KR101166721B1 - Manufacturing method of high density boroncarbide sintered body using spark plasma sintering - Google Patents

Abstract

The present invention is a method for filling boron carbide powder into a mold provided in a chamber of a discharge plasma sintering apparatus and applying pressure to form a molded body of a desired shape, and operating a pump to exhaust the impurity gas existing in the chamber, and reducing agent gas. Supplying phosphorus hydrogen (H ₂ ) gas, applying a direct current pulse while pressurizing the boron carbide powder, and boron oxide (B ₂ O ₃ ) present on the surface of the boron carbide powder Firstly raising the temperature to a temperature higher than the volatilized temperature, secondly raising the temperature of the chamber to a sintering temperature higher than the temperature at which the boron oxide is volatized and lower than the melting temperature of boron carbide, and boron carbide at the sintering temperature hydrogen while applying a pressure to an article in a reducing gas atmosphere, the powder (H ₂₎ and the chamber step of the discharge plasma sintering the boron carbide in the gas atmosphere, Cooling to a method of manufacturing a high-density boron carbide sintered body using a spark plasma sintering method comprises the step of obtaining the boron carbide sintered body.

Description

Manufacturing method of high density boroncarbide sintered body using spark plasma sintering}

The present invention relates to a method for producing a boron carbide (B ₄ C) sintered body, and more particularly, high density boron carbide sintered body used as an abrasive material or a cutting tool material exhibiting properties such as high hardness, wear resistance, grinding resistance, and neutron absorption It relates to a manufacturing method of.

Boron carbide (B ₄ C) is the third-hardest material after diamond and boron nitride cubes, and is applied to various fields in the form of powder or sintered body due to its properties such as high hardness, abrasion resistance, grinding resistance, and neutron absorption. have. Boron carbide powder is used for polishing glass, light metals or artificial minerals, and since the sintered body has a very high wear resistance, sand blasting nozzle, computer disk, grinding motor, sliding friction It is mainly used for sliding friction parts, bearing liners, protective clothing, fire-resistant antioxidants and anti-wear agents. Boron carbide (B ₄ C) is also used as a nuclear shield due to its high neutron absorption per unit area.

Boron carbide (B ₄ C) is there is a high melting point and hardly used as the abrasive material or the cutting tool material is used as a covalent bond substance, such a boron carbide (B ₄ C) is generally a carbon (C), Y ₂ O sintering of the powder _{3, SiC, Al 2 O 3} , TiB 2, AlF 3, W 2 has a sintering aid such as B ₅ are used. However, such a sintering aid is known to form a secondary phase, and the secondary phase formed by sintering with the addition of the sintering aid adversely affects the physical properties of boron carbide (B ₄ C). It is well known that the hardness and mechanical properties of boron carbide decrease rapidly as the content of the secondary phase formed by the sintering aid increases. For example, inde boron carbide (B ₄ C) is a well-known carbon (C) as a sintering aid for, the use of carbon as a sintering aid to obtain a carbon-boron (B ₄ C) having a high relative density, but the boron / carbon solid solution Excessive or less than the bonding ratio (about 20 mol% of carbon content in boron carbide) of may lower the mechanical properties of boron carbide. Therefore, there is research on the method without the addition of a sintering aid to obtain a boron carbide (B ₄ C) sintered body made recently.

It is also known that boron oxide (B ₂ O ₃ ) is formed on the surface of boron carbide (B ₄ C). Boron oxide (B ₂ O ₃ ) present on the surface of boron carbide (B ₄ C) causes pores or voids to form between crystal grains during sintering. Pores or voids formed between the grains by boron oxide (B ₂ O ₃ ) may interfere with crystal growth and degrade the mechanical properties of the boron carbide (B ₄ C) sintered body. Works. Therefore, there is a need for a method of effectively removing boron oxide (B ₂ O ₃ ) from boron carbide (B ₄ C) which adversely affects the physical properties of the boron carbide (B ₄ C) sintered body.

The present invention has been made to solve the above problems, an object of the present invention is not only the secondary phase is formed by sintering without adding a sintering aid but also sintered in a reducing gas atmosphere to boron carbide (B ₄ C) Since boron oxide (B ₂ O ₃ ) present on the surface is reduced and decomposed, no pores or voids are formed between the crystal grains, so the crystal state is excellent, and the mechanical properties of the sintered body are excellent. The present invention provides a method for producing a high density boron carbide sintered body having a very close spacing.

The present invention comprises the steps of (a) filling boron carbide powder into a mold provided in a chamber of a discharge plasma sintering apparatus and applying pressure to form a molded body of a desired shape; and (b) operating a pump to operate an impurity gas present in the chamber. Exhausting and supplying hydrogen (H ₂ ) gas, which is a reducing agent gas, (c) applying a direct current pulse while pressurizing the boron carbide powder, and (d) adjusting the temperature of the chamber to the surface of the boron carbide powder. Firstly raising the temperature of the boron oxide (B ₂ O ₃ ) present at a temperature higher than the volatilization temperature, and (e) sintering the temperature of the chamber higher than the temperature at which the boron oxide is volatilized and lower than the melting temperature of boron carbide. and the step of the secondary rise in temperature, (f) the hydrogen (H ₂₎ gas atmosphere in the discharge plasma sintering the boron carbide, while the pressure on the molded article the reducing gas atmosphere of boron carbide powder in the sintering temperature And (g) cooling the chamber to obtain a boron carbide sintered body, wherein the temperature rising rate of the chamber in step (e) is set smaller than the temperature rising rate of the chamber in step (d). By gradually raising the sintering temperature to minimize the thermal stress on the boron carbide powder compact, and sintering in a reducing gas atmosphere to reduce the boron oxide (B ₂ O ₃ ) present on the surface of the carbon boron powder to be reduced and decomposed It provides a method for producing a high density boron carbide sintered body using the discharge plasma sintering method.

The temperature at which the boron oxide (B ₂ O ₃ ) is volatilized is 1200 to 1400 ° C., and the temperature higher than the temperature at which the boron oxide (B ₂ O ₃ ) is volatilized is 1400 to 1600 ° C., and the chamber in step (d) It is preferable that the temperature increase rate of the temperature is set in the range of 5 ~ 50 ℃ / min, the temperature increase rate of the chamber in the step (e) is set to 1 ~ 30 ℃ / min range.

The sintering temperature is 1800 ~ 2100 ℃, the sintering is preferably carried out for 5 minutes to 3 hours in consideration of the microstructure and particle size of the sintered body.

The DC pulse is applied in the range of 0.1 to 2000A, and the pressure applied to the molded body of the boron carbide powder in the step (f) is in the range of 10 to 60 MPa, and preferably, the uniaxial compression of the mold is performed.

In the step (f), the hydrogen gas is supplied at a flow rate in the range of 0.1-10 ml / min, and the mold is preferably made of a graphite material of the same material as the carbon component of boron carbide.

In addition, the present invention provides a high-density boron carbide sintered body which is a boron carbide sintered body manufactured using the method for producing a high-density boron carbide sintered body whose apparent density is greater than 90% of the theoretical density.

The boron carbide (B ₄ C) produced according to the present invention sintered body is the apparent density is more than 90% of the theoretical density, the distance between the particles is very dense and pore are not substantially form a high density boron carbide (B ₄ C) sintered body .

In addition, since it made of sintering without the addition of a sintering aid in the boron carbide (B ₄ C) sintered body has a second phase (secondary phase) is not formed, and thus a very good hardness and mechanical properties of boron carbide (B ₄ C) sintered body Do.

By sintering in a reducing gas atmosphere, boron oxide (B ₂ O ₃ ) present on the surface of boron carbide (B ₄ C) is reduced and decomposed, so that no pores or voids are formed between grains. The state is excellent, and the mechanical properties of the boron carbide (B ₄ C) sintered body are also excellent.

1 is a view schematically showing a discharge plasma sintering apparatus.
2 is a view illustrating a sintering process for forming a carbon boron (B ₄ C) sintered body according to a preferred embodiment of the present invention.
3 is a graph showing an X-ray diffraction (XRD) pattern of the boron carbide (B ₄ C) sintered body prepared in Example 4. FIG.
4 is a graph showing the relative density of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 according to the sintering temperature.
5 is a graph showing the average grain size (average grain size) according to the sintering temperature of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4.
6 is a graph showing Vickers hardness according to the sintering temperature of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4;
7 is a graph showing the flexural strength according to the sintering temperature of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments are provided to those skilled in the art to fully understand the present invention, and may be modified in various forms, and the scope of the present invention is limited to the embodiments described below. It doesn't happen.

The present invention uses a spark plasma sintering (SPS) method to produce a high density boron carbide (B ₄ C) sintered body without adding a sintering aid.

The discharge plasma sintering (SPS) method is a technique using plasma as a technique capable of synthesizing or sintering a desired material in a short time. In the discharge plasma sintering (SPS) method, electric energy in a pulse form is directly injected into a gap between particles of a green compact, and high energy of a high-temperature plasma (discharge plasma) generated instantly by a spark discharge is applied to thermal diffusion, electric field, etc. It is an effective application process. The sintering temperature can be controlled from low temperature to more than 2000 ℃ by the generated plasma, and can be sintered or sintered in a short time including the temperature raising and holding time in the temperature range of 200 ~ 500 ℃ lower than other sintering processes. to be. In addition, since rapid temperature rising is possible, the growth of particles can be suppressed, a dense sintered body can be obtained in a short time, and the sintered material can be easily sintered.

Hereinafter, a method of manufacturing a high density boron carbide (B ₄ C) sintered body according to a preferred embodiment of the present invention using the discharge plasma sintering (SPS) method will be described. 1 is a view schematically showing a discharge plasma sintering apparatus, Figure 2 is a view showing a sintering process for forming a carbon boron (B ₄ C) sintered body according to a preferred embodiment of the present invention to be.

The boron carbide (B ₄ C) powder 120 is charged into the mold 110 provided in the chamber 100, and the hydrogen (H ₂ ) gas, which is a reducing agent gas, is injected and pressurized while pressurizing with a punch 130 in one axis. Sintering by applying a DC pulse current in a direction parallel to the direction. Due to the increase in temperature due to the pressurization and high current application during sintering, a reaction occurs between the powder particles, thereby obtaining a boron carbide (B ₄ C) sintered body. It will be described in more detail below.

1 and 2, boron carbide (B ₄ C) powder is prepared. Since the particle size of the boron carbide (B ₄ C) powder affects the density, mechanical properties, etc. of the boron carbide (B ₄ C) sintered body, the particle diameter of the boron carbide (B ₄ C) powder is selected in consideration of this. Preferably, it is preferable to use spherical boron carbide (B ₄ C) powder having a particle diameter of 1 µm or less in consideration of the use of a high density boron carbide (B ₄ C) sintered body in an abrasive or cutting tool.

Boron carbide (B ₄ C) powder 120 is filled in the mold 110 provided in the chamber 100. The mold 110 may be provided in a cylindrical or prismatic shape, and the mold 110 has a high hardness and a high melting point and is made of graphite (C) having the same material as that of carbon (C) constituting a component of boron carbide (B ₄ C). It is preferably made of a graphite) material, because in the case of using a mold made of a different material may act as an impurity in the subsequent sintering process.

After filling the boron carbide (B ₄ C) powder 120 in the mold 110 is subjected to uniaxial compression using a punch 130 to form a molded body of the desired shape. At this time, the pressure applied to the boron carbide (B ₄ C) powder (pressure compressed by the mold) is preferably about 10 ~ 60MPa, when the pressure is less than 10MPa between the boron carbide (B ₄ C) powder particles Since there are many voids, it is difficult to obtain a desired high density boron carbide (B ₄ C) sintered body, and a high current must be applied for sintering, which may result in a high temperature rise.If the pressurization pressure exceeds 60 MPa, further effects cannot be expected. The design of molds, hydraulic devices, etc. according to the high pressure may be added, thereby increasing the cost of manufacturing equipment.

In order to remove the impurity gas existing in the chamber 100 of the discharge plasma sintering apparatus and to reduce the pressure, a rotary pump (not shown) may be operated to obtain a vacuum state (for example, about 1.0 × 10 ⁻² to 9.0 × 10 ⁻² torr). Exhaust until reduced pressure.

The rotary pump is stopped and hydrogen (H ₂ ) gas, which is a reducing gas, is supplied into the chamber. The hydrogen gas is preferably supplied at a flow rate of about 0.1 to 10 ml / min.

In the state where the boron carbide (B ₄ C) powder is pressurized, a DC pulse is slowly applied using a DC pulse generator (Pulsed DC Generator) 140. The DC pulse is preferably applied in the range of 0.1 ~ 2000A. When the current is rapidly applied when applying the DC pulse, it may be difficult to control the temperature, so it is preferable to raise the same width for a predetermined time.

The temperature of the chamber is raised to a temperature higher than the temperature at which boron oxide (B ₂ O ₃ ) is volatilized (1200-1400 ° C.) and lower than a target sintering temperature (1800-2100 ° C.) (eg, 1400-1600 ° C.) T1 section in Figure 2). The hydrogen gas is preferably supplied at a flow rate of about 0.1 to 10 ml / min. It is preferable that the rising temperature of the chamber is about 5 to 50 ° C / min. If the ramp-up rate of the chamber is too slow, it takes a long time to decrease productivity and the ramp-up rate of the chamber is too fast. It is preferable to raise the temperature of the chamber at a ramp-up rate in the above range because no dense sintering is achieved by rapid temperature rise. Boron oxide (B ₂ O ₃ ) present on the surface of the boron carbide (B ₄ C) is generally pyrolyzed and volatilized at a temperature of 1200 ~ 1400 ℃ or more, and thus boron oxide (B ₂ O) when the chamber temperature is 1400 ℃ or more ₃ ) pyrolysis starts to occur.

The temperature of the chamber is raised to a target sintering temperature of 1800-2100 ° C., which is lower than the melting temperature (2450 ° C.) of boron carbide (B ₄ C) (T2 section in FIG. 2). At this time, the rising temperature of the chamber is preferably about 1 ~ 30 ℃ / min, if the ramp-up (ramp-up rate) of the chamber is too slow, it takes a long time to reduce productivity and the ramp-up rate of the chamber is too It is preferable to raise the temperature of the chamber at a ramp-up rate in the above range because it may adversely affect the characteristics of the sintered body by rapid temperature rise. It is preferable that the ramp-up rate in the T2 section of FIG. 2 is slower than the ramp-up rate in the T1 section of FIG. 2, which is gradually increased to the sintering temperature in the T2 section of FIG. 2 by boron carbide (B ₄ C) powder. This is to minimize the thermal stress on the molded body.

Target sintering temperature which rises to (e.g., boron carbide (B ₄ C) is lower than the melting temperature of a temperature of 1800 ~ 2100 ℃ a), to maintain a certain amount of time (e.g., 5 minutes to 3 hours) boron carbide (B ₄ C ) Is sintered (T3 section in FIG. 2). Since hydrogen (H ₂ ) gas, which is a reducing gas, is injected into the chamber, some boron oxide (B ₂ O ₃ ) remaining on the surface of boron carbide (B ₄ C) is reduced as in Scheme 1 below. The reducing agent gas flows an amount such that boron oxide (B ₂ O ₃ ) can be sufficiently reduced, for example, it is supplied at a flow rate of about 0.1 ~ 10ml / min. The boron oxide (B ₂ O ₃ ) is reduced by hydrogen (H ₂ ) gas, which is a reducing agent gas, as shown in Scheme 1 below.

[Reaction Scheme 1]

B ₂ O ₃ + 3H ₂ → 2B + 3H ₂ O

As shown in Scheme 1, while boron carbide (B ₄ C) is sintered, boron oxide (B ₂ O ₃ ) is reduced to boron (B). At this time, water vapor (H ₂ O) which is a reaction by-product generated by reduction of boron oxide (B ₂ O ₃ ) is evaporated. By sintering boron carbide (B ₄ C) in a reducing gas atmosphere, boron oxide (B ₂ O ₃ ) partially remaining on the surface of boron carbide (B ₄ C) may be reduced to be completely decomposed. Since boron oxide (B ₂ O ₃ ) present on the surface of boron carbide (B ₄ C) is completely removed during the sintering process, pores or voids are not formed between the grains, so the crystalline state is excellent and It is possible to produce a high density boron carbide sintered body having excellent mechanical properties and very close spacing between particles.

Sintering temperature is preferably about 1800 ~ 2100 ℃ in consideration of the diffusion of boron carbide (B ₄ C) particles, necking between the particles, etc. If the sintering temperature is too high, mechanical properties due to excessive grain growth If the sintering temperature is too low and the sintering temperature is too low, the sintered body may not be good due to incomplete sintering, and therefore, sintering at the sintering temperature in the above range is preferable. According to the sintering temperature, there are differences in the microstructure, particle size, etc. of the sintered body, because the surface diffusion is dominant when the sintering temperature is low, but the lattice diffusion and grain boundary diffusion are progressed when the sintering temperature is high. The sintering time is preferably 5 minutes to 3 hours when using a chamber for general heat treatment. If the sintering time is too long, it is not only economical because it consumes a lot of energy and it is difficult to expect further sintering effects. When the size of the sintered body becomes large and the sintering time is small, the characteristics of the sintered body may be poor due to incomplete sintering. The pressure applied to the boron carbide (B ₄ C) powder compact during sintering is preferably about 10 to 60 MPa. If the pressurization pressure is too small, it is difficult to obtain the desired high density carbon boron sintered body and the sintering process if the pressurization pressure is too large. Cracks and the like may occur in the sintered body after this completion.

After performing the sintering process, the chamber temperature is lowered to unload the boron carbide (B ₄ C) sintered body. When the temperature of the chamber is lowered, it is preferable to cut off the supply of hydrogen gas which is a reducing agent gas when the temperature is about 800 to 1200 ° C. The chamber cooling may be caused to cool down in a natural state by shutting off the chamber power, or optionally by setting a temperature drop rate (eg, 10 ° C./min).

The boron carbide (B ₄ C) sintered body manufactured according to the preferred embodiment of the present invention has an apparent density of 90% or more of the theoretical density, a very high density of boron carbide (B ₄ ) with a very small gap between particles, and little pores. C) It is a sintered compact.

In addition, since it made of sintering without the addition of a sintering aid in the boron carbide (B ₄ C) sintered body has a second phase (secondary phase) is not formed, and thus a very good hardness and mechanical properties of boron carbide (B ₄ C) sintered body Do.

Boron oxide (B ₂ O ₃ ) present on the surface of boron carbide (B ₄ C) is reduced during the sintering process so that no pores or voids are formed between the crystal grains, and thus the crystal state is excellent. The mechanical properties of the boron (B ₄ C) sintered body are also very good.

The invention is described in more detail with reference to the following examples, which do not limit the invention.

≪ Example 1 >

A boron carbide (B ₄ C) powder (product name C Grade) manufactured by Herman C Stark having an average particle diameter of 0.8 μm was prepared.

Table 1 below shows the characteristics of the boron carbide (B ₄ C) powder of Herman C. Stark.

Specific surface area 18㎡ / g
Particle size
D 90% of particle ≤ 3.0 μm
50% particle ≤ 0.8 μm
D 10% of particle ≤ 0.2 μm

Impurity levels


Up to 1.7 wt% oxygen (O)
Up to 0.7 wt% nitrogen (N)
0.05 wt% iron (Fe)
Up to 0.15wt% Silicon (Si)
0.05 wt% aluminum (Al)
Other impurities up to 0.5wt% Boron content 75.65wt% Carbon content 21.2 wt% B / C molar ratio of boron (B) and carbon (C) 3.7

The boron carbide (B ₄ C) powder was sintered using a discharge plasma sintering apparatus shown in FIG. 1 in a hydrogen gas atmosphere which is a reducing gas atmosphere.

Looking at the sintering process using the discharge plasma sintering (SPS) method in detail, after filling the boron carbide (B ₄ C) powder in the mold provided in the chamber, reducing the inside of the chamber and supplying hydrogen (H ₂ ) gas, A direct current pulse current was applied in a direction parallel to the pressing direction while pressing in one axis.

More specifically, the boron carbide (B ₄ C) powder 120 was filled in the mold 110 provided in the chamber 100, and molded into a molded body by applying pressure. At this time, the mold was made of a graphite graphite material, and charged with boron carbide (B ₄ C) powder and then uniaxial compression, the pressure applied to the boron carbide (B ₄ C) powder (the The pressure compressed by the mold) was about 40 MPa.

In order to remove the impurity gas present in the chamber and to create a vacuum state, the rotary pump was operated to exhaust the impurity gas, the rotary pump was stopped, and hydrogen (H ₂ ) gas, a reducing agent gas, was supplied into the chamber. The hydrogen (H ₂ ) gas was supplied at a flow rate of about 5 ml / min.

Directly applying a DC pulse while pressurizing the boron carbide (B ₄ C) powder. The DC pulse was applied to 1 ~ 1000A.

The temperature of the chamber was raised to 1500 ° C. At this time, the rising temperature of the chamber was about 20 ° C / min.

After raising the temperature of the chamber to 1500 ° C., the temperature of the chamber was raised to 1900 ° C., which is lower than the melting temperature (2450 ° C.) of boron carbide (B ₄ C). At this time, the rising temperature of the chamber was about 5 ° C / min.

After raising the temperature of the chamber to 1900 ° C., boron carbide (B ₄ C) was sintered for 1 hour. The pressure applied to the boron carbide (B ₄ C) powder compact during sintering was kept constant at about 40 MPa. During sintering, hydrogen (H ₂ ) gas was supplied at a flow rate of about 5 mL / min. When sintering, reaction occurs between powders due to an increase in temperature due to pressurization and current application, thereby obtaining a boron carbide (B ₄ C) sintered body, while boron carbide (B ₄ C) is sintered and simultaneously boron oxide (B ₂ O ₃ ) Is reduced to boron (B) and water vapor (H ₂ O) which is a reaction by-product generated by the reduction of boron oxide (B ₂ O ₃ ) is evaporated.

After performing the sintering process, the chamber temperature was lowered to unload the boron carbide (B ₄ C) sintered body. When the temperature of the chamber was decreased, the supply of hydrogen (H ₂ ) gas, which is a reducing agent gas, was cut off when the temperature reached about 1000 ° C. The chamber cooling shuts off the chamber power, allowing the chamber to cool in its natural state.

<Example 2>

A high-density boron carbide (B ₄ C) sintered body was produced in the same manner as in Example 1 except that the sintering temperature was set to 1950 ° C and sintered.

<Example 3>

A high-density boron carbide (B ₄ C) sintered body was produced in the same manner as in Example 1 except that the sintering temperature was set to 2000 ° C. and sintered.

<Example 4>

A high-density boron carbide (B ₄ C) sintered body was produced in the same manner as in Example 1 except that the sintering temperature was set to 2050 ° C and sintered.

&Lt; Comparative Example 1 &

The same boron carbide (B ₄ C) powder used in Example 1 was prepared, and a molded body was made in the same manner using the same mold as in Example 1.

In order to remove the impurity gas present in the chamber and to create a vacuum state, the rotary pump was operated to exhaust the impurity gas, the rotary pump was stopped, and argon (Ar) gas was supplied into the chamber. The argon (Ar) gas was supplied at a flow rate of about 5 ml / min.

Subsequent processes were carried out in the same manner as in Example 1, and during sintering, unlike Example 1, argon (Ar) gas was supplied at a flow rate of about 5 ml / min to prepare a boron carbide (B ₄ C) sintered body. When the temperature of the chamber was lowered to about 1000 ° C., the supply of argon (Ar) gas was cut off.

Comparative Example 2

A boron carbide (B ₄ C) sintered body was produced in the same manner as in Comparative Example 1 except that the sintering temperature was set to 1950 ° C and sintered.

&Lt; Comparative Example 3 &

A boron carbide (B ₄ C) sintered body was produced in the same manner as in Comparative Example 1 except that the sintering temperature was set to 2000 ° C. and sintered.

&Lt; Comparative Example 4 &

A boron carbide (B ₄ C) sintered body was produced in the same manner as in Comparative Example 1 except that the sintering temperature was set to 2050 ° C and sintered.

FIG. 3 is a graph showing an X-ray diffraction (hereinafter referred to as 'XRD') pattern of the boron carbide (B ₄ C) sintered body manufactured according to Example 4. FIG. In Figure 3 (a) is a XRD pattern of boron carbide (B ₄ C) powder used in Example 4, (b) is equal to the boron carbide (B ₄ C) powder used in Example 4 and Example 1 XRD pattern when the hydrogen (H ₂ ) gas is supplied and heat-treated for 1 hour at a temperature of 1200 ℃ in a reducing atmosphere, (c) is XRD of the boron carbide (B ₄ C) sintered body prepared according to Example 4 A graph showing a pattern.

Referring to Figure 3, boron carbide (B ₄ C) powder, the boron oxide (B ₂ O ₃₎ boron carbide (B ₄ C), the boron oxide the surface of the powder by a peak appears in as shown in (a) (B ₂ O ₃₎ to check that it is present, (b) and (c), can be concluded that the boron oxide (B ₂ O ₃₎ a peak is not as boron oxide (B ₂ O ₃₎ is removed, not a.

4 is a graph showing the relative density of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4 according to the sintering temperature. Relative density is measured using the Archimedes method. As shown in FIG. 4, when Examples 1 to 4 which sintered in a hydrogen gas atmosphere as a reducing gas atmosphere to remove boron oxide (B ₂ O ₃ ) were sintered at the same sintering temperature, sintering was performed in an argon (Ar) gas atmosphere. It can be seen that the relative density was higher than that of Comparative Examples 1 to 4.

5 is a graph showing the average grain size (average grain size) according to the sintering temperature of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4. As shown in FIG. 5, when Examples 1 to 4 sintered in a hydrogen gas atmosphere to remove boron oxide (B ₂ O ₃ ) are the same in sintering temperature, Comparative Examples 1 to sintered in an argon (Ar) gas atmosphere It can be seen that the average particle size was smaller than that of 4.

6 is a graph showing Vickers hardness according to the sintering temperature of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4; As shown in FIG. 6, in Examples 1 to 4, which were sintered in a hydrogen gas atmosphere to remove boron oxide (B ₂ O ₃ ), when the sintering temperatures were the same, Comparative Examples 1 to sintered in an argon (Ar) gas atmosphere It can be seen that Vickers hardness was higher than that of 4.

7 is a graph showing the flexural strength according to the sintering temperature of the boron carbide (B ₄ C) sintered body prepared according to Examples 1 to 4 and Comparative Examples 1 to 4. As shown in FIG. 7, Examples 1 to 4, which were sintered in a hydrogen gas atmosphere to remove boron oxide (B ₂ O ₃ ), were sintered in an argon (Ar) gas atmosphere when the sintering temperatures were the same. It can be seen that the bending strength was higher than that of 4.

As mentioned above, although preferred embodiment of this invention was described in detail, this invention is not limited to the said embodiment, A various deformation | transformation by a person of ordinary skill in the art within the scope of the technical idea of this invention is carried out. This is possible.

Claims (6)

(a) filling the boron carbide powder into a mold provided in the chamber of the discharge plasma sintering apparatus and applying pressure to form a molded body of a desired shape;
(b) operating the pump to exhaust the impurity gas present in the chamber, and supplying hydrogen (H ₂ ) gas which is a reducing agent gas;
(c) applying a direct current pulse in a direction parallel to the pressing direction while pressing the boron carbide powder in one axis;
(d) first raising the temperature of the chamber to 1400-1600 ° C. which is higher than the temperature at which the boron oxide (B ₂ O ₃ ) present on the surface of the boron carbide powder is volatilized;
(e) raising the temperature of the chamber to a sintering temperature of 1800 to 2100 ° C. higher than the temperature at which the boron oxide is volatilized and lower than the melting temperature of boron carbide;
(f) discharge the boron carbide in a hydrogen (H ₂ ) gas atmosphere, which is a reducing gas atmosphere, by supplying hydrogen gas at a flow rate in the range of 0.1 to 10 ml / min while applying pressure to the molded body of the boron carbide powder at the sintering temperature. Making; And
(g) cooling the chamber to obtain a boron carbide sintered body,
In step (d), the temperature increase rate of the chamber is set in a range of 5 to 50 ° C./min, and in step (e), the temperature increase rate of the chamber is set in a range of 1 to 30 ° C./min.
In step (e), the temperature increase rate of the chamber is set to be smaller than the temperature increase rate of the chamber in step (d), and gradually raised to a target sintering temperature, thereby minimizing thermal stress on the boron carbide powder compact.
Sintering in a reducing gas atmosphere causes boron oxide (B ₂ O ₃ ) present on the surface of the carbon boron powder to be reduced and decomposed.
The pressure applied to the molded body of the boron carbide powder in the step (f) is in the range of 10 to 60 MPa,
In the step (f), the mold is subjected to uniaxial compression,
When cooling the chamber, when the temperature of 800 ~ 1200 ℃ to cut off the supply of hydrogen gas,
The mold is a method of producing a high density boron carbide sintered body using the discharge plasma sintering method, characterized in that the mold made of a graphite material of the same material as the carbon component of the boron carbide.
The method for producing a high density boron carbide sintered body using the discharge plasma sintering method according to claim 1, wherein the boron oxide (B ₂ O ₃ ) is volatilized at 1200 to 1400 ° C.
The method of claim 1, wherein the sintering is performed for 5 minutes to 3 hours in consideration of the microstructure and particle size of the sintered compact.
The method for producing a high density boron carbide sintered body using the discharge plasma sintering method according to claim 1, wherein the direct current pulse is applied in a range of 0.1 to 2000 A. delete delete

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