JP2002068846A - Silicon nitride sintered compact, and sliding member and bearing ball using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide silicon nitride sintered compacts, together eliminating badness, capable of effectively releasing heat of friction generated by high velocity revolution, when used for sliding members for electronic equipment such as hard disk drives and for bearing balls. SOLUTION: The silicon nitride sintered compacts contain carbide particles and nitride particles as electric conductivity imparting particles, and have the content of iron components of >=10 ppm and <=200 ppm. The strength and rotational life are prolonged by controlling the quantity of iron components in the sintered compacts and the size of aggregated parts composed of the iron components and/or the electric conductivity imparting particles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a silicon nitride sintered body having an appropriate electric resistance value, or a sliding member and a bearing ball using the same.

[0002]

2. Description of the Related Art In recent years, hard disk drives (HD)
D) and other magnetic recording devices, optical disk devices or DVDs,
The development of mobile products and various game machines has been remarkable. Usually, these various disk drives are made to function by rotating a rotation shaft at high speed by a rotation drive device such as a spindle motor. Conventionally, metal such as bearing steel has been used for a bearing (bearing) member for supporting such a rotating shaft, particularly for a bearing ball. However, since metals such as bearing steel do not have sufficient wear resistance, in fields where high-speed rotation of 5,000 rpm or more is required, for example, in the above-mentioned electronic devices, etc., there is a large variation in life and a reliable rotation drive. Could not provide. In recent years, attempts have been made to use silicon nitride for bearing balls in order to solve such problems. Silicon nitride has excellent abrasion resistance because of its excellent sliding properties among ceramics, and it has been confirmed that a reliable rotation drive can be provided even at high speed rotation.

[0003]

However, since the bearing balls made of silicon nitride are electrically insulative, static electricity generated during high-speed rotation is reduced by a rotating shaft made of a metal member such as bearing steel. , Ball receiving part (components of bearing members other than so-called bearing balls)
It turned out that the problem that static electricity was not dissipated well occurred. If the static electricity is not sufficiently dissipated and charged more than necessary, electronic devices, for example, a recording medium using a magnetic signal such as a hard disk drive are adversely affected, and as a result, the electronic device itself such as a hard disk is damaged. There was a phenomenon saying it would be destroyed. In addition, with the miniaturization and high capacity of hard disk drives, the number of revolutions has been increased to 8,000 rpm and 10,000
Higher speed rotations of more than rpm are required. When such high-speed rotation is performed, the bearing balls are heated by sliding. At this time, the heat conductivity of the conventional silicon nitride bearing ball was as low as about 20 W / m · k, and the frictional heat could not be dissipated well. From the viewpoint of heat dissipation, the higher the rotation speed, the more the problem becomes. In particular, it is not sufficient to cope with long-time rotation.

[0004] On the other hand, there has conventionally been a silicon nitride sintered body having a low electric resistance having an electric resistance of about 10 ^-3 Ω · cm.
Such a silicon nitride sintered body is mainly used for a cutting tool or the like, but in order to realize a low electric resistance, a large amount of conductive particles such as carbide and iron must be dispersed in a microstructure. Although a silicon nitride sintered body in which a large amount of conductivity-imparting particles are dispersed certainly has a lower electric resistance value, it means that these conductivity-imparting particles are present in the microstructure as a material different from silicon nitride, a so-called different material. In addition, the reliability of the silicon nitride sintered body used as an important structural member is reduced. In particular, the iron component cannot be present in the microstructure as a compound with silicon nitride and should be considered as a defect that degrades the mechanical properties. For example, in an application such as a bearing ball, which is always subjected to a compressive load from the whole, if a large amount of such dissimilar material is distributed, cracks are likely to be formed from the dissimilar material or its interface, and the sliding characteristics deteriorate. In particular, when the iron component is widely distributed, due to its rolling characteristics, it causes adhesion to a metal material as a mating material (race) and eventually causes peeling. Therefore, in a bearing ball which is used while receiving a compressive load from the whole, such as a bearing ball, it is preferable that the content of iron is not so large in terms of sliding characteristics, while it is useful for promoting conductivity.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has a predetermined electric resistance value while having excellent sliding characteristics, and is capable of dispersing conductive particles. An object of the present invention is to provide a silicon nitride sintered body having controlled conductivity. Further, by applying such a conductive silicon nitride sintered body to a sliding member for an electronic device such as a hard disk, for example, a bearing ball, it is possible to prevent static electricity from being charged more than necessary.
In addition, since the heat conductivity is 40 W / m · k or more, heat at the time of sliding can be efficiently dissipated, so that it is suitable for sliding members for electronic devices. Therefore, an object of the present invention is to provide a sliding member and a bearing ball using a silicon nitride sintered body having conductivity.

[0006]

According to the present invention, in order to achieve the above object, the state of dispersion between the conductivity imparting particles present in the silicon nitride sintered body and the iron component present in the sintered body is specified. ing. Specifically, carbide particles and nitride particles are dispersed and contained as conductivity imparting particles in a silicon nitride sintered body, and the content of an iron component present in the sintered body is 10 ppm or more and 200 ppm or less, A silicon nitride sintered body having a value of 10 ² Ω · cm or more and 10 ⁷ Ω · cm or less. Further, the maximum diameter of the iron component present in the sintered body is preferably 20 μm or less. Also,
The closest distance between the iron component and the conductivity imparting particles is
It is preferable that the particle distribution satisfying the positional relationship in an arbitrary cross section of not less than 0.5 μm and not more than 5 μm accounts for 80% or more. The carbide particles are preferably made of at least one of carbides of group 4a, 5a, 6a, and 7a, silicon, and boron, and the nitride particles are at least one of nitrides of group 4a.
Preferably it is a seed. Furthermore, the thermal conductivity is 40W / mk
It is preferable that it is above. It is particularly effective to apply such a silicon nitride sintered body to a sliding member, for example, a bearing ball. In particular, in the case of a bearing ball applied to the rotational drive of an electronic device such as a hard disk drive, a sliding member for an electronic device can prevent static electricity generated due to the rotational drive from being charged more than necessary, and also has a thermal conductivity. Since it is high, it has excellent heat dissipation.

[0007]

Embodiments of the present invention will be described below. The silicon nitride sintered body of the present invention contains carbide particles and nitride particles as the conductivity imparting particles, the iron component content in the sintered body is 10 ppm or more and 200 ppm or less, the iron component and the conductivity imparting particles. Regarding the dispersion state, the closest interparticle distance between the iron component and the conductivity-imparting particles is 0.5 μm or more and 5 μm or more.
m, the particle distribution satisfying this positional relationship in an arbitrary cross section accounts for 80% or more.

[0008] The iron component refers to all iron components of iron compounds such as metallic iron elements and iron nitrides and oxides. The closest distance between the iron component and the conductivity-imparting particles is the distance between the iron component particles, the distance between the conductivity-imparting particles, the distance between the iron component particles and the conductivity-imparting particles. Indicates the closest inter-particle distance among all the inter-particle distances. The method of obtaining the content of the iron component in the sintered body is as follows. First, the sintered body is finely pulverized and powdered, then hydrofluoric nitric acid is added, and the solution is heated at 180 ° C. in a pressurized container to form a solution. It is effective to wash off the hydrofluoric acid with sulfuric acid and to perform ICP emission analysis on the solution. The distribution state of the iron component and the conductivity-imparting particles can be determined by subjecting the surface or section of the sintered body to mirror finishing (0.01 μm or less in surface roughness Ra) and a unit area of 30 μm on the surface.
It is effective to take a color map by EPMA and a secondary electron image by a scanning electron microscope for mx 30 μm (or more area) and specify the distribution of the iron component and the conductivity imparting particles by comparing the two images. is there.

For the color map and the secondary electron image photographing, a magnification of 2000 times or more (50 μm is displayed in 10 cm) or more is preferable.
By observing the mirror surface of the surface (or cross section) of the silicon nitride sintered body at a magnification of this level or more, it is possible to reduce the dispersion of the interparticle distance measurement. In addition, if the unit area is 30 μm × 30 μm in calculating the area of the iron component and the conductivity-imparting particles in the silicon nitride sintered body, the dispersion state of the iron component and the conductivity-imparting particles in the material is regarded as a representative value. In the present invention, the unit area
30 μm × 30 μm was applied. Also, for the measurement location of the distance between the iron component and the conductivity-imparting particles in a unit area of 30 μm × 30 μm in the silicon nitride sintered body, the conductivity-imparting particles are uniformly mixed if uniform mixing described later is used. Therefore, there is no problem even if the measurement is simply performed on only one surface. However, in general, at least four arbitrary locations on the surface or cross section of the sintered body are determined by the color map of each measurement location and the secondary location. It is preferable to measure the particle distribution in an area corresponding to 30 μm × 30 μm with respect to the electronic image and indicate the average value. In addition, when judging from the EPMA color map, when the spherical shape is taken as a color map like a bearing ball, the end of the color map is curved and thus does not accurately show the existence state of the conductive particles which are aggregated on the surface. However, there is practically no problem in taking an image of a minute area such as a unit area of 30 μm × 30 μm without taking this problem into consideration. From this point of view, the unit area is 30μm × 30μ
m is preferable.

In the present invention, the conductive particles include carbide particles and nitride particles, and the iron component content is
The content is 10 ppm or more and 200 ppm or less, and the particle diameter of the iron component is preferably 20 μm or less. The closest distance between the iron component and the conductivity-imparting particles is 0.5 μm.
It is preferable that the particle distribution satisfying this positional relationship in any cross section having a size of m to 5 μm occupies 80% or more.

Since the silicon nitride crystal particles constituting the silicon nitride sintered body are insulators as described above, the electric resistance value is usually 10 ¹⁰ Ω · cm or more. Therefore, in the present invention, conductivity imparting particles are added to make the electric resistance value a predetermined value. It is enough to add only the conductivity-imparting particles if focusing only on lowering the electrical resistance value.However, when applied to a bearing ball for an electronic device, for example, if there is variation in the electrical resistance value of each bearing ball, The antistatic effect of static electricity varies. Static electricity is basically where the electrical resistance is high (where insulation is high)
When the antistatic effect of the static electricity varies, the static electricity concentrates on a portion having the highest electric resistance value, which may cause a malfunction in the electronic device due to the static electricity. Such a phenomenon is not so problematic at a rotational speed of about 5,000 rpm, but is gradually being observed at a high rotational speed of 9,000 rpm or more. In particular, malfunctions in electronic devices due to static electricity are also affected by the instantaneous charge amount. Therefore, in a sliding member that uses a combination of multiple balls, such as a bearing ball, the electrical resistance value of each bearing ball is reduced. Eliminating variations is important.

Accordingly, in the present invention, in addition to the uniform distribution of the conductivity-imparting particles, by controlling the content, size and distribution of the iron component that affects the conductivity, individual silicon nitride can be produced without deteriorating the sliding characteristics. This is to improve the variation of the electric resistance value of the sintered body. The content of iron component is 10pp
m to 200 ppm, and the particle diameter of the iron component is 20
It is preferably not more than μm. The closest distance between the iron component and the conductivity-imparting particles is 0.5 μm or more and 5 μm or less, and the particle distribution satisfying this positional relationship occupies 80% or more in an arbitrary cross section. By doing so, the variation in the electric resistance value can be suppressed to ± 20% / 100 without lowering the sliding characteristics.

When the content of the iron component is less than 10 ppm, the dispersion of the electric resistance value depends on the dispersion state of the conductivity imparting particles, and the dispersion between lots or within the lot tends to increase. is there. In addition, in order to reduce this variation, it is necessary to perform a uniform mixing process of the conductive particles having a small particle size distribution, which increases the production cost and is disadvantageous commercially. On the other hand, when the content of the iron component is 200
If it exceeds ppm, it can suppress the variation of the electric resistance value, but if it is used as a sliding member, the number of defects, that is, the starting point of fracture increases, and it is impossible to apply it to critical applications such as bearing balls in terms of reliability. Become.

When the maximum diameter of the iron component exceeds 20 μm, the number of defects, that is, the starting point of fracture increases, and application to critical applications such as bearing balls becomes impossible in terms of reliability. Therefore, the maximum diameter of the iron component is 20μ.
m or less, more preferably 2 μm or less. As described above, since the silicon nitride sintered body is an insulator, the presence of the iron component and the conductivity-imparting particles is necessary to make the electric resistance value a predetermined value. However, in the case of a microstructure having a distribution in which the closest inter-particle distance between the iron component and the conductivity-imparting particles is too large, the effect of lowering the electric resistance value is not sufficient, and the variation between lots increases.
Therefore, it is necessary to stabilize the electric resistance value within a predetermined value range (elimination of variation) by appropriately bringing the distance between the iron component and the particles imparting conductivity to each other and making the distribution uniform. And the closest interparticle distance between the iron component and the conductivity-imparting particles is preferably 5 μm or less.

On the other hand, when the distance between the iron component and the conductivity-imparting particles is less than 0.5 μm, it is the same as the fact that the conductivity-imparting particles are excessively aggregated.
Although the variation in the electric resistance value is reduced, this portion serves as a starting point of destruction, resulting in a decrease in strength. Further, the rolling life of a sliding member such as a bearing ball is reduced.

Therefore, the closest distance between the iron component and the conductive particles is 0.5 μm or more and 5 μm or less. Further, as for such a distance between particles, it is preferable that a particle distribution satisfying the positional relationship in an arbitrary cross section accounts for 80% or more. Within such a range, the inherent sliding characteristics of the silicon nitride sintered body need not be degraded, and the variation in electric resistance can be further improved to ± 20% / 100. In other words, if it is 20% or less, the distance between the particles may be less than 0.5 μm or more than 5 μm, but particularly, the one where the distance between the particles is less than 0.5 μm tends to be an agglomerated portion. Therefore, the iron component and / or the conductivity-imparting particles forming the aggregated portion preferably have a maximum diameter of the aggregated portion of 5 μm or less, more preferably 3 μm or less. If the maximum diameter of the agglomerated portion exceeds 5 μm, the agglomerated portion becomes a fracture starting point, so that the sliding characteristics are deteriorated. That is, in the present invention, the variation in the electric resistance value is suppressed by providing a predetermined form for the distance between the conductivity-imparting particles in the silicon nitride sintered body, and further, the size of the aggregated portion serving as a fracture starting point Is controlled.

As described above, when the content of the iron component is 10 pp
m or more and 200 ppm or less, and the maximum diameter of the iron component is 2
0 μm or less, and the effect of imparting conductivity is reduced if the distance between the iron component and the conductivity-imparting particles is too large.
It is preferable that the particle distribution satisfying the positional relationship in any cross section of 5 μm or more and 5 μm or less occupies 80% or more.
The silicon nitride sintered body having the dispersion state of the conductivity imparting particles has an electric resistance of 10 ⁷ to 10 ² Ωcm,
Variation in electric resistance can be suppressed to ± 20% / 100.

Further, the silicon nitride sintered body of the present invention is suitable for a sliding member because the silicon nitride sintered body has good wear resistance and high strength. By using the bearing ball for equipment, the static electricity accompanying the rotational drive can be efficiently dissipated, and it is possible to suppress charging more than necessary, and it is possible to exhibit excellent sliding characteristics. Next, the material of the conductivity-imparting particles will be described. The material of the conductivity-imparting particles is not particularly limited as long as it is a carbide or a nitride capable of lowering the electric resistance value of the silicon nitride sintered body, but preferably, the carbide particles are a 4a group, 5a group, or 6a group. , Group 7a element, silicon,
It is a compound comprising at least one kind of carbide of boron, and more preferably at least one kind of carbide of tantalum, titanium, niobium, tungsten, silicon and boron. Further, the nitride particles are at least one kind of a nitride of a Group 4a element. In addition, since the nitride particles as the conductivity imparting particles have an effect of lowering the electric resistance value of the silicon nitride sintered body, the silicon nitride particles themselves are not included.

Since the silicon nitride sintered body of the present invention is used for a sliding member such as a bearing ball, the conductivity imparting particles contained therein are naturally slid together with the silicon nitride sintered body. For this reason, the above-mentioned carbides are preferred because the conductivity imparting particles are required to have some sliding properties. The carbide not only has excellent sliding properties, but also has excellent thermal conductivity, so that the thermal conductivity of the silicon nitride sintered body is 40 W /
It is easy to increase to m · k or more.

The nitride particles are preferably a nitride of a Group 4a element, particularly preferably titanium nitride. A nitride of a Group 4a element is preferable because not only the effect of imparting conductivity but also an effect as a sintering aid can be obtained, and titanium nitride is particularly preferable because the effect is remarkable. Further, when the nitride of the group 4a element is dispersed and contained, the oxide of the group 4a element is contained and the sinterability can be improved by precipitating the oxide into the nitride at the time of sintering.

The contents of the carbide particles and the nitride particles are not particularly limited as long as they contain a predetermined amount of agglomerated parts, but the content of the carbide particles is 10 wt% to 35 wt% and the content of the nitride particles is 0.1 wt% or less. It is not less than wt% and not more than 5 wt%. As described above, carbide particles have excellent sliding properties, so 10wt% or more and 35w
Even if the content is less than 5% by weight, the strength and sliding characteristics of the silicon nitride sintered body will not be unnecessarily reduced.However, since the nitride particles themselves are relatively weak and brittle, they exceed 5% by weight. If it is contained, the strength and the sliding characteristics of the silicon nitride sintered body are reduced. The maximum diameter of the conductive particles present in the silicon nitride sintered body is 2 μm or less, preferably 0.3 to 1.2 μm. The maximum diameter of the conductivity-imparting particles of the present invention is the size of the individual conductivity-imparting particles, the longest of the conductivity-imparting particles when looking at the color map in EPMA of the surface mirror portion of the silicon nitride sintered body The diagonal is the maximum diameter.

When comparing the average particle size of the carbide particles with the average particle size of the nitride particles, it is preferable that the average particle size of the carbide particles ≦ the average particle size of the nitride particles. Specifically, the average particle diameter of the carbide particles is preferably 0.3 μm or more and 1 μm or less, and the average particle diameter of the nitride particles is preferably 1 μm or more and 2 μm or less. Since carbide particles are contained more than nitride particles, they tend to aggregate. Therefore, it is necessary to prevent the particles from agglomerating more than necessary by making the particle diameter smaller than that of nitride particles.

The electric resistance of the silicon nitride sintered body having such a form is 10 ² Ω · cm or more and 10 ⁷ Ω · cm. The use of the silicon nitride sintered body of the present invention is not particularly limited,
It is optimally used for a sliding member, for example, a bearing ball provided in a motor device for rotatingly driving an electronic device such as a hard disk drive. At this time, if the electric resistance value exceeds 10 ⁷ Ω · cm, it is difficult to efficiently prevent electrostatic charge generated when the bearing ball slides, and if the electric resistance value is less than 10 ² Ω · cm, the electrostatic charge becomes smaller. Although it is possible to prevent the silicon nitride sintered body from being easily added to the silicon nitride sintered body in a state where a large amount of the conductivity-imparting particles are added to the silicon nitride sintered body, the silicon nitride sintered body has sufficient inherent wear resistance and strength. It is not so preferable because it disappears.

In addition, since the silicon nitride sintered body of the present invention contains particles for imparting conductivity, the thermal conductivity can be improved to 40 W / m · k or more. The silicon nitride sintered body of the present invention,
It is mainly used for sliding members for electronic equipment. In an electronic device, for example, as can be seen from a semiconductor device substrate, the problem of heat is very important. For this reason, it is important that even a sliding member for an electronic device has excellent heat dissipation. In particular, when the bearing balls used for the rotational drive of electronic devices such as hard disks are formed of the silicon nitride sintered body of the present invention, which has a heat conductivity of 40 W / m.k or more and excellent heat dissipation, the aforementioned electrostatic charge is prevented. In addition to this, it is possible to efficiently dissipate the frictional heat associated with the rotational drive, and it is possible to obtain both the effects of preventing static electricity and dissipating heat.
In the case of a bearing member, the rotating shaft and the ball receiving portion are often formed of a metal member such as bearing steel, and problems such as deformation due to heat during sliding are likely to occur. In particular, electronic devices tend to rotate at a high speed of 8,000 rpm or more, and even 10,000 rpm or more, and the problem of heat dissipation is more likely to occur than in the past. Therefore, a bearing ball using the silicon nitride sintered body of the present invention having a high thermal conductivity is suitable for electronic equipment, and is particularly suitable for a bearing member in which a rotating shaft and a ball receiving portion are made of a metal member such as bearing steel. It can be said.

Further, the diameter of the bearing ball is 3 mm
Hereafter, it is more preferably 2 mm or less. The silicon nitride sintered body of the present invention has a high thermal conductivity of 40 W / m · k or more, but is inferior in terms of thermal conductivity as compared with a metal member constituting a rotating shaft or the like. Therefore, from the viewpoint of heat dissipation, the bearing ball made of silicon nitride becomes a thermal resistor, so that the thermal resistance as a bearing member can be reduced by reducing the diameter to 3 mm or less, and further to 2 mm or less.

Although the description has mainly been given of the conductivity-imparting particles, it goes without saying that other components such as a sintering aid may be added in the present invention. As the sintering aid, those generally used may be used, and rare earth compounds such as yttrium oxide and metal oxides such as magnesium oxide are preferable. Further, an aluminum compound such as aluminum oxide or aluminum nitride may be used in combination. The amount of addition is not particularly limited, but 3w
It is preferably at least t% and at most 20 wt%.

Next, the manufacturing method will be described. The production method relates to the dispersion state of the iron component and the conductivity-imparting particles, wherein the content of the iron component is 10 ppm or more and 200 ppm or less, the particle diameter of the distributed iron is 20 μm or less, and the iron component and the conductivity-imparting particles are dispersed. The closest distance between particles is 0.5
There is no particular limitation as long as it is not less than μm and not more than 5 μm. For example, the following method is available.

First, a predetermined amount of a silicon nitride powder, a sintering aid, and a conductivity imparting particle powder are uniformly mixed, followed by granulation, iron removal, molding, degreasing, and sintering. In particular, it is important to uniformly mix the conductivity-imparting particles and prevent excessive mixing of raw materials and iron components generated during the raw material processing step. Therefore, for example, it is important that the amount of iron component in each raw material powder be controlled and not contained more than necessary. When the amount of iron component is small, a treatment such as adding a predetermined amount is also required. In addition, in order to make the interparticle distance between the iron component and the conductivity-imparting particles a predetermined relative value, granulation is performed in advance so that the conductivity-imparting particles can be uniformly dispersed in silicon nitride, and a necessary amount is satisfied so as to satisfy a predetermined dispersion state. After weighing, there is a method of adding to a slurry containing silicon nitride powder and a sintering aid and mixing for a predetermined time.

At the time of addition and mixing, for example, the following method is effective in achieving uniform dispersion. First, when mixing the raw material powder for one lot, each raw material powder is divided into two or more parts, preferably three to five parts, and a relatively small amount is mixed and finally mixed together. Further, there is a method of subjecting the slurry obtained by the above treatment to spray granulation treatment, subjecting the obtained granulated powder to dry iron removal, and removing iron contained in the powder until a desired amount is obtained. is there. The granulated powder is poured into gaps opposed by the magnet rotor at regular intervals, and the magnetic field in the space connecting the opposed points is, for example, 10,000 gauss or more and 30,000 gauss.
The rotor is applied with a current or voltage that is about Gauss or less, and iron is removed in this strong magnetic field. If necessary, this process is repeated until the iron content in the powder reaches a desired amount. In particular, the removal of the iron component by the magnetic field is effective because the iron component having a large maximum diameter can be positively removed.

If the powder is produced by such a method, the content of the iron component, the particle diameter and the distance between the particles can be controlled, so that the content of the iron component is 10 ppm to 20 ppm.
0 ppm or less, the particle diameter of the iron component is 20 μm or less, and the closest interparticle distance between the iron component and the conductivity-imparting particles is 0.
The thickness can be set to 5 μm or more and 5 μm or less.

Although the size of each raw material powder is not particularly limited, the average particle size of the silicon nitride powder is not less than 0.2 μm and not more than 3 μm.
m or less, and the average particle size of the sintering aid is preferably 2 μm or less. The size of the conductive particles is 3 μm or less in average particle size, preferably 0.2 μm or more and 2 μm or less. When the conductivity-imparting particles are less than 0.2 μm, when the particles are applied to a bearing ball, the particles easily fall off the surface during surface processing or sliding. On the other hand, if it exceeds 3 μm, the maximum diameter will exceed 5 μm with only slight aggregation, which is not preferable. Further, it is preferable to use a powder having a small variation in the average particle diameter, for example, a standard deviation of 1.5 μm or less so that the above-mentioned maximum diameter can be easily controlled.

Further, in order not to impair the sliding characteristics as a bearing ball, it is not preferable to use whiskers or fibers as the conductivity-imparting particle powder even if the above-mentioned size is satisfied, and it is desirable to use a particulate powder. . Whiskers and fibers have projections such as thorns on the surface due to their shapes, and if such objects are present on the surface of the bearing ball, the wear resistance is degraded.

As a molding method, a method for producing a sintered body made of silicon nitride or a bearing ball can be applied. Therefore, normal molding methods and hydrostatic molding (CI
P) and the like can be applied, and hydrostatic molding is preferable when manufacturing a bearing ball. Regarding the sintering method, a method for manufacturing a sintered body made of silicon nitride and a bearing ball can be applied. Therefore, normal pressure sintering, pressure sintering, and hot isostatic pressing (HIP) sintering can be applied. When manufacturing bearing balls, normal pressure sintering or pressure sintering is performed and then HIP sintering is performed. It is preferable to carry out knotting.
After the above steps, when used as a bearing ball, the surface is polished to obtain the surface roughness specified by the JIS standard.

[0034]

Examples (Examples 1-4, Comparative Examples 1-2, Reference Example 1)
20 wt% of silicon carbide powder having an average particle diameter of 0.7 μm or less (standard deviation of 1.3 μm or less) as the conductivity-imparting particle powder, and an average particle diameter of 0.
1wt of 9μm (standard deviation 1.5μm or less) titanium oxide powder
%, Yttrium oxide powder having an average particle diameter of 0.8 μm was 5 wt%, aluminum oxide powder having an average particle diameter of 0.9 μm was 4 wt%, and silicon nitride powder having an average particle diameter of 0.7 μm was prepared as a sintering aid. Each raw material powder was divided into three parts and mixed to obtain three mixed powders, and then the three mixed powders were combined and mixed to produce a mixed raw material powder, thereby preparing a mixed raw material powder slurry. Next, the mixed raw material powder slurry was treated in a magnetic field of 10,000 gauss to 30,000 gauss to prepare a mixed raw material powder in which the amount of the iron component was changed. At this time, the amount of the iron component in the mixed raw material powder was in the range of 10 ppm or more and 100 ppm or less. Therefore, the mixed raw material for obtaining the silicon nitride sintered body having the iron component amount shown in Table 1 by adding metallic iron as necessary. The powder was prepared. This mixed raw material powder was molded by the CIP method, and sintered under normal pressure at 1600 ° C. or more and 1900 ° C. or less in an inert atmosphere.
HIP sintering was performed at a temperature of not less than 1900 ° C. and a silicon nitride sintered body shown in Table 1 was produced.

In each of the examples, a square column-shaped sample having a size of 3 × 4 × 40 mm was used, and a surface polishing process equivalent to grade 3 of a bearing ball certified by the JIS standard was performed. The closest distance between the iron component and the conductivity-imparting particles was 0.5 μm or more and 5 μm or less. For each such embodiment, the electrical resistance,
Table 1 also shows the results of measuring the variation of the electric resistance value, the three-point bending strength (room temperature), and the thermal conductivity. The electric resistance value was obtained by lapping the top and bottom of each sample, placing two electrodes on the same plane, and measuring the resistance between them at room temperature with an insulation resistance meter. The thermal conductivity was measured by a laser fresh method using a sample which was additionally processed to 3 × 3 × 10 mm. In each measurement, 100 samples according to each example were prepared, and the average value was shown. Regarding the variation of the electric resistance value, the electric resistance value having the largest difference with respect to the average value was expressed as a percentage (%) as the difference with respect to the average value. In addition,
In the present embodiment, the sample shape is a quadratic prism shape for convenience in each measurement value. However, for example, even when measuring each characteristic of a true spherical bearing ball, it can be dealt with by lapping similarly.

The area ratio of the agglomerated portion of the conductivity-imparting particles in each silicon nitride sintered body was measured by measuring the surface roughness Ra of each sample to 0.
Polishing to less than 01μm and any 4 on the polished surface
Places (arbitrary area equivalent to unit area 30μm × 30μm)
Was selected, and the color map of each measurement location (magnification: 2000 times) was used. For comparison, a sample in which the amount of the iron component was excessive was prepared as Comparative Example 1. Further, a silicon nitride sintered body similar to that of the example except that no conductivity-imparting particles were added was used as comparative example 2.

[0037]

[Table 1]

As can be seen from Table 1, the silicon nitride sintered body of the present invention has a three-point bending strength of 1000 MPa or more and a thermal conductivity of 40 W / m · k in an electric resistance value of 10 ⁷ to 10 ² Ω · cm. It turns out that it is above. On the other hand, in Comparative Example 1, since the iron component amount was large, the variation in the electric resistance value was small, but the strength was reduced. On the other hand, Comparative Example 2 in which no conductivity-imparting particles were added had an electric resistance value of 10 ¹⁰ Ω · cm or more, and poor thermal conductivity. The iron component in the silicon nitride sintered bodies of Examples 1 to 4 and the one in which the closest interparticle distance between the conductivity imparting particles was 0.5 μm or more and 5 μm or less were all 8
More than 0% was present. In addition, the distance between particles is 0.5 μm
The followings were about 5% or more and about 15% or less, and the maximum diameter of the aggregated part was 3 μm or less in each case. On the other hand, those of Comparative Example 1 were about 60%, those having a distance between particles of less than 0.5 μm were about 20%, and those having a maximum diameter of the aggregated part of more than 5 μm. When the silicon nitride sintered body having such characteristics as the electric resistance value is used for a bearing ball for an electronic device such as a hard disk drive to be described later, it is possible to eliminate problems caused by static electricity.

(Examples 5 to 8, Comparative Examples 4 and 6, Reference Example 2) Next, a silicon nitride sintered body having the same electrical resistance value and different iron component ratios in the same manufacturing process as in Example 1 is used. A bearing ball having a diameter of 2 mm was produced. Each bearing ball had a surface polished grade 3. Each bearing ball was assembled into a set of ten bearing balls in a bearing member of a spindle motor for rotating a hard disk drive. In addition, as other bearing members,
A rotating shaft and a ball bearing made of bearing steel SUJ2 were used.
When the motor was continuously operated at a rotation speed of 8,000 rpm and 11,000 rpm for 200 hours, the presence or absence of a defect due to static electricity was examined.
The malfunction due to static electricity was determined based on whether or not the hard disk drive normally operated after 200 hours of continuous operation. The presence or absence of a defect due to each static electricity was measured by preparing 100 hard disk drives each. For comparison, those having the silicon nitride sintered body of Comparative Example 1 were Comparative Example 4, those using the silicon nitride sintered body of Comparative Example 2 were Comparative Example 5, and those having a reduced electric resistance were Comparative Examples. 6 and the same measurement was performed. Table 2 shows the results.

[0040]

[Table 2]

As can be seen from Table 2, it was found that the one using the bearing ball according to the present embodiment did not have any trouble due to static electricity. On the other hand, in Comparative Example 5, since the electric resistance value was relentlessly higher than that of the present invention, a problem caused by static electricity originated (3 out of 100 units). Comparative Example 4
Did not cause any troubles due to static electricity, but the bearing balls were not sufficiently strong due to insufficient strength of the bearing balls after 200 hours. Was. This is considered to be because the ratio of the iron component was too large, and the iron component became a fracture starting point. Comparative Example 6
At 8,000 rpm, no malfunction was detected due to static electricity, but at 11,000 rpm, hard disk drives were not completely stopped, but some malfunctions (one out of 100) were confirmed. It is described as "somewhat." It is considered that this is because static electricity instantaneously concentrated on the bearing ball having the largest electric resistance value because the electric resistance value varied widely. Further, similarly to Comparative Example 4, the damage of the bearing ball was confirmed after 200 hours, and it was found that the bearing ball was not suitable for long-time sliding.

(Examples 9 to 13, Comparative Examples 7 to 9)
The rolling life of the bearing balls was measured using the bearing balls of Examples 5 to 8 and Comparative Examples 4 and 6. In the bearing ball according to this example, the maximum diameter of the agglomerated portion of the iron component and the conductivity-imparting particles was 5 μm or less. The maximum diameter of the agglomerated portion of the iron component and the conductivity-imparting particles of Comparative Example 7 using the bearing ball of Comparative Example 4 was 9 μm, and the iron component and the conductive material of Comparative Example 9 using the bearing ball of Comparative Example 6. The maximum diameter of the aggregation portion of the property imparting particles was 23 μm. Regarding the measurement of rolling life,
Using a thrust type bearing tester and rotating on a SUJ2 steel plate as the mating material, the load is up to 400 hours under the conditions of maximum contact stress of 5.9 GPa per ball, rotational speed of 1200 rpm, and oil bath lubrication conditions of turbine oil The time required for the surface of the bearing ball to peel was measured. Table 3 shows the results.

[0043]

[Table 3]

As can be seen from Table 3, in the bearing balls according to the present example, those having an iron component within the range of the present invention exhibit excellent rolling life equivalent to that of Comparative Example 8 in which no conductive particles were added. I understood that. For it,
As in Comparative Examples 7 and 9, it was found that the sliding characteristics were degraded outside the range of the present invention. It can be said that as a result, the iron component or the conductivity-imparting particles become too large in the silicon nitride matrix, and the good sliding characteristics of the silicon nitride sintered body cannot be maintained. In addition, it is considered that since the maximum diameter of the aggregated portion of the iron component and the conductivity-imparting particles exceeds 5 μm, the aggregated portion has become a fracture starting point.

Examples 13 and 14 and Comparative Example 10 In order to investigate the effect of the particle diameter of the iron component, the same bearing balls as in Example 11 were prepared except that the particle diameter of the iron component was changed. The same rolling life test as in Example 11 was performed on each bearing ball. In addition, the crushing strength and the three-point bending strength (room temperature) were also measured. Crushing strength measurement is old
This was addressed by applying a compressive load with an Instron type testing machine and measuring the load at the time of destruction by a measuring method according to JIS standard B1501. Table 4 shows the results.

[0046]

[Table 4]

As can be seen from Table 4, the particle diameter of the iron component is 2
It was found that those having a thickness of 0 μm or less, and more preferably 5 μm or less, had excellent rolling life and also exhibited excellent crushing strength of 210 MPa or more. On the other hand, it was found that the properties of Comparative Example 10 out of the preferred range of the present invention were degraded even though the content of the iron component was within the range of the present invention. It is considered that this is because the iron component particles became the starting point of fracture because the particle diameter of the large iron component particles was too large. In other words, if the iron component content is within the range of the present invention, the iron component having a particle size exceeding 20 μm cannot be said to be suitable for bearing balls.

(Examples 15 and 16) Silicon carbide powder having an average particle size of 0.8 μm or less (standard deviation of 1.5 μm or less) and titanium oxide powder having an average particle size of 0.9 μm (standard deviation of 1.5 μm or less) were used as the conductive particles. , Average particle size 1.5μ as sintering aid
5% by weight of yttrium oxide powder with an average particle size of 0.8μ
3% by weight of aluminum oxide powder less than m
A 0.5 μm silicon nitride powder was prepared. Next, Example 15
, A silicon nitride powder and a sintering aid powder are mixed, and a predetermined amount of silicon carbide powder and titanium oxide powder are divided into three times to obtain 1
Addition and mixing were performed at intervals, and finally a mixed raw material powder slurry in which the conductivity imparting particles were uniformly mixed was prepared.

In Example 16, each raw material powder was divided into three parts, mixed, and then mixed to prepare a mixed raw material powder slurry. As Reference Example 5, a mixed raw material powder slurry in which all the raw material powders were mixed at once was prepared. Each mixed raw material slurry is 10,000 gauss or more 3
Treated in a magnetic field of 0000 gauss or less to reduce the iron content to 10
A mixed raw material powder within the range of ~ 200 ppm was prepared. Each of the mixed raw material powders was molded by the CIP method, and sintered at 1740 ° C. under normal pressure in an inert atmosphere.
IP sintering was performed to produce a bearing ball made of silicon nitride having a diameter of 2 mm and a square pillar sample having a size of 3 × 4 × 40 mm. One hundred such samples were prepared, and the area ratio of the aggregated portion and the maximum diameter of the aggregated portion composed of the iron component and / or the conductivity-imparting particles were measured. The maximum diameter of the aggregation part is arbitrary 30μ
The measurement was performed at four points of mx 30 µm, and the largest diameter of the largest aggregated portion was found. Table 5 shows the results. Here, the agglomerated portion means that the distance between particles is within a range of 0 (zero) μm or more and less than 0.5 μm when observed with a 2000-times enlarged photograph.

[0050]

[Table 5]

As can be seen from Table 5, it was found that the silicon nitride sintered body having the preferred embodiment of the present invention can be produced by the addition and mixing method of Example 15 or Example 16. On the other hand, in Reference Example 5, although the aggregation portion of the conductivity-imparting particles is partially 3 μm or more and 20 μm or less and partially falls within the preferred range of the present invention, a relatively large aggregation portion is likely to be formed. Do you get it. In such a silicon nitride sintered body, the strength is reduced and the rolling life is also reduced, as in the above-described embodiment.

(Examples 17 to 26) Next, the same silicon nitride sintered body as in Example 2 was produced except that the conductivity imparting particles were changed to the materials shown in Table 6. The same measurement as in Example 2 was performed on each of the manufactured silicon nitride sintered bodies.

[0053]

[Table 6]

As can be seen from Table 5, even when the material of the conductivity-imparting particles was changed, the electrical resistance, the three-point bending strength and the thermal conductivity all exhibited excellent characteristics.

(Examples 27 to 42) The same bearing balls as those of Example 10 were produced except that the silicon nitride sintered bodies of Examples 17 to 26 were used, and the crushing strength and the rolling life were obtained in the same manner as in Example 13. The properties were measured. As a result of the measurement, it was found that all the bearing balls exhibited excellent crushing strength of 210 MPa or more and a rolling life of 400 hours or more. From the above, it can be said that the silicon nitride and the sliding member of the present invention exhibit excellent characteristics even when the material of the conductivity imparting particles is changed.

[0056]

As described above, the silicon nitride sintered body of the present invention contains carbide particles and nitride particles as conductivity imparting particles, and has an iron component content of 10 ppm to 200 ppm.
By the following specification, a specific electric resistance value is provided. When such a silicon nitride sintered body is used for a sliding member of an electronic device such as a hard disk drive, for example, a bearing ball of a bearing member mounted on a motor for rotationally driving, it prevents electrostatic charging due to rotational driving. It becomes possible. Further, by using a carbide or the like as the conductivity-imparting particles, it is possible to improve the thermal conductivity of the sintered body itself, so that it is possible to efficiently radiate frictional heat due to rotational driving. Furthermore, since the variation of the electric resistance value is suppressed, the rotation speed is 8000 rpm
As described above, even when the motor is rotated at a high speed of 10,000 rpm or more, it is possible to efficiently suppress the occurrence of a problem due to static electricity. Further, the sliding characteristics and the like can be improved by preventing aggregation of the iron component and / or the conductivity-imparting particles. With such a configuration, the bearing balls made of silicon nitride sintered body do not unnecessarily reduce the sliding characteristics of silicon nitride, and when used in electronic devices such as hard disk drives, excellent sliding characteristics are obtained. Shows dynamic characteristics.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hisao Yabe 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa Prefecture Inside the Toshiba Yokohama Office (72) Minoru Takao 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock Company (72) Inventor Yukihiro Takenami Eighteen Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Inside the Toshiba Yokohama office (72) Inventor Etsuyuki Fukuda Eighth Shin-Sugita-cho, Isogo-ku, Yokohama-shi, Kanagawa (72) Inventor Kimiya Miyashita 8th place Shin-Sugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture F-term (reference) 3J011 AA08 BA08 DA01 KA07 LA01 MA02 SB02 SD03 SE02 3J101 AA02 BA10 EA44 EA72 EA75 FA31 GA53 4G001 BA03 BA09 BA13 BA22 BA32 BA71 BB03 BB09 BB22 BB23 BB24 BB43 BB71 BC43 BC52 BC54 BD03 BD12

Claims (10)

[Claims] In a silicon nitride sintered body containing carbide particles and nitride particles as conductivity imparting particles, the iron component content is 10 ppm or more and 200 ppm or less, and the electric resistance value is 10 ² Ω · cm.
A silicon nitride sintered body having a resistivity of at least 10 ⁷ Ω · cm or less. 2. The maximum diameter of the iron component present in the sintered body is
2. The silicon nitride sintered body according to claim 1, wherein the thickness is 20 μm or less. 3. The method according to claim 1, wherein the closest interparticle distance between the iron component and the conductivity-imparting particles is 0.5 μm or more and 5 μm or less, and a particle distribution satisfying this positional relationship occupies 80% or more in an arbitrary cross section. The silicon nitride sintered body according to claim 1 or 2, wherein 4. The method according to claim 1, wherein said carbide particles are made of at least one of carbides of Group 4a, 5a, 6a and 7a, silicon and boron. The silicon nitride sintered body according to the above. 5. The silicon nitride sintered body according to claim 1, wherein said nitride particles are at least one kind of a nitride of a Group 4a element. 6. The method according to claim 1, wherein the ratio of the average particle size of the carbide particles to the average particle size of the nitride particles is such that the average particle size of the carbide particles ≦ the average particle size of the nitride particles. The silicon nitride sintered body according to claim 5. 7. The silicon nitride sintered body according to claim 1, having a thermal conductivity of 40 W / m · k or more. 8. A sliding member using the silicon nitride sintered body according to any one of claims 1 to 7. 9. A silicon nitride sintered body containing carbide particles and nitride particles as conductivity imparting particles, wherein the iron component content is 10 ppm or more and 200 ppm or less, and the electric resistance value is 10 ⁷ to 10 ^2.
A bearing ball comprising a silicon nitride sintered body of Ω · cm. 10. The bearing ball according to claim 9, wherein the bearing ball is used for an electronic device.