JP4837304B2 - Boron carbide-containing metal matrix composite having neutron absorption and method for producing the same - Google Patents

Description

  The present invention relates to a boron carbide-containing metal matrix composite material having a recriticality preventing action and a neutron absorption action and useful as a material for transporting or storing a spent nuclear fuel that emits neutrons, and a method for producing the same. .

  As a means to safely transport and store spent nuclear fuel without recriticality and without excessive leakage of radiation, the container itself (eg, a basket for containing fuel assemblies) Various studies have been conducted on the design and materials used. The materials used for these applications are required to have properties such as the ability of the materials themselves to absorb neutrons and the like, and the ability to cool spent nuclear fuel efficiently. As materials for neutron absorption, Al-based alloys and composite materials containing boron, and materials called borals with boron-containing materials sandwiched between Al plates have been widely used. It is used as a constituent material for storage containers.

The method disclosed in Patent Document 1 suppresses the total amount of boron in Al by increasing the concentration of isotope boron ¹⁰ B having a high neutron absorption capability, thereby reducing the neutron absorption effect and mechanical properties of the alloy material. To achieve both. However, the problem is that the isotope boron ¹⁰ B is expensive in price. Further, a material called “boral” that has been used for a long time is uneasy to be used for transporting or storing spent nuclear fuel due to insufficient strength of the boron-containing layer. The method disclosed in Patent Document 2 uses inexpensive B ₄ C as a boron source, and creates a target composite material by pressure sintering with Al powder.
JP 2003-268471 A JP 2001-042089 A

In general, as an inexpensive method for producing a metal matrix composite material, there is a non-pressure permeation method introduced in Patent Document 3. This is a composite of a reinforcing material in a metal matrix. This method is suitable for those with a volume ratio of reinforcement of 50% or more, and the volume ratio of the reinforcement is too high to satisfy the mechanical properties required here, such as elongation, and strengthens B ₄ C. When used as a material, the neutron absorption capacity is excessive. The method of creating a low reinforcing material concentration by the non-pressure permeation method is disclosed in Patent Document 4, and a composite material of about 40 to 50% is produced by the non-pressure permeation method and dissolved again. Then, it is diluted with a matrix alloy to a predetermined amount. While this approach is practical if reinforcement of SiC, when applied to a B ₄ C, seemed to react between the aluminum is B ₄ C and the matrix metal, and B ₄ C by the pressureless permeation Although there was a composite material of Al, there was a problem that even if it was heated to dissolve again to dilute it, it did not dissolve. As a method for making the filling rate of the reinforcing material variable in the non-pressure permeation method, there is Patent Document 5. Although it is possible to create a composite material containing B ₄ C by this method, it is difficult to say that it is an inexpensive manufacturing method because it is necessary to process a composite material that is difficult to process in order to obtain the required plate shape. As a method for reducing the processing cost, as introduced in Japanese Patent Application No. 2004-306340, it has been proposed to leave a metal material that is relatively easy to process in the processed portion.
Japanese Patent No. 2641901 Patent No. 2905520 Japanese Patent No. 2905521

As mentioned above, boron-containing Al alloys have many preconditions that significantly increase production costs, such as the use of extremely expensive concentrated boron in order to increase neutron absorption capacity, making it difficult to put it to practical use at the industrial level. Met. Also, Bola, which has a high B ₄ C content of 30 to 40% by weight, has a problem in workability and cannot be used as a structural material. Against this background, it has high neutron absorption capacity by increasing the B content, as well as excellent mechanical properties such as tensile strength and elongation, and can be easily processed and used as a structural material. There has been a demand for an Al-based composite material having neutron absorption capability and an inexpensive manufacturing method thereof.

Therefore, in view of the current situation as described above, the present invention uses ordinary B ₄ C that is distributed at low cost in the city as an abrasive or refractory material, is easy to process, and has the necessary neutron shielding ability and strength. The company has created a method for producing an Al-based composite material satisfying a good balance of properties at a low cost by using a non-pressure infiltration method.

The present invention employs the following means in order to solve the above problems.
a) boron or a boron compound (e.g., B ₄ C) used as a filler, b) of coating the matrix metal powder matrix metal (aluminum powder) in and said filler is mixed with the filler A breathable material is formed by at least one , c) the breathable material and the first matrix metal source are placed in contact with each other in a mold made of a thermally and chemically stable material; d A) a second matrix metal source is further arranged to connect to the first matrix metal source; e) the matrix metal is heated to a temperature range above its melting point to form a molten matrix metal; and f) an osmotic atmosphere. At least at some point during the process and supplying at least one of a penetration enhancer or a penetration enhancer precursor to allow the molten matrix metal to pass through. It is spontaneously penetrate into sexual material, by complex machining operations unnecessary boron - metal composite (e.g., B ₄ C-Al composites) is provided. Furthermore, by arranging the supply path matrix metal source to sandwich the breathable material in the mold, or arranging the breathable material to sandwich the supply path matrix metal source, the boron-metal composite material And a method of forming a material having a sandwich structure of matrix metals.

According to the above-described method for producing a metal matrix composite having neutron absorption capability of the present invention, the following effects can be obtained. After adding B ₄ C powder with neutron absorption ability to aluminum or aluminum alloy powder and mixing, the metal matrix composite manufactured using non-pressure infiltration method is the conventional melting method and pressure sintering method Compared to, manufacturing at a low cost becomes possible. Moreover, by making it infiltrate in a type | mold, the shape required after infiltration is obtained, and a process becomes unnecessary. Furthermore, it can be made into the structure which has the layer of only the metal which has the elongation compared with a metal matrix composite in the center or both sides | surfaces of a plate-shaped material, and can have the characteristic of both a metal and a metal matrix composite. . That is, by using the present invention, it is possible to obtain a metal matrix composite material that not only has a high neutron absorption capability but is suitable as a structural member at a low price.

Definitions As used herein, “aluminum” refers to substantially pure metal (eg, relatively pure and commercially available unalloyed aluminum) or impurities and / or iron, silicon, copper, magnesium, manganese, It means and includes other grades of metals and metal alloys such as commercially available metals having alloy components such as chromium and zinc. The aluminum alloy used in this definition is an alloy or intermetallic compound containing aluminum as a main component.
As used herein, “Infiltrating Atmosphere (Infiltrating
“atmosphere” ”means the presence atmosphere that interacts with the matrix metal and / or filler and / or penetration enhancer precursor and / or penetration enhancer to cause or promote spontaneous penetration of the matrix metal.
As used herein “Infiltration enhancer (Infiltration
"Enhancer)" means a substance that promotes or assists the matrix metal to spontaneously penetrate the filler. The penetration enhancer may be, for example, by reacting a penetration enhancer precursor with the penetration atmosphere to (1) a gaseous product and / or (2) a reaction product of the penetration enhancer precursor and the penetration atmosphere and / or (3 ) By producing a reaction product of a penetration enhancer precursor and a filler. Furthermore, the penetration enhancer is fed directly to at least one of the filler and / or the matrix metal and / or the penetration atmosphere to generate a penetration enhancer produced by a reaction between the penetration enhancer precursor and another species. You may make it act in the substantially similar method. Basically, at least during spontaneous penetration, the penetration enhancer must be located in at least a portion of the filler to achieve spontaneous penetration.
As used herein, “infiltration enhancer precursor (Infiltration
"Enhancer Precurcor)" means a substance that, when used in combination with a matrix metal and / or osmotic atmosphere, induces or assists spontaneous penetration of the matrix metal into the filler. Without being limited to a particular principle or description, it is necessary that the penetration enhancer precursor be able to be placed or moved to a location where the penetration enhancer precursor can interact with the penetration atmosphere and / or filler and / or metal. For example, in certain matrix metal / penetration enhancer precursor / penetration atmosphere systems, it is desirable for the penetration enhancer precursor to volatilize at the melting temperature of the matrix metal, near it, or in some cases somewhat higher. . Such volatilization may result in (1) the generation of gaseous matter that enhances the wetting of the filler by the matrix metal by reaction of the penetration enhancer precursor with the penetration atmosphere; and / or (2) the penetration enhancer precursor; Generation of a solid, liquid or gaseous penetration enhancer that promotes wetting to at least a portion of the filler by reaction with an osmotic atmosphere; and / or (3) a solid that enhances wetting within at least a portion of the filler. The reaction of the penetration enhancer precursor within the filler to produce a liquid or gaseous penetration enhancer occurs.

In the present invention, boron or a boron compound is used as a filler. In particular, B ₄ C is preferable in terms of price and availability. Boron or a boron compound is preferably used as a powder, but may be granular.

  Next, the breathable material is formed by mixing the filler with powdered matrix metal and / or coating the filler with the matrix metal. For example, after the filler and powdered matrix metal are mixed, they can be simply put into a mold to make a breathable material with a low level of filling rate, or press-molded into a plate shape. In order to improve the mixing state, a powder in which a filler is coated with a matrix metal may be used. For coating, plating, thermal spraying or mechanochemical reaction can be used.

  Here, in forming the breathable material, the content of the matrix metal in the breathable material is preferably 1 to 98% by volume. When the content exceeds 98% by volume, the content of boron or boron compound becomes relatively small, and the ability of neutron absorption may be insufficient.

Next, a thermally and chemically stable mold is prepared, and the breathable material and a supply path matrix metal source (corresponding to a first matrix metal source) are arranged in the mold. At this time, the matrix metal source for supply path is arranged so as to contact the breathable material. The size of the matrix metal source for the supply path should be determined considering that it remains after infiltration. The function of the matrix metal source for the supply path is to supply the matrix metal before voids due to shrinkage generated when the matrix metal particles contained in the breathable material are heated to the melting point or higher are grown. Therefore, it is necessary to contact evenly from the whole breathable material. For example, as shown in FIG. 1, a material (such as a plate) made of a matrix metal is preferably brought into contact with the center of a breathable material molded or deposited in a plate shape. Although depending on the matrix metal ratio and the filling property of the breathable material, the amount of the matrix metal to be supplied to the breathable material is likely to be insufficient. Therefore, it is necessary to further arrange a matrix metal source (reservoir matrix metal source (corresponding to the second matrix metal source) ) so as to be in contact with the supply path matrix metal source. That is, the former matrix metal source functions as a path for supplying the matrix metal to the breathable material very quickly, whereas the latter serves as a reservoir. The reservoir matrix metal source is not necessarily in the mold. The flow of matrix metal from the reservoir matrix metal source to the supply path preferably utilizes gravity and is preferably placed on top of the supply path matrix metal source as shown in FIG. At this time, the total amount of matrix metals contained in both matrix metal sources is made to be sufficiently larger than the amount penetrating into the breathable material. For example, it may be about twice the theoretical amount penetrating into the breathable material (obtained from the difference between the bulk density of the breathable material and the theoretical density of the metal composite to be produced).

The mold must be a thermally and chemically stable material. That is, when a structure comprising a breathable material and two types of matrix metal sources is heated, it is placed in a mold made of a material that does not react or deform. A carbon material is suitable in terms of workability and cost, but besides the carbon material, a metal (for example, iron) whose surface does not melt at the permeation temperature of the matrix metal can be used.
Next, the entire mold in a state where the air-permeable material and the matrix metal source are arranged is heated to form a molten matrix metal. The heating temperature may be a temperature that exceeds the melting point of the matrix metal. The heating method is not limited. For example, a method in which a mold containing a matrix metal source and a breathable material is placed in an electric furnace and heated is preferable.

  Further, the molten matrix metal is supplied to the breathable material by supplying an infiltration atmosphere at least at a certain point in the process from a) to e) and supplying at least one of an infiltration enhancer or an infiltration enhancer precursor. To penetrate spontaneously. The permeation atmosphere may be supplied continuously from the beginning to the end of the step of heating the breathable material, or the supply may be stopped during the process. It is preferable to supply at least until the formation of the molten matrix metal and continue to supply until the end of heating. Further, it is preferable that the permeable atmosphere is in communication with at least one of the breathable material and the molten matrix metal for at least a part of the osmosis period.

  Here, in order to supply a penetration enhancer or a penetration enhancer precursor, they should be mixed with the breathable material in advance or added beforehand to the matrix metal source disposed adjacent to the breathable material. Alternatively, it is possible to supply the mixture in an osmotic atmosphere.

  The matrix metal used in the present invention is typically metallic aluminum, but may be an alloy containing aluminum as a main component. Specific examples include 1050 alloy and 5052 alloy that are easily available. In addition to magnesium metal, magnesium compounds such as AlMg can be used as the penetration enhancer precursor. Nitrogen is preferred as the infiltration atmosphere.

Furthermore, the boron compound used for the filler is most preferably B ₄ C because of its price and availability. However, BN or the like may be used.

  Through the process as described above, for example, as shown in FIG. 2, a plate-like material made of a metal matrix composite material made of a boron compound and a matrix metal and made of a matrix metal inside can be obtained. Since it was placed in the mold and infiltrated, there was no need for side processing, and it was sufficient to cut out only the portion of the matrix metal source arranged as a reservoir.

Hereinafter, an embodiment of an aluminum composite material having a neutron absorption capability and a method for producing the same according to the present invention will be described. In the following embodiments, B ₄ C as a filler, aluminum powder as a powdered matrix metal, an aluminum alloy having a composition of 1050 alloy as a metal source of the molten matrix metal, nitrogen as an infiltration atmosphere, metal as an infiltration enhancer precursor Although magnesium powder was used, the present invention is not limited to this.
A 2 mm-thick aluminum alloy plate 2 that functions as a matrix metal source for the supply path is placed in the center of a carbon jig 4 having a 10 mm-thick gap, and about 7% by volume B ₄ C, 0.3% by volume magnesium and A mixture (breathable material) 1 made of a powdered aluminum alloy having a composition having the remainder was put, and an aluminum alloy lump 3 serving as a matrix metal source for the reservoir was placed so as to contact the central aluminum alloy plate 2 (FIG. 1). .

The air-permeable material and aluminum alloy plate in the state shown in Fig. 1 were heated to 790 ° C in about 3 1/2 hours in a nitrogen atmosphere furnace, kept for 8 hours, and naturally cooled to achieve non-pressure permeation (Fig. 1). 2). What was created was a metal matrix composite 5 consisting of B ₄ C and Al on both sides, and further aluminum alloy was supplied from the center to the voids of the mixture before infiltration, and the concentration of B ₄ C in the metal matrix composite As it was about 5%. In addition, since the aluminum alloy is supplied to the central aluminum alloy plate 2 from above, the thickness is not particularly reduced and no voids are generated. Since it was put into the mold and allowed to penetrate, the final shape was obtained by cutting the upper aluminum lump without polishing the flat surface. When the obtained plate was bent, the metal matrix composite layers on both sides were ruptured, but the central aluminum layer was not ruptured, and as a whole, it was found that it was more resistant to bending than the metal matrix composite alone. It was.

[Comparative example]
A metal matrix composite was prepared under the same conditions as in Example 1 except that no aluminum alloy plate was placed at the center. That is, the mixture was simply put in a carbon jig, an aluminum alloy lump as a matrix metal source for the reservoir was placed on the top, and the same heat treatment was performed.
FIG. 3 shows a cross section of the resulting structure, which was a non-uniform structure in which metal-only portions 7 were found in stripes in the metal matrix composite structure. Since there is no matrix metal source in the immediate vicinity of the breathable material and it is supplied only from the matrix metal source placed above, it takes time, and during that time the growth of voids due to melting shrinkage of the metal in the breathable material has progressed Conceivable. Eventually, since the matrix metal enters there, no voids remain, but the above-described metal-only portion is generated, resulting in a non-uniform structure. Therefore, since the mechanical strength is insufficient, the composite material cannot be used as a structural material. In addition, since there are regions with different hardnesses, it was expected that the processing accuracy would be insufficient.

FIG. 3 is a schematic cross-sectional view of a layup before infiltration of a breathable material and a matrix metal source in Example 1. It is a cross-sectional photograph after the penetration of the breathable material and the matrix metal source in Example 1. It is a cross-sectional photograph after the penetration of the breathable material and the matrix metal source in a comparative example.

Explanation of symbols

1 Breathable material, ie mixed layer of boron compound and powdered matrix metal (before penetration)
2 Matrix metal source (supply path)
3 Matrix metal source (reservoir)
4 Graphite mold 5 Composite layer of boron compound and matrix metal (after infiltration)
6 Striped metal only part

Claims (6)

A method of forming a metal matrix composite comprising the following steps:
a) using boron or boron compound as filler,
b) forming a breathable material with at least one of coating the matrix metal matrix metal to and the filler is mixed with the filler,
c) In a mold made of a thermally and chemically stable material, the breathable material is opposed to the plate-like first matrix metal source, or the first matrix metal source is the vent. Place the sex materials so that they are in contact with each other,
d) further arranged to connect a second matrix metal source to the first matrix metal source;
e) heating the matrix metal to a temperature range above its melting point to form a molten matrix metal; and
f) spontaneously infiltrating the molten matrix metal into the breathable material by providing an infiltration atmosphere at least at some point during the process and supplying at least one of an infiltration enhancer or an infiltration enhancer precursor. ,
A method of forming a metal matrix composite comprising:   The forming method according to claim 1, wherein the permeation atmosphere is in communication with at least one of the breathable material and the molten matrix metal for at least a part of the permeation period.   3. The method according to claim 1, wherein at least one of the penetration enhancer precursor and the penetration enhancer is supplied to at least one of the molten metal matrix, the breathable material, and the penetration atmosphere. The formation method of crab.   The forming method according to any one of claims 1 to 3, wherein the breathable material contains 1 to 98% by volume of a matrix metal.   The method of claim 1, wherein the matrix metal comprises aluminum, the penetration enhancer precursor comprises magnesium, and the penetration atmosphere comprises nitrogen. The formation method according to claim 1, wherein the boron compound of the filler is B ₄ C.