JPH092900A - Nickel base single crystal alloy and gas turbine using the same - Google Patents

Abstract

PURPOSE: To obtain a nickel base single crystal alloy which has high strength and excellent resistance to oxidation and corrosion suitable for moving blades in gas turbine for power generation by forming the surface layer of a boride, cabide or nitride on a Ni-base single crystal alloy. CONSTITUTION: A surface layer of a boride, carbide or nitride is formed on a nickel base single crystal alloy. The intrusion of sulfur can be inhibited by the surface layer of a high melting point compound rich in covalent bonds and the surface layer is formed by the reaction diffusion in a thickness of <=150μm and the concentration of B, C or N becomes low inward in the ingredient distribution of the concentration. Additionally, active boron is reaction- diffused on the surface of the Ni base single crystal alloy to convert the surface to boride. Or nitrogen gas or a hydrocarbon gas is converted to plasma and the surface is treated with the plasma.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Ni-base single crystal alloy for a heat resistant structural material which is suitable for use in gas turbine blade and nozzle materials and which is excellent in high temperature strength, oxidation resistance and corrosion resistance.

[0002]

2. Description of the Related Art In order to realize an ultra-high temperature gas turbine for a high-efficiency combined cycle power generation system, it is necessary to use a Ni-base single crystal alloy having an excellent service temperature for the first stage rotor blade.
Ni-based alloys with excellent high temperature strength are being developed as jet engine materials for aircraft, but there are Ni-based single crystal alloys that balance high temperature strength, oxidation resistance and corrosion resistance in a high dimension as gas turbine materials for power generation. do not do. Therefore, conventionally, in order to improve the high temperature strength, the addition of the third element, which is expected to be solid solution strengthened, has been performed.

A third element that forms a stable oxide film is selected for improving the oxidation resistance, and a third element effective for preventing sulfuration of the alloy surface Ni is selected for improving the corrosion resistance. Elements have been selected. However, even with the addition of these third elements, it is difficult to completely prevent sulfidation and oxidation from the surface to the inside of the alloy, and excessive addition of the third element is detrimental to high temperature strength. It was difficult to balance high temperature strength, oxidation resistance and corrosion resistance at a high level.

Further, Japanese Unexamined Patent Publication No. 5-195193 discloses a method of improving the surface strength by forming a deep nitrided layer on the surface of a Ni-based alloy by heating and holding it.

As described above, it has been desired to develop an alloy having excellent high temperature strength, oxidation resistance and corrosion resistance as a gas turbine material for power generation.

[0006]

As the Ni-based single crystal alloy, an alloy excellent in high temperature strength, oxidation resistance and corrosion resistance is desired, and addition of various third elements effective for improving these characteristics has been studied. . However, it has been difficult to select a third element as a gas turbine material for power generation, which has a high level of balance with high-temperature strength, oxidation resistance, and corrosion components in combustion gas.

The process by which a Ni-based single crystal alloy is deteriorated by exposure to combustion gas is as follows.

1) An Al ₂ O ₃ protective film is formed on the surface of the Ni-based single crystal alloy to prevent the invasion of sulfur. Sulfidation does not proceed until this film is broken.

2) A part of the Al ₂ O ₃ protective film is broken by heat cycle and the like, and sulfur penetrates. Therefore, Cr sulfide is formed inside. Since it is difficult to regenerate the Al ₂ O ₃ protective film, a large amount of sulfur invades from the broken part.

3) Since the content of Cr is not usually so high as to convert all invading sulfur into a Cr compound, the infiltration of sulfur cannot be completely captured by Cr alone, and Ni sulfide is formed. Since the melting point of Ni sulfide is low, the surface is partially melted. Therefore, sulfide corrosion proceeds at an accelerated rate.

That is, as long as the Al ₂ O ₃ film formed first is not broken, it is effective for oxidation resistance and corrosion resistance.
Once the coating peels off, sulfidation corrosion is unavoidable.

Further, since the method disclosed in Japanese Patent Laid-Open No. 5-195193 is held by heating, it cannot be applied to a single crystal Ni-based alloy, and only a layer of several tens of μm can be formed, and the strength and corrosion resistance at high temperature are high. I had a problem with.

Therefore, an object of the present invention is to provide a Ni-base single crystal alloy suitable for a gas turbine blade material for power generation, which is excellent in high temperature strength, oxidation resistance and corrosion resistance, by using a surface modification method.

[0014]

In order to achieve the above object, in the present invention, a boride, carbide or nitride surface layer is formed on a Ni-based single crystal alloy. A high melting point compound surface layer with a high degree of covalent bond prevents the invasion of sulfur, and a surface layer by reaction diffusion is formed with a thickness of 150 μm or less, and the composition of boron, carbon, and nitrogen gradually increases from the surface to the inside. It is preferable to gradually reduce the concentration distribution.

The alloy surface is borated by reactive diffusion of active boron on the surface of the Ni-based single crystal alloy.

Alternatively, it can be manufactured by converting nitrogen gas or hydrocarbon gas into plasma. Such alloys can be applied to power generation gas turbine blades and nozzles that require high-temperature strength, oxidation resistance, and corrosion resistance.

[0017]

The improvement of the high temperature strength of the Ni-based single crystal alloy according to the present invention is expected to suppress the movement of dislocations by the solid solution hardening mechanism due to the size effect due to the difference in atomic size. It is achieved by dispersing it inside the single crystal alloy.

Next, the composition range of the Ni-based single crystal alloy will be described.

Although Cr improves corrosion resistance,
If added excessively, harmful phase precipitation and carbide coarsening occur, and the high temperature strength decreases. In addition, it reacts with oxygen and sulfur that have entered the interior of the alloy, and prevents the invasion of oxygen and sulfur. The proper addition amount is Cr: 6.0 to 9.0% by weight.

Al precipitates the γ'phase, which is a strengthening factor of the Ni-based single crystal alloy, that is, Ni ₃ Al, and contributes to the high temperature strength, but if added in excess, the weldability deteriorates. The proper amount of addition is 4.5 to 6.0% by weight.

[0021] W and Mo are solid-dissolved in the matrix and strengthened, and are particularly effective for improving the strength for a long time, but if added in excess, they promote precipitation of a harmful phase and reduce the strength. The addition amount is W: 2.0 to 12.0% by weight, Mo: 6.0
Weight% or less is appropriate.

Ta dissolves in the γ'phase, which is a strengthening factor, to improve the high temperature strength, but if added in excess, it forms coarse carbides at the grain boundaries and lowers the strength. The proper addition amount is Ta: 2.5 to 9.0% by weight.

[0023] Re improves the high temperature corrosion resistance, but if it is added excessively, the effect is saturated and the ductility and toughness are rather deteriorated. In addition, it reacts with oxygen and sulfur that have entered the interior of the alloy, and prevents the invasion of oxygen and sulfur. Re: 0.1 to 4.0% by weight is suitable as the addition amount.

Hf, Co, and Nb react with oxygen and sulfur that enter the inside of the alloy to prevent the invasion of oxygen and sulfur. The addition amount is Hf: 3.0 wt% or less, Co:
Appropriate values are 0.1 to 3.0% by weight and Nb: 0.2 to 0.3% by weight.

The purpose of adding the third element of Cr, Co, Nb, Re and Hf to the Ni-based single crystal alloy is to improve the mechanical properties, oxidation resistance and corrosion resistance of the alloy as described above. At this time, the third element contributes to the improvement of one property but adversely affects another property (for example, addition of Cr contributes to the improvement of oxidation resistance but adversely affects the mechanical properties). Is often the case. Therefore, in order to design the Ni-based single crystal alloy composition, it is necessary to determine the component ratio in consideration of the delicate balance between the additional elements, and as shown above, the composition in which the effect of each additional element can be sufficiently realized. Decided.

Further, on the surface of a normal alloy, oxidation resistance and corrosion resistance can be imparted by the Al ₂ O ₃ protective film, but peeling of this film is inevitable. Therefore, the high melting point compound surface layer rich in covalent bond prevents the invasion of oxygen and sulfur, and
A surface layer of 150 μm or less is formed by reaction diffusion, and the composition of boron, carbon, and nitrogen is gradually reduced from the surface to the inside to prevent the film from peeling. These actions are 1) Ni
Since it has a higher melting point than the base single crystal alloy, it is stable even in high-temperature gas. 2) Compared with metal bonds, these compounds are bonds that are rich in covalent bond, so even if atoms of different types enter, their diffusion It is slow, and 3) the surface layer of these compounds is a surface layer which is changed by reaction diffusion, so that it is basically achieved by having a structure that is compatible with the alloy and is hard to peel off.

The surface layer is composed of the oxidation resistance of the Ni-based single crystal alloy,
A layer thickness of 150 μm or less is desirable in order to draw out the corrosion resistance, high temperature strength, and strength of the layer itself in a well-balanced manner. In the case of a film having a thickness of 150 μm or more, thermal stress occurs due to the difference in the coefficient of thermal expansion between the parent phase of the Ni-based single crystal alloy and the surface forming layer, and the surface layer is peeled off. Although this problem also occurs when the thickness is 150 μm or less, the thermal stress can be relaxed by making the composition gradient, the peeling of the surface layer can be prevented, and the adhesion with the Ni-based single crystal alloy can be maintained. As a result, high temperature strength, oxidation resistance and corrosion resistance were all balanced at a high level.

[0028]

【Example】

(Example 1) An example in which a Ni-based single crystal alloy according to the present invention was produced will be described. A master ingot was prepared from the samples having the compositions shown in Table 1 by a high frequency melting furnace, and single crystallized by a unidirectional solidification furnace.

[0029]

[Table 1]

The single crystal sample was macroetched with a corrosive solution of HCl: H ₂ O ₂ = 9: 1, and after visually confirming that it was single crystallized, it was further heat-treated in a high-purity argon atmosphere. Samples having compositions No. 1, 2, and 3 in Table 1 were used as test materials for forming a surface-modified layer by boriding, nitriding, or carbonizing. Sample No. 4 was not surface-treated and was used as a reference for comparison with Nos. 1, 2, and 3. Sample N
Regarding o.1, surface modification was carried out by subjecting the alloy surface to boride treatment by reactive diffusion of the active boron on the surface of the Ni-based single crystal alloy. Here, active boron was generated at 700 ° C. using a mixed gas of B ₂ H ₆ + H ₂ and diffused from the alloy surface. Regarding sample No. 2, the surface of the alloy surface was modified by ion nitriding treatment by converting nitrogen gas into plasma. Here, nitrogen was made into plasma by glow discharge (500 V) of N ₂ in a vacuum furnace. At this time, nitrogen becomes extremely high energy state due to collision of electrons, and changes into highly reactive plasma species, which diffuses from the alloy surface to the inside. With respect to Sample No. 3, the surface of the alloy surface was modified by ion carburizing treatment by converting hydrocarbon gas into plasma. Since it is difficult to directly obtain the carbon gas for the carbonization treatment, a hydrocarbon gas plasma was used. As in the case of Sample No. 2, this was turned into plasma by glow discharge (500 V) of hydrocarbon in a vacuum furnace. The surface modification method using these plasmas has a high processing speed, easy control of the processing layer,
It is characterized by less distortion. Further, the single crystal of the Ni-based single crystal alloy can be maintained.

The samples Nos. 1, 2, and 3 were subjected to compositional analysis in the depth direction by EPMA in order to confirm how much boron, carbon, and nitrogen penetrated into the alloy. This profile is shown in FIG. The horizontal axis indicates the distance from the surface in the depth direction. As a result, a surface layer of boride, nitride or carbide is formed on the surface of the alloy in about 150
It can be seen that the amount of boron, carbon, and nitrogen is reduced each time the alloy is formed on the order of μm and progresses inward from the alloy surface.

Thus, with a surface layer having a thickness of about 150 μm,
By reducing the composition of boron, carbon, and nitrogen in the depth direction from the surface of the surface layer to the boundary with the Ni-based single crystal alloy, exfoliation of the surface layer is prevented and adhesion with the Ni-based single crystal alloy is prevented. Has improved.

Next, the samples produced here were subjected to a corrosion resistance test by a burner rig method which is considered to be a corrosion resistance test method close to the actual environment. The test piece uses a 9 mm round bar,
After maintaining at 900 ° C. for 7 hours in a light oil-fired combustion gas, an air cooling cycle was repeated 7 times, and corrosion resistance was evaluated from the weight change after the test, that is, the corrosion weight loss and the maximum erosion depth. The amount of light oil used for combustion was 140 g / min, and 0.3% NaCl water was added to this for 30-min to accelerate corrosion.
40cc was sprayed. The air volume of the combustion gas was set to 1.3 Nm ³ per minute. FIG. 2 shows the corrosion weight loss per unit area and the maximum erosion depth of all the samples after the burner rig test. The left horizontal axis shows the corrosion weight loss, and the right horizontal axis shows the maximum erosion depth.

For the sample of No. 4 without the surface modification layer, both the corrosion weight loss and the maximum erosion depth are large, and practical problems remain in the corrosion resistance. On the other hand, the samples Nos. 1, 2, and 3 having the surface layer of the compound of boride, carbide, and nitride showed excellent weight resistance with almost no weight loss and a maximum erosion depth of 0.4 mm or less. I understand.

Further, a high temperature oxidation test was conducted on these samples. As conditions for the high temperature oxidation test, 1100 ° C. × 16 h was repeated 10 times by heating in an electric furnace in the atmosphere.
The weight was measured without descaling each time, and the oxidation resistance was evaluated by the weight reduction per unit area at that time.
FIG. 3 shows the results of the high temperature oxidation test of all the samples. No.4
The samples of No. 1, 2, and 3 having the surface-modified layer showed almost no weight loss, while the samples of No. 1, No. 2, and No. 3 having the surface-modified layer showed no significant reduction in weight. It turns out to be excellent.

Further, a creep rupture test was conducted to examine the high temperature strength. The test was conducted by raising the temperature to a predetermined temperature, holding the temperature for about 2 hours, and applying a load. The test conditions are 870 ° C.-539.0 MPa, 940 ° C.-343.
0 MPa, 1040 ° C-205.8 MPa, 1040 ° C
-166.6 MPa and 1040 ° C.-137.2 MPa. The results are converted into Larson-Miller curves and shown in FIG. The Larson-Miller curve shows that at the test temperature, the higher the curve is on the right side, the higher the high temperature strength is.

From this, a compound surface layer of a boride, carbide or nitride compound surface layer is formed with an inclination of 150 μm or less, and the composition of boron, carbon and nitrogen is gradually reduced from the surface to the inside. I have No. 1, 2, 3
It can be seen that the sample No. 1 is excellent in oxidation resistance and corrosion resistance and is suitable for a gas turbine blade material.

(Embodiment 2) FIG. 5 is an inclined view of a gas turbine blade for power generation according to an embodiment of the present invention. The turbine blade 3 includes a blade 13 and a platform 13 having a flat portion connected to the blade 12 and the platform 1.
The shank 15 is connected to the shank 15, the fins 14 are formed on both sides of the shank 15, and the dovetail 16 is connected to the shank 15. FIG. 6 is an inclined view of a gas turbine nozzle for power generation that is an embodiment of the present invention. The turbine nozzle 10 has one blade portion and sidewalls formed at both ends of the blade portion.

FIG. 7 is a sectional view of a rotating portion of a gas turbine device having a turbine blade 3 and a turbine nozzle 10 using the Ni-based single crystal alloy of the present invention.

1 is a turbine stub shaft, 2 is a distant piece, 4 is a turbine disk, 5 is a turbine stacking bolt, 6 is a compressor disk, 7 is a compressor blade, 8 is a turbine spacer, 9 is a compressor stub shaft, and 11 is a compressor. It is a tacking bolt.

In the gas turbine of the present invention, the compressor disk 6 has 17 stages and the turbine blade 3 has 3 stages. Turbine blades 3 are also available in four stages,
The Ni-based single crystal alloy having the surface layer of the present invention can be applied to any of them.

The gas turbine in this embodiment is mainly composed of a heavy duty type, a single axis type, a horizontal split casing, a stacking type rotor, a compressor is a 17-stage axial flow type, and a turbine is a 3-stage impulse type. The first and second stages of blades and nozzles are of air cooling type, the combustor is of verse flow type, 16 cans, and slot cool type. In this embodiment, the turbine blade 3 and the turbine nozzle 1
No. 1, No. 1 and No. 1 in Table 1 in Example 1 in the first stage.
Ni-based single crystal alloys having compositions of No. 2 and No. 3 and having compound surface layers of boride, carbide and nitride, respectively, were used. As a result, by applying the Ni-based single crystal alloy having high creep rupture strength and high temperature strength to the gas turbine blade and the gas turbine nozzle, the combustion gas temperature at the turbine inlet can be made higher than that of the conventional one, and the thermal efficiency can be improved. It is possible to provide a high gas turbine for ultra-high temperature power generation.

[0043]

According to the present invention, it is possible to provide a surface modification method for forming a compound surface layer of a boride, carbide or nitride on the surface of a Ni-based single crystal alloy, and to improve high temperature strength, oxidation resistance and corrosion resistance. There is an effect that an excellent Ni-based single crystal alloy can be provided to the gas turbine blade.

[Brief description of drawings]

FIG. 1 is a result of composition analysis of a sample by EPMA.

FIG. 2 is a result of a burner rig corrosion resistance test.

FIG. 3 shows the results of a high temperature oxidation test.

FIG. 4 is a result of a high temperature strength test based on a Larson Miller curve.

FIG. 5 is a gas turbine blade that is an embodiment of the present invention.

FIG. 6 is a gas turbine nozzle according to an embodiment of the present invention.

FIG. 7 is a diagram showing a cross section of a gas turbine device according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Turbine stub shaft, 2 ... Distant piece, 3 ... Turbine blade, 4 ... Turbine disk, 5
... Turbine stacking bolts, 6 ... Compressor disk, 7 ... Compressor blade, 8 ... Turbine spacer, 9 ... Compressor stub shaft, 10 ... Nozzle,
11 ... Compressor tacking bolt.

Claims (8)

[Claims] 1. A Ni-based single crystal alloy having a compound surface layer of boride, carbide or nitride. 2. A boride, carbide or nitride compound surface layer is provided, and in weight%, Cr 6.0 to 9.0%, Al 4.
5 to 6.0%, W 2.0 to 12.0%, Mo 6.0% or less,
Co 0.1-3.0%, Nb 0.2-3.0%, Ta 2.5
.About.9.0%, Re 0.1 to 4.0%, Hf 3.0% or less, and N having a surface layer composed of Ni and the balance unavoidable impurities.
i-based single crystal alloy. 3. By weight%, Cr 6.0-9.0%, Al 4.
5 to 6.0%, W 2.0 to 12.0%, Mo 6.0% or less,
Co 0.1-3.0%, Nb 0.2-3.0%, Ta 2.5
~ 9.0%, Re 0.1-4.0%, Hf 3.0% or less, and the balance of unavoidable impurities and the Ni-based single crystal alloy surface consisting of Ni with a boride, carbide or nitride compound surface layer of 150 μm or less. Then, the composition of boron, carbon, or nitrogen gradually decreases gradually from the surface of the compound surface layer to the surface of the Ni-based single crystal alloy, and the Ni-based single crystal alloy having a surface layer. . 4. A surface of a Ni-based single crystal alloy is ion-nitrided by plasmaizing nitrogen gas to form a nitride compound surface layer having good adhesion to the parent phase of the Ni-based single crystal alloy. A method for modifying the surface of a Ni-based single crystal alloy, which is characterized. 5. A method of ion carburizing the surface of a Ni-based single crystal alloy by plasmaizing a hydrocarbon gas to form a compound surface layer of a carbide having good adhesion to the parent phase of the Ni-based single crystal alloy. A method for modifying the surface of a Ni-based single crystal alloy, which is characterized. 6. A method for modifying the surface of a Ni-based single crystal alloy, wherein the surface of the Ni-based single crystal alloy is borated by reactive diffusion of active boron on the surface of the Ni-based single crystal alloy. 7. A gas turbine blade for power generation, which is made of a Ni-based single crystal alloy having the surface layer according to claim 1. 8. A gas turbine nozzle for power generation, which is made of a Ni-based single crystal alloy having the surface layer according to claim 1.