JPS635328B2 - - 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 reduce the cost of the boron structural material. Boron B has a hardness second only to diamond and has very high wear resistance, so it is a useful 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 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 lumps by methods such as casting or rolling. For this reason, when manufacturing various boron-applied products, in most cases a boron coating is deposited on a substrate made of a material other than boron by vapor deposition, sputtering, chemical vapor deposition (CVD), etc. It is used as a complex formed by 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 poses an extremely serious problem when used in acoustic materials such as speaker diaphragms, cartridge cantilevers, etc., or video disk cantilevers, etc., which utilize the magnitude of specific elastic modulus.
That is, 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 largely destroyed. In addition, conventionally, boron is deposited on tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), etc. wires (0.2 to 0.4 mmφ) using the CVD method, and then these core wires are dissolved and removed to form pure boron. However, it is difficult to produce large-sized objects 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 fact that This was difficult due to the internal stress of boron. In particular, 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 Mo or W. The present inventor deposited boron on a Mo substrate metallized with chromium by low-pressure chemical vapor deposition (LP-CVD method), and then deposited MoB ₂ , Mo ₂ B ₅ , or a mixed crystal thereof on the Mo surface by heat treatment. The object of the present invention is to provide a method for obtaining a boron coating having mechanical strength and good yield by forming a layer and depositing a boron layer thereon. The present invention will be specifically explained below. A method for forming boron on a substrate by the LP-CVD method is, for example, by heating the substrate placed in a reduced pressure reactor by infrared heating, high frequency heating, energization, etc., and reducing it as shown in the following formula. Boron is precipitated by a decomposition reaction. _{2 B _} Further, in this boron precipitation reaction, various crystal forms can be obtained depending on the heating temperature, reduced pressure state, gas pressure, amount of raw material gas flowing into the reactor, etc. Especially under reduced pressure, the above reaction can be carried out at temperatures between 700℃ and 1000℃.
Amorphous boron is obtained at 1000°C to 1300°C, and β-rombohedral boron is obtained at 1000°C to 1300°C. Especially normal pressure
Compared to CVD, the LP-CVD method is advantageous because amorphous boron and β-rombohedral boron are precipitated at low temperatures, so there is less thermal strain between the substrate and the deposited boron. Amorphous boron on Mo substrate at 700-800℃
The reason why it is preferable to precipitate with is as follows. In other words, at temperatures below 700°C, the precipitation rate is very slow and the precipitation occurs in powder form, making it difficult to create CrB ₂ , MoB ₂ , and Mo ₂ B ₅ through heat treatment. This is because strain easily occurs between the base Mo and the amorphous boron layer. Next, the reason why it is preferable to heat-treat these amorphous boron layers at a temperature of 850 to 1250°C is that below 850°C, CrB ₂ , MoB ₂ , Mo ₂ B ₅
This is because it is difficult to form, and on the other hand, at temperatures above 1250°C, thermal distortion is likely to occur. In addition, it is preferable to form MoB ₂ , Mo ₂ B ₅ , or a mixed crystal of these as a boride of Mo because these crystal systems have a coefficient of thermal expansion closer to that of boron than Mo ₂ B and MoB. This is because the boron film is less susceptible to strain. Also,
The thickness of MoB ₂ , Mo ₂ B ₅ or their mixed crystal layer (diffusion layer) was selected to be 20 μm to 200 μm.
This is because if the thickness is less than 20 μm, thermal strain between the boron layer and the Mo substrate cannot be alleviated, and if the thickness exceeds 200 μm, the substrate itself becomes brittle and difficult to maintain its shape. Furthermore, the reason for metallizing Mo with Cr is to weaken the adhesion between boron and MoB ₂ or Mo ₂ B ₅ and to make it easier to remove the substrate chemically or mechanically. In this case Cr reacts with boron and forms CrB ₂
This has the effect of weakening the adhesion between boron and MoB ₂ or Mo ₂ B ₅ , thereby improving the etching yield. Note that the thickness of the Cr film is preferably about 1 μm. Next, boron is deposited on this boride, and then the substrate is removed chemically or mechanically,
A structural material made of simple boron is obtained. Examples of the present invention will be described in detail below. Example A Mo wire with a diameter of 2.0 mm and a length of 100 cm was prepared. After degreasing and cleaning, Cr was coated to a thickness of about 1 micron by sputtering. 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 minutes per minute for 4 minutes to form amorphous boron on the surface. At this time, the depressurization state is 100Torr
This was controlled using a rotary pump and valve. After that, stop only the BCl ₃ gas and 850
Heat treatment was performed at ℃ for 3 minutes to diffuse the amorphous boron formed on the surface to the base side.
MoB ₂ (20 μm) was used. At this time, the Cr layer is about 1 μm thick.
It had _two layers of CrB. (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. The sample prepared in this way was cut into 4 cm length, and H ₂ SO ₄ and HNO ₃
was immersed in a mixed solution of Mo and MoB ₂ to dissolve it. Next, the length of the beam was set to 3.5 cm, a load W was applied in the form of a beam supported at both ends, and the load was determined from the load when the pipe broke. As a result, out of 20 cut samples,
16 were good (after etching) and their average strength was
It weighed 1.81Kg. These results are shown in Sample No. 1 in Table 1. A boron structural material was obtained in the same manner as in the example below by varying the conditions. The results are shown in Table 1.
However, sample numbers 10 to 14 are comparative examples. In addition, the inner and outer diameters of all samples were 2.0 mm and 2.1 mm, respectively.
The amount of boron precipitated was controlled so that the thickness remained constant at 50 μm.

[Table] As can be seen from the examples [sample numbers 1 to 9] and comparative examples [sample numbers 10 to 14] in Table 1 above, amorphous boron was deposited on Mo by the reduced pressure chemical vapor deposition method, and then by heat treatment. spread this
The method of precipitating boron on a substrate on which CrB ₂ , MoB ₂ , and Mo ₂ B ₅ has been generated and then removing the substrate to obtain simple boron has a high yield of high-strength boron structural materials compared to conventional methods. Moreover, it can be obtained at low cost and has great industrial value.

Claims (1)

[Claims] 1. Low pressure chemical vapor deposition method (LP-CVD method) on a molybdenum (Mo) substrate metallized with chromium.
After that, amorphous boron was precipitated by heat treatment, and then a crystal layer of CrB ₂ , MoB ₂ , Mo ₂ B ₅ or a mixture thereof (boride layer) was formed on the Mo surface, and then a boron layer was precipitated on top of this. A method for producing a boron structural material, comprising removing a rear substrate. 2 The precipitation temperature of amorphous boron is 700℃~800℃
The method for producing a boron structural material according to claim 1, wherein the temperature is .degree. 3 CrB ₂ , MoB ₂ , Mo ₂ B ₅ on Mo by heat treatment
2. The method for producing a boron structural material according to claim 1, wherein the temperature at which the . 4. The method for producing a boron structural material according to claim 1 or 3, wherein the thickness of the layer of MoB ₂ , Mo ₂ B ₅ or a mixture thereof is 20 μm to 200 μm.