JPS6149248B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a pipe-shaped 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 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, and the like. It also has the excellent characteristic of having the highest specific elastic modulus (elastic modulus/density) among currently known materials. This property not only makes it an excellent structural material, but also means that the propagation velocity 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 by methods such as casting or rolling. For this reason, in the production of various boron-applied products, in most cases, materials such as vapor deposition, sputtering, or chemical vapor deposition (hereinafter referred to as CVD) are used on substrates made of materials other than boron. Used as a composite with a boron film formed. Composite structural materials made by such conventional methods do not pose any major problems when used 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 thermal expansion coefficients between the deposited boron film and the substrate, and as a result, boron Cracks appeared in the film, 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 at least one metal selected from iron, cobalt, and nickel and chromium are added to a base wire made of a suitable metal. It has been found that it is effective to deposit an alloy of or a boride of this alloy to a desired thickness to form a substrate, and then chemically vapor deposit boron onto this substrate. The method of the present invention will be specifically explained below. To form boron on a substrate by CVD method,
The substrate placed in the reactor may be heated by a method such as infrared heating, high frequency heating, or energization, and boron may be precipitated by a reductive decomposition reaction as shown in the following formula, for example. _{2 B _} . In addition, in this boron precipitation reaction, depending on the heating temperature, the amount of raw material gas flowing into the reactor, etc.
Various crystal forms are obtained. Among various crystal forms, β-rombohedral, tetragonal,
Alternatively, amorphous boron is preferable. Next, the base is dissolved and removed by a chemical method to obtain a pipe mainly made of simple boron. As a liquid having such a chemical action, a liquid mainly containing hydrofluoric acid can be considered. A particularly effective solution is one in which bromine, chlorine, iodine, a compound of two or more of these (such as iodine trichloride or iodine monochloride), or a mixture thereof is dissolved in absolute alcohol. Since boron CVD is performed at high temperatures (above 1000°C) and the substrate can be easily heated by electricity, metals for forming the base wire include tantalum, niobium, molybdenum, Titanium and tungsten are preferred. Among these materials, when CVD is performed in a hydrogen stream, tantalum, molybdenum, and tungsten are preferred because of their low hydrogen embrittlement. In addition, in order to reduce the thermal strain between the deposited boron film and the substrate, tantalum (approximately 7 to 8 × ^{10 -6} /°C) or Titanium (approximately 8×10 ^-6 /°C) is preferable. The main points of the method of the present invention are that a layer of an alloy of chromium and at least one metal selected from iron, cobalt and nickel, or a boride of this alloy is formed on the base wire by electroplating or Chemistry,
The purpose is to form a substrate by depositing it to a desired thickness using CVD, sputtering, vapor deposition, or the like. Thereafter, boron is deposited on the substrate, and the substrate is further selectively dissolved or peeled off to obtain a pipe-shaped structural material made of boron. Among the above methods for removing the substrate, the selective dissolution method is superior in terms of reliability and productivity. In the past, there have been cases in which the boron film has been destroyed during the process of selectively dissolving the substrate, and the mechanical properties of the obtained boron structural material have been poor. By the method of the present invention,
Significant improvements have been made in these respects. If a plate made of chromium, iron, cobalt, nickel, or an alloy of these materials is used as a substrate, the substrate itself may be deformed due to high temperatures during CVD, or the thermal expansion coefficient may be larger than that of boron. , cracks occurred in the boron coating when CVD of boron was completed. Also, borides of chromium, iron, cobalt, or nickel,
Alternatively, a block consisting of borides of these alloys,
To use it as it is as a substrate for boron CVD,
This is not desirable due to differences in thermal properties such as thermal expansion coefficient and mechanical properties between boron and boride substrates. Therefore, in order to exhibit the effects of the present invention, the thickness of the alloy layer or the boride layer covering the base wire naturally has a desirable thickness. This desired thickness depends on the type of material covering the base and the type and thickness of the base. When a linear tantalum having an outer diameter of, for example, 200 to 300 .mu.m is used as the substrate, the desired thickness of the layer of material covering the substrate is approximately 20 .mu.m or less. If it is too thick, cracks will easily occur in the boron film. However, when the thickness becomes thinner than 0.05 μm, the improvement effect of the present invention is no longer clearly observed. The most desirable thickness of the coating layer in this case was 0.5 to 2.0 μm. The effects of the present invention are even greater when tantalum is used as the base wire. 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 present invention exhibits its effects by coating the base wire with a layer consisting of an alloy of chromium and at least one metal selected from iron, cobalt, and nickel, or a boride of this alloy. be. According to a study of the boron film quality and mechanical properties of the boron structural material finally obtained, the effects of the present invention are exhibited even when an appropriate proportion of the above alloy or boride of the alloy is used. The above-mentioned appropriate ratio naturally changes depending on the type of base, the composition of the alloy, the conditions during CVD, etc. These factors are thought to be related to the reaction of nickel, cobalt, and iron with the substrate, and to the fact that these borides melt at relatively low temperatures. As a method for coating the above-mentioned alloy in a layer on the base wire, depending on the material used, electroplating, chemical plating, sputtering, vapor deposition, or CVD from an appropriate raw material gas can be used. The vapor deposition method and the sputtering method were superior in that alloys with any type of substrate or any ratio of constituent elements could be deposited on the substrate. When two or more types of coating methods could be adopted, a comparative study was attempted, and the results showed that the effects of the present invention are exhibited in any case compared to the case without coating, and that they are qualitatively the same. Ta. Approximately 1 part of the above alloy is applied to a tantalum wire with a thickness of 250 μm.
It was coated to a thickness of .mu.m, and further boron was chemically vapor deposited thereon. The cross section of the obtained material was as shown in the figure. In the figure, 1 is a tantalum wire and 2 is a boron layer. No. 3 was examined by X-ray diffraction and was found to be a boron compound layer of a material coated on a tantalum base. 4 is a void. This indicates that the alloy coated on the tantalum base is converted to boride during CVD of boron. Note that the voids 4 may not be clearly recognized by microscopic observation of the cross section. From the above, the effects of the present invention are exhibited when the above-mentioned alloy is coated on the base wire material.
Second, the alloy or its boride has a larger coefficient of thermal expansion than boron, and as shown in the figure, voids are likely to be formed between the boron layer and the boride material layer. It is thought that this may be related to the fact that the bond with boron is relatively weak (therefore, the above-mentioned voids are likely to occur). Therefore, distortions such as thermal distortions existing between the base and boron are alleviated by the voids, thereby reducing cracks in the boron structural material and improving its manufacturing yield. In order to form a layer of boride of the above alloy on the base wire, these alloys and boron halide may be reacted, CVD may be performed from an appropriate raw material gas, or sputtering may be performed using the boride as a target. method was adopted. As a result of examining boron structural materials made through these methods, no essential difference was observed from the case where the above-mentioned alloy was used as the coating material. As described in detail above, according to the conventional method, the boron film may be destroyed during CVD of boron, or
The substrate may be destroyed when removed by methods such as melting, or
Alternatively, the mechanical properties of a pipe-shaped boron structural material made only of boron were poor, but the method of the present invention improved them in all respects. Depending on the CVD conditions, boron crystal forms include amorphous, α-rombohedral, β-rombohedral, and tetragonal. However, among these crystal forms, α-rombohedral is slightly more difficult to use than other crystal forms due to the denseness of the boron film. Further, the effects of the present invention were essentially exhibited no matter which crystal form the boron film was produced. Next, examples will be specifically explained. A tantalum wire with a diameter of 250 μm was prepared. After the tantalum wire was degreased, etched with acid, and washed, an alloy layer of about 1.5 μm was formed thereon by high-frequency sputtering, targeting an alloy of chromium and cobalt. The target consisted of an alloy of 70 at% chromium and 30 at% cobalt. Next, a tantalum wire coated with an alloy is used as a base, which is heated by electricity, and a mixed gas of 1 part by volume of boron trichloride and 3 parts by volume of hydrogen is added to it at a rate of 1 part per minute.
A boron layer with a thickness of about 50 μm was formed. The sample thus prepared was cut into a length of 5 mm using a Yag laser, etc., and immersed in a solution containing 50 g of bromine dissolved in 200 ml of commercially available anhydrous methanol. was 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. As a result of examination using X-ray diffraction and the like, the crystal form contained amorphous and β-rombohedral. Next, the bending strength of this pipe was measured. The measurement was performed with a beam length of 4 mm, a beam supported at both ends, a load W applied to the center, and the load when the pipe broke. As a result, in the process of dissolving and removing the substrate from a sample cut to 5 mm, the yield was 80% for removing the pipe without destroying it.
The average bending strength of the 20 pipes obtained was 450.
It was hot at 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 17 and researched them as well. The table below shows the base material used, the material used to cover the base, the coating method, the thickness of the coating layer, the yield of melting the base to obtain a boron pipe, the average bending strength, and the crystal form examined by X-ray diffraction, etc. Shown together. The average bending strength is the average value of 20 samples. In the table, when sputtering is employed as the coating method, the composition of the alloy written in the column of material for coating the base indicates the ratio of the target. Further, boronization treatment was performed using boron trichloride. For comparison, a tantalum wire or tungsten wire was used as a substrate without being coated, and boron was deposited directly on it to a thickness of about 50 μm by CVD. The results are also shown in the table below.

【table】

[Table] From the above table, the effect of the method of the present invention is clear. Although the above table shows the case where tungsten and tantalum wire were used as the underlying metal, the effects of the present invention were significant regardless of the underlying metal (other than molybdenum, niobium, and titanium).
Furthermore, although the coating methods differ in their degree of difficulty, there was no essential difference in the effects of the present invention among electroplating methods, chemical plating methods, sputtering methods, vapor deposition methods, or CVD methods.

[Brief explanation of the drawing]

The drawings are for explaining the method for manufacturing a boron structural material according to the present invention. 1...Tantalum wire, 2...Boron layer, 3...Boron compound layer, 4...Void.

Claims (1)

[Claims] 1. An alloy of at least one metal selected from iron, cobalt and nickel with chromium, or an alloy of chromium and at least one metal selected from iron, cobalt and nickel, on a wire made of a metal selected from tantalum, molybdenum, niobium, titanium and tungsten. A layer of boron alloy is formed as a substrate, a boron layer is formed on the substrate by chemical vapor deposition, and then a layer of boron is formed on the substrate.
A method for producing a boron structural material, which comprises dissolving and removing the base to obtain a pipe-shaped structural material made of simple boron. 2. The method for manufacturing a boron structural material according to claim 1, wherein a boron layer is formed on the substrate by chemical vapor deposition while the substrate is heated. 3. The method for producing a boron structural material according to claim 1, characterized in that the metal wire is energized to generate heat, and in this state a boron layer is formed on the substrate by chemical vapor deposition. 4. A method for producing a boron structural material according to claim 1, characterized in that a boron layer having a main crystalline form of β-rombohedral, tetragonal or amorphous is formed on a substrate by a chemical vapor deposition method. .