Note: Descriptions are shown in the official language in which they were submitted.
"'~7 93/22258 P~.°T/SE92/00297
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A ceramic composite, particularly for z
s
use at temperatures above 1400°C
The present invention refers to a ceramic composite
material comprising matrix and possibly reinforcing mate-
rials and an intermediate weak interface material and parti-
cularly adapted for use at temperatures above 1400°C and in
oxidizing environment, said matrix and possibly reinforcing
materials consisting of the same or different ceramic oxides
having a melting point above 1600°C.
Ceramic composite materials might be divided into
materials reinforced by particles, whiskers or elongated
ffibres. Said materials are prepared by powder processes
and sintering or by gas-phase infiltration. The materials
hitherto mentioned in the literature often are based on the
provision of desired composite characteristics by means of a
weak interface material between the matrix and the reinfor-
cing material, preferably fibres, said interface material
consisting of carbon or boron nitride, see e.g. Frety, N. ,
Boussuge, M., "Relationship between high-temperature
development of fibre-matrix interfaces and the mechanical
behaviour of SiC-SiC composites", Composites Sci: Techn. 37
177-189 (1990) and Singly R.N., "Influence of high tempera-
ture exposure on mechanical properties of zircon-silicon
carbide composites", J. Mater. Sci. 26 117-126 (1991),
respectively. Both carbon and boron nitride have a layered
structure which makes them weak in one direction and this
can be utilized for deflecting cracks along the interface
between fibre and matrix. Both carbon and boron nitride,
however, are very sensitive to oxidation which starts al-
ready at relatively low temperatures of about 500-800°C. In
a
order to enable the use of ceramic composites at high tempe-
ratures in oxidizing atmosphere, such as in combustion
chambers of gas turbines, rocket nozzles etc. other oxida- '
tion-resistent weak interface materials are required. An
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WO 93!Z2258 pCT/SE921002~'"'
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2
attempt to provide such materials has been mentioned in
Carpenter, H.W., Bohlen, J.W., "Fiber coatings for ceramic '
matrix composites", Ceram. Eng. Sci. Proc. vol 13 9-10
(1992). In said attempt composites have been manufactured
with SiC fibres and a layered SiC interface in an SiC mat-
s
rix. Experiments also have been made with interfaces of a
porous oxide in a SiC/SiC composite. However, SiC is stable
in an oxidizing environment only up to 1000°C, at higher
temperatures a Si02 layer always is formed on the surface in
oxidizing atmosphere. Often Si02~is not stable together with
other oxides but reacts therewith and forms strong bonds to
adjacent materials. Therefore, Si02 does not constitute a
useful interface material in the present connection. Thus
there is still a need for improved composite materials which
might be used in oxidizing environments at temperatures
above 1400°C.
The object of the present invention now is to suggest
such a ceramic composite material and the feature essen-
tially distinguishing the invention is that the interface
material consists of one or more ceramic oxides not exhi-
biting solid solubility, eutecticum below the temperature
of manufacture or use or reaction with any of the matrix
E..
or possibly reinforcing materials and in combination with
said materials providing a stress field liable to micro
cracking, said matrix and reinforcing materials being sub
stantially pure.
One of the most obvious interface materials is Zr02
which fills the requirements as to oxidation resistance and
good high temperature characteristics. In US A 4 732 877
recently has been suggested an interface of Zr02 in a compo-
site of A1203/A12o3. According to said patent, however, the
only object of Zr02 is to act as a diffusion barrier and ~ t
prevent a reaction between reinforcing fibres and matrix.
The interface obtained is strong by its binding to said
materials and not weak as is necessary in ceramic composi
tes for the present use.
CA 02135061 2002-07-24
3
Thus the present invention refers to an interface
material for a ceramic composite material in which the
matrix and/or the reinforcing material consist of a ceramic
oxide comprising one or more metals and having a melting
point above 1600°C, said oxide not exhibiting solid solubi
lity, eutecticum below the temperature of manufacture or use
or reactivity with any of the other oxides. in the interface
or the matrix or reinforcing materials. As examples of such
oxides there can be mentioned A120~, ZrO~, Hf02, A12Ti05,
Sn02, Y203, BeA1204, yttrium aluminium garnet (YAG), LaCr03,
mullite, Be0 and Cr2o3. Preferably the reinforcing material
is present as fibres but also particulate and layer form are
possible.
The present i.nz-ent;ion <~l:~o concerns a ceramic
composite materia.:L compoi: _ing rr;atr:.x ruaterial,reinforcing
fibers and an intermediate irlterfac_e mat=eri_al, wherein said
matrix material and reinforcing fiLaers con~:ists of the same
or different ceramic o~~i.des having a mell=ing point above
1600C; said interface material., ire ~vombinati on with t=he
matrix and reinforcing materials L:~rcvides a stress
field
liable to microc:rack.=.ng bEi_ng apl:%1.:_ed ting on said
~s a coa
fibers and consisting of at Least or:~r cerami c oxide not
exhibiting soiicl so:_ubil.ity, c~utE~ci=icum below the
temperature c>f mar~ufccture or i:m>e c>r re=~acti with any
it.y of
said matrix or rei.nforcng materia.l~; said matrix and
reinforcing mat:erial~. k~ei.n~~ :~ub~tar~t.:i_a and wherein
i 7. y pure,
the combinats.on f=iber/:interface rnatc~.r-ia~l/matrixmaterial.
is
selected from t=he group :~orzsi st i n<~ ~ ~ iv
A1z03/A12Ti05/A12C?3, YAG/A_L2Ti05/A1~03,
3 0 Al 2~3 /YAG/Al z03 , A1.20_ / SnO~yA1203 ,
YAG/Sn02/A1 X03, A.L.~O:,%mullite/A1203 .
CA 02135061 2001-08-03
3a
In combination with the matrix and possibly reinfor
cing materials the interface material has to form a stress
field which either results into micro cracks in the inter
face material or into cracks between the latter and the
matrix/reinforcing material. Alternatively, the stress field
might cause crack deflection as such also without micro
cracks occuring. The desired stress field occurs either by
the difference in thermal expansion coefficient between the
interface material and the matrix/reinforcing materials or
by differences in thermal expansion coefficient between
various inherent phases of the interface material. Stresses
also might be generated by the fact that the interface
material as such has an anisotropic structure with diffe-
rent thermal expansion coefficients in various crystal
directions. A further possibility to form stresses is that
phases of the interface material undergo a phase conversion
which results in a change of volume. The interface material
also might be a composite in which the two inherent phases
have different elastic characteristics or different thermal
expansion coefficients which creates the desired stress
situation. As examples of some well-serving interface mate-
rials it might be mentioned A12Ti05, cordierite, unstabili-
Zed Zr02, Sn02, Hf02, mullite, YAG, YAG+Zr02, A1203+Zr02 and
CA 02135061 2002-07-24
A12Ti05+A1203. Of said substances, A12Ti05 and cordierite
act as iflterface materials due to their anisotropy, while
Zr02 and Sn02 act by micro-cracks. YAG, Hf02, Zr02, A12Ti05,
cordierite, mullite and Sn02 act as interface
materials due
to differences in thermal expansion while
Zr02 and possibly
Hf02 might be subjeacted to phase conversion.
Preferably, the
interface material has a thickness of
at least 2 um. When
the interface material is Zr02, i t is used in the form of
powder or sol during coating of a f ibre reinforcing material
in order to avoid chemical binding of Zro2 to the fibres.
Based on the above mentioned the fol:Lowing examples
of
well-serving composite systems of reinforcing material/in-
terface/matrix might be mentioned.
A1203/AlzTiO,'/A1203 YAG/A12Ti05/YAG
A1203/A12Ti0,~/YAG YAG/A12Ti05/A1203
A1203/Zr02/A:L203 YAG/Zr02/YAG
YAG/Zr02JA1~t73 A1203/Zr02/YAG
A1203 /Hf02 /A:L203 YAG/Hf02 / YAG
A1203,'Hf02/Yi~G YAG/Hf02/A1203
Hf02/A12Ti05,IHf02 A1203/YAG/A1203
A1203 /Sn02 /A:L203 YAG/ Sn02 /YAG
YAG/Sn02/Al2c)3 A12D3/Sno2/YAG
A1203/mullite~/A1203 mullite/Zr02/mullite
.
rc~2/YAG A1203/YAG+Zr02/A1203
YAG/A1203+Z
YAG/A1203+A12Ti05/YAG Hfc72/A1,203+A12Ti05/Hf02
Example 1
Plates of A12(?3 of 0,25 mm thickness were coated with
a thin layer of A12Ti05. This was made by submerging the
plates in.a slurry of Al2Tio5 powder in water. After drying
the covered plates were stacked and sintered by hot-pressing
at 1700°C for 4 hours. After sintering the.A12Ti05 layer was
about 5 um thick. The Al2z'i05 layer comprised micro cracks
deflecting cracks, which was proved by diamond indentation
or bending tests.
CA 02135061 2001-08-03
Example 2
Fibres of A1203 (ALMAX, Mitsui, Japan) were covered
with a thin layer of A12Ti05. This was made by immersing the
fibres into a A1-Ti-alkoxide. After gelling and drying the
5 coated fibres were stacked in a plaster mould and a A12~3
powder slurry was poured thereon.
After drying the slip-cast bodies were sintered by
hot-pressing at 1500°C for 4 hours. After sintering the
A12Ti05 layer was about 3 ~Cm thick. The A12Ti05 layer com-
prised micro-cracks deflecting cracks which was proved by
diamond indentation or bending tests.
Example 3
Plates of A1203 of 0,25 mm thickness were coated with
a thin layer of Zr02. This was made by immersing the plates
in a slurry of Zr02-powder in water. After drying the coated
plates were stacked and sintered by hot-pressing at 1700°C
or 4 hours. The Zr02 layer had a thickness of about 5 ~cm
after sintering. Stress-induced micro cracks occurred bet-
ween the layer and the A1203-material. These deflected
cracks which was proved by diamond indentation or bending
tests.
Example 4
_ Plates of A1203 of 0,25 mm thickness were coated with
a thin layer of Hf02. This was made by immersing the plates
in a slurry of Hf02-powder in water. After drying the coated
plates were stacked and sintered by hot-pressing at 1700°C
for 4 hours. The layer of Hf02 was about 5 ~,m thick after
sintering. Stress-induced micro-cracks occurred between the
layer and the A1203-material. These deflected cracks, which
was proved by diamond indentation or bending tests.
_Example 5
Single-crystal-fibres of A1203 (from Saphicon, USA)
were coated with a thin layer of Zr02. This was made by
immersing the fibres in an aqueous Zro2-sol. After gelling
and drying the coated fibres were stacked in a plaster mould
and an A1203-powder slurry was poured thereon. After drying
* (trademark)
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WO 93/22258 PGT/SE92/002
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the slip-cast bodies were sintered by hot-pressing at 1500°C
for 4 hours. After sintering the zr02 layer was about 3 ~Cm
thick . Stress-induced micro-cracks occurred between the
layer and the A1203-material. These deflected cracks which
s
was proved by diamond indentation or bending tests.
Example 6
Plates of A1203 of 0,25 mm thickness were coated with
a thin layer of Sn02. The plates were immersed in Sn02-sol
and stacked on each other and then dried after which they
to were sintered in air at 1450°C under a certain uniaxial
pressure for 4 hours. After sintering the Sn02-layer was
about 2,5 ~m thick.. The Sn02-layer formed micro-cracks
deflecting cracks which was proved by diamond indentation or
bending tests.
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