JP5088851B2 - Silicon nitride sintered body for wear-resistant member, method for producing the same, and wear-resistant member using the same - Google Patents

Description

The present invention relates to a silicon nitride sintered body for wear-resistant members, a method for producing the same, and a wear-resistant member using the same, and in particular, by incorporating a conductivity-imparting material, electric discharge machining is possible, and static electricity is accumulated. The present invention relates to a non- wearable silicon nitride sintered body for a wear-resistant member , an efficient manufacturing method thereof, and a wear-resistant member that uses the silicon nitride sintered body for wear-resistant member to improve problems caused by static electricity.

  In recent years, there have been remarkable developments in magnetic recording devices such as hard disk drives (HDD), optical disk devices such as CD-ROM and DVD, and various game machines. In an electronic apparatus having these disk media, a rotary shaft is usually rotated at a high speed by a rotary drive device such as a spindle motor, and various disks mounted on the rotary shaft are functioned.

  Metal materials such as bearing steel have been mainly used for bearing members, particularly bearing balls, that support the rotating shaft of the rotary drive unit for electronic equipment as described above. However, since metal materials such as bearing steel have insufficient wear resistance, for example, in fields where high-speed rotation of 5000 rpm or more is required, such as electronic equipment, the life varies widely and is highly reliable over a long period of time. However, there is a problem that it is not possible to guarantee the rotational drive having the property.

  In order to solve such problems, in recent years, ceramic materials such as a silicon nitride sintered body have been used as a component of a bearing ball (see, for example, Patent Document 1). A silicon nitride sintered body is excellent in sliding characteristics among ceramic materials and has good wear resistance. Therefore, it has been confirmed that a mechanically reliable rotational drive can be provided even when high-speed rotation is performed.

  However, since a silicon nitride bearing ball is an electrically insulating material, static electricity generated during high-speed rotation is generated by a bearing other than the bearing ball such as a rotating shaft or ball receiving portion made of a metal material such as bearing steel. There arises a problem that the member cannot be effectively diffused. Thus, if static electricity is not smoothly dissipated and the bearings and peripheral components are charged more than necessary, it will adversely affect an electronic device having a recording medium using a magnetic signal such as a hard disk drive, for example. As a result, there was a phenomenon that the electronic devices such as hard disks were destroyed.

Therefore, in order to prevent the accumulation of static electricity more than necessary, development of bearing balls made of silicon nitride with reduced insulation has been underway. For example, a conductive silicon nitride sintered body having an electric resistance value of about 10 ⁻⁵ Ω · m has been conventionally known (see, for example, Patent Document 2). In this conductive silicon nitride sintered body, a conductivity imparting material such as metal carbide or metal nitride is added. A silicon nitride sintered body containing a conductive compound such as metal carbide or metal nitride is also described in Patent Document 3, Patent Document 4, Patent Document 5, Patent Document 6, and the like. Also in bearing balls used for rotation drive parts of electronic devices, it has been studied to use a silicon nitride sintered body with reduced insulation by using a conductivity imparting material such as metal carbide or metal nitride. ing.

  Another problem is that electronic devices such as portable personal computers, electronic notebooks, and various mobile products are becoming smaller and more portable year by year, and the hard disks used in these electronic devices are also becoming more technical and technical. The demand is getting stronger. In order to cope with such high capacity and small size, it is premised on further high speed rotation, and it is predicted that high speed rotation of about 10,000 rpm or more will be realized in the future.

Usually, the mechanism for realizing the high-speed rotation as described above is a bearing member including a rotating shaft member, a bearing ball portion, and a ball receiving portion, and excessive pressure generated by the rotational motion is substantially concentrated on the bearing ball. Become. Since conventional bearing steel bearing balls have low rigidity, there has been a problem that when high-speed rotation is continued for a long time, the rotational noise increases and the bearing balls themselves are easily destroyed. On the other hand, a bearing member for rotationally driving an electronic device such as a hard disk drive (HDD) by realizing stable high-speed rotation and reducing the amount of static electricity by using silicon nitride with reduced insulation. Suitable bearing balls are applied.
JP 2000-314426 A Japanese Patent Publication No. 2-343699 Japanese Patent Publication No. 7-29855 Japanese Patent No. 2566580 JP-A-6-227870 JP 2003-292378 A

  As shown in Patent Document 6 and the like, there is a method of adding a large amount of carbide such as SiC or nitride such as TiN as a method for imparting conductivity to a silicon nitride sintered body that originally has insulation. In this case, carbide and nitride as a sintering aid and a conductivity imparting material are present at the grain boundaries of the silicon nitride sintered body. In particular, carbides have the effect of suppressing the grain growth of silicon nitride crystals, and the tendency to impair the mechanical strength of the sintered body is remarkable. In other words, since grain growth is hindered, it becomes difficult to form the original microstructure of silicon nitride in which a large number of needle-like crystals are intricate, and at the same time the grain boundary strength is reduced, so that the grain boundary is selectively worn. Became clear. This wear is a minute wear having a size of about several nanometers. However, when a bearing ball made of a silicon nitride sintered body as described above is applied to a rotary drive unit such as an HDD, the wear of the bearing ball is about several nm. Even so, there is a problem of increasing the noise of the bearing portion.

  For this reason, selective wear based on a decrease in wear resistance of the silicon nitride sintered body caused by the compounding of a conductivity imparting material such as a metal carbide or metal nitride, particularly a decrease in the strength of the grain boundary phase. Suppression is a problem of a bearing ball for electronic equipment to which conductivity is imparted.

  In addition, in order to solve the above-mentioned problem of micro-abrasion, there is also known a method that does not inhibit grain growth by defining the grain size of carbide added to the silicon nitride sintered body and dispersed in the structure to 400 nm or less. Yes. However, since these carbide particles enter the silicon nitride crystal grains, the effect of lowering the insulating properties of the silicon nitride sintered body is hardly seen. Therefore, with such a silicon nitride sintered body having insulating properties, electric discharge machining is difficult, and it is virtually impossible to manufacture a jig having a fine and complicated shape from the sintered body using electric discharge machining. There was a problem that it was possible.

  The present invention has been made in order to solve the above-described problems, and includes a conductivity imparting material to enable electric discharge machining, and a silicon nitride sintered body having no accumulation of static electricity and its efficient production. It is an object of the present invention to provide a wear-resistant member that has improved problems due to static electricity using the method and the silicon nitride sintered body.

  In addition, when applied to bearing balls for electronic equipment, etc., it has wear resistance that can realize stable high-speed rotation, can prevent noise due to wear, and contains a predetermined amount of conductivity imparting material. Wear resistance such as bearing balls suitable for bearing members for rotating and driving electronic equipment such as hard disk drives, etc. The object is to provide a member.

In order to achieve the above object, a silicon nitride sintered body for wear-resistant members according to the present invention comprises a silicon nitride powder, a sintering aid powder and carbon nanotubes, silicon carbide and titanium nitride as conductivity imparting materials. In the silicon nitride sintered body for wear-resistant members mixed and sintered, the carbon nanotube is 1 to 5% by mass, the silicon carbide is 5 to 20% by mass, and the titanium nitride is 0.1 to 5% by mass, respectively. contained, the range der of electrical resistance 10 ^-2 ~10 ³ Ω · cm is, characterized in that the electrical conduction path continuous by contact with silicon carbide or titanium nitride and the carbon nanotube is formed .

In the silicon nitride sintered body for wear-resistant members according to the present invention, the silicon nitride sintered body for wear-resistant members preferably contains 0.1 to 5% by mass of metal carbon silicide.

Furthermore Te the wear resistant member for a silicon nitride sintered body odor, before Symbol silicon nitride sintered body and 10 mass% in terms of oxide of the rare earth elements, and 2-10 wt% of aluminum in terms of oxide It is preferable to contain.

Moreover, Te the wear resistant member for a silicon nitride sintered body odor, it is preferable prior Symbol carbon nanotubes are multi-wall carbon nanotube.

Furthermore Te the wear resistant member for a silicon nitride sintered body odor, it is preferable prior Symbol metal carbonitride silicide is carbon molybdenum silicide.

In the method for producing a silicon nitride sintered body for wear-resistant members of the present invention, silicon nitride powder contains 1 to 5% by mass of carbon nanotubes as a sintering aid powder and a conductivity-imparting material, and 5 to 5% of silicon carbide. 20% by mass and 0.1-5% by mass of titanium nitride are mixed, the molding step of molding this mixture into a predetermined shape, and the molded body obtained by the molding step is heated to 1700-1850 ° C. A primary sintering step of preparing a primary sintered body by sintering in a temperature range, and a secondary sintering in which the obtained primary sintered body is subjected to a hot isostatic pressing (HIP) treatment in a temperature range of 1500 to 1750 ° C. In the primary sintering step, the heating time in the temperature rise range of 1500 to 1650 ° C. is 30 minutes or more and 120 minutes or less, and the obtained silicon nitride sintered body has an electric resistance value of 10 ^{−. 2-10} range der of ^{3 Ω} · cm is, the mosquitoes Wherein the continuous electrical conduction path by contact with carbon nanotube and the carbide or titanium nitride is formed.

Furthermore, the manufacturing method smell of the wear resistant member for a silicon nitride sintered body Te, before SL and 1 to 10 mass% in the silicon nitride powder a rare earth element in terms of oxide, 2-10 wt% aluminum in terms of oxide Are preferably mixed.

In the silicon nitride sintered body for wear-resistant members of the present invention, carbon nanotubes, silicon carbide and titanium nitride are blended as conductivity imparting materials, respectively, so that 0.01-10 ³ Ω · An electric resistance value (conductivity) in the range of cm is given.

  By blending carbon nanotubes, silicon carbide and titanium nitride as the conductivity imparting material, conductivity suitable for preventing electrostatic retention and electric discharge machining is imparted to the silicon nitride sintered body. In particular, since carbon nanotubes having high contact probability and excellent conductivity with conductive particles of silicon carbide and titanium nitride dispersed in the silicon nitride sintered body are contained, the conductive particles and the carbon nanotubes It is easy to form a continuous electrical conduction path due to the contact of the silicon nitride, the conductivity of the silicon nitride sintered body is increased, the problems due to static electricity can be solved, and it is possible to form a wear-resistant member with a complicated shape by electric discharge machining Become.

  Moreover, in this invention, it is preferable to mix | blend metal carbon silicide in a raw material, and to make metal carbon silicide particle | grains exist in a sintered compact as a crystal phase. That is, metal carbon silicide (MxSiyCz) has a lower grain boundary hardness than silicon carbide or titanium nitride, but is a material that forms a grain boundary excellent in toughness. By making it exist in the grain boundary phase, the grain boundary phase can be strengthened.

  Moreover, the metal carbon silicide has the same conductivity as silicon carbide or titanium nitride. Therefore, by causing the metal carbon silicide particles to exist in the grain boundary phase or the like, without impairing the conductivity of the silicon nitride sintered body, wear resulting from the blending of silicon carbide or titanium nitride as a conductivity imparting material, In particular, selective wear of the grain boundary phase can be suppressed. That is, it is possible to provide a low insulating (conductive) silicon nitride sintered body having both good conductivity and wear resistance.

Wear resistant member of the present invention is characterized in that it is constituted of a conductive silicon nitride sintered body of the present invention that describes above. Wear resistant member of the present invention is suitable as a material for the bearing balls or jig electronic devices especially. Specific examples of electronic equipment jigs include tweezers and alignment jigs in electronic equipment production lines. According to the above-described bearing ball for an electronic device, it is possible to realize stable high-speed rotation while properly discharging static electricity that has various adverse effects on the electronic device.

Furthermore the wear resistant member of the present invention is suitable as a material for the semi-conductor manufacturing equipment jig. Specific examples of the jig for a semiconductor manufacturing apparatus include a vacuum chuck, a heater block, a guide rail, and a wafer cassette.

  According to the silicon nitride sintered body, the manufacturing method thereof, and the wear-resistant member using the same according to the present invention, contact with silicon carbide and titanium nitride conductive particles dispersed in the silicon nitride sintered body structure Because carbon nanotubes with high probability and excellent conductivity are contained, a continuous electric conduction path is easily formed by contact between the conductive particles and the carbon nanotubes, and the conductivity of the silicon nitride sintered body is increased. Problems due to static electricity can be solved, and a complex wear-resistant member can be formed by electric discharge machining.

  In addition, since carbon nanotubes having high contact probability with silicon carbide and titanium nitride conductive particles and having excellent conductivity are contained, sufficient conductivity can be obtained in a smaller amount than the conductive particles. Therefore, it becomes possible to reduce the content of the conductive particles as compared with the conventional case, and it is possible to effectively suppress the decrease in grain boundary strength and the occurrence of selective wear of the grain boundaries caused when a large amount of conductive particles are contained. . Therefore, it is possible to provide a wear resistant member having excellent wear resistance characteristics and high durability.

Hereinafter, modes for carrying out the present invention will be described. The low insulating (conductive) silicon nitride sintered body of the present invention has an electric resistance value in the range of 0.01 to 10 ³ Ω · cm. Here, silicon nitride itself is essentially an insulating material, and generally has an electric resistance value of 10 ⁸ Ω · m or more. Therefore, carbon nanotubes as the conductivity imparting agent to the silicon nitride sintered body in the present invention, respectively is contained silicon carbide and titanium nitride, 0.01 to 10 ³ Omega silicon nitride sintered body by such conductivity imparting agent -An electrical resistance value in the range of cm is given.

When the electrical resistance value of the silicon nitride sintered body exceeds 10 ³ Ω · cm, the characteristics as the conductive silicon nitride sintered body cannot be satisfied, and for example, it is applied as a bearing ball to an HDD rotational drive unit or the like. At this time, static electricity generated by high-speed rotation cannot be conducted well to a bearing member made of a metal material such as a rotating shaft or a ball receiving portion and dissipated. That is, when the electrical resistance value of the silicon nitride sintered body exceeds 10 ³ Ω · cm, a sufficient amount of conduction such as static electricity cannot be secured. In addition, since the conductivity of the sintered body becomes insufficient, it becomes difficult to efficiently process the sintered body into a complicated shape by electric discharge machining, and the mass productivity of wear-resistant parts having a precise shape is reduced. .

On the other hand, even if the electric resistance value of the silicon nitride sintered body is less than 0.01 Ω · cm (10 ⁻² Ω · cm), not only the effect on the dissipation of static electricity is not obtained, but also In order to obtain a resistance value, it is necessary to add a large amount of conductivity imparting material. When a large amount of conductivity imparting material is added to the silicon nitride sintered body, a large amount of agglomerates of the conductivity imparting materials are generated. The characteristics will be impaired. The electric resistance value of the silicon nitride sintered body is more preferably in the range of 0.1 to 10 ² Ω · cm.

In the low-insulating silicon nitride sintered body of the present invention, carbon nanotubes (CNT), carbonized carbon dioxide are included in the silicon nitride sintered body in order to obtain the electric resistance value in the range of 0.01 to 10 ³ Ω · cm. Silicon (SiC) and titanium nitride (TiN) are contained as conductivity imparting materials, respectively. Titanium nitride may be added as titanium oxide and nitrided during the sintering process. Also, silicon carbide and metal carbon silicide may be used in the sintering process to form respective compounds.

  Carbon nanotubes (CNT) function as a kind of conductivity imparting material, and in particular connect conductive particles such as silicon carbide (SiC) and titanium nitride (TiN) dispersed in the sintered body structure, This is a component that imparts conductivity to the silicon nitride sintered body by forming a continuous electric conduction path in which long carbon nanotubes are intertwined in a complicated manner.

  Carbon nanotubes also function as a solid lubricant, and when this silicon nitride sintered body containing CNTs is applied to a sliding member, the aggressiveness of the carbon nanotubes against the counterpart material is greatly reduced by the lubricating action of the carbon nanotubes. As a result, an effect of effectively reducing the wear amount of the counterpart material can be obtained.

  Here, the carbon nanotube (CNT) is a graphite cylindrical body having a hollow portion, and is an ultrafine hollow carbon fiber that is considerably thinner than a normal solid carbon fiber. The CNT generally has a diameter (minor axis) of 0.8 nm to 300 nm and a length (major axis) of about 5 to 20 μm. The types of CNTs are roughly classified into single wall type CNTs having a single cylindrical wall and multi wall type CNTs in which a plurality of cylindrical walls are concentrically nested and stacked in multiple layers.

  The single wall type CNT and the multi wall type CNT have little difference in the function as a conductivity imparting material, but the multi wall type CNT is inexpensive in terms of the price due to the difference in the manufacturing method and the purification method. In view of the above and multi-walled CNTs are preferably used in the present invention from the viewpoint of being hard to be burned down by a high temperature during the sintering operation. In particular, it is preferable to use a multi-wall type carbon nanotube having a minor axis of 30 to 100 nm and a major axis of 5 to 20 μm. The presence of carbon nanotubes in the silicon nitride sintered body can be analyzed by a transmission electron microscope (TEM).

On the other hand, silicon carbide and titanium nitride have an electric resistance value of 10 ⁻⁵ Ω · m (10 ⁻³ Ω · cm) or less and are chemically stable, so that they have characteristics and shapes even during the sintering process. Can keep good. Therefore, low electrical insulation (conductivity) can be satisfactorily imparted to the silicon nitride sintered body with a relatively small blending amount. Furthermore, it has the feature that it is excellent also in heat resistance and sliding characteristics. The presence of the conductivity imparting material can be analyzed by EPMA or X-ray diffraction (XRD).

  The conductivity imparting material made of silicon carbide or titanium nitride described above preferably has a particle shape with an average particle diameter of 3 μm or less, and more preferably with an average particle diameter of 1 μm or less. Further, the conductivity imparting material preferably has a maximum diameter of 4 μm or less, and a more preferable average particle diameter is 2 μm or less. By using silicon carbide particles or titanium nitride particles having such a shape, the conductivity imparting material can be favorably dispersed in the silicon nitride sintered body. On the other hand, when a whisker or fiber is used as the conductivity imparting material, the whisker or fiber has a large diameter with respect to the grain boundary of the silicon nitride sintered body, and cracks are easily generated from the interface between the whisker and the fiber. On the other hand, since CNT is sufficiently small with respect to the grain boundary phase, cracks are unlikely to occur.

The blending amount of the conductivity imparting material is appropriately set according to the electric resistance value of the target silicon nitride sintered body. In obtaining the above-described electric resistance value in the range of 0.01 to 10 ³ Ω · cm, the total content of carbon nanotubes, silicon carbide, and titanium nitride is 10 to 30% by volume with respect to the silicon nitride sintered body. It is preferable to be in the range. When the content of the conductivity imparting material exceeds 30% by volume, the hardness of the silicon nitride sintered body is increased more than necessary, and the properties such as wear resistance and fracture toughness value are lowered, and the silicon nitride grains grow. Inhibitory factors increase and selective wear and the like are more likely to occur. When the content of the conductivity imparting material is less than 10% by volume, it is difficult to control the electric resistance value to a predetermined value, which is not preferable. The blending amount of the conductivity imparting material is more preferably in the range of 15 to 25% by volume.

  The specific content of carbon nanotubes (CNT) as the conductivity imparting material is in the range of 1 to 5% by mass. When the content of the carbon nanotube is less than 1% by mass, the conductivity of the silicon nitride sintered body becomes insufficient. On the other hand, when the content is excessive so that the content exceeds 5% by mass, silicon nitride Densification is inhibited. Therefore, the carbon nanotube content is in the range of 1 to 5% by mass, but more preferably in the range of 1.5 to 4% by mass.

  For example, when only conductive silicon particles having a particle size of 0.3 μm (300 nm) and titanium nitride are dispersed, an insulating layer (glass) is formed between the conductive particles (electrodes) in the grain boundaries of silicon nitride. In order to increase the conductivity of the sintered body, it is necessary to shorten the insulating layer distance. To achieve the conductivity directed in the present invention, the conductive particles are contained in an amount of 20 to 40 vol%. It is necessary to add a large amount. In this case, as described above, the growth of crystals is hindered by the presence of a large amount of conductive particles, and the original high-strength crystal structure of silicon nitride cannot be formed.

  On the other hand, as in the present invention, for example, by containing a predetermined amount of carbon nanotubes having a minor axis of 30 to 100 nm and a major axis of 5 to 20 μm, the content of conductive particles is relatively reduced. Is possible. That is, one carbon nanotube has the effect of imparting conductivity to 3 to 10 conductive particles, and the carbon nanotube itself has high conductivity and also has a high contact probability with the conductive particles. In addition, sufficient conductivity can be realized in a smaller amount than the conductive particles.

  Further, the specific content of silicon carbide (SiC) as the conductivity imparting material is in the range of 0.1 to 20% by mass, while the specific content of titanium nitride (TiN) is 0.8. It is preferable that it is the range of 1-5 mass%. When the content of the silicon carbide or titanium nitride is less than the lower limit, the effect of imparting conductivity is insufficient, while when the content exceeds the upper limit, the sintered body Crystal grain growth is hindered and the original high mechanical strength of the silicon nitride sintered body cannot be obtained. The particle diameters of SiC, TiN and the metal carbon silicide as the conductivity imparting material are not particularly limited, but it is preferable to use fine particles having an average particle diameter of 3 μm or less.

  Here, although the grain boundary phase of the silicon nitride sintered body depends on the kind of the sintering aid used, for example, a Si—R (rare earth element) -O compound, a Si—Al—R—O compound, Formed with oxides or oxynitrides such as Si-Al-O compounds, Si-R-O-N compounds, Si-Al-R-O-N compounds, Si-Al-O-N compounds, etc. The When a large amount of high-hardness silicon carbide particles or titanium nitride particles are present in such a grain boundary phase (glass phase), the toughness or stickiness of the grain boundary phase decreases, and as described above, the selective selection of the grain boundary phase. Wear is likely to occur.

  Therefore, in the silicon nitride sintered body according to the present invention, the content of silicon carbide particles and titanium nitride particles is relatively reduced by adding a small amount of carbon nanotubes that are extremely effective for developing conductivity. It is preferable that a crystalline phase of metal carbon silicide (MxSiyCz) is present in the silicon nitride sintered body. Here, M is an arbitrary transition metal, and x, y, and z are arbitrary coefficients. Crystal phases such as metal carbon silicide particles exist mainly in the grain boundary phase of the silicon nitride sintered body. Although metal carbon silicide particles (MxSiyCz particles) have lower hardness than silicon carbide particles and titanium nitride particles, on the other hand, since they are excellent in toughness, toughness and stickiness are imparted to the grain boundary phase. In other words, the grain boundary phase is strengthened, and selective wear of the grain boundary phase can be suppressed.

  Further, metal carbon silicide (MxSiyCz) is not an insulating material such as silicon nitride, but has conductivity as compared with silicon carbide or titanium nitride. Therefore, by causing the metal carbon silicide particles to exist in the grain boundary phase or the like, without impairing the conductivity of the silicon nitride sintered body, wear resulting from the blending of silicon carbide or titanium nitride as a conductivity imparting material, In particular, selective wear of the grain boundary phase can be suppressed. That is, good conductivity and wear resistance can be imparted to the silicon nitride sintered body. Note that the presence of the crystalline phase of the metal carbon silicide can be identified by X-ray diffraction.

  As the metal carbon silicide (MxSiyCz) described above, carbon silicides of various transition metal elements can be used, and particularly selected from molybdenum (Mo), tungsten (W), niobium (Nb) and tantalum (Ta). It is preferable to use at least one metal carbosilicate. Of the above-mentioned carbon silicides, molybdenum carbon silicide is particularly preferable. Such a metal carbon silicide (M1xSiyCz: M1 is at least one selected from Mo, W, Nb and Ta, and x, y, and z are arbitrary numbers) has even better wear resistance such as grain boundary phase. Therefore, it is preferably used in the present invention. The metal carbon silicide (MxSiyCz) referred to in the present invention is a transition metal carbon silicide and does not include silicon carbide (SiC).

  Moreover, it is preferable to make content of metal carbon silicide into the range of 0.1-5 mass% with respect to the whole quantity of a silicon nitride sintered compact. When the content of the metal carbon silicide is excessively low, less than 0.1% by mass, the effect of increasing the toughness and stickiness of the grain boundary phase is insufficient, and for example, the selective wear of the grain boundary phase is sufficient. It cannot be suppressed. On the other hand, when the content of the metal carbon silicide exceeds 5% by mass, densification and sintering of silicon nitride may be hindered. Therefore, the content of the metal carbon silicide is preferably in the range of 0.1 to 5% by mass, more preferably in the range of 2 to 3% by mass with respect to the silicon nitride sintered body. In addition, when producing | generating a metal carbon silicide during a sintering process, compound powders, such as a metal carbide, shall be converted into a metal carbon silicide, and an addition amount shall be adjusted.

  The silicon nitride sintered body according to the present invention supports various metal compounds in the same manner as a general silicon nitride sintered body except that carbon nanotubes, silicon carbide, and titanium nitride are blended as conductivity imparting materials. It can be included as an agent. As the sintering aid, for example, an oxide of a rare earth element (lanthanoid element including yttrium), an oxide of an alkaline earth element, or the like is used. As the rare earth element oxide, an oxide such as yttrium (Y), ytterbium (Yb), or erbium (Er) is preferably used. These are constituents of the grain boundary phase. Further, it is preferable to use an oxide of magnesium or calcium as the oxide of the alkaline earth element. As the compound as the sintering aid, a rare earth element or alkaline earth element compound (such as carbonate) that becomes an oxide during sintering may be used.

  In addition to the oxides of rare earth elements and alkaline earth elements described above, aluminum compounds such as aluminum nitride and aluminum oxide, and oxides and nitrides such as titanium, zirconium, and hafnium are used as part of the sintering aid. It is also effective to use as The aluminum compound contributes to strengthening the bonding force between the silicon nitride crystal grains. These compounds may be added as oxides or nitrides, or compounds that become oxides or nitrides during sintering may be added.

  The sintering aid as described above is preferably contained in the range of 5 to 20 parts by mass with respect to 100 parts by mass of silicon nitride. If the amount of the sintering aid is less than 5 parts by mass, the silicon nitride sintered body may not be sufficiently densified. On the other hand, when the amount of the sintering aid exceeds 20 parts by mass, the amount of segregation of the grain boundary phase and the sintering aid component increases more than necessary, thereby improving the wear resistance and strength of the silicon nitride sintered body. There is a risk of lowering. Among the sintering aids described above, the rare earth oxide content is preferably in the range of 1 to 10% by mass with respect to the sintered body, and the alkaline earth oxide content is 0.5 to 5%. It is preferable to set it as the range of the mass%. Further, in addition to these, aluminum elements such as aluminum nitride and aluminum oxide are preferably contained in the range of 2 to 10% by mass in terms of oxides.

  Although the manufacturing method of the silicon nitride sintered compact concerning this invention is not specifically limited, For example, manufacturing by the method as shown below is preferable. First, a predetermined amount of each of silicon nitride powder, sintering aid powder, conductivity imparting material powder, and if necessary, metal carbon silicide powder is weighed and uniformly mixed to prepare a raw material mixture.

  For each of the raw material powders described above, it is preferable to use a particulate powder in consideration of sliding characteristics except for long carbon nanotubes. The size of each raw material powder is not particularly limited, but the silicon nitride powder preferably has an average particle size in the range of 0.2 to 1 μm, and the sintering aid powder has an average particle size of 2 μm or less. preferable. The carbon nanotube as the conductivity imparting material is preferably a multi-wall type carbon nanotube having a minor axis of 30 to 100 nm and a major axis of 5 to 20 μm. The average particle size of the conductivity imparting material powder of silicon carbide or titanium nitride is preferably 2 μm or less. When the average particle diameter of the conductivity imparting material powder exceeds 2 μm, the sinterability is significantly impaired. Moreover, when using metal carbon silicide powder, the average particle diameter of metal carbon silicide powder is 5 micrometers or less, and the average particle diameter of 3 micrometers or less as the whole electroconductivity imparting powder containing silicon carbide etc. is preferable.

  Further, when mixing each raw material powder, first, a silicon nitride powder and a sintering aid powder are mixed to prepare a first mixed powder, and a conductivity imparting material powder is mixed with the first mixed powder. Then, after preparing the second mixed powder, it is preferable to mix the metal carbon silicide powder with the second mixed powder. Thus, by preparing a mixed powder stepwise and finally preparing a raw material mixture containing all raw materials, the conductivity imparting material and the metal carbon silicide can be uniformly dispersed. It is preferable to perform mixing at each stage for 30 minutes or more, and after the mixed powders are sufficiently homogenized, the next mixing step is performed.

  The raw material mixture described above is granulated as necessary, and then formed into a desired shape. With respect to the molding method, a normal molding method can be applied. For example, it is preferable to produce a molded body by applying a cold isostatic press (CIP). By sintering the molded body thus obtained, the silicon nitride sintered body according to the present invention is obtained. Regarding the sintering method, normal pressure sintering, pressure sintering, hot isostatic pressing (HIP) and the like are applicable, and in particular, a primary sintering step by pressure sintering or pressure sintering, It is preferable to apply two-stage sintering combined with a secondary sintering process by HIP.

The primary sintering step is performed at a temperature in the range of 1700 to 1850 ° C. under atmospheric pressure or atmospheric pressure. As a pretreatment for such a primary sintering step, first, a temperature at which a liquid phase is generated by a sintering aid and silicon nitride is changed from an α phase to a β phase to cause rearrangement of crystal grains, that is, 1400 to 1600. When the heating time in the temperature range of ° C. is short, the conductivity imparting material is segregated. In particular, in a temperature range of 1500 to 1650 ° C., which is a temperature range in which gases such as SiO, CO, and CO ₂ generated during sintering are released and a liquid phase is generated and densification sintering is started. When the heating time is long, SiO in the grain boundary reacts with the carbon component C of the carbon nanotube according to the following reaction formula. As a result, SiC is generated and at the same time, the carbon component C is evaporated as CO.

[Chemical 1]
Reaction formula: SiO + C → SiC + CO ↑

  As a result, the carbon nanotubes burn out, and it becomes difficult to impart conductivity to silicon nitride by the carbon nanotubes. Therefore, in the primary sintering step, it is important to manage so that the heating time in the temperature rising range of 1500 to 1650 ° C. is 30 minutes or more and 120 minutes or less.

  That is, when the heating time in the above temperature rising range is as short as less than 30 minutes, the outgassing becomes insufficient and pores remain, making it difficult to densify, and SiC at the start of densification sintering. The progress of dispersion and densification of particles and TiN particles becomes nonuniform, and in any case, the mechanical strength and wear resistance of the silicon nitride sintered body are lowered. On the other hand, if the heating time in the temperature increase range is longer than 120 minutes, the carbon nanotubes are burned out in accordance with the reaction formula, so that it is difficult to impart conductivity to the silicon nitride sintered body. Therefore, the heating time in the temperature rising range of 1500 to 1650 ° C. in the primary sintering step is defined as 30 minutes or more and 120 minutes or less.

  After passing through such pretreatment, a primary sintered body is produced by holding at a temperature in the range of 1700 to 1850 ° C. for a predetermined time. Here, if the primary sintering temperature is less than 1700 ° C., a sufficiently dense silicon nitride sintered body cannot be obtained even if a subsequent HIP treatment is performed. Moreover, even if the primary sintering temperature is set to exceed 1850 ° C., not only the effect is not obtained, but also segregation of silicon nitride crystal grains and sintering aid components becomes coarse and Mechanical strength is reduced. In addition, the consumption of the firing furnace and the like becomes severe.

  Next, a secondary sintering step is performed in which a primary sintered body obtained by the primary sintering step is subjected to a HIP (hot isostatic pressing) process to increase the density of the silicon nitride sintered body. The temperature of the HIP process as the secondary sintering step is in the range of 1500 to 1750 ° C. If the HIP treatment temperature is less than 1500 ° C., the silicon nitride sintered body (secondary sintered body) cannot be sufficiently densified. On the other hand, when the HIP treatment temperature exceeds 1750 ° C., unnecessary coarsening of silicon nitride crystal grains occurs, and the mechanical strength of the silicon nitride sintered body may be lowered. The applied pressure during HIP treatment is preferably in the range of 90 to 170 MPa.

  By carrying out the primary sintering step and the secondary sintering step under the conditions as described above, the intended conductive silicon nitride sintered body can be obtained. Such a conductive silicon nitride sintered body can be used as a wear-resistant member applied to a normal machine tool or the like, but is particularly preferably used as a wear-resistant member for electronic equipment. is there. Specific examples of the wear-resistant member for electronic devices include rolling elements, such as bearing balls, used in the rotation drive unit of various electronic devices. The shape of the rolling element is usually a true sphere, but it may be cylindrical or rod-like. The wear resistant member of the present invention is particularly effective for small-sized bearing balls having a diameter of 3 mm or less.

  FIG. 4 is a view showing an example of a bearing having a bearing ball for electronic equipment made of a conductive silicon nitride sintered body according to the present invention. A bearing 1 shown in FIG. 4 has a plurality of bearing balls 2 made of a conductive silicon nitride sintered body according to the present invention, and an inner ring 3 and an outer ring 4 that support these bearing balls 2. The inner ring 3 and the outer ring 4 are preferably formed of bearing steel such as SUJ2 defined by JIS-G-4805, and this makes it possible to achieve reliable high-speed rotation. The basic configuration is the same as that of a normal bearing.

  Electronic devices to which the above-described bearings are applied include magnetic recording devices such as HDDs, in particular, bearings for HDD pivots, optical disk devices such as CD-ROMs and DVDs, and various disk-type game devices. The optical disk apparatus includes various apparatuses such as a magneto-optical recording apparatus, a phase change optical recording apparatus, and a reproduction-only optical disk apparatus. Further, in addition to these, any electronic device having a rotation drive unit such as a copier antistatic bearing can be applied to various devices.

  It is also possible to produce a bearing ball from the silicon nitride sintered body according to the present invention and use it for an ordinary machine tool or the like. Further, in a magnetic recording device, an optical disc device, a disc-type game device, etc., the wear-resistant member according to the present invention is used as a bearing ball or the like in a rotational drive portion of a medium driving spindle motor. In these electronic devices, the spindle motor is driven at a rotational speed of, for example, 4000 rpm or higher, and further at a rotational speed of 7000 rpm or higher. A bearing ball made of a conductive silicon nitride sintered body can stably release static electricity generated by high-speed rotation while realizing stable high-speed rotation. As a result, it is possible to eliminate problems caused by static electricity of the electronic device, and further generation of noise due to wear of the bearing balls.

  Next, specific examples of the present invention and evaluation results thereof will be described.

[Examples 1 to 25 and Comparative Examples 1 to 8]
For silicon nitride powder having an average particle size of 0.7 μm, various rare earth oxide powders having an average particle size of 0.8 μm as a sintering aid, and alumina (Al ₂ O ₃ ) having an average particle size of 0.5 μm Table 1 shows the ratio of powder, magnesium oxide (MgO) powder having an average particle size of 0.5 μm, and aluminum nitride (AlN) powder having an average particle size of 0.5 μm in the sintered body. After adding and blending in this manner, the mixture was mixed for 24 hours in a ball mill consisting of a silicon nitride container and balls.

  To each of the mixed powders thus prepared, a multiwall-type carbon nanotube (CNT) having a short diameter of 50 nm and a long diameter of 15 μm as a conductivity-imparting material, and a silicon carbide (SiC) powder having an average particle diameter of 0.5 μm, In addition, titanium nitride (TiN) powder having an average particle diameter of 0.8 μm and various metal carbon silicide powders having an average particle diameter of 0.7 μm are added so that the ratio in the sintered body becomes the value shown in Table 1. After that, they were mixed for 24 hours in a ball mill consisting of a silicon nitride container and balls. Each of these mixed powders was transferred to a suitable container and dried for several hours, and then an aqueous PVA solution was added and stirred, and further passed through a sieve having an opening of 500 μm to prepare raw material mixed powders.

  The addition amount of the carbon nanotube powder, silicon carbide powder, titanium nitride powder and metal carbon silicide powder was adjusted so that the final content in the sintered body would be the value shown in Table 1.

  Next, each raw material mixed powder was die-pressed at a pressure of 98 MPa, and then subjected to isostatic pressing (CIP) under a pressure of 300 MPa to produce a compact. Each obtained compact was degreased and then sintered in a nitrogen atmosphere at the primary sintering temperature shown in Table 1 for 2 hours. In the temperature raising process of the primary sintering step, the heating time in the temperature range of 1500 to 1650 ° C. was set to the time shown in Table 1, and the primary sintering was subsequently performed after the heating time passed. Subsequently, HIP sintering (secondary sintering) was performed at the HIP temperatures shown in Table 1. The HIP pressure was 98 MPa for all. Further, the surface of each sintered body was polished to grade 5 (Ra 0.02 μm) defined by JIS-B-1501. Thus, the flat silicon nitride sintered compact which concerns on each target Example was produced.

Moreover, the silicon nitride sintered compact (Comparative Examples 1-4) which did not add the carbon nanotube as an electroconductivity imparting material was created for the comparison with this invention. Further, as Comparative Example 5, an alumina (Al ₂ O ₃ ) sintered body containing a predetermined amount of carbon nanotubes was prepared by the following procedure.

That is, as a raw material powder, an α-phase type alumina (Al ₂ O ₃ ) powder having an average particle size of 0.5 μm, an amount of carbon nanotubes corresponding to 1% by volume of the alumina powder, and a dispersion medium are blended, and alumina is obtained. It mixed for 24 hours with the ball mill which consists of a container and a ball | bowl made. Thereafter, the obtained slurry was transferred to a container and dried for several hours. Thereafter, an aqueous PVA solution was added, and after stirring, mixed raw material powder was prepared by passing through a sieve having an opening of 500 μm. Next, the obtained mixed raw material powder was subjected to die press molding at a pressure of 98 MPa, and then subjected to isostatic pressing (CIP) at a pressure of 300 MPa to obtain a molded body. Next, after degreasing the obtained molded body, it was sintered at a temperature of 1700 ° C. for 8 hours in a non-oxidizing atmosphere (Ar gas), and further subjected to a hot isostatic pressing (HIP) treatment at a temperature of 1600 ° C. By doing so, the flat alumina ceramic sintered body according to Comparative Example 5 was obtained.

Furthermore, for comparison with the present invention, a silicon nitride sintered body (Comparative Example 6) in which the heating time in the pretreatment (1500 to 1650 ° C.) of the primary sintering step is set to 180 minutes, as a sintering aid, Silicon nitride sintered body (Comparative Example 7) added in an excess amount (12 mass%) so that the addition amount of Al ₂ O ₃ powder exceeds the preferred range, and the addition amount of carbon nanotubes as the conductivity imparting material is less than the preferred range A silicon nitride sintered body (Comparative Example 8), which was excessively small so as to be, was produced in the same manner as in the Examples except for those conditions.

The Vickers hardness, fracture toughness value, electrical resistance value, and bending strength of each silicon nitride sintered body or alumina sintered body according to Examples 1 to 25 and Comparative Examples 1 to 8 prepared as described above were measured. The results are shown in Table 2. In addition, a test piece is cut out from each sintered body, the bending strength is measured according to the method specified in JIS R1603, the sintered body after the bending test is mirror-polished, and the Vickers hardness is applied at a load of 20 kg according to the method specified in JIS R160X. The fracture toughness value (MPa · m ^1/2 ) was calculated by Nihara's calculation formula based on the IF method. The electrical resistance value was obtained by lapping the upper and lower surfaces of each sintered body, placing electrodes on the upper and lower surfaces, and measuring the resistance (volume resistance value) between them at room temperature with an insulation resistance meter.

  Moreover, each silicon nitride sintered compact or alumina sintered compact which concerns on Examples 1-25 and Comparative Examples 1-8 was mirror-polished, and it was set as the flat rolling life test piece. The rolling life test was performed on a flat plate made of each silicon nitride sintered body (in the comparative example 5, made of alumina sintered body) using a thrust type bearing tester and using a SUJ2 steel ball (3/8 inch) as a counterpart. Was measured. The rolling contact life was measured under the following conditions: the maximum contact stress per ball was 5.9 GPa, the rotation speed was 1200 rpm, and rotation was performed for up to 400 hours under turbine oil lubrication. The rolling life was evaluated by the time until peeling. “Canceling” means that no peeling occurred after 400 hours. The wear depth is the amount of wear on the surface of the flat plate (test piece) and the mating material (ball) after 400 hours. The rolling life, test piece and ball wear depth were measured, and the results shown in Table 2 below were obtained.

  As is clear from the results shown in Table 2 above, the silicon nitride sintered bodies according to the respective examples each containing carbon nanotubes, silicon carbide, and titanium nitride as the conductivity imparting material have appropriate electrical resistance values. In addition to eliminating problems due to static electricity, it has been found that the amount of wear is small and the rolling life and wear resistance are excellent.

  FIG. 1 is a cross-sectional view schematically showing the structure of a silicon nitride sintered body according to Example 1 containing carbon nanotubes (CNT) 6 as a conductivity imparting material and conductive particles 5 of SiC or TiN. . Most of the electric conduction paths are formed by entanglement of the CNTs 6, and further conductive conduction paths are formed by interposing the conductive particles 5 in the non-contact portions between some of the CNTs 6.

  FIG. 2 shows silicon nitride according to Example 14 containing a small amount (1% by mass) of carbon nanotubes (CNT) 6 as a conductivity imparting material and a large amount (20% by mass) of SiC as conductive particles 5. It is sectional drawing which shows the structure | tissue structure of a sintered compact typically. Most of the electrical conduction paths are formed by the connected conductive particles 5, and carbon nanotubes (CNT) 6 are interposed in non-contact portions between some of the conductive particles 5 to form further electrical conduction paths. Has been. In both of the sintered bodies shown in FIGS. 1 and 2, since the electric conduction path is sufficiently formed, the sintered body has good electrical conductivity, and the adverse effects due to static electricity can be eliminated.

On the other hand, in the silicon nitride sintered bodies according to Comparative Examples 1 to 4 in which the carbon nanotubes as the conductivity imparting material were not added, the electrical resistance value exceeded 10 ⁵ Ω · cm, Is not obtained, and malfunctions due to static electricity accumulation are expected. This problem of low electrical conductivity is not solved even if a large amount (20% by mass) of SiC is contained as in Comparative Examples 3 and 4.

  FIG. 3 shows a conventional particle-dispersed silicon nitride sintered body containing no carbon nanotubes, and the structure of the silicon nitride sintered body according to Comparative Example 3 containing a large amount (20% by mass) of SiC particles 5. It is sectional drawing which shows a structure typically. In this case, by containing a large amount of the conductive particles 5, the conductive particles 5 are partially connected to form a part of the electric conduction path. Since the conduction path is not formed, the electric resistance value is excessive.

  Wear of a ball as a counterpart when a rolling life test was conducted on the sintered body according to each example containing carbon nanotubes (CNT) and the sintered bodies of comparative examples 2 to 4 not containing CNT When the amounts were compared, it was found that the wear amount of the balls was significantly reduced when the sintered bodies according to the respective examples were used. This is presumably because carbon nanotubes (CNT) also act as a solid lubricant, and the aggressiveness against the counterpart material is greatly reduced.

On the other hand, the alumina (Al ₂ O ₃ ) sintered body according to Comparative Example 5 containing a predetermined amount of carbon nanotubes has a high electrical resistance value even when CNT is contained, and has structural strength such as fracture toughness value and bending strength. The characteristics as a low wear-resistant member cannot be obtained at all.

  Further, in the silicon nitride sintered body according to Comparative Example 6 in which the heating time in the pretreatment (1500 to 1650 ° C.) of the primary sintering process is set to be as long as 180 minutes, the carbon nanotubes are partially burned down and become disconnected. It was found that the electrical resistance value could not be reduced due to the large proportion.

Furthermore, in the silicon nitride sintered body according to Comparative Example 7 in which an excessive amount (12% by mass) of the additive amount of Al ₂ O ₃ powder as a sintering aid exceeds the preferable range, the electric resistance value is high. The rolling life can hardly be expected.

  In addition, in the silicon nitride sintered body according to Comparative Example 8 in which the amount of carbon nanotubes added as the conductivity imparting material is excessively small (0.5% by mass) so as to be less than the preferable range, the electric resistance value is set to a predetermined value. It was found that the level could not be reduced below the level.

  As described above, according to the silicon nitride sintered body according to the present invention, when applied to a wear-resistant member for electronic equipment having high conductivity, it is possible to prevent accumulation of static electricity more than necessary. In addition, it is possible to suppress wear and the like due to the blending of the conductive particles. Moreover, according to the manufacturing method of the present invention, such a conductive silicon nitride sintered body can be manufactured with good reproducibility. Furthermore, according to the wear-resistant member to which the conductive silicon nitride sintered body according to the present invention is applied, for example, after solving the problems due to static electricity of various electronic devices, the rotation drive unit can perform high-speed rotation with excellent reliability. It can be realized.

Sectional drawing which shows typically the structure | tissue structure of the silicon nitride sintered compact concerning Example 1 of this invention. Sectional drawing which shows typically the structure | tissue structure of the silicon nitride sintered compact concerning Example 14 of this invention. Sectional drawing which is a conventional silicon nitride sintered compact which does not contain a carbon nanotube, and shows the structure | tissue structure of the silicon nitride sintered compact which concerns on the comparative example 3 typically. Sectional drawing which shows one structural example of the bearing using the bearing ball as an abrasion-resistant member which consists of a silicon nitride sintered compact concerning this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Bearing (bearing), 2 ... Bearing ball (wear-resistant member), 3 ... Inner ring, 4 ... Outer ring, 5 ... Conductivity imparting material (conductive particle), 6 ... Carbon nanotube (CNT).

Claims (10)

In a silicon nitride sintered body for wear-resistant members obtained by mixing and sintering silicon nitride powder with a sintering aid powder and carbon nanotubes, silicon carbide and titanium nitride as conductivity imparting materials, mass%, and 5 to 20 wt% silicon carbide, titanium nitride containing respectively a 0.1 to 5 wt%, Ri range der of electrical resistance ¹⁰ -2 ^{~10 3 Ω} · cm, the A silicon nitride sintered body for a wear-resistant member, characterized in that a continuous electric conduction path is formed by contact between a carbon nanotube and silicon carbide or titanium nitride. 2. The silicon nitride sintered body for wear-resistant members according to claim 1, wherein the silicon nitride sintered body for wear-resistant members contains 0.1 to 5 mass% of metal carbon silicide. Sintered silicon nitride sintered body. 3. The silicon nitride sintered body for wear-resistant members according to claim 1, wherein the silicon nitride sintered body further contains 1 to 10 mass% of rare earth elements in terms of oxide and 2 in terms of oxide of aluminum. A silicon nitride sintered body for a wear-resistant member, which contains 10% by mass to 10% by mass. The silicon nitride sintered body for wear-resistant members according to any one of claims 1 to 3, wherein the carbon nanotubes are multiwall carbon nanotubes. Sintered body. 3. The silicon nitride sintered body for wear-resistant member according to claim 2, wherein the metal carbon silicide is molybdenum carbon silicide. Mixing 1-5 mass% of carbon nanotubes as a sintering additive powder and conductivity imparting material, 5-20 mass% of silicon carbide, and 0.1-5 mass% of titanium nitride in silicon nitride powder. Then, a molding process for molding the mixture into a predetermined shape, and a primary sintering process for preparing a primary sintered body by heating the molded body obtained by the molding process and sintering it in a temperature range of 1700 to 1850 ° C. And a secondary sintering step of subjecting the obtained primary sintered body to a hot isostatic pressing (HIP) treatment in a temperature range of 1500 to 1750 ° C. In the primary sintering step, the temperature is 1500 to 1650 ° C. the heating time in the temperature elevation range is not more than 120 minutes 30 minutes or more, the range der in the electrical resistance of the resulting silicon nitride sintered body is 10 ^-2 ~10 ³ Ω · cm is, with the carbon nanotubes carbonized Contact with silicon or titanium nitride Method for producing a wear resistant member for a silicon nitride sintered body, characterized in that continuous electrical conduction path is formed by. In the manufacturing method of the silicon nitride sintered compact for wear-resistant members of Claim 6, 1-10 mass% of rare earth elements are converted into oxide to the silicon nitride powder as a sintering aid powder, and aluminum is converted into oxide. And 2 to 10% by mass of the silicon nitride sintered body for wear-resistant members. An abrasion resistant member comprising the silicon nitride sintered body for an abrasion resistant member according to any one of claims 1 to 5. The wear-resistant member according to claim 8, wherein the wear-resistant member is a bearing ball or a jig for electronic equipment. The wear-resistant member according to claim 8, wherein the wear-resistant member is a jig for a semiconductor manufacturing apparatus.

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