JP2013082965A - Method of producing porous metal, and porous metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing porous metal, capable of producing the porous metal at a low cost.SOLUTION: The method of producing the porous metal 13 comprises: a step of blending a spacer 12 and metal 11 or an alloy in a prescribed blend ratio; a step of sintering the blend of the spacer 12 and the metal 11 or the alloy by virtue of friction and a pressure; and a step of subsequently removing the spacer 12 to obtain the porous metal 13 comprising the metal 11 or the alloy.

Description

  The present invention relates to a porous metal manufacturing method and a porous metal obtained by this manufacturing method.

  Porous metal including many pores is lightweight, and has excellent impact energy absorption and sound deadening properties. It is attracting attention as an ultralight and multifunctional material in various fields such as automobiles, railways, aerospace, and architecture. Yes.

Porous metal has “open cell type” (continuous pores, open pores) where the interface between pores is open, and “closed cell type” (independent pores, closed pores) where the pores are separated from each other. is there.
Both types are lightweight members, but the open cell type is suitable for heat dissipation materials and filters because the open cell type is a continuous hole, and the closed cell type is suitable for soundproofing materials and electromagnetic shielding materials.

  As a method for producing porous metal, for example, a foaming agent is mixed into a base metal to produce a precursor (foamed metal precursor), and the precursor is heated to decompose the foaming agent to generate gas. Thus, a so-called precursor method has been proposed in which a base material softened by the generation of gas is expanded (see, for example, Patent Documents 1 to 3).

  However, in the precursor method using a foaming agent, since the foaming agent is expensive, the manufacturing cost of the porous metal increases.

  As a method for producing a porous metal without using a foaming agent, a spacer method is proposed in which a base metal and a spacer are mixed and sintered, and then the spacer is removed to produce a porous metal ( For example, see Patent Literature 4 and Non-Patent Literature 1).

JP 2007-61865 A German Patent Application No. 1048360 German Patent Application No. 4101630 JP 2004-156092 A

Y.Y.Zhao and D.X.Sun: Scr Mater, 2001, vol. 44, pp. 105-110

  However, in the conventionally proposed spacer method, heating from the outside is performed for sintering, and thus a heating heat source is required, which increases the manufacturing cost.

  In order to solve the above-described problems, the present invention provides a method for producing a porous metal that makes it possible to produce the porous metal at a low cost. Moreover, the porous metal obtained by this manufacturing method is provided.

  The method for producing a porous metal of the present invention is a method for producing a porous metal having pores in a base material made of a metal or an alloy, and a step of mixing a metal or an alloy with a predetermined mixing ratio and a spacer. And sintering the mixed metal or alloy and spacer by friction and pressure, and then removing the spacer to leave a porous metal made of metal or alloy.

In the method for producing a porous metal of the present invention, the spacer is water-soluble, and the spacer can be removed by immersing in water.
In the method for producing a porous metal of the present invention, a metal or alloy plate and a spacer plate can be mixed at a predetermined mixing ratio.

  The porous metal of the present invention is a porous metal having pores in a base material made of a metal or an alloy, and the pores in the base material are different in a part and a part other than the part.

  In the porous metal of the present invention, a part of the pores may have a shape that is longer than that of the part other than the part.

  According to the porous metal manufacturing method of the present invention described above, the mixed metal or alloy and the spacer are sintered by friction and pressure, and then the spacer is removed to leave the porous metal. Since sintering is performed by friction and pressure, it is possible to sinter at a much lower temperature and in a shorter time than the sintering conditions used in the conventional spacer method.

  According to the structure of the porous metal of the present invention described above, since the pores in the base material are different in a part and a part other than this part, there is a difference in strength characteristics in a part and other parts. Have.

According to the above-described porous metal manufacturing method of the present invention, a heating heat source is not required, so that the manufacturing equipment can be simplified and the manufacturing cost can be reduced as compared with the conventional spacer method. .
In addition, the sintering can be performed at a much lower temperature than the sintering conditions used in the conventional spacer method, and the time can be shortened. Thereby, the energy required at the time of manufacture can be reduced significantly, and also in this respect, the manufacturing cost can be reduced.

  According to the porous metal of the present invention, since there is a difference in strength characteristics in a part and other parts, it can be used as a functionally gradient material using the difference in strength characteristics.

  In particular, when a metal or alloy plate material and a spacer plate material are mixed at a predetermined mixing ratio, the porous metal can be enlarged according to the size of the plate material.

It is a manufacturing-process figure of one Embodiment of the manufacturing method of the porous metal of this invention. AC is a manufacturing process diagram of another embodiment of the method for manufacturing a porous metal of the present invention. It is a manufacturing-process figure of 1 process of the Example of this invention. It is a figure which shows the relationship between the washing time and the removal rate of NaCl. (A)-(d) It is a X-ray CT figure of porous Al. (A)-(c) It is an electron micrograph of porous Al. (D) It is a microscope picture of NaCl (spacer). It is a figure which shows the compression characteristic of porous Al. It is a manufacturing-process figure of the conventional manufacturing method of AE porous metal.

  Hereinafter, the best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described.

  The present invention is a method for producing a porous metal by applying shearing force, frictional heat, and pressure to a metal material and a spacer by friction and pressure, sintering the metal material, and then removing the spacer.

Here, FIGS. 8A to 8E show manufacturing process diagrams of the spacer method, which is a conventionally proposed method for manufacturing a porous metal.
First, as shown in FIG. 8A, a metal fine powder 11 of a porous metal raw material such as aluminum and spacer particles 12 such as a salt (sodium chloride) are prepared.
Next, as shown in FIG. 8B, the metal fine powder 11 and the spacer particles 12 are mixed by using a stirring blade 22 or the like in the container 21.
Next, as shown in FIG. 8C, the mixed product is put into a die (formwork) 51 to be in a high temperature (for example, 610 ° C.) pressure from above and below by a punch (pressing material) 52 (for example, 200 MPa). Add and sinter. Thereby, the metal which contains the spacer particle | grains 12 inside is formed.
Thereafter, as shown in FIG. 8D, the metal 13 containing the spacer particles 12 inside is immersed in water 25 to remove the salt of the spacer particles 12 and leave the metal 13.
In this manner, as shown in FIG. 8E, the porous metal 10 in which the pores 13A are formed inside the metal 13 can be manufactured.

In contrast to the above-described conventional method, a method of performing a treatment for about 10 minutes with a discharge plasma in vacuum has also been proposed. This manufacturing method is called a spark plasma sintering (SPS) method.
In addition, since the above-described conventional method is sintered by applying high temperature and pressure, an external heat source, pressing equipment, and the like are required, so that the manufacturing apparatus becomes complicated and the manufacturing cost increases.

  In contrast, in the present invention, instead of sintering at high temperature and pressure, sintering is performed using friction and pressure.

1A to 1E show manufacturing process diagrams of an embodiment of the porous metal manufacturing method of the present invention.
First, as shown in FIG. 1A, a metal fine powder 11 made of a porous metal such as aluminum and spacer particles 12 such as a salt (sodium chloride) are prepared.
Next, as shown in FIG. 1B, the metal fine powder 11 and the spacer particles 12 are mixed by using a stirring blade 22 or the like in the container 21.
The process up to this point is the same as the conventional manufacturing method shown in FIG.
Next, as shown in FIG. 1C, friction and pressure are used to press the metal fine powder 11 and spacer particles 12 housed in the mold 23 while rotating the jig 24, thereby causing friction. The fine metal powder 11 and the spacer particles 12 are sintered with heat. Thereby, the metal which contains the spacer particle | grains 12 inside is formed.
Thereafter, as shown in FIG. 1D, as in the conventional method, the metal 13 including the spacer particles 12 therein is immersed in water 25 to remove the salt of the spacer particles 12 and leave the metal 13.
In this way, as shown in FIG. 1E, the porous metal 10 in which the pores 13A are formed inside the metal 13 can be manufactured.

  In the present invention, not only the fine metal powder 11 as shown in FIG. 1 but also a porous metal can be produced using a plate-like metal.

As another embodiment of the method for producing a porous metal of the present invention, production process diagrams of a production method in the case of using a plate-like metal are shown in FIGS.
First, as shown in FIG. 2A, a metal plate 14 made of a porous metal such as aluminum and a spacer plate 15 made of a salt (sodium chloride) are prepared. The spacer plate 15 can be produced, for example, by using a commercially available square salt or by sintering the salt.
Next, as shown in FIG. 2B, the metal plate 14 and the spacer plate 15 are accommodated in the mold 23 at a predetermined ratio. In FIG. 2B, the metal plate 14 and the spacer plate 15 are arranged at a ratio of 1: 1, but other ratios may be used.
Next, as shown in FIG. 2C, by using friction and pressure, the jig 24 is rotated against the metal plate 14 and the spacer plate 15 while being pressed, so that the metal and the spacer can be moved with friction and pressure. Are mixed and sintered at the same time. Thereby, a metal including a spacer is formed.
Thereafter, as shown in FIG. 1D, the metal containing the spacer is immersed in water to remove the salt of the spacer, leaving the metal.
In this way, a porous metal in which pores are formed inside the metal can be manufactured.

The metal fine powder 11 and the metal plate material 14 are not limited to aluminum, and various metal materials can be used. For example, a metal such as copper or magnesium or an alloy containing the metal can be used.
According to the present invention, since the sintering can be performed at a relatively low temperature, the present invention can be applied to a magnesium alloy or the like that has a risk of powder explosion.

In the manufacturing method of the present invention, since friction and pressure are used, the porous metal can be produced in the shape of a large plate.
Further, by moving the jig 24 in the same manner as the NC milling machine, it is possible to further increase the size.
In a conventionally proposed manufacturing method such as the SPS method, it is difficult to increase the size of the porous metal.

In the manufacturing method of the present invention, since a spacer is used, it is possible to produce a porous metal with a thin plate material of about 1 mm. Since the pore diameter can be easily controlled by the spacer particles, for example, if the pore diameter is about several tens of μm to several hundreds of μm, a porous metal with a thin plate material can be produced.
On the other hand, with a conventional manufacturing method using a foaming agent, it is difficult to produce a porous metal with a thin plate material.

  As a material for the spacer, various water-soluble salts can be used in addition to sodium chloride. Water-soluble substances such as organic fertilizers and sugars can also be used.

The manufacturing method of the present invention uses friction and pressure to sinter the metal and the spacer, so that the following effects can be obtained by the manufacturing method of the present invention.
(1) The metal of the raw material is not limited to fine powder, and a plate material and metal cutting waste can also be used as the raw material. If metal cutting scraps are used, recyclability is also improved.
(2) Heating from the outside is not necessary, and a melting process, a foaming process, and the like are not necessary, and thus energy efficiency is high. Further, it can be sintered at a much lower temperature (about 200 ° C. or less) and in a shorter time (about several minutes) than the sintering conditions used in the conventional spacer method. From these things, the energy required at the time of manufacture can be reduced significantly. And since a heating heat source becomes unnecessary, compared with the conventional spacer method, since manufacturing equipment can be simplified, manufacturing cost can be reduced.
(3) Sintering is possible using a normal milling machine or lathe. Further, it can be sintered at high speed by a simple process.
(4) Since the frictional heat generated by the rotating body is used, a shearing force is applied to the metal surface, and the metal structure can be refined. Moreover, since it is a solid-phase process, the coarsening of a crystal grain can be prevented. Furthermore, since the required time can be shortened, the coarsening of the crystal grains can be prevented in this respect. For these reasons, the mechanical properties of the porous metal can be improved.
(5) In the case of a metal whose surface is easily oxidized, such as aluminum, the oxide film on the surface can be destroyed by friction and pressure. As a result, the metals are easily bonded to each other, so that a discharge plasma treatment or the like in vacuum for removing the oxide film becomes unnecessary.
(6) It is easy to produce a functionally gradient material using different materials. For example, it is possible to change the type of metal, change the size of the pores, or make a part of the porous metal and the rest be a metal material without pores.
(7) It is possible to manufacture a porous metal in which the surface in contact with the jig (tool) and the vicinity thereof and the other portions have different shapes of pores in the base material. In these portions, since the pores have different shapes, there is a difference in strength characteristics.

  In the production method of the present invention, frictional heat generated by a rotating body is used, so that a shearing force is applied to the surface of a metal such as aluminum, and the oxide on the surface can be destroyed. And it can be sintered in a short time. Therefore, it is predicted that the tensile strength and the collision energy absorption amount of the porous metal manufactured by this method are improved to about three times that of the porous metal manufactured by the spacer method.

  Porous metal was actually produced by the production method of the present invention, and its characteristics were examined.

First, Al powder (particle diameter of about 20 μm) was prepared as the metal fine powder 11 in FIG. 1A, and NaCl powder was prepared as the spacer particles 12.
Next, these powders were mixed at a ratio (mass ratio) of Al: NaCl = 3: 7 as shown in FIG. 1B.
Next, instead of the mold 23 shown in FIG. 1C, as shown in FIG. 3, an A1050 plate (Al plate) 26 having a thickness of 14 mm in which a circular hole 27 having a diameter of 14 mm is formed is used. The mixed powder was added.
Then, a cylindrical SUS304 jig (tool) 24 having a flat tip at a diameter of 16 mm was pushed from above the hole 27 while rotating. The rotation speed of the jig (tool) 24 was 950 rpm, the feed rate was about 1 mm / min, and the pushing amount was 3.5 mm, and the jig (tool) 24 was held in the A1050 plate 26 for 30 seconds.
The raw material powder is sintered by the frictional heat and shear force generated by the friction between the jig (tool) 24 and the base material (A1050 plate and Al powder) during pressing, and the pressure during pressing.
After sintering, it was cut into a size of 5 mm × 5 mm × 5 mm by machining.
Then, as shown to FIG. 1D, it was immersed in the water 25 and washed with water. Thereby, the NaCl of the spacer particles 12 is dissolved and removed in the water 25, pores are formed, and porous Al is produced.
In this way, a porous Al sample was prepared.

At this time, the CT image of the sample and the measurement of the mass were performed before the water washing and at each time point of the water washing time of 5 min, 10 min, 15 min, 30 min, 60 min, 90 min, and 120 min.
Imaging and measurement at each washing time were performed by taking a sample from the water 25 each time. Unnecessary moisture was removed as needed.
The CT image was captured using a microfocus X-ray CT system (SMX-225CT manufactured by Shimadzu Corporation), and the process of removing NaCl from the sample was observed.
The measurement result of the mass at each time point was compared with the measurement result of the mass before washing with water, and the removal rate of NaCl was obtained from the ratio of these masses and the original mixing ratio (Al: NaCl = 3: 7).

Furthermore, the produced porous Al was observed with a scanning electron microscope (SEM).
As a comparative control, porous Al was produced by the above-described discharge plasma sintering (SPS) method and compared.

Furthermore, the produced porous Al was subjected to a compression test to evaluate the compression characteristics.
The compression test conditions were a crosshead speed of 0.5 mm / min at room temperature.

FIG. 4 shows the relationship between the water washing time and NaCl removal rate in the produced porous Al.
5A to 5D show X-ray CT images of porous Al before washing with water (0 min) and with washing times of 30 min, 60 min, and 120 min.

From FIG. 4, it can be seen that NaCl in the porous Al is rapidly removed immediately after the start of water washing, but it becomes difficult to remove with the passage of time.
From FIG. 5A to FIG. 5D, it was found that NaCl in the porous Al was removed at a substantially uniform rate in all directions. Thereby, NaCl is removed from the outside of all surfaces. However, as it approaches the center of the porous Al, it becomes difficult for a sufficient amount of water to reach the back, and it is considered that a long time is required for the removal.

(Cross section observation)
In the porous Al produced in the above-described embodiment, the contact surface side with the jig (tool) 24 is the upper part, and the surface side farthest from the jig (tool) 24 is the lower part.
Then, an electron micrograph was taken of the upper and lower parts of the porous Al produced in the example, a sample produced by mixing Al and NaCl powders at a ratio of 3: 7 by the SPS method, and the NaCl powder used.
Photographs obtained by photographing are shown in FIGS. 6 (a) to 6 (d). 6A is a photograph of the upper part of the porous Al of the example, FIG. 6B is a photograph of the lower part of the porous Al of the example, and FIG. 6C is a sample produced by the SPS method. FIG. 6 (d) is a photograph of the NaCl powder used.

As can be seen by comparing FIG. 6A and FIG. 6B, the porous Al produced in the example has different pore shapes at the upper part and the lower part. That is, as shown in FIG. 6A, the upper pores of the porous Al have an elongated shape.
Usually, in the powder sintering method such as the SPS method, as shown in FIG. 6C, the shape of the NaCl powder used as the spacer has a pore shape almost transferred.
From FIG. 6 (b), the lower part of the porous Al of the example has a pore shape similar to that of the sample produced by the SPS method of FIG. 6 (c).

The reason why the pore shape of the upper part of the porous Al is different from that of the lower part is considered to be due to the influence of the shearing force by the jig (tool) 24 that rotates during sample preparation. And it is estimated that this shearing force deformed the NaCl powder into an elongated shape, and as a result, the pores became elongated.
On the other hand, only the frictional heat and the indentation pressure were applied to the lower part of the porous Al, and the shearing force was not transmitted. Therefore, it is considered that the pore shape was different from the upper part.

Comparing FIG. 6 (b) and FIG. 6 (c), it has a similar pore shape and almost coincides with the shape of the NaCl powder in FIG. 6 (d). It can be seen that is formed.
From this, it is considered that the raw material powder can be sintered also by frictional heat and indentation pressure due to the rotation of the tool, as in the case of using the SPS method.
Further, as a result of observing the cell wall in FIG. 6 (b) in detail, the presence of minute holes in the cell wall was confirmed. It is thought that NaCl in the porous Al was removed by washing with water through this hole.
In addition, although the particle size of the used NaCl powder is unknown, in the range of the photograph of FIG.6 (d), it is the range of 200-500 micrometers.

(Compression test)
FIG. 7 shows the compression test result of porous Al produced according to the example.
As can be seen from FIG. 7, three regions of an elastic region, a plateau region, and a densified region were confirmed as in the case of conventional porous aluminum.
However, the deformation at the time of compression started from the lower part of the porous Al, the upper part was deformed in the latter half of the plateau region, and hardly deformed while the lower part was deformed.
This is thought to be due to a slight difference in strength in the porous Al due to the difference in the pore shape between the upper and lower pores in the porous Al in FIGS. 6 (a) and 6 (b).

  Therefore, it can be seen that in the above-described embodiment employing the manufacturing method of the present invention, porous metals having different pore shapes and different strength characteristics are obtained between the upper portion and the portion other than the upper portion.

  The present invention is not limited to the above-described embodiment, and various other configurations can be taken without departing from the gist of the present invention.

10 porous metal, 11 fine metal powder, 12 spacer particles, 13 metal, 13A pores, 14 metal plate, 15 spacer plate, 22 stirring blade, 23 mold, 24 jig, 25 water, 26 A1050 plate (Al plate) , 27 holes

Claims (5)

A method for producing a porous metal having pores in a base material made of a metal or an alloy,
A step of mixing the metal or the alloy and a spacer with a predetermined mixing ratio;
Sintering the mixed metal or alloy and the spacer by friction and pressure;
And removing the spacer to leave a porous metal made of the metal or the alloy.   The method for producing a porous metal according to claim 1, wherein the spacer is water-soluble, and the spacer is removed by being immersed in water.   The method for producing a porous metal according to claim 1, wherein the metal or the alloy plate and the spacer plate are mixed at a predetermined mixing ratio. A porous metal having pores in a base material made of metal or alloy,
A porous metal in which pores in the base material are different in a part and a part other than the part.   The porous metal according to claim 4, wherein the part of the pores has an elongated shape than the part of the pores other than the part.