KR101527112B1 - Method for diffusion bonding of nickel-based alloys - Google Patents

Abstract

The present invention relates to a diffusion bonding method of a nickel-based alloy, and more particularly, to a method of diffusion bonding a nickel-based alloy by 1) physical vapor deposition of aluminum or nickel aluminide on the surface of a nickel- a step of forming an intermetallic compound layer by performing a diffusion heat treatment process for forming an intermetallic compound layer on the intermetallic compound layer; and 3) And performing a diffusion bonding process. The diffusion bonded nickel based alloy produced according to the present invention has excellent bonding strength and can improve high temperature corrosion resistance.

Description

[0001] METHOD FOR DIFFUSION BONDING OF NICKEL-BASED ALLOYS [0002]

More particularly, the present invention relates to a method for surface-modifying a nickel-based alloy applicable to a plate-type heat exchanger of a plate-type heat exchanger of an ultrahigh-temperature gas-cooled furnace and diffusion bonding the nickel-based alloy.

The compact heat exchanger is proposed as a candidate for the intermediate heat exchanger because it has a relatively small volume and weight as compared with the spiral tube heat exchanger, which is an intermediate heat exchanger of the conventional ultra-high temperature gas cooling furnace. In addition, it has the advantage of being able to withstand high temperature and high pressure, high temperature proximity, and high efficiency. Various concepts of compact heat exchangers have been proposed, among which printing plate heat exchangers are reported to have the highest degree of tightness.

The press plate heat exchanger was commercialized in the world by Heatric in the UK for the first time. The application range of the plate-type heat exchanger is far wider than that of other general heat exchangers, and is currently applied to heat exchangers of various fields such as high-temperature and high-pressure petrochemical plants, fuel cell reactors and reformers, CO ₂ heat pumps, Demand is expanding globally.

The manufacturing process of plate type heat exchanger uses diffusion bonding. The diffusion bonding is performed in the following order. First, the chemically etched microchannel sheet is laminated in the unit of mm. Thereafter, the material is compressed to such a degree that plastic deformation of the base material does not occur at a high temperature below the melting point. At high-temperature compression, atomic diffusion occurs between the junctions, and the junctions between the thin plates are called diffusion junctions.

The operation conditions of the ultra-high temperature gas cooling furnace, which is one of the fields where the plate-type heat exchanger is used, are operated under more severe conditions than the existing power plants. In particular, trace amounts of impurities contained in the helium coolant due to operating temperatures above 900 ° C can have a significant impact on the integrity of the structural material.

On the other hand, nickel-based alloys are used in harsh environments such as heat exchangers, gas turbines, and reaction vessels of chemical process plants, because they have excellent mechanical properties at high temperatures and excellent oxidation resistance and corrosion resistance. In particular, in the case of a nickel-based alloy used in a high-temperature environment, oxidation and corrosion occur on the outside or inside of the material due to environmental influences including oxygen, water vapor, and carbon, thereby reducing the mechanical properties of the material. Such deterioration of the material properties 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.

However, since the size of the flow path of the plate-type heat exchanger in the unit of mm is smaller than that of the other heat exchangers, the performance of the heat exchanger at the time of contamination with impurities is greatly reduced even in a relatively small amount of corrosion. Therefore, there is a need for a method for further improving the ultra-high temperature corrosion resistance while maintaining the ultrahigh temperature strength of existing materials.

The present invention relates to a method for producing a stable heat exchanger even at an ultra-high temperature of 900 ° C or higher, which is an operating condition of an ultra-high temperature gas cooling furnace, by surface-modifying a nickel-based alloy applicable to a plate-type heat exchanger of a super- .

Therefore,

1) physical vapor deposition of aluminum or nickel aluminide on the surface of the nickel based alloy,

2) performing an inter-diffusion heat treatment process at a temperature of 550 to 650 ° C to form an intermetallic compound layer; and

3) performing a diffusion bonding process using the intermetallic compound layer as a junction between two nickel-based alloys formed with an intermetallic compound layer formed from the step 2)

Based alloy according to the present invention.

Further, the present invention provides a diffusion-bonded nickel-based alloy produced from the diffusion bonding method of the nickel-based alloy.

The present invention also provides a plate-type heat exchanger comprising the diffusion-bonded nickel-based alloy.

The diffusion-bonded nickel-based alloy produced by the diffusion bonding method of the nickel-based alloy according to the present invention can produce a stable plate-type heat exchanger even at an ultra-high temperature. The diffusion-bonded nickel-based alloy can reduce contamination due to impurities generated by ultra-high temperature corrosion, thereby preventing performance deterioration due to contamination which is a disadvantage of a plate-type heat exchanger of a printing plate. Can increase. It can also bring economic benefits to the energy industry due to reduced replacement costs over the lifetime.

FIG. 1 is a cross-sectional photograph of a surface-modified nickel-based alloy which is subjected to mutual diffusion heat treatment after aluminum deposition as one embodiment of the present invention.
FIG. 2 is a cross-sectional view of a surface-modified nickel-based alloy subjected to an interdiffusion heat treatment after aluminum deposition and hot pressing at 1,100 ° C. and 10 MPa for 2 hours according to an embodiment of the present invention.
FIG. 3 is a cross-sectional view of a surface-modified nickel-based alloy subjected to an interdiffusion heat treatment after aluminum deposition and hot pressing at 1,100 ° C. and 10 MPa for 4 hours as one embodiment of the present invention.

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

Diffusion bonding is a method in which a member to be bonded is contacted and heated and pressed so that the base member is bonded by diffusion between atoms without melting. It differs from welding in that it does not melt the base material and differentiates it from brazing in that no separate bonding material is used. The greatest advantage of diffusion bonding is that it does not change the compositional or structural characteristics of the joint surface due to the melting of the base material or the use of no separate bonding material. Therefore, the heat resistance and bonding strength .

1) physical vapor deposition of aluminum or nickel aluminide on the surface of the nickel-based alloy; 2) inter-diffusion heat treatment at a temperature of 550 to 650 ° C; diffusion heat treatment to form an intermetallic compound layer, and 3) a step of forming an intermetallic compound layer between the two nickel-based alloys formed with the intermetallic compound layer formed from the step 2) And performing a diffusion bonding process.

In the diffusion bonding method of the nickel-based alloy according to the present invention, the physical vapor deposition of the aluminum or nickel aluminide in the step 1) may be performed by a method known in the art. More specifically, a sputtering method or the like may be used, but the present invention is not limited thereto. The thickness of the aluminum or nickel aluminide deposit layer formed from the step 1) may be 3 to 5 탆.

In the diffusion bonding method of a nickel-based alloy according to the present invention, an intermetallic compound layer containing Al ₃ Ni ₂ may be formed on the surface of the nickel-based alloy from the step (2). The intermetallic compound layer can exhibit an ultra-high temperature oxidation corrosion resistance higher than that of the base alloy and can form a stable protective film at the time of ultra-high temperature oxidation.

The thickness of the intermetallic compound layer is preferably 10 to 20 占 퐉, but is not limited thereto.

In the diffusion bonding method of the nickel-based alloy according to the present invention, the mutual diffusion heat treatment step in step 2) is performed at a temperature of 550 to 650 ° C. If the temperature of the step (2) is less than 550 ° C., the diffusion may not be sufficiently performed. If the temperature is higher than 650 ° C., the aluminum may not be used for surface modification for the heat exchanger Which is not preferable.

The conventional heat treatment process of the nickel-based alloy was performed at a temperature of about 800 캜 or higher. However, the present invention can reduce the process cost, time, and the like by performing the interdiffusion heat treatment process at a temperature of 550 to 650 ° C.

The interdiffusion heat treatment process in the step 2) is preferably performed at a temperature of 550 to 650 ° C for 2 to 4 hours.

In the diffusion bonding method of the nickel-based alloy according to the present invention, in the step 3), two kinds of nickel-based alloys each formed with an intermetallic compound layer formed from the step 2) are prepared, And the diffusion bonding process is performed using the intermediate compound layer as a junction.

The diffusion bonding process in the step 3) may use a method known in the art. The diffusion bonding process in the step 3) is preferably performed by pressurizing the substrate at a temperature of 1,000 to 1,200 ° C and 5 to 15 MPa for 1 to 5 hours, but the present invention is not limited thereto.

Further, the present invention provides a diffusion-bonded nickel-based alloy produced from the diffusion bonding method of the nickel-based alloy.

As described above, when aluminum or nickel aluminide is physically deposited on the surface of the nickel-based alloy, the surface treatment is performed by a diffusion heat treatment method, and then diffusion bonding is performed, only an intermetallic compound is present on the surface of the nickel- So that it is possible to improve the ultra-high temperature corrosion resistance.

The present invention also provides a plate-type heat exchanger comprising the diffusion-bonded nickel-based alloy.

The diffusion-bonded nickel-based alloy produced by the diffusion bonding method of the nickel-based alloy according to the present invention can produce a stable plate-type heat exchanger even at an ultra-high temperature. The diffusion-bonded nickel-based alloy can reduce contamination due to impurities generated by ultra-high temperature corrosion, thereby preventing performance deterioration due to contamination which is a disadvantage of a plate-type heat exchanger of a printing plate. Can increase. It can also bring economic benefits to the energy industry due to reduced replacement costs over the lifetime.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments. It will be apparent to those skilled in the art, however, that these examples are provided to further illustrate the present invention, and the scope of the present invention is not limited thereto.

< Example  1>

1) Surface Reformed Nickel group  Manufacture of alloys

An aluminum thin film with a thickness of about 3 μm was deposited by sputtering using a superconducting gas as a base metal of a nickel-based superalloy (Inconel 617) as a structural material candidate. The conditions of the sputtering are as follows.

Deposition temperature: room temperature

Preliminary pressure: <3 × 10 ^-6 torr

Deposition pressure: 5 × 10 ^-3 torr

DC power: 180W

Deposition time: 2 hours

Since the melting point of aluminum is 660.32 ℃, the conditions of diffusion heat treatment were diffusion heat treatment at 600 ℃ below the melting point for 24 hours. A cross section of a nickel-base superalloy whose surface was modified by aluminum after the diffusion heat treatment was performed is shown in Fig. It was confirmed that the diffusion layer was formed after the diffusion heat treatment, and that the diffusion layer was distributed to about 10 탆. The composition distribution of each layer is shown in Table 1 below. As a result of the surface modification, it is confirmed that nickel-aluminum intermetallic compound is formed.

[Table 1]

2) Surface Reformed Nickel group  Diffusion bonding of alloys

A hot press method was used as a method for diffusion bonding the surface modified nickel based superalloy. The conditions of hot pressing are as follows.

Temperature: 1,100 ° C

Atmosphere: inert atmosphere (Ar)

Pressure: 10 MPa

Time: 2 hours and 4 hours

The cross-sectional microstructure using a scanning electron microscope (SEM) after hot pressing of the two metals is shown in FIG. As a result of observation of microstructure, diffusion bonding was confirmed by hot pressing. It can be seen that the conditions of pressurization and high temperature also slightly changed the shape of the remaining diffusion layer. The characteristic feature is that Mo-rich phases appear in the intermediate Cr-rich layer of the diffusion layer. The composition of each diffusion layer is shown in Table 2 below.

[Table 2]

The time of hot pressing had little effect on the change of the diffusion layer. 3 shows the microstructure when the hot pressing time is different. It was observed that there was almost no change in the thickness or shape of the diffusion layer.

From the above results, it can be seen that the diffusion-bonded nickel-based alloy manufactured by the diffusion bonding method of the nickel-based alloy according to the present invention can produce a stable plate type heat exchanger even at an ultra-high temperature. The diffusion-bonded nickel-based alloy can reduce contamination due to impurities generated by ultra-high temperature corrosion, thereby preventing performance deterioration due to contamination which is a disadvantage of a plate-type heat exchanger of a printing plate. Can increase. It can also bring economic benefits to the energy industry due to reduced replacement costs over the lifetime.

Claims (7)

1) physical vapor deposition of aluminum or nickel aluminide on the surface of the nickel based alloy,
2) performing an inter-diffusion heat treatment process at a temperature of 550 to 650 ° C to form an intermetallic compound layer; and
3) performing a diffusion bonding process using the intermetallic compound layer as a junction between two nickel-based alloys formed with an intermetallic compound layer formed from the step 2)
Based alloy. &Lt; RTI ID = 0.0 &gt; 11. &lt; / RTI &gt; The method according to claim 1,
Wherein the thickness of the aluminum or nickel aluminide deposition layer formed from step 1) is 3 to 5 占 퐉. The method according to claim 1,
Wherein the intermetallic compound layer in step 2) comprises Al ₃ Ni ₂ . The method according to claim 1,
Wherein the thickness of the intermetallic compound layer in step 2) is 10 to 20 占 퐉. The method according to claim 1,
Wherein the diffusion bonding step in the step 3) is performed by hot pressing at a temperature of 1,000 to 1,200 ° C and 5 to 15 MPa for 1 to 5 hours. A diffusion bonded nickel based alloy produced from the diffusion bonding method of the nickel based alloy according to any one of claims 1 to 5. A plate-type plate heat exchanger comprising the diffusion-bonded nickel-based alloy of claim 6.

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