JP2000303162A - Production of aluminum-infiltrated nickel member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To densely control the concn. of Al in an Ni base material and to obtain an intermetallic compd. having excellent mechanical properties and corrosion and oxidation resistances at high temp. by storing an Ni base material and an Al source in a closed vessel, executing heating to the same or different temp. to generate an Al-contg. carrying medium from the Al source and executing the cementation of A1 into the Ni base material. SOLUTION: As an Al source, the use of an Al compd. is preferable, and Al chloride, or the like, can be selected. Preferably, based on the relation between the balanced alloy compsn. of an Al-Ni binary system and the temp., the heating temp. of the Al source to a desired Al concn. in the Ni base material and the heating temp. of the Ni base material are found, and the heating temp. of the Al source and the Ni base material is controlled to this temp. to attain the desired Al concn., or the temp. difference between the heating temp. of the Ni base material and the heating temp. of the Al source is controlled to attain the desired Al concn. In this way, both heating temps. are suitably controlled to form an NiAl phase, an Ni3Al phase and an α phase having optional compsns.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a member containing an intermetallic compound composed of aluminum and nickel, and more particularly, to a method of diffusing and infiltrating aluminum into a nickel base material by a gas transport method, and The present invention relates to a method for manufacturing an aluminum-penetrated nickel member in which an intermetallic compound made of nickel is formed on at least a surface of a nickel base material.

[0002]

2. Description of the Related Art Nickel-based superalloys are indispensable materials for heat engine components such as gas turbines and jet engines.
The i ₃ Al intermetallic compound plays an important role as a main component in this superalloy because the yield stress exhibits inverse temperature dependence. Engines such as gas turbines and jet engines require higher operating temperatures in order to achieve higher power and higher efficiency, but materials are subject to more stringent conditions in terms of hot corrosion and oxidation. Will be done.

[0003] Therefore, attempts have been made to reduce the oxidation rate by forming a protective film on the surface of this type of superalloy component, and an aluminizing method, also called a pack method, has been implemented. However, in this conventional method, it is difficult to control the aluminum concentration on the surface, and it is impossible to control the surface composition with good reproducibility.

[0004] The present invention has been made in view of the above circumstances, and in general, it is possible to precisely control the aluminum concentration in a nickel base material, so that it has excellent mechanical properties at high temperatures and corrosion resistance and oxidation resistance. It is an object of the present invention to provide a method for producing an aluminum-infiltrated nickel member capable of obtaining an intermetallic compound composed of nickel and aluminum having a desired composition having the following.

[0005]

Means for Solving the Problems and Embodiments of the Invention In order to achieve the above object, a method for manufacturing an aluminum-infiltrated nickel member according to the present invention comprises the steps of: The source is housed in a closed container and heated to the same or different temperature, and a transport medium containing aluminum is generated from the aluminum source to diffuse and infiltrate aluminum into the nickel substrate.

[0006] Since the production method according to the present invention uses a gas transport method based on a diffusion process of solute atoms, the concentration of aluminum in a nickel base material can be controlled with an accuracy of, for example, 1% or less, and a high temperature can be obtained. It is possible to easily obtain an intermetallic compound composed of nickel and aluminum having a desired composition having excellent mechanical properties and corrosion resistance and oxidation resistance. Further, according to the production method of the present invention, aluminum is uniformly diffused and penetrated from the surface of the base material into the base material in a gaseous state, so that it is easy to form a coating layer on a product having a complicated shape. In addition, because of the gas-solid diffusion process, the formed coating layer is defect-free, dense and uniform in thickness.

The nickel substrate used in the production method according to the present invention includes not only the above-mentioned nickel-based superalloy substrate, but also a substrate made of pure nickel metal, and other nickel-based alloys. As such a nickel base material, one processed or manufactured into a shape close to the final product is used.

In the manufacturing method according to the present invention, the phase growth rate largely depends on the diffusion rate of solute atoms, ie, aluminum. This means that forming a thick intermetallic compound layer on a substrate such as a rod or a plate requires a considerably long time of treatment. However,
In the case of a substrate such as a thin plate or a wire, it is extremely easy to control the aluminum concentration up to the center of the substrate. Is very effective. Therefore, the production method according to the present invention preferably provides a member made of an intermetallic compound of nickel and aluminum in which aluminum is diffused and infiltrated throughout the depth direction of the nickel base material. Is infiltrated into at least the surface portion of the nickel substrate to produce a member having a coating layer of an intermetallic compound of nickel and aluminum formed on the surface of the nickel substrate.

The aluminum source used in the production method according to the present invention may be any source as long as the gas transport method can be carried out. However, since the vapor pressure of metallic aluminum is relatively low, an aluminum compound is used. Is generally preferred, and a compound such as aluminum chloride can be suitably selected.

[0010] Thus, the nickel base and the aluminum source are housed in a closed container, and in this case, the nickel base and the aluminum source are preferably housed at separate positions in the closed container. The closed container may be a single container or a structure in which two closed containers are connected by a pipe or the like.
When aluminum chloride is selected as the aluminum source, for example, pure aluminum and ammonium chloride are housed in the closed container.

Then, the inside of the closed container is evacuated to a vacuum,
The internal aluminum source and the nickel substrate are heated to the same or different temperatures. At this time, by controlling the heating conditions of the aluminum source and the nickel substrate, the concentration of aluminum that diffuses and penetrates into the nickel substrate is adjusted. can do. That is, in the case of an aluminum source, the heating temperature needs to be a temperature at which the above-mentioned aluminum or aluminum compound is generated, and in the case of a nickel base material, the heating temperature may be the same as or different from the heating temperature of the aluminum source. By appropriately controlling both heating temperatures, a NiAl phase, a Ni ₃ Al phase and an α phase having arbitrary compositions can be obtained.

More specifically, the heating temperature of the aluminum source and the heating temperature of the nickel base for a desired aluminum concentration in the nickel base are determined based on the relationship between the alloy composition and the temperature which are balanced in the aluminum-nickel binary system. Ask for. Then, by setting the heating temperature of the aluminum source and the nickel base material to the determined heating temperature and performing a heating operation, an aluminum-penetrated nickel member having a desired aluminum concentration can be obtained. Also, by adjusting the temperature difference between the heating temperature of the nickel base material and the heating temperature of the aluminum source, a desired aluminum concentration can be achieved. In the above, in order to heat the aluminum source and the nickel substrate to different temperatures, for example, a heater such as an electric resistance furnace having a predetermined temperature gradient is used to adjust the arrangement position of the aluminum source and the nickel substrate.

Here, in order to facilitate understanding of the contents of the present invention, the principle of the present invention in the case where aluminum chloride gas is selected as a medium for transporting aluminum and pure nickel is used as a base material will be schematically described. .

[0014] First, in order to generate an aluminum chloride gas, when heated to temperatures T ₁ put pure aluminum and ammonium chloride in a sealed container, the reaction ammonium chloride of the following degrades (1) occurs. NH ₄ Cl (s) = NH ₃ (g) + HCl (g) (1) The generated hydrogen chloride gas is pure aluminum and the following formula (2)
To generate aluminum chloride gas. HC (g) + [1/3] Al (s) = [1/3] AlCl ₃ (g) + [1/2] H ₂ (g) (2) where the equilibrium constant of the reaction (2) is _Assuming that the partial pressures of k ₂ , ammonium chloride, hydrogen, and hydrogen chloride gas are P _AlCl3 , P _H2 , and P _HCl , respectively, k ₂ is represented by the following equation (2) ′. k ₂ = P _AlCl3 ¹ / _{3.P H2} ^1/2 / P _HCl (2) ′

[0015] Then, the closed vessel is filled with gas of the respective partial pressures determined by the heating temperature T ₁ of the aluminum source. On the other hand, place the material in nickel in the container, when heated to the same temperature T _1, the following equation in the surface of the nickel (3)
Reaction occurs, and aluminum is absorbed by nickel. _{[1/3] Ni (s) +} [1/3] AlCl 3 (g) + [1/2] H 2 (g) = [1/3] [Ni-Al] (g) + HCl (g) ( 3) Since the hydrogen chloride gas generated as a result of the reaction (3) returns to the aluminum source and reacts with pure aluminum to produce aluminum chloride, the partial pressure of each gas in the container is considered to be in a steady state.

The aluminum concentration c on the nickel surface corresponds to the aluminum activity a _Al (c%), and the reaction (3)
When the equilibrium constant is k _3, activity of aluminum in the nickel surface is expressed by Equation (3) '. a _Al (c%) = k ₃ · P _{AlCl 3} ^1/3 · P _H2 ^1/2 / P _HCl = k ₃ · k ₂ (3) ′

Here, it is assumed that when both the aluminum source and nickel are heated to the same slightly higher temperature, the surface aluminum concentration becomes the same as when the temperature is lower. That is, it is assumed that the activity a _Al (c%) does not change. This means that the free energy change of the reaction (2) and the reaction (3) together is constant regardless of the temperature. Since the reaction of equation (2) is an endothermic reaction, k ₂ increases as the temperature of the aluminum source increases. That is, the ratio between the partial pressure of ammonium chloride gas and the partial pressure of hydrogen chloride increases.

[0018] Heating the nickel to a higher temperature T ₂ than the heating temperature T ₁ of the aluminum source, the surface of the nickel is the respective gas partial pressures in equilibrium at a temperature T ₁ of the aluminum source. This gas has a small k ₂ than when the temperature of the aluminum source to T _2, the ratio of the partial pressure of the aluminum gas and hydrogen chloride gas chloride is low. Therefore, the activity of aluminum absorbed by nickel decreases. That is, the aluminum concentration decreases. From the above, it can be seen that the aluminum concentration on the nickel surface can be controlled by using aluminum as the evaporation source and using aluminum chloride as the transport medium and controlling the respective heating temperatures of the aluminum source and the nickel substrate.

[0019]

The present invention will be described in more detail with reference to the following examples. Example 1 A nickel-aluminum alloy was formed on the surface of a pure nickel base material by a method according to the present invention using an experimental apparatus whose schematic configuration is shown in FIG. The pure nickel substrate was prepared from a commercially available industrial pure nickel plate. One of the reaction tubes 1 constituting a closed vessel has an inner diameter of a closed end of 16 mm and a length of 100 mm.
A 0 mm high-purity alumina tube was prepared. Then, a substrate having a thickness of 1 mm was placed on the closed end side of the reaction tube 1 in a 10 mm ×
While placing several nickel substrates 2 cut out to 10 mm,
An alumina boat 3 containing pure aluminum and ammonium chloride was placed slightly away from the substrate 2 as an aluminum source 4. Then, the other end is closed with a glass cap 6 using wax 5 for high vacuum.
^It was evacuated to a vacuum of ^-4 Pa.

The amounts of pure aluminum and aluminum chloride put in the alumina boat 3 are approximately 5 g and 1 g, respectively.
20 mg. Then, the reaction tube 1 was placed in an electric resistance furnace 7 having a temperature gradient shown in FIG. The heating temperature of the aluminum source was between 1073K and 1573K, and the heating temperature of the pure nickel substrate was between 1070K and 1600K. The heating time was from 7.2 ks to 1430 ks.

The concentration distribution of aluminum in the nickel-aluminum alloy layer on the surface of the pure nickel substrate formed as described above was measured using an electron probe microanalyzer.

FIG. 2 shows the aluminum concentration distribution in the pure nickel base material after the diffusion treatment at a temperature of 1170 K to 1209 K for 603 ksec. In this embodiment, the aluminum source is heated at a constant temperature of 1174K,
1170K, 1179K and 1192 pure nickel base
Heated at each K temperature. As a result, nickel
It was confirmed that among all the phases existing in the aluminum binary system equilibrium diagram, a NiAl phase, a Ni ₃ Al phase, and an α phase were formed under all heating conditions. The step in the concentration distribution corresponds to a two-phase region. From this figure, it can be seen that as the temperature difference between the aluminum source and the nickel base increases, the aluminum concentration on the nickel base surface decreases.

When the nickel substrate was heated to 1204K, a Ni ₃ Al phase was formed, and when heated to 1209K, only the α phase was formed. From the concentration distribution shown in FIG.
The thickness of the Ni ₃ Al phase in a nickel substrate heated at a temperature lower than 1192 K at which 0 μm NiAl is formed is:
It is significantly thinner than one heated at a temperature of 1204 K with Ni ₃ Al formed on the substrate surface. This is because the diffusion rate of aluminum in the Ni ₃ Al phase is lower than that in the NiAl phase, and as a result, the diffusion rate of aluminum in the nickel base material was dominated by the Ni ₃ Al phase.

FIG. 3 shows the effect of the heating temperature of both the aluminum source and the nickel substrate on the aluminum concentration on the surface of the pure nickel substrate. The aluminum concentration obtained under different heating conditions was compared with the nickel-aluminum binary. This is plotted on a system equilibrium diagram. From this figure, it is clear that all equilibrium phases such as the NiAl phase, Ni ₃ Al phase and α phase existing in the nickel-aluminum binary equilibrium diagram can be obtained. However, no aluminum composition in the two-phase region was obtained. This is because the aluminum activity of each phase coexisting in the two-phase region is the same. Thus, the surface layer within the composition range of the NiAl phase, the Ni ₃ Al phase and the α phase having a wide composition range could be formed without difficulty, but such a result was obtained for any phase having the expected composition. It shows that it can be formed.

Next, FIG. 4 shows the effect of the heating temperature difference between the aluminum source and the pure nickel substrate on the aluminum concentration on the surface of the pure nickel substrate. In the figure, a negative value of the temperature difference indicates that the heating temperature of the pure nickel base is lower than the heating temperature of the aluminum source. From this figure,
It can be seen that when the temperature of the aluminum source is kept constant, the aluminum concentration on the surface of the pure nickel substrate increases as the temperature difference between the aluminum source and the pure nickel substrate decreases.

When the aluminum source is heated at a temperature lower than 1174K, a Ni @ 1 phase of 55 at% Al is formed. However, when the temperature exceeds 1274K, the formation is difficult, and under the heating conditions, 50 at% Al is the maximum. You can see that. In either case, as the temperature difference between the aluminum source and the pure nickel substrate decreases, the aluminum concentration on the surface of the pure nickel substrate increases slightly. If the temperature of the aluminum source is 1174K or lower, it is impossible to form a nickel base material having a surface aluminum concentration in the Al composition range of 44 to 52 at% regardless of the temperature of the pure nickel base material.

Example 2 Using a device similar to the device of Example 1, a Ni ₃ Al alloy (Ni-25 at% Al alloy) substrate
A diffusion process of 7.2 ks was performed at a temperature of 5K. Ni ₃ A
The alloy used was made from a button ingot melted in an arc furnace under an argon atmosphere. The aluminum source was heated at 1571K.

FIGS. 5A and 5B show the fine structure (vertical cross section) of the Ni ₃ Al substrate after the above diffusion treatment and the concentration distributions of aluminum and nickel, respectively. The aluminum concentration obtained on the surface of the Ni ₃ Al substrate is about 42 at%.
Al, which is a non-stoichiometric NiAl phase low in aluminum. Under this heating condition, an aluminum diffusion region of about 330 μm was obtained. In this diffusion area,
There is a step from 25 to 31 at% in the Al concentration distribution. This corresponds to the two-phase region between the Ni ₃ Al phase and the NiAl phase in the nickel-aluminum binary equilibrium diagram. In addition, a sawtooth-shaped concentration distribution was observed inside the diffusion region of 160 to 330 μm. This is shown in FIG.
This corresponds to the lamellar structure of the microstructure, but is thought to be due to the intermediate phase precipitated during the cooling step. Judging from the microstructure in FIG. 5A, the diffusion region seems to be composed of an outer layer of 100 μm and an inner layer of 230 μm.

FIG. 6 shows the growth rate of the NiAl phase when the Ni ₃ Al substrate was heated at a temperature of 1575 K to 18 ks. In this experiment, the aluminum source was set to 1571.
Heated to K constant temperature. FIG. 5A shows that Ni ₃ Al
Since it is clear that the NiAl layer on the substrate consists of two regions, an outer layer and an inner layer, the thicknesses of both layers were measured. As a result of electron probe microanalyzer analysis, it was confirmed that both the inner layer and the outer layer were made of NiAl and had the same aluminum concentration. FIG. 6 also shows the overall growth rate. From this, the thickness of NiAl is (t)
It can be seen that it is proportional to ^1/2 . From this result, NiA
The thickness of the 1 layer is estimated to reach 1000 μm after heating for 72 ks.

From the results of Examples 1 and 2 above, in particular,
By controlling the heating temperature of both the aluminum source and nickel, it is possible to obtain an equilibrium phase of NiAl, Ni ₃ Al and α having an arbitrary composition, and change the aluminum concentration by adjusting the difference between the two heating temperatures. We can see that we can do it.

[0031]

According to the production method of the present invention, it is possible to precisely control the aluminum concentration in the nickel base material, and thus to have excellent mechanical properties at high temperatures and corrosion resistance and oxidation resistance. An intermetallic compound composed of nickel and aluminum having the following composition can be obtained. In addition, according to the method of the present invention, aluminum is diffused and permeated from the surface of the base material into the base material in a gaseous state. The coating layer formed is defect-free, dense and uniform in thickness due to the solid diffusion process. In addition, in the case of an intermetallic compound having a wide composition width such as NiAl, the characteristics such as the mechanical properties change remarkably with a slight change in the composition. The method is very effective.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of an experimental apparatus for performing a manufacturing method according to the present invention.

FIG. 2 is a diagram showing a concentration distribution of aluminum in a pure nickel base material subjected to diffusion treatment by heating an aluminum source at various temperatures.

FIG. 3 is a diagram showing the influence of the heating temperature of a pure nickel substrate and an aluminum source on the aluminum concentration in the pure nickel substrate.

FIG. 4 is a diagram showing the influence of a heating temperature difference on the aluminum concentration in a pure nickel base material.

FIGS. 5A and 5B are diagrams illustrating a case where aluminum is diffused into a Ni ₃ Al substrate, wherein FIG. 5A is an electron micrograph, and FIG. 5B is a concentration distribution of nickel and aluminum.

6 is a diagram showing the growth rate of the _Ni 3 Al phase on Ni ₃ Al substrate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reaction tube (closed vessel) 2 Nickel base material 4 Aluminum source 7 Electric resistance furnace (heating device)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toshiyuki Suzuki 4-17-11 Shinkawa, Mitaka-shi, Tokyo (72) Inventor Masahiko Kato 3-1-1-11 Misono-cho, Kodaira-shi, Tokyo F-term (reference) 4K029 AA02 BA03 CA01 DA01 EA08

Claims (7)

[Claims] 1. A nickel base made of pure nickel or a nickel-based alloy and an aluminum source are housed in a closed container and heated to the same or different temperatures, and a transport medium containing aluminum is generated from the aluminum source to produce aluminum. Is produced by diffusing and penetrating into the nickel base material. 2. The method according to claim 1, wherein the aluminum transport medium is a compound of aluminum. 3. The method according to claim 1, wherein the concentration of aluminum that diffuses and penetrates into the nickel base is adjusted by controlling the heating temperature of the aluminum source and the nickel base. 4. A heating temperature of an aluminum source and a heating temperature of a nickel base for a desired aluminum concentration in a nickel base are determined based on a relationship between an alloy composition and a temperature which are balanced in an aluminum-nickel binary system. The method according to claim 3, wherein the heating temperature of the aluminum source and the nickel substrate is set to the heating temperature to achieve a desired aluminum concentration. 5. The manufacturing method according to claim 3, wherein a desired aluminum concentration is achieved by adjusting a temperature difference between a heating temperature of the nickel base material and a heating temperature of the aluminum source. 6. The method according to claim 1, wherein aluminum is diffused and penetrated into a surface portion of the nickel base material, and a coating layer made of an intermetallic compound of aluminum and nickel is formed on the surface of the nickel base material. Or the production method according to claim 1. 7. The method according to claim 1, wherein aluminum is diffused and infiltrated throughout the depth direction of the nickel base material.