JP2001303152A - Iridium based cemented carbide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce an iridium based cemented carbide which has excellent high temperature strength, or higher strength and in which grain boundaries are strengthened, and intergranular cracking is suppressed. SOLUTION: In the iridium based cemented carbide having a composition consisting of iridium as a base, to which one or more kinds of metals selected from the metallic groups consisting of vanadium, titanium, niobium, tantalum, hafnium and zirconium are added by 2 to 22 atomic %, and in which precipitates having an LI2 structure are comformably precipitated into a base phase having an fcc structure, further, carbon or boron (in the case of boron, by 200 wppm at most) in a trace amount by which a third phase does not appear is added.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high melting point superalloy. More specifically, the invention of this application relates to an iridium-based superalloy in which excellent high-temperature strength is maintained or higher strength is achieved, and grain boundaries are strengthened and grain boundary cracks are suppressed.

[0002]

2. Description of the Related Art Components such as turbine blades and turbine vanes used in high-temperature equipment such as gas turbines for power generation, jet engines, rocket engines, etc.
Used under high stress. Conventionally, members such as these turbine blades and turbine vanes have high heat resistance,
A nickel-base superalloy that is excellent in high-temperature strength is applied. This nickel-base superalloy is an alloy containing cobalt, chromium, molybdenum, tungsten, aluminum, titanium, tantalum, niobium, rhenium, hafnium and the like as main constituent elements based on nickel, and has a service temperature of about 1100 ° C. It is.

On the other hand, the operating temperatures of members such as turbine blades and turbine vanes are becoming severer year by year. This is because increasing the combustion gas temperature is the most effective way to further increase the output and thermal efficiency of high temperature equipment. Accordingly, members such as turbine blades and turbine vanes are required to have higher high-temperature strength, and this is not necessary, and it is necessary to improve the high-temperature strength and high-temperature corrosiveness of the materials applied to these members. means.

Therefore, the inventors of the present invention have proposed an iridium-based superalloy as an alloy having characteristics exceeding those of a nickel-based superalloy. Iridium is a noble metal having high strength at high temperature and excellent oxidation resistance, and an iridium-based superalloy based on this has a two-phase coherent structure of fcc + Ll ₂ .

However, subsequent studies have found that this iridium-based superalloy does not always have a strong grain boundary and is susceptible to grain boundary cracking.

[0006] The invention of this application has been made in view of the circumstances described above, and while maintaining excellent high-temperature strength or realizing higher strength, grain boundaries are strengthened and grain boundary cracking is prevented. It is intended to provide a suppressed iridium-based superalloy.

[0007]

The invention of the present application solves the above-mentioned problems by selecting a metal group based on iridium from vanadium, titanium, niobium, tantalum, hafnium, and zirconium. An iridium-based superalloy in which one or more metals are added in an amount of 2 to 22 atomic% and precipitates having an Ll ₂ structure are consistently precipitated in a matrix having an fcc structure,
An iridium-based superalloy (Claim 1) is characterized in that it is added in a small amount so that the third phase does not appear.

Further, the invention of this application is based on iridium to which 2 to 22 atomic% of one or more metals selected from the group consisting of vanadium, titanium, niobium, tantalum, hafnium and zirconium is added. ,
An iridium-based superalloy in which precipitates having an Ll ₂ structure are aligned and precipitated in a matrix having an fcc structure, and further characterized in that boron is added at a maximum of 200 wppm (claim Item 2) is provided.

Further, the invention of this application provides, as a preferred embodiment, that in the above iridium-based superalloy, the volume ratio of the precipitate having the Ll ₂ structure is 20 to 80% (claim 3).

[0010]

DETAILED DESCRIPTION OF THE INVENTION A so-called iridium-based superalloy is:
Based on iridium (Ir), with vanadium (V),
Titanium (Ti), niobium (Nb), tantalum (Ta), hafnium (H
f) and at least one metal selected from the group consisting of zirconium (Zr) is added in an amount of 2 to 22 atomic%, and a precipitate having an Ll ₂ structure is deposited in a matrix having an fcc structure in a consistent manner. Alloy. When the precipitate having the Ll ₂ structure is deposited in conformity with the parent phase, strain accumulates at the interface between the parent phase and the precipitate, and the strength of the alloy increases. Even if a precipitate having an Ll ₂ structure is deposited, high strength cannot be obtained unless the interface is matched. That is, it is considered that the strength of the alloy is determined by the amount of the matching interface. Therefore, in the iridium-based superalloy of the invention of the present application, as a preferable condition for achieving sufficient strength, the volume ratio of the precipitate having the Ll ₂ structure is 20% or more and 80% or more.
The following is exemplified.

[0011] In the iridium-based superalloy of the present invention, a small amount of carbon (C) or boron (B) is added in such an amount that the third phase does not appear. The maximum amount of boron (B) added is 200 wppm. On the other hand, carbon (C) can be added in an amount of 4000 wppm as shown in Examples described later. Such a small amount of carbon or boron is effective in improving the grain boundaries of the iridium-based superalloy and suppressing grain boundary cracks, while maintaining excellent high-temperature strength or realizing higher strength. . When the third phase appears, the strength of the alloy drops dramatically.

Examples of the iridium-based superalloy of the present invention will be described below.

[0013]

EXAMPLE [Ir-Nb-C alloy] Ir-15 produced as an ingot by arc melting in an argon atmosphere in a vacuum furnace.
At% (8 wt%) Nb alloy is carbon melted by arc melting
Was added to prepare a sample of a ternary alloy of Ir-15at% -C. Then, the metal structure and the strength were examined.

FIGS. 1a to 1c are scanning electron microscope (SEM) photographs instead of drawings each showing a metal structure of a sample after heat treatment at 1300 ° C. for 100 hours. FIG. 1a shows Ir
-15at% Nb-100wppmC metal structure, FIG. 1b shows Ir-15at
% Nb-500 wppm C metallurgical structure, and FIG.
The metal structures of 5 at% Nb-4000 wppm C are shown.

As can be seen from FIGS. 1a to 1c,
The metal structure of the Ir-15at% Nb-C alloy is a dendritic structure, and a fine matched structure of fcc + Ll ₂ is formed in each of the dendritic structures.

FIGS. 2A and 2B show the above Ir-15, respectively.
at% Nb-500wppmC alloy sample, Ir-15at% Nb-4000w
It is a scanning electron microscope (SEM) photograph instead of a drawing showing a metal structure after heat-treating a ppmC alloy sample at 1800 ° C for 72 hours.

As shown in FIGS. 2a and 2b,
Precipitates of cubic coherent precipitation are present, confirming the stability of the coherent structure.

FIG. 3 shows an Ir-15 at% Nb-100 wppm C alloy, Ir
-15at% Nb-500wppmC alloy and Ir-15at% Nb-4000wp
5 is a graph showing the strength of a pmC alloy up to 1200 ° C. FIG. 3 also shows, for comparison, Ir-15 without carbon addition.
It also shows the strength of the at% Nb alloy.

As apparent from FIG. 3, all of the above ternary alloys show higher strength than the binary alloy Ir-15at% Nb alloy at all measured temperatures. It is confirmed that the addition of carbon achieves higher high-temperature strength.

FIGS. 4a to 4c are scanning electron microscope (SEM) photographs instead of drawings showing the microstructures of fractured surfaces of the alloy samples shown in FIGS. 1a to 1c, respectively.

As can be seen from FIG.
In the Ir-15at% Nb-C alloy to which 100 wppm was added, intragranular cracking occurred. However, grain boundary cracking has also occurred, and fracture is in a mixed mode of grain boundary cracking and flow cracking. On the other hand, Ir-1 added with 500 and 4000 wppm of carbon
The 5 at% Nb-C alloy is completely transgranular. From the above, it is confirmed that the properties of the grain boundaries of the iridium-based superalloy are improved by the addition of carbon. [Ir-Nb-B
Alloy] A raw material containing 99.99 wt% of iridium, 99.98 wt% of niobium, and 99.5 wt% of boron (B).
% Nb alloy was produced as a 50 g button ingot by arc melting in an argon atmosphere in a vacuum furnace. Then this I
Boron 80, 200, 50 by arc melting to r-15at% Nb
0,2000 wppm was added. Then, a test piece having a height of 6 mm and a diameter of 3 mm was cut out from each ingot by electronic discharge cutting. This is annealed at 1300 ° C for 72 hours,
Next, after furnace cooling under a vacuum of 3 × 10 ⁻⁴ Pa, the surface was polished, and electrolytic etching was performed in a 5% HCl-ethanol solution.

A compression test was performed on the test piece thus manufactured. The compression test was performed in air at 20 to 1200 ° C., and the initial strain rate was 3.0 × 10 ⁻⁴ s ⁻¹ . The test temperature was raised in the furnace in 12 to 20 minutes and held at that temperature for 5 minutes before applying a load in order to make the temperature distribution uniform.

The ductility of the test piece at room temperature was measured. The compression strain was determined from the load-deformation curve obtained during the compression test.

Further, the fine structure of the test piece and the fracture surface after the compression test were observed using a scanning electron microscope (SEM) and a scanning electron microscope (SEM), respectively. The composition of the phases constituting the tissue was identified by energy dispersive X-ray analysis (EDS).

FIGS. 5a to 5e are scanning electron microscope (SEM) photographs instead of drawings, each showing the metal structure of the alloy subjected to aging treatment at 1300 ° C. for 72 hours.

FIG. 5A shows the metal structure of an Ir-15 at% Nb alloy without boron, and FIGS. 5B to 5E show the structures of Ir-15atNb-B alloys with boron addition amounts of 80, 200, 500 and 2000 wppm, respectively. It is a metal structure.

As can be seen from FIG. 5a, Ir-15 at%
The metallic structure of the Nb alloy is a dendritic structure, and the core of the dendritic crystal has fcc / Ll ₂ (Ir / Ir ₃ Nb) containing an Ll ₂ phase of about 400 nm.
The two-phase structure is seen. Ir-15at% with boron added
In the case of the Nb-B alloy, the addition amount is 200 wppm or less (ie, FIG.
5b) and the dendritic structure is maintained, and the size of the Ll ₂ phase is almost the same as the size of the boron-free Ir-15at% Nb alloy. Also, fine rod-like and plate-like lamellar structures appear in the core, and the lamellar structures become coarser as the added amount of boron increases. However, when the added amount of boron reaches 500 wppm (ie, FIG. 5 d), the size of the Ll ₂ phase and the lamellar structure increases, while the area of these phases decreases. In an alloy containing 2,000 wppm of boron (ie, FIG. 5E), both the fcc / Ll ₂ two-phase structure and the lamellar structure disappear.

FIG. 6 is a graph showing the yield strength at room temperature and 1200 ° C. and the ductility at room temperature in relation to the amount of boron (B) added.

The proof stress at room temperature increases with the addition of boron. At 200 wppm, the proof stress is twice the proof stress without boron, reaching 2400 MPa. On the other hand, when the amount of boron exceeds 200 wppm, the proof stress decreases, and when the amount of boron is 2000 wppm, the yield becomes lower than when no boron is added. The proof stress at 1200 ° C. also increases with the addition of boron, peaking at 200 wppm and showing 1410 MPa. When the addition amount becomes 500 wppm,
The yield strength drops sharply to 500 MPa, half of the unadded yield strength.

The addition of boron hardly affects the compression ductility, but when the addition amount is 80 wppm, the compression ductility becomes 8%.

FIGS. 7a to 7e are scanning electron microscope (SEM) photographs instead of drawings, each showing a fracture surface of a test piece broken in a compression test at room temperature.

FIG. 7A is a fractured surface of a specimen to which boron is not added, and FIGS.
The fracture surface of 200, 500 and 2000 wppm specimens.

The boron-free Ir-15at% Nb alloy is broken mainly by intergranular cracking (FIG. 7a). In contrast,
The boron-added Ir-15at% Nb-B alloy shows intragranular fracture. Intragranular fracture is characterized from a crystallographic point of view and shows a river pattern similar to cleavage fracture. Ir-15at% Nb-2000wppmB alloy with the addition amount of 2000wppm (Fig. 7
In e), several bright phases as shown by arrows in the figure are observed along the grain boundaries. According to energy dispersive X-ray analysis (EDS), this phase is richer in boron and iridium. This means that boron segregates at the grain boundary in the Ir-15at% Nb alloy. [Ir-
Hf-B alloy] Hafnium (Hf) 15at instead of niobium (Nb)
% Of Ir-15at% Hf alloy, boron (B) was added in the same manner as the Ir-15at% Nb alloy, and the metal structure of the alloy, the compression test, and the fracture surface were observed.

FIGS. 8a to 8c show boron-free,
Boron added 200,500wppm Ir-15at% Hf alloy 1300
FIG. 3 is a scanning electron microscope (SEM) photograph as a substitute for a drawing showing a metal structure after heat treatment at 100 ° C. for 100 hours.

As can be seen from FIGS. 8a to 8c,
Even with the addition of boron, the metal structure shows a dendritic structure,
In the dendritic tissue, a fine matched texture of fcc + Ll ₂ is formed.

FIG. 9 is a graph showing the yield strength at room temperature and 1200 ° C. and the ductility at room temperature in relation to the amount of boron (B) added.

Like the Ir-15at% Nb alloy, the proof stress at room temperature increases with the addition of boron, peaks at 200 wppm, and reaches 2300 MPa. On the other hand, when the amount of boron exceeds 200 wppm, the proof stress decreases, and when the amount of boron is 2000 wppm, the yield becomes lower than when no boron is added. The proof stress at 1200 ° C. also increases with the addition of boron, peaking at 200 wppm and showing 1420 MPa. When the addition amount becomes 500 wppm, the proof stress rapidly decreases to 500 MPa.

The addition of boron hardly affects the compression ductility, but when the addition amount is 200 wppm, the compression ductility is 8%.
Becomes

FIGS. 10a to 10e are scanning electron microscope (SEM) photographs instead of drawings, each showing a fracture surface of a test piece broken in a compression test at room temperature.

FIG. 10a is a fractured surface of a specimen without boron addition, and FIGS. 10b to 10d are fractured surfaces of specimens with boron addition amounts of 200, 500 and 2000 wppm, respectively.

As in the case of the Ir-15at% Nb alloy, the Ir-15at% Hf
Also in the alloy, the alloy without boron is broken mainly by intergranular cracking (FIG. 10a). On the other hand, in the Ir-15at% Nb-B alloy to which boron is added, intragranular cracking occurs.

Of course, the invention of this application is not limited by the above embodiments. It goes without saying that various aspects are possible for details such as composition and manufacturing method.

[0043]

As described in detail above, according to the invention of this application, excellent high-temperature strength is maintained as it is, or higher strength is realized, and at the same time, the iridium-based superalloy in which grain boundaries are strengthened and grain boundary cracks are suppressed is suppressed. An alloy is provided. It is expected to be applied as a material for members used under high temperature and high stress in place of nickel-base superalloy.

[Brief description of the drawings]

FIGS. 1A to 1C are scanning electron microscope (SEM) photographs each showing a metal structure of an Ir-15 at% Nb-C alloy after heat treatment at 1300 ° C. for 100 hours.

[FIG. 2] a and b are Ir-15 at% Nb-500 wppmC, respectively.
It is a scanning electron microscope (SEM) photograph instead of a drawing which showed a metal structure after heat-treating at 1800 ° C for 72 hours for an alloy and Ir-15at% Nb-4000wppmC alloy.

FIG. 3 Ir-15at% Nb-100wppmC alloy, Ir-15at% Nb-
500wppmC alloy and Ir-15at% Nb-4000wppmC alloy
5 is a graph showing the strength up to 0 ° C. together with the strength of an Ir-15 at% Nb alloy.

FIGS. 4a to 4c are scanning electron microscope (SEM) photographs instead of drawings showing the metal structures of the fracture surfaces of the alloy samples shown in FIGS. 1a to 1c, respectively.

5A to 5E respectively show Ir-15at% Nb alloy and Ir-15at% Nb-C after aging treatment at 1300 ° C. for 72 hours.
It is a scanning electron microscope (SEM) photograph instead of the drawing which showed the metal structure of the alloy.

FIG. 6 is a graph showing the yield strength and room temperature ductility of an Ir-15 at% Nb alloy at room temperature and 1200 ° C. in relation to the amount of boron added.

FIGS. 7A to 7E show Ir-15at% Nb alloy test pieces and Ir-15at% Nb- specimens broken in a compression test at room temperature, respectively.
It is a scanning electron microscope (SEM) photograph instead of the drawing which showed the fracture surface of the B alloy test piece.

FIGS. 8a to 8c show the results of Ir-15 at% Hf alloy containing no boron and 200, 500 wppm of boron at 1300 ° C., respectively.
5 is a scanning electron microscope (SEM) photograph as a substitute for a drawing showing a metal structure after heat treatment for an hour.

FIG. 9 is a graph showing the yield strength and room temperature ductility of an Ir-15 at% Hf alloy at room temperature and 1200 ° C. in relation to the amount of boron added.

FIGS. 10A to 10D are Ir-15 at% Hf alloy test pieces and Ir-15 at% Hf fractured in a compression test at room temperature, respectively.
4 is a scanning electron microscope (SEM) photograph replacing a drawing showing a fracture surface of a -B alloy test piece.

Continued on the front page (72) Inventor Hiroshi Harada 1-2-1 Sengen, Tsukuba, Ibaraki Pref.

Claims (3)

[Claims] 1. An fcc structure based on iridium, wherein at least one metal selected from the group consisting of vanadium, titanium, niobium, tantalum, hafnium and zirconium is added to the iridium base in an amount of 2 to 22 atomic%. L in mother phase
A iridium-base superalloy precipitates are precipitated in alignment with l ₂ structure, further carbon, iridium-base superalloy third phase is characterized by being trace amount in the amounts do not appear. 2. An fcc structure based on iridium to which 2 to 22 atomic% of at least one metal selected from the group consisting of vanadium, titanium, niobium, tantalum, hafnium and zirconium is added. L in mother phase
An iridium-based superalloy in which precipitates having an l ₂ structure are aligned and deposited, and further characterized in that boron is added at a maximum of 200 wppm. 3. The volume fraction of the precipitate having an Ll ₂ structure is 20 to 20.
The iridium-based superalloy according to claim 1 or 2, which is 80%.