JP5636639B2 - Ni-base superalloy - Google Patents

Description

  The present invention relates to a Ni-base superalloy, which is a heat-resistant alloy used in high-temperature equipment such as jet engines and industrial gas turbines. More specifically, the present invention relates to excellent heat resistance at high temperatures as well as excellent oxidation resistance at high temperatures and The present invention relates to a Ni (nickel) -based superalloy having corrosion resistance.

Ni-base superalloys are widely used as materials for high-temperature equipment because of their excellent structure stability and creep characteristics at high temperatures, and patent applications have been filed.
In particular, Ni-based single crystal superalloys containing Mo and Co have remarkable heat resistance, as shown in Patent Documents 1 to 7, and have recently been used in high-temperature equipment such as jet engines and industrial gas turbines. It has been proposed as a suitable Ni-base superalloy, and some of the Ni-base superalloys described in these patent documents are widely used.
Ni-based single crystal superalloys are also suitable for energy efficient turbine blades and turbine vanes for nuclear power generation from the viewpoint of suppressing carbon dioxide emissions that contribute to global warming. Expected as a material.
Since Co has an excellent function of increasing the solid solubility limit at high temperatures for gamma matrix phases such as Al and Ta, and dispersing and precipitating fine gamma prime phases by heat treatment to improve the high temperature strength. It has been considered as an indispensable component for the Ni-base superalloy used in the above. However, Co is an expensive metal compared to Ni, and a Ni-base superalloy containing as little Co as possible is desired. In addition, since Co has a long half-life, the maintenance of the Ni-base superalloy containing Co becomes radioactive when it is contaminated with radioactivity. When using it as a component for high temperature equipment, it is desired to realize a Ni-base superalloy having creep strength characteristics equivalent to or higher than those containing Co, even if it does not contain Co with a long half-life. .
Mo (molybdenum) is generally known as an element that contributes to high-temperature strength by precipitation hardening, but degrades oxidation resistance and corrosion resistance at high temperatures. There is a tendency.
Therefore, in order to spread the utility of the Ni-based single crystal superalloy, it is desired to develop a new Ni-based superalloy that uses as little Co and Mo as possible.

In addition, Ni-based single crystal superalloys containing Re have remarkable heat resistance compared to conventional Ni-based superalloys, and have recently been widely used in high-temperature equipment such as jet engines and industrial gas turbines. (Patent Documents 1 and 2).
Recently, from the viewpoint of soaring fuel or reducing carbon dioxide emissions, it is excellent in heat resistance, corrosion resistance and oxidation resistance at high temperatures in equipment such as jet engines and industrial gas turbines for the purpose of improving energy efficiency. In addition, the use of Ni-based single crystal superalloys has attracted attention, and Ni-based single crystal superalloys containing expensive metals such as Re have been put into practical use. However, with the spread of these alloys, the price of metals such as Re is on the rise, so in Ni-based single crystal superalloys containing Re, the mechanical properties at high temperatures have been improved without increasing the amount of Re used. In addition, development of a Ni-based single crystal superalloy excellent in corrosion resistance and oxidation resistance at high temperatures is strongly desired.

  In view of such circumstances, the present invention does not add Co or Mo, or adds a very small amount compared to the prior art, with a Ni-based alloy having a heat resistance equal to or higher than that of a conventional alloy, and a Re content as low as possible. Another object of the present invention is to provide a Ni-base superalloy having heat resistance equal to or higher than that of conventional alloys and improved corrosion resistance at high temperatures.

The Ni-base superalloy of the invention 1 is
Cr: more than 7.5% by mass and 12.0% by mass or less,
W: 6.0% by mass or more and 10.0% by mass or less,
Al: 4.0 mass% or more and 7.0 mass% or less,
Ta + Nb: 5.0% by mass or more and 12.0% by mass or less, Ta: more than 5.0% by mass, Nb: 0.1% by mass or more and 5.0% by mass or less,
Hf: 2.0 mass% or less,
Re: 0.1% by mass or more and 3.5% by mass or less,
The balance has a composition consisting of Ni and inevitable impurities,
When casting as a polycrystalline alloy, a unidirectional solidification alloy, or a single crystal alloy by a normal casting method, a unidirectional solidification method, or a single crystal solidification method,
After performing a pre-heat treatment at 1260 to 1300 ° C. for 20 minutes to 2 hours after this casting, solution treatment at 1300 to 1350 ° C., primary aging treatment at 2 to 8 hours in a temperature range of 1050 to 1150 ° C., and characterized by being conducted secondary aging treatment 10 to 24 hours at 800 to 900 ° C..

The Ni-base superalloy of the invention 2 is
Cr: more than 7.5% by mass and 12.0% by mass or less,
W: 6.0% by mass or more and 10.0% by mass or less,
Al: 4.0 mass% or more and 7.0 mass% or less,
Ta + Nb: 6.0% by mass or more and 12.0% by mass or less, and Ta: more than 6.0% by mass,
Hf: 2.0 mass% or less,
Re: 0.1% by mass or more and 3.5% by mass or less,
The balance has a composition consisting of Ni and inevitable impurities,
When casting as a polycrystalline alloy, a unidirectional solidification alloy, or a single crystal alloy by a normal casting method, a unidirectional solidification method, or a single crystal solidification method,
After performing a pre-heat treatment at 1260 to 1300 ° C. for 20 minutes to 2 hours after this casting, solution treatment at 1300 to 1350 ° C., primary aging treatment at 2 to 8 hours in a temperature range of 1050 to 1150 ° C., and characterized by being conducted secondary aging treatment 10 to 24 hours at 800 to 900 ° C..

Invention 3 is the Ni-base superalloy of Invention 1 or Invention 2 , characterized by containing W: 7.0% by mass or more and Al: 4.5% by mass or more and 6.5% by mass or less .

Invention 4 is the Ni-base superalloy according to any one of Inventions 1 to 3 , wherein Si: 0.4 mass% or less, V: 3 mass% or less, Zr: 3 mass% or less, C: 0.3 mass% Hereinafter, B: 0.2% by mass or less, Y: 0.2% by mass or less, La: 0.2% by mass or less, Ce: 0.2% by mass or less .

Invention 5 is the Ni-base superalloy according to any one of Inventions 1 to 4 , having a creep rupture life at 1100 ° C. of 137 MPa of 161 hours or more, and 75% Na ₂ SO ₄ + 25% NaCl component. The corrosion weight loss in a sulfidation corrosion test in which a sample is immersed in the salt heated and melted at 900 ° C. for 20 hours is less than 10 ⁻³ mm.
Invention 6 is characterized in that in the Ni-base superalloy described in Invention 5 , the creep rupture life at 137 MPa at 1100 ° C. is 318 hours or more.
Invention 7 is a member composed of a Ni-base superalloy, wherein the Ni-base superalloy is the Ni-base superalloy according to any one of Inventions 1 to 6 .

Invention 8 is a method for producing a Ni-base superalloy member according to Invention 7 , wherein the Ni-base superalloy according to any one of Inventions 1 to 6 is produced by a normal casting method, a unidirectional solidification method, or a single crystal solidification method. It is characterized by being cast and molded by the method.

According to the present invention, it is possible to provide a Co and Mo-free Ni-base superalloy having heat resistance similar to or higher than that of a Ni-base superalloy containing Co and Mo, as is apparent from the following examples. It was. Furthermore, by controlling the Ni-based superalloy to a specific composition while suppressing the amount of expensive Re used as much as possible, the Ni-based superalloy combines excellent heat resistance, excellent oxidation resistance at high temperatures, and corrosion resistance. It has also become possible to provide alloys.
The present invention has the features as described above, and an embodiment thereof will be described in detail below.

It compares the appearance photograph of the sample after a sulfidation corrosion test about the alloy of alloy number 2, and the alloy of alloy number 7 (comparative alloy). The relationship between heat resistance (creep life time) and corrosion resistance (corrosion weight loss) is illustrated for the alloys of the present invention (alloy numbers 1 to 5 and 8 to 13) and comparative alloys (alloy numbers 6, 7, and 14). . It is the figure which showed the change of the mass at the time of exposing a sample by repetition of 200 cycles under the high temperature of 1100 degreeC in the 1 hour cycle about the alloy of the alloy number 2 and the alloy number 7 (comparative alloy). .

Co has a function of increasing the solid solubility limit at a high temperature with respect to a gamma matrix phase such as Al and Ta, and dispersing and precipitating a fine gamma prime phase by heat treatment to improve the high temperature strength. Further, Mo dissolves in the alloy base to increase the high temperature strength and contributes to the high temperature strength by precipitation hardening. Therefore, it has been conventionally considered that both are indispensable components for a Ni-base superalloy having excellent structure stability and creep characteristics at high temperatures. However, even if Co and Mo, which have been considered to be indispensable in high-strength Ni-base superalloys in the invention of the present application, are not added, by making the Ni-base superalloy a specific composition, high creep strength and excellent It was clarified that a Ni-base superalloy having both heat resistance, excellent oxidation resistance at high temperatures, and corrosion resistance can be realized. If the Co content is less than 1.0 mass% and the Mo content is 0.1 mass% or less, the excellent oxidation resistance and corrosion resistance of the alloy of the present invention will not be impaired.
That is, Cr: 1.0% by mass or more and 12.0% by mass or less, W: 6.0% by mass or more and 10.0% by mass or less, Al: 4.0% by mass or more and 7.0% by mass or less, Ta + Nb: 5 0.0% by mass or more and 12.0% by mass or less, Hf: 2.0% by mass or less, Re: 0.1% by mass or more and 5.0% by mass or less, with the balance being Ni and inevitable impurities By doing so, it became clear that it has heat resistance which is not inferior to CMSX-4 containing Co and Mo which has been used as a second generation Ni-based single crystal alloy.

In the present invention, depending on the specific application of the high temperature equipment using the Ni-base superalloy, for example, Si: 0.4 mass% or less, V: 3 mass% or less, Zr: 3 mass% or less, C: 0.3 mass % Or less, B: 0.2 mass% or less, Y: 0.2 mass% or less, La: 0.2 mass% or less, Ce: 0.2 mass% or less It is possible to further improve the physical properties of the product according to various uses.

  The Ni-base superalloy of the present invention has excellent structure stability at high temperatures, creep characteristics, and oxidation / corrosion resistance, and is particularly suitable for the production of turbine blades or turbine vane parts.

  The optimum content range of the components of the Ni-base superalloy of the present invention will be described below.

Cr (chromium) is an element excellent in oxidation resistance, and improves the high temperature corrosion resistance of the Ni-base superalloy. If the Cr content is too small, the effect is small. If the Cr content is too large, the balance with other heat-resistant strengthening elements deteriorates and the performance deteriorates, which is not preferable. The Cr content is preferably in the range of 1.0% to 12.0% by mass, more preferably Cr: 6.0% to 11.0% by mass, and even more than 7.5% by mass. 11.0 mass% or less is the most preferable.

W (tungsten) has the effects of solid solution strengthening and precipitation hardening, and improves the high temperature strength of the Ni-base superalloy. If the W content is too small, the effect of improving the high-temperature strength is small, and if it is too large, a harmful phase is precipitated, which is not preferable. Further, an increase in the amount of W is not preferable because the specific gravity of the entire alloy increases and the alloy cost also increases. The W content is preferably in the range of 6.0 mass% to 10.0 mass%, and more preferably 7.0 mass% to 10.0 mass%.

Al (aluminum) forms an intermetallic compound represented by Ni3Al constituting a gamma prime phase that combines with Ni and precipitates in the gamma matrix phase at a volume fraction of 50 to 70% to increase the high temperature strength. Improve. If the Al content is too small, the effect of precipitation strengthening of the gamma prime phase will not be sufficiently exhibited, and if it is added too much, the ductility of the alloy will be lowered, which is not preferable. The content of Al is preferably in the range of 4.0% by mass or more and 7.0% by mass or less, and more preferably 4.5% by mass or more and 6.5% by mass or less.

Ta (tantalum) and Nb (niobium) are both effective elements for strengthening the gamma prime phase and improving the creep strength. When the composition of Ta + Nb is small, the effect of precipitation strengthening of the gamma prime phase does not sufficiently appear, and when too much is added, the ductility of the alloy is lowered, which is not preferable. Although it is necessary to add one or more of these, the composition range of Ta + Nb should be 5.0% by mass or more, and if the total content of elements exceeds 12% by mass, the generation of harmful phases is promoted. Therefore, it is used as 12.0 mass% or less. The composition of Ta + Nb is preferably in the range of 5.0% by mass to 12.0% by mass and Ta over 5.0% by mass, and the composition of Ta + Nb is 6.0% by mass to 12.0% by mass and Ta is included. A range of more than 6.0% by mass is more preferable. Nb is effective in improving the creep strength and is effective in lowering the density of the alloy by substituting some alloy elements such as Ta. The composition range of Nb is 0.1 mass% or more and 5% or more. It is usually used in an amount of 0.0 mass% or less, preferably 0.1 mass% or more and 4.0 mass% or less.

Hf (hafnium) has an effect of improving oxidation resistance, and is therefore preferably added and used in many cases. However, if the content is too large, it tends to promote the generation of a harmful phase. Therefore, the content of Hf is preferably 2.0% by mass or less.

Re (rhenium) has the effect of improving the corrosion resistance as well as improving the high temperature strength by solid solution strengthening in the gamma phase. If the content of Re is extremely small, the effect of improving the high temperature strength and corrosion resistance is not remarkably observed. On the other hand, if the content of Re is too large, the TCP phase may precipitate at high temperatures and the high temperature strength may be lowered. In addition, it is not preferable to use a large amount of expensive Re because it increases the alloy cost. Accordingly, the Re content is preferably 0.1 to 5.0% by mass, and more preferably 0.1 to 3.5% by mass. More preferred.

Si (silicon) improves the oxidation resistance as a protective film by generating a SiO2 film on the alloy surface. However, when Si is contained in a large amount, the solid solubility limit of other elements is lowered, so that 0.4% by mass or less is preferable.

V (vanadium) is dissolved in the gamma prime phase to strengthen the gamma prime phase. However, an excessive content is preferably 3% by mass or less because it reduces the creep strength.

Zr (zirconium) reinforces grain boundaries in the same manner as B (boron) and C. However, the excessive content is preferably 3% by mass or less because it reduces the creep strength.

C (carbon) contributes to grain boundary strengthening. However, an excessive content is preferably 0.3% by mass or less because it impairs ductility.

B (boron), like C, contributes to grain boundary strengthening. However, an excessive content is preferably 0.2% by mass or less because it impairs ductility.

Y (yttrium), La (lanthanum), and Ce (cerium) improve the adhesion of a protective oxide film that forms alumina, chromia, and the like during use of a Ni-based superalloy at high temperatures. However, since excessive content will lower the solid solubility limit of other elements, the range of Y: 0.2 mass% or less, La: 0.2 mass% or less, Ce: 0.2 mass% or less Is preferably used.

The Ni-base superalloy of the present invention can have high creep strength by heat treatment after casting. Standard heat treatment is pre-heat treatment at 1260 to 1300 ° C. for 20 minutes to 2 hours, followed by solution treatment at 1300 to 1350 ° C., heating at 1550 to 1150 ° C. for 2 to 8 hours, air cooling I do. This treatment can be combined with a coating treatment for heat resistance and oxidation resistance. After air cooling, a secondary aging treatment for the purpose of stabilizing the gamma prime phase is subsequently performed at 800 to 900 ° C. for 10 to 24 hours, followed by air cooling. Each air cooling may be replaced with an inert gas. High temperature parts such as a turbine blade of a gas turbine or a turbine vane are realized by the Ni-base superalloy produced by this manufacturing method.

  Seven types having different compositions shown in Table 1 were cast into a single crystal and subjected to a solution treatment and an aging treatment by an ordinary method. As a solution treatment, after holding at 1300 ° C. for 1 hour, the temperature was raised to 1330 ° C. and held for 5 hours. Moreover, the aging treatment performed the primary aging which hold | maintains at 1100 degreeC for 4 hours, and the secondary aging treatment which hold | maintains at 870 degreeC for 20 hours.

Next, the creep strength was measured with respect to alloy numbers 1 to 5 and alloy numbers 6 and 7 which were comparative alloys subjected to solution treatment and aging treatment. In the creep test, the lifetime was defined as the time until the sample creep ruptured under the conditions of 800 ° C.-735 MPa, 900 ° C.-392 MPa, 1000 ° C.-245 MPa, 1100 ° C.-137 MPa. Further, for the purpose of comparing the corrosion resistance of various alloys, a sulfide corrosion test was performed by immersing the sample in a salt obtained by heating and melting a salt of 75% Na ₂ SO ₄ + 25% NaCl at 900 ° C. for 20 hours. The degree of corrosion is indicated by converting the weight loss of sulfide corrosion into length. In Table 2, the alloy of this example and the comparative alloy are summarized by the corrosion rupture life (h) and the corrosion weight loss which is a measure of the corrosion resistance.

  As shown in Table 2, the alloys of Alloy Nos. 1 to 5 in this example have excellent heat resistance sufficient as a heat resistant member in a wide alloy composition range. From the results of the corrosion weight loss shown in Table 2, it can be seen that the alloys of Alloy Nos. 1 to 5 in this example have significantly superior corrosion resistance as compared with the alloys shown in the reference examples. FIG. 1 is a comparison of external appearance photographs of samples after the sulfidation corrosion test of an alloy of alloy number 2 and an alloy of alloy number 7. Almost no change in appearance was observed in the alloy No. 2 even after the corrosion test. On the other hand, in the alloy No. 7, which is an existing alloy (CMSX-4), it was observed that corrosion was clearly progressing. That is, when the alloy of Alloy No. 2 in this example is compared with the existing alloy of Alloy No. 7, the content of expensive Re (1.2% by mass) in the alloy of Alloy No. 2 is half that of the existing alloy. In spite of the following, it has outstanding heat resistance and corrosion resistance at high temperature, which is an outstanding feature of this alloy. It is clear from these examples that this alloy is an excellent alloy with a very balanced heat resistance and corrosion resistance.

Next, seven alloys with different compositions shown in Table 3 having the alloy numbers 8 to 14 were cast into a single crystal and subjected to a solution treatment and an aging treatment by an ordinary method. As a solution treatment, after holding at 1300 ° C. for 1 hour, the temperature was raised to 1330 ° C. and held for 5 hours. Moreover, the aging treatment performed the primary aging which hold | maintains at 1100 degreeC for 4 hours, and the secondary aging treatment which hold | maintains at 870 degreeC for 20 hours. Creep strength was measured for alloys Nos. 8 to 14 subjected to solution treatment and aging treatment. In the creep test, the time until the sample ruptured at 900 ° C.-392 MPa and 1100 ° C.-137 MPa was defined as the lifetime. In order to compare the corrosion resistance of these alloys, a sulfide corrosion test was conducted by immersing the sample in a salt obtained by heating and melting a salt of 75% Na ₂ SO ₄ + 25% NaCl at 900 ° C. for 20 hours. These evaluation results are also shown in Table 3.

  FIG. 2 shows the relationship between heat resistance (creep life time) and corrosion resistance (corrosion weight loss) for alloy numbers 1 to 5, 8 to 13 (invention alloy) and alloy numbers 6, 7, and 14 (comparative alloy). It is illustrated. From this figure, it is clear that the alloy of the present invention is a Ni-based single crystal superalloy having a remarkable performance balance that is excellent not only in heat resistance but also in corrosion resistance under high temperature use conditions.

  Furthermore, in order to examine the oxidation resistance of the alloys at high temperatures, repeated exposure tests of about 200 cycles were performed at a high temperature of 1100 ° C. for 1 hour in air, and the change in mass due to each alloy is shown in FIG. . As is apparent from the figure, the alloy of the present invention not only has excellent corrosion resistance, but also has excellent performance in terms of oxidation resistance at high temperatures.

  As is clear from the above examples, the alloy of the present invention has excellent creep characteristics at high temperatures over a long period of time as compared with CMSX-4, which has been used as a second generation Ni-based single crystal alloy. It can be said that it is a cobalt-free Ni-based superalloy having a very good balance of performance and having excellent oxidation resistance and corrosion resistance.

  According to the present invention, it is possible to provide an excellent alloy having a very balanced heat resistance, corrosion resistance at high temperature, and oxidation resistance. In addition, the amount of expensive metal such as expensive Re used can be significantly reduced compared to existing alloys. Therefore, according to the present invention, it is possible to provide a well-balanced alloy from a middle temperature part to a high temperature part suitable as a turbine blade or turbine vane such as a jet engine or a power generation gas turbine. In addition, since it does not contain Co, which has a particularly long half-life, it is expected to be practically used as a material for nuclear power generation. That is, it becomes possible to produce a cobalt-free Ni-base superalloy having high structural stability over a long period of time suitable as a turbine blade or turbine vane for nuclear power generation and the like, and excellent creep characteristics at high temperatures.

: US Pat. No. 4,643,782 : US Pat. No. 4,908,183 : US Pat. No. 5,043,138 : US Pat. No. 5,068,084 : US Pat. No. 5,069,873 : US Pat. No. 5,151,249 : US Pat. No. 6,905,559

Claims (8)

Cr: more than 7.5% by mass and 12.0% by mass or less,
W: 6.0% by mass or more and 10.0% by mass or less,
Al: 4.0 mass% or more and 7.0 mass% or less,
Ta + Nb: 5.0% by mass or more and 12.0% by mass or less, Ta: more than 5.0% by mass, Nb: 0.1% by mass or more and 5.0% by mass or less,
Hf: 2.0 mass% or less,
Re: 0.1% by mass or more and 3.5% by mass or less,
The balance has a composition consisting of Ni and inevitable impurities,
When casting as a polycrystalline alloy, a unidirectional solidification alloy, or a single crystal alloy by a normal casting method, a unidirectional solidification method, or a single crystal solidification method,
After performing a pre-heat treatment at 1260 to 1300 ° C. for 20 minutes to 2 hours after this casting, solution treatment at 1300 to 1350 ° C., primary aging treatment at 2 to 8 hours in a temperature range of 1050 to 1150 ° C., and 800 to 900 Ni-base superalloy, characterized in that it has performed secondary aging treatment 10 to 24 hours at ° C.. Cr: more than 7.5% by mass and 12.0% by mass or less,
W: 6.0% by mass or more and 10.0% by mass or less,
Al: 4.0 mass% or more and 7.0 mass% or less,
Ta + Nb: 6.0% by mass or more and 12.0% by mass or less, and Ta: more than 6.0% by mass,
Hf: 2.0 mass% or less,
Re: 0.1% by mass or more and 3.5% by mass or less,
The balance has a composition consisting of Ni and inevitable impurities,
When casting as a polycrystalline alloy, a unidirectional solidification alloy, or a single crystal alloy by a normal casting method, a unidirectional solidification method, or a single crystal solidification method,
After performing a pre-heat treatment at 1260 to 1300 ° C. for 20 minutes to 2 hours after this casting, solution treatment at 1300 to 1350 ° C., primary aging treatment at 2 to 8 hours in a temperature range of 1050 to 1150 ° C., and 800 to 900 Ni-base superalloy, characterized in that it has performed secondary aging treatment 10 to 24 hours at ° C..   3. The Ni-base superalloy according to claim 1, wherein W: 7.0% by mass or more and Al: 4.5% by mass to 6.5% by mass.   The Ni-base superalloy according to any one of claims 1 to 3, wherein Si: 0.4 mass% or less, V: 3 mass% or less, Zr: 3 mass% or less, C: 0.3 mass% or less, B Ni: more than 0.2% by mass, Y: 0.2% by mass or less, La: 0.2% by mass or less, Ce: 0.2% by mass or less alloy. A Ni-base superalloy according to any one of claims 1 to 4, with the creep rupture life of at 137MPa at 1100 ° C. is not less than 161 _hours, a _{75% Na 2 SO 4 + 25} % salt NaCl ingredient 900 A Ni-base superalloy characterized by having a corrosion weight loss of less than 10 ⁻³ mm in a sulfidation corrosion test in which a sample is immersed in the salt heated and melted at C for 20 hours. The Ni-base superalloy according to claim 5 , wherein a creep rupture life at 137 MPa at 1100 ° C is 318 hours or longer. A Ni-based superalloy member comprising a Ni-based superalloy, wherein the Ni-based superalloy is the Ni-based superalloy according to any one of claims 1 to 6 . A method for producing a Ni-base superalloy member according to claim 7 , wherein the Ni-base superalloy according to any one of claims 1 to 5 is produced by a normal casting method, a unidirectional solidification method, or a single crystal solidification method. A method for producing a Ni-based superalloy member, characterized by being produced by casting using the above method.