KR20110130931A - Method for preparing surface modified nickel-based alloys - Google Patents

Abstract

PURPOSE: A method of manufacturing surface-reformed nickel-base alloy is provided to enhance long-term oxidation resistance and corrosion resistance since aluminum can be continuously supplied. CONSTITUTION: A method of manufacturing surface-reformed nickel-base alloy comprises next steps. Aluminum or nickel aluminide is physically deposited on the surface of nickel-base alloy(a first step). An inter-diffusion thermal treating process is performed under a temperature of 550~650°C(a second step). The thickness of an aluminum or nickel aluminide deposited layer formed by the first step is 3 ~ 6μm. An inter-metal compound coated layer of Al3Ni2 is formed on the surface of the nickel-base alloy from the second step. The thickness of the inter-metal compound coated layer is 10 ~ 20μm.

Description

METHODS FOR PREPARING SURFACE MODIFIED NICKEL-BASED ALLOYS}

The present invention relates to a method for producing a surface-modified nickel-based alloy, and more particularly to a method for producing a surface-modified nickel-based alloy that can improve the oxidation resistance, creep properties and the like of the nickel-based alloy.

Nickel-based alloys are used in harsh environments such as heat exchangers, gas turbines, and reaction vessels in chemical process plants because of their excellent mechanical properties at high temperatures, as well as excellent oxidation and corrosion resistance. In particular, in the case of nickel-based alloys used in a high temperature environment, due to the environmental effects including oxygen, water vapor, carbon, etc., oxidation and corrosion proceed to the outside or inside of the material, thereby reducing the mechanical properties of the material. Such degradation of the material due to the high temperature environment can be prevented by blocking the external environment by forming an oxide film on the outside of the material.

Existing methods of improving oxidation resistance and corrosion resistance are firstly, by increasing the amount of chromium (Cr) or aluminum (Al), which is an alloying element, to form Cr ₂ O ₃ and Al ₂ O ₃ on the outside, thereby lowering the mechanical properties of the material. There is a way to prevent this. Second, ZrO ₂ , Al ₂ O ₃ , and Y ₂ O ₃ oxides are coated on the outside using various coating methods such as chemical vapor deposition, thermal spray coating, and reactive sputtering. Or a thermal barrier coating method using MCrAlY bond coating between the nickel-based alloy and the oxide film.

In the existing method, the alloying element is added, and as the oxide film grows, the alloy element deficiency region is generated in the outermost layer of the alloy, and when the oxide film is cracked, it is impossible to continuously supply the oxide film forming element from the base material. . Therefore, it is impossible to continuously block the external environment through the oxide film, which may cause long-term integrity. In addition, in the case of aluminum (Al), an increase in the amount of addition brings about a decrease in mechanical properties such as creep and strength and a disadvantage in causing workability such as welding.

In the case of anodized coating method, since the bond strength between the base material and the oxide film is low, the stability of the oxide film becomes a problem when a load is applied to the base material, and there is a problem that is not appropriate in the long term because the base material is exposed to the environment during cracking. .

Finally, thermal barrier coatings are used in gas turbines due to the advantage of preventing the external environment of high temperature and highly reactive gas elements from reaching the base material due to the thick coating layer of several hundred μm to several tens of mm. However, in the case of an ultra-high temperature gas, an intermediate heat exchanger has a microchannel of about 1 mm and has excellent heat transfer. Therefore, a heat shield coating in which the coating layer blocks heat transfer to the base material improves oxidation resistance and corrosion resistance. This is not a suitable way to make it work.

Therefore, there is a need in the art for a method for improving the oxidation resistance, creep properties, and the like of nickel-based alloys more excellently.

The present invention is to provide a method for improving the oxidation resistance, corrosion resistance, etc. of the nickel-based alloy that can be applied to an intermediate heat exchanger, a high temperature gas furnace, and the like, and exhibit excellent thermal conductivity.

Thus, the present invention

1) physically depositing aluminum or nickel aluminide on the surface of the nickel-based alloy, and

2) performing an inter-diffusion heat treatment process at a temperature of 550 ~ 650 ℃

It provides a method for producing a surface-modified nickel-based alloy comprising a.

The present invention also provides a surface-modified nickel-based alloy prepared from the method for producing the surface-modified nickel-based alloy.

In addition, the present invention provides an intermediate heat exchanger with ultra-high temperature gas containing the surface-modified nickel-based alloy.

The method for producing a surface-modified nickel-based alloy according to the present invention can be applied to complex shapes by forming a thin coating layer of several μm on the nickel-based alloy, and a sufficient amount in the lower layer even if cracks or peeling of an oxide film formed on the outside occur. Because it contains aluminum (Al), it is possible to continuously supply aluminum, which has the advantage of improving long term oxidation resistance and corrosion resistance. In addition, unlike other coating methods, it is possible to maintain excellent thermal conductivity due to a thin coating layer through simple heat treatment by receiving aluminum elements from the outside. Therefore, when applied to an intermediate heat exchanger with ultra-high temperature gas, the long life and long-term integrity of high-temperature structural materials can be maintained. It can be secured.

1 is a view showing a scanning electron microscope (Scanning Electron Microscopy) image of a nickel-based alloy in which aluminum is deposited using a physical vapor deposition method on the surface of the nickel-based alloy as an embodiment of the present invention.
FIG. 2 is a diagram showing an X-ray diffraction peak of a nickel-based alloy in which aluminum is deposited by using a physical vapor deposition method on the surface of the nickel-based alloy as one embodiment of the present invention.
FIG. 3 is a diagram showing an EDS (Energy Dispersive Spectroscopy) analysis spectrum result of a nickel-based alloy in which aluminum is deposited using a physical vapor deposition method on a surface of a nickel-based alloy as one embodiment of the present invention.
4 is a view showing a scanning electron microscope (Scanning Electron Microscopy) image of the surface-modified nickel-based alloy that is subjected to the interdiffusion heat treatment after aluminum deposition as an embodiment of the present invention.
FIG. 5 is a diagram showing an X-ray diffraction peak of a surface-modified nickel-based alloy subjected to interdiffusion heat treatment after aluminum deposition as an example of the present invention.
FIG. 6 is a diagram showing an energy dispersive spectroscopy (EDS) analysis spectrum result of a surface-modified nickel-based alloy subjected to interdiffusion heat treatment after aluminum deposition as an embodiment of the present invention.
7 is a view showing a scanning electron microscope (Scanning Electron Microscopy) image of the surface-modified nickel-based alloy prepared by oxidizing the surface-modified nickel-based alloy prepared in accordance with one embodiment of the present invention in 900 ℃ air environment for 550 hours.
FIG. 8 is a graph illustrating a weight increase and decrease graph of a surface-modified nickel-based alloy and a general nickel-based alloy obtained by oxidizing a surface-modified nickel-based alloy prepared according to one embodiment of the present invention at 900 ° C. for 550 hours.
9 is a diagram showing an X-ray diffraction peak of a surface-modified nickel-based alloy obtained by oxidizing the surface-modified nickel-based alloy prepared according to one embodiment of the present invention at 900 ° C. for 550 hours.
FIG. 10 is a graph showing EDS (Energy Dispersive Spectroscopy) analysis spectrum results of a surface modified nickel-based alloy prepared by oxidizing the surface-modified nickel-based alloy prepared according to one embodiment of the present invention at 900 ° C. for 550 hours.

Hereinafter, the present invention will be described in more detail.

One embodiment of the method for producing a surface-modified nickel-based alloy according to the present invention is 1) physical deposition of aluminum or nickel aluminide on the surface of the nickel-based alloy, and 2) interdiffusion heat treatment at a temperature of 550 ~ 650 ℃ performing an inter-diffusion heat treatment process.

In the method for producing a surface-modified nickel-based alloy according to the present invention, physical deposition of aluminum or nickel aluminide of step 1) may use a method known in the art. The thickness of the aluminum or nickel aluminide deposited layer formed from the step 1) may be 3 ~ 6㎛.

In the method for producing a surface-modified nickel-based alloy according to the present invention, an intermetallic compound coating layer of Al ₃ Ni ₂ is formed on the surface of the nickel-based alloy from the step 2).

The thickness of the intermetallic compound coating layer is preferably 10 ~ 20㎛, but is not limited thereto.

In the method for producing a surface-modified nickel-based alloy according to the present invention, the step of cross-diffusion heat treatment step 2) is characterized in that it is carried out at a temperature of 550 ~ 650 ℃. If the temperature of the cross-diffusion heat treatment process of step 2) is less than 550 ° C., diffusion may not occur sufficiently, and if it exceeds 650 ° C., the melting point of aluminum may render it unusable for surface modification for a heat exchanger. It can be undesirable.

The heat treatment process of the conventional nickel-based alloy was carried out at a temperature of about 800 ℃ or more. However, the present invention can reduce the process cost, time, etc. by performing the interdiffusion heat treatment process at a temperature of 550 ~ 650 ℃.

The interdiffusion heat treatment process of step 2) is preferably performed for 24 to 48 hours at a temperature of 550 ~ 650 ℃.

In addition, the present invention provides a surface-modified nickel-based alloy prepared by the method for producing a surface-modified nickel-based alloy.

The surface-modified nickel-based alloy according to the present invention can be applied to complex shapes by including a thin coating layer of several μm on the nickel-based alloy, and a sufficient amount of aluminum in the lower layer even if cracking or peeling of an oxide film formed on the outside occurs. Al), which enables continuous supply of aluminum, improving long-term oxidation and corrosion resistance.

In addition, the present invention provides an intermediate heat exchanger with ultra-high temperature gas containing the surface-modified nickel-based alloy.

Unlike other conventional coating methods, it is possible to maintain excellent thermal conductivity due to a thin coating layer through simple heat treatment by receiving aluminum elements from the outside. Therefore, when applied to an intermediate heat exchanger with ultra-high temperature gas, the long life and long-term integrity of high-temperature structural materials It can be secured.

Hereinafter, the present invention will be described in more detail with reference to preferred examples. However, these examples are intended to illustrate the present invention in more detail, it will be apparent to those skilled in the art that the scope of the present invention is not limited thereby.

< Example  1> surface Modified Nickel  Manufacture of alloys

Aluminum (Al) was coated on a nickel-based alloy (Alloy 617) by physical vapor deposition (Physical Vapor Deposition) method, and then a coating layer was formed by heat treatment in a vacuum furnace (vacuum furnace). At this time, deposition conditions and heat treatment conditions are as follows.

1) Deposition Conditions

Deposition equipment vacuum degree: 7 × 10 ^-3 torr

DC power output: 120W

Atmosphere: Argon (10 sccm)

2) heat treatment condition

-Vacuum furnace vacuum degree: below 1 × 10 ^-6 torr

Temperature: 600 ℃

-Time: 24 hours

< Experimental Example  1>

To evaluate the properties of the surface-modified nickel-based alloy prepared in Example 1, it is shown in Figures 1 to 10 below.

FIG. 1 is a scanning electron microscopy image of an aluminum (Al) coating layer using a physical vapor deposition method. A deposition layer having a thickness of about 5 μm was obtained, and X-ray diffraction and energy dispersive spectroscopy (EDS) analysis were performed for composition analysis. As a result, it can be seen that the coating layer formed as shown in Figures 2 and 3 consists of pure aluminum (Al).

5 μm of aluminum (Al) deposited specimens were subjected to inter-diffusion heat treatment in a vacuum furnace, and the results can be seen in FIG. 4. It can be seen that the deposition material aluminum (Al) and the base material nickel (Ni) formed a layer mixed with each other by the difference in concentration at the interface. As a result of the composition analysis, as shown in FIGS. 4 and 5, it can be seen that an Al ₃ Ni ₂ intermetallic compound coating layer is formed.

As a result of performing a 550-hour oxidation experiment in an atmosphere of 900 ° C. to evaluate the oxidation resistance of the Al ₃ Ni ₂ intermetallic compound coating layer, a uniform coating layer and an oxide film were formed as shown in FIG. As can be seen, when the coating and heat treatment are performed, the increase in weight is significantly reduced. 9 and 10, it can be seen that Al ₂ O _{3, which} is dense and stable at high temperatures, is formed on the surface of the material, thereby greatly increasing oxidation resistance.

From the above results, the method for producing a surface-modified nickel-based alloy according to the present invention can be applied to complex shapes by forming a thin coating layer of several μm on the nickel-based alloy, the cracks or peeling of the oxide film formed on the outside Even if it occurs, it contains a sufficient amount of aluminum (Al) in the lower layer can be seen that the continuous supply of aluminum can improve the long-term oxidation and corrosion resistance. In addition, unlike other coating methods, it is possible to maintain excellent thermal conductivity due to a thin coating layer through simple heat treatment by receiving aluminum elements from the outside. Therefore, when applied to an intermediate heat exchanger with ultra-high temperature gas, the long life and long-term integrity of high-temperature structural materials can be maintained. It can be secured.

Claims (6)

1) physically depositing aluminum or nickel aluminide on the surface of the nickel-based alloy, and
2) performing an inter-diffusion heat treatment process at a temperature of 550 ~ 650 ℃
Method of producing a surface-modified nickel-based alloy comprising a. The method of claim 1,
The method of manufacturing a surface-modified nickel-based alloy, characterized in that the thickness of the aluminum or nickel aluminide deposited layer formed from the step 1) is 3 ~ 6㎛. The method of claim 1,
Method for producing a surface-modified nickel-based alloy, characterized in that the intermetallic compound coating layer of Al ₃ Ni ₂ is formed on the surface of the nickel-based alloy from the step 2). The method of claim 3,
Method for producing a surface-modified nickel-based alloy, characterized in that the thickness of the intermetallic compound coating layer is 10 ~ 20㎛. Surface-modified nickel-based alloy prepared by the method for producing a surface-modified nickel-based alloy of any one of claims 1 to 4. Ultra-high temperature gas intermediate heat exchanger comprising the surface-modified nickel-based alloy of claim 5.

Images