EP0683239A1

EP0683239A1 - Oxidation resistant nickel based super alloy

Info

Publication number: EP0683239A1
Application number: EP94303644A
Authority: EP
Inventors: William J. Gostic; Paul P. Norris Jr.
Original assignee: United Technologies Corp
Current assignee: Raytheon Technologies Corp
Priority date: 1994-05-20
Filing date: 1994-05-20
Publication date: 1995-11-22
Anticipated expiration: 2014-05-20
Also published as: EP0683239B1; JPH07331365A; JP3474634B2

Abstract

A nickel superalloy is disclosed having superior resistance to oxidation under conditions such as those encountered in jet engines. The superalloy comprises 0.25 to 0.40 weight percent zirconium, 0.004 to 0.010 weight percent boron, 5.0 to 8.0 weight percent aluminum, 5.0-12.0 weight percent chromium, 0.75-2.0 weight percent hafnium, 0-10.0 weight percent cobolt, 0-12 weight percent tungsten, 0-12 weight percent molybdenum, 0-12 weight percent tantalum, 0-12 weight percent titanium, 0-2 weight percent niobium, 0.06-0.20 weight percent carbon and the balance nickel and inevitable impurities. Under burner rig oxidation conditions, this alloy can form a zirconium stabilized alumina barrier layer which greatly reduces the oxidation rate of the alloy. A method of making the superalloy and a method for casting the engine components made of the superalloy are also disclosed.

Description

The present invention relates to nickel superalloys and methods for making nickel superalloys having high oxidation resistance and containing controlled amounts of boron and zirconium. Such nickel superalloys are suitable for use in articles requiring good strength and superior oxidation resistance at high temperatures, including jet engine combustors, nozzles, and low turbine components.

A variety of nickel based superalloys are known in the art. Superalloys are those alloys which maintain high strength at high temperatures. Examples of nickel based superalloys can be found in U.S. Patent Nos. 3,322,543 (Shaw et al.), 3,526,499 (Quigg et al.), 3,653,987 (Boesch), 3,667,938 (Boesch), 3,832,167 (Shaw et al.), and 4,719,080 (Duhl et al.). Other, commercially available, nickel based superalloys include B1900+Hf and Mar-M 247, the nominal compositions of which are, in weight percent,

	B-l900+HF	Mar-M-247
Nickel	Balance	Balance
Chromium	8.0	8.4
Cobalt	10.0	10.0
Carbon	0.11	0.15
Titanium	1.0	1.1
Aluminum	6.0	5.5
Molybdenum	6.0	0.65
Tungsten	-	10.0
Boron	0.015	0.015
Hafnium	1.15	1.4
Tantalum	4.25	3.1
Zirconium	0.08	0.055

Due to their ability to maintain good mechanical strength at high temperatures, these alloys are especially useful as a material for making components of jet engines.

Boron is typically added in the range of 0.010 to 0.020 weight percent to conventionally cast superalloys for the enhancement of grain boundary strength and ductility. Zirconium is typically added in the range of 0.03 to 0.13 weight percent for further grain boundary property enhancement. Yttrium can be added to nickel superalloys to enhance their oxidation resistance.
The nickel superalloys of the prior art which demonstrate excellent oxidation resistance at high temperature (above about 1093°C (2000⁰F)) are too brittle. Thus, there remains a need for nickel superalloys which have excellent oxidation resistance at high temperatures, while at the same time possessing good ductility. There is also a need for turbine components in jet engines which have good strength and excellent oxidation resistance within the temperature range of 760°C (1400⁰F) to 1038°C (1900⁰F).
Thus, it is an object of the present invention to provide nickel based superalloys which have excellent oxidation resistance at high temperatures and also have good ductility.
It is a further object of the present invention to provide nickel based superalloys suitable for use in components of jet engines which maintain good strength within the temperature range of 760°C (1400⁰F) to 1038°C (1900⁰F).
According to one aspect of the present invention, there is provided a polycrystalline nickel based superalloy having between about 0.25 to 0.40 weight percent zirconium and about 0.004 to 0.010 weight percent boron. The alloys of the present invention have demonstrated excellent oxidation resistance up to 1093°C (2000°F), and in preferable instances up to 1204°C (2200°F). The nickel superalloys of the present invention have demonstrated good strength within the temperature range of 760°C (1400⁰F) to 1038°C (1900⁰F). The excellent oxidation resistance of the superalloys of the present invention makes them suitable for use in high temperature applications such as in a jet engine combustor, nozzle and low turbine components. In a preferred embodiment, superalloys of the present invention contain between 5.0 and 8.0 weight percent aluminum in order to form an effective barrier layer which impedes oxidation of the superalloy. Having zirconium present in the superalloy promotes formation of the alumina barrier layer.
Burner rig oxidation testing revealed the detrimental effect of boron on high temperature (1093°C-1204°C (2000-2200°F)) oxidation resistance. Removing boron from the nickel superalloy solved the oxidation problem, but the resulting alloy had unacceptable ductility. Adding low levels of boron (0.002 to 0.010 weight percent) provided acceptable oxidation behavior, but ductility was marginal at best. The addition of yttrium also presented embrittlement problems due to the formation of surface oxide particles during casting, which result from the reaction between yttrium and the casting ceramics. Through further experimentation, it was discovered that the combination of zirconium and boron at the levels designated in this specification can greatly enhance the oxidation resistance of conventionally cast nickel superalloys, while maintaining grain boundary properties and avoiding inclusion formation during casting.
In addition to the critical concentrations described above for zirconium and boron, the nickel superalloy of the present invention has been found to work when elements are added in the following weight percentages:

Element Percentage

Chromium 5.0 - 12.0

Hafnium 0.75 - 2.0

Cobalt O - 10.0
The following alloy elements can be added for alloy strengthening:

Element Percentage

Tungsten 0 - 12

Molybdenum 0 - 12

Tantalum 0 - 12

Titanium 0 - 2

Columbium (Niobium) 0 - 2

Carbon 0.06 - 0.20
The elements manganese, phosphorus, sulfur, silicon, iron, bismuth, lead, selenium, tellurium, and thallium are preferably controlled to low levels in order to prevent degradation to the properties of the superalloy.

In another embodiment of the present invention, the superalloy is comprised of the following elements given in weight percentages:

Element	Percentage
	min	max
Carbon	0.08	- 0.13
Chromium	9.50	- 10.50
Molybdenum	1.75	- 2.25
Tungsten	3.00	- 3.40
Aluminum	6.50	- 6.70
Tantalum	3.90	- 4.30
Hafnium	1.05	- 1.25
Boron	0.004	- 0.010
zirconium	0.25	- 0.35
Nickel	remainder¹

¹ Essentially the balance of the superalloy

Optionally, the superalloy of the present invention may contain additive materials, such as the following, up to the indicated percent by weight maximum amounts: manganese (0.20), phosphorus (0.015), sulfur (0.015), silicon (0.10), iron (0.25), titanium (0.10), columbium (0.10), bismuth (0.00005, 0.5 ppm), lead (0.0002, 2 ppm), selenium (0.0001, 1 ppm), tellurium (0.00005, 0.5 ppm), and thallium (0.00005, 0.5 ppm).
A number of preferred embodiments of the invention will now be described by way of example only and with reference to the accompanying drawing figures in which:

Fig. 1 shows the results of burner rig oxidations at 1093°C (2000°F), comparing the weight loss vs. time of a nickel superalloy of the present invention, with other commercially available nickel superalloys, B1900+Hf, and MAR M-247. The composition of these alloys is shown in Table l.
Fig. 2 illustrates the results of burner rig oxidations at 1204°C (22OO°F), comparing the weight loss vs. time of a nickel superalloy of the present invention with other commercially available nickel superalloys.

In a preferred embodiment of the present invention, articles are fabricated by taking an ingot of the requisite composition, which has been cast from a single furnace charge under vacuum, and vacuum remelting and recasting using investment casting procedures that are conventionally used for nickel based alloys. Conventional investment casting procedures for superalloys, procedures for forming ingots of superalloys, and other general information regarding superalloys can be found in Superalloys II, Sims et al., eds., John Wiley & Sons, New York, 1987. Typically, alloying elements in their commercially pure form are added to the master heat during ingot formation. In a preferred embodiment, the alloying elements contain less than maximum ("max") specified amounts of the following additive materials set forth above: Mn, P, S, Si, Fe, Ti, Cb (Nb), Bi, Pb, Se, Te, and T1.
The composition of certain alloys discussed herein is shown in Table I.
In a non-limiting example of the present invention, a nickel superalloy was made having the composition shown in Table I. The invention showed superior ductility compared to a compositionally similar nickel alloy whose boron and zirconium content falls outside the critical range defined in the present invention as demonstrated below in Table II. Table II

Tensile Elongation (percent)

Alloy Temperature

24°C (75°F) 644°C (1200°F) 871°C (1600°F) 982°C (1800°F)

Invention 6.0 5.3 6.6 7.0

Alloy 1 1.3 0.7 3.3 2.0
Tensile elongation testing is described in Metals Handbook, 9th ed., American Society for Metals, Vol. 8, 1985. The tensile elongation properties of the superalloys of the present invention were tested according to guidelines described in ASTM E 8.
In one embodiment, superalloys of the present invention have a mean tensile elongation of three ASTM E 8 tests at 649°C (1200⁰F) exceeding 3.0%. In a preferred embodiment, mean tensile elongation of three ASTM E 8 tests at 649°F (1200⁰F) exceeds 5.0%.
Burner rig oxidation testing demonstrated that the alloy of the present invention had superior oxidation resistance compared to the conventional nickel superalloys Bl900+HF and Mar-M-247 (see Table I and Figures 1 and 2). After 70 cycles of 1204°C (2200°F) burner rig oxidation, the alloy of this invention lost only about 2% of its weight, as compared to 55% for B1900+HF and 75% for Mar-M-247.
In the cyclic burner rig testing used to evaluate the superalloys of the present invention, a liquid fuel burner is controlled by fuel pressure to maintain the temperature of interest. To cycle, the specimens or the flame are withdrawn, with the specimens cooled by directing high pressure ambient air upon them. The specimens are typically cylindrical rods (12mm (0.47") diameter x 82.5mm (3.25") long in this case). Individual specimens can be tested. Multiple specimens are tested in a rotating spindle. Specimen weight and diameter are measured at intervals during the test to monitor the loss of material via oxide spallation. Oxidation rate is proportional to weight loss (greater weight corresponds to greater oxidation rate).
A second method of testing oxidation resistance can also be used to characterize the nickel superalloys of the present invention. In this method, coupons of a superalloy are suspended from a wire and placed into a furnace maintained at 1149°C +/- 14°C (2100⁰F +/- 25⁰F), while exposed to ambient air. In this method, alloy samples are 12.7 x 19mm +/- 3mm (0.50 X 0.75 in. +/-0.12 in.) by 1.02mm +/- 0.25mm (0.040 in. +/- 0.010-in.). Prior to the initial insertion into the furnace, corners and edges on the sample are rounded. Samples are heated in cycles of 24 +/- 4 hours. At the end of each cycle, samples are removed from the furnace, cooled in ambient air, and weighed. Material which spalls off during heating or cooling is not weighed. As an example of oxidation resistance of the alloys of the present invention, weight loss from testing at 1149°C (2100⁰F) under cyclic conditions in ambient air for 300 hours does not exceed 10% of the initial sample weight. As an example of oxidation resistance for a preferred embodiment of the alloys of the present invention, weight loss from testing at 1149°C (2100⁰F) under cyclic conditions in ambient air for 300 hours does not exceed 5.0% of the initial sample weight.
When the procedure described above was applied to a sample of the superalloy of the present invention for 302 hours (11 cycles), the sample was found to have lost 4.7% of its initial weight.

Additional non-limiting examples of superalloys within the scope of the present invention were also prepared, and their compositions are presented below in Table III.

Table III

Compositions Evaluated
	Ni	Cr	Al	Mo	W	Ta	Hf	C	B	Zr
Alloy A	Bal	9.99	6.50	2.02	3.17	4.07	1.23	0.12	0.004	0.26
Alloy B	Bal	10.09	6.53	1.98	3.11	4.10	1.24	0.13	0.004	0.34
Alloy C	Bal	10.42	6.66	2.11	2.98	4.19	1.32	0.11	0.010	0.26
Alloy D	Bal	9.86	6.66	1.98	3.15	4.32	1.22	0.09	0.004	0.29

* - In weight percent

In a preferred embodiment, a nickel superalloy component of the present invention is heated to 1079 ± 14°C
In a preferred embodiment, a nickel superalloy component of the present invention is heated to 1079 ± 14°C (1975 ± 25⁰F) in air for 4 hours and air cooled at a minimum of 22°C/min (40⁰F/min). The component is then heated to 871 ± 14°C (1600 ± 25⁰F) for 16 hours and then air cooled at a minimum of 22°C/min (40⁰F/min). This heat treatment serves to improve the tensile and creep Properties of the superalloy component.
In a preferred embodiment, the polycrystalline nickel superalloy of the present invention is equiaxed; in another embodiment, the polycrystalline nickel superalloy of the present invention is columnar.
The nickel superalloy of the present invention which is shown in Table I has been successfully used as a component of a float wall combustor.
Although the present invention has been described in conjunction with certain preferred embodiments, it is understood that modifications and variations may be practiced without departing from the scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the present invention and appended claims.

Claims

A polycrystalline nickel superalloy comprising 0.25 to 0.40 weight percent zirconium and 0.004 to 0.010 weight percent boron.
The alloy of claim l, further comprising 5.0 to 8.0 weight percent aluminum.
The alloy of claim 1 or 2, wherein the grains are equiaxed.
The alloy of claim 1 or 2, wherein the grains are columnar.
The alloy of claim 2 or any of claims 3 to 4 when dependant upon claim 2, wherein, after exposure to severe oxidizing conditions, an alumina layer is formed on the surface of the alloy, said layer being capable of reducing the oxidation rate of said superalloy.
The alloy of any preceding claim, wherein chromium, hafnium and cobalt are present in the weight percent ranges 5.0-12.0 Cr, 0.75-2.0 Hf, and 0-10.0 Co.
The alloy of any preceding claim, further comprising elements in the following weight percent ranges: Tungsten 0 - 12 Molybdenum 0 - l2 Tantalum 0 - 12 Titanium 0 - 12 Columbium 0 - 2 Carbon 0.06 - 0.20.
The alloy of any preceding claim, wherein manganese, phosphorus, sulfur, silicon, iron, bismuth, lead, selenium, tellurium, and thallium are present in levels that are sufficiently low, so as to prevent a substantial decrease in the ductility in said superalloy as measured by said superalloy's tensile elongation.
The alloy of any preceding claim wherein said alloy contains 0.007 or less weight percent boron.
The alloy of any preceding claim comprising elements in the following weight percentages: Element Percentage min max Carbon 0.08 - 0.13 Chromium 9.50 - 10.50 Molybdenum 1.75 - 2.25 Tungsten 3.00 - 3.40 Aluminum 6.50 - 6.70 Tantalum 3.90 - 4.30 Hafnium 1.05 - 1.25 Boron 0.004 - 0.010 Zirconium 0.25 - 0.35 Nickel remainder.
The alloy of any preceding claim, further comprising the following additive materials containing from zero up to the maximum percent by weight indicated amounts: manganese (0.20), phosphorus (0.015), sulfur (0.015), silicon (0.10), iron (0.25), titanium (0.10), columbium (0.10), bismuth (0.00005, 0.5 ppm), lead (0.0002, 2 ppm), selenium (0.0001, 1 ppm), tellurium (0.00005, 0.5 ppm), and thallium (0.00005, 0.5 ppm).
The superalloy of any preceding claim, wherein the mean tensile elongation of three ASTM E 8 tests at 649°C (1200⁰F) exceeds 3.0%, and weight loss from testing a sample of said superalloy having dimensions of 12.7 x 19mm +/- 3mm (0.50 X 0.75 in. +/- 0.12 in.) by 1.02mm +/- 0.25mm (0.040 in. +/-0.010 in.) at 1149°C (2100⁰F) under cyclic conditions of 24 +/- 4 hours in ambient air for 300 hours does not exceed 10% of the initial sample weight.
The superalloy of any preceding claim, wherein the mean tensile elongation of three ASTM E 8 tests at 649°C (l200⁰F) exceeds 5.0%, and weight loss from testing a sample of said superalloy having dimensions of 12.7 X 19mm +/- 3mm (0.50 X 0.75 in. +/- 0.12 in.) by 1.02mm +/- 0.25mm (0.040 in. +/-0.010 in.) at 1149°C (2100⁰F) under cyclic conditions of 24 +/- 4 hours in ambient air for 300 hours does not exceed 5.0% of the initial sample weight.
A jet engine component comprising the nickel superalloy of any preceding claim.
The component of claim 14, selected from the group consisting of combustor, nozzle and low turbine components.
A method of making a polycrystalline nickel superalloy, with high oxidation resistance, comprising the step of incorporating 0.25 to 0.40 weight percent zirconium and 0.004 to 0.010 weight percent boron in the superalloy.
A method of making jet engine components comprising the step of casting a nickel superalloy, said superalloy comprising 0.25 to 0.40 weight percent zirconium and 0.004 to 0.010 weight percent boron.
The method of claim l7, wherein said superalloy has been cast from a single furnace charge under vacuum.
The method of claim 18, wherein an ingot of said superalloy is remelted in vacuo and is subsequently cast using investment casting procedures for nickel alloys.