JPS6141844B2 - - 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. 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 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, an attempt is made to utilize the magnitude of the specific elastic modulus. This is a very serious problem for acoustic materials such as speaker diaphragms and cartridge cantilevers. 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 proposed a method using a metal such as tantalum, niobium, molybdenum, tungsten, or titanium as a base material, and containing 5.0 mol% to 70 mol% of silicon on the surface. It has been found that it is effective to deposit chromium to the 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 formed by a reductive decomposition reaction as shown in the following equation. is precipitated. _{2 B _} 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 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 5.0 mol% to 70.0 mol% silicon on the metal by electroplating, CVD, sputtering, vacuum evaporation, etc., and then 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 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 in which only chromium is coated on a metal substrate, the boron film may be destroyed during selective dissolution or mechanical peeling, or mechanical damage to the resulting boron structure may occur. There were cases where the quality was inferior. The method of the present invention provides significant improvements in these respects. Particularly, when boron is amorphous, it is greatly improved. 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 silicon contained in chromium is
The reason why we limited it to 5.0 mol% to 70.0 mol% is that
When it is less than 5.0 mol%, the yield of the pipe obtained by dissolving and removing the substrate is not very good.
Moreover, if it exceeds 70.0 mol%, the substrate will deform during boron CVD, and the strength of boron will decrease. When a chromium plate containing silicon 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 5.0 mol % to 70.0 mol % of silicon naturally has a desirable thickness. This desired thickness also depends on the thickness of the base metal. As a base metal, for example, thickness 200~
When using 300μm linear tantalum,
The thickness of the chromium layer containing silicon was 15 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 silicon can be formed on the substrate by electroplating, sputtering, or CVD. The results were almost the same no matter what coating method was used. 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 5.0 mol % of silicon was deposited on it by sputtering to form a layer of approximately 1.0 μm. Next, electricity is applied to a tantalum wire coated with a chromium layer containing 5.0 mol _% silicon to generate heat, and the temperature is maintained at ₁₀₀₀ °C. The mixed gas with volume part was flowed for 2.5 minutes at a rate of 1 part per minute. 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 silicon 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. Next, 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 breaks. Next, a sample cut into 5 mm pieces from a sample length of 800 mm was cut to 20% by the process of dissolving and removing the base material.
Destroyed. In other words, the yield was 80%. The average bending strength of the resulting pipe was 519 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 silicon-containing chromium using a DC sputtering method using a silicon-chromium compacted powder as a target. For all samples 2 to 13, the CVD time was adjusted so that the boron film thickness was 50 μm. For comparison, 50 μm of boron was also deposited when the tantalum wire was coated with only chromium (sample 12) or when the tantalum wire was coated with only tantalum wire (sample 13). 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 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 silicon inclusion than with chromium coating alone. In the above example, a boron pipe was shown, but similar results were obtained with a plate of boron. In addition to tantalum, the base material is molybdenum, niobium,
Similar results were obtained with titanium and tungsten. And other elements besides silicon can be added to chromium to further enhance the results.

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 5.0 mol% to 70.0 mol% silicon on a base metal, and then the substrate is selectively A method for producing a boron structural material, the method comprising removing the boron structural material 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. .