GB2628174A - A nickel base alloy having high oxidation resistance and good wear resistance, powder and method - Google Patents

Abstract

A nickel-based superalloy comprising (by weight): 6.0-12.0 % cobalt, 6.0-12.0 % iron, 14.0-18 % chromium, 2.0-5.0 % tungsten, 4.0-5.5 % aluminium, 2.0-3.5 % tantalum, 0.03-0.3 % carbon, 0.005-0.03 % boron, 0.005-0.03 % zirconium, 0.005-0.5 % silicon, 0.002-0.2 % of the sum of Y, Sc, lanthanides and actinides, 0.05-3.0 % hafnium, 0-2.0 % molybdenum, 0-0.2 % titanium and 0-2.0 % manganese, with the balance being Nickel and unavoidable impurities.

Description

A nickel base alloy having high oxidation resistance and good wear resistance, powder and method The invention relates to a nickel base alloy having high °xi-dation resistance, good hot corrosion resistance, good wear resistance, sufficient formability and ductility for e.g., hot sealing structures in gas turbines, and sufficient weldability for e.g., manual welding, Laser Metal Deposition (LMD) and powder bed processes such as Laser Powder Bed Fusion (LPBF).

A turbine section in a gas turbine contains blades, vanes and heat shields made in Nickel base highly y" strengthened superalloys, from here on referred to as blade alloys.

It also contains sealing structures such as strips between components, flap seal plates and honeycombs made from thin sheets of nickel base superalloys which are solution strengthened and/or at most moderately y' strengthened.

To a first approximation, the microstructure in a correctly heat treated blade alloy consists of grains which essentially consist of y' particles embedded in a y matrix. 7" is to a first approximation Ni,A1 with elements like Titanium (Ti), Tantalum (Ta), Hafnium (Hf) and Niobium (Nb) in solution.y is to a first approximation Nickel (Ni) with elements like Cobalt (Co), Iron (Fe), Molybdenum (Mo) and Tungsten (W) in solution. The grain boundaries are decorated with borides and carbides which provide adherence between the grains, Zirconium (Zr) also provide grain boundary strength. However, while e.g. Aluminum (Al) partitions mostly to the y' phase, some Aluminum (Al) partitions to the y phase. The partitioning behavior of Aluminum (Al) is not the same for all blade alloys, it is affected by the levels of other alloy elements.

A blade alloy is to a first approximation able to form a protective, i.e. continuous and adherent, Cr203 layer within its oxide scale if it contains at least about 12.0wt% Chromium (Cr).

Classically, in land based gas turbines, blade alloys were chosen from the group of Industrial Gas Turbine (IGT) alloys such as IN738LC which, with >12.0wt% Chromium (Cr), are able to form protective Cr:03, but contain too little Aluminum (Al) and too much Titanium (Ti) to enable formation of protective AliO3. Since CriO3 is protective only up to about 1123K w.r.t. the long term service, typically >30kh between overhauls, in land based gas turbine increased firing temperatures has required the introduction of coatings on the IGT alloys and/or replacement of IGT alloys with blade alloys such as STAL125C01 able to form protective A1203.

Classically, in land based gas turbines, sheet alloys such as Hastelloy-X and 0-263 were used for sealing structures. These alloys are, like the IGT alloys, able to form protective Cri02, but are not able to form protective A1203, and, consequently subject to the same 1123K limit.

When the allowable metal temperatures in the vanes, blade and heat shields were increased thanks to coatings and introduction of A1203 forming blade alloys such as STAL1250C1, it was difficult to avoid increased metal temperatures also in said sealing structures.

Since it is usually impractical to apply coatings on such structures, coatings tend to crack when the sheet alloys are bent and twisted during production and/or when they are attached, this led to oxidation problems with the classical sheet alloys.

An often useful solution to these problems has been replacement of the classical sheet alloys with the sheet alloy Haynes2l4 which, with 16.0wt% Chromium (Cr) and 4.5wt% Aluminum (Al), is able to form protective Cr,03 up to about 1123K and protective A1,03 above about 1123K. With ever increasing firing temperatures it would however be beneficial with an even higher oxidation resistance.

"B.A.Pint et al. 'The use of two reactive elements to optimize oxidation performance of alumina-forming alloys', Materials at High Temperatures, 2003" teaches the high cyclic oxidation resistance in Haynes2l4 provided by its ability to form protective alumina and the inclusion of Zr, Y and Si.

It should also be noted that Haynes2l4 is weldable implying that it can be used also for welding processes. This includes manual welding and Laser Metal Deposition (LMD) using wire.

This also includes LMD using powder. This also includes powder bed processes such as IPSO using powder.

It is therefore aim of the invention to solve this problem.

It is the aim of this invention to provide an alloy which provides higher oxidation, creep and wear resistance than Haynes2l4, but which is still possible to use for production and forming of sheet metal. This sheet metal can be used for e.g., hot sealing structures in gas turbines.

It is a further aim of this invention to utilize this alloy for production of wire for welding and LMD. It is a further objective with this invention to utilize this alloy for production of powder for LMD as well as powder bed processes such as, but not restricted to, LPBF.

It is a further aim of this invention to utilize this alloy for casting of parts such as sealing devices which can act as parts of the cooling systems and provide damping. In the latter case a high wear resistance is beneficial.

The problem is solved by an alloy according to claim 1, a 10 powder according to claim 11 and method according to claim 12.

The inventive alloy is provided by the composition (in wt' 6.0% -12.0% Cobalt (Co) 6.0% -12.0% Iron (Fe) 14.0% -18% Chromium (Cr) 2.0% -5.0% Tungsten (W) 4.0% -5.5% Aluminum (Al) 2.0% -3.5% Tantalum (Ta) 0.03% -0.3% Carbon (C) 0.005 -0.03% Boron (B) 0.005% -0.03% Zirconium (Zr) 0.005% -0.5% Silicon (Si) 0.002% -0.04% of the sum of Yttrium (Y), Scandium (Sc), Lanthanides and Actinides 0.05% -3.0% Hafnium (Hf) up to 2.0%. Molybdenum (Mo) up to 0.2%. Titanium (Ti) up to 2.0 wt% Manganese (Mn) and unavoidable impurities, Nickel (Ni), especially the rest being Nickel (Ni).

It would furthermore be beneficial with increased creep strength and wear resistance relative to Haynes214. It should be noted that while Haynes214 includes 16.0wt% Chromium (Cr) and 4.5wt% Aluminum (Al) to enable formation of protective A1102, it is also produced with a clean production process, levels of Zr and Y for sulfur suppress the very detrimental adherence of the Al203 layer.

Al Ti Ta Hf Si C Zr B RE AIA 0.1 0.5 2.2.05.03.005 4.5.04.01.01Y 2.2 4.5 3.0 0.1.01.05.01.01.01Y 7.0 4.5 3.0 1.0.01.15.01.01.01Y 7.7 4.5 3.0 2.0.01.25.01.01.01Y 8.4 4.5 3.0 0.1.01.05.01.01.02M 7.0 3.5 3.5 1.4.07.02.01 5.5 8.0 0.5.01.07.01.015 4.3 in [wt117] for some commercial alloys and embodiments for the invention. RE denotes Rare Earth. AlA is relative Aluminum activity at 1273K. M is either a mix of 0.1wt96-La and 0.1 wt96 Y, or, 0.2wt% Mischmetal.

Haynes214 is strengthened by 7-particles up to the 7-Solvus at about 1193K, but, neither the y matrix nor the y" particles are strengthened. The 7-particles provide creep, yield and wear resistance. Haynes214 has a low Carbon content, hence the creep, yield and wear resistance provided by carbides is small.

It would be advantageous if the y and y" phases were at least moderately strengthened to provide higher strength and wear 25 resistance.

In addition, it would be advantageous if more and/or harder and includes small measured gettering. This is done to effect of Sulfur (S) on the Alloy Ni Fe Co Cr Mn Mo W HasteloyX B 18.0 22.0 9.0 C263 B 20.0 20.0 0.2 6.0 Haynes214 B 3.0 16.0 E214LC B 8.0 8.0 16.0 3.0 E214MC B 8.0 8.0 16.0 3.0 E214HC B 8.0 8.0 16.0 3.0 E214LC_M B 8.0 8.0 16.0 3.0 IN738LC B 8.5 16.0 1.8 2.6 STAL125CC1 B 5.0 12.5 1.5 3.5 Table: Nominal compositions carbides were formed to further improve the strength and, especially, the wear resistance.

It would furthermore be advantageous if y" was stable up to at least 1273K to provide strength and wear resistance in the 1173K to 1273K range since sealing structures such as sealing strips can be subjected to such temperatures in high firing temperature gas turbines.

However, at the same time the level of 7' at lower temperatures should preferably not be increased since it 10 would lead to increased concentrations of brittle phase formation prone alloy element in the 7 matrix.

In one embodiment, E214LC, Tungsten and Tantalum have been added relative to Hayne2l4 to increase the strength of the y and 7' phases respectively. This has increased the predicted 7' solvus by about 100K and the predicted y' curve is quite close to the preferred 7' curve. The predicted level of unwanted phases is low despite the addition of Cobalt (Co), Tungsten (W) and more Iron (Fe), and, thanks to the fact that the y" content is moderate. The beneficial change in the slope of the y" curve is an effect of the Cobalt (Co) and Iron (Fe) recipe which affects the partitioning of Aluminum (Al) between the y and y' phases.

The predicted Aluminum activity at 1273K is very significantly increased relative to Haynes214, and it is also significantly higher than in e.g., the highly oxidation resistant blade alloy STAL125CC1. Since the Aluminum activity is a marker for oxidation resistance this strongly suggests an increased oxidation resistance relative to Haynes2l4. The Cobalt (Co) + Iron (Fe) recipe contributes significantly to the increased Aluminum (Al) activity, but Chromium (Cr) and the inclusion of Tantalum (Ta) are also beneficial. The potential for increased oxidation resistance via an increased Aluminum (Al) activity cannot be realized unless the detrimental effect of sulfur is suppressed, preferably even more efficiently than for Haynes2l4. To this end E214LC should preferably be produced with a clean production process.

In addition, E214LC contains small measured levels of Hafnium (Hf), Zirconium (Zr) and Yttrium (Y) for sulfur (S) gettering. Silicon (Si) is furthermore prudently included in the composition at a low measured level to avoid the risk for a reduction in oxidation resistance which might occur if the production process for a component turned out to result in an unusually low level of Silicon (Si) since Silicon (Si) has a beneficial catalytic effect on the selective oxidation of protective oxide layers.

The preferred change to MC carbides is not predicted for 20 E214LC and might not have resulted in a significant improvement in wear resistance anyway given the low Carbon (C) content inherited from Haynes2l4. The wear resistance is nevertheless increased relative to Haynes2l4 since the strengthening elements increase the hardness of the alloy. It 25 is particular improved at higher temperatures given the increased 7' Solvus.

In another embodiment, E214MC, the Carbon (C) content is increased to 0.15wt% to enable formation of more carbides for further increased wear resistance, and, Hafnium has been included at 1.0wt% to bind the additional Carbon (C) in MC carbides. All carbides are now predicted to be MC carbides down to below 1273K, and some MC is predicted to be stable down to below 873K. This strongly suggests further increased wear resistance relative to E214LC. The level of MC carbides at 1273K is predicted to be 1.4mol%. The predicted Aluminum activity is further increased relative to E214LC. The predicted 7" curve is only marginally changed from that for E214LC.

In a further embodiment, E214HC, the Carbon (C) content is increased to 0.251 to enable formation of further MC carbides relative to E214MC for further increased wear resistance. To this end Hafnium has been increased to 2.0wt= to bind the additional Carbon (C) into MC carbides. All carbides are predicted to be MC carbides down to below 1273K, and some MC is predicted to be stable down to below 873K. The level of MC carbides at 1273K is predicted to be 2.4mol%. This strongly suggests increased wear resistance. The predicted Aluminum (Al) activity is further increased relative to E214MC. The predicted 7' curve is somewhat changed from that for E214LC in the sense that the 7" Solves is somewhat decreased.

The inventive Nickel base sheet alloy has the following composition (in wt%): 6.0% -12.0% Cobalt (Co) 6.0% -12.0% Iron (Fe) 14.0 -18% Chromium (Cr) 2.0% -5.0% Tungsten (W) 4.0% -5.5% Aluminum (Al) 2.0% -3.5% Tantalum (Ta) 0.03% -0.3% Carbon (C) 0.005% -0.03% Boron (B) 0.005% -0.03% Zirconium (Zr) 0.005% -0.5% Silicon (Si) 0.002% -0.04% of the sum of Yttrium (Y), Scandium (Sc), Lanthanides and Actinides 0.05% to 3.06 Hafnium (Hf) up to 2.0%. Molybdenum (Mo) up to 0.2%. Titanium (Ti) up to 2.0 wt% Manganese (Mn) and Nickel (Ni) and unavoidable impurities.

Cobalt (Co) and Iron (Fe) are both included with at least 6.0wt% to ensure that a combination of them beneficially affects the partitioning of Aluminum (Al) to keep the 7' levels moderate, and significantly contributes to the high Aluminum (Al) activity. They are both capped at 12.0wt% to avoid excessive formation of brittle phases.

Chromium (Cr) is included at a level which provides good hot 15 corrosion resistance and contributes to the high Aluminum activity, but is capped at 18.0wt1 to avoid excessive formation of brittle phases.

Tungsten (W) is included with at least 2.0wt% to provide 20 strengthening of the y matrix but is capped at 5.0wt% to avoid excessive formation of brittle phases.

Aluminum (Al) is included with at least 4.0wt,i'5 to enable a high Aluminum activity and a useful level of y" particles. It 25 is capped at 5.5wt% to avoid excessive formation of brittle phases.

Tantalum (Ta) is included with at least 2.0wt to provide strengthening of the y' particles. It is capped at 3.5wt% to 30 avoid excessive y" formation.

Carbon (C) is included with at least 0.03wt% to add to the grain boundary strengthening and capped at 0.3wt% to ensure that the formability and general ductility are useful.

Boron (B) and Zirconium (Zr) are included within ranges typical for most high temperature Nickel base alloys and combine with Carbon (C) for grain boundary strengthening. Zirconium (Zr) is also a part of the sulfur gettering recipe together with Hafnium (Hf) and Yttrium (Y).

Silicon (Si) is included with at least 0.005wt% to help accelerate the selective oxidation of protective Cr2O.H. and protective AIM but is capped at 0.5wt% to avoid embrittling of the grain boundaries.

Rare earths such as Yttrium (Y), Scandium (SC), the Lanthanides and the Actinides are combined with Zirconium (Zr) and Hafnium (Hf) in a sulfur (S) gettering recipe.

Rare earth additions as low as 0.002wt% can be efficient, especially if clean processing has been used, while more than 0.2wt% can result in excessive formation of rare earth oxides inside alloys.

Hafnium (Hf) is included with at least 0.05wt% to add to the 25 sulfur gettering recipe and capped at 3.0wt%.

Molybdenum (Mo) can complement Tungsten (W) as matrix strengthening element. It is capped at 2.0wt% since higher levels can reduce the hot corrosion resistance.

[Goldschmidt] "D.Goldschmdt 'Single Crystal Blades', Materials for Advanced Power Engineering, Part 1, 1994" teaches the significant reduction in hot corrosion resistance in SC16 (16wt% Cr, 3 wt% Mo) relative to IN738LC (16 wtt Cr, 1.8 wt % Mo).

While Titanium (Ti) is detrimental to the oxidation resistance at high temperature as it increases the permeability of the A1-0 layer, it is inclusion at a low level can contribute to the sulfur gettering. It can also be used as a sacrificial element such that Ti nitrides rather than Al nitrides are formed.

Manganese (Mn) is often found in sheet alloys, especially those which are also used as weld fillers, see e.g., the C263 composition in table 1. It is sometimes regarded as beneficial for oxidation and hot corrosion resistance by acting as a sulfur getter, especially w.r.t. sulfur from external sources. The word sometimes here is natural given the wide spectrum of corrosive agent compositions. It is also sometimes regarded as beneficial for weldability. The word sometimes here is natural given the wide spectrum of welding processes and weld parameters utilized. It is capped at 2wt% to avoid embrittlement.

An increased level of MC carbides will unavoidably restrict the formability and to some extent also the oxidation resistance, hence embodiments with high levels of MC carbides are preferable in structures such as, but not restricted to, such flap seals which can see wear but are not formed into complex shapes, and are typically at a lower risk for hot gas ingestion than e.g., sealing strips between adjacent vanes and adjacent heat shields.

Embodiments optimized for oxidation resistance can beneficially be used for such sealing strips. When such sealing strips are significantly curved the preferable level of MC carbides can be adjusted downwards by those skilled in the art.

The use of Lanthanum (La) and Yttrium (Y) is more costly but has been seen to provide improved oxidation resistance in in-house repair alloys than the use of only one rare earth.

Embodiments to be used for welding can also require composition adjustments by those skilled in the art as required by the specific welding process.

"J.B.Wahl, K.Harris 'Advances in Single Crystal Superalloys Control of Critical Elements', Parsons Conf. Glascow, 2007" teaches that the use of Hafnium together with Lanthanum and Yttrium is more efficient than the use of Hafnium and Lanthanum, or, Hafnium and Yttrium, in cyclic oxidation tests on CMSX-4.

Claims (13)

1. Claims 1. Nickel based superalloy, comprising (in wt%): 6.0% -12.0% Cobalt (Co) 6.0% -12.0% Iron (Fe) 14.0% -18% Chromium (Cr) up to 2.0% Molybdenum (Mo) 2.0% -5.0% Tungsten (W) 4.0% -5.5%, Aluminum (Al) 2.0% -3.5% Tantalum (Ta) up to 0.2% Titanium (Ti) 0.03%. -0.3% Carbon (C) 0.005% -0.03% Boron (B) 0.005% -0.03% Zirconium (Zr) 0.005% -0.5% Silicon (Si) 0.002% -0.2% of the sum of Yttrium (Y), Scandium (Sc), Lanthanides and Actinides 0.05% to 3.0% Hafnium (Hf) up to 2.0% Manganese (Mn) Nickel (Ni), especially the rest being Nickel (Ni), and unavoidable impurities.
2. 2. Nickel based superalloy according to claim 1, comprising (in wt%) 7.0% -9.0% Cobalt (Co) 7.0% -9.0% Iron (Fe) 15.0% -17.0% Chromium (Cr) 2.5% -3.5% Tungsten (W) 4.2% -4.8% Aluminum (Al) 2.5% -3.5% Tantalum (Ta) 0.03%. -0.07% Carbon (C) 0.007% -0.013% Boron (B) 0.007% -0.013% Zirconium (Zr) 0.007%. -0.015% Silicon (Si) 0.005%. -0.03% Yttrium (Y) 0.07% -0.13% Hafnium (Hf).
3. 3. Nickel based superalloy according to claim 2, comprising (in wt%) 8.0% Cobalt (Co) 8.0% Iron (Fe) 16.02, Chromium (Cr) 3.0% Tungsten (W) 4.5% Aluminum (Al) 3.0% Tantalum (Ta) 0.053 Carbon (C) 0.01-?, Boron (B) 0.01% Zirconium (Zr) 0.01% Silicon (Si) 0.0159_ Yttrium (Y) 0.1% Hafnium (Hf)
4. 4. Nickel based superalloy according to claim 1, comprising (in wt%) 7.0% -9.01 Cobalt (Co) 7.0% -9.0% Iron (Fe) 15.0% -17.0% Chromium (Cr) 2.5% -3.5% Tungsten (W) 4.2% -4.8% Aluminum (Al) 2.5% -3.5% Tantalum (Ta) 0.12% -0.18% Carbon (C) 0.007% -0.013% Boron (B) 0.007% -0.013% Zirconium (Zr) 0.007% -0.015% Silicon (Si) 0.005%. -0.03% Yttrium (Y) 0.9% -1.1% Hafnium (Hf).
5. 5. Nickel based superalloy according to claim 4, comprising (in wt) 8.0% Cobalt (Co) 8.0% Iron (Fe) 16.0-?, Chromium (Cr) 3.0% Tungsten (W) 4.5% Aluminum (Al) 3.0% Tantalum (Ta) 0.152, Carbon (C) 0.01% Boron (B) 0.01% Zirconium (Zr) 0.01% Silicon (Si) 0.015% Yttrium (Y) 1.0% Hafnium (Hf)
6. 6. Nickel based superalloy according to claim 1 comprising (in wt%) 7.0% -9.0% Cobalt (Co) 7.0% -9.0% Iron (Fe) 15.0% -17.0% Chromium (Cr) 2.5% -3.5% Tungsten (W) 4.2% -4.8% Aluminum (Al) 2.5% -3.5% Tantalum (Ta) 0.22% -0.28% Carbon (C) 0.007% -0.013% Boron (B) 0.007% -0.013% Zirconium (Zr) 0.007% -0.015% Silicon (Si) 0.005% -0.03% Yttrium (Y) 1.9% -2.1% Hafnium (Hf).
7. 7. Nickel based superalloy according to claim 6, comprising (in wt%) 8.0% Cobalt (Co) 8.0% Iron (Fe) 16.04 Chromium (Cr) 3.0% Tungsten (W) 4.5% Aluminum (Al) 3.0% Tantalum (Ta) 0.25% Carbon (C) 0.014 Boron (B) 0.01% Zirconium (Zr) 0.01% Silicon (Si) 0.015% Yttrium (Y) 2.0% Hafnium (Hf).
8. 8. Nickel based superalloy according to claim 1, comprising (in wt%): 7.0% -9.0% Cobalt (Co) 7.0% -9.0% Iron (Fe) 15.0% -17.0% Chromium (Cr) 2.5% -3.5% Tungsten (W) 4.2% -4.8% Aluminum (Al) 2.5% -3.5% Tantalum (Ta) 0.03% -0.07% Carbon (C) 0.007% -0.013% Boron (B) 0.007% -0.013% Zirconium (Zr) 0.007% -0.015% Silicon (Si) 0.003% -0.02% Yttrium (Y) 0.003% -0.02% Lanthanum (La) 0.07% -0.13% Hafnium (Hf).
9. 9. Nickel based superalloy according to claim 8, comprising (in wt%) 8.0% Cobalt (Co) 8.0% Iron (Fe) 16.0%. Chromium (Cr) 3.0% Tungsten (W) 4.5% Aluminum (Al) 3.06 Tantalum (Ta) 0.25% Carbon (C) 0.011 Boron (B) 0.01% Zirconium (Zr) 0.01% Silicon (Si) 0.01%. Yttrium (Y) 0.01% Lanthanum (La) 0.1% Hafnium (Hf).
10. 10. Nickel based superalloy according to any of the claims 1 to 9 in which at least two rare earth elements are intentially utilized, and in which both are present at at least 0.002wt%.
11. 11. Powder having a composition to any of the previous alloys.
12. 12. Method to repair or to newly build a component, wherein an alloy of any of the previous claims 1 to 10 or a powder according to claim 11 is used.
13. 13. Method according to claim 12, wherein a printing or casting method is applied.