KR20100024213A - Method for making nanostructured metal carbides and a metal carbides made there by - Google Patents

Abstract

PURPOSE: A manufacturing method of a nano structure metal carbide and the and nano structure metal carbide manufactured from thereof are provided to perform a pressing molding and a sintering operation at high temperature in several minutes by heating nano powder with a heat generated from an inducing current or an impulse current. CONSTITUTION: A manufacturing method of a nano structure metal carbide comprises the following steps: nano pulverizing the metal carbide powder to make a nano particle size by ball milling; pressing molding and sintering the powder from the nano pulverizing step while heating the powder with a heat generated from an electric current; and cooling the pressing molded and sintered nano structure at room temperature when the contraction length does not change by blocking the electric current. The metal carbide powder is selected from the group consisting of titanium carbide, tungsten carbide, silicon carbide, tantalium carbide, vanadium carbide, and niobium carbide.

Description

METHOD FOR MAKING NANOSTRUCTURED METAL CARBIDES AND A METAL CARBIDES MADE THERE BY

The present invention relates to a method for producing metal carbide, and more particularly to a method for producing a nanostructure metal carbide and a nanostructure metal carbide produced therefrom.

Metal carbide is a high hardness material obtained by press molding and sintering metal carbide powder, also called a cemented carbide material, and manufactured using a hot pressing molding machine, a hot isostatic pressing molding machine, or the like.

For example, conventional metal carbides are different depending on the particle size, but typically, the powder is introduced into a hot compression molding machine or a hot hydrostatic pressure molding machine, and then press-molded and sintered by heating at least 1 hour at a high temperature of about 1700 ° C or higher. To prepare.

In practice, silicon carbide is produced by press forming and sintering silicon carbide powder by heating at a hydrostatic pressure molding machine for 1 hour at 2000 MPa or more under 100 MPa pressure.

However, the above-described method has a disadvantage in that it is not economical as a method of manufacturing at a high temperature and a long time, and as described above, when the metal carbide powder is heated at a high temperature for a long time under pressure molding and sintering, crystal grains of the metal carbide produced are grown. The grain size of the carbides is large and mechanical properties are disadvantageous as well. In addition, for the cemented carbide or cemented carbide sintered body, the manufacturing method was not simple using a water-soluble salt (Korean Patent No. 374705) or a method of first growing a specific surface of a crystal (Korean Patent Publication No. 1999-69647). .

The present invention is to solve the above-mentioned conventional problems, an object of the present invention after the nano-powder milling by a ball milling method so that the particle size of a specific metal carbide powder has a nanostructure, the induction current or Pressing and sintering the nanostructured powder until the shrinkage length of the nanostructured powder does not change while applying the heat generated by the pulse current, thereby completing high temperature pressing and sintering operations in a short time and thus grain growth The more restrictive and mechanical properties are to provide a method for producing nanostructured metal carbides for producing metal carbides having relatively good nanostructures. Another object of the present invention is to provide a nanostructured metal carbide produced by the above method.

The present invention to achieve the object of the present invention as described above;

Ball milling the metal carbide powder to nano-powder the particle size to have a nanostructure (S1);

Press molding and sintering while applying heat generated by current to the nanopowder in the step (S1) (S2); And if there is no change in the shrinkage length of the nano-powder provides a method for producing a nanostructure metal carbide comprising the step (S3) of blocking the current and cooling the pressurized and sintered nanostructure to room temperature just before the current blocking.

In the above, the metal carbide in the step (S1) is titanium carbide (TiC), tungsten carbide (WC), silicon carbide (SiC), tantalum carbide (TaC), vanadium carbide (VC), niobium carbide (NbC) At least one selected from the group consisting of is preferable, and nano-powdering of the metal carbide in the step (S1) is preferably such that the particle size is 100nm or less.

In addition, the press molding and sintering in the step (S2) is preferably performed for 2 to 5 minutes.

In addition, the heat generated by the current in the step (S2) is a heat generated by the induction current, the induction current is preferably used induction current having a frequency of 1 kHz ~ 100 kHz.

In the present invention, the heat generated by the current in the step (S2) may also use heat by the pulse current, the pulse current at this time, it is preferable to use a pulse current of 1 ㎲ ~ 1 주기 period, The heating rate of the heat is carried out at 100 ~ 5000 ℃ / min, the press molding in the step (S2) is preferably carried out while applying a pressure of 10 ~ 1000 MPa, the press molding and sintering is in the vacuum state of 0.01 ~ 1 Torr You can also do

In addition, the observation of the change in the shrinkage length of the nanopowder in the step S3 can be performed by a molding displacement differential transformer (LVDT).

In the above, the amount of metal carbide when carrying out the method of the present invention is about 10-20 g.

The present invention is also a nanostructure metal carbide prepared by the above method, the metal carbide is titanium carbide (TiC), tungsten carbide (WC), silicon carbide (SiC), tantalum carbide (TaC), vanadium carbide (VC) It provides, at least one nanostructure metal carbide selected from the group consisting of niobium carbide (NbC).

According to the method of manufacturing a nanostructure metal carbide according to the present invention as described above, since the powder generated by the ball milling method so that the particle size has a nanostructure, the heat generated by the induced current or the pulse current is applied, so that the moisture, For example, high temperature press forming and sintering operations can be performed within 2 to 5 minutes, and as a result, it is possible to produce nanostructure metal carbides having more limited grain growth and excellent mechanical properties than conventional ones. .

Hereinafter, with reference to the accompanying drawings, the present invention will be described in more detail through preferred embodiments.

Nanostructured metal carbide production method according to the invention is carried out as follows.

First, the specific metal carbide powder is nanopowdered by ball milling so that the particle size has a nanostructure.

The metal carbide may be selected from titanium carbide (TiC), tungsten carbide (WC), silicon carbide (SiC), tantalum carbide (TaC), vanadium carbide (VC), niobium carbide (NbC), and the like.

The metal carbide powder as described above is preferably nano-powdered so as to have a particle size of 100 nm or less in order to speed up the production and sintering rate of the nanostructure metal carbide. In the present invention, any method may be applied as long as it is a method capable of nanopowdering these powders, but it is most preferable to nanopowder these mixtures by a ball milling method, which is different from other grinding methods. Otherwise, the energy applied during powder preparation is large enough to be suitable for nanoning the powder.

The nano-powdered carbide as described above is then subjected to heat generated by an external current, for example, heat and pressure generated by an induced current or a pulsed current, whereby the nanostructured carbide is pressed and sintered to form a nanostructured metal. Carbide is produced. In this case, the nanostructure metal carbide production is preferably made in the atmospheric state or vacuum state, when performing in the vacuum state can be set differently depending on the material, but it is good to maintain at 0.01 ~ 1torr, if the vacuum degree is good, good sintering by oxidation inhibition Since the material can be obtained, but the manufacturing time is high and the apparatus cost is high, the degree of vacuum must be varied according to the material, and the range is good in the above range, and most preferably, 0.04 torr is maintained to suppress the oxidation of the metal.

In addition, in the press molding, the pressure is preferably added at 10 to 1000 MPa, but it is possible at normal pressure. If the pressure range is less than 10 MPa, there is a problem that the specimen can not be sufficiently densified, and if the pressure range exceeds 1000 MPa, there is a problem in that the manufacturing cost of manufacturing a device for manufacturing nanostructure metal carbide is high.

In addition, in the state in which the pressure is added, the nanostructure carbide is press-molded and sintered by applying heat generated by an induced current or a pulse current, and specifically, the nanostructure carbide is not in contact with the outside of the nanostructure carbide. Applying a high frequency induction current to a conductive metal coil such as, for example, a copper coil surrounding the copper coil, and indirectly heating and pressurizing and sintering the nanostructure mixture by Joule heat generated by the induced current, or The nanostructure carbide may be heated, press-molded and sintered by Joule heat generated by pulse current applied to the die member in which the nanostructure carbide is accommodated.

Here, the frequency of the high frequency induction current applied to the external coil when using the high frequency induction current is preferably 1 kHz to 100 kHz, which may vary depending on the size of the sintered specimen, and the larger the specimen, the penetration of the induced current. The depth must be large, so the frequency must be lowered. In addition, the period of the pulse current when using the pulse current is preferably 1 ㎲ ~ 1, because, as a result of the experiment, the short pulse period is easy to trap the trapped gas and sintered well. At this time, the frequency range of the induced current should be properly adjusted according to the size of the specimen because the penetration depth of the high frequency current depends on the frequency. In addition, the heating rate by heat generated indirectly by the high frequency induction current or heat generated by pulse current is preferably set to 100 to 5000 ° C./min, and when the heating rate is less than 100 ° C./min, sintering is performed. It takes a long time to cause a problem that the grain grows, and if it exceeds 5000 ℃ / min because the heating rate is too fast there is a problem that the thermal stress occurs in the specimen.

When press-molding and sintering the nanostructure mixture while heating the induction current heating / pressurizing sintering method or the pulse current heating / pressurizing sintering method as described above, the nanostructured carbide is densified by the continuously applied pressure and the shrinkage length is reduced. When the densification is completed and there is no longer a change in contraction length, at this point, the induced current or pulse current is blocked and the pressure is removed.

From the moment of applying pressure, induction current or pulse current to the nanostructure mixture as described above, from the moment when the nanostructure mixture reacts to solid phase and is fully densified, the moment when the pressure, induction current or pulse current is removed is no longer changed. It takes about 2 to 5 minutes, because if less than 2 minutes the thermal stress on the specimen is difficult to obtain the nanostructure, according to the present invention, the dense nanostructure metal carbide without pore formation in the carbide according to the present invention It can be produced in a short time.

Thereafter, the nanostructure carbide is cooled to room temperature, and the cooling may be performed according to a conventional method.

In addition, since the post-treatment process is not required after the preparation of the nanostructure metal carbide, the nanostructure metal carbide can be manufactured in a short time using a single process.

Nanostructure metal carbide of the present invention as described above can be produced using an induction current heating / pressure sintering machine, or a pulse current heating / pressure sintering machine. Referring to this with reference to the drawings, Figure 1 is an induction current heating / pressure sintering machine used to implement the nanostructure metal carbide manufacturing method according to the present invention.

Referring to FIG. 1, the induction current heating / pressurizing sinterer 100 includes a die member 110, a pressing member 120, and an induction current generating member 130.

The die member 110 is for accommodating nano-powdered metal carbide, preferably a graphite die, a through hole is formed therein, the nano-structure carbide is stored in the central portion in the through hole To form. In addition, it is preferable to maintain the vacuum degree inside the through hole filled with the nanostructure carbide in the die member 110 to be 0.01 to 1 torr.

The pressing member 120 is to apply the pressure transmitted from the external pressure generating device to the nanostructure carbide inside the through hole. The pressing member 120 is inserted into upper and lower portions of the through hole to apply uniaxial pressure to the nanostructure carbide. That is, the nanostructure carbide is densified by the pressure exerted by the pressing member 120, and the through hole and the pressing member 120 are operated in order to measure the change in shrinkage length of the nanostructure carbide, which is the degree of completion of the densification. A linear variable differential transformer (LVDT) may be attached to the portion. The pressure through the pressing member 120 is preferably added to 10 ~ 1000MPa.

The induction current generating member 130 is formed to be spaced apart from the periphery of the die member 110, and serves to generate an induction current. The induction current generating member 130 is made of a high frequency current coil, indirect heat is applied to the die member 110 and the nanostructure carbide by the induction current generated by the current applied to them, thereby forming a heat-forming and Sintering takes place.

At this time, the induction current frequency is preferably 1 to 100 kHz to flow to the induction coil, the heating rate by the induced current generated in this way is preferably 100 ~ 5000 ℃ / min.

2 is a die assembly of a pulsed current heating / pressurizing sintering machine used to implement the method for producing nanostructured metal carbide according to the present invention.

Conventional pulse current heating / pressure sintering machine is composed of a water-cooled vacuum chamber, a die assembly, a pulse current supply device, a pressurization device, a vacuum device, a cooling device, and various control and measuring devices. The water-cooled vacuum chamber is a container for controlling the atmosphere during heating / pressing molding and sintering. The water-cooled vacuum chamber is made of stainless steel, and has a double container having a viewing window for internal monitoring and a door for mounting the die assembly. Flow.

Referring to FIG. 2, the die assembly 200 of the pulse current heating / pressurizing sintering machine is a top and bottom press block made of high purity graphite, a cylindrical die 220, and an insulating material such as alumina. It is composed of 230, the powder is filled in the inner space generated by the upper and lower punch 210 and the cylindrical die 220, the vacuum degree of the process factor is preferably about 0.01 ~ 1torr, depending on the material is possible in the atmosphere. The pulse current supply device 300 supplies a pulse current to the specimen by the operation of the control switch 310, the pressurization device applies a uniaxial pressure to the punch 210 of the die assembly 200 through the pressure block 230, On the moving part of the hydraulic cylinder is fitted a linear displacement differential transformer (LVDT) which measures the change in length of the specimen. The pressure through the punch 210 is determined experimentally to the extent that the specimen can be sufficiently densified, and is preferably added at 10 to 1000 MPa. The pulse current is applied until the densification of powder occurs during sintering after heating / pressing molding, and the period is preferably 1㎲ ~ 1㎳, and the heating rate by pulse current is 100 ~ 5000 ℃ / min. desirable. Conventional rotary pumps and cooling water pumps may be used as the vacuum device and the cooling device, respectively. The control and measurement device controls process factors such as pressure and current, and measures various data in process progress.

The following examples are provided to aid the understanding of the present invention and are not intended to limit the present invention to the following examples.

Example 1

15 g of tungsten carbide raw powder having a particle size of 1.3 μm was prepared as a nano powder having a size of about 45 nm by ball milling. After the nanopowder was filled into the graphite die of the die member 110 of FIG. 1, a mechanical pressure of 80 MPa was applied and a vacuum atmosphere of 0.04 torr was made.

A high frequency induction current heating / pressurization sintering was started by applying a current of 14.4 mA to the external coil, that is, the induction current generating member 130 of FIG. At this time, the heating rate by Joule heat generated by the induction current heating was to be 500 ℃ / min.

After the heating / pressing start, the shrinkage length change of the specimen during the sintering was observed with a linear displacement differential transformer (LVDT) to remove the induced current and pressure at the point of stabilization without changing the length, and then cooled to room temperature A ceramic having a tungsten carbide grain size of 87 nm was obtained.

After the ball milling of the tungsten carbide raw powder in Example 1, before the high frequency induction current heating / pressure sintering, and after the high frequency induction current heating / pressure sintering changes in temperature and shrinkage length, SEM (Scanning Electron Microscope) photos, and XRD (X-ray diffraction) patterns are shown in FIGS. 3 to 5, respectively.

Figure 3 shows the temperature change (■) and shrinkage displacement (□ ◇ △ ○) according to the heating time by high-frequency induction current heating / pressure sintering, it can be seen that sintering occurs at a low temperature as the ball milling time is longer. . As can be seen from Figure 3, according to the present invention using a high-frequency induction current heating / pressure sintering method in a short time within 3 minutes in a compact nanostructure metal carbide of a dense nano structure with almost no pores at 1250 degrees It indicates that the preparation.

Fig. 4 (a) is an SEM photograph showing a raw material powder of about 45 nm after ball milling, and Fig. 4 (b) is an SEM photograph after heating / pressurizing sintering. In FIG. 4 (a), fine tungsten carbide having many pores was dispersed after ball milling, but after heating / pressurizing sintered, a dense tungsten carbide phase was obtained as shown in FIG. 4 (b), from which heating with little change in shrinkage length was obtained. It can be seen that the heating / pressurization sintering is completed at the temperature.

Figure 5 is a photograph showing the XRD pattern, the crystal grain size of about 87nm from the half width of the X-ray diffraction peak, it was confirmed that the tungsten carbide of the desired nanostructure was obtained by heating / pressure sintering. The hardness and fracture toughness of this sintered material were 3020 kg / mm <^2> and 8.1 Mpa.m ^1/2 , respectively.

Example 2

Nanostructure metal carbide manufacturing method using the pulse current heating / pressure sintering machine is made of five steps, each step is as follows.

Step 1: The powder is ball milled to a size of 30 nm or less.

Step 2: The ball milled nanopowder is filled and mounted in a graphite die, ie, the cylindrical die 220 of FIG. 2, and brought to a vacuum of about 0.4 torr.

Step 3: Applying a pressure of 80 MPa to the nano powder to form a molded body.

Step 4: Applying a constant pulse current to the graphite die and the specimen by continuously applying a pressure of 80 MPa to the molded body, heating the specimen at a heating rate of 1000 ° C./min by Joule heat, and at this time, heating / press molding starts. After sintering, the shrinkage length change of the specimen was observed with a linear displacement differential transformer (LVDT) to remove the pulse current and pressure at the point of stabilization without changing the length.

Step 5: Cool the specimen to room temperature.

The method for producing a nanostructure metal carbide according to the present invention described above is not limited to the above embodiments, and has a general knowledge in the field of the present invention without departing from the gist of the present invention as claimed in the following claims. Anyone who grows up will see that it includes a range of changes that can be made.

1 is an induction current heating / pressure sintering machine used to implement the method for producing nanostructured metal carbide according to the present invention.

2 is a die assembly of a pulsed current heating / pressurizing sintering machine used to implement the method for producing nanostructured metal carbide according to the present invention.

Figure 3 is a graph showing the temperature change (■) and shrinkage displacement (□ ◇ △ ○) according to the heating time by the induced current.

4 is a SEM (Scanning Electron Microscope) photograph of the powder (a) nano-powdered by the ball milling method and a SEM photograph of the nanostructured tungsten carbide (b) prepared after heating / pressurizing sintering by induction current.

5 is an X-ray diffraction (XRD) pattern of nanostructured tungsten carbide (b) prepared after heating / pressurizing sintering by powder (a) nanopowdered by ball milling method and induced current.

<Description of the symbols for the main parts of the drawings>

100: induction current heating / pressure sintering machine 110: die member

120: pressing member 130: induction current generating member

200: die assembly 210: punch

220: cylindrical die 230: pressure block

300: pulse current supply device 310: control switch

Claims (13)

Ball milling the metal carbide powder to nano-powder the particle size to have a nanostructure (S1); Press molding and sintering while applying heat generated by current to the nanopowder in the step (S1) (S2); And Blocking the current if there is no change in the shrinkage length of the nano-powder and cooling the press-formed and sintered nanostructures to room temperature until just before the current blocking (S3), characterized in that it comprises a nanostructure metal carbide manufacturing method. The method of claim 1, wherein the metal carbide in the step (S1) is titanium carbide (TiC), tungsten carbide (WC), silicon carbide (SiC), tantalum carbide (TaC), vanadium carbide (VC), niobium carbide ( NbC) nanostructure metal carbide manufacturing method characterized in that at least one member selected from the group consisting of. The method of claim 1 or 2, wherein the nano-powder of the metal carbide in the step (S1) is characterized in that the particle size is 100nm or less. The method of claim 1, wherein the pressing and sintering in the step (S2) is a nanostructure metal carbide manufacturing method, characterized in that performed for 2 to 5 minutes. The method of claim 1, wherein the heat generated by the current in the step (S2) is a nanostructure metal carbide manufacturing method, characterized in that the heat by the induced current. The method of claim 5, wherein the induced current is a nanostructure metal carbide manufacturing method, characterized in that the induced current having a frequency of 1kHz ~ 100kHz. The method of claim 1, wherein the heat generated by the current in the step (S2) is a nanostructure metal carbide manufacturing method, characterized in that the heat by the pulse current. The method of claim 7, wherein the pulse current is a nanostructure metal carbide manufacturing method, characterized in that the period of the pulse current of 1㎲ ~ 1㎳. 9. The method of claim 1, wherein the heating rate of the heat is 100 to 5000 ° C./min. The method of claim 1, wherein the pressing in the step (S2) is a nanostructure metal carbide manufacturing method, characterized in that is carried out while applying a pressure of 10 ~ 1000MPa. The method of claim 1, wherein the pressing and sintering in the step (S2) is a nanostructure metal carbide manufacturing method, characterized in that carried out in a vacuum of 0.01 to 1 Torr. The method of claim 1, wherein the observation of the change in shrinkage length of the nanopowder in step S3 is performed by a linear displacement differential transformer (LVDT). Claims 1, 2, 4, 5, 6, 7, 8, 10, 11, 12 prepared by the method of any one of the nanostructured metal carbide, the metal carbide is titanium carbide (TiC), tungsten carbide (WC), silicon carbide (SiC), tantalum carbide (TaC), vanadium carbide (VC), niobium carbide (NbC) nanostructure characterized in that at least one selected from the group consisting of Metal carbide.

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