of the composite increases linearly from a negative to a positive value with increasing Ti0₂ content up to 12 wt%. The in situ composite containing 8-10 wt% Ti0₂ exhibits near zero CTE values up to l000°C. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/38638 |
| Date | 19 June 2006 |
| Creators | Lee, Kyoung-Ho |
| Contributors | Materials Engineering Science, Brown, Jesse J., Jr., Gordon, Ronald S., Gibbs, Gerald, Hirschfeld, Deirdre A., Reynolds, William T. Jr. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | ix, 116 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 28528803, LD5655.V856_1993.L445.pdf |
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