JPS6337069B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a ZrB ₂ (zirconium diboride) sintered body. In general, metal boride ceramics have the characteristics of high melting point, high hardness, high strength, and high corrosion resistance, and have traditionally been used as materials for cutting tools and machine parts, but although they have not been put into practical use yet. Most of them are titanium borides, and the reality is that zirconium borides are hardly ever put into practical use. The _ZrB2 composite sintered body of the present invention has a high melting point, high strength,
It has excellent characteristics such as high corrosion resistance, high hardness, electrical conductivity, and oxidation resistance, so it is a material that can be widely used for high-temperature corrosion-resistant parts, mechanical parts, heating elements, electrodes, crucibles for induction furnaces, etc. (Prior Art) There are currently very few ZrB _2- quality composite sintered bodies that are in widespread practical use, but various ones have been proposed in patents and the like. That is, silicides such _{as MoSi 2 ,}
Nitrides such as TaN and HfN, oxides such as ZrO ₂ ,
Carbides such as SiC and B ₄ C, and various metals are known. (Problems to be Solved by the Invention) For example, regarding silicides, zirconium silicide is disclosed in Japanese Patent Publication No. 38-6098, and MoSi ₂ is disclosed in U.S. Pat. No. 3,705,112, but these Si-based compounds are Because it melts or decomposes during sintering in a high-temperature atmosphere, the structure is often porous and the grain growth of the crystals becomes large.As a result, the strength and corrosion resistance are often insufficient, and the oxidation resistance is also lower than that of SiO ₂ . Although it is expected to be effective as a film, these subcomponents alone are not sufficient for use in air. Next, regarding nitrides, U.S. Patent No. 3305374
TaN disclosed in ZrB ₂ as a high hardness material,
It is added to TiB ₂ , etc. and applied to tool materials and decorative materials, and although it is excellent in terms of high hardness and high strength, it is used in high-temperature oxidizing atmospheres such as high-temperature corrosion-resistant parts, heating elements, electrodes, induction furnace crucibles, etc. When used, oxidation resistance,
It is not sufficient in terms of spall resistance, corrosion resistance, etc. Next, regarding carbides, refer to U.S. Patent No. 3775137.
SiC, B ₄ C and SiC are disclosed in U.S. Patent No. 3325300, but U.S. Patent No. 3775137 discloses
The addition of SiC alone is insufficient in terms of oxidation resistance, and the addition of No. 3325300 MoSi ₂ + B ₄ C, MoSi ₂ + SiC +
With the addition of B ₄ C, MoSi ₂ has a lower melting point than the sintering temperature, so it melts during sintering, decomposes, and promotes grain growth, making the structure porous, making it difficult to increase density, and reducing oxidation resistance. Not enough. Further, an example of using a nitride and a carbide in combination is disclosed in US Pat. No. 4,199,480. That is, in US Patent No. 4199480, TiB ₂ is combined with SiC.
Refractories with added BN are shown, instead of TiB ₂
It is also disclosed that ZrB ₂ is used. This patent describes a conductive boat for vacuum deposition of metal, and the atmosphere in which this material is used is vacuum. However, when this material is heated in air, it is susceptible to oxidation, and _TiB2 -based materials in particular undergo oxidation and turn white. Additionally, this material has more than 15% SiC, so
It does not have sufficient corrosion resistance against molten metals such as molten steel, molten slag, etc., and is not suitable for use in environments where these materials must be used in an atmosphere. Regarding oxides, a composite with ZrO ₂ is disclosed in Japanese Patent Publication No. 47-38048, but this is a tetragonal crystal.
The aim is to achieve high strength and high toughness through transfer strengthening of ZrO ₂ , and when used in conditions such as high temperature oxidizing atmospheres, high strength and high toughness can be achieved by using tetragonal crystals.
It was observed that ZrO ₂ decreased due to the transfer to the monocline, and the oxidation resistance and spalling resistance were also insufficient. Furthermore, JP-A No. 47-31831, 1982-10084, 1983-
38365 etc. is a sintered body whose main component is _TiB2 , but it is a sintered body whose main component is hexagonal BN or AlN, and vice versa.
Products with BN as the main component and TiB ₂ or ZrB ₂ added as subcomponents are known, and are mainly intended for use in non-oxide atmospheres such as molten metal containers or vacuum evaporation motors. There is. However, mixtures containing BN, which is difficult to sinter, as shown in these examples, have extremely low densification and oxidation resistance, and are only suitable for use in air. In view of these points, we have developed an approach to overcome the conventional problems with the ZrB ₂ -quality sintered body, which has excellent properties but is not fully utilized and is actually used only in extremely limited applications. As a result of our research, we have developed a sintered body that has excellent properties such as high density, high strength, oxidation resistance, corrosion resistance, and spalling resistance, and has significantly improved some of its properties. It was successful. (Means for Solving the Problem) That is, the present invention is a ZrB bi-material sintered material containing 1 to 12% and 1 to 35% by weight of SiC and BN as subcomponents, respectively, and the remainder substantially consisting of _{ZrB2 .} The body is the gist. The ZrB ₂ used in the present invention can be obtained, for example, by reacting a mixture of zirconium oxide, boron oxide, and carbon at high temperatures, and it is preferable to use ZrB 2 with the highest possible purity for producing the present sintered body.
Further, a powder having a particle size as small as possible is preferable. Specifically, it has a purity of 99% or more and an average particle size of 10 μm, particularly 5 μm or less. Furthermore, regarding SiC and BN, which are present as by-products, it is sufficient that they are present in a predetermined amount as such compounds in the sintered body, so they may be blended in any form as starting materials. However, if raw materials other than SiC and BN are used, special consideration is required at the sintering stage, so it is better to prepare them as SiC and BN as the usual blended raw materials. The SiC and BN raw materials are preferably as pure as possible, usually 99% or higher. The raw material mixture is usually prepared by uniformly mixing these three types of fine powders, but the same effect can be obtained by ultrafinely pulverizing them for the purpose of pulverizing and mixing. In general, the particle size of the mixed raw material is preferably 10 μm or less, preferably the average particle size
It is necessary to sufficiently adjust the thickness to 1 μm or less. The sintered body of the present invention is produced by filling the mixture into a graphite mold, for example, and firing it in vacuum or in a neutral or reducing atmosphere such as argon, helium, carbon monoxide, etc. under normal pressure or at a rate of 50 to 2000 kg/cm. It is possible to fire under pressure of about ² or under any pressure. The firing temperature is 1,600 to 2,200℃, and the firing time is 30
Approximately 1 minute to 1 hour is appropriate. The proportion of the subcomponents in the sintered body of the present invention is 2 to 50% by weight (the same applies hereinafter),
Although the remainder essentially consists of ZrB ₂ , a small amount of this ZrB ₂ may be replaced with other components, such as TiB ₂ , to the extent that the characteristics of ZrB ₂ are not impaired. At least 1% or more of each of BN and SiC as subcomponents is required, but this is because if BN is less than 1%, the characteristics of spalling resistance, oxidation resistance, and high corrosion resistance will not be fully exhibited, and if SiC is less than 1%, This is because the oxidation resistance is not sufficient and it is difficult to increase the density. It is not clear why the presence of SiC improves the oxidation resistance of this sintered body, but it may be due to the formation of a highly viscous B ₂ O ₃ -SiO ₂ film during use. This fact indicates that the present sintered body can be used satisfactorily in applications such as heating elements. Furthermore, in applications such as heating elements, it is advantageous to be able to make the electric resistance variable, and the sintered body of the present invention is very advantageous because it uses SiC together with BN, which acts as an insulating component. On the other hand, it is possible for each of BN and SiC to exist up to about half the amount in the sintered body, but BN
If the SiC content exceeds 50%, sintering becomes difficult and a high-density product cannot be obtained, and if the _SiC content exceeds 50%, the spalling resistance effect will not be exhibited, which is undesirable. Therefore, the total amount of BN and SiC should be 5 to 45%.
It is necessary to keep it. A more desirable range within these ranges is
The total amount of SiC and BN is 10 to 30%, and SiC and BN
The ratio of the former is 5-50% of the total amount of both, and the latter is 95%.
~50%. Furthermore, the corrosion resistance for applications that require high corrosion resistance, especially against molten steel and molten slag, deteriorates as SiC increases, so it is desirable to keep SiC at a maximum of 12%, especially 3 to 10%. That's true. And from this comprehensive perspective,
BN is desirably 1 to 35%, particularly 3 to 25%. It should be noted that other components may of course be included as subcomponents to the extent that they do not essentially impair the intended effects of the sintered body of the present invention, but it is necessary to keep them in as small a quantity as possible, including unavoidable impurities. be. (Effects of the Invention) As described above, the sintered body of the present invention obtained in this way is a dense sintered body with high density, oxidation resistance, spalling resistance, high strength, and excellent corrosion resistance. Because it is a ZrB material, it is especially suitable for high-temperature corrosion-resistant parts such as molten steel and molten slag that are used in the air, heating elements, crucibles, etc. It can also be applied to other mechanical parts materials, tools, _etc. It can be used for various purposes that exhibit the characteristics of a sintered body,
Its practical value is great. (Example) Example 1 85 parts of ZrB ₂ powder (purity 99 or higher), 10 parts of hexagonal BN powder, and 5 parts of SiC powder were thoroughly mixed and ground.
Grind and mix for 3 hours using SiC balls in ethanol solvent using a pot mill. The obtained powder was thoroughly dried by removing alcohol with an evaporator to obtain a powder with an average particle size of 0.15μ. This powder was packed in a graphite mold under an argon gas atmosphere to produce 350kg/
A sintered body was obtained by heating at 2000° C. for 30 minutes under a pressure of cm ² . The characteristics of the obtained sintered body were that the relative density was 98%, the bending strength was 45 Kg/mm ² , the oxidation resistance (Note 1) remained unchanged, and the spall resistance (Note 2) was ΔT=700°C. Furthermore, there was no change in the corrosion resistance (Note 3) test. Examples 2 to 5, 9 to 11 and Comparative Examples 1 to 4 Predetermined amounts of ZrB ₂ , BN, and SiC powders similar to those in Example 1 were placed in the same graphite mold as in Example 1, and under specific sintering conditions (atmosphere). was obtained by sintering with argon). Examples 6 to 8 The above powders were molded at 2000 kg/cm ² using a rubber press and baked at 2100° C. for 1 hour under normal pressure in an argon atmosphere. Table 1 shows the characteristics of each sintered body. (The weight ratio in each sintered body increases by about 2% from the sample composition ratio in the example because there is an increase in SiC due to SiC mixing from the grinding balls compared to the sample composition ratio.Comparative example 1 does not use SiC balls and is mixed by dry grinding, so there is no SiC contamination.)

[Table] Comparative Examples 5 to 7 TiB ₂ powder (purity 99% or more), BN powder (purity 99%)
% or more) and SiC powder (purity of 99% or more) were pulverized and mixed for three days using a pot mill and SiC balls in an ethanol solvent in order to sufficiently pulverize them.
The obtained powder was thoroughly dried by removing alcohol with an evaporator to obtain a powder with an average particle size of 0.15μ.
This powder was filled into a graphite mold and heated at a pressure of 350 Kg/cm ² at 2000° C. in an argon atmosphere for 30 minutes. The properties of the sintered body are shown in Table 2.

【table】
Coloration * All other than those listed are Ti except for unavoidable impurities.
B ₂ , and the stated amount is 100 parts by weight minus TiB ₂ .
This is the remainder after subtraction.

Claims (1)

[Claims] 1. A ZrB binary composite sintered body containing 1 to 12% and 1 to 35% by weight of SiC and BN as subcomponents, respectively, with the remainder essentially consisting of _{ZrB 2} . 2. The sintered body according to claim 1, wherein the total amount of SiC and BN is 5 to 45%. 3. The sintered body according to claim 1 or 2, wherein SiC is 3 to 10%. 4. The sintered body according to claim 3, wherein BN is 3 to 25%. 5. The sintered body according to claim 4, wherein the total amount of SiC and BN is 10 to 30%.