KR102079215B1 - Metal-ceramic composites for gasket composed of dissimilar material and preparation method thereof - Google Patents

Abstract

 The present invention relates to a metal-ceramic heterocomposite for gaskets comprising (i) 50 to 99.9 volume percent aluminum or aluminum alloy, and (ii) 0.1 to 50 volume percent single-wall carbon nanotubes (SWCNTs). The metal-ceramic heterocomposite material for gasket according to the present invention has high strength, high toughness and high corrosion resistance as well as excellent radiation shielding performance through the combination of aluminum (or aluminum alloy) and carbon nanotubes. It can be customized for extreme environment gaskets and sealing parts that require high performance and is very useful as a material for parts that require very high safety, such as parts for machinery, automobiles, trains, ships, aerospace, especially nuclear power plants. In addition, the manufacturing method of the metal-ceramic heterocomposite for the gasket according to the present invention is used a lot in the conventional metal material manufacturing method Has the advantage of being environmentally friendly process is melting method instead have been manufactured according to solid-phase powder metallurgy process of the low-energy process which does not require that the burden on the environment such as the chromate treatment.

Description

Metal-ceramic heterocomposites for gaskets and methods for manufacturing the same {METAL-CERAMIC COMPOSITES FOR GASKET COMPOSED OF DISSIMILAR MATERIAL AND PREPARATION METHOD THEREOF}

The present invention relates to a novel heterogeneous composite material used as a gasket material and a manufacturing method thereof.

In general, gaskets are installed at joints of various pipes in nuclear power plants, petrochemical plants, thermal power plants, and the like to prevent accidents that may be caused by leakage of fluid flowing through the interior.

In particular, in the case of nuclear power plants, human body may be exposed to radiation when normal operating conditions as well as loss of coolant accident (LOCA), main steam line break (MSLB), high energy line brake (HELB), etc. occur at the end of the reactor life. The human body exposed to radiation is a major part of nuclear power plants because the ionization of radiation destroys tissues in the living body and when a dose is received to a certain degree, acute or chronic radiation disturbances and genetic mutations are caused. The gaskets used in the system are required for stability against radiation.

In general, diene-containing terpolymers (EPDMs) containing dienes are used in radiation environments due to their excellent properties as sealing materials, such as moisture resistance, corona resistance, excellent temperature characteristics and mechanical flexibility. It is widely used as a sealing material for safety systems, satellites and spacecraft gaskets.

However, when the rubber-based material is used as a sealing material such as a gasket used in a radiation environment such as a nuclear power plant or a spacecraft, an auto-oxydation process is faced with radiation deterioration.

On the other hand, most gaskets for vehicle engines such as automobiles have a structure in which a plurality of stainless steel sheets are laminated, and the stainless steel is generally used after cold rolling (temper rolling) for the purpose of strength adjustment. High strength is obtained.

However, as environmental protection has emerged as an important issue in recent years, there is an increasing demand for improving fuel efficiency and power output of vehicle engines.In response, automotive gasket materials require more high strength and excellent processability in complex shapes. In the stainless steel described above, the deterioration of workability accompanying high strength is inevitable and the reality of both high strength and workability cannot be sufficiently satisfied.

In addition, a rubber coated stainless steel sheet used as a material such as a head gasket mounted on an engine of a vehicle such as an automobile is a chromate coating made of chromium compound, phosphoric acid and silica on one or both surfaces of the stainless steel sheet in order to maintain the rubber layer more firmly. Gasket material in which a rubber layer is laminated on a chromate film is widely used, but the gasket material subjected to the chromate treatment has a big problem in terms of environment such as hexavalent chromium is contained in the chromate treatment liquid.

Korea Patent Publication No. 10-2017-0135884 (Published: 2017.12.08.) Korean Patent Publication No. 10-2011-0048533 (Published: 2011.05.11.) Korea Patent Publication No. 10-2010-0134642 (Published: 2010.12.23.)

The technical problem to be solved by the present invention is to provide a heterogeneous composite material for gaskets having excellent mechanical properties, corrosion resistance and light weight at the same time, paying attention to the problems of the existing gasket material and a method of manufacturing the same.

In order to achieve the above technical problem, the present invention is a metal for gasket comprising (i) 50 to 99.9% by volume of aluminum or aluminum alloy, and (ii) 0.1 to 50% by volume of single wall carbon nanotubes (SWCNT)- We propose ceramic heterocomposites.

In addition, we propose a metal-ceramic heterocomposite for gaskets, which is prepared by a method comprising the following steps:

(a) mixing (i) aluminum or aluminum alloy powder and (ii) single-walled carbon nanotube powder; And (b) spark plasma sintering (SPS) the mixed powder obtained in step (a) to produce a composite material.

In addition, the average particle size of the aluminum or aluminum alloy powder proposes a metal-ceramic heterocomposite for gasket, characterized in that 1 to 5 ㎛.

In addition, in the step (a), the weight ratio of the aluminum or aluminum alloy powder and the single-wall carbon nanotube powder to the ball (10) is set to 10: 1 to 1: 1 planetary ball milling process (planatary ball milling process) We propose a metal-ceramic heterocomposite for gasket characterized in that).

In addition, the planetary ball milling process proposes a metal-ceramic heterogeneous composite material for a gasket, characterized in that performed for 1 to 20 hours at 100 to 500 rpm.

In addition, in the step (b) proposes a metal-ceramic heterocomposite for the gasket characterized in that the spark plasma sintering for 5 to 20 minutes at a temperature of 500 to 700 ℃ and a pressure of 750 to 850 MPa.

In addition, the present invention proposes a gasket composed of the metal-ceramic heterocomposite material in another aspect of the invention.

The metal-ceramic heterocomposite material for gasket according to the present invention has high strength, high toughness and high corrosion resistance as well as excellent radiation shielding performance through the combination of aluminum (or aluminum alloy) and carbon nanotubes. It can be customized for extreme environment gaskets and sealing parts that require high performance and is very useful as a material for parts that require very high safety, such as parts for machinery, automobiles, trains, ships, aerospace, especially nuclear power plants. Can be utilized.

In addition, the manufacturing method of the metal-ceramic heterocomposite material for the gasket according to the present invention is manufactured by a low-energy solid-state powder metallurgical process instead of the melting method commonly used in the conventional metal material manufacturing method and burdens the environment such as chromate treatment It has the advantage of being an environmentally friendly process that does not require a process.

1 is a process flowchart of a method for manufacturing a metal-ceramic heterocomposite for a gasket according to the present invention.
Figure 2 is a schematic diagram showing a method of manufacturing an aluminum-SWCNT composite material for the gasket according to the embodiment of the present application.
FIG. 3 is a photograph of an aluminum-SWCNT composite specimen for a gasket manufactured in the form of discs of different diameters according to an embodiment of the present disclosure.

In the following description of the present invention, if it is determined that detailed descriptions of related known functions or configurations may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

Embodiments according to the concepts of the present invention may be variously modified and may have various forms, and specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiments in accordance with the concept of the present invention to a particular disclosed form, it should be understood to include all changes, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. As used herein, the terms "comprise" or "having" are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof that is described, and that one or more other features or numbers are present. It should be understood that it does not exclude in advance the possibility of the presence or addition of steps, actions, components, parts or combinations thereof.

Hereinafter, the present invention will be described in detail.

The present invention provides a gasket and a sealing heterogeneous composite material which satisfies both the toughness of the metal, the corrosion resistance and the high strength of the ceramic, which are obtained by complexing a dissimilar material of a metal and a ceramic using a spark plasma sintering method and a manufacturing method thereof. It is about.

When utilizing the advantages of each material through the complexation of aluminum and carbon nanotube materials as in the present invention, having excellent mechanical properties, corrosion resistance and light weight at the same time used in nuclear power plants, machinery, automobiles, trains, ships, aerospace It is possible to manufacture possible packing composite materials, and it is possible to reduce costs with various property control according to the composition ratio of each material.

Specifically, the metal-ceramic heterocomposite for gasket according to the present invention comprises (i) 50 to 99.9 volume% of aluminum or aluminum alloy, and (ii) 0.1 to 50 volume% of single wall carbon nanotube (SWCNT). Characterized in that made.

For reference, aluminum is used as an industrial part in various fields due to its relatively easy processing and light characteristics among metal materials, but has a disadvantage of low corrosion resistance and low mechanical strength. On the other hand, carbon nanotubes are low in density, have excellent mechanical properties and corrosion resistance peculiar to ceramics, and many studies have been conducted to apply them to various industrial materials.

Particularly, when the bulk with controlled properties of aluminum and carbon nanotubes is efficiently controlled as in the present invention, it is possible to produce heterogeneous composite materials of ultra-light weight, high strength and high toughness, and at the same time, it does not interfere with various industrial materials, in particular, fluid It should be highly elastic and flexible with respect to pressure and temperature, and have a very high utility as a material for sealing members such as gaskets that require airtightness without losing strength.

The gasket made of the metal-ceramic heterocomposite material according to the present invention can be used regardless of temperature and atmosphere (liquid and gaseous phase) according to the control of the composition of the material. Moreover, carbon nanotubes have radiation shielding ability, which makes them applicable to gaskets and packing materials for nuclear power plants.

In addition, although the conventional carbon gasket has low toughness, the metal-ceramic heterocomposite material for gasket according to the present invention has an advantage of increasing sealing performance even further due to the inherent ductility of aluminum. Furthermore, the high conductivity of the CNTs can reduce radio wave leakage at radio frequencies like conventional conductive gaskets.

The gasket metal-ceramic heterocomposite material according to the present invention may be made of a functionally graded material (FGM) as necessary.

That is, the metal-ceramic heterocomposite material for gasket according to the present invention has a structure in which aluminum (or aluminum alloy) and SWCNT composition and physical properties are continuously or intermittently changed in at least one of thickness, width, and length directions thereof. Can be.

For example, one side surface portion of the material that requires excellent hardness and corrosiveness includes a higher content of carbon nanotubes than the inside of the material, and the closer to the other surface portion from the one side surface portion of the inclined layer is reduced carbon content It can solve problems such as peeling and stress concentration due to the extreme characteristic difference, and the other surface portion of the material may be made of only aluminum to give a high toughness function.

Of course, when the gasket metal-ceramic heterocomposite material according to the present invention is an inclined functional material, the configuration is not limited to the above example, and may be freely changed depending on the use environment or shape of the material.

On the other hand, the metal-ceramic heterocomposite material for the gasket according to the present invention is preferably manufactured through a powder metallurgy process by spark plasma sintering (SPS).

For example, as shown in Figure 1, (a) mixing (i) aluminum or aluminum alloy powder and (ii) single-walled carbon nanotube powder; And (b) producing a composite material by spark plasma sintering (SPS) the mixed powder obtained in step (a), according to the manufacturing method of the metal-ceramic heterogeneous composite material for a gasket according to the present invention. Can be prepared.

At this time, in the step (a), it is possible to produce a composite powder having a uniform dispersion by ball milling the aluminum or aluminum alloy powder and single-wall carbon nanotube powder.

The aluminum or aluminum alloy powder may have an average particle size of 0.1 to 5 μm, and the aluminum or aluminum alloy powder may have an average particle size of less than 0.1 μm, wherein the single-walled carbon nanotube powder is in the sintering process. It is difficult to obtain a homogeneous composite material which is aggregated together with aluminum or aluminum alloy powder, and when the average particle diameter of the aluminum or aluminum alloy powder exceeds 5 μm, uniform dispersion of the carbon nanotubes is difficult, resulting in a nonuniform composite material. May be formed, it is preferable to use an aluminum or aluminum alloy powder having an average particle diameter in the above range, more preferably the aluminum or aluminum alloy powder may be used having an average particle size of 0.1 to 2 ㎛ have.

In addition, the single-walled carbon nanotube powder is excellent in mechanical, electrical, thermal properties, etc., and the diameter is small to further improve the properties of the aluminum or aluminum alloy powder, the physical properties of the composite material produced in the steps to be described later An improvement effect can be expected.

The mixed powder may include 50 to 99.9% by volume of aluminum or aluminum alloy powder and 0.1 to 50% by volume of single wall carbon nanotube powder, and when the single wall carbon nanotube powder is less than 0.1% by volume, mechanical properties If it falls, if it exceeds 50% by volume it is difficult to expect further improvement in physical properties. Preferably it may be configured to include 0.1 to 1% by volume of the single-walled carbon nanotube powder.

In addition, in this step, a homogeneous mixed powder may be prepared by mixing the aluminum or aluminum alloy powder and single-walled carbon nanotube powder through various types of ball milling processes such as electric ball milling, stirring ball milling, and planetary ball milling. Can be. Preferably, a mixed powder may be prepared by performing a planetary ball milling process, and a weight ratio (BPR) of the aluminum or aluminum alloy powder and single-wall carbon nanotube powder to a ball is determined. It is possible to perform the planetary ball milling process by setting to 10: 1 to 1: 1, preferably, by performing the planetary ball milling process by setting the BPR to 6: 1, it is possible to produce a homogeneous mixed powder. In particular, the ball used in the planetary ball milling process may use a zirconia ball having excellent properties such as self-lubrication, toughness and mechanical strength.

In addition, the planetary ball milling process may be performed for 100 to 500 rpm for 1 to 20 hours, when the time to perform the planetary ball milling process is less than 1 hour, aluminum or aluminum alloy powder and single-wall carbon nanotube powder There may be a problem that the physical properties of the composite material produced through the spark plasma sintering in the step to be described later by forming the coarse particles, more preferably, the planetary ball milling process performed at 250 rpm for 5 to 10 hours It can be configured to produce a homogeneous mixed powder.

In addition, in this step, in order to ball mill the aluminum or aluminum alloy powder and the single-wall carbon nanotube powder, a release agent is additionally supplied to the mixed powder of the aluminum or aluminum alloy powder and the single-wall carbon nanotube powder to provide a ball milling process. It may be configured to prevent sticking phenomenon that may occur, and the mixed powder may be added in a range that does not harm the physical properties of the bulk composite material prepared by spark plasma sintering.

Next, in the step (b), a plasma plasma sintering (SPS) of the mixed powder prepared in the previous step is to prepare a metal-carbon nanotube composite material.

In the spark plasma sintering, a spark discharge phenomenon is generated by a pulsed DC current flowing between particles of the mixed powder by applying a direct current to the mixed powder under a pressure applied condition, whereby a high energy of the spark plasma is generated instantly. The composite powder is sintered by the thermal diffusion and electric field diffusion by heat, the heat generated by the electrical resistance of the mold, and the pressure and electrical energy applied to it, so that the aluminum (or aluminum alloy) and single-wall carbon nanotubes are mixed in a short time. Through the sintering ability, it is possible to effectively control the growth of the composite material grains, and to prepare a metal-ceramic heterocomposite having a uniform microstructure.

In the present invention, for the spark plasma sintering process, for example, the upper electrode and the lower electrode is provided with a chamber to supply a current to generate a spark plasma to form a space for accommodating the mold for sintering the mixed powder, the cooling water A cooling unit capable of circulating and cooling the chamber, a current supply unit supplying current to the upper electrode and the lower electrode, a temperature sensing unit capable of detecting a temperature in the chamber, and a bet inside the chamber may be discharged to the outside. A spark plasma sintering apparatus having a pump, a pressure supply unit capable of supplying pressure to the chamber, a control unit controlling a temperature of the spark plasma sintering process according to a temperature sensed by the temperature sensing unit, and an operation unit controlling the control unit. The spark plasma sintering process can be performed.

In this step, in order to spark sinter the mixed powder, by using a pump provided in the spark plasma apparatus, the inside of the chamber is evacuated and depressurized until the inside of the chamber is in a vacuum state, thereby removing impurities in the gas phase present in the chamber. In order to prevent oxidation, the spark plasma sintering process may be performed.

Further, the mixed powder is heated to a sintering temperature at a heating rate of 100 ° C./minute to preheat the mixed powder, and then spark plasma sintering may be performed, and the mixed powder may be preheated at the temperature rising rate as described above. Since the uniform temperature is supplied to the inside and the outside of the mixed powder through the plasma sintering process, it is possible to form a heterogeneous composite material having a uniform structure.

In addition, the spark plasma sintering process can suppress the growth of the composite particles of aluminum (or aluminum alloy) and single-walled carbon nanotubes by controlling the temperature increase rate to control the size of the composite material produced.

The spark plasma sintering process is preferably configured to be performed for 5 to 20 minutes at a temperature of 500 to 700 ℃ to produce a composite material of metal and single-walled carbon nanotubes. At this time, when the spark plasma sintering temperature is less than 500 ℃, a sintered body having a low density is produced, when the spark plasma sintering temperature exceeds 700 ℃, the grains of the metal and single-walled carbon nanotube composite material rapidly grows and mechanical properties are deteriorated Can be. In addition, when the spark plasma sintering process is performed in less than 5 minutes, it is difficult to expect a sufficient sintering effect due to incomplete sintering, and when the sintering time exceeds 20 minutes, the energy consumption increases, which is not only economical, but also sintering It is difficult to expect the densification effect by.

In addition, the spark plasma sintering process is configured to be carried out under a pressure of 750 to 850 MPa to pressurize the mixed powder to produce a composite material of aluminum (or aluminum alloy) and single-walled carbon nanotubes, pressure less than 750 MPa Under the disadvantages, the density of the composite material of the metal and single-walled carbon nanotubes is lowered, and when the pressure is higher than 850 MPa, cracks may occur in the composite material of the metal and the single-walled carbon nanotubes. A spark plasma sintering process can be performed.

In addition, in this step, after sintering the composite material of the metal and single-walled carbon nanotubes as described above, it may further include the step of cooling the composite material, through which the metal-carbon nanotube composite with excellent mechanical properties The material can be obtained.

In this step, the composite of the aluminum (or aluminum alloy) and the single-walled carbon nanotubes is cooled to maintain the pressure of 100 to 300 MPa so that the composite of the aluminum (or the aluminum alloy) and the single-walled carbon nanotubes Formation of voids and the like formed on the surface and inside of the material can be suppressed.

The metal-ceramic heterocomposite material for gasket according to the present invention described above has high strength, high toughness and high corrosion resistance as well as excellent radioactivity shielding performance through the combination of aluminum (or aluminum alloy) and carbon nanotubes. It can be customized for extreme environment gaskets and sealing parts that require corrosion resistance and light weight, and material of parts that require very high safety such as parts for machinery, automobiles, trains, ships, aerospace, especially nuclear power plants It can be very useful as

In addition, the manufacturing method of the metal-ceramic heterocomposite material for the gasket according to the present invention is manufactured by a low-energy solid-state powder metallurgical process instead of the melting method commonly used in the conventional metal material manufacturing method and burdens the environment such as chromate treatment It has the advantage of being an environmentally friendly process that does not require a process.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Embodiments according to the present disclosure may be modified in many different forms, and the scope of the present disclosure is not to be construed as limited to the embodiments described below. The embodiments of the present specification are provided to more fully describe the present specification to those skilled in the art.

<Examples and Comparative Examples>

1. Preparation of Aluminum-Single Wall Carbon Nanotube Heterogeneous Composite Material (Al-50vol% SWCNT) for Gasket (Example)

As shown in FIG. 2, in order to prepare an aluminum composite, first, 50% by volume of aluminum powder (average particle size: 75 μm) and single-walled carbon nanotubes (average length: about 10 um, average diameter: about 5 nm) 50% by volume of powder was fed to the planetary ball milling apparatus and 20 mL of heptane was added. The ball was added by setting the weight ratio of the ball to the mixed powder to 8: 1, and a mixed powder was prepared by performing a planetary ball milling process at 250 rpm for 6 hours.

The prepared mixed powder was charged into a carbon mold (˜φ30 mm), and the mold was mounted in a chamber of a spark plasma sintering apparatus. The pressure in the chamber was adjusted to a vacuum state, and a spark plasma sintering process was performed for 10 minutes at a temperature of 650 ° C. and a pressure of 800 MPa by applying an electric current to the upper electrode and the lower electrode, thereby dispersing the aluminum-single-wall carbon nanotube Material specimens were obtained (FIG. 3).

2. Preparation of Aluminum Sintered Body (Comparative Example 1)

An aluminum sintered body was manufactured in the same manner as in the above example except that sintering using only aluminum powder was used.

3. Preparation of single-walled carbon nanotube sintered body (Comparative Example 2)

A single-walled carbon nanotube sintered body was manufactured in the same manner as in the above example, except that sintering using only single-walled carbon nanotube powder was used.

Experimental Example

The density and mechanical properties of the specimens prepared in Examples, Comparative Examples 1 and 2 were measured, and the results are shown in Table 1 below.

Referring to Table 1 below, the specimen according to the present invention obtained by complexing carbon nanotubes with aluminum in the above embodiment is a high carbon nanometer through a simple and environmentally friendly spark plasma sintering process as compared to a conventional composite material manufacturing method such as a melting method. Although it has a tube content, it has a high relative density, and also has an improved light weight and elasticity compared with aluminum, and in particular, it has a high hardness as much as four times that of aluminum, and thus it is confirmed that it is optimized as a material for sealing parts such as gaskets. have.

TABLE 1

Claims (7)

(i) 50% by volume of aluminum; And
(ii) 50 vol% single-walled carbon nanotubes (SWCNTs);
A metal-ceramic heterocomposite for a gasket, which is prepared by a method comprising the following steps:
(a) Performing a planetary ball milling process for 6 hours at 250 rpm with the weight ratio of the ball, aluminum powder and single-walled carbon nanotube powder to 8: 1, aluminum powder and single Mixing the wall carbon nanotube powder; And
(b) preparing a composite material by spark plasma sintering (SPS) the mixed powder obtained in step (a) at a temperature of 650 ° C. and a pressure of 800 MPa for 10 minutes. delete delete delete delete delete A gasket composed of the metal-ceramic heterocomposite material according to claim 1.

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