JPS6141845B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a boron structural material, and particularly aims to improve the film quality and mechanical properties of boron constituting the boron structural material, and to improve the manufacturing yield and productivity of the boron structural material. It is. 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. It also 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 plates, 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 material in which a boron film is formed on a substrate made of a material other than boron by a method such as a method (referred to as 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 Cracks occurred in the process, 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 have developed a method that uses metals such as tantalum, niobium, molybdenum, tungsten, and titanium as a base, and chromium containing 5.5 mol% to 65.0 mol% of vanadium on the surface. It has been found that it is effective to apply a chemical vapor deposition layer onto the desired thickness. 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 formed by a reductive decomposition reaction as shown in the following equation. is precipitated. _{2 B _} be. 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 rhombohedral, tetragonal, or amorphous boron is preferable in order to obtain a boron film that is dense and has excellent mechanical properties. Next, the substrate is dissolved or removed using a chemical or mechanical method to obtain a pipe or plate 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 900°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 minimize thermal distortion 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 that chromium containing 5.5 mol% to 65.0 mol% of vanadium is deposited on the metal by electroplating, CVD, sputtering, vacuum evaporation, etc., and then deposited to a desired thickness. The purpose is to coat it with a layer of to form a substrate. Thereafter, boron is deposited on the substrate, and the substrate is further selectively dissolved or mechanically removed to obtain a structure made of boron. Conventionally, when using only a metal substrate or a substrate with only chromium coated on a metal substrate,
In some cases, the boron film was destroyed during selective dissolution or mechanical peeling, and the mechanical properties of the resulting boron structure were not very good. The method of the present invention provides significant improvements in these respects. 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 vanadium contained in chromium is limited to 5.5 mol% to 65.0 mol% because
When it is less than 5.5 mol%, the yield of the pipe obtained by dissolving and removing the substrate is not very good.
Also, if it exceeds 65 mol%, boron
This is because the substrate deforms during CVD, reducing the strength of boron. If a chromium plate containing vanadium is used as a substrate, CVD
At high temperatures, the substrate itself deforms, resulting in cracks in the boron film upon completion of boron CVD. Therefore, in order to exhibit the effects of the present invention, vanadium must be contained in an amount of 5.5 mol% to
The thickness of the chromium layer containing 65.0 mol% 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 vanadium was 10 μm or less. If it is too thick, cracks will easily occur in the boron film. However, if it is 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 0.3 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 vanadium is formed by electroplating method,
The coating can be formed on the substrate by a sputtering method or a CVD method. Regardless of the coating method used, the results were almost the same. More details will be explained in Examples. 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 5.5 mol % vanadium was deposited on it by sputtering to form a layer of about 1.0 μm. Next, a tantalum wire covered with a chromium layer containing 5.5 mol % of vanadium was heated by passing an electric current through the wire and maintained at a temperature of 1000°C, and 1 volume part of boron trichloride (BCl ₃ ) and hydrogen (H ₂ ) Mixed gas with 3 parts by volume 1/min
It was run for 2.5 minutes at a rate of This resulted in the formation of a boron layer approximately 50 μm thick. 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 commercially available solution containing 50 g of bromine in 200 ml of anhydrous methanol. ,
Borides such as vanadium were dissolved. At this time, boron does not dissolve. The dimensions of the resulting pipe are the inner diameter
The diameter was 250 μm, the outer diameter was 350 μm, and the length was 5 mm. As a result of examination by X-ray diffraction, the crystal form was mainly amorphous. The bending strength of this pipe was measured. The measurement was carried out using a beam having a length of 4 mm, with both ends serving as support beams, applying a load W, and determining the load from the load when the pipe was broken. Next, 25% of the samples cut into 5 mm pieces from the 800 mm long sample were broken during the process of dissolving and removing the substrate. In other words, the yield was 75%. The average bending strength of the resulting pipe was 510 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 made 9 and researched them as well. The tantalum wire was coated with vanadium-containing chromium using a direct current sputtering method using a vanadium-chromium powder target. Samples 2 to 13 all have 50 μm of boron.
The CVD time was adjusted to obtain a film thickness of . For comparison, when the tantalum wire was coated only with chromium (sample 12), or when the tantalum wire was coated only with the tantalum wire (sample 13), boron was deposited to a thickness of 50 μm. The boron deposition temperature, yield, average bending strength, and crystal system at that time are also summarized in the table below.

[Table] As is clear from the results in the table below, according to the method of the present invention, the yield of boron pipes is high and the average bending strength thereof is also high. In particular, for amorphous boron, the yield strength is better when it is coated with chromium alone than when it is coated with chromium 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 add other elements in addition to vanadium to chromium to further enhance its effectiveness.

Claims (1)

[Scope of Claims] 1. A boron layer is formed by chemical vapor deposition on a substrate formed by forming a layer of chromium containing 5.5 mol% to 65.0 mol% of vanadium on a base metal, and then the substrate is selectively A method for producing a boron structural material, the method comprising removing the boron 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. .