JPS6154113B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a boron structural material, and aims to improve the film quality and mechanical properties of boron constituting the boron structural material and to reduce the cost of the boron structural material. Boron (B) has a hardness second only to diamond and has extremely high wear resistance, so it is a useful 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 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 using methods such as casting or rolling, and for this reason, in most cases, boron-applied products are manufactured from materials other than boron. Vapor deposition method, sputtering method, chemical vapor deposition method (CVD method) on the substrate
It is used as a composite with a boron coating formed by et al. Such conventional methods do not pose any major problems in the case of products that take advantage of the hardness of boron and its excellent wear resistance. However,
This is a very serious problem in acoustic materials such as speaker diaphragms, cartridge cantilevers, and video disk cantilevers that utilize a high specific elastic modulus. 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. In addition to the above methods, tantalum (Ta),
It has become possible to deposit boron on wires (0.2 to 0.4 mmφ) of niobium (Nb), molybdenum (Mo), tungsten (W), etc. using the CVD method, and then dissolve and remove these core wires to obtain simple boron. However, it is difficult to produce large shapes such as diaphragms and video disc cantilevers with a good yield using these core wires and substrates due to the difference in thermal expansion with the substrate and the internal stress of the deposited boron. It was hot. Especially Mo
It has been difficult to produce a large structural material made of simple boron with a good yield using an inexpensive core material such as or W. The present invention has been made to eliminate such conventional drawbacks, and involves depositing boron on a W substrate coated with chromium by low pressure chemical vapor deposition (LP-CVD method), and then depositing boron on the surface of the W substrate by heat treatment.
By forming a crystal layer consisting of at least one of CrB ₂ , WB ₂ , and W ₂ B ₅ and depositing a boron layer on top of this, a boron structural material with mechanical strength and high yield can be provided. This is how it was done. The manufacturing method of the present invention will be specifically explained below. To form boron on a substrate by the LP-CVD method, for example, the substrate is placed in a reduced pressure reactor and heated by infrared heating, high frequency heating, energization, etc., and reductive decomposition as shown in the following formula is performed. Boron is precipitated by the reaction. _{2 B _} In addition, in this boron precipitation reaction, heating temperature, reduced pressure state, gas pressure,
Various crystal forms can be obtained depending on the amount of raw material gas flowing into the reactor. In particular, under reduced pressure, the above reaction occurs when boron in an amorphous state at 700°C to 1000°C
β-rombohedral boron is obtained at 1000°C to 1300°C. In particular, compared to the normal pressure CVD method, LP−
Since amorphous boron and β-rombohedral boron are precipitated at a low temperature, the CVD method is advantageous because there is little thermal strain between the substrate and the deposited boron. The appropriate temperature for depositing amorphous boron on a W substrate using the LP-CVD method is 700 to 800°C. At temperatures lower than 700°C, the precipitation rate is very slow and the precipitation is in the form of a powder. It is difficult to produce CrB ₂ , WB ₂ , and W ₂ B ₅ by post-heat treatment, and strain tends to occur between the substrate (W) and amorphous boron at temperatures exceeding 800°C. In addition, the temperature at which amorphous boron is diffused by heat treatment to form a crystal layer consisting of at least one of CrB ₂ , WB ₂ , and W ₂ B ₅ is as follows:
A temperature of 850 to 1250℃ is suitable; at temperatures lower than 850℃, CrB ₂ , WB ₂ , and W ₂ B ₅ are difficult to generate;
Temperatures exceeding this temperature tend to cause thermal distortion. In addition, we limited the W boride to crystals of WB ₂ , W ₂ B ₅ or a mixture thereof because these crystal systems have a coefficient of thermal expansion closer to that of boron than W ₂ B or WB. , Therefore, strain is less likely to occur in the boron film. Also in WB ₄ , boron and
This has the disadvantage that the bonding force between WB ₄ becomes too strong, making etching difficult. _CrB2 , _WB2 ,
The thickness of the crystal layer consisting of at least one of W ₂ B ₅ is 20
~200 μm is good; if it is thinner than 20 μm, it will not be possible to alleviate the thermal strain of the boron layer and W substrate,
Furthermore, if the thickness exceeds 200 μm, the substrate itself becomes brittle and has difficulty maintaining its shape. Further, the reason why the W substrate is coated with Cr is to weaken the adhesion between boron and WB ₂ or W ₂ B ₅ and to make it easier to remove the substrate chemically or mechanically. In this case, Cr reacts with boron to form CrB ₂ , which serves to weaken the adhesion between boron and WB ₂ or W ₂ B ₅ , which has the effect of improving the etching yield. In addition
The thickness of the Cr film is preferably about several μm.
Next, boron is deposited on this boride using a vapor deposition method, a CVD method, etc., and then the substrate is removed chemically or mechanically to obtain a structural material made of simple boron. An embodiment of the present invention will be described below. Prepare a W wire with a diameter of 2.0 mm and a length of 100 cm, and after degreasing and cleaning, use the sputtering method to create a wire with a thickness of about 1 micron.
Coated with Cr. Next, this wire was placed in a CVD furnace, the air inside the furnace was removed using a rotary pump, and the wire was heated to 700°C by electricity. Next, 1 volume part of boron trichloride (BCl ₃ ) and 3 volume parts of hydrogen (H ₂ ) were flowed at a rate of 2 per minute for 4 minutes. At this time, the decompression state is
It was controlled with a rotary pump and valve to achieve 100Torr. Thereafter, only the BCl ₃ gas was stopped, and heat treatment was performed at 850° C. for 3 minutes to diffuse amorphous boron and form WB ₂ with a thickness of 20 μm (results of X-ray analysis). Next, BCl ₃ gas was flowed again, the base core wire was kept at 1000° C., and the gas was flowed for 6 minutes. As a result, 50 μm of amorphous boron was deposited on WB ₃ . The thus prepared sample was cut into a length of 4 cm and immersed in a mixed solution of Br and methanol to dissolve W and WB ₂ . Next, the length of the beam was set to 3.5cm, and a load was applied to the beam with both ends supported, and the average strength was determined from the load when the pipe broke. As a result, the cut sample 20
Seventeen of the books were of good quality, and their average strength was 1.85 kg. The results are shown in sample No. 1 in the following table. Hereinafter, boron structural materials were obtained in the same manner as in the examples, with different conditions. The results are shown in the table below. However, sample numbers No. 10 to No. 15 are comparative examples. In addition, all samples have an inner diameter and an outer diameter of 2.0
mm, so that it is a constant value of 2.1 mm (thickness is 50μ
(constant at m) The amount of boron precipitation was controlled.

[Table] As is clear from the table, the samples within the scope of the present invention have high bending strength, good yield, and have extremely excellent characteristics as acoustic materials. As explained above, the manufacturing method of the present invention involves depositing amorphous boron on a W substrate by the LP-CVD method, and then diffusing it by heat treatment.
CrB ₂ , WB ₂ , W ₂ B ₅ are generated, boron is further precipitated on a substrate, and the substrate is then removed to obtain simple boron. This method of the present invention is different from conventional methods. Compared to the above method, high-strength boron structural materials can be obtained at a higher yield and at a lower cost, so its industrial value is high.

Claims (1)

[Claims] 1 Tungsten substrate coated with chromium 700 ~
A first step of depositing amorphous boron on the substrate using a reduced pressure chemical vapor deposition method while maintaining the temperature at 800°C, and heat treating the substrate on which the amorphous boron has been deposited at a temperature of 850°C to 1250°C. , a second step of forming a crystal layer of at least one of CrB ₂ , WB ₂ , and W ₂ B ₅ to a thickness of 20 to 200 μm on the surface of the substrate; and a second step of depositing boron on the crystal layer. 3. A method for producing a boron structural material, characterized in that the material is produced through step 3 and a fourth step of removing the substrate by chemical means or mechanical means.