Applications of Textured Microstructures

1
Templated Grain Growth (TGG) is a technique to
develop crystallographic texture in
polycrystalline ceramic bodies via the grain
growth of aligned template particles.
The Requirements ? Homogeneous, dense,
finegrained polycrystalline matrix ?
Thermodynamically stable template particles (or
single crystals) ? Epitaxy at the
template/polycrystalline matrix interface ?
Driving force and mechanism for boundary migration
Applications of Textured Microstructures Structura
l ? Toughness increases with the incorporation of
anisotropic grains due to crack deflection and
bridging by anisotropic grains ? Improved cutting
performance in textured WCCo cutting
tools Functional ? Increase the critical current
density in superconductors ? Improved conduction
in ionic conductors ? Improved magnetic
properties in hexaferrite ceramics ? Improved
piezoelectric properties in Bi4Ti3O12, Sr2Nb2O7,
(Sr,Ba)Nb2O6, PbNb2O6, Ba(Zr,Ti)O3,
Pb(Mg1/3Nb2/3)O335PbTiO3
2
TEXTURED CERAMICS BY TGG
Access to single crystal properties in
polycrystalline materials
Template Particles
T1
T2
Initial microstructure consists of large template
particles oriented in fine matrix
Late microstructure development is characterized
by template impingement and subsequent thickening
Early microstructure development is often
characterized by template elongation
Textured Ceramics
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SINGLE CRYSTALS BY TGG
Regulation of growth direction and increase of
crystallographic and microstructural orientation
Growth of a single crystal BaTiO3 into a Ti-rich
BaTiO3 sintered ceramic after 8 h at 1350C. (J.
Appl. Phys., 863, 1657-61, 1999)
Other TGG grown single crystals (MnxZn1-x)Fe2O4
(U.S. Patent 4339301, 1982) Y3Fe5O12 (1st Jap.
Intl. SAMPE Symp., 419-24, 1989) Pb(Mg1/3Nb2/3)O3
- 35 mol PbTiO3 (J. Am. Ceram. Soc., 81 1
244-8, 1998)
4
TGG - modeling and experiment
Effect of the template concentration and size
can be predicted by modeling
(Seabaugh et. al., J. Interface Sci., 8, 257-267,
2000)
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CHARACTERIZATION- Texture
Crystallographic texture ? Pole figures,
rocking curves, and Rietveld refinements from
X-ray diffraction (XRD) analysis Morphological
texture ? Stereological measurements from SEM
micrographs (e.g., template dimensions)
Al2O3
Model function ? March-Dollase Equation P(f,a,r)
f (r2cos2(a)) (sin2(a)/r)-3/2 (1-f) r
degree of orientation parameter f texture
fraction ? angle from the perfect alignment
(Seabaugh et. al., J. Am. Ceram. Soc. 838,
2049-54, 2000)
Orientation Image Microscopy ? both
crystallographic and morphological textures ?
grain orientation from the Kikuchi patterns
formed by electron diffraction of individual
grains.
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CHARACTERIZATION- Properties
80-Textured PMN-32.5PT (BaTiO3 Template)
Strain
Fracture Toughness (MPam 1/2 ) Tabular grain
face normal to indent
6.020.46 Tabular grain edge normal to indent
6.850.32 Equiaxed alumina
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Electric Field (kV/cm)
Textured PMN-PT ceramics show higher strain than
untextured samples and approach the single
crystal value with increasing texture.
(Sabolsky et. al., Appl. Phys. Lett. 2000)
(M. M. Seabaugh, Ph.D. Dissertation, 1998)
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CHARACTERIZATION- Properties
Unipolar Polarization of TGG-grown BaTiO3 Single
Crystals
Piezoelectric charge coefficient (d33) approaches
the single crystal value in highly textured
Sr0.53Ba0.47Nb2O6 ceramics along the
001. (Duran et. al., J. Am. Ceram. Soc.
839, p. 2203, 2000)
Single crystal values are Psat 26 µC/cm2 and
d33 90 pC/N
(Rehrig et. al., J. Appl. Phys., 863, 1657-61,
1999)