KR0153154B1 - Process for preparing sintered hard cubic boron nitride - Google Patents

Abstract

In the production of a lightly cubic boron nitride sintered body, the present invention relates to a method for producing a hard cobalt boron nitride sintered body, which comprises using as a sintering aid a titanium compound selected from the group consisting of titanium carbide, titanium nitride, carbonitride titanium and titanium boride and nickel, molybdenum or molybdenum carbide and (85 to 15%): (10 to 50%) :( 5-30%) :( 0 to 10%).

Description

Method for producing hard cubic boron nitride sintered body

The present invention relates to a method of producing a lightly cubic boron nitride sintered body. More specifically, the present invention relates to a method for preparing a hard cubic boron nitride sintered body by adding a sintering auxiliary agent to a cubic boron nitride powder and sintering the sintered auxiliary material to prepare a sintered alumina sintered body, wherein the sintering aid is selected from the group consisting of titanium carbide, titanium nitride, titanium carbonitride and titanium boride A titanium compound of the species and a mixture of nickel, olivodenium or molybdenum carbide and aluminum nitride.

Cubic boron nitride is a crystalline form of boron nitride which is stable even under high pressure. Such cubic boron nitride has been used as a material for abrasives, cutting tools and cutting tools since it has the second highest hardness and thermal conductivity in the physical properties of diamond (refer to: Applied Technology Seminar on Superabrasive Tools and Materials, GE Superabrasive Division, Korea Applied Technology Development Center (KADE) (1990)]. Cubic boron nitride is a completely synthetic material synthesized from hexavalent boron nitride by a high temperature and high pressure process, a process similar to diamond synthesis (Wentorf, J. Chem. Phys., 26, 956 (1957): C. F. Cardinier, Ceramic Bull., 67, 1006 (1988)]. However, in terms of its physical aspect, it is more resistant to heat than diamond, which is carbon, and unlike diamonds in terms of chemistry, there is no catalytic reaction with iron elements (iron, nickel, cobalt) It is a substance with application range.

However, in order to utilize cubic boron nitride as a cutting tool, a sintered body must be prepared from the powder or the powder thereof (see R. E. Hanneman and L. E. Hibbs, Technical Information Series Report No. 73 CRD182, General Electric (1973)). Since cubic boron nitride is a high-pressure stable phase, high pressure is also required in sintering the powder or powder. In addition, cubic boron nitride is a typical covalent bonding material and is an ovoid-forming material like other covalent bonding materials. Although sintering of cubic boron nitride requires a high temperature, cubic boron nitride is unstable at normal pressure (1 atm) and at high temperature, so that it tends to be converted into hexagonal boron nitride which is in a more stable crystal form. Therefore, in order to produce a sintered body of cubic boron nitride, a high temperature and a high pressure must be simultaneously applied, and an appropriate sintering auxiliary agent should be added to promote sintering.

In the sintering of cubic boron nitride, up to 50% by volume of a sintering auxiliary agent is usually added, and it is known that the mechanical properties of the sintered body vary greatly depending on the content of the sintering auxiliary agent (refer to Fukushin, Technical Cooperation, Vol. 431 (1985)]. A single substance or an alloy of a metal such as nickel, cobalt, aluminum or titanium, a carbide such as silicon carbide or titanium carbide, a nitride such as titanium nitride, silicon nitride or aluminum nitride, an oxide such as alumina or titanium dioxide, titanium carbonitride, sialon, etc.) have been used as sintering additives [refer to: Ito Hidekazu, T. Hirata, Y. Eiji, Inoue Katsuya, (1984): H. Itoh, T. Matsudaira, K. Inoue and S. Naka, Intersection of the magnetic field and the magnetic field, J. Mater. Sci., 25, 203 (1990): Kotoo Mitsuhiro, Korean Patent Publication (B1), Publication No. 93-3642 (1993)

The sintering aid should first allow the transfer of the material necessary for the sintering, and the bonding strength with the cubic boron nitride should be strong while the reaction with the cubic boron nitride is not severe. Further, it should have strength and heat resistance enough to not significantly impair the physical properties of cubic boron nitride. Except for titanium nitride, a single material is rarely used as a sintering aid, and most of the materials are mixed with two or more materials. Existing sintering aids were those which were used without consideration of the sinterability of the sintering aids themselves. That is, a simple liquid metal was used or a solid phase sintering auxiliary agent was used.

The present inventors have experimented with various materials as sintering aids for the production of hard cubic boron nitride sintered bodies having a sintering aid content of up to 15% by volume, and found that titanium carbide (TiC), titanium nitride (TiN) (Ni), molybdenum (Mo) or molybdenum carbide (Mo ₂ C) and aluminum nitride (Al ₂ O ₃ ) are added to one kind of titanium compound selected from the group consisting of titanium (Ti (C, N) (AlN) -based sintering aids were found to be very effective for the production of hard cubic boron nitride sintered bodies, and the present invention has been accomplished.

Accordingly, the present invention relates to a method of producing a hard cubic boron nitride sintered body by mixing a cubic boron nitride powder with a sintering auxiliary agent, and subjecting the mixture to pulverization and deaeration treatment and then sintering to produce a sintered boron nitride material, wherein titanium sulphide (TiC) ), carbo-nitride of titanium (Ti (C, N) and a boride of titanium (TiB ₂₎ 1 species of the titanium compound and the nickel (Ni), molybdenum (Mo) or carbide molybdenum (Mo ₂ C is selected from the group consisting of ) And aluminum nitride (AlN).

The sintering auxiliary agent according to the present invention is prepared as follows. First, nickel powder, molybdenum or molybdenum disulfide powder and aluminum nitride powder are added to one kind of titanium compound powder selected from the group consisting of titanium carbide, titanium nitride, titanium carbonitride and titanium boride, preferably TiX: Ni : Mo or Mo ₂ C: AlN wherein X is C, N, C and N or B ₂ is in the range of (85-15)% :( 10-50%) :( 5-30%) :( 0-10%). The mixture is charged into a stainless steel bar together with a cemented carbide ball and pulverized. The pulverization can be carried out wet by adding alcohol, acetone or hexane. The pulverized powder slurry is dried in an oven and then pulverized again to obtain a fine homogeneous mixture.

Cubic boron nitride powder is mixed with the sintering aid mixed powder prepared as described above at a ratio of about 85 to 98% by volume based on sintered mixed powder and cubic boron nitride powder. The mixed powder is wet pulverized in the same manner as described above and then dried. The dried powder is degassed under nitrogen atmosphere or vacuum. Degassed powders can be used immediately after treatment or stored in a nitrogen atmosphere.

The mixture of the sintering assistant powder and the cubic boron nitride powder is molded into a disc disc shape preferably under a suitable pressure and charged into a high-temperature high-pressure generator. In order to avoid direct contact of the powder compact with the pressure transmission medium, the powder compact is surrounded by zirconium foil, molybdenum foil, tungsten foil or tantalum foil. The charged sample is preferably sintered by keeping it at 4.5 to 6.5 ㎬ and at 1400 to 1550 캜 for 1 to 2 hours. The powder compact is completely densified and a hard cubic boron nitride sintered body having strong bonding between particles is obtained. The sintered body according to the present invention has a hardness of 4000 kg / mm < ² > and has a very uniform microstructure.

The following examples are provided to further illustrate the present invention and are not intended to limit the scope of the present invention thereby.

[Example 1]

Preparation of sintering aids

Nickel powder having an average particle size of 2.4 占 퐉, molybdenum powder having an average particle size of 2.2 占 퐉, and aluminum nitride powder were mixed in a weight ratio of 55: 20: 20: 5. 200 g of this mixture was charged into a stainless steel bar together with a cemented carbide ball, and alcohol was added thereto, followed by wet grinding for 72 hours. The pulverized powder slurry was dried in a vacuum oven at 40 DEG C and then pulverized (granulated). The pulverized powders were uniformly mixed and finely divided.

[Example 2]

Manufacture of mixed powders for sintering

Cubic nitric bromide powders having particle sizes of 1 to 2 占 퐉 were mixed into the powders prepared in Example 1 at a ratio of 90% by volume. The mixed powder was wet pulverized in the same manner as in Example 1 for 24 hours and then dried. The dried powder was degassed under vacuum at 900 < 0 > C for 5 hours. The degassed powder was stored under a nitrogen atmosphere until use.

[Example 3]

Preparation of sintered body

0.5 g of the mixed powder prepared in Example 2 was molded into a disc shape having a diameter of 7 mm and a height of 1.0 mm under a pressure of about 150 MPa. This powder compact was placed in a high-temperature and high-pressure generating apparatus while being placed on a previously prepared cemented carbide disk. At this time, the powder compact / cemented alloy plate was enclosed with a zirconium foil in order to prevent the powder compact / cemented carbide plate from directly contacting with the pressure transmission medium. The charged samples were sintered at 6.5 ㎬ and 1550 ℃ for 1 hour. The powder compact was completely densified and strong bonds were formed between the cubic boron nitride particles.

Claims (5)

Titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiC) and the like as sintering aids in preparing a hard cubic boron nitride sintered body by mixing the cubic boron nitride powder with the sintering auxiliary agent, (Ni), molybdenum (Mo) or molybdenum carbide (Mo ₂ C), and aluminum nitride (Ti ₂ O ₃ ) selected from the group consisting of titanium (Ti) AlN). ≪ / RTI > The method according to claim 1, wherein the sintering aid is a mixture of Ti: Ni: Mo or Mo ₂ C: AlN (wherein X is C, N, C and N or B ₂ ) -50%) :( 5-30%) :( 10% or less). The method according to claim 1, wherein the sintering aid is mixed at about 2 to 15% by volume based on the sintering aid mixed powder and the cubic boron nitride powder. The method of claim 1, wherein the sintering aid is wet milled first, then cubic boron nitride powder is added to the dry powder and the powder is pulverized again. The method of claim 1 wherein the powder of the ground cubic boron nitride / sintering aid is degassed under a nitrogen atmosphere or under vacuum.