Ni Based Alloy, a Component, a Gas Turbine Arrangement and Use of Pd in Connection With Such an Alloy
The invention concerns a Ni based alloy suitable for single crystalline, directionally solidified or polycrystalline components to be used at high temperatures. The alloy is a γ′/γ alloy and consists of different alloying elements within defined ranges. Among other defined ranges of elements, the alloy contains Pd in a significant amount sufficient to provide the alloy with an improved resistance against hydrogen embrittlement. The invention also concerns a component designed for use as a component in a high temperature environment. Furthermore, the invention concerns a gas turbine arrangement. Moreover, the invention concerns the use of Pd for providing an alloy with improved resistance against hydrogen embrittlement.
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 γ′ (“gamma prime”), based on Ni3(Ti, Al), within the host material (γ).
The document U.S. Pat. No. 6,177,046 B1 describes γ/γ′ superalloys containing Pd. According to this document, Pd is added in 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 % (Table 7), 5-45 weight % (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 U.S. Pat. No. 6,007,645 describes γ/γ′ 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 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 γ/γ′ 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 γ/γ′ alloys are quite complex alloys. These alloys have a matrix of the γ phase, which is Ni with other elements like Cr, Co, Fe, W, Mo and Re in solution. Furthermore, such alloys contain particles of the γ′ 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 γ and γ′ phases, i.e. a certain element may tend to be drawn to a certain one of these phases such 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 γ′ phase. It has also been reported that Pd tends to partition favourably to the γ′ phase. Furthermore, the partition of an element between the γ and γ′ 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 INVENTIONComponents of Ni based γ/γ′ 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 γ/γ′ alloy suitable to be used for components exposed to high temperatures. A particular object it thereby that the alloy 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 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 γ/γ′ 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 γ/γ′ alloy and consisting, in weight %, of:
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 γ′ phase by Pd. As is mentioned above, Pd partitions favourably to the γ′ phase.
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 γ′ 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 γ/γ′ alloys such that slightly more Al partitions to the y phase. This means, for a given γ′ 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.
According to a further embodiment, the content of Cr >3.0, preferably >6.0. 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 ≦3.0. 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 >3.0. The content of Co can for example be >6.0. 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 >3.0. 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 <1.0. 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 >1.0. The content of Al can for example be >3.0 but <10.0. 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 γ′ phase. Furthermore, Al can increase the oxidation and hot corrosion resistance.
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 <5.0. The addition of elements from this group can be used to control the partition of other elements between the two phases γ and γ′.
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 γ′/γ >0.4 (40%) or even >0.6 (60%). A quite high fraction of γ′ 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 particular, the component can be used at high temperatures and still have a good resistance against hydrogen embrittlement.
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 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.
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 γ/γ′ alloys. The ratio γ′/γ can for example be 0.4 (40%) or >0.6 (60%). This ratio can for example be 0.5 (50%).
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
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 γ/γ′ superalloys of the prior art. The alloys can be used for producing single crystal, directionally solidified or polycrystalline components in a 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.
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.
Claims
1.-32. (canceled)
33. A Ni based γy/γ′ alloy consisting of (in weight %): 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 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: is suitable for single crystalline, directionally solidified or polycrystalline components to be used at high temperatures, and contains Pd in a significant amount sufficient to provide the alloy with an improved resistance against hydrogen embrittlement.
34. The alloy according to claim 33, wherein the content of additional elements is less than 1.0. (in weight %).
35. The alloy according to claim 34, wherein the content of the additional elements is 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.
36. The alloy according to claim 33, wherein (in weight %):
- the content of Pd is between 0.05 and 4.0, or
- the content of Pd is between 0.05 and 2.0, or
- the content of Pd is between 0.05 and 1.0.
37. The alloy according to claim 33, wherein the content of Cr is (in weight %):
- between 0.5 and 3.0, or
- between 0.5 and 6.0, or
- between 3.0 and 25.0.
38. The alloy according to claim 33, wherein (in weight %):
- the content of one or more elements selected from the group consisting of: Co, Fe and Mn is greater than 3.0, or
- the content of Co is greater than 6.0 and less than 25.0.
39. The alloy according to claim 38, wherein the content of Co is greater than the sum of the content of Fe plus the content of Mn.
40. The alloy according to claim 39, wherein the content of one or more elements selected from the group consisting of: Mo, W, Re and Rh is greater then 3.0 (in weight
41. The alloy according to claim 40, wherein the content of W is greater than the content of Mo.
42. The alloy according to claim 41, wherein the sum of the content of Re plus the content of Rh is less than 1.0 (in weight %).
43. The alloy according to claim 42, wherein the content of Al is greater than 1.0 (in weight %).
44. The alloy according to claim 43, wherein the content of Al is greater than 3.0 and less than 10.0 (in weight %).
45. The alloy according to claim 44, wherein the molar fraction of Al in the alloy is greater than the molar fraction of the other elements selected from the group consisting of Al, Ti, Ta, Nb, and V.
46. The alloy according to claim 33, wherein (in weight %):
- the content of one or more elements selected from the group consisting of: Ru, Os, Ir and Pt is greater than 0.01 and less then 5.0, or
- the content of Hf is greater than 0.05, or
- the content of Si is greater than 0.02, or
- the content of one or more elements selected from the group consisting of: B, C, N and Zr is greater than 0.05 and less than 0.8, or
- the content of one or more elements selected from the group consisting of: Y, La, Sc, actinides, Ce and lanthanides are greater than 0.005, or
- the content of Ni is greater than 35.0, or
- the content of Ni is greater than 50.0.
47. The alloy according to claim 46, wherein (in weight %):
- the volume ratio γ′/γ is greater than 0.4 (40%), or the volume ratio γ′/γ>0.6 (60%).
48. A high temperature gas turbine component material, comprising: 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; 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; and balance Ni.
49. The component according to claim 48, wherein the component is at least part of a guide vane or at least part of a turbine rotor blade.
50. The component according to claim 49, wherein the at least part guide vane or at least part rotor blade exhibits improved resistance against hydrogen embrittlement.
Type: Application
Filed: Dec 21, 2005
Publication Date: May 1, 2008
Inventors: Douglas James Arrell (Oviedo, FL), Magnus Hasselqvist (Finspong)
Application Number: 11/794,071
International Classification: C22C 19/05 (20060101);
