Note: Descriptions are shown in the official language in which they were submitted.
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A Ni based alloy, a component, a gas turbine
arrangement and use of Pd in connection with such an
alloy
BACKGROUND OF THE INVENTION AND PRIOR ART
The present invention relates to the field of nickel based
alloys with excellent properties for use at high
temperatures. The alloys according to the invention may for
example be used for components in gas turbines. The
invention also relates to components made from an alloy
according to the invention. Furthermore, the invention
relates to a gas turbine arrangement. Moreover, the invention
relates to the use of Pd in alloys.
Many different alloys for high temperature applications are
known. A group of such alloys are called superalloys. The
term "superalloy" is used to represent complex alloys based
on e.g. nickel, iron, and cobalt, containing additional
elements such as chromium, carbon, aluminium, tungsten,
rhenium, titanium, silicon and molybdenum. The term "based"
as used herein means that that element is the largest weight
fraction of the alloy, i.e. that there is no other element in
the alloy that is present in a weight % that is the same as
or higher than the weight % of the base element. The
additives are normally used to impart high values of
mechanical strength and creep resistance at elevated
temperatures and improved oxidation and hot corrosion
resistance. For nickel based superalloys, high hot strength
is obtained partly by solid solution hardening using such
elements as tungsten or molybdenum and partly by
precipitation hardening. The precipitates are often produced
by adding aluminium and titanium to form the intermetallic
compound y' ("gamma prime"), based on Ni3(Ti,Al), within the
host material (y).
The document US 6 177 046 B1 describes y/y' superalloys
containing Pd. According to this document, Pd is added in
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order to provide improved weldability to the alloy. The
document lists quite wide ranges for the contents of the
alloying elements. Concerning Pd, the range 4-32 weight % is
specified in the claims. According to the most preferable
ranges of the alloying elements according to different
examples in this document, the Pd content should be 5-40
weight o(Table 7), 5-45 weight o(Table 8) or 8-27 weight %
(the table in column 17). In the concrete examples in this
document, the Pd content is quite high. It is proposed that
up to approximately half of the Ni content in existing Ni
based superalloys should be substituted by Pd (see column 9).
The document US 6 007 645 describes y/y' Ni based
superalloys. The document describes alloys said to have good
hot corrosion resistance, a high creep-rupture strength and
good microstructural stability. The document stresses that
the Cr content should be low. The document suggests several
different alloy compositions. The Cr content is never above
2.9 weight %. The document mentions that the alloy, among
other alloying elements, can contain 0-10 weight % of one or
more of the elements selected from the group consisting of
Ru, Rh, Pd, Os, Ir and Pt. It is mentioned that such elements
are effective in increasing the creep-rupture strength and
oxidation and corrosion resistance. The document does not
seem to mention any concrete example where Pd is present in
the alloy.
The article "Effect of palladium on the hydrogen
embrittlement of B-doped Ni3Al" by Liu Yang and Rex B.
McLellan in the Journal of Materials Research, vol. 11, no.
4, April 1996, pp. 862-864 discusses that hydrogen
embrittlement in B-doped Ni3Al can be reduced by the addition
of Pd.
It is known that hydrogen may diffuse into alloys and thereby
be the cause of disadvantageous properties of the alloy. For
example, the hydrogen may reduce the ductility of the
material, may be the cause of the occurrence of cracks and
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may make the material hard but brittle. The most important
mechanism for these effects is associated with the weakening
of grain and particle boundaries. There may also be a
possible disadvantageous synergy effect between H and S such
that hydrogen sulphides are formed at the grain and particle
boundaries. It is also known that S may tend to segregate
preferentially to grain boundaries. Even very low contents of
S may be sufficient to form hydrogen sulphide layers at these
boundaries. Such problems can also occur by the formation of
nickel hydrides in the absence of sulphur. Problems of the
described kinds can be referred to as hydrogen embrittlement
(HE).
HE can be caused by the presence of hydrogen gas but may also
occur under humid conditions. Alloy elements such as Al may
oxidise in water such that free hydrogen is formed, see the
paper mentioned earlier by Yang&McLellan on gamma prime
alloys and the paper "Environmental effects on tensile and
low cycle fatigue behaviour of single crystal nickel base
superalloys" by Nazmy et al. In Scripta Materialia 48 (2003).
This hydrogen can diffuse into the alloy and cause HE.
Ni based y/y' alloys are known to have excellent properties
for use at high temperatures, such as for components in gas
turbines. However, HE has been reported also for these
alloys, see the paper by Nazmy et al mentioned above.
Ni based y/y' alloys are quite complex alloys. These alloys
have a matrix of the y phase, which is Ni with other elements
like Cr, Co, Fe, W, Mo and Re in solution. Furthermore, such
alloys contain particles of the y' phase, which normally is
Ni3Al with other elements like Ti, Ta and Nb in solution.
Furthermore, such alloys may contain other elements, for
example in order to strengthen grain boundaries and/or to
stabilise a protective oxide layer. It can also be noted that
different alloying elements tend to be present in different
concentrations in the y and y' phases, i.e. a certain element
may tend to be drawn to a certain one of these phases such
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that a concentration of the element is higher in this phase
than in the other phase. It has for example been reported
that Al tends to partition favourably to the y' phase. It has
also been reported that Pd tends to partition favourably to
the y' phase. Furthermore, the partition of an element
between the y and y' phases may change in the presence of
further elements. It has been noted that the addition of Pd
can have as an effect that Al tends to partition more
favourably to the y phase.
SUMMARY OF THE INVENTION
Components of Ni based y/y' alloys usually have a protective
oxide layer that will prevent hydrogen embrittlement.
However, the inventors of the present invention have noticed
that in particular in components that are subject to a
variation in temperature, for example between ambient
temperature and a high service temperature, and in particular
if these components are also exposed to humidity, the
microstructure of the oxide scale will change with time such
that the protective oxide layer can loose at least part of
its protective effect or fail mechanically exposing the
parent material. The inventors have found that for such
components, hydrogen embrittlement is likely to occur. Since
normal air contains a certain amount of humidity, humidity
can be a problem in many cases. Furthermore, the inventors
have found that hydrogen embrittlement may be a problem in
for example gas turbines using "wet process" such as fogging
and steam cooling. The hydrogen embrittlement can shorten the
time during which such components can be used. Since for
example gas turbines are expensive devices, it is important
that components in such devices can function during a long
time.
An object of the invention is to provide an improved Ni based
y/y' alloy suitable to be used for components exposed to high
temperatures. A particular object it thereby that the alloy
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should have improved robustness and be resistant to hydrogen
embrittlement. In particular the risk of hydrogen
embrittlement should be reduced when components made from the
alloy are subjected to thermal cycling with humid conditions
5 under at least parts of the cycle. An object it thereby to
provide alloys for such components which can function without
failing during a long time. A further object of the invention
is to provide a component with advantageous properties, in
particular a component that will resist hydrogen
embrittlement. Still an object is to provide a gas turbine
arrangement including one or more components that have
advantageous properties when used at high temperatures.
Another object of the invention is to use Pd in Ni based y/y'
alloys in order to achieve an advantageous technical effect.
The first objects above are achieved by a Ni based alloy
suitable for single crystalline, directionally solidified or
polycrystalline components to be used at high temperatures,
the alloy being a y/y' alloy and consisting, in weight %, of:
0.5-25 Cr
0-25 of one or more elements selected from the
group consisting of Co, Fe and Mn
1-25 of one or more elements selected from the
group consisting of Mo, W, Re and Rh
3-25 of one or more elements selected from the
group consisting of Al, Ti, Ta, Nb, and V
0-10 of one or more elements selected from the
group consisting of Ru, Os, Ir and Pt
< 4.0 Pd
0-3 Hf
0-2 Si
0-2 of one or more elements selected from the
group consisting of B, C, N and Zr
0-1 of one or more elements selected from the
group consisting of Y, La, Sc, the
actinides and Ce and the other lanthanides
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0-2 of one or more additional elements
selected from the group consisting of all
elements except for Ni and except for
those referred to above in this table
balance Ni
wherein the alloy contains Pd in a significant amount
sufficient to provide the alloy with an improved resistance
against hydrogen embrittlement.
It should be noted that when in this document a content of a
group of elements is specified (for example: "of one or more
elements selected from the group consisting of...") the content
means the total content of all the elements from the group
that are present in the alloy. Consequently, in case the
alloy contains only one element from the group in question,
the specified content is the content of this element.
It should also be noted that in this document, if nothing
else is said, the contents of different elements or groups of
elements always concern weight %.
It can also be noted that when a range of contents begins
with 0, this means that the presence of the element or
elements in question is optional.
The inventors of the present invention have thus found that
an improved alloy is obtained by selecting the different
elements as defined above. It has thereby been found that in
particular an improved resistance against hydrogen
embrittlement is obtained. It has been found that this
improved resistance can be obtained also with very low
concentrations of Pd. Since Pd is an expensive material, it
is an advantageous aspect of the invention that only small
amounts of Pd are needed. The improved resistance against HE
is probably due to the fact that H present at the grain or
particle boundaries is drawn into the y' phase by Pd. As is
mentioned above, Pd partitions favourably to the y' phase.
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Furthermore, the addition of Pd may have further advantageous
effects. It has for example been reported that Pd may be
advantageous in preventing the formation of TCP
(topologically close packed) areas. Furthermore, since Pd is
very similar to Ni, its solubility in Ni is very high.
Moreover, since Pd preferentially partitions to the y' phase,
also the solubility in Ni3Al is excellent. As indicated
above, it has also been reported that the addition of Pd may
change the partitioning factors of Ni based y/y' alloys such
that slightly more Al partitions to the y phase. This means,
for a given y' content, that it is possible to add slightly
more Al to the alloy. This would seem to increase the
resistance to oxidation and hot corrosion. Moreover, since it
is sufficient to use a small amount of Pd in order to obtain
the advantageous effects, no significant negative effect of
the addition of Pd has been noted (it has been reported that
Pd potentially could cause problems with heat treatment
procedures and a reduction in creep strength at high
temperatures).
According to an embodiment of the alloy according to the
invention, the content of said additional elements < 1.0, or
even only at the level of impurities that are normally
accepted in alloys for components to be used at high
temperatures, such as components used in gas turbines. The
properties of the alloy are easier to control if the alloy
only contains a small amount (or no amount) of such
additional elements.
According to a further embodiment, the content of Pd > 0.05.
The content of Pd can be < 2.0, preferably < 1.0 and even <
0.5. It is an advantageous aspect of the present invention
that the effects aimed at can be achieved also with small
amounts of Pd. This is particularly important since Pd is an
expensive material and since large amounts of Pd possibly
could have some negative effects.
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According to a further embodiment, the content of Cr > 3.0,
preferably > 6Ø With a fairly large amount of Cr an
excellent corrosion and oxidation resistance is obtained.
However, according to an alternative embodiment, the content
of Cr <_ 3Ø According to this alternative embodiment, a low
amount of Cr is thus used. This may increase the creep-
rupture strength of the alloy. By a careful selection of the
other elements, a sufficient corrosion and oxidation
resistance can be obtained even if the Cr content is low.
According to an embodiment, the content of one or
more elements selected from the group consisting of
Co, Fe and Mn > 3Ø The content of Co can for
example be > 6Ø Furthermore, the content of Co can
be > (the content of Fe + the content of Mn). Co is a
material that is known to provide an alloy of this
kind with advantageous properties, in particular a
sufficient hardness at higher temperatures.
According to still another embodiment, the content of one or
more elements selected from the group consisting of Mo, W, Re
and Rh > 3Ø The content of W can, according to a preferred
embodiment, be > content of Mo. Moreover, (the content of Re
+ the content of Rh) can be < 1Ø With a sufficient amount
of for example W, the strength of the alloy is increased.
Furthermore, the creep resistance is improved.
According to a further embodiment, the content of Al > 1Ø
The content of Al can for example be > 3.0 but < 10Ø The
molar fraction of Al in the alloy is preferably larger than
the molar fraction of any of the other elements selected from
the group consisting of Al, Ti, Ta, Nb, and V. Al, in
particular, is an advantageous material for the formation of
the y' phase. Furthermore, Al can increase the oxidation and
hot corrosion resistance.
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According to another embodiment, the content of one or more
elements selected from the group consisting of Ru, Os, Ir and
Pt > 0.01 but < 5Ø The addition of elements from this group
can be used to control the partition of other elements
between the two phases y and y'.
The content of Hf can, according to an embodiment, be > 0.05.
According to an embodiment, the content of Si is > 0.02. Hf
and/or Si can be used for promoting the formation of a
protective oxide layer.
The content of one or more elements selected from the group
consisting of B. C, N and Zr can for example be > 0.05 but <
0.8. These elements may be used to increase the strength at
the grain boundaries.
The alloy can, according to an embodiment, have a content of
one or more elements selected from the group consisting of Y.
La, Sc, the actinides and Ce and the other lanthanides >
0.005. These elements can be used to bind S. which can have
as an effect that the risk of the formation of unwanted
hydrogen sulphides decreases.
Preferably, the content of Ni > 35, and, more preferred, >
50. The alloy thus preferably contains a quite large amount
of the base element Ni.
According to a further embodiment, the volume ratio y'/y >
0 . 4 (40%) or even > 0. 6(60 0) . A quite high fraction of y' is
advantageous for providing a high hot strength.
According to another object of the invention, a component
designed for use as a component in a high temperature
environment is provided in that the component is made from an
alloy according to any of the preceding embodiments. Such a
component thus has advantageous properties as described above
in connection with the embodiments of the alloy. In
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particular, the component can be used at high temperatures
and still have a good resistance against hydrogen
embrittlement.
5 According to an embodiment, the component is a component for
a gas turbine arrangement. The component can for example be a
guide vane or part of a guide vane or a turbine rotor blade
or part of a turbine rotor blade. It has been found to be
particularly advantageous to use the alloy according to the
10 invention for such components. The components can be used for
a very long time without risking being damaged by for example
hydrogen embrittlement.
A gas turbine arrangement according to the invention
comprises at least one component as defined above. Such a gas
turbine arrangement will thus include components with
advantageous properties as described above.
A use according to the invention is achieved by using Pd
which forms part of the alloy according to any of the above
embodiments for providing said alloy, according to any of the
above embodiments, with improved resistance against hydrogen
embrittlement. The inventors of the present invention have
thus found a technical effect achieved by a careful use of Pd
in alloys of the above described kind. In particular, it is
advantageous that only a small amount of Pd is sufficient for
achieving the advantageous effects described above.
BRIEF DESCRIPTION OF THE DRAWING
Fig 1 shows very schematically a turbine arrangement
according to the invention with a plurality of components
according to the invention.
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DESCRIPTION OF PREFERRED EMBODIMENTS
Below different examples of the composition of alloys
according to the invention are given. The balance is Ni in
all the below examples. In addition to Ni and to the elements
specified in these examples, the alloys, according to these
examples, may contain small amounts of impurities with a
concentration which is normally accepted in alloys of these
kinds for use for components which are intended for use at
high temperatures, for example in gas turbines. Furthermore,
all the alloys are Ni based y/y' alloys. The ratio y' /y can
for example be 0.4 (40%) or > 0.6 (600). This ratio can for
example be 0.5 (500).
The first example is one concrete example with specified
amounts of the different elements. Each of the examples 2-10
defines small ranges for the different elements. The alloys
according to examples 2-10 can be obtained by slightly
changing the composition of known alloys, i.e. in particular
by adding a small amount of Pd.
The alloys are suitable for the fabrication of single crystal
or polycrystalline articles.
Example 1
12.0 Cr
8.0 Co
2.0 Mo
4.0 W
4.0 Al
2.0 Ti
1.5 Ta
1.5 Nb
0.4 Pd
0.1 Hf
0.1 Si
0.01 B
0.05 C
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Example 2
15-17 Cr
8-9 Co
1.5-2.5 Mo
3-4 W
3-4 Al
3-4 Ti
1.5-2.5 Nb
0.1-0.5 Pd
0.05-0.2 C
0.005-0.015 B
0.05-0.015 Zr
Example 3
12-14 Cr
8-10 Co
1.5-2.5 Mo
3-5 W
3-4 Al
3.5-5 Ti
3-5 Ta
1.5-2.5 Nb
0.1-0.5 Pd
0.1-0.3 C
0.015-0.025 B
0.005-0.015 Zr
Example 4
12-14 Cr
8-10 Co
1.5-2.5 Mo
3-5 W
3-4 Al
3.5-4.5 Ti
3-5 Ta
0.1-0.5 Pd
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Example 5
7.5-9 Cr
8-11 Co
0.4-0.8 Mo
9-11 W
5-6 Al
0.5-1.5 Ti
2-4 Ta
0.1-0.5 Pd
0.05-0.2 C
0.01-0.02 B
0.005-0.05 Zr
1-2 Hf
Example 6
21-25 Cr
18-20 Co
1-3 W
1.5-2.5 Al
3-4 Ti
1-2 Ta
0.5-1.5 Nb
0.1-0.5 Pd
0.1-0.2 C
0.005-0.015 B
0.05-0.15 Zr
Example 7
21-25 Cr
18-20 Co
1-3 W
2-3 Al
3-4 Ti
1-2 Ta
0.5-1.5 Nb
0.1-0.5 Pd
0.1-0.2 C
0.005-0.015 B
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0.05-0.15 Zr
0.5-1.5 Hf
Example 8
8-9 Cr
4-6 Co
1-3 Mo
7-9 W
4.5-5.5 Al
1-2 Ti
5-7 Ta
0.1-0.5 Pd
0.05-0.15 Hf
0.05-0.15 Si
0.005-0.015 C
0.005-0.015 B
Example 9
6-7 Cr
9-11 Co
0.4-0.8 Mo
5-7 W
2.5-3.5 Re
5-6 Al
0.5-1.5 Ti
5-7 Ta
0.1-0.5 Pd
0.05-0.15 Hf
0.005-0.015 Y
Example 10
2.2-2.8 Cr
10-14 Co
8-10 w
6-7 Re
1.5-2.5 Ru
5.5-6.5 Al
5-6 Ta
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0.1-0.5 Pd
0.05-0.15 Hf
0.05-0.15 Si
5 The alloys according to the invention can be produced in a
manner which is known to a person skilled in the art for
producing Ni based y/y' superalloys of the prior art. The
alloys can be used for producing single crystal,
directionally solidified or polycrystalline components in a
10 manner known to the person skilled in the art. The alloy
according to the invention can be used for any component, or
part of a component, intended for use at high temperatures.
Fig 1 shows very schematically a sectional view of a part of
15 a typical gas turbine arrangement according to the invention.
In the embodiment shown in Fig 1, the gas turbine arrangement
has an annular combustion chamber 11. In Fig 1 only a lower
part of this combustion chamber 11 is shown. The annular
combustion chamber can be arranged around a symmetry axis
marked X-X in Fig 1. This symmetry axis X-X can also
constitute the axis of rotation of a rotor that forms part of
the gas turbine arrangement. The combustion chamber 11 is
fixed relative to a stator part 14. The gas turbine
arrangement comprises a number of guide vanes 13. In Fig 1,
two guide vanes 13 are shown. The guide vanes 13 are fixed
relative to the stator 14. The gas turbine arrangement also
has a number of turbine rotor blades 15. Two such rotor
blades 15 are shown in Fig 1. The rotor blades 15 form part
of the rotor that rotates around the axis of rotation X-X.
The gas turbine arrangement can of course comprise other
parts which are known to a person skilled in the art. The gas
turbine arrangement can for example have one or more
compressor stages and also additional turbine stages.
Different components in a gas turbine arrangement can be made
from alloys according to the present invention. For example,
the guide vanes 13 and/or the turbine rotor blades 15 can be
made of alloys according to the present invention. The alloys
according to the invention can also be used for parts of
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components, for example for a protective layer on a guide
vane 13, turbine rotor blade 15 or other part of a gas
turbine.
The invention also concerns the use of Pd. According to this
use, Pd, for example in the amounts according to the above
examples, is used in an alloy of the described kind for
providing the alloy within improved resistance against
hydrogen embrittlement.
The invention is not limited to the described embodiments but
may be varied and modified within the scoop of the following
claims.
