JPS6141846B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a boron structural material, and in particular aims to improve the film quality and mechanical properties of boron constituting the boron structural material, and to reduce production pending and improve productivity of the boron structural material. It is something. Boron has a hardness second only to diamond, and has extremely high wear resistance, making it a suitable material for cutting tools, sliding machine parts, bearings, etc. Additionally, it has the excellent characteristic of having the highest specific elastic modulus (elastic modulus/density) among currently known materials. This property means that the propagation speed of sound waves is the highest among existing materials, making it particularly useful as an acoustic material. It is difficult to obtain boron-applied products in the form of dense blocks, thin walls, thin-walled pipes, etc. by methods such as casting or rolling. For this reason, when manufacturing various boron-applied products, in most cases vapor deposition, sputtering, or chemical vapor deposition (CVD) is used on substrates made of materials other than boron.
It is used as a composite in which a boron film is formed on a substrate made of a material other than boron, using a method such as a method called a boron method. Composite structural materials made by such conventional methods do not cause any major problems in products that utilize the hardness of boron and its excellent wear resistance. However, this poses a very serious problem in acoustic materials such as speaker diaphragms and cartridge cantilevers that utilize the large specific modulus of elasticity. In other words, the density and elastic modulus of the composite are greatly influenced by the properties of the substrate, and the inherent properties of boron are thereby greatly reduced.
On the other hand, there have been many attempts to separate boron from the substrate through chemical or physical treatments, but distortion occurs due to differences in coefficient of thermal expansion between the deposited boron film and the substrate, and as a result, the boron film is Cracks and the like occur, making it difficult to obtain a boron film with sufficient mechanical strength at a high yield. In order to eliminate the drawbacks of such conventional methods, the inventors believe that a metal such as tantalum, niobium, molybdenum, tungsten, or titanium is used as a base material, and 1.0 mol% to 35.0 mol% of aluminum is added to the surface of the base metal.
It has been found that it is effective to deposit chromium containing a mole percent of chromium to a desired thickness and then chemical vapor deposit it thereon. The method of the present invention will be specifically explained below. To form boron on a substrate using the CVD method, for example, the substrate placed in a reactor is heated using methods such as infrared heating, high-frequency heating, or energization, and boron is removed by a reductive decomposition reaction as shown in the following equation. Let it precipitate. 2BX ₃ +3H ₂ →2B+6HX (However, X is a halogen element such as Cl, Br, I, etc.) In addition to boron halide BX ₃ , boron hydrogen There are also compounds. In addition, in this boron precipitation reaction, depending on the heating temperature and the amount of raw material flowing into the reactor,
Various crystal forms are obtained. Among various crystal forms, β-rombohedral, tetragonal,
Alternatively, amorphous boron is preferable. Next, the substrate is dissolved or removed by chemical or mechanical methods to obtain pipes or plates made mainly of simple boron. As a chemical method, it is conceivable to use a solution mainly containing hydrofluoric acid. A particularly effective solution is one in which bromine, chlorine, iodine, or a compound or mixture of two or more of these is dissolved in absolute alcohol. Boron is the metal used to form the base.
Tantalum, niobium, molybdenum, titanium, tungsten, etc. are desirable because CVD is carried out at high temperatures (over 9000°C) and because they are easy to conduct electricity and high-frequency heating. Among these materials, tantalum, molybdenum, and tungsten, which are less susceptible to hydrogen embrittlement, are more desirable because CVD is performed in a hydrogen stream. Further, in order to reduce the thermal strain between the deposited boron film and the substrate, tantalum or titanium, which has a coefficient of thermal expansion close to that of boron, is more desirable. The main point of the method of the present invention is to deposit chromium containing 1.0 mol% to 35.0 mol% aluminum on the metal by electroplating, CVD, sputtering, or vacuum evaporation, and deposit it to a desired thickness. The purpose is to coat it with a layer and use it as a substrate. Thereafter, boron is deposited on the substrate, and then the substrate is selectively dissolved and removed or mechanically removed to obtain a structure made of boron. Conventionally, when using only a metal substrate or a substrate in which only chromium was coated on a metal substrate, the boron film was destroyed during the selective dissolution or mechanical peeling process, and the mechanical properties of the resulting boron structure deteriorated. There were cases where things were not very good. With the method of the present invention, in these respects,
Significant improvements have been made. In particular, when boron was amorphous, the improvement was significant. As a result, for example, when the base body is made into a linear shape, a pipe-shaped boron structural material is obtained, and when it is made into a plate-like shape, a thin plate-like boron structural material is obtained. In the present invention, the amount of aluminum contained in chromium is limited to 1.0 mol% to 35.0 mol% because if it is less than 1.0 mol%, the yield of the pipe obtained by dissolving and removing the base is not very good. . Moreover, if it exceeds 35 mol%, the substrate will be deformed during CVD of boron, and the strength of boron will decrease. When a chromium plate containing aluminum is used as a substrate, the substrate itself deforms when exposed to high temperatures during CVD, resulting in cracks in the boron film when CVD of boron is completed. Therefore, in order to exhibit the effects of the present invention, the thickness of the chromium layer containing 1.0 mol % to 35.0 mol % of aluminum naturally has a desirable thickness. This desired thickness also depends on the thickness of the base metal. For example, when linear tantalum having a thickness of 200 to 300 μm was used as the base metal, the thickness of the chromium layer containing aluminum was 10 μm or less. That is, if it is too thick, cracks will easily occur in the boron film. However, if the thickness is too thin, about 0.05 μm, the improvement effect of the present invention cannot be clearly recognized. The most desirable thickness of the coating layer in this case was 0.1 to 2.0 μm. The effects of the present invention are even greater when tantalum is used as the base metal. This is thought to be due to the fact that the coefficient of thermal expansion is close to that of boron and the degree of hydrogen embrittlement is relatively small. The chromium layer containing aluminum can be formed on the substrate by electroplating, sputtering, or CVD. Regardless of the coating method used, the results were almost the same. More details will be explained using a practical example. A tantalum wire with a diameter of 250 μm and a length of 800 mm was prepared. After degreasing and cleaning the tantalum wire, chromium containing 1.0 mol % of aluminum was deposited on it by a sputtering method to form a layer of about 1.0 μm. next,
A tantalum wire coated with a chromium layer containing 1.0 mol% aluminum is heated by passing an electric current through it and maintained at a temperature of 1000°C, and 1 part by volume of boron trichloride (BCl ₃ ) and 3 parts by volume of hydrogen (H ₂ ) are added to this. The mixed gas was flowed at a rate of 1/min for 2.5 minutes. This results in approximately 50μ
A boron layer of m thickness was formed. The sample thus prepared was cut into a length of 5 mm by irradiating a laser beam, etc., and the cut sample was immersed in a solution containing 50 g of bromine dissolved in 200 ml of commercially available anhydrous methanol. Borides such as aluminum and aluminum were dissolved. At this time, boron does not dissolve. The dimensions of the obtained pipe were an inner diameter of 250 μm, an outer diameter of 350 μm, and a length of 5 mm. X
As a result of examination by line diffraction, the crystal form was mainly amorphous. The bending strength of this pipe was measured. The measurement was carried out by using a beam with a length of 4 mm, with both ends serving as support beams, applying a load W, and determining the load when the pipe breaks. Next, 15% of the samples cut into 5 mm pieces from the 800 mm long sample were broken during the process of dissolving and removing the base. That is, the yield was 85%.
The average bending strength of the resulting pipe was 515 g. The results are summarized as Sample 1 in the table below. Samples 2 to 2 shown in the table below were prepared in the same manner as in the above example.
I created 13 and researched them as well. As a method for coating the tantalum wire with chromium containing aluminum, a method was used in which aluminum-chromium compacted powder was used as a target and the coating was performed by a direct current sputtering method. Samples 2 to 13 also all contain 50 boron.
The CVD time was adjusted to obtain a film thickness of μm. For comparison, boron was deposited to a thickness of 50 μm when only chromium was applied to the tantalum wire (sample 12) or when only tantalum wire was applied (sample 13). The boron deposition temperature, yield, average bending strength, and crystal system at that time are also summarized in the table below.

【table】

[Table] As is clear from the results in the above table, according to the method of the present invention, the yield of boron pipes is high and the average bending strength thereof is also high. Particularly for amorphous boron, the yield strength is better with aluminum than with chromium coating alone. In the above example, a boron pipe was shown, but similar results were obtained with a plate of boron. Similar results were also obtained when the substrate was molybdenum, niobium, titanium, or tungsten in addition to tantalum. It is also possible to further enhance the effect by adding other elements besides aluminum to chromium.

Claims (1)

[Claims] 1. 1.0 mol% to 35.0 mol% of aluminum in base metal
On a substrate formed by forming a layer of chromium containing mol%,
A method for producing a boron structural material, comprising forming a boron layer by a chemical vapor deposition method and then selectively removing the substrate to obtain a boron structural material. 2. A method for producing a boron structural material according to claim 1, characterized in that a boron layer whose main crystalline form is β-rombohedral or amorphous is formed on a substrate by a chemical vapor deposition method. .