KR101181022B1 - Method for Making Nanostructured Ti from Titanium Hydride Powder - Google Patents

Abstract

Disclosed are a method for producing titanium (Ti) having a nanostructure from titanium hydride (TiH ₂ ) powder and a nanostructured Ti produced therefrom. After the screen in the present invention, a nano-sized powders by ball milling the TiH ₂ powder to have a nanostructured particle size method, and the heat generated by the induced current in the TiH ₂ powder having the nano structure wherein the nanostructure TiH ₂ powder The nanostructured TiH ₂ powder is press-molded and sintered until there is no change in shrinkage length, thereby producing Ti having a nanostructured particle size.

According to the present invention, since titanium hydride (TiH ₂ ) is subjected to heat generated by an induced current to the powdered TiH ₂ powder, which is powdered by ball milling so that the particle size has a nanostructure, a high temperature within a few minutes, for example, 2 to 5 minutes. By performing the pressing and sintering operations of Ti, the grain growth of Ti is relatively limited compared to the prior art, and nanostructured Ti having excellent mechanical properties can be manufactured.

 Ti, TiH₂ powder, nanostructure, press forming, sintering

Description

Method for Making Nanostructured Ti from Titanium Hydrogen Powder {Method for Making Nanostructured Ti from Titanium Hydride Powder}

 The present invention relates to a method for preparing nanostructured Ti from titanium hydride powder, and more particularly, to a method for preparing Ti having a nanostructure and a nanostructured Ti prepared therefrom.

 Titanium is used in various fields such as implants and golf club heads because of its excellent mechanical properties and biocompatibility. However, titanium has a disadvantage of being expensive due to its high reactivity and difficult processing. Typically, Ti is formed by molding Ti powder and then injecting it into a heating furnace by heating and sintering at least 1 hour at a high temperature of about 1,300 ° C or more.

   However, the above method has a disadvantage in that it is not economical because it is produced over a high temperature and a long time, as described above, when the titanium hydride powder is heated at a high temperature for a long time and press-molded and sintered to produce grains of titanium, titanium particles are grown. There is a disadvantage in that the mechanical properties are bad due to the larger size.

The present invention has been made to solve the above-mentioned conventional problems, an object of the present invention is to produce a titanium sintered body from titanium hydride powder which is cheaper than titanium and has good oxidation resistance. The powder of the titanium hydride is powdered to a nano size by a ball milling method so that the particle size has a nanostructure, and the nanostructure powder is applied with heat generated by an induced current until there is no change in the shrinkage length of the nanostructure powder. By pressing and sintering the nanostructured powder, it is possible to finish pressurization and sintering at a high temperature in a short time, thereby providing a method of manufacturing titanium having nanostructures having more excellent grain growth and relatively excellent mechanical properties. have. The present invention also has another object to provide titanium produced by the above method.

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

      Ball milling the titanium hydride powder to nano-powder the particles to have a nanostructure (S1);

       Forming a molded body from the nano powder in the step S1 (S2);

      Pressure molding and sintering while applying heat generated by current to the molded body in the step S2 (S3);

      And if there is no change in the shrinkage length of the nano-powder provides a method for producing a titanium nanostructure comprising the step of blocking the current, and cooling the sintered nanostructure to room temperature just before the current blocking (S4).

In the above, the titanium hydride in the step (S1) is preferably TiH ₂ , nano-powdering in the step (S1) is preferably such that the particle size is 100nm or less.

In addition, the molding of the nano powder in the step (S2) is preferably 30 to 60% of the relative density.

       In addition, the sintering in the step (S3) is preferably performed for 2 to 5 minutes.

      In addition, the heat generated by the current in the step (S3) is a heat generated by the induced current, it is preferable to use an induced current having a frequency of 1 kHz to 100 kHz.

     Pressure molding and sintering in the step (S3) is preferably performed while applying a pressure of 0 to 1,000 MPa,

The press forming and sintering may be performed in a vacuum of 0.01 to 1 Torr.

      In addition, the change in the shrinkage length of the nano-powder in the step (S4) can be observed with a linear variable differential transformer (LVDT).

According to the method for producing a nanostructured titanium according to the present invention as described above, the heat generated by induction current after the titanium hydride powder is formed by nano-powdered by a ball milling method so that the particle size has a nanostructure Since the sintering operation can be performed by a high pressure or no pressure in a few minutes, for example, within 2 to 5 minutes. As a result, the grain growth of titanium is more limited and the mechanical properties are superior to those of the prior art. The titanium of the structure can be manufactured. In addition, by using titanium hydride which is cheaper than titanium and excellent in oxidation resistance, manufacturing cost can be drastically lowered.

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

     Method for producing a nanostructured titanium according to the invention is carried out as follows.

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

The titanium hydride may be used by selecting TiH ₂ .

     The titanium hydride powder as described above is preferably nano-powdered to have a particle size of 100 nm or less in order to speed up the production and sintering speed of the titanium nanostructure. 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 titanium hydrides by a ball milling method. Unlike the method, the energy applied during powder preparation is large enough to be suitable for nanoning the powder.

     The nano-powdered titanium hydride as described above is then subjected to heat generated by an external current, for example, heat and pressure generated by an induced current, whereby the titanium hydride of the nanostructure is press-molded and sintered to Titanium of structure is produced. In this case, it is preferable that the nanostructured titanium is produced in a vacuum state, and when it is performed in the vacuum state, it is preferable to keep it at 0.01 to 1 torr. If the vacuum degree is improved, a good sintered material can be obtained by oxidation inhibition, but the production time Since it takes much time and costs a lot of equipment, the degree of vacuum should be varied depending on the material, and the range is good in the above range, and most preferably, 0.01 tor is maintained to suppress oxidation of the metal.

In addition, when the pressure is sintered, the pressure is preferably added at 10 to 1,000 MPa, but is also possible at normal pressure. If the pressure range is less than 10 MPa, there is a problem in that the specimen cannot be sufficiently densified. There is a problem that the manufacturing cost of the device for producing titanium of the structure takes a lot.

In addition, the sintering is performed by applying heat generated by an induced current to the titanium hydride of the nanostructure in the state where the pressure is added, specifically, the surroundings of the titanium hydride of the nanostructure without being in contact with the outside. A high frequency induction current is applied to a conductive metal coil such as, for example, a copper coil surrounding the coil, and the Joule heat generated by the induction current indirectly heats the nanostructured TiH ₂ powder to pressurize or pressurize it. Sinter.

     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 when the specimen size is large, penetration of the induced current The depth must be large, so the frequency must be lowered. At this time, the frequency range of the induced current should be appropriately 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 due to heat generated indirectly by the high frequency induction current is preferably set to 100 to 5,000 ℃ / min, when the heating rate is less than 100 ℃ / min takes a long time to sinter the crystal grain grows The problem may occur, and when the temperature exceeds 5,000 ° C./min, the heating rate is so fast that thermal stress occurs in the specimen.

      In the induction current heating, pressing or heating and pressureless sintering method as described above, when sintering while heating the titanium hydride powder of the nanostructure, the titanium hydride of the nanostructure is densified by the pressure applied continuously, the shrinkage length is When the densification is completed and the contraction length is no longer changed, at this point, the induced current is cut off and the pressure is released.

     About 2 to 5 minutes from the time when the pressure and induction current is applied to the titanium hydride powder of the nanostructure as described above until the pressure and induction current is removed when the nanostructure powder is completely densified and the shrinkage length is no longer changed. It takes time, because if the time is less than 2 minutes the thermal stress on the specimen is difficult to obtain the nanostructure, according to the present invention it can be produced in a short time without dense titanium nanostructure titanium without pore formation in titanium. .

    Then, the step of cooling the nanostructured titanium to room temperature, the cooling may be carried out according to a conventional method.

    In addition, after the process as described above, after the production of the nano-structured titanium does not require a post-treatment process it can be produced in a short time nanostructured titanium in a single process.

The nanostructured titanium of the present invention as described above can be produced using an induction current heating pressure sintering machine. Referring to the drawings, Figure 1 is an induction current heating-pressurized sintering machine used to implement the method for producing a nanostructured titanium according to the present invention.

    Referring to FIG. 1, the induction current heating and pressure sintering machine 100 includes a die member 110, a pressing member 120, an induction current generating member 130, and a punch 140.

The die member 110 is for accommodating the nano-powdered TiH ₂ , preferably a graphite die, a through hole is formed therein, the inside of the through hole is a nano structure TiH ₂ is stored in the central portion To form. In addition, it is preferable to maintain the vacuum degree inside the through hole filled with the nano structure TiH ₂ 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 TiH ₂ of the nanostructure inside the through hole, and is formed in the upper and lower portions of the through hole to apply uniaxial pressure to the nanostructure TiH ₂ . Will be added. That is, due to the pressure applied by the pressing member 120, the TiH ₂ of the nanostructure is densified, and the through-hole and the pressing member 120 are measured to measure the change in the shrinkage length of the TiH ₂ of the nanostructure, which is the degree of completion of the densification. A linear displacement differential transformer (LVDT) may be attached to the movable portion followed by. The pressure through the pressing member 120 is preferably added to 10 to 1,000 MPa.

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 guide consists of a current generation member 130 is a high-frequency current coils, by the induced current generated by the current applied to them is applied indirectly to the heat of the die member 110 and TiH ₂ of the nanostructures of the nanostructure TiH ₂ Heating molding and sintering are carried out.

    At this time, the induced 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 to 5,000 ℃ / min.

The induction current heating and pressure sintering machine 100 is a high and low graphite upper and lower punch 140, the die member 110, the upper and lower pressing member 120 and the induction current generating member 130 of an insulating material such as alumina. ) And nanostructured TiH ₂ The powder is filled in the inner space generated by the upper and lower punch 140 and the die member 110, and the vacuum degree, which is a process factor, is preferably about 0.01 to 1 torr, and may be in the air depending on the material. A uniaxial pressure is applied to the punch 140 of the die assembly through the pressure member 120, and a linear displacement differential transformer LVDT for measuring a change in length of the specimen is attached to the movable portion of the hydraulic cylinder. The pressure through the punch 140 is determined experimentally enough to sufficiently densify the specimen, and is preferably added at 10 to 1,000 MPa. 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

20 g of TiH ₂ powder having a particle size of 500 mesh was prepared as a nanostructured powder having a size of about 20 nm by using ball milling. After the nanostructured powder was filled in the graphite die of the die member 110 of FIG. 1, a mechanical pressure of 80 MPa was applied thereto, and a vacuum atmosphere of 0.04 torr was made.

    A high frequency induction current heating and pressure 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 700 ℃ / min.

   The shrinkage length change of the specimen during the sintering after the start of heating and pressing molding 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 to finally obtain nano Titanium in a structure was obtained.

   After ball milling the powder of titanium hydride in Example 1, changes in temperature and shrinkage length, SEM (Scanning Electron Microscope) photographs and X-ray diffraction patterns before and after high frequency induction current heating and pressure sintering are respectively shown in FIGS. 4 is shown.

  Figure 2 shows the temperature change and shrinkage displacement according to the heating time by high frequency induction current heating-pressurized sintering, it can be seen that the sintering occurs at a low temperature as the ball milling time is longer. In addition, the shrinkage length of titanium decreases rapidly with heating time, but the shrinkage length of titanium hydride increases rapidly after increasing slowly with heating time. This is thought to be due to the decomposition of titanium hydride when titanium hydride is heated. As can be seen from FIG. 2, according to the present invention, a dense nanostructured titanium having almost no pores at a relatively low temperature of 1,080 ° C. in a short time within 2 to 5 minutes using a high frequency induction heating and pressure sintering method according to the present invention. It indicates that was prepared.

    3 is a SEM photograph after heating and pressure sintering. (a) shows the microstructure of the specimen sintered after milling titanium for 5 hours, and (b) shows the microstructure of the specimen sintered after milling titanium hydrogen compounds for 5 hours. After heating and pressure sintering, a dense nanostructured titanium was obtained. From this, it can be seen that heating and pressure sintering were completed at a heating temperature with little change in shrinkage length. In addition, it was confirmed that titanium having a desired nanostructure was obtained as the grain size of titanium was 50 nm or less.

Figure 4 is a photograph showing the X-ray diffraction pattern (a) and (b) shows the X-ray diffraction peaks of the specimens not sintered titanium and the powder milled for 5 hours, (c) And (d) show the X-ray diffraction peaks of the specimens not milled with titanium hydride and the samples sintered from powder milled for 5 hours. Since the peaks were all titanium, titanium of desired nanostructures could be produced. The hardness of the sintered material thus obtained was about 560 kg / mm 2, which is higher than the titanium hardness of 320 kg / mm 2, which is the conventional micron grain size.

 1 is an induction current heating and pressure sintering machine used to implement a method for manufacturing a nanostructured titanium according to the present invention.

      Figure 2 is a graph showing the temperature change (■) and shrinkage displacement (□) according to the heating time by the induced current.

      3 is a SEM image of a titanium structure prepared after heating and pressurizing sintering by induction current, (a) is a specimen obtained by sintering titanium after 5 hours, and (b) is sintered after milling titanium hydrogen compounds for 5 hours. It is a psalm.

      FIG. 4 is an X-ray diffraction pattern of nanostructured titanium prepared after heating and pressure sintering by induction current, wherein (a) and (b) are sintered specimens after milling titanium for 0 hours and 5 hours, respectively. , (c) and (d) are sintered specimens after milling titanium hydrogen compounds for 0 hours and 5 hours, respectively.

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

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

       120: pressure member 130: induction current generating member

140: punch

Claims (11)

Ball milling the titanium hydride powder to nanopowder the particles to have a nanostructure (S1); Forming a molded body from the nano powder in the step S1 (S2); Pressure molding and sintering while applying heat generated by current to the molded body in the step S2 (S3); And blocking the current if there is no change in the shrinkage length of the nanopowder, and cooling the sintered nanostructure to room temperature immediately before the current blocking (S4). The method of claim 1, wherein the titanium hydride in step S1 is titanium hydride (TiH ₂ ).          The method of claim 1 or 2, wherein the nano-powdering in the step (S1) is to produce a nanostructured Ti, characterized in that the particle size is less than 100nm. The method of claim 1, wherein the press forming and sintering in the step (S3) is performed for 2 to 5 minutes.        The method of claim 1, wherein the heat generated by the current in the step (S3) is a heat produced by the induced current.       The method of claim 5, wherein the induction current has a frequency of 1 kHz to 100 kHz.      The method of claim 1, wherein the heating rate of the heat is 100 to 5,000 ° C./min.      The method of claim 1, wherein the press molding and sintering in the step (S3) is performed while applying a pressure of 0 to 1,000 MPa.      The method of claim 1, wherein the pressure forming and sintering in the step (S3) is carried out in a vacuum of 0.01 to 1 Torr.      The method of claim 1, wherein the change in shrinkage length of the nanopowder in step S3 is observed with a linear displacement differential transformer (LVDT). The nanostructured titanium (Ti) according to claim 1, 2, 4 to 6, or 8 to 10.

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