Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates -to nickel-base metal-
ceramic heat-resistant sealing materials produced by conventional
powder metallurgical methods. Such rnaterials prove to be most
advantageous when producing sealing memhers (parts) for such
units as turbine wheel rims exposed to the effect of gas flows
at high temperatures. The nickel-base materials belong to heat-
resi~tant metal-ceramic materials which find use in gas turbine
pumps and in certain types of surface transport ~ehicles and
aircraft.
A nickel-base metal-ceramic heat-resistant material
is klown comprising the following alloying elements in per cent
by weigh;t: silicon, up to 3, and graphite, up to 8. The material
is employed in ~.he manufacture of plates for radial and labyrinth
turbine seals.llowever, at a gas flow temperature of about 1000C
these materials are not capable of providing long service life
for the machines. This is attributable to the burning-out of
their graphite component, through which the surface hardness of
the sealing members produced from this material is enhanced with
the ensuing higher wear of rotating turbine parts (turbine
blades) found in contact therewith.
Moreover, this material is not suitable for producing
sealing members (parts) in the form of rolled band, since
graphite increases alloy brittleness.
Some nickel-base materials contain from 5 to 20 per
cent by weight of silicon, copper, mica, chrom~um or boron r
nitride. Such materials are capable of providing long service
life of machines but a temperature not in excess of 850C. Thus,
the nickel-base materials containing copper can operate, as a ,
rule, at a temperature not exceeding 600C. Those, comprising
mica or micaceous compounds such as vermiculite in muscovite
eature lower thermal stability. The materials, compxising
chromium (or nichrome-base compounds with the nicke:L-to-chromium
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ratio of 4:1) and boron nitride are inapplicable in machines
operating at a temperature above 850~C.
As is commonly known, boron nitride is similar in
structure to graphite, bu-t in contras-t to the latter, it has
a higher heat resistance and does not burn out in service.
However, the nickel-base materials, containing boron nitride,
are prone to cubical oxidation by end products of fuel combustion
which causes the geometry of sealing plates to be disturbed and
bands in this material to he distorted duriny its usage. At a
temperature of gas flows of about 1000C these materials do
not provide long-term turbine operation. As the turbine blades
wear out, the clearance between the turbine rotary shroud rim
and its rotating blades, ~hrough which hot yases can leak, in-
creases, this resulting in excessive fuel consumption, lower
turbine efficiency and in a decrease in the range of operation
of a flying vehicle.
Since the speed of transport vehicles is on the
rise, turbine ratings increase as well, with the ensuing rise
in the tempera-ture of a gas flow in such turbines. Therefore a
need has arisen for providing a nickel-base material which would
feature a higher heat resistance, improved thermal stability,
heat conductivity and minimum wearing of conjugate working parts
such as blades. Moreover, the coefficient of linear expansion
of such materials must be equal to or approximate that of an
alloy from which the turbine rotary shroud rim is fabricated,~
and the turbine sealing members must retain their geometry,
should not fall out of the shroud rim and should have a hardness
allowing conjugated parts to fit in without appreciable wear in
their contact places.
The present invention provides a metal-ceramic nickel-
base heat-resistant sealing material whose properties allow its
use for manufacturing radial sealing members (parts) operating
continuously in gas flows heated to 1000C. 3
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The present invention also provides a sealing material
which has a small hardness ranging from 25 to 40 kg/mm2 and a
higher heat resistance and thermal stability.
The present invention further provides a material
suitable for producing insert-pieces for turbine rotary shrouds
and allowing turbine blades to fit in without their marked wear.
According to the present invent:ion there is provided
a nickel-base metal ceramic heat-resistant sealing material in-
cluding boron nitride and silicon dioxide, the weight percentage
` 10 of all the components being:
silicon dioxide, from 0.5 to 8.0
boron nitride, from 1.0 to 10.0
nickel, the balance.
Such material is useful for producing sealing parts
and is capable of providing machine, e.g. gas turbine, operation
within 3000 hours at a temperature of a gas flow of up to 1000C
or up to 1100C within 500 hours. This is possible because the
material comprises the above-specified components in appropriate
amounts. As shown experimentally, the introduction of silicon
dioxide into the base of the material for instance into powdered
nickel makes it possible to enhance heat resistance of the
material owing to an increased resistance of nickel against
oxidation.
The addition of boron nitride into nickel powder,
in the form of a fine powder, enables the hardne~ss of the material E
to ~e decreased owing to separation of nickel grains by boron
nitride grains.
The combined introduction of both silicon dioxide and
boron nitride in said amounts makes it possible to obtain an oxide .
film at a surface of the material at a working temperature about
1000C. The film adhering firmly to the material, protecting it
against further oxidation and very importantly, the thickness of
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, ~~he film does not increase in use.
When the silicon dioxide content is less than 0.5 weight
per cent, the heat resistance of the mater:Lal decreases and hard- ¦
ness of the working surfaces of the sealing members, produced from
this material increases when silicon dioxide is introduced in
amounts more than 8 weiyht per cent, the strength of the oxide
film deteriorates, it shows a tendency to~ward cracking with the L
film particles being entrained by the gas flow travelling with
considerable speeds which may result in a failure of turbine
blades.
With a boron nitride content less than 1.0 weight per
cent the hardness of the working surfaces of the sealing members
increases which causes excessive wear of conjugated parts in ser-
vice. When the amount of boron nitride in the material exceeds
10.0 weight per cent, the heat resistance, thermal stability and
mechanical strength of such materials deteriorate.
The present invention will be further illustrated by
way of the following examples.
Example 1
The following componen-ts are ta~en (weight per cent)
for producing a material:
silicon dioxide, 0.5
hexagonal boron nitride, 1.0
nickel, the balance
The above-specified components are b~lended in a pow-
dered state in a drum mixer. On being charged into a steel die,
the mixture is compacted in a hydraulic press to impar-t it the
prescribed shape and required strength. The powder compacts then
are sintered in electric furnaces in reducing or neutral gases.
The above-outlined procedure is applicable for produc-
ing sealing members in the form of plates, rings and bushes. As
for the sealing members in the form of band, these can be obtained
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;,
~y rolling bar stock manufactured by compacting and sintering.
The material, according to the invention, from which
the abov~-described sealing members were produced comprises,
weight per cent: silicon dioxide, 0.5: boron nitride, l.0 and
- nickel, the balance.
Said parts are secured either mechanically or by solder-
ing them to the rim of a turbine shroud band.
The thus-produced material has the following properties. ¦
An increase in weight upon oxidizing in air at a temperature of
1000C within 100 hours was 0.53 kg/m2, surface hardness amounted
to 45 kg/mm2, density - 7.0 g/cm3 and porosity - l9~.
Example 2
A material is produced similarly to that described in
Example 1.
The material comprises, weight per cent:
silicon dioxide, 5.0
boron nitride, 5.0
nickel, the balance.
The material has the following properties.
An increase in weigh-t upon oxidizing in air at a
temperature of 1000C within 100 hours amounted to 0.70 kg/m2,
surface hardness was equal to 4~ kg/mm2, density 6.5 g/cm3 and
porosity to 23%
Example 3
A material comprises, weight per cen~:
silicon dioxide, ~.0 ~r
boron nitride, 10.0
nickel, the balance.
The material was produced in a similar way to that
described in Example 1.
The thus-obtained material has the following proper-
ties.
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An increase in weight upon oxidizing in air at a
temperature of 1000C within 100 hours amounted to 1.1 kg/m2, sur-
face hardness was 45 kg/mm2, density - 6.3 g/cm3 and porosity -
25~.
As shown by te~t results, the above-specified material
can be advantageously used at elevated temperatures up to 1000C
over several thousand hours. It is also suitable for short-time
operation up to 100 hours at a temperature of 1200C.
The material of the present invention has a stable
chemical composition, e.g. the chemical composition of a sealing
member operated within 2000 hours in a gas flow at a temperature
of 1000C did not change and the sealing parts did not exhibit
any contraction in spite of continuous vibration.
The sealing material produced according to the present
.invention had a higher heat resistance. Upon oxidizing in air at
a temperature of 1000C increase in weight amounted to:
during 100 hours 0.38 kg/m2
during 450 hours 0.64 kg/m L
during 1050 hours 0.91 kg/m
during 1250 hours 0.95 kg/m2
during 1450 hours 0.95 kg/m2
during 1650 hours 1.04 kg/m2
during 1800 hours l.OS kg/m t
during 2000 hours 1.06 kg/m2
during 3000 hours 1.10 kg/m2
The density of the specimens produced from the above
material varied from 6.2 to 6.8 g/cm3 and their porosity from 13
to 17%. Initial Brinell hardness amounted to 20-40 kg/mm2. The
material features adequate machinability and solderability. Upon
testing for thermal stability in a gas burner flame, no cracks
were revealed after 300 cycles with each specimen being heated to r
1000C for 60 s and then cooled to 100C within 60 s during
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~ach cycle.
A band, 1-2 mm thick, in the material has an adequate
ductility to be bent into a riny at least 30 mm in dia or to be
bent and unbent 30 times in one and the same plane.
Coefficient of linear expansion (~ . 106)
(20-100) 12.9J1C
~20-700) 15.5/1C
(20-800) 15.9/1C
(20-900) 16.3/1C
(20-1000) 16.4/1C
Coefficient for heat conductivity (cal/cm s C)
25 0.088
100 0.084 F
500 0.078
700 0.078
1000 0.076
. l
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