Note: Descriptions are shown in the official language in which they were submitted.
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lT~.,-~~0 I,~.-BA.Ng COI~OSI~'~
BACI~OI20I~ O~' T~ INV)~NTION
The present invention relates to powder metallurgy and, in
particular, to laminated metal-ceramic composite materials, which can be used
for manufacture of some engineering parts of a high-temperature apparatus,
s specifically for thermal-protection linings, nozzles, combustion chambers,
turbine blades and guide vanes of jet engines, crucibles, protection tubes of
immersion thermometers for molten metals.
As it is well known, in different branches of industry there is a
need for in principle new high-temperature (1500-2800°C) composites,
which
to should be able to v~~ithstand extreme conditions of large mechanical loads,
abrasive and oxidative influences, thermal shocks, etc.
In accordance with thermal and mechanical requirements the
composites can be subdivided into the following groups:
Group l: Composites, keeping for a long time in oxidizing media at a
is temperature up to 1504=1800°C an enough strength, impact resistance,
hardness. The most important applications of the composites include
turbine blades, guide vanes and combustion chamber lining of jet engines;
Group 2: Composites, working at temperatures up to 2000oC and in a
conditions of large thermal shocks, but are not exposed to serious
2o ri~echanical loads. The most important applications of the composites
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include crucibles for high-temperature metals casting, protection tubes of
immersion thermometers for molten metals;
~CTroup 3: Composites, working at a temperature up to 2500-2800oC in
abrasive and oxidative high-speed gas fluxes, at moderate mechanical
s loads, but in conditions of large heat flows and thermal shocks. The most
important applications of the composites include nozzles, combustion
chambers, turbopump parts, thermal protection plates.
A number of composite material classes have been considered as
potential candidates for these applications.
1o There are known metal-ceramic composites, which comprise a
ceramic matrix and a powder or fibrous metallic inclusions. Thermal and crack
endurance, fracture toughness of a such dispersion- or fibrous reinforced
composites are insufficient for a majority of the above mentioned
applications.
With considerable advantages possess a metal-ceramic composites with a
I5 laminated structure which provides an increase of the above mentioned
properties as a result of metallic component addition in the form of thin
layers.
The characteristic feature of the laminated composites is the
braking of cracks on ceramic-metal interfaces: a crack, arising in ceramic
layer, canceling at approach to metallic layer mainly because of the layer
larger
2o ductility.
In this subgroup of composites are the best known a multilayer
composites (Figure 1 a), which consist, in particular, of alternating metallic
and
oxide layers.
The manufacture methods of such composites are based on use of
2s organo-ceramic and organo-metallic films, making from a pastes,
suspensions,
slurries, cements, mastics, containing metallic and oxide powders with
different
organic binders (US 3556837, US 4929295, US 5223064, JP 4114981, SU
1089077).
Composites of the subgroup have usually a good thermal shock
3o resistance, high heat-insulating properties, but at the same time trhey
have a
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number of typical drawbacks: limited interlayer adhesion and, as a
consequence, lower mechanical properties, poor abrasion and wear resistance,
and, as it must be especially noted, with such composites there is a problem
of
complex shape forming.
s In this subgroup of metal-ceramic composites with a laminated
structure are known also composites with so called laminar-granular structure,
comprising randomly arranged cube-like multilayer granules (Figure lb) (for
example: The composite Hf02/Mo, J. Space/Aeron., 1965, v.43, No. 4, p.54).
Substantially more complex parts can be manufactured from such composites,
to than from above mentioned multilayer composites, but there are a lot of
different imperfections at interfaces of the multilayer granules, that results
in
reduction of strength, abrasion resistance and other mechanical properties
SUMMARY OF THE INVENTION
The object of the present invention is to provide an isotropic metal
15 ceramic mufti matrix composite, built from randomly interlaced multilayer
curved band-like chips (Figure 1 c), with a high strength, thermal-shock and
abrasion resistance and with other high physico-mechanical properties, which
can be used at a temperature of 1500-2800°C, and the simple and
available
method of its manufacture, which allows the production of complicated shape
2o articles.
The aim is achieving by those way, that the composite consists of
the following components:
a refractory oxide, for example, such as alumina, yttria, zirconia or
hafnia.
2s This component is not obligatory for all versions of the composite;
a an oxygen devoid compound, possessing increased high-temperature
creep resistance, for example, zirconium carbide or hafnium carbide.
This component is not obligatory for all versions of the composite;
a ductile component of refractory metal, for example, molybdenum
or tungsten metal.
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Every component of the novel composite is in the form of curved
tapes with a thickness in the range of 5-200 microns, with a length in the
range
25 150 thickness of the tape and with a width that is in the range of ~ 50
thickness of the tape. The tapes form multilayer curved band-shaped chips,
s which are randomly interlaced, that provide the isotropic properties of the
composite.
The laminar-band structure has amongst others advantages, such
as:
~ The metallic tapes create, because of their plasticity, like in other
multilayer
to structures with a metallic component, numerous barriers against cracks
spreading and development, that provides a dramatic increase of a thermo-
and crack-endurance;
~ Because in the novel composite at least one component forms a continuum,
it has increased, as compared with other laminated composites of equal
is chemical composition, strength, fracture toughness, wear resistance,
erosion
resistance and oxidation resistance;
~ As a result of random arrangement of the multilayer band-shaped curved
chips the novel composite structure is isotropic.
The experimental research results (see the discussion of
Zo Tables 2-5), have shown that in the novel composites the volume fraction of
metallic component, parameter "m", can be from 0.15 up to 0.7, preferably
from 0.2 up to 0.5. With an increase of "m" takes place an increase of crack
resistance and thermal endurance of the novel composites, and also an increase
of strength, but at the same time takes place an increase of specific gravity,
2s decrease of hardness, decrease of erosion-corrosion resistance and of wear
resistance.
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Table 1
The ranges of volume fractions of components in the three different
groups of the novel composites:
Group of Maximum Components:
the novel work
temperature,______________________.__________________________
composites oC Oxide Carbide
Metal
1 1500 0.3-0.8 - 0.2-0.7
2 2000 0.5=0.85 - 0.15=0.5
3 2800 0.3-0.85 0-0.3 0.2=0.7
The above three groups of high-temperature ( 1500-2800°C)
composites are needed in different branches of industry.
The novel composites are applicable in the three groups. In many
situations the novel composites are probably the only solution of the problem
to of new high-temperature composites.
The aYticles o GYOUp 1 (see classification in the "Background of
the Invention" section), such as nozzle guide vanes and turbine blades of gas
turbine engines (Figure 2), must keep for a long time a high strength,
fracture
Is toughness, chemical erosion resistance, thermal shock and oxidizing
resistance,
fatigue and creep resistance at a temperature up to 1300=1500oC.
As a Group 1 composites can serve the novel composites, in
which as an oxide component are used, for example, some compounds in the
systems on the basis of A1203, Si02, Y203, fully stabilized Zr02, which
2o sintering temperature do not exceed 1400=1600oC, for example, it can be
such
a compound as 3A1203 ~ 2Si02 (mullite), or a different compounds in such
systems as A1203-Ti02, or Zr02-Y203-A1203.
As a ductile component of the Group 1 composites are used
alloys, possessing a prolonged oxidizing resistance at a temperature of
2s 1300=1500oC and compatibility with the oxide component as concern the
sintering temperature.
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For example, there can be used Cr metal and its alloys, and also
such alloy as NiAI-Cr and some other alloys on their basis.
A very good example of the Group 1 composite is a
Mullite/Chromium composite. The specimens of this composite have very good
s properties just after pressureless sintering: bending strength bend-300 20
MPa, the strength is steady practically in the temperature range up to 1200oC;
fracture toughness K1~ 10 14 MPa~ ml/2; the maximum deformation is
reaching 0.17% at room temperature; specimens mass changes are absent at a
heating in air up to 1200oC during a period of 200 hours; the specimens
to possess with very high resistance to multiple quenches in water: for
instance,
the specimens withstood no less than 80 to 100 quenches 1200oC-~
20oC(water).
The articles of Gf~oup 2, intended for work at temperatures up to 2000oC and
at
Is severe thermal shocks, but not at too large tensions (for example, such
parts, as
crucibles (figure 4), protection tubes of immersion thermometers (figure 3),
heat resistant linings), can be manufactured from the novel composites, which
contain as a metal component the refractory metals Nb, Mo, W and others, and
as oxide component they contain the following refractory oxides: A1203,
2o Y203, fully stabilized Zr02 or Hf02 and others. Some important properties
of
Group 2 the novel composites are shown in Table 3 and Table 4.
As an example of a very effective application of the Group 2 composites can
serve protection tubes of immersion thermometers for liquid steel and its
alloys, liquid copper and brass, and many other metals and their alloys, made
2s from n(A1203+Ti02)/Mo the novel composites (figure 3). The protection tubes
possess a very high resistance against erosion in slag, thermal shock
resistance,
small inertness, life time in liquid steel more than 3=5 hours, and provide
continuous and precise temperature measurement. Such protection tube wall
thickness can be, for example, from 2 to 5 mm.
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T'he a~°ticles o~GYOUp 3, must work at a temperatures up to 2500
2800oC in
aggressive gas jets at large heat fluxes and thermal shocks (nozzles,
combustion chambers (figure 5), etc.), must keep at the ultra high
temperatures
s an enough strength, hardness and other mechanical properties, and
simultaneously they must possess a high oxidizing and abrasion resistance.
The thermochemical influence of such aggressive gas jets must
not cause appreciable mass loss, erosion, within a work time of 10 to 5000
seconds. These articles must withstand a large number of thermal shocks and
to be light weight because of their most frequent applications in a
sufficiently
light weight apparatus.
As Group 3 composites can serve the novel composites where as
metallic component use refractory metals, for example, W, Mo, Ta and their
alloys, melting temperatures of which are over 2500 3000oC, and as an oxide
is component are used the oxides with the highest refractoriness, in the first
place
fully stabilized Zr02, Hf02, Th02.
The most important properties of some two-component the novel
composites of the Group 3 are shown in Table 4.
In the novel three-component composites of Group 3 are used as
2o an oxygen devoid component some carbides of transition metals, such as ZrC,
NbC, HfC, TaC. These carbides and some compounds on their basis (see
Table 5) are the only substances which keep strength and creep-resistance up
to about 2500 3 OOOoC. But since the carbides don't possess any plasticity and
oxidizing resistance, their volume contents in the novel composites must be no
2s more than 20 to 30%.
From Group 3 the novel composites can be made j et engine
nozzles, mainly non cooled, with a throat diameter of 1 to 200 mm which are of
the most practical importance.
2~ozzles with a bigger throat diameter, for instance, up to X00 to
800 lnm, can be manufactured with use of a mufti-part design approach only. ~t
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must be specially noted that such a multi-part design provides a substantial
increase of a nozzle thermal endurance.
For the same purpose of an enlarged thermal endurance providing
the wall thickness of the nozzle throat inserts must not exceed 3 6 mm.
s Three major characteristics that the rocket motor nozzle material
must possesses and which are dictated by the above mentioned functional
conditions, are a very high erosion resistance, thermal shock resistance and
adjustable thermal conductivity according to the application. The novel
composites of the Group 3 are probably the only materials which possess
io simultaneously all of the characteristics.
The Group 3 novel composites have an adjustable in a very wide
range thermal conductivity, which is chosen according to permitted
temperature on the internal (hot) and external surfaces of nozzle, and also
depends on the needed local heat flux through the nozzle wall.
is The maximum work temperature on the internal (hot) surface of
rocket nozzle can be reached by use of the novel composites, which comprise
as a compound devoid of oxygen component post eutectic carbide-graphites in
the systems ZrC-C, TaC-C, NbC-C or HfC-C and as metallic component the W
with addition of up to 2 wt.% of Th02; for instance, the novel composites
2o n(HfC-C)/W can be used. Beside of a very high work temperature and erosion
resistance such composite possesses a high thermal endurance, that is typical
for the post eutectic carbide-graphites.
1~~THG~ ~~' ~J~A~~'
2s The invention can't be realized by using known methods of
laminar and multilayer composite manufacture.
The essence of the novel method consists in operations sequence,
which insure production of composite with above-described laminar-band
structure.
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In accordance with the present invention, the method of the novel
composite article forming comprises the steps of providing oxide, metal and
carbide powders possessing an average particle size 0.5 2.0 microns and a
maximum agglomerated particles size of 10 microns. Then, by mixing of oxide,
s carbide and metallic powders with a corresponding film-forming binder is
prepared a slurry from which are cast films with thickness 20=300 microns. As
a film-forming binder it is preferable to use synthetic carboxilated
butadiene-nitrite rubber. The synthetic rubber is added in slurry as a 5 16%
solution in the benzine-acetone (1:1) mixture, in quantity 1 5 mas.% (in
I o account on dry weight of the system: rubber + component of the composite).
For manufacture of ductile organo-ceramic films some other film
forming binders can be used (R.Mistler, Ceramic Bull.,v.69,No.6).
The cast films are cut to fixed length pieces, which then are
collected into 2 5 mm thickness packets, consisting of alternatively ordered
Is metal, carbide and oxide based films. The quantity of the same type films
in
every layer depend upon the filins thickness and upon the desirable
composition of the composite. The layers must have a minimum thickness to
obtain the best quantity of interfaces.
The filin packets are subjected subsequently to densification in a
2o roll mill, resulting in the reduction of their thickness to about 0.5 1 mm.
This is
done to reduce porosity, which take place in the ex-casted filins. The films,
which constitute these multilayer packets, may have a thickness, after
rolling,
in the range of 5 50 microns.
Further operations are connected with manufacture of the
2s so-called complex-mass. The film packets, that were densified by the roll
mill
treatment, are packed, for instance, in spiral shape, into a steel cylindrical
press
die to form a multilayer cylindrical billet by uniaxial compaction.
These laminated billets are subjected to turning on a lathe to
produce multilayer chips with a width h=2=7 mm, a thickness of ~=0.1=0.5
mm and a length 1=3-30 mm, preferably I=5-IO mm (figure ~).
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Then an article of desired shape and dimensions (taking into
consideration shrinkage during sintering) is formed from the multilayer chips
in
a press die at a pressure in the range of 50=1000 MPa.
The compacted article is then heated in a vacuum or in an inert
s gas for removal of binder, in the temperature range from RT to SOOoC with a
temperature growth rate of 1-10 oC/hour.
The "brown" article is subjected to a preliminary sintering at a
temperature in the range of 1150=1450oC until an article is reached of
approximately 50=75% of theoretical density.
to The pre-sintered porous article is then densified to approximately
80 90% of its theoretical density by sintering the body in a vacuum furnace at
a temperature in the range of 1300-2000oC.
A composite body of a comparatively simple shape, practically
devoid of pores, can be produced by a Hot Pressing operation after the above
Is described pressureless sintering. The ceramic article is subjected to Hot
Pressing in a graphite mold at a pressure in the range of 5=100 MPa and at a
temperature in the range of 1400-2000oC, in vacuum or in an inert gas, in a
resistively heating furnace or in an inductively heating furnace, for a period
of
time that is sufficient to reach practically the theoretical density.
2o Articles with more complicated and, especially, with thin-walled
shape can be densified up to a practically pore-less condition by the use of
Hot
Isostatic Pressing (HIP) in inert gas under a pressure in the range of 100-300
MPa and at a temperature in the range of 1400-2000oC, also for a period of
time that is sufficient for reaching practically the theoretical density.
J~R~P~RTI~~ ~~' T~~ N~~IJ ~~l~P~SIT~S
Properties of the novel composites strongly depend on their
composition. In Tables 2 5 are represented physical-mechanical properties of
some typical composites: Table 2 for Group 2 Composites nY2Q3/Ia,4o, Table 3
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for some composites of Group 1 and Group 2, Table 4 and Table 5 for some
composites of the Group 3.
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Table 2:
The properties of vacuum pressureless sintered nY203/Mo composites
(maximum work temperature 2050oC):
Type Fraction, Bending Number pxidizing
vol.% strength, of quenches,
MPa resistance
------------"' N
at 20C R at 1400oC
Y203 at
Mo 600C
after
one
quench*
Y 100.0 - 80 12 12 1-2 -
9Y/M 90.0 10.0 55 50 22 2-3 >20
7Y/M 87.5 12.5 62 60 37 2-4 >20
SY/M 83.3 16.7 74 ~ 100 85 14-20 8-10
3Y/M 75.0 25.0 110 170 140 16-24 5-8
Y/M 50.0 50.0 175 270 200 20=30 2-5
Y/2M 33.3 66.7 266 415 320 20-30 0.2-0.5
Y/3M 25.0 75.0 360 570 410 20-30 0.1-0.2
N -- Number of cold quenches 1000oC-j20oC (water), until destruction.
(moderate velocity heat to 1000oC and quench in water at 20-25oC)
R -- Time, in hours, before start of specimen destruction;
to *) -- after one quench 1000oC~20oC (water).
SUBSTITUTE SHEET (RULE 26)
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Table 3:
The Properties of composites usable at work temperature up to 2000oC:
Type Fraction, ApparentHardness,Bending Number Max, work,
vol.% density,GPa strengthof temperature,
Component: g/cm' at 20C, quenchesC
Ceramic MPa N
Metal
COMPOSITE
Mullite/Chromium
Ml/Cr 50 50 5.15 - 320 60-100 1350
COMPOSITE
(0.98A1203
+
0.02Ti02)/Cr
AT/Cr 50 50 5.50 14.0 340 25-30 1400
COMPOSITE
(0.8(Zr02~0.04Y?O;)
+
0.2Ah03)/Mo
PSZA/M 50 50 7.81 8.5 480 25-30
1750
COMPOSITE
(0.9TiN
+
O.ICr)/Nb
TN/Nb 50 50 6.92 14.1 680 35-40 1800
COMPOSITE
(0.45TiC
+
0.5TiN
+
0.05Cr)/Mo
TCN/M 50 50 7.25 15.3 650 40-50 1800
COMPOSITE
nY203/Nb
3Y/Nb 75 25 5.08 - 160 16-20
1800
2Y/Nb 66.6 33.4 5.17 - 144 -
1800
Y/Nb 50 50 5.87 - 190 16-20
1800
COMPOSITE
(0.9TiB2
+
O.INi)/Nb
TB/Nb 50 50 7.05 17.5 420 40-50 1800
COMPOSITE
n(0.98A1203
+
0.02BaTi0~)/Mo
3AB/M 75 25 4.91 13.5 226 15-20 1850
AB/M 50 50 6.64 9.0 360 25-30 1850
COMPOSITE
n(Zr02~0.04Y203)/Nb
PSZ/Nb 50 50 7.02 7.2 450 35-40 2000
i
N -- Number of cold quenches 1000°C X20°C (water), until
destruction
(moderate velocity heat to 1000°C and quench in water at
20+25°C)
SUBSTITUTE SHEET (RULE 26)
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Table 4:
The Properties of two-component super high-temperature composites:
Type Fraction, Bending K1, Number Max.
I vol.% strengthMPa~ml~~ work
i at 20C, of temp.
Apparent MPa quenches C
~ N
~,,
at
~
Components:
density
600C
Oxide
Metal
a~cm'
W/m.K
COMPOSITE
n~'~03/Mo
(see
also
Table
2)
3Y/M 75 2050
~ 25
~
5.57
22.1
110
5.5-7
16-24
i Y/M 50 2050
50
i
6.78
j
44.0
175
6-8
20-30
COMPOSITE
I n(ZrO2~0.1Y~03)/Mo
SZ/M 83
16
~
5.65
~
15.4
270
-
10-12
2200
i 3Z/M75
i
25
6.01
i
24.0
~
290
7.5-11
22-26
2200
i
Z/M 50
i
50
~
7.07
'I
49.8
~
365
-
24-30
2200
COMPOSITE
nY~03/W
3Y/W 75 25 345 - 14 2200
~ ~~
7.56
24.9
~~
~ 2Y/W67 33 - - 2200
~
8.59
31.5
295
I
Y/W 50 10.77 6-9 20 2200
~ 48.9
i
360
50
COMPOSITE
n(ZrO~~O.lY~03)/W
SZ/W 83 7-10.5 2500
17 12-15
6.99
15.0
~
216
~ 3Z/W75 6-9 10-15 2500
i
25
~
8.01
~
23.0
200
2Z/W 67 6.5-9 ~ 10-15 2500
i
33
~
8.99
~
26.0
265
Z/W 50 i 235 - 15-20 2500
'I
50
11.07
~
45.9
COMPOSITE
n(Hf02~0.1
Y203)/W
3H/W 75 7=11 10=18
i ~ 2600
25
i
11.05
21.0
305
H/W 50 13.10 43.4 i 7.5-11.5 2600
i 440 10-14
50
~
H~/2W-33 14.49 55.4 i 7.5-12 2800
j 460 22-26
67
'
N -- Number of cold quenches 1000°C '~20°C (water), until
destruction
(moderate velocity heat to 1000°C and quench in water at 20-
25°C)
SUBSTtTUTE SHEET (RULE 26)
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Table 5
The properties o~ some three-component ultra
high-temperature composites:
Type Fraction,Apparent 7~, W/m~KBending Number Max. work,
vol. density, at 600C strength,of temperature
%
g/cm3 MPa, at quenchesC
20C N
COMPOSITE
0.5(Zr02~0.1Y203)/0.3ZrC/0.2W
Z/ZrC/W 50/30/208.22 3.7 460 12-15 2600
COMPOSITE
0.5(Hf02~0.1
Y203)/0.3HfC/0.2W
H/HfC/W 50/30/2012.20 - 420 8-14 2750
COMPOSITE
O.STh02/0.3(Hfo,6~Tao.23Wo.iC)/0.2W
Th02/ 50/30/2011.8 - 610 14-18 2800
Hfl'aWC/
W
N -- Number of cold quenches 1000°C X20°C (water), until
destruction
(moderate velocity heat to 1000°C and quench in water at
20=25°C)
SUBSTITUTE SHEET (RUi..E 26)
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The influence of composition on the novel composite properties
are considered on the basis of the example of nY2O3/Mo composites. In
Table 2 are represented results of measurements of bending strength, heat
conductivity, resistance to multiple quenching and oxidizing resistance for
s some variants of nY203/Mo composites.
From the data of Table 2 one can see that only those composites
of the type have practical significance, which have a volume ratio of oxide
component to metallic component in the range from 1 to 5.
The composites with Vox:Vmet < 1 do not possess a good
to high-temperature oxidizing resistance because of a considerable content of
the
metallic component.
In such composites, as, for instance, composite Y/2M and composite Y/3M,
already at heating in air up to 1400=1700oC occurs a degradation of surface
within 1-2 hours, but they have a considerably increased abrasive resistance
as
is compared with pure molybdenum. On the other hand, the composites of the
type with a low metal content, for instance the composite 7Y/M and composite
9Y/M have a low thermal endurance and thermal-shock resistance, that does
not differ from the corresponding properties of pure Y2O3.
In Figure 6 are shown the concentration dependencies of bending strength and
2o thermal shock resistance at multiple water quenches of the composite
nY203/Mo.
In Figure 7 are shown experimental results of strength
degradation of the composite nY203/Mo specimens after a single quench in
water from different temperatures of heating up.
2s As it is evident from Figure 7 the strength of composites,
containing more than 17 vol.% of Mo (the composites Y/M, 3Y/M and SY/M),
is practically not reduced after quenches in water from the heating up
temperatures right up to 1000oC, and at a certain temperature interval
(400-700oC) even increases. At the same time, the strength of nY2O3/Mo
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composites with a metal component content below the critical value of 1 ~
vol.% (for example, composites 7Y/M and 9Y/IVi~, at their quench from the
temperature, that exceeds 140=160oC, substantially go down, which is typical
for the behavior of the pure oxide.
s All this data show that nY203/Mo composites must be used only
with n=1=5.
I~ES~P,IPTI~N OF TIDE PP,EFERA~L.E TEC~IN~L,~GY
The technology of the novel composite articles starts with the
to preparation of oxide, metal and carbide powders with an average particle
size
of 1 to 2 microns and a maximum agglomerated particle size of I O microns.
For grinding and de-agglomerating the powders are used a
grinding media which don't create a danger of powder contamination. For
example, there can be used a polyurethane or a rubber lined milling jar and
Is grinding bodies from zirconia or yttria.
Use ~f highly effective WC-Co balls in vibration mill leads to
contamination of powder with up to 0.2 0.5% of tungsten - depending on
grinding time and the powder hardness. But for the novel composites this is
not
dangerous, and in some situations the impurity of tungsten is a useful metal
2o additive.
A contamination of the powder, in the process of its grinding,
with traces of Fe, Ni and other elements, which are ground out from a jar wall
material, are also permissible, because these elements, in most cases, are not
high-melting and are easily evaporated during sintering.
2s In general an average particle size has not to be less than 0.5 1
micron, as powder with elevated specific surface area requires a rise of
quantity
of binder for ensuring a necessary viscosity and cast properties of the
slurry,
that Iead, ultimately, to an undesirably high shrinkage at sintering.
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On the other hand, with the use of particles with an average size,
considerably above 2 3 microns, the sintering conditions get worse, dwell
temperature and/or dwell time, necessary for porosity reduction, are
increased.
After grinding and de-agglomerating the powders are dried: oxide
s powders are dried at 400=800oC during 2 5 hours, metallic and carbide
powders are dried at 250=350oC during 2 5 hours.
After milling and drying, the powder is passed through a 400
mesh sieve to remove large agglomerates.
Then an organic binder is added to the dry and de-agglomerated
io powders. As a film forming binder can be used as many different substances.
For the novel composite production is especially suitable synthetic
butadiene-nitrite rubber. The rubber is added in slip as the 5 16% solution
(mas.%) of it in benzine-acetone (which are mixed in proportion from l:l to
4:3 volume parts) mixture in quantity 1 5 mas.% ( in account on dry weight of
Is the system: rubber+powder).
Such rubber binder has a number of advantages compared with
well known binders (acrylic polymer, hydroxyethyl cellulose, polyurethane,
polyvinyl butyral, etc.), and, in particular, has a good ductility that is
necessary
for making the, so called, complex-mass.
2o For instance, a binder such as polyvinyl butyral permits to cast
films of 20-40 microns thickness even more easily than the butadiene-nitrite
rubber binder, but the polyvinyl butyral binder is uncomfortable for the
laminated chips making by lathe machining: multilayer billets consisting of
films, which were cast using polyvinyl butyral, show ease of cracking at lathe
2s machining at room temperature and for prevention of the cracking it needs
heating during the machining.
Mixing of the binder with corresponding powder is better to be
executed in the same type ball vibration mill during 1.5 2 hours.
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Casting of the organo-ceramic films can be earned out on any of
conventional industrial machines, which are used for ceramic film casting by
the "doctor blade" method.
It was established experimentally that satisfactory properties of
s the composite material can be reached by use of films with a thickness from
20
to 300 microns.
Films with a thickness of less than 20 microns are difficult to
make by usual methods of ceramic tape casting.
Films with a thickness that is greater than 300 microns are
to unreasonable to be cast, because it is impossible to get multilayer chips
with
the necessary frequency of interfaces.
It is most preferable to use films, which were cast with a
thickness of 50-100 microns.
On the operations of the film packets uniaxial compaction and
~s following roll milling a thickness of the films are reducing usually in a 3
8
times -- up to 15 20 microns.
Films, which were cast with the use of the above listed different
powders, are then cut to pieces of 120 180 mm long.
From the film pieces are assembled packets in accordance with
2o the desirable composition of the composite. These packets are then rolled
out to
1 mm thickness.
For example, at manufacture of specimens from SY/M, 3Y/M and
Y/M composites, containing accordingly 17, 25 and 50 vol.% of molybdenum,
the film pieces were collected in 3-S mm thickness packets, consisting of
2s alternatively ordered oxide and metal films, with thickness ratio of oxide
to
metal films 5:1 (0.6 and 0.12 mm) in SY/M, 3:1 (0.36 and 0.12 mm) in 3Y/M
and l:l (0.12 and 0.12 mm) in Y/M. These packets were rolled out to 0.7-1
mm thickness; thanks to rolling process a thickness of the constituent films
were reduced in 2.5=4 times.
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The densified filin packets are then laid as spiral into a cylindrical
press die and subjected to uniaxial pressing with the purpose of cylindrical
multilayer billet manufacture.
These multilayer billets are used for manufacture of the
s multilayer chips. With this purpose the billets are subjected to turning on
a
lathe to manufacture multilayer chips with 0.2 0.5 mm thicknesses, 2 6 mm
~Tidth, and 5 25 mm length (Figure 8).
It was found experimentally that the width of the chip must be no
more than 5 7 mm, that is no more than 15 25 thicknesses of the chip, and no
to less then 5 10 thicknesses of the chip.
It was shown experimentally that the length of the multilayer chip
must be no less then 25 5 0 thicknesses of the chip.
Of course, the chips with such dimensions can be manufactured
by other methods, for example by mechanical treatment of a multilayer plate on
Is a planer, but in the variant of technological process it is need to use
sufficiently
large multilayer plates, which are usually difficult for manufacture.
In the following technological operation the multilayer chips are
put into the press die for cold pressing.
Depending on the shape of the article shaping can be carried out
2o by the use of uniaxial pressing in a "usual" metallic press die or by the
use of
cold isostatic or quasi-isostatic pressing, usually under a pressure in the
range
of 100=500 MPa, preferably 150-250 MPa.
The press die that is intended for cold quasi-isostatic pressing can
contains, for example, a TEFLON-coated steel mandrel, which forms the
2s internal surface of the article to be formed, and a rubber sleeve, which
forms
the external surface of the article (Figure 9).
Some products from the novel composites, in particular nozzles
and combustion chambers (Figure 5), can have comparatively thin walls, which
does not allow ~"he use of a conventional press die.
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It was shown experimentally that in this situation it is
advantageous to apply the following double stage pressing technology:
In the first stage the billet is formed in a steel press die under a
moderate pressure, and then the billet is subjected to quasi-isostatic
pressing.
s After the article has been removed from the mold it is subj ected
to a thermal treatment.
For simple shape articles, possess thick walls, the thermal
treatment in a vacuum tungsten furnace is started from the stage of the binder
(and it's solvents) removal and preliminary sintering at a temperature in the
io range of 1100=1400oC during span, which is necessary to reach the article
density, which is approximately 50 75% of theoretical density. In the stage of
thermal treatment the shrinkage usually is in the range from 3 to 12%.
A tungsten furnace is used, because in graphite furnace can take
place a reduction of the novel composite oxide component and a carbidization
is of it's metallic component, as result of a chemical interaction with such a
reducing agent as carbon, which presents in atmosphere of the graphite
furnaces.
For provision of a gradual diffusion removal of decomposition
products of the rubber binder the rate of a temperature rise must be in the
range
20 of 1 1 OoC/hour up to the temperature of a total binder burnout, which for
most
binders is about SOOoC.
In the following stage the firm enough but quite porous yet article
is sintered in a vacuum furnace at a temperature in the range of 1300-2000oC
up to required density, which consists 85 95% of theoretical density.
2s If necessary, a following densification of the simple shape
articles up to a density of 97 100% of theoretical density, can be carried out
by
Hot Pressing at a temperature in the range of 1300-2000oC and under a
pressure of 20-1 OO IVIPa.
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Final densification of articles with more complicated shape,
especially those having thin walls and which are uncomfortable for hot
pressing, is earned out in a two-step process: the step of high-temperature
vacuum sintering and the step of Hot Isostatic Pressing.
s At the first step, the article of such type is pressureless sintered
up to approximately 95 9 ~% of theoretical density, that is up to a state with
a
very large fraction of closed porosity. The high-temperature "dwell" span of
the corresponding firing profile usually is 1 to 2 hours.
In the second step, the pressureless sintered article is densified up
to to practically 100% of theoretical density by Hot Isostatic Pressing at .a
temperature in the range of 1300-2000oC and in an inert gas pressure of
150-200 MPa. If the HIP plant is equipped with a graphite furnace the article
can be shielded from interaction with carbon by Y203 powder or by another
oxide.
~s While we have described our invention in detail it will of course
be understood that we have done so for the purpose of illustration only and
not
for the purpose of limitation.
LIST ~F F~~U1~ES
Figure 1: Metal-ceramic laminated composites with different structures:
a - multilayer composite; b - laminar-granular composite;
c - laminar-band composite.
2s Figure 2: Turbine Wheel, Turbine Blade and Guide Vane made of the novel
composite:
1 -- Turbine Wheel; 2 -- Turbopump blade; 3 -- Nozzle Guide
Vane.
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Figure 3: Immersion Thermometers for molten metals with an application
of the novel composites:
1 -- Protection Tube made of the novel composite;
2 -- Two Round Hole Insulator; 3 -- Thermowires;
s 4 -- Thermocouple Hot Spot; ~ -- Stainless Steel Chuck.
Figure 4: Crucibles of the novel composites for molten metals and salts.
Figure 5: Combustion chambers and nozzles with application of the novel
composites of the Group 3
a -- Liquid Propelled Combustion Chamber:
1 -- Combustion chamber made of high strength and low permeability
composite;
2 -- Heat Insulator made of low thermal conductivity composite;
is 3 -- Nozzle Insert made of ultra erosion resistant composite.
b -- Nozzle of Solid Propelled Motor:
4 -- Thin wall nozzle throat insert made of ultra erosion resistant composite;
-- Cartridge made of carbon phenolic;
6 -- Graphite cartridge.
Figure 6: Concentration dependencies of bending strength bend ~d
thermal shock resistance at multiple quenching in water N
of nY203/Mo composites.
2s Figure 7: nY203/Mo composites strength degradation after a
single quench in water from different temperatures
of heating up.
Figure ~: Scheme of laminated metal-ceramic chips manufacture:
1 -- multilayer cylinder billet; 2 -- mandrel; 3 -- cutting tool
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Figure 9: Mold for quasi-isostatic forming of thin wall articles from
the novel composite;
1 - "brown" article; 2 - punch; 3 - mandrel; 4 - steel
s matrix; 5 - rubber; 6 - TEFLON film.
