JPH0317243A - Super alloy containing tantalum - Google Patents

Abstract

PURPOSE: To develop an Ni base alloy excellent in high temp. strength and ductility by subjecting an Ni base alloy obtd. by adding Ni with specified amounts of Ta and the other elements and substantially contg. no Nb to heat treatment under specified conditions.

CONSTITUTION: A slab of an Ni alloy having a compsn. contg., by weight, 8 to 16% Ta, 17 to 22% Cr, <25% Fe, <16% Co, 2 to 6% Mo, 1 to 5% Ti, 0.1 to 5% Al, B by 30 to 150 ppm (by 30 to 60 ppm in the case of casting and by 80 to 100 ppm in the case of forging) and 0.01 to 0.1% C, contg. Nb by <0.1% which is the amt. in a degree in which it is not substantially contained, contg. one or two kinds of Zr and Hf, and the balance Ni is heated at about 2000°F for 1 hr and is successively subjected to hydrostatic pressing treatment at 2050°F under 12 to 15 KSi for 3 to 5 hr. Then, it is heated at 1920°F for 4 hr, is successively heated at 1600°F for 2 hr and is moreover heated at 1350°C for 8 hr according to necessary to develop the Ni base alloy excellent in both strength and ductility in a wide temp. range from a room temp. to 1500°F.

COPYRIGHT: (C)1991,JPO

Description

BACKGROUND OF THE INVENTION TECHNICAL FIELD This invention relates to an improved nickel-based alloy that possesses a particularly advanced combination of strength properties and ductility in the temperature range from about room temperature to about 1500"F. .

These improvements are generally achieved by incorporating significant amounts of tantalum into the alloy by atom-for-atom substitution for niobium and then heat treating the alloy at very high temperatures for long periods of time.

PRIOR ART Although the prior art nickel-based superalloys have improved length, they suffer from deficiencies from a strength or ductility standpoint, particularly at high temperatures, i.e., temperatures above about 1200°C. These alloys are generally nickel-based alloys with an IP content of chromium, iron, and cobalt. ! Contains the above. Furthermore, these alloys can contain various elements in various combinations to produce desired effects.

The following elements have been used in nickel-based superalloys to improve one or more of the following properties: That is, for the strength, the peak,1”,, w,
Ra, Cr for oxidation resistance, /V, NL for phase stability. Alternatively, it is 6, etc. for a preferable increase in the volume fraction of secondary precipitates. Other additive elements include N and T+ for forming hardenable precipitates which are γ'. and γ
There is a cb for forming a hardenable precipitate. Trace elements C and B are added to form carbides and borides. Other Cc. Fk2 is added for the purpose of controlling the Trumbu element. B. Zr, Hf'
is added to promote favorable grain boundary effects. Many elements (e.g., Co. t%. W, Cr) are added because of their favorable alloying properties, but under some circumstances participate in the formation of undesirable phases (e.g., σ, μ, Laves).

γ' is a resting tetragonal NL3Nb reinforcing precipitate, which is generally believed to form when niobium is present in the nickel-based superalloy. Inconel (!oconel) is a superalloy with γ′ reinforcement.
There are 7 1 8, and this is Eiselstein (E!
Solsteln) US Pat. No. 3,046,108. According to Eiselstein, the alloy should contain from about 4 to about g'ii% columbium, although the columbium in the alloy may be partially replaced by tantalum in up to 4% of the alloy. It is considered okay to do so.

If the columbium content of the alloy were to be partially replaced by tantalum, Eiselstein states that twice the weight of tantalum would have to be used to obtain the same effect on properties. Additionally, Eiselstein states that only alloys that do not contain tantalum and/or that have tantalum substituted for less than 50% columbium are notch ductile at high temperatures. Therefore, Eiselstein teaches that tantalum and niobium have the same effect in nickel-based alloys when tantalum is present in limited amounts.

The γ' phase is usually not a stable phase since it can change to γ' or δ when exposed to high temperatures for long periods of time. Alloys hardened by γ" exhibit high tensile strength and very good creep rupture properties at relatively low temperatures, but at temperatures above about 1250"F, γ' changes to γ' or δ. Therefore, the strength is significantly reduced. (Donachie, M. G., "Relationship between properties of superalloys and microscopic structures", Superalloy Materials Collection, American Institute of Metals, 1984) [Summary of the Invention] Nowadays, tantalum is the same as niobium in nickel-based superalloys. I discovered that it does not work. Rather, we have discovered that tantalum produces alloys that possess superior phase stability and different phase relationships than comparable niobium-containing alloys.

Due to this difference in phase stability, alloys containing Nb
It is much more resistant to higher temperatures than alloys containing .

Furthermore, the γ'' in the alloys of the present invention does not readily transform into the δ phase as occurs in the corresponding Nb-containing alloys.

The present invention specifically contemplates a nickel-based alloy comprising about 30% by weight or more of NL, about 8 to about 16% by weight tantalum, and is substantially free of niobium.

Other elements included in the alloy are primarily selected from the group consisting of chromium, iron, cobalt, molybdenum, titanium, zirconium, tungsten, hafnium, aluminum, boron and carbon, and combinations thereof. Additionally, other elements such as manganese, silicon, phosphorous, sulfur, lead, bismuth, tellurium, selenium, niopium and silver may be present as accompanying impurities.

Furthermore, the present invention extends to a method for improving the high-temperature strength properties of a niobium-containing nickel-base superalloy by replacing substantially all of the niobium contained in the niobium-containing nickel-base superalloy with tantalum on an atom-by-atom basis. is widespread.

In order to improve the high temperature strength properties of the tantalum-containing nickel-base superalloys of the present invention, the method also includes subjecting the tantalum-containing nickel-base superalloys to heat treatments at higher temperatures and for longer times than comparable diopter-containing superalloys.

[Preferred Sharpening Embodiments] The alloys of the present invention have a NL of about 30% or more (all percentages expressed in this specification and claims are weight percentages unless otherwise indicated) and a NL of about 8 to about 1
Contains 6% tantalum. The remainder of the alloy is chromium,
Other elements commonly used to alloy with nickel to form superalloys, such as elements selected from the group consisting of iron, cobalt, molybdenum, titanium, zirconium, tungsten, hafnium, aluminum, boron, carbon, and combinations thereof. It will be empty. Additionally, other elements such as manganese, silicon, phosphorous, sulfur, lead, bismuth, tellurium, selenium and silver may be present as incidental impurities in the alloy. These alloys are atomically free of niop, ie, less than about 1%, preferably about 0. It will contain less than 5% Nb, most preferably less than about 0.1%.

Generally, in addition to nickel and tantalum, up to about 25% chromium, up to about 40% iron, and up to about 25% cobalt;
Molybdenum of about 8% or less, titanium of about 394 or less, about 2
% or less aluminum, about 7% or less tungsten, about 30 to about 150 ppm boron, and about 0.
The alloy will contain less than 1% carbon. Other elements, such as the other alloying elements described above, may be present in amounts of up to about 1% each and up to about 5% in total.

One preferred alloy is about 8 to about 16% tantalum, about 17 to about 22% chromium, up to about 25% iron, about 16%
The following cobalt, provided that the total of iron and cobalt is 12% or more, about 2 to about 6% molybdenum, about 1 to about 5% titanium, about 0.1 to about 5% aluminum, about 30 to about 15
0 ppII1 boron, about 0.01 to about 0. 1
% present, the remainder nickel (including incidental impurities), and the total amount of iron and cobalt is approximately 1
2 to about 25%.

A second preferred alloy includes about 8.5 to about 10% tantalum, about 18 to about 20% chromium, about 17 to about 19% iron;
About 265 to about 4% molybdenum, about 0.75 to about 2.
5% titanium, about 0.6% to about 0.75% aluminum, about 30 to about 60 ppm (if the alloy is cast) or about 80 to about 150 ppm (if the alloy is wrought) boron, about 0. 0.03 to about 0.05% carbon, and the balance nickel. The most preferred embodiment of this alloy is about 9% tantalum, about 19% chromium, about 18% iron, about 3% molybdenum, about 1% titanium, about 0.9% tantalum, about 1% titanium, about 1% titanium, about 1% titanium. 5% aluminum, about 30 to about 60
ppm (if the alloy is cast) or about 80 to about 1
00ppm (if the alloy is wrought) of boron, approx.
．． It consists essentially of 0.5% carbon and the balance nickel.

A third preferred alloy is about 30 to about 40% nickel;
About 30 to about 40% iron, about 15 to about 23% cobalt,
about 8 to about 16% tantalum, and about 30 to about 150p
Consisting essentially of p- boron. More preferred embodiments of this alloy include about 35 to about 38% nickel, about 35 to about 38% iron, about 17 to about 20% cobalt, about 8 to about 1
0% tantalum, and about 30 to about 60 ppm (if the alloy is cast) or about 80 to about 100 ppm @ (
When the alloy is wrought) it consists essentially of boron.

The most preferred embodiments of this alloy include about 36% to about 37% nickel, about 36% to about 37% iron, about 17% to about 19% cobalt, about 8.5% to about 9.5% tantalum, and about 30%
~about 60 ppm (when casting the alloy) or about 8
0 to about 100pl)ffl (when forging the alloy)
Consists essentially of boron.

These alloys of the invention may be cast or wrought and may be manufactured by conventional methods.

In order to achieve improvements in the high temperature properties of these alloys of the invention, it is necessary to carry out a heat treatment.

The heat treatments are conducted at higher temperatures and for significantly longer times than conventional heat treatments for similar niobium-containing alloys.

A preferred heat treatment according to the present invention for a second preferred alloy is heating at about 2000°F for about 1 hour, followed by about 2050"F and a pressure of about 12 to about 15 ksi for about 3 to about 51 ksi. hot isostatically treating (HIP) and heating at about 1925° F. for about 4 hours;
It then consists of heating at about 1600°F for about 2 hours.

Further heat (age) at approximately 1350°F for approximately 8 hours.
This may be useful for obtaining optimal properties for some alloys. When this alloy is conventionally heat treated in a niobium-containing embodiment, the 1600″F step is not included;
It would include a lower temperature aging step at about 1150° F. for about 4 to 8 hours.

By incorporating tantalum without substantially niobium and employing higher temperature heat treatment conditions, an alloy is produced that utilizes more gamma prime strengthening than conventional niobium-containing alloys. The alloys of the invention are characterized by being age hardenable and malleable, yet possessing a high combination of strength and ductility, especially at high temperatures. Furthermore, it is believed that when aluminum and titanium are included in the alloy, the total amount of aluminum and titanium can be higher than is typically used in niop-containing alloys without strain age cracking of the weld.

Another effect of substituting tantalum for niop in the alloy is improved weldability. This is Nb-
This is because the Ta-NL eutectic temperature is higher than the NL eutectic temperature, which improves the resistance to fine cracking in the heat-affected zone.

The following Examples are not intended to limit the scope of the invention, but are provided to demonstrate the preparation of the aggregates of the present invention and their improved properties, particularly high temperature properties.

Fire Example 1 48.6% nickel, 19.2% chromium, 18.0
% iron, 0.02% niobium, 9.1% tantalum, 3
,0% molybdenum, 1.04% titanium, 0.47%
aluminum, 0.0043% boron, 0.044
A tantalum-containing alloy similar to Alloy 718 was prepared by melting a composition consisting of 1.5% carbon and 0.02% silicon in a vacuum induction furnace. The molten alloy was cast into ceramic molds to produce 2" x 4" x 174" slabs.

A test piece made from the slab was subjected to the following heat treatment. That is, 2 0 0 0 ”F 1 11.'7
3 hours of hot isostatic pressure treatment at 14.7 ksi at 2050"F, 1925"F4 special, 1600"F 2 hours, and 1350"F 8 hours.

A conventional 718 alloy of the same composition, except containing essentially no tantalum and about 4.6% niobium, was prepared as described above and prepared as is normally done for 718 alloys (No. Heat treated (as shown in footnote 1 of Table 1).

What has been found in the microstructure of tantalum-containing alloys is that the stability of the Laves phase during solidification is comparable to lower than that of the conventional 718 alloy. Furthermore, tantalum-containing alloys do not develop a δ phase after exposure to temperatures in the range below 1600”F to 1800F, a heat treatment used to promote component segregation in 718 alloys, δ dump. Tantalum-containing alloys possess a microstructure with a favorable distribution of γ′ and γ″ dimensions that provide a moderate strengthening effect. In the tantalum-containing alloy compared to conventionally cast 71B, the γ' and γ'' precipitates are much more uniformly distributed throughout the dendrite core and interstices.

Specimens of the above two alloys were tested to determine their mechanical properties at room and elevated temperatures. The test results are as follows.

Table 1 Room temperature 120G +30 (1'M temperature 12
00 Room temperature 12110 1400 Ultimate tensile strength 1551 130 122 15
1 117 178.2 147.7 1
33.30.2% offset 118.1 114
106.5 133 104 142.
5 117.11 112.8 But proof stress elongation (%) 1.9 11.5
9 15 11 12 If
G aperture (%) 29.1
22.5 21.5 29. 29
18 8 G1.2000″F
″71 hours.2050 guns/1 4.7ksi/3
HIP between L'j. 1925 lower 71 hours; 1350 lower/8
II! between r. L15[]'' between F/BPj.

2.2000″F/1 hour; 2050′F/1 4.
7ksi/3B. 'j between HIP. 1925″F71 hours; 1600″F/2 hours. 1350'F/8!5 between.

Table 1 shows that the tantalum-containing type 718 superalloy has superior high-temperature strength properties compared to its niobium-containing counterpart, and that The properties can be further improved by employing suitable heat treatments.

Tip Example 2 The procedure of Example 1 was repeated for an alloy with a composition of 36.6% nickel, 36.6% iron, 17.7% cobalt, 9.1% tantalum, and 45 ppm boron. Ta. A corresponding conventional alloy, ie, an alloy in which Illitantalum was replaced atom by atom with niobium and the niop content was 4.5%, was prepared for comparison. These alloys were tested as in Example 1 to determine mechanical properties.

The results are as follows.

Table 2 Ultimate tensile strength (ksi) IIt2.
5 141.8 135 10
80.2% offset yield strength (ksi) 159.4
12a. B 120 89 Nakabi (%) 4.5 3
．． 0 4.8 7.0 Aperture (%)
8.5 B.
5 7.0 13.0 The tantalum-containing alloys of the present invention are significantly strengthened in terms of tensile strength and yield strength compared to otherwise equivalent alloys containing niobium,
It decreases with respect to aperture and shows a similar value with respect to elongation.

Evaluation of various alloys shows that the tantalum-containing alloys of the present invention are superior to corresponding niopium-containing alloys.

Example 3 The conventional 718 alloy described in Example 1 is highly resistant to strain age cracking during weld stress relief, but elution cracking in the weld heat affected zone, and weld failure under highly restrained conditions. It tends to cause solidification cracking of the molten part. In order to evaluate the effect of tantalum replacing niobium in the present invention, the alloy preparation procedure of Example 1 was carried out again to prepare a weldability test piece having a test piece size of 5 ml in a cast state. Prior to weldability testing, all specimens were placed in a vacuum for 20 minutes.
Heat treated at 00°F for 1 hour and cooled to 1200″F in 20 minutes.
The susceptibility to heat-affected zone elution cracking and molten zone solidification cracking was evaluated using the M!nf Varcstralnt) weldability test and the Mini Palestrain (M!nf Varcstralnt) weldability test. In the spot pale strain test, strain is applied to a gas tungsten arc spot weld immediately after the arc is extinguished to limit cracking to the heat shadow area. In the mini-pare restraint test,
Distortion occurs continuously during gas tungsten arc weld formation, and cracks are mainly formed in the previously solidified molten part. The total crack length is used as a quantitative measure of crack susceptibility.

As shown in Table 3, tantalum-containing alloys exhibit the lowest weld heat affected zone cracking susceptibility across strained water turbines tested under increasing strains ranging from 0.25 to 3% in the spot pale strain test.

Table 3 0.29% 24. 4220.29
% 28. 493t. ta%
33. G71l. 16% 35
．． 7752.9% 42 1
．． 00112.9% 48 1.1
08 Cracks; Number of cracks per welding location TCL: Total crack size MCL: Maximum crack size Although the present invention has been described in connection with specific examples and modes of implementation, the present invention does not extend beyond the scope of the claims. It will be understood by those skilled in the art that modifications may be made without departing from the spirit and scope of the invention.

Claims (16)

[Claims] (1) A nickel-based alloy containing about 30% by weight or more of nickel, about 8 to about 16% by weight of tantalum, about 30 to about 150 ppm of boron, and substantially no niobium. (2) Claim (1) characterized in that the remainder of the constituent components of the alloy consists of one or more elements selected from the group consisting of chromium, iron, cobalt, molybdenum, titanium, aluminum, tungsten, and carbon. Alloys listed in . (3) The alloy according to claim (2), wherein the alloy further contains one or more elements selected from the group consisting of zirconium and hafnium. (4) about 8 to about 16% tantalum, about 17 to about 22% chromium, about 25% or less iron, about 16% or less cobalt;
about 2 to about 6% molybdenum, about 1 to about 5% titanium, about 0.1 to about 5% aluminum, about 30 to about 150pp
1. A nickel-based superalloy consisting essentially of m boron, about 0.01% to about 0.1% carbon, and the balance nickel, with the total amount of iron and cobalt being about 12% or more. (5) about 8.5 to about 10% tantalum, about 18 to about 20
% chromium, about 17% to about 19% iron, about 2.5% to about 4%
% molybdenum, about 0.75% to about 2.5% titanium, about 0.25% to about 0.75% aluminum, about 30 to about 60 ppm when cast, about 80 to about 60 ppm when wrought.
A nickel-based superalloy characterized in that it consists essentially of about 100 ppm boron, about 0.03 to about 0.05% carbon, and the balance nickel. (6) the alloy is about 9% tantalum and about 19% chromium;
Approximately 18% iron, approximately 3% molybdenum, approximately 1% titanium,
Approximately 0.5% aluminum, approximately 30~ if cast
Approximately 60 ppm, approximately 80 to 100 ppm when training
An alloy according to claim 5, characterized in that it consists essentially of m boron, about 0.05% carbon and the balance nickel. (7) About 30 to about 40% nickel, about 30 to about 40%
of iron, about 15 to about 23% cobalt, about 8 to about 16% tantalum, and about 30 to about 150 ppm boron. (8) the alloy is about 35% to about 38% nickel, about 35% to about 38% nickel;
about 38% iron, about 17 to about 20% cobalt, about 8 to about 10% tantalum, and if cast, about 30 to about
Approximately 60ppm, when training, approximately 80 to 100p
An alloy according to claim 7, characterized in that it consists essentially of pm boron. (9) the alloy is about 36% to about 37% nickel;
About 37% iron, about 17 to about 19% cobalt, about 8.5
~9.5% tantalum, and about 30 to about 60 ppm if cast, and about 80 to about 1 ppm if wrought.
An alloy according to claim 8, characterized in that it consists essentially of 00 ppm boron. (10) A method for improving the high-temperature strength properties of a niobium-containing nickel-base superalloy by replacing substantially all of the niobium contained in the niobium-containing nickel-base superalloy with tantalum on an atom-to-atom basis. (11) The alloy contains about 30% by weight or more of nickel, about 8 to
Approximately 16% by weight of tantalum, as well as chromium, iron, cobalt, molybdenum, titanium, aluminum, tungsten,
The method according to claim 10, characterized in that it contains one or more elements selected from the group consisting of boron and carbon. (12) The method according to claim 11, wherein the alloy further contains one or more elements selected from the group consisting of zirconium and hafnium. (13) The alloy is heat treated at about 2000°F for about 1 hour, followed by about 12 to about 15 ksi at about 2050°F.
hot isostatically treated for about 3 to about 5 hours at a pressure of about 1
Heated at 925°F for about 4 hours, then heated to about 1600°F
Claim (1) characterized in that the method is heated for about 2 hours at
The alloy described in 1). 14. The method of claim 13, wherein the alloy is further heat treated at about 1350 degrees Fahrenheit for about 8 hours. (15) A method of heat treating a nickel-base superalloy containing tantalum and substantially free of niobium, comprising the steps of heating the superalloy at about 2000°F for about 1 hour, followed by heating the superalloy at about 2050°F for about 12 hours. hot isostatically treating at a pressure of ~15 ksi for about 3 to about 5 hours, followed by heating at about 1925° F. for about 4 hours, and a further step of about 16
A method of heat treatment comprising heating at 00°F for about 2 hours. 16. The method of claim 15, further comprising the step of heat treating said alloy at about 1350<0>F for about 8 hours.