High strength, hot corrosion and oxidation resistant, equiaxed nickel base superalloy and articles and method of making

Abstract

Corrosion and oxidation resistant, high strength, directionally solidified superalloy alloys and articles are described. The articles have a nominal composition in weight percent of about 12.1% Cr, 9% Co, 1.9% Mo, 3.8% W, 5% Ta, 3.6% Al, 4.1% Ti, 0.013% B, 0.1% C, up to about 0.01 Zr, balance essentially nickel. The resultant articles have good hot corrosion resistance, oxidation resistance and creep properties. The articles are preferably cast as equiaxed articles such as gas turbine engine components.

Description

CROSS REFERENCE TO RELATED APPLICATION

Some of the material described herein is described and/or claimed in co-pending and commonly owned application Ser. No. 10/023,565 entitled “HIGH STRENGTH, HTO CORROSION AND OXIDATION RESISTANT, DIRECTIONALLY SOLIDIFIED NICKEL BASE SUPERALLOY AND ARTICLES”, which is expressly incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to the field of nickel base superalloys for use in equiaxed articles, and more particularly to such alloys providing articles having good mechanical properties at elevated temperatures, good resistance to hot corrosion, and good oxidation resistance.

BACKGROUND OF THE INVENTION

The increasing demands for efficiency in gas turbine engines have resulted in a demand for materials capable of withstanding more severe operating conditions. In particular, good strength is required for certain applications along with the resistance to hot corrosion, oxidation and creep.

U.S. Pat. No. 3,619,182 describes a moderate strength superalloy, commercially known as IN 792, having purportedly superior corrosion resistance. The '182 patent describes an alloy having a composition, in weight percent, of: 9.5-14 Cr; 7-11 Co; 1-2.5 Mo; 3-4 W; 1-4 Ta; up to 1 Cb; 3-4 Al; 3-5 Ti; Al +Ti =6.5-8; 0.005-0.05 B; 0.01-0.25 Zr; 0.02-0.25 C; bal. Ni. At the time the '182 application was filed, the alloy would have been cast to form an equiaxed (e.g., no indication of crystallographic orientation) article, e.g., for gas turbine engine components. The '182 patent is expressly incorporated herein by reference.

An alloy, commonly known as GTD-111 which has been cast in equiaxed and directionally solidified forms. In equiaxed castings, GTD-111 has a nominal composition, in weight percent, of: 14 Cr; 9.7 Co; 1.5 Mo; 3.8 W; 3 Ta; 3 Al; 0.10 C; 5 Ti; 0.02 B; 0.04 Zr, bal. Ni. See, e.g., Schilke, et el. “Advanced Materials Propel Progress in Land-Based Gas Turbines”, Advanced Materials and Processes, April 1992, page ______; and U.S. Pat. No. 6,416,596; see also, U.K. Patent GB 1,511,562 (13.7-14.3 Cr; 9-10 Co; 1-1.5 Mo; 4.8-5.5 Ti; 2.8-3.2 Al; 3.7-4.3 W; 1-1.5 Nb; 2.5-3 Ta; 2.8-3.2 Al; 0.08-0.2 C; 4.8-5.5 Ti; 0.01-0.02 B; 0.02-0.1 Zr; and either 1.5-3.5 mixture of Ta, Cb and Hf, or 2.5-3 Ta or 2-2.5 Hf or 1-1.5 Cb [or Ta+Cb+Hf=1.5-3.5]; and consisting of a matrix and a monocarbide phase distributed through the matrix consisting of: Ti, Mo, W and/or Ta and/or Cb and/or Hf in proportions such that the total of Mo and W is less than 15 weight percent of the carbide phase); see also U.S. Pat. No. 6,428,637. In directionally solidified castings, the nominal composition is similar except for slightly lower amounts of zirconium. See, G. K. Bouse, “Eta (η) and Platelet Phases in Investment Cast Superalloys”, presented at Superalloys 1996, Seven Springs, Pa.

U.S. Pat. No. 3,615,376 is directed to an alloy with a claimed composition, in weight percent, of: 0.15-0.3 C (described as more than is required for de-oxidation and sufficient to form grain boundary carbides); 13-15.6 Cr; 5-15 Co; 2.5-5 Mo; 3-6 W; 4-6 Ti; 2-4 Al; 0.005-0.02 Zr; balance Ni and incidental impurities; and also requires that Ti/Al be 1:1-3:1; Ti+Al between 7.5-9; Mo+0.5W between 5-7; with a substantial absence of sigma phase and a stress rupture life of at least 25 hours at 27.5 ksi at 1800° F. A directionally solidified version of this alloy may also include a significant, intentionally added amount of Hf, e.g. up to or over 0.5 wt. %.

U.S. Pat. No. 6,231,692 is directed to a nickel base alloy with improved machinability. The alloy has a composition in weight percent of 12.5-15 Cr, 5-15 Co, 2.5-5 Mo, 3-6 Al, 4-6 Ti, 0.005-0.02 B, up to about 0.01 Zr, 0.055-0.075 C (“below about 0.08”), balance essentially Ni. The patent asserts that the alloy is easier and quicker to machine relative to Rene 80 alloy.

It would be desirable to provide a material for the fabrication of equiaxed articles, and to provide such articles, which have adequate strength, and which also demonstrate good oxidation and corrosion resistance.

It would also be desirable to provide the benefits of an alloy composition adapted for use as in cast equiaxed parts which maintain the benefits of the alloy.

It would likewise be desirable to provide such an alloy which provides oxidation resistance in equiaxed grain form at least comparable to that in directionally solidified form.

SUMMARY OF THE INVENTION

Alloys for equiaxed solidified articles are disclosed which have at least comparable oxidation resistance relative to directionally solidified counterparts, and corrosion resistance at least comparable to such alloys. Moreover the inventive alloys have oxidation resistance greater than directionally solidified counterparts, and comparable corrosion resistance. In many instances, the alloys of the present invention provide articles in equiaxed form with superior oxidation resistance.

The inventive alloys comprise, in weight percent, of about 11-13.25% chromium; 8-10% cobalt; 1.5-2.5% molybdenum; 3.25-4.5% tungsten; 4.5-5.5% tantalum; 3.25-4% aluminum; 3.5-4.5% titanium; 0.005-0.02% boron; up to about 0.03% zirconium; 0.05-0.2% carbon; up to about 0.15% hafnium; and balance essentially nickel; and in another variation about 11-13% chromium; 8.25-9.75% cobalt; 1.5-2.25% molybdenum; 3.4-4.3% tungsten; 4.7-5.5% tantalum; 3.3-4% aluminum; 3.75-4.3% titanium; 0.008-0.02% boron; up to about 0.03% zirconium; 0.05-0.15% carbon; up to about 0.15% hafnium; and balance essentially nickel.

In equiaxed form, the alloy exhibits oxidation resistance at 2000° F. of at least roughly 2.5×, creep rupture life at 1400° F. of at least roughly 2.5×, at 1600° F. of at least roughly 2×, and at 1800° F. of at least roughly 1.3× compared to a similar article having a composition of equiaxed GTD 111 nominally composed of 14 Cr, 4.9 Ti, 1.6 Mo, 3.8 W, 2.8 Ta, 3 Al, 9.5 Co, 0.01 B, 0.02 Zr, 0.1 C, and balance Ni.

The invention composition may be cast in equiaxed form according to the teachings of various prior patents as is known in the art. Where needed, the present composition after being cast can be heat treated in order to improve the mechanical properties of the alloy by controlling the gamma prime particle size in accordance, e.g., with the teachings of U.S. Pat. No. 4,116,723 which is also expressly incorporated herein by reference. Such parts, for example for industrial gas turbines may be quite large, on the order or up to about 60 inches long, although most parts such as blades and vanes are between about 5-50 inches long.

Other features and advantages will be apparent from the specification and claims which illustrate an embodiment of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph illustrating creep rupture life of the inventive alloy versus a prior art equiaxed alloy.

FIG. 2 is a graph illustrating the relative creep rupture life of the inventive alloy at 1800 F.

FIG. 3 is a graph illustrating the relative creep rupture life of the inventive alloy at 1600 F.

FIG. 4 is a graph illustrating the relative creep rupture life of the inventive alloy at 1400 F.

FIG. 5 is graph illustrating the effect of aluminum and hafnium content on oxidation resistance of the inventive alloy.

FIG. 6 is a graph illustrating the relative hot corrosion resistance of the inventive alloy.

FIG. 7 is a graph illustrating the relative oxidation resistance of the inventive alloy.

FIG. 8 is a graph illustrating the creep life and oxidation life for several hot corrosion resistant alloys.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is based on altering the chemistry originally adapted for use in single crystal articles, e.g., commonly owned U.S. Pat. No. 4,597,809 and co-pending, commonly owned application Ser. No. 10/023,565 entitled “HIGH STRENGTH, HTO CORROSION AND OXIDATION RESISTANT, DIRECTIONALLY SOLIDIFIED NICKEL BASE SUPERALLOY AND ARTICLES” which are expressly incorporated by reference herein, into an alloy that is particularly useful in the production of equiaxed articles. In equiaxed form, cast articles in accordance with the present invention, such as gas turbine engine turbine blades and vanes, are characterized by good hot corrosion resistance, good oxidation resistance, and good creep-rupture properties. We also considered the composition of an alloy generally designated “GTD-111”, see, e.g., GB Pat. No. 1,511,652 and U.S. Pat. No. 6,416,596, which is used in equiaxed and columnar grain forms, and has a nominal composition in weight percent of 14 Cr, 4.9 Ti, 1.5 Mo, 3.8 W, 2.8 Ta, 3 Al, 9.5 Co, 0.01 B, ˜0.02 Zr, ˜0.1 C, and balance Ni.

We believe that beneficial and different properties may be achieved, among other things, by altering the composition of the single crystal '809 alloy by significantly increasing the carbon and boron levels (and allowing a maximum amount of zirconium in the alloy) on one hand, or by altering the nominal content of the equiaxed/columnar grain -111 alloy by significantly increasing tantalum, aluminum and molybdenum contents, and significantly decreasing the titanium and chromium contents on the other hand (e.g., the '562 patent teaches among other things high chromium (above 13.7 wt. %); relatively higher cobalt (over 9.5 wt. %); that more than 0.02% zirconium is acceptable; and that tantalum over 3-3.5 wt. % will cause unacceptable microstructural instability).

The generally preferred composition of the present invention consists essentially of, in weight percent, about 11-13.25% chromium; 8-10% cobalt; 1.5-2.5% molybdenum; 3.25-4.5% tungsten; 4.5-5.5% tantalum; 3.25-4%:aluminum; 3.5-4.5% titanium; 0.005-0.02% boron; zirconium in impurity levels (less than about 0.025% zirconium); 0.05-0.2% carbon; up to about 0.15% hafnium; and balance essentially nickel. In another variation, the alloy consists of about 11-13% chromium; 8.25-9.75% cobalt; 1.5-2.25% molybdenum; 3.4-4.3% tungsten; 4.7-5.5% tantalum; 3.3-4% aluminum; 3.75-4.3% titanium; 0.008-0.02% boron; up to about 0.03% zirconium; 0.05-0.15% carbon; up to about 0.15% hafnium; and balance essentially nickel. The article has advantages over prior art equiaxed alloys, such as creep rupture at 1400° F. of at least roughly 2.5×, and at 1600° F. of at least roughly 2× compared to a similar equiaxed article having a nominal composition of 14 Cr, 4.9 Ti, 1.6 Mo, 3.8 W, 2.8 Ta, 3 Al, 9.5 Co, 0.01 B, 0.02 Zr, 0.1 C, and balance Ni. More preferably, the alloy comprises about 11-13% chromium; 8.5-9.5% cobalt; 1.6-2.25% molybdenum; 3.25-4.25% tungsten; 4.75-5.25% tantalum; 3.25-4% aluminum; 3.75-4.35% titanium; 0.0075-0.02% boron, 0.08-0.015 carbon, balance nickel. Preferably, the inventive alloy has a nominal composition of about 12% chromium; 9% cobalt; 1.9% molybdenum; 3.8% tungsten; 5% tantalum; 3.6% aluminum; 4.1 % titanium; 0.01 % boron; 0.01 % zirconium; 0.1 % carbon; balance essentially nickel.

We discovered in the course of developing the alloy of the '565 application that even small additions of zirconium detrimentally affected the castability of directionally solidified parts, particularly large parts such as land based gas turbine engine blades. Articles having more than about 0.02 wt. % zirconium tended to tear on investment casting, during cooling and solidification of the molten material. While not fully understood, the tearing problem was obviated where zirconium was present in less than about 0.02 wt. percent. In the case of equiaxed alloys and articles, the inventive composition preferably includes small intentional additions of zirconium of up to 0.01%, which do not adversely affect castability. Whether or not it is practical to tolerate about up to about 0.03 wt. %, we prefer less. We prefer that the alloy and articles also include no intentional addition of hafnium, as we have discovered an unexpected connection between Hf additions and oxidation resistance in low Al containing alloys. As noted in FIG. 5, there is an unexpected relationship or effect of hafnium content on alloys having relatively low aluminum content (which effect holds for alloys having less than about 3.5-4 wt. % and may hold for higher aluminum contents up to about 5 wt. % ). As oxidation resistance is the ability of an alloy to form an adherent alumina scale, and is in part related to aluminum content, it is generally more difficult to form an alumina scale on alloys having lower aluminum contents, e.g., less than about.4-5 wt %, and the hafnium does not significantly aid in the formation of an alumina scale in these low aluminum alloys. What we did not expect was that the presence of hafnium in these low aluminum alloys is in fact detrimental to the formation of alumina scales, and adversely affect oxidation resistance of these low aluminum alloys.

The articles to be evaluated were investment cast, and then given similar heat treatments a primary heat treat at about 2050° F. for 2 hours, followed by coating diffusion heat treat at 1975 F for 4 hours, followed by precipitation heat treat at about 1550° F. for 24 hours. In some cases, articles were solution heat treated at 2150-2200° F. for less time, but showed no significant increase in properties. The articles may be finish machined as needed or desired.

The articles may also include one or more internal passages through which cooling air may be passed to cool the part. Such passages are well known in the art, and are not further discussed herein. The internal passages, and also some or all portions of the external surface of the parts may be coated with corrosion and/or oxidation resistant coatings like aluminides and overlay or MCrAlY coatings. A broad composition range for MCrAlY materials, in wt. %, is 10-25% Cr, 5-15 Al, 0.1-1.0 Y balance selected from Fe, Ni, and Co and mixtures of Ni and Co. See, e.g., commonly owned U.S. Pat. No. 4,585,481 and Re. 32,121 both of which are expressly incorporated by reference herein. Additions of up to 5% each of Hf, Ta or Re, up to 1% of Si and up to 3% each of Os, Pt, Pd, or Rh may also be made. Table I describes exemplary MCrAlYs that can be applied by thermal spray processes, by EBPVD processes, by electroplating and other suitable manners.

TABLE I
(wt %—Exemplary MCrAlY Compositions)
	Ni	Co	Cr	Al	Y	Hf	Si
NiCrAlY	Bal	—	19.5	12.5	.45	—	—
CoCrAlY	—	Bal	18	11	.45	—	—
NiCoCrAlY	Bal	23	18	12.5	.3	—	—
NiCoCrAlY	Bal	22	17	12.5	.6	.25	.4

An alternate bond coat is a diffusion aluminide formed by diffusing aluminum into the substrate surface. Diffusion aluminides are well known and may be applied using a mixture (termed a pack) containing an aluminum source, such as an aluminum alloy or compound, an activator (usually a halide compound such as NaF) and an inert material such as alumina. The part to be coated is buried in the pack and heated to 1500-2000° F. while a carrier gas, such as hydrogen, is flowed through the pack. Out of pack processes, during which the part is not buried in the pack, are also known. The incorporation of precious metals such as Pt, Rh, Pd and Os into aluminide coatings is known. See, e.g., U.S. Pat. No. 5,514,482 for a description of aluminide coating processes.

Combinations of overlay and aluminide coatings are also possible. See, commonly owned U.S. Pat. No. 4,897,315 for a description of a system having an inner MCrAlY overlay coating and an outer aluminide coating. See, commonly owned U.S. Pat. No. 4,005,989 for a description of the reverse combination, an inner aluminide coating and an outer overlay coating. The common feature of these bond coats and bond coat combinations is that they form an adherent layer of alumina on their outer surface. The parts may then be coated with a ceramic thermal barrier coating, the composition and application of which are well known in the art.

The following data were generated using test bars cast from the referenced alloys as described above, and were tested in a non-HIP'd condition.

	INVENTION 0 wt. % Zr	INVENTION .02 Zr	GTD 111
		Time			Time			Time
	Rupture	to 1%		Rupture	to 1%		Rupture	to 1%
Test	Life	Creep	Elong	Life	Creep	Elong	Life	Creep	Elong
Cond.	Hours	Hours	%	Hours	Hours	%	Hours	Hours	%
1400	910.3	260	5.6	535.6	111	5.4	115.9	83	2.0
F/85 ksi	611.9	195	4.6	517.3	107	4.5	186.0	71	3.4
				288.5	170	2.1
AVE	761.0	227.5	5.1	447.1	129	4.0	151.0	77	2.7
1600	342.3	102	4.6	260.8	75	7.2	127.1	45	6.3
F/50 ksi	313.2	99	4.5	202.7	65	5.3
	306.3	73	6.0	299.2	82	6.4
AVE	320.6	91	5.0	254.2	74	6.3	127.1	45	6.3
1800	91.5		4.3	95.2	48	7.1	50.5	22	6.5
F/27 ksi	87.0		4.0	73.1	45	4.5	70.0	35	7.0
	63.7	36	3.7	80.3	55	3.4
AVE	80.7	50	4.0	82.9	49	5.0	60.3	28.5	6.8

As is also shown by the data above, FIG. 1 shows some of the benefits of the inventive equiaxed alloy over equiaxed GTD-111. As shown in the FIG., the inventive alloy exhibits superior creep rupture resistance at 1400F, 1600F and 1800F. The time to produce 1% creep was tested in specimens at 1400° F. with an applied stress of 85 ksi, at 1600F with an applied stress of 50ksi. and at 1800° F. with an applied stress of 27 ksi. Again, the inventive alloy exhibited creep rupture lives exceeding the equiaxed -111 alloy. In the case of equiaxed articles, we observed no noticeable effect on creep rupture properties of Zr content of 0 and 0.02 wt. %.

FIG. 6 shows the relative hot corrosion resistance of the inventive alloy compared to other alloys, including the -111 alloy. Corrosion testing was performed at 1650° F. in a corrosion gaseous environment produced by combustion of Jet A fuel (30:1 air fuel ratio) with addition of 20 ppm of ASTM sea salt and sufficient sulfur dioxide to produce a sulfur content equivalent to a 1.3% S content in the fuel. The numbers presented are the hours of exposure required to produce 1 mil of corrosive attack. As seen in the FIG., the inventive alloy exhibits corrosion resistance comparable to GTD-111 and significantly better than single crystal alloys of similar compositions, see, commonly owned U.S. Pat. Nos. 4,209,348 and 4,719,080 both of which are expressly incorporated by reference herein.

FIG. 7 shows the relative uncoated, burner rig oxidation resistance of the inventive alloy at 2000° F. and several other alloys. While the oxidation resistance exceeds the oxidation resistance of GTD-111 and Rene 80, the inventive alloy is significantly higher (at least 2.5×) and similar to the oxidation resistance of the single crystal alloy of the '809 patent. The increase in aluminum content and decrease in titanium content of the inventive alloy over GTD-111 is largely responsible for the inventive alloy's greater oxidation resistance.

FIG. 8 illustrates the relative creep and uncoated oxidation lives of a number of well known hot corrosion resistant alloys. As shown, the inventive alloy combines the best combined oxidation and creep lives of these well known alloys. In addition, alloys of the present invention have shown to be readily castable by convention methods including investment casting, and in large sizes for parts such as large industrial gas turbine parts. Articles formed of the inventive alloy composition also surprisingly exhibit strengths comparable to those of angle crystal articles of similar compositions.

In sum, the present invention is based on a modification of a published single crystal composition, which in turn was modified to created a composition useful in the production of directionally solidified articles. Beginning with prior art columnar grain or equiaxed compositions, the present invention includes among other things significantly increasing tantalum, aluminum and molybdenum contents, and significantly decreasing the titanium and chromium contents. The inventive alloy and articles fabricated from the alloy exhibit superior combinations of oxidation resistance, corrosion resistance and creep-rupture resistance at various temperatures.

It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit and scope of this novel concept as defined by the following claims.

Claims

1. A high strength, corrosion and oxidation resistant nickel base superalloy consisting essentially of, in weight percent, of: 11-13.25% chromium; 8-10% cobalt; 1.5-2.5% molybdenum; 3.25-4.5% tungsten; 4.5-5.5% tantalum; 3.25-4% aluminum; 3.5-4.5% titanium; 0.005-0.02% boron; up to about 0.03 zirconium; 0.05-0.2% carbon; up to about 0.15% hafnium; and balance essentially nickel; said article having creep rupture at 1400° F. of at least roughly 2.5×, and at 1600° F. of at least roughly 2× compared to a similar equiaxed article having a nominal composition of 14 Cr, 4.9 Ti, 1.6 Mo, 3.8 W, 2.8 Ta, 3 Al, 9.5 Co, 0.01 B, 0.02 Zr, 0.1 C, and balance Ni.

2. An article composed of the alloy of claim 1.

3. The alloy of claim 1 having stress rupture resistance sufficient to ensure that a load of about 27 ksi applied ruptures after more than about 75 hours, and also has a time to 1 % creep of more than 50 hours, at 1800° F.

4. The alloy of claim 3, wherein stress rupture occurs only after more than 85 hours.

5. The alloy of claim 1, further characterized by having about 11-13% chromium; 8.5-9.5% cobalt; 1.6-2.25% molybdenum; 3.25-4.25% tungsten; 4.75-5.25% tantalum; 3.25-4% aluminum; 3.75-4.35% titanium; 0.0075-0.02% boron, and 0.005-0.010 zirconium.

6. The alloy of claim 1, having about 12% chromium; 9% cobalt; 1.9% molybdenum; 3.8% tungsten; 5% tantalum; 3.6% aluminum; 4.1% titanium; 0.01% boron; 0.01% zirconium; 0.1% carbon; balance essentially nickel.

7. The article of claim 2 comprising a gas turbine engine component.

8. The article of claim 7, comprising a turbine blade or vane.

9. A high strength, corrosion resistant, nickel base superalloy article adapted for use in equiaxed grain articles, comprising in weight percent 11-13.25% chromium; 8-10% cobalt; 1.5-2.5% molybdenum; 3.25-4.5% tungsten; 4.5-5.5% tantalum; 3.25-4% aluminum; 3.5-4.5% titanium; 0.005-0.02% boron; less than about 0.03% zirconium; 0.05-0.2% carbon; up to about 0.15% hafnium; and balance essentially nickel; said article having creep rupture at 1400° F. of at least roughly 2.5×, and at 1600° F. of at least roughly 2× compared to a similar equiaxed article having a nominal composition of 14 Cr, 4.9 Ti, 1.6 Mo, 3.8 W, 2.8 Ta, 3 Al, 9.5 Co, 0.01 B, 0.02 Zr, 0.1 C, and balance Ni.

10. The article of claim 9 comprising a gas turbine engine component.

11. The article of claim 10 comprising a turbine blade or vane.

12. The article of claim 1 having stress rupture resistance sufficient to ensure that a load of about 27 ksi applied ruptures after more than about 80 hours, and also has a time to 1 % creep of more than 40 hours, at 1800° F.

13. The article of claim 12, wherein stress rupture occurs only after more than 85 hours.

14. The article of claim 9, further characterized by having 11-13% chromium; 8.5-9.5% cobalt; 1.6-2.25% molybdenum; 3.25-4.25% tungsten; 4.75-5.25% tantalum; 3.25-4% aluminum; 3.75-4.35% titanium; 0.0075-0.02% boron; 0.01 % zirconium.

15. The alloy of claim 14, having about 12% chromium; 9% cobalt; 1.9% molybdenum; 3.8% tungsten; 5% tantalum; 3.6% aluminum; 4.1 % titanium; 0.01 % boron; less than about 0.03% zirconium; 0.1% carbon; balance essentially nickel.

16. The article of claim 2 comprising a gas turbine engine component.

17. The article of claim 16, comprising a turbine blade or vane.

18. The article of claim 9, wherein the article is up to about 60 inches long.

19. A method of producing an equiaxed, cast, high strength, corrosion resistant, nickel base superalloy article comprising the steps of:

melting an alloy consisting of in weight percent 11-13.25% chromium; 8-10% cobalt; 5-2.5% molybdenum; 3.25-4.5% tungsten; 4.5-5.5% tantalum; 3.25-4% aluminum; 3.5-4.5% titanium; 0.005-0.02% boron; less than about 0.03% zirconium; 0.05-0.2% carbon; up to about 0.15% hafnium; and balance essentially nickel; and

casting the alloy to form an article, wherein the article has creep rupture at 1400° F. of at least roughly 2.5×, and at 1600° F. of at least roughly 2× compared to a similar equiaxed article having a nominal composition of 14 Cr, 4.9 Ti, 1.6 Mo, 3.8 W, 2.8 Ta, 3 Al, 9.5 Co, 0.01 B, 0.02 Zr, 0.1 C, and balance Ni.

20. The article of claim 19, further comprising the step of machining the article.

21. The article of claim 19, further comprising the step of applying an oxidation and/or corrosion resistant coating to the article.

22. The method of claim 21, where in the article has at least one internal passage, further comprising the step of applying an oxidation and/or corrosion resistant coating to the internal passage.

23. The article of claim 9, further comprising a thermal barrier coating applied to one or more portions of the article.