Characterization and evaluation of Y{sub 2}O{sub 3}-stabilized cubic ZrO{sub 2} for single crystal fibers. Final report Page: 4 of 32
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high load carrying capabilities at temperatures where matrix creep can be
pronounced.
There are a number of factors that must be considered when choosing a
fibrous reinforcement for a composite. A high melting point for the fiber is usually
desirable. Related considerations are stability with respect to the matrix and an
oxidizing atmosphere, creep resistance, specific stiffness and high temperature
strength. Thermal fatigue is also an important issue, and for metallic and
intermetallic matrices, a high coefficient of thermal expansion (CTE) has
considerable advantage. Sapphire (a-A1203) fibers have received the most attention
as a candidate reinforcement material, and at this time, constitute the benchmark by
which other candidate oxide fibers must be judged.
Considerable attention has been focused on intermetallic matrix composites,
with much recent effort on the aluminide family (NiAl, Ni3Al, TiAl, Fe3Al, etc.).
In terms of high melting points and thermodynamic stability, oxide reinforcements
are promising fiber candidates. One major drawback, however, is the large
mismatch in thermal expansion coefficients between the intermetallics and many
oxide ceramics (e.g. sapphire). Table 1 shows that sapphire and YAG, the two
most studied oxide fibers, have much lower CTE's than the aluminide family of
intermetallics. Y203 fully-stabilized cubic ZrO2 (Y-CSZ), on the other hand, has a
fairly high CTE and provides a good thermal expansion match with this family of
materials (the thermal properties of Y-CSZ, including the composition dependence
of the CTE, are discussed elsewherel. This is one of the factors that has sparked
the present interest in ZrO2 as a potential fibrous reinforcement.
Table 1: Thermal expansion coefficients and specific moduli of a number of
intermetallics and ceramics
103 E/p
CTE x10-6 /K GPa/(kg/m3)
293 K 500 K 700 K 900 K 1100 K 293 K
NiAl 11.9 13.9 15.2 15.8 16.0 29
Ni3A1 12.3 13.4 14.3 14.9 15.4 24
TiA 10.0 11.1 11.4 11.8 12.2 43
Ti3A1 10.0 - - - - 34
FeAl 17.3 19.3 20.7 21.4 21.7 47
Fe3Al 8.8 14.3 18.2 24.7 25.0 21
MoSi2 7.4 8.0 8.5 8.9 9.4 70
A12O3 6.8 7.2 7.6 7.9 8.3 97
ZrO2* 10.7 11.1 11.1 11.7 13.0 41
YAG** 8.5 8.7 8.9 9.0 9.2 68
* 21 m/o Single Crystal Y203-stabilized ZrO2
** Single Crystal "white" Y3A15012
Significant research has been done over the years on the high temperature
deformation of bulk ZrO2 alloy single crystals. Y-CSZ demonstrates potent solid
solution strengthening,2 with an increase in solute content from 9.4 to 21 m/o
Y203 resulting in a corresponding -two-fold increase in flow stress (from 180 to
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Heuer, A. H. Characterization and evaluation of Y{sub 2}O{sub 3}-stabilized cubic ZrO{sub 2} for single crystal fibers. Final report, report, June 20, 1993; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc680407/m1/4/: accessed March 28, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.