<p><a>Zirconium
oxide (zirconia, ZrO<sub>2</sub>) is one of the essential structural ceramics
for industrial applications due to its superb strength and fracture toughness.
ZrO<sub>2</sub> has three main polymorphs: cubic, tetragonal, and monoclinic
phase, depending on temperature, type, and concentration of dopants. Stabilized
zirconia with metastable tetragonal phase can transform into monoclinic phase
with ~ 4% volume expansion under an applied external stress. The
tetragonal-to-monoclinic transformation can hinder crack propagations by
generating a compressive stress field near crack field, thereby enhancing
fracture toughness. In addition, other deformation mechanisms such as
dislocation activities, crack deflection, and ferroelastic domain switching can
further enhance its deformability. Bulk ZrO<sub>2</sub> is typically prepared
by sintering at high temperatures over a long period of time. Recently,
field-assisted sintering techniques such as flash sintering and spark plasma
sintering have been applied to effectively sinter ZrO<sub>2</sub>. These
techniques can significantly decrease sintering temperature and time, and more
importantly introduce a large number of defects in the sintered fine grains.</a></p>
<p>The
miniaturization of sample dimension can alter the mechanical properties of
materials by increasing the surface-to-volume ratio and decreasing the
likelihood of retaining process-induced flaws. The knowledge of mechanical
properties of ZrO<sub>2</sub> at micro and nanoscale is critical in that
superelasticity and shape memory effect of ZrO<sub>2</sub> can be utilized for
applications of actuation, energy-damping, and energy-harvesting at small scale.
Here, we performed <i>in-situ</i> microcompression tests at various
temperatures inside a scanning electron microscope to examine and compare the mechanical
properties of ZrO<sub>2</sub> prepared by flash sintering, spark plasma
sintering, plasma spray, and thermal spray. Detailed microstructural analyses
were conducted by transmission electron microscopy. The unique microstructures
in ZrO<sub>2</sub> prepared by field-assisted sintering largely improved their
plasticity. Temperature and processing technique-dependent underlying
deformation mechanisms and fracture behavior of ZrO<sub>2</sub> are discussed.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12712091 |
| Date | 29 July 2020 |
| Creators | Jaehun Cho (9167816) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY-NC-SA 4.0 |
| Relation | https://figshare.com/articles/thesis/SMALL-SCALE_MECHANICAL_BEHAVIORS_OF_ZIRCONIA_PROCESSED_BY_DIFFERENT_TECHNIQUES/12712091 |
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