JP2003034577A - Silicon nitride-based composite sintered body and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive silicon nitride-based composite sintered body having a smooth surface after electrical discharge machining and good mechanical properties, and to provide a method for producing the same. SOLUTION: Silicon nitride powders, sintering aid powders, titanium metal powders and boron nitride powders are ground and mixed until the silicon nitride, titanium nitride, and titanium boride have an average particle diameter of 30 nm or less, and are sintered in a non-oxidizing atmosphere. There is obtained the silicon nitride-based composite sintered body comprising the silicon nitride having an average particle diameter of 100 nm or less, titanium nitride compounds and titanium boride having an average minor axis diameter of 20 nm or less and an aspect ratio of 3 or more, wherein fracture strength is 600 MPa or more and resistivity is 10<0> Ω.cm or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride composite sintered body having conductivity which is useful as a wear resistant member such as various mechanical members, cutting tools and sliding members.

[0002]

2. Description of the Related Art Silicon nitride has excellent hardness, mechanical strength, heat resistance, and is chemically stable. Therefore, various mechanical members typified by automobile engine parts, cutting tool materials, bearings, and other wear resistant materials are used.・ Widely used for sliding members. In any of these fields in recent years, the performance level imposed on materials has become severe, and the processing accuracy and the like required for those materials have become severe. As a result, when these materials are used as a product, the processing cost becomes high, and the product cost becomes high, which is the biggest factor that hinders the expansion of the market.

Therefore, various processing methods have been proposed.
There is. The most commonly used method is conductive particles
Dispersed in a matrix composed of silicon nitride and a grain boundary phase.
This makes the silicon nitride-based composite sintered body conductive.
In addition, there is a method of performing electric discharge machining. In the present invention,
"Silicone-based" means silicon nitride (Si ₃
N_Four) And / or ceramics containing sialon
Point to. Also, "silicon nitride-based composite sintered body" is
In a matrix with such ceramics as the main crystal phase,
It refers to a material in which different components are dispersed and composited.

As such a conductive material, according to Ceramics 21, P719-725 (1986),
It is described that by dispersing 20 to ₄₀ vol% of conductive particles in Si ₃ N ₄ , a silicon nitride material having conductivity can be produced and electric discharge machining can be performed. However, the surface roughness of such a silicon nitride material after electric discharge machining is poor, and melting and surface cracks due to thermal shock and electric discharge during electric discharge machining exist. Therefore, if you do not grind to remove the surface cracks after electrical discharge machining,
It had poor mechanical properties and could not be used practically.
In addition, unless TiN is added in an amount of 20 vol% or more, it is not possible to obtain conductivity that allows electric discharge machining. Further, since TiN and Si ₃ N ₄ have large thermal expansion coefficients, there is a problem that when TiN is added in an amount of 20 vol% or more, the thermal shock temperature is reduced to about half that in the case of no addition.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. That is, the present invention provides a conductive silicon nitride-based composite sintered body having a smooth surface after electrical discharge machining and excellent mechanical properties, and a method for producing the same.

[0006]

The silicon nitride-based composite sintered body of the present invention comprises silicon nitride having an average particle size of 100 nm or less,
A silicon nitride-based composite sintered body containing a titanium nitride compound and titanium boride having an average minor axis diameter of 20 nm or less and an aspect ratio of 3 or more, and a breaking strength of 600 MPa or more.

Further, silicon nitride composite sintered body of the present invention, since the titanium nitride-based compound and titanium boride are uniformly dispersed in the network structure in the nano-order, while entangled, resistivity is 10 ⁰ Omega · cm or less.

The sintered body of the present invention comprises a step of preparing powders of silicon nitride powder, a sintering aid, titanium metal and boron nitride, and the powders of silicon nitride, titanium nitride and boride. A step of pulverizing and mixing until the average particle diameter becomes 30 nm or less, a step of molding the mixed powder to form a molded body, and 1100 to 150 of the molded body in a non-oxidizing atmosphere.
It can be obtained by a manufacturing method including a step of sintering in a temperature range of 0 ° C. to obtain a sintered body.

Further, the composition of the starting material of the sintered body of the present invention is such that titanium metal is 10 to 60 vol% and boron nitride is 3
It is preferable that the content is ˜20 vol%, and the balance is silicon nitride and a sintering aid.

The titanium nitride compound is TiN or T
It refers to titanium nitride or oxynitride such as iON.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The composite sintered body of the present invention will be described in detail below, including the manufacturing method thereof. The average particle size of the silicon nitride particles and the titanium nitride-based compound of the composite sintered body of the present invention,
It is 100 nm or less. As used herein, silicon nitride includes sialon, silicon oxynitride, and the like that are inevitably generated by a sintering aid or a process. Further, the average minor axis system of titanium boride (TiB ₂ ) contained in the sintered body of the present invention is 20 nm or less, and the aspect ratio, which is the ratio of the average major axis diameter to the average minor axis diameter, is 3 or more. . When a composite sintered body having an average particle size of silicon nitride and a titanium nitride-based compound larger than 100 nm is used, the material cannot be removed efficiently during electric discharge machining. It gets worse. If the average minor axis system of TiB ₂ exceeds 20 nm or the aspect ratio is less than 3, a network structure cannot be efficiently formed and the conductivity decreases.

To enable electrical discharge machining, conductivity is required. Therefore, it is necessary that the conductive particles contained in the material are uniformly dispersed in a network form on the order of nanometers. When titanium metal having an average particle size of 20 μm or less and boron nitride are mixed as a starting material with a silicon nitride powder having an average particle size of 10 μm or less and a sintering aid, sinter obtained through the steps of crushing, mixing, molding, and sintering. Body has an average particle size of 10
Silicon nitride and a titanium nitride-based compound of 0 nm or less, and an average short axis system of 20 nm or less and titanium boride having an aspect ratio of 3 or more are included, and the breaking strength is 600 MPa or more. Since titanium nitride compound particles and the titanium boride particles are dispersed uniformly in the network-like nanometric while entangled, resistivity of the sintered body becomes less 10 ⁰ Ω · cm, the discharge can be performed.

The silicon nitride composite sintered body of the present invention contains the titanium nitride compound and titanium boride as the conductive particles as described above. Since the specific resistance of titanium boride is as low as about 1/4 of the specific resistance of titanium nitride, titanium nitride can obtain the electrical conductivity of a sintered body to the extent that electric discharge machining is possible with a smaller addition amount than before. . The thermal expansion coefficient of titanium boride is smaller than the thermal expansion coefficient of titanium nitride and is close to the thermal expansion coefficient of silicon nitride, so that the thermal shock temperature of the sintered body can be kept high.

The material of the present invention is a silicon nitride powder,
A step of preparing powders of a sintering aid, titanium metal, and boron nitride; and a step of pulverizing and mixing these powders with silicon nitride until the average particle diameter of titanium nitride and boride becomes 30 nm or less. It can be obtained by a manufacturing method including a step of molding the mixed powder into a molded body, and a step of sintering the molded body at 1100 to 1500 ° C. in a non-oxidizing atmosphere to form a sintered body. . In this crushing and sintering process, boron nitride is changed to titanium boride, and titanium boride particles having a minor axis diameter of 20 nm or less and an aspect ratio of 3 or more are formed.

Any raw material powder may be commercially available. The crystal form of the Si ₃ N ₄ powder may be either α type or β type, and either imide decomposition powder or direct nitriding powder may be used. Both the Si ₃ N ₄ powder and the sintering aid powder are preferably as small as possible average particle diameters in order to facilitate particle size control and improve mechanical properties, but those having an average particle diameter of 5 μm or less, and more preferably 2 μm or less are more desirable. The average particle size of titanium metal and boron nitride is preferably as small as possible, but is preferably about 20 μm or less, and more preferably 10 μm or less.

The average particle diameters of the pulverized and mixed powders of silicon nitride powder and titanium nitride and boride powders are 30 nm.
Grind and mix as follows. When it exceeds 30 nm, it becomes difficult to control the average particle diameter of the silicon nitride particles and the titanium nitride and boride particles in the sintered body to 100 nm or less, and the structure becomes non-uniform, resulting in a machined surface after electrical discharge machining. The surface roughness deteriorates. The mixing is preferably performed by a method such as a ball mill or an attritor that involves grinding.
For example, as described in Japanese Patent Laid-Open No. 10-338576, mechanical alloying is performed using this type of mixing device. According to this method, a fine mixed powder having an average particle size of 30 nm or less is obtained due to the plastic deformability and the mechanochemical reaction of the metal powder added as the dispersed particle source. The conditions such as the acceleration of the pulverization, the charge amount ratio of the powder and the pulverizing medium, the pulverizing time, etc. are appropriately selected according to the average particle size level of the initial raw material powder.

The composition of the starting material powder is titanium metal 10
The range of -60 vol% and boron nitride 3-20 vol% is preferable. The balance is silicon nitride and a sintering aid. Titanium metal, it is less than 10 vol%, a conductive particle and the amount of titanium nitride or titanium boride decreases discharge machining is possible resistivity 10 ⁰ Ω · cm difficult to obtain less conductive Become. If the titanium metal content exceeds 60 vol%, the amount of titanium nitride, which has low strength, is increased, so that the strength of the sintered body is remarkably deteriorated and cannot be put to practical use.
Further, when the boron nitride content is less than 3 vol%, titanium boride is reduced, so that the conductivity is lowered and the fracture strength of the sintered body is lowered, which makes it unusable for practical use. Further, when the boron nitride content exceeds 20 vol%, the amount of the remaining boron nitride increases, so that the fracture strength of the sintered body also decreases.

The mixed powder prepared as described above can be used in a known molding method such as a normal dry press molding method, an extrusion molding method, a doctor blade molding method and an injection molding method, to obtain a desired shape. In addition, the most desirable molding method in terms of quality and production should be selected. It is also possible to granulate the mixed powder after pulverization and mixing prior to molding to increase the bulk density in advance to improve moldability.

The molded product is 1100-110 in a non-oxidizing atmosphere.
Sinter in the temperature range of 1500 ° C. As a heating means for sintering, normal atmospheric pressure sintering may be used, but a means such as a pulse discharge sintering method or a high frequency induction heating type sintering method capable of heating and uniformly heating a compact in a short time is desirable. . It should be noted that the sintering may be performed under pressure by applying pressure with an atmosphere gas or by mechanically applying an external pressure. If the sintering temperature is 1100 ° C. or lower, it will not be sufficiently sintered. Further, when the temperature exceeds 1500 ° C., grain growth becomes remarkable and it becomes difficult to obtain the composite sintered body of the present invention.

[0020]

EXAMPLES α-type silicon nitride powder having an average particle size of 0.5 μm, metallic Ti powder having an average particle size of 10 μm, boron nitride (BN) powder having an average particle size of 5 μm, and a sintering aid for silicon nitride. 5 wt% Y ₂ O ₃ and 1 wt% Al
₂ O ₃ was prepared. Each powder is commercially available. After adjusting the Ti and BN amounts shown in Table 1, 150G
The mixture was mixed for 16 hours using a planetary ball mill having an acceleration of. The average particle diameter of the primary particles of the obtained mixed powder was all 30 nm or less.

[0021]

[Table 1] * Indicates comparative example

The prepared mixed powders were pressure-sintered by a pulse discharge heating method at a pressure of 1300 ° C. and a pressure of 30 MPa in a nitrogen atmosphere of 1 atm. The temperature was measured with a two-color thermometer using a die. The surface of each of the obtained sintered bodies was mirror-finished and then observed with a transmission electron microscope to measure the average particle diameter of each particle of silicon nitride and titanium nitride. For the titanium boride particles, the average minor axis diameter and the average major axis diameter were measured, and the aspect ratio was calculated. Each particle was identified by EELS (electron energy loss spectroscopy). As one example, No.
Transmission electron micrographs and EELS results for the sample of No. 6 are shown in FIGS. 1 and 2. It can be seen from FIGS. 1 and 2 that the TiB ₂ particles are columnar particles and are entangled so as to penetrate the TiN particles.

Furthermore, the conductivity, measured by a four-point resistance measuring instrument, the electrical resistance is possible electric discharge machining 10 ⁰ Omega ·
○ those with cm or less, × with those larger
Indicated by. As mechanical properties, JIS R1601
The test piece was finished into the strength test piece shape specified in 1 above, and the three-point bending strength was measured according to the same specification. The surface to which the tensile stress was applied during the strength test was left as it was in electrical discharge machining. The results of measuring these characteristics are shown in Table 2.

[0024]

[Table 2]

From this table, it is understood that the sintered bodies of the present invention all have a breaking strength of 600 MPa or more. Also, N
o. As in the case of No. 2, the conventional addition of TiN alone does not make electrical discharge machining possible. Even with a small addition amount of Ti of 10 vol%, it was possible to obtain electrical conductivity that enables electrical discharge machining. If 10% by volume of Ti is converted to TiN, the amount of TiN is 10.7 vo.
It becomes 1%.

No. With respect to the sintered body of No. 6, a sample was cut and processed using a wire electric discharge machine (Sodick AP450), and the surface roughness (Ra) of the electric discharge machined surface was measured by a contact surface roughness meter. As a result, the surface roughness of the EDM surface is
It was 0.2 μm or less over the entire electric discharge machined surface.

Further, in No. The fracture toughness value of the sintered body of No. 6 measured by the indentation method (IF method) is 6.5 MP.
It was a · m ^1/2 . Vickers hardness (Hv) is 1
It was 9.6 GPa. Further, it was confirmed that the thermal shock fracture resistance (ΔT: so-called thermal shock temperature) by the underwater quenching method was 600 ° C. or higher, which was about the same as the thermal shock temperature of silicon nitride to which TiN was not added.

[0028]

According to the present invention, the electric discharge machining is performed by uniformly dispersing the titanium nitride compound and titanium boride in a nano-order in a network in a fine matrix containing Si ₃ N ₄ as a main component. It is possible to provide a silicon nitride-based composite sintered body having excellent mechanical properties even in the electrical discharge machining state, at a lower cost than ever before.

[Brief description of drawings]

FIG. 1 shows an example No. 6 shows a transmission electron micrograph of No. 6.

FIG. 2 (a) shows the EELS results of the particles indicated by 1 in FIG. (B) shows the EELS results of the particles indicated by 2 in FIG.

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Claims (4)

[Claims] 1. Silicon nitride having an average particle size of 100 nm or less,
A silicon nitride-based composite sintered body containing a titanium nitride-based compound and titanium boride having an average minor axis diameter of 20 nm or less and an aspect ratio of 3 or more, characterized by a breaking strength of 600 MPa or more. Silicon nitride composite sintered body. 2. Silicon nitride having an average particle size of 100 nm or less,
A titanium nitride compound, an average minor axis diameter of a silicon nitride composite sintered body containing the less is the aspect ratio of 3 or more titanium boride 20 nm, specific resistivity of 10 ⁰ Ω · c
A silicon nitride-based composite sintered body characterized by being m or less. 3. A silicon nitride powder, a sintering aid, titanium metal,
A step of preparing each powder of boron nitride, a step of pulverizing and mixing these powders with silicon nitride until the average particle diameter of metal nitride and boride becomes 30 nm or less, and molding and molding the mixed powder The method for producing a silicon nitride-based composite sintered body according to claim 1, comprising a step of forming a body and a step of sintering the formed body in a non-oxidizing atmosphere to form a sintered body. 4. A starting material containing titanium metal in an amount of 10 to 60 vol.
%, And boron nitride is contained in an amount of 3 to 20% by volume. 4. The method for manufacturing a silicon nitride-based composite sintered body according to claim 3, wherein