Alloys or metallic compositions – Nickel base – Chromium containing
Reexamination Certificate
2002-05-13
2004-05-04
Sheehan, John P. (Department: 1742)
Alloys or metallic compositions
Nickel base
Chromium containing
C148S428000, C420S449000, C420S450000
Reexamination Certificate
active
06730264
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to nickel-base alloys. In particular, the present invention relates to nickel-base alloys that can be affordable and can exhibit superior temperature capability and comparable processing characteristics relative to certain nickel-based superalloys, such as the well-known Alloy 718, versions of which are available from Allegheny Ludlum Corporation, Pittsburgh, Pa., and Allvac, Monroe, N.C. under the names Altemp® 718 and Allvac® 718 alloys, respectively. The present invention is also directed to a method of making a nickel-base alloy and an article of manufacture that includes a nickel-base alloy. The nickel-base alloy of the present invention finds application as, for example, components for gas turbine engines, such as disks, blades, fasteners, cases, or shafts
DESCRIPTION OF THE INVENTION BACKGROUND
The improved performance of the gas turbine engine over the years has been paced by improvements in the elevated temperature mechanical properties of nickel-base superalloys. These alloys are the materials of choice for most of the components of gas turbine engines exposed to the hottest operating temperatures. Components of gas turbine engines such as, for example, disks, blades, fasteners, cases, and shafts all are fabricated from nickel-base superalloys and are required to sustain high stresses at very high temperatures for extended periods of time. The need for improved nickel-base superalloys has resulted in many issued patents in this area, including, for example, U.S. Pat. Nos. 3,046,108; 4,371,404; 4,652,315; 4,777,017; 4,814,023; 4,837,384; 4,981,644; 5,006,163; 5,047,091; 5,077,004; 5,104,614; 5,131,961; 5,154,884; 5,156,808; 5,403,546; 5,435,861 and 6,106,767.
In many cases, improved performance is accomplished by redesigning parts so as to be fabricated from new or different alloys having improved properties (e.g., tensile strength, creep rupture life, and low cycle fatigue life) at higher temperatures. The introduction of a new alloy, however, particularly when introduced into a critical rotating component of a gas turbine engine, can be a long and costly process and may require a compromise of certain competing characteristics.
Alloy 718 is one of the most widely used nickel-base superalloys, and is described generally in U.S. Pat. No. 3,046,108. Alloy 718 has a typical composition as illustrated in the table below.
Typical Chemical Composition of Alloy 718
Element
Weight Percent
Carbon
0.08 maximum
Manganese
0.35 maximum
Phosphorous
0.015 maximum
Sulfur
0.015 maximum
Silicon
0.35 maximum
Chromium
17-21
Nickel
50-55
Molybdenum
2.8-3.3
Niobium plus Tantalum
4.75-5.5
Titanium
0.65-1.15
Aluminum
0.2-0.8
Cobalt
1 maximum
Boron
0.006 maximum
Copper
0.3 maximum
Iron
Balance
The extensive use of Alloy 718 stems from several unique features of the alloy. Alloy 718 has high strength, along with balanced creep and stress rupture properties up to about 1200° F. (649° C.). While most high strength nickel-base superalloys derive their strength by the precipitation of &ggr;′ phase, with aluminum and titanium being major strengthening elements, i.e., Ni
3
(Al, Ti), Alloy 718 is strengthened mainly by &ggr;″ phase with niobium, i.e. Ni
3
Nb, being a major strengthening element and with a small amount of &ggr;′ phase playing a secondary strengthening role. Since the &ggr;″ phase has a higher strengthening effect than &ggr;′ phase at the same volume fraction and particle size, Alloy 718 is generally stronger than most superalloys strengthened by &ggr;′ phase precipitation. In addition, &ggr;″ phase precipitation results in good high temperature time-dependent mechanical properties such as creep and stress rupture properties. The processing characteristics of Alloy 718, such as castability, hot workability and weldability, are also good, thereby making fabrication of articles from Alloy 718 relatively easy. These processing characteristics are believed to be closely related to the lower precipitation temperature and the sluggish precipitation kinetics of the &ggr;″ phase associated with Alloy 718.
At temperatures higher than 1200° F. (649° C.), however, the &ggr;″ phase has very low thermal stability and will rather rapidly transform to a more stable &dgr; phase that has no strengthening effect. As a result of this transformation, the mechanical properties, such as stress rupture life, of Alloy 718 deteriorate rapidly at temperatures above 1200° F. (649° C.). Therefore, the use of Alloy 718 typically is limited to applications below 1200° F. (649° C.).
Due to the foregoing limitations of Alloy 718, many attempts have been made to improve upon that superalloy. U.S. Pat. No. 4,981,644 describes an alloy known as the Rene' 220 alloy. Rene' 220 alloy has temperature capabilities of up to 1300° F. (704° C.), or 100° F. (56° C.) greater than Alloy 718. Rene' 220 alloy, however, is very expensive, at least partly because it contains at least 2 percent (typically 3 percent) tantalum, which can be from 10 to 50 times the cost of cobalt and niobium. In addition, Rene' 220 alloy suffers from relatively heavy &dgr; phase content, and only about 5% rupture ductility, which may lead to notch brittleness and low dwell fatigue crack growth resistance.
Another nickel-base superalloy, known as Waspaloy® (a registered trademark of Pratt & Whitney Aircraft) nickel-base superalloy (UNS N07001), available from Allvac, Monroe, N.C., is also widely used for aerospace and gas turbine engine components at temperatures up to about 1500° F. (816° C.). This nickel-base superalloy has a typical composition as illustrated in the table below.
Typical Chemical Composition of Waspaloy Nickel-Base Alloy
Element
Weight Percent
Carbon
0.02-0.10
Manganese
0.1 maximum
Phosphorous
0.015 maximum
Sulfur
0.015 maximum
Silicon
0.15 maximum
Chromium
18-21
Iron
2 maximum
Molybdenum
3.5-5.0
Titanium
2.75-3.25
Aluminum
1.2-1.6
Cobalt
12-15
Boron
0.003-0.01
Copper
0.1 maximum
Zirconium
0.02-0.08
Nickel
Balance
While Waspaloy nickel-base superalloy possesses superior temperature capability compared to Alloy 718, it is more expensive than Alloy 718, resulting, at least partly, from increased amounts of the alloying elements nickel, cobalt, and molybdenum. Also, processing characteristics, such as hot workability and weld ability, are inferior to those of Alloy 718, due to strengthening by &ggr;′, leading to higher manufacturing cost and more limited component repairability.
Thus, it is desireable to provide an affordable, weldable, hot workable nickel-base alloy that has high temperature capability greater than that of Alloy 718.
SUMMARY OF THE INVENTION
According to one particular embodiment of the present invention, the nickel-base alloy comprises, in weight percent: up to about 0.10 percent carbon; about 12 up to about 20 percent chromium; 0 up to about 4 percent molybdenum; 0 up to about 6 percent tungsten, wherein the sum of molybdenum and tungsten is at least about 2 percent and not more than about 8 percent; about 5 up to about 12 percent cobalt; 0 up to about 14 percent iron; about 4 percent up to about 8 percent niobium; about 0.6 percent up to about 2.6 percent aluminum; about 0.4 percent up to about 1.4 percent titanium; about 0.003 percent up to about 0.03 percent phosphorous; about 0.003 percent up to about 0.015 percent boron; nickel, and incidental impurities. According to the present invention, the atomic percent of aluminum plus titanium is from about 2 to about 6 percent, the atomic percent ratio of aluminum to titanium is at least about 1.5; and/or the sum of atomic percent of aluminum plus titanium divided by the atomic percent of niobium equals from about 0.8 to about 1.3. The present invention relates to nickel-base alloys characterized by including advantageous levels of aluminum, titanium and niobium, advantageous levels of boron and phosphorous, and advantageous levels of iron, cobalt and
ATI Properties Inc.
Sheehan John P.
Viccaro Patrick J.
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