KR20110130929A - Method for preparing surface modified nickel-based alloys - Google Patents

Abstract

PURPOSE: A method for preparing a nickel-based alloy having a modified surface is provided to improve the oxidation-resistance and corrosion-resistance of a nickel-based alloy by consecutively supplying a large amount of aluminum to a cracked oxide film. CONSTITUTION: A method for preparing a nickel-based alloy having a modified surface is as follows. Aluminum or nickel aluminide is physically plated on the surface of a nickel based alloy. A laser beam is irradiated to the nickel based alloy plated with the aluminum or nickel aluminide.

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 heat exchangers (IHX, Intermediate Heat Exchanger) and Hot Gas Ducts in Very High Temperature Reactors (VHTRs) due to their excellent creep, mechanical resistance and oxidation resistance at high temperatures. Is expected. Despite these excellent properties, the mechanical properties of the material can be greatly reduced due to gas impurities and other environmental influences under prolonged high temperature environments where the material will be subjected. Research is underway to protect the material through various treatments on the surface of the material that will ultimately react with the environment in order to improve the corrosion and oxidation resistance while maintaining mechanical properties.

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) irradiating a laser beam

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 improve the oxidation behavior through the surface remelting treatment using a laser beam which is useful in the industry in the air environment. In the case of remelted specimens, the lack of internal oxidation can have a positive effect on the tensile test data of nickel-based alloys. Meanwhile, by increasing the aluminum content near the surface through surface alloying after physical deposition, a large amount of aluminum (Al), which was present in the lower layer during the cracking of the oxide film, is continuously supplied to improve long-term oxidation resistance and corrosion resistance.

1 is a view showing a scanning electron micrograph (scanning electron microscopy) of the surface-modified nickel-based alloy according to an embodiment of the present invention.
2 is an enlarged view of an alloying region of a surface-modified nickel-based alloy according to one embodiment of the present invention.
3 is a view showing the results of Energy Dispersive Spectroscopy (EDS) analysis of the alloying region of the surface-modified nickel-based alloy according to one embodiment of the present invention.
4 and 5 are scanning electron micrographs of the alloying region of the surface-modified nickel-based alloy according to an embodiment of the present invention.
6 is a view showing the oxidation behavior of the specimen exposed to the 900 ℃ atmospheric environment of the conventional nickel-based alloy for 100 hours.

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

The method for producing a surface-modified nickel-based alloy according to the present invention includes 1) physically depositing aluminum or nickel aluminide on the surface of the nickel-based alloy, and 2) irradiating a laser beam.

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 ~ 5㎛.

In the method for producing a surface-modified nickel-based alloy according to the present invention, the irradiation of the laser beam of step 2) is performed using a laser beam having a beam diameter of Φ 0.6 to Φ 0.9, the wavelength of 1.00 ~ 1.12㎛ It is preferable.

From step 2), the surface of the nickel-based alloy is redissolved and alloyed to form an alloying region. The thickness of the alloying region is preferably 50 ~ 100㎛, but is not limited thereto.

The alloying region may include Ni, Cr, W, Fe, Mn, Al, and the like, in particular, the content of Al in the alloying region is preferably 3 to 5% by weight.

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

By depositing aluminum (Al) 4㎛ on the nickel-based alloy (Haynes 230) through physical deposition and alloying by using a laser beam to change the surface microstructure and chemical composition.

The conditions of the laser beam used for re-dissolution and alloying are as follows.

1) Laser beam condition

Laser model: L150 from Alpha Laser Corporation

Laser Crystal: Nd: YAG

Wavelength: 1.06 mu m

DC power output: 500W (164V)

Beam diameter: 0.9

Deposition Environment: Atmosphere

Scan speed: about 1 cm / s

Prior to alloying, aluminum (Al) was coated on the surface of the nickel-based alloy by physical vapor deposition (Physical Vapor Deposition) method. At this time, the deposition conditions are as follows.

2) deposition conditions

Deposition equipment vacuum degree: 5 × 10 ^-3 torr

DC power output: 180W

Atmosphere: Argon (10 sccm)

< Experimental Example  1>

The properties of the surface-modified nickel-based alloys prepared in Example 1 were evaluated, and are shown in Table 1 below and FIGS. 1 to 6.

FIG. 1 is a scanning electron obtained by coating an aluminum (Al) layer of about 4 μm on a surface of a nickel-based alloy using a physical vapor deposition method and then irradiating a laser beam of Φ 0.9 to obtain an alloying region of about 100 μm. Scanning Electron Microscopy.

FIG. 2 shows an enlarged portion of the alloying region to show cellular and dendrite structures. Compared to Haynes 230 as-received specimens, it can be seen that no grain boundary carbides and no grain carbides exist.

3 and Table 1 show the results of Energy Dispersive Spectroscopy (EDS) analysis on the alloying region. Compared to the Haynes 230 as-received specimens, the chemical composition of each element is not significantly different, but it can be seen that tungsten (W) has a very high value. In addition, it can be seen that the chemical composition is more than five times higher by the effect of coating the aluminum (Al) through physical vapor deposition.

[Table 1]

Both redissolution and alloying were conducted to investigate the oxidation behavior of nickel-based alloys under high temperature atmosphere. For this purpose, oxidation experiments were performed at 900 ° C for 100 hours. 6 shows the oxidation behavior of the as-received specimens not subjected to laser beam treatment. Some internal oxides (Al ₂ O ₃ ) were formed under the oxide layer on the surface, and the decarbonized region having a thickness of 20 μm was also observed. 4 and 5 are scanning electron microscope (SEM) photographs of alloying regions. Grain-based carbides formed in the base material and carbides within the grains were not observed, and regions having no precipitates of about 5 μm were formed, and precipitates were formed throughout the alloying region. In addition, on the scanning electron microscope (SEM), it can be seen that a precipitate having a contrast similar to that of internal oxidation exists. Due to the high aluminum (Al) content, it can be seen that more than as-received specimens are formed.

From the above results, it can be seen that the method of manufacturing the surface-modified nickel-based alloy according to the present invention can improve the oxidation behavior through surface remelting treatment using a laser beam which is useful in the industry in the air environment. have. In the case of remelted specimens, the lack of internal oxidation can have a positive effect on the tensile test data of nickel-based alloys. Meanwhile, by increasing the aluminum content near the surface through surface alloying after physical deposition, a large amount of aluminum (Al), which was present in the lower layer during the cracking of the oxide film, is continuously supplied to improve long-term oxidation resistance and corrosion resistance.

Claims (8)

1) physically depositing aluminum or nickel aluminide on the surface of the nickel-based alloy, and
2) irradiating a laser beam
Method of producing a surface-modified nickel-based alloy comprising a. The method of claim 1,
Method for producing 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 ~ 5㎛. The method of claim 1,
Irradiation of the laser beam of step 2) using a laser beam having a beam diameter of Φ 0.6 to Φ 0.9, and a method of producing a surface-modified nickel-based alloy, characterized in that performed at a wavelength of 1.00 ~ 1.12㎛. The method of claim 1,
Method for producing a surface-modified nickel-based alloy, characterized in that from the step 2) the surface of the nickel-based alloy is redissolved and alloyed to form an alloying region. The method of claim 4, wherein
The alloying region has a thickness of 50 ~ 100㎛ method for producing a surface-modified nickel-based alloy, characterized in that. The method of claim 4, wherein
The alloying region includes aluminum, the content of aluminum is a method of producing a surface-modified nickel-based alloy, characterized in that 3 to 5% by weight. The surface-modified nickel-based alloy prepared by the method for producing the surface-modified nickel-based alloy of any one of claims 1 to 6. An ultra-high temperature gas intermediate heat exchanger comprising the surface-modified nickel-based alloy of claim 7.

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