JP2001146480A - Silicon nitride sintered member, ceramic ball and ceramic ball bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain both a silicon nitride sintered member capable of readily distinguishing defects of different appearance color and foreign matters and increasing examination accuracy and a ceramic ball using the silicon nitride sintered member. SOLUTION: The appearance brightness VS on the surface of the silicon nitride sintered member is made to have 3.0-9.0 so that in examination of the surface, especially the polished surface, a background color readily distinguishable from both defects such as pore, chip, cut, etc., and foreign matters having a background color different from those of the defects is actualized and examination accuracy by an automatic testing machine, etc., can be improved. After abrasion processing of ceramic part, when a metal foreign matter and defects such as pore, etc., on the surface are examined, a parent material constituting the background is distinguished from the foreign matter, the pore, etc., by color difference or brightness difference. The metal foreign matter is observed in an appearance color close to black by polarized light observation of a stereoscopic microscope or a metallurgical microscope and the internal pore and cut are observed in an appearance color close to white. When the appearance brightness VS of the background part is 3.0-9.0, at a part in which the metal foreign matter, the pore, etc., exist, the background color approaches their intermediate color, produces a clear contrast to the foreign matter, the pore, etc., having the appearance color different from the intermediate color and a discrimination test can be readily carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered member and a ceramic ball using the same.

[0002]

2. Description of the Related Art Silicon nitride ceramic parts have been used in bearings of hard disks of machine tools and computers in recent years because of their high strength and excellent wear resistance.
Also, they are used for bearings and sliding parts used in high-temperature and corrosive special environments, such as driving parts of semiconductor devices by utilizing high-temperature corrosion resistance, and sliding parts for automobiles such as tappets.

[0003] By the way, in the above-mentioned ceramic parts, precise polishing is performed, and after the polishing, the presence or absence of material defects such as foreign matters and pores or defects such as scratches, nicks and chips during the polishing is inspected. are doing. This inspection may be performed using a stereoscopic microscope or a metallographic microscope, but recently, it may be performed using an automatic appearance inspection machine or the like in order to cope with mass production and cost reduction. Specifically, for a defective portion such as a polished surface foreign matter or a pore, an image is taken of the polished surface, and the defective portion is identified based on the color or contrast between the background and the background.

[0004]

In general, the appearance of a silicon nitride-based sintered body is generally white or light gray, but defects such as pores and chips are similarly bright in appearance. Therefore, there is a problem that it is difficult to obtain contrast between the defect and the background, and the identification accuracy cannot be sufficiently secured. In particular, in the automatic appearance inspection machine, the defect inspection is performed by the data processing based on the color difference and / or the lightness difference between the background and the defective portion, which directly leads to a decrease in the inspection accuracy. On the other hand, JP-A-04-254471 or JP-A-04-254473 discloses that a sintered body is intentionally prepared by firing a molded body containing a carbon source or impregnating a porous body with carbon. A method of reducing the unevenness of the color of a sintered body by discoloring the sintered body to black or dark gray is disclosed. However, in the case of a black or dark gray background color, defects such as pores and chips that appear in a relatively bright appearance color are easy to identify, but conversely, foreign matter that appears in black or a gray color close to it, particularly metallic foreign matter, etc. There is a drawback that identification becomes difficult.

SUMMARY OF THE INVENTION An object of the present invention is to provide a silicon nitride-based sintered member capable of easily identifying defects and foreign matters having different appearance colors and improving inspection accuracy, and a ceramic ball using the same. is there.

[0006]

In order to solve the above problems, a silicon nitride based sintered member of the present invention is
It is composed mainly of silicon nitride and has a surface appearance lightness VS of 3.0 to 9.0 when the lightness in the color display method defined in JISZ8721 is VS. .

In the present invention, the term "main component" (also synonymous with "main component" or "mainly") refers to a substance of interest having a content of 50% by weight or more, unless otherwise specified. Means that.

In the present invention, by setting the appearance lightness VS of the surface of the silicon nitride-based sintered member to 3.0 to 9.0, when inspecting the surface, particularly the polished surface, the pores, chips, It is possible to realize a background color that can be easily identified for both defects such as sharpness and foreign matters having different appearance colors, and it is possible to improve inspection accuracy by an automatic appearance inspection machine or the like. In this specification, the term “color” includes not only a chromatic color but also an achromatic color having a saturation of zero as a concept. Further, "different colors" means that any of lightness, saturation, and hue is different enough to be distinguished.

In other words, when inspecting the surface of a ceramic component after polishing for defects such as metal foreign matter, pores, cracks, and chips (collectively referred to as pores),
This is identified by the color difference or lightness difference between the base material forming the background and the foreign material or pore. In particular,
The metallic foreign matter is observed with a stereoscopic microscope or a deflection observation with a metal microscope with an appearance color close to black, and the internal pores and sharpness are observed with an appearance color close to white. However, if the appearance lightness VS of the background portion is 3.0 to 9.0, the background color is close to the intermediate color of the portion where metal foreign matter, pores and the like exist, and foreign matter having a different appearance color from the background color. Since a clear contrast is generated for any of the pores and the like, the discrimination inspection can be easily performed by deflection observation of a stereoscopic microscope or a metal microscope.

[0010] When the brightness of the base material is less than 3.0, that is, dark black, the metallic foreign matter is observed in black, making it difficult to determine. Similarly, when the lightness of the base material is larger than 9.0, the base material is close to white and pores and the like are observed in white, making it difficult to determine. Note that the above lightness VS
Is preferably 4.0 to 8.5, more preferably 4.5.
It is desirably ~ 8.0. In addition, the appearance of the silicon nitride-based sintered member is preferably such that the saturation CS specified in the JIS is 3.0 or less, and more preferably 2 from the viewpoint of further clarifying the contrast with foreign substances or pores. 0.0 or less, more preferably 1.0 or less.

Here, the method of measuring the lightness VS and the saturation CS is defined in "4. Spectral colorimetric method" and "4.3. Reflective object measuring method" in JIS-Z8722 "Color measuring method". The method used shall be used. The conditions a to d defined in 4.3 are appropriately selected as appropriate according to the shape of the surface to be measured. For example, when a polished surface of a ceramic ball described later is used as a measurement surface, the condition d
(It is desirable to illuminate the sample with a single light beam whose angle between the optical axis and the normal to the sample surface does not exceed 10 °, and to collectively receive light reflected in all directions.) However, as a simple method, it is also possible to know the lightness and the saturation by visual comparison with a standard color chart prepared in accordance with JIS-Z8721.

The typical application field of the silicon nitride based sintered member of the present invention is a bearing ball, for example, a bearing of a hard disk of a machine tool or a computer, or a driving part of a semiconductor device utilizing high-temperature corrosion resistance. It is a ceramic ball used as a bearing ball used in a corrosive special environment. Further, the present invention can be applied to mechanical sliding parts other than bearings, such as tappets for automobiles, but is not limited thereto. For example, when applied to a bearing ball, its outer diameter is about 1 to 30 mm. Further, when applied to sliding parts such as bearings and tappets, a portion including the sliding surface is configured as at least the silicon nitride-based sintered member of the present invention, and the sliding surface is usually a mirror-polished surface. Often done. When the appearance brightness or chroma of the mirror-polished surface is in the above-described range, the above-described defect or foreign matter on the mirror-polished surface can be more reliably inspected and identified. The mirror polished surface is, for example, a polished surface having an arithmetic average roughness Ra of 0.10 μm or less. The arithmetic average roughness Ra in the present invention refers to an arithmetic average roughness measured by a method specified in JIS-B0601 (1994). In addition,
The cut-off value and the evaluation length used for the measurement adopt the values recommended by the JIS according to the roughness level to be measured.

[0013] The silicon nitride based sintered member of the present invention is mainly composed of silicon nitride, and the remaining component is a sintering aid component, which is 3A, 4A, 5A, 3B in the periodic table.
At least one element selected from the group consisting of elements (for example, Al) and 4B (for example, Si) and Mg can be contained in an amount of 1 to 10% by weight in terms of oxide. These exist mainly in the oxide state in the sintered body. If the sintering aid component is less than 1% by weight, it is difficult to obtain a dense sintered body, and if it exceeds 10% by weight, insufficient strength, toughness or heat resistance is caused. It also leads to a decline. The content of the sintering aid component is desirably 2 to 8% by weight.
It is good to do.

The sintering aid component of Group 3A includes S
c, Y, La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, and Lu are generally used. The content of these elements R is RO only for Ce.
₂ and others are calculated using R ₃ O ₃ type oxide. Of these, oxides of heavy rare earth elements of Y, Tb, Dy, Ho, Er, Tm, and Yb are preferably used because they have the effect of improving the strength, toughness, and wear resistance of the silicon nitride sintered body. used.

The structure of the silicon nitride-based sintered member has a form in which main phase crystal grains containing silicon nitride as a main component are bonded by vitreous and / or crystalline binder phases. The main phase has a β conversion of 70% by volume or more (preferably 90% by volume).
(% By volume or more) of Si ₃ N ₄ phase. In this case, the Si ₃ N ₄ phase is a phase in which a part of Si or N is substituted by Al or oxygen, and a phase in which metal atoms such as Li, Ca, Mg, and Y are solid-dissolved. There may be. For example, it can be exemplified Sialon which is expressed by the following general formula; _{beta-sialon: Si 6-z Al z O} z N 8-z (z =
0-4.2) α-sialon: M _x (Si, Al) ₁₂ (O, N)
₁₆ (x = 0 to 2) M: Li, Mg, Ca, Y, R (R is a rare earth element excluding La and Ce).

The above-mentioned sintering aid component mainly constitutes a binder phase, but a part thereof may be taken into the main phase. The binder phase may contain unavoidable impurities, for example, silicon oxide contained in the silicon nitride raw material powder, in addition to components intentionally added as a sintering aid.

Next, the color of at least the surface layer of the silicon nitride sintered member of the present invention is determined by comparing the lightness VS (or the saturation C).
S) As a specific method of adjusting to be within the range,
A method of containing a transition metal cation in the range of 0.1 to 3% by weight can be exemplified. Transition metal cations function as colorants because they behave as color centers in many ceramic materials. When the content of the transition metal cation is less than 0.1% by weight, the coloring effect is insufficient. On the other hand, when the content is more than 3% by weight, the degree of coloring is too strong, and in either case, the lightness VS may be out of the above range. is there. In addition,
In the present specification, the “surface layer portion” refers to a region having a thickness from the member surface (when the state after mirror polishing described below becomes a problem, the thickness from the mirror polished surface) up to 500 μm. Say.

The transition metal cations include Ta, Co,
It is particularly desirable to use one or more ions selected from Ti and Fe. These are apt to behave as components that generate a grayish color with low saturation in the silicon nitride-based sintered material, and are effective in improving the discriminability between pores and other foreign substances and the background base material. In this case, Ta, C
o, one or more selected from Ti and Fe,
a is Ta ₂ O ₅ conversion, Co is CoO conversion, Ti
Later terms of TiO _2, Fe is in terms _{of Fe} 2 _{O 3,} it is contained in a range of 0.1 to 3 wt% in total, preferably in ensuring the level of lightness VS described above.

The transition metal cation as a coloring component such as Ta, Co, Ti and Fe can be added, for example, in the form of an oxide. When added as an oxide, most of them are taken in the binder phase in the form of oxide in the sintered body. These may function as a sintering aid component. However, if the content is too large, in addition to the problem that the lightness level becomes too low, the strength of the binder phase may be reduced, and the toughness and wear resistance of the sintered body may be insufficient.

On the other hand, as for the form of addition of the transition metal cation as a coloring component, if it can behave as a color center or the like exhibiting coloring performance, the presence state in the silicon nitride sintered body is oxidized. It is not limited to the physical state. And, of course, it is also possible to add in a form other than the oxide, such as a nitride (for example, titanium nitride). When added in the form of nitride, it may be present in the form of nitride in the sintered body, or may be converted to oxide under the influence of excess oxygen or the like. In any case, in the present specification, the content of the transition metal cation as the coloring component is expressed in terms of the above-mentioned oxide regardless of the addition form. Note that Ta, Co, Ti and Fe
Whether or not an element component that can be a coloring component exists in a cationic state, for example, can be easily confirmed by, for example, X-ray photoelectron spectroscopy (XPS or ESCA). Specifically, in a photoelectron spectrum obtained by analysis by XPS or ESCA, when a chemical shift in a direction in which the ionic valence becomes positive occurs in the binding energy peak of the element of interest, Can be seen to exist in a cationic state.

Next, as another method of coloring the surface layer portion of the sintered body, a method of forming a carbon-enriched layer having a higher carbon concentration than the inner layer portion on the surface layer portion can be exemplified. In this case, the carbon-enriched layer has the lightness VS in the range (3.0 to 9.0).
In order to achieve the above, it is desirable that the amount of carbon present is very small. For example, when a large amount of carbon is present, the appearance color of the sintered body becomes black, and a defect inspection cannot be performed by an automatic appearance inspection or the like.

The presence of such a trace amount of carbon can be detected by Raman spectroscopy. In the present invention, the presence of carbon at a specific level in the Raman spectroscopy results in adjusting the lightness VS to the above range. It is important from the viewpoint of doing. Specifically, when the surface of the member is subjected to Raman spectroscopic analysis, it is estimated that the peak existing at 206 ± 10 cm ⁻¹ (resulting in β-silicon nitride:
X1, 1584 ± 2
0 cm ^-1 (estimated to be reduced to graphite:
The peak ratio represented by X2 / X1 is desirably 0.001 to 0.5, where X2 is the intensity of the peak present in the graphite-based peak. If this peak ratio exceeds 0.2, the appearance color of the sintered body becomes black,
In some cases, it is difficult to detect the above-described foreign matter or the like. On the other hand, if it is less than 0.001, the appearance color of the sintered body becomes close to white, and it may be difficult to detect the above-mentioned pores and the like.

In Raman spectroscopy, a β-silicon nitride-based peak and a graphite-based peak are simultaneously observed, and the ratio of graphite-based peak intensity X2 to β-silicon nitride-based peak intensity X1 is about 0.5. This means that the carbon content is very small. This is because when a large amount of carbon is present, the appearance color of the sintered body becomes black, and it becomes impossible to perform a defect inspection by an automatic appearance inspection or the like. Then, when the peak ratio X2 / X1 is 0.
When the carbon content is increased to an extent exceeding 5, the appearance color of the sintered body becomes close to black, and it becomes difficult to detect the above-mentioned foreign substances and the like. On the other hand, if it is less than 0.001, the appearance color of the sintered body becomes close to white, and it becomes difficult to detect the above-mentioned pores and the like.
Here, each of the peak intensities is measured as a peak height from a background level. The peak ratio X2 / X1 is desirably 0.2 or less. The carbon component may be present in the form of polycrystalline graphite in addition to amorphous carbon. In the latter case, the peak usually detected by Raman spectroscopy is usually one peak.
350 ± 20 cm ⁻¹ , 1584 ± 20 cm ⁻¹ and 2
Appears at three places of 710 ± 20 cm ⁻¹ . in this case,
The peak with the highest intensity is adopted as X2.

The appearance lightness VS of the sintered body was 3.0 to 3.0.
As a method of coloring to 9.0, a method of blending a transition metal cation as a coloring component and a method of forming a carbon-concentrated layer on the surface layer are exemplified, but this is only a specific method of adjusting the appearance brightness. This is merely an example, and the present invention is not limited to this. For example, it is also possible to obtain an appearance color in the above lightness range by adjusting the mixing ratio of the sintering aid components and the firing conditions.

[0025]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a silicon nitride based sintered member according to the present invention will be described together with an example of a method of manufacturing the same. First, the silicon nitride powder as a raw material has an α ratio of 70.
% Or more, and as a sintering aid, at least one element selected from the group consisting of rare earth elements, 3A, 4A, 5A, 3B and 4B elements, in an amount of 1 to 10 wt. %, Preferably 2 to 8% by weight. At the time of compounding the raw materials, in addition to oxides of these elements, compounds that can be converted to oxides by sintering,
For example, you may mix | blend in the form of a carbonate, a hydroxide, etc. Molding of the compounded raw material powder can be performed using a pressure molding method such as a mold press, and a desired shape can be obtained. In addition, Ta, Co, Ti or Fe
When Ta is added, Ta is converted to Ta ₂ O ₅ , Co is converted to CoO, Ti is converted to TiO ₂ , and Fe is Fe.
_It is blended in the raw material powder in a total of 0.1 to 3% by weight in terms of ₂ O ₃ . Also in this case, in addition to oxide powders of these elements, compounds that can be converted to oxides by sintering,
For example, it may be blended in the form of a carbonate (for example, CoCO ₃ ) or a hydroxide. It is also possible to mix in the form of a nitride such as TiN.

For example, when a ceramic ball such as a bearing ball is manufactured, as shown in FIG. 9A, the upper and lower press punches 103, 103 inserted into the die hole 102 of the forming die 101 are provided with respective tip surfaces. Hemispherical recess 103
a, 103a are formed respectively, and both punches 103, 10 are formed.
By compressing the powder between the three, a spherical ceramic molded body 104 can be obtained.

On the other hand, in the above-mentioned die press method, the pressing force from the press punches 103, 103 is insufficient at the outer peripheral edge of the hemispherical concave portions 103a, 103a, so that the density of the ceramic molded body 104 becomes non-uniform. 103a,
Defects such as cracks and chips may occur in the molded body near the alignment position of 103a. In this case, as shown in FIG. 9B, a method of flattening the outer peripheral edge of the punch surface of the press punches 103, 103 and increasing the press pressure in the area can be adopted. However, in this method, the flattened portions 103b, 103b of the press punches 103, 103
Correspondingly, the molded body 104 necessarily has a flange-shaped unnecessary portion 104. This unnecessary portion 104 needs to be removed by polishing or the like before or after firing.

In addition to the die press, a cold isostatic press (CIP) method can be employed.

Except for the molding method, a method in which the raw material powder is dispersed in a thermoplastic binder to form a slurry, the slurry is allowed to freely fall from a nozzle into a spherical shape by surface tension, and is cooled and solidified in air (for example, 63-2
No. 29137), or a slurry comprising a raw material powder, a monomer (or a prepolymer) and a dispersion solvent is dispersed as droplets in a liquid that is immiscible with the slurry, and the monomer or prepolymer is dispersed in that state. Examples of the method include a method of obtaining a spherical molded body by polymerization (for example, disclosed in Japanese Patent Application Laid-Open No. 8-52712).

On the other hand, the following can be exemplified as more desirable methods. FIG. 1 shows an embodiment of an apparatus used in the raw material powder preparation step. In the device,
The hot air flow passage 1 is formed to include a vertically arranged hot air duct 4, and a gas circulating body, such as a net or a hole, which allows the passage of hot air but does not allow the drying medium 2 to pass between the hot air ducts 4. A medium holding portion 5 such as an opening plate is formed. Then, on the media holding unit 5,
Dry media 2 composed of ceramic spheres mainly composed of one of alumina, zirconia, and a mixed ceramic thereof are stacked to form a layered dry media integrated body 3.

On the other hand, the raw material is in the form of a slurry obtained by adding a water-based solvent to a blend of silicon nitride powder and sintering aid powder and wet-mixing (or wet-mixing / grinding) with a ball mill or an attritor. Be prepared. In this case, the size of the primary particles is adjusted so that the BET specific surface area value is 5 to 13 m ² / g.

As shown in FIG.
On the other hand, the hot air is circulated in the hot air duct 4 so as to move upward from the lower side of the medium holding portion 5 while moving the drying medium 2 up. On the other hand, as shown in FIG.
Is pumped up from the slurry tank 20 by the pump P, and is dropped and supplied to the dry media assembly 3 from above. Thereby, as shown in FIG. 3, the slurry is dried by hot air and adheres to the surface of the drying medium 2 in the form of the powder aggregation layer PL.

Then, by the flow of hot air, the dry medium 2 repeatedly hits and falls and strikes each other, and the powder agglomeration layer PL is pulverized into raw powder particles 9 by rubbing by the strike. The crushed raw material powder particles 9 include those in the form of isolated primary particles, but are mostly secondary particles in which the primary particles are aggregated.
The raw material powder particles 9 having a particle size of a certain size or less flow downstream along with the hot air (FIG. 1). On the other hand, the crushed particles larger than a certain size are not blown off by the hot air but fall again to the dry media assembly 3 and are further crushed between the media.

In this way, the raw material powder particles 9 that have flowed to the downstream side together with the hot air are recovered as the raw material powder 10 in the recovery unit 21 via the cyclone S. The recovered raw material powder 10 has an average particle diameter of 0.3 to 2 μm measured by a laser diffraction type particle sizer, and also has a 90% particle diameter of 0.7 to 2 μm.
3.5 μm, and a BET specific surface area value of 5 to 13 m ² /
g.

In FIG. 1, the diameter of the drying medium 2 is
It is set appropriately according to the flow cross-sectional area of the hot air duct 4. If the diameter is insufficient, the impact force on the powder agglomeration layer formed on the medium is insufficient, and a raw material powder having a particle diameter within an intended range may not be obtained. On the other hand, if the diameter is too large, the turbulence of the drying medium 2 is unlikely to occur even when hot air is circulated, so that the impact force is also insufficient, and a raw material powder having a particle diameter within the intended range cannot be obtained. There is. It should be noted that it is preferable to use the same size as the drying medium 2 by forming an appropriate gap between the media,
This is desirable in promoting the movement of the media during hot air circulation.

The filling depth t1 of the drying medium 2 in the drying medium assembly 3 is appropriately set within a range in which the flow of the medium 2 occurs without excess or shortage according to the flow rate of the hot air. If the filling depth t1 is too large, the flow of the dry medium 2 becomes difficult, and the impact power is insufficient, so that a raw material powder having a particle diameter within a desired range may not be obtained. On the other hand, if the filling depth t1 is too small, the amount of the dry medium 2 is too small, and the frequency of impact is reduced, leading to a reduction in processing efficiency.

Next, the temperature of the hot air is appropriately set within a range in which the drying of the slurry proceeds sufficiently and no problems such as thermal deterioration occur in the powder. For example, when the solvent of the slurry is mainly water, when the temperature of the hot air is lower than 100 ° C., the supplied slurry does not sufficiently dry, and the water content of the obtained raw material powder becomes too high to cause agglomeration. In some cases, powder having the desired particle size cannot be obtained.

Further, the flow velocity of the hot air is appropriately set within a range in which the drying medium 3 is not blown to the collecting section 21. If the flow velocity is too low, the flow of the drying medium 2 becomes difficult, and the impact power is insufficient, so that a raw material powder having a particle diameter within an intended range may not be obtained. On the other hand, if the flow velocity is too high, the drying medium 2 rises too high and the collision frequency is rather reduced, leading to a reduction in processing efficiency.

The raw material powder 10 thus obtained is shown in FIG.
The sphere is formed by the rolling granulator 30 shown in FIG. As the tumbling granulation apparatus 30, a known one can be used. For example, a granulation vessel 3 having a somewhat flat cylindrical shape and an open upper side is used.
2, which is rotatably driven by a rotation drive unit (not shown) via a rotation shaft 32 having one end coupled to the center of the bottom surface of the bottom in a substantially orthogonal manner.

Then, the granulation container 32 is driven to rotate at a constant peripheral speed, and the raw material powder is supplied thereto together with water (for example, by spraying). As shown in FIG. 4 (b), the charged raw material powder P is supplied to the rotating granulation container 32.
Rolling on the inclined powder layer formed therein forms a compact G by spherical aggregation. The operating conditions of the tumbling granulator 30 are adjusted so that the diameter of the obtained compact G is 5 mm or less and the relative density is 61% or more. Specifically, the rotation speed of the granulation container 32 is adjusted at 10 to 200 rpm, and the water supply amount is adjusted so that the moisture content in the finally obtained molded body is 10 to 20% by weight. . If this formed body G is fired by the method described below, the diameter is 4.5.
mm or less can be obtained.

The molded body obtained as described above can be fired by two-stage firing of primary firing and secondary firing. The primary firing is performed at 1900 ° C. or less in a non-oxidizing atmosphere containing nitrogen at 1 to 10 atm or less, and the relative density of the sintered body after the primary firing is 78% or more, preferably 90% or more.
% Is desirable. If the relative density of the sintered body after the primary firing is less than 78%, many defects such as pores tend to remain after the secondary firing, which is not preferable. The secondary firing can be performed at 1600 to 1950 ° C. in a non-oxidizing atmosphere containing nitrogen at 10 to 1000 atm. If the firing pressure is less than 10 atm, decomposition of silicon nitride cannot be suppressed, and even if the pressure exceeds 1,000 atm, there is no change in the effect, and there is a disadvantage in cost. If the firing temperature is lower than 1600 ° C., defects such as pores cannot be eliminated and the strength decreases. On the other hand, if the firing temperature exceeds 1950 ° C., the strength of the sintered body decreases due to grain growth. Not preferred.

As shown in FIG. 5, after the sintering as described above, a ceramic ball 43 whose surface is precisely polished is incorporated between an inner ring 42 and an outer ring 41 made of metal or ceramic, whereby a ball bearing 40 is obtained. Can be If the shaft SH is fixed to the inner surface of the inner ring 42 of the ball bearing 40, the ceramic ball 43 is held rotatably or slidably with respect to the outer ring 41 or the inner ring 42. Further, the present invention is not limited to the ball bearing, but can be applied to other sliding parts, for example, the ceramic tappet 50 as shown in FIG. In FIG. 6, a ceramic plate 53 configured as a silicon nitride based sintered member of the present invention is replaced with a metal main body 51.
Has a structure joined to the end face via a brazing material layer 52. A sliding surface 53a is provided on the side opposite to the joining surface of the ceramic plate 53.
Are formed. At least the appearance color of this sliding surface
The lightness VS is adjusted so as to be 3.0 to 9.0.

In order to adjust the appearance color of these silicon nitride-based sintered bodies (ceramic balls 43, ceramic plates 53, etc.) so that the lightness VS becomes 3.0 to 9.0, the main colors of the sintered bodies are controlled. Component (Si ₃ N ₄ powder), sintering aid component (Y ₂ O ₃ , Al ₂ O ₃ or MgO powder), and colorant component (Ta, Co, Ti or Fe oxide or carbonate) Can be mixed and fired, for example, as described below. (1) 93 wt% Si ₃ N ₄ -3 wt% Y ₂ O ₃ -3 wt% Al ₂ O ₃ -1 wt% Ta ₂ O ₅ (2) 92 wt% Si ₃ N ₄ -3 wt% Y ₂ O ₃ -3 wt% Al ₂ O ₃ -2 wt% Ta ₂ O ₅ (3) 93 wt% Si ₃ N ₄ -3 wt% Y ₂ O ₃ -3 wt% Al ₂ O ₃ -1 wt% CoCO ₃ (4) 93.7% by weight Si ₃ N ₄ -3% by weight Y ₂ O ₃ -3
_Wt% Al ₂ O 3 -0.3 wt% CoCO ₃ (5) 93 _wt% Si _{3 N} 4 -3 _wt% Y _{2 O} 3 -3 _wt% Al _{2 O} 3 -1 wt% TiO ₂ (6) 93 Weight% Si ₃ N ₄ -3 weight% Y ₂ O ₃ -3 weight% Al ₂ O ₃ -1 weight% Fe ₂ O ₃ (7) 93 weight% Si ₃ N ₄ -3 weight% Y ₂ O ₃ -3 % By weight Al ₂ O ₃ -0.5% by weight CoCO ₃ -0.5% by weight
Fe ₂ O ₃ (8) 93% by weight Si ₃ N ₄ -3% by weight Y ₂ O ₃ -3% by weight Al ₂ O ₃ -0.5% by weight TiO ₂ -0.5% by weight F
e ₂ O ₃ (9) 93 wt% Si ₃ N ₄ -3 wt% Y ₂ O ₃ -3 wt% Al ₂ O ₃ -0.5 wt% Ta ₂ O ₅ -0.5 wt%
Fe ₂ O ₃ (10) 97% by weight Si ₃ N ₄ -1% by weight MgO -1% by weight
Al ₂ O ₃ -0.5% by weight TiO ₂ -0.5% by weight Fe
₂ O ₃ (11) 96.5 wt% Si ₃ N ₄ -2 wt% MgO-1 wt% Al ₂ O ₃ -0.5 wt% TiO ₂ (12) 96.5 wt% Si ₃ N ₄ -2 wt% MgO-1 _wt% Al ₂ O 3 -0.5 wt% _Fe 2 _{O 3}

As another method for forming a carbon-enriched layer on the surface layer of the sintered body, the surface of the sintered body is covered with a carbon component source material, and the sintered body is heated in that state to thereby form a carbon component source material. A method of performing a carburizing heat treatment step of diffusing the carbon component of the above into the surface of the sintered body. This carburizing heat treatment step may be performed separately after sintering is completed, or when sintering is performed in two stages, the surface of the sintered body is covered with a carbon component source material after the primary sintering is completed, Secondary baking, which also serves as a carburizing heat treatment, may be performed. In particular, it is desirable to adopt the latter step from the viewpoint of uniformity and uniformity and easy adjustment of the brightness VS to the above-mentioned range. In addition, this method can be combined with the above-described method of blending the coloring agent.

As the carbon component source material, a simple carbon powder such as graphite or amorphous carbon black can be employed, but a polymer material powder mainly composed of carbon may also be used. When a carbon component source powder is used, it is used alone or in combination with an auxiliary powder such as boron nitride (BN) powder to mix an organic solvent to form a paste. In addition, as the organic solvent, for example, alcohols, ketones, halogenated hydrocarbons, and the like can be used. In particular, a low-molecular solvent having 2 to 3 carbon atoms, for example, ethyl alcohol, propyl alcohol, acetone, or trichloroethane can be used. it can.

Then, by applying such a paste to the surface of the sintered body and performing the above-mentioned carburizing heat treatment, carbon from the carbon component source powder contained in the paste is diffused to the surface of the sintered body, and the carbon concentration is increased. An oxide layer is formed. Instead of applying the above paste, there is also a method of directly depositing the carbon component source powder on the surface of the primary fired body by an electrostatic powder coating method or the like. Needless to say, the form of the carbon component source material is not limited to a powdery material, and the primary fired body may be covered with a carbon component source fiber such as carbon fiber.

The color of the carbon-enriched layer as described above (ie,
The carbon content) and the thickness are affected by the amount of the carbon component source covering the surface of the sintered body, the temperature, time and pressure of the carburizing heat treatment, and also the density of the sintered body to be carburized. In any case, what is important is that when the surface of the carbon-enriched layer is subjected to Raman spectroscopic analysis, the intensity of the peak (β-silicon nitride-based peak) existing at 206 ± 10 cm ⁻¹ in the profile of the obtained Raman scattering spectrum. X1, 1584
Assuming that the intensity of the peak (graphite peak) existing at ± 20 cm ^-1 is X2, the carbon content in the carbon-enriched layer is such that the peak ratio represented by X2 / X1 is 0.001 to 0.5. Is to select the processing conditions that make the amount very small. The appearance lightness VS of the final carbon-enriched layer is 3.0.
９9.0.

For example, in the case where the surface of the primary fired body is covered with the carbon component source material and the secondary firing is performed together with the carburizing heat treatment, the density of the primary fired body is desirably kept to less than 97%. This is because the amount of carbon contained in the surface layer portion of the sintered body after the secondary firing becomes large, and the brightness VS may not be able to clear 3.0 or more. Further, the coating amount of the carbon component source powder is preferably from 50 to 800 g / m ² per unit surface area of the primary fired body in terms of the weight of carbon alone. If the coating amount of the carbon component source powder is less than 50 g / m ^{2 in} terms of the carbon simple substance weight, color unevenness occurs on the surface of the sintered body, making it difficult to determine a defect and increasing the pores in the sintered body. , And tend to increase. Further, when the coating amount of the carbon component source powder is 800 g / m ² or more in terms of the carbon simple substance weight, the amount of carbon in the carbon-enriched layer becomes too large, and it may be impossible to secure lightness VS of 3.0 or more. . By performing the secondary firing under the above-mentioned conditions while employing these conditions, a carbon-enriched layer having the desired brightness can be formed on the surface of the sintered body after the secondary firing.

In the case of a bearing ball or the like, the surface is precisely mirror-polished after sintering in order to improve sphericity and the like. This polishing can be performed in two ways: a case where the carbon-enriched layer is left, and a case where the carbon-enriched layer is removed so that the inner layer appears on the polished surface.

In the former case, the carbon-concentrated layer mainly plays the role of adjusting the appearance color of the member surface. In this case, since the thickness of the carbon-enriched layer also decreases with polishing, it is necessary to secure a sufficient thickness of the carbon-enriched layer to be formed at the stage before polishing in consideration of the polishing allowance. However, if the thickness of the carbon-enriched layer is extremely increased, the carburizing heat treatment will be significantly lengthened.
m or less. Note that the thickness of the carbon-enriched layer can be determined by enlarging the cross-section of the sintered body and changing the brightness in the thickness direction. When the brightness of the surface layer is V0,
The depth position where the brightness V0 decreases to 60% is determined as the boundary position of the carbon-enriched layer.

On the other hand, in the latter, an inner layer appearing on the member surface by polishing plays a role of adjusting the appearance color of the member surface. In this embodiment, the role of the carbon-enriched layer is as follows. That is, when the boundary between the carbon-enriched layer and the inner layer is determined as described above, if the carburizing treatment is performed so that the lightness of the carbon-enriched layer becomes smaller, the progress of carburization from the carbon-enriched layer side Thereby, the carburizing concentration of the inner layer can be homogenized. Then, by exposing this to the surface by polishing, it is possible to obtain a stable appearance color with less color unevenness. In this case, when Raman spectroscopic analysis is performed on the polished surface, the peak ratio represented by X2 / X1 in the profile of the obtained Raman scattering spectrum is 0.001 to 0.5. Desirably, this allows the appearance lightness VS to be in the range of 3.0 to 9.0.

Here, the carbon in the carbon-enriched layer may contribute to improving the solid lubrication performance of the carbon-enriched layer and improving the wear resistance of the member, in addition to adjusting the lightness of the carbon-enriched layer. This effect is remarkable when carbon exists particularly in a polycrystalline graphite state. It should be noted that whether carbon is present in the form of polycrystalline graphite is usually determined by peaks detected by Raman spectroscopy at 1350 ± 20 cm ⁻¹ and 1584 ± ¹ .
It can be confirmed by appearing at three places of 20 cm ⁻¹ and 2710 ± 20 cm ⁻¹ .

Incidentally, in order to adjust the appearance color of the sintered body,
The method of blending the coloring agent and the method of forming the carbon-concentrated layer by the carburizing heat treatment described above can be performed independently of each other, or can be performed by combining both. For example, when the desired surface appearance color is achieved only by blending the colorant, it is not necessary to form the carbon-enriched layer, and conversely, the intended surface appearance color is achieved by forming the carbon-enriched layer. In this case, the coloring agent may be omitted. Also, even when the desired surface appearance color is achieved by the colorant compounding, if color unevenness is likely to occur on the member surface, in order to prevent this, it is possible to combine the formation of a carbon-concentrated layer by carburizing heat treatment. Becomes effective. That is, it is also possible to use the formation of the carbon-concentrated layer subordinately to remove color unevenness.

When the surface was subjected to Raman spectroscopy, the peak ratio represented by X2 / X1 was 0.001
The fact that it is 0.5 means that the portion including the surface, that is, the surface layer portion contains at least the concentration of carbon at which the peak ratio represented by X2 / X1 is 0.001 to 0.5. I do. This does not limit the carbon concentration inside the sintered body at all, and the structure in which the carbon concentration in the inside is lower than the surface layer, the structure in which the carbon concentration in the surface layer and the inside are almost the same, and the surface layer Any configuration that increases the internal carbon concentration may be used. For example, it is conceivable to increase the average carbon concentration in the finally obtained ceramic for the purpose of increasing the hardness and the like of the sintered body, but in this case, the appearance color inside the ceramic naturally becomes dark. However, if sintering is performed in an atmosphere that imparts a slight oxidizing property by introducing a small amount of oxygen or the like, the surface layer of the sintered body reversely decarburizes and the carbon concentration becomes lower than the inside, As a result, it is also possible to adjust the brightness to a desired value by increasing the brightness of the surface layer from the inside.

[0055]

[Experimental Examples] In order to confirm the effects of the present invention, the following experiments were conducted. (Experimental example 1) As a main component of a sintered body, an average particle diameter is 0.5 μm.
Silicon nitride (Si ₃ N ₄ ) powder (silicon nitride purity 90% by weight), yttria (Y ₂ O ₃ ) powder having an average particle diameter of 1.5 μm as a sintering aid component, and alumina (A) having an average particle diameter of 1 μm
1 ₂ O ₃ ) powder and magnesia (MgO) powder having an average particle size of 0.5 μm were prepared. Also, as a colorant component,
Powders of oxides or carbonates and nitrides of Ta, Co, Ti and Fe were prepared. The test was conducted so that the total of the sintering aid components was 1 to 10% by weight in terms of oxide, the total of the colorant components was 0.1 to 3% by weight in terms of oxide, and the remainder was a silicon nitride component. A formulation was prepared. Table 1 shows the compositions and amounts of these compounds. In addition, the coloring agent components are not blended for Nos. 5 to 9.

[0056]

[Table 1]

Water or an organic solvent was added to these compounds, and the mixture was wet-mixed and pulverized by a ball mill for 30 hours. The raw material slurry thus obtained was dried by the drying adjustment device in FIG. 1 to obtain a base powder. Next, the base powder was put into a granulating container 32 of a tumbling granulator 30 shown in FIG. The rotation speed of the granulation container 32 at this time was changed in the range of 5 to 30 rpm depending on the size of the sphere. The obtained molded body is primarily fired at 1500 to 1700 ° C. under 1 atm of nitrogen gas, and then housed in a carbonaceous sheath under 1 atm of nitrogen gas at 1750 ° C.
To obtain a sintered body. In addition, about Nos. 5 and 6, 700 g of carbon powder (product name: EG-120 (manufactured by Toyo Tanso Co., Ltd.)) was added to 900 ml of ethyl alcohol.
Using a paste in which kneaded and kneaded
The surface of the sintered body after the primary firing was coated so as to have an application amount of 90 g / m ² and the latter of 150 g / m ² , respectively, and then the secondary firing was performed.

Next, the surface of the sintered body was mirror-polished, and the appearance color of the polished surface of each sintered body was visually compared with a standard color chart prepared in accordance with JIS-Z8721. And chroma. Further, the polished surface of each sintered body was observed with a stereoscopic microscope and a metallographic microscope of 10 to 200 times magnification, and it was visually confirmed whether or not metal foreign matter, pores, and the like could be distinguished from the background base material. Table 2 shows the above results.

[0059]

[Table 2]

Further, FIG. 7 shows an enlarged photograph of metal foreign matters and internal pores observed on the polished surface of the sintered body of sample No. 5 in Table 2. Metallic foreign matter (FIG. (A)) is observed with an appearance color close to black, and internal pores (FIG. (B)) are observed with an appearance color close to white. However, since the appearance lightness VS of the background portion of Sample No. 5 was 6.0, the background color was close to the intermediate color between them, and it was clear for both the metallic foreign matter and the internal pores having different appearance colors. High contrast occurs. Therefore, it is possible to easily discriminate and inspect metal foreign matter, pores, and the like by deflection observation of a stereoscopic microscope or a metallographic microscope. FIG.
(C) shows sample numbers 3, 5, 8, 10, and 10 shown in Table 2.
12 is an enlarged photograph showing the appearance color of a sintered body No. 12. The colors are as follows: No. 3: Lightness 4, achromatic color No. 5: Lightness 6, achromatic color No. 8: Lightness 8.5, achromatic color No. 10: Hue 5PB, lightness 4, saturation 1 No. 12: Hue 5Y, lightness 6, saturation 3

As described above, from Tables 1 and 2 and FIG.
When the total of the colorant components selected from a, Co, Ti and Fe is in the range of 0.1 to 3% by weight in terms of oxide, the lightness VS of the polished surface of the sintered body becomes 3.0 to 9.0, It can be seen that detection of metal foreign matter and pores is possible.

(Experimental Example 2) As a raw material powder, 94% by weight of silicon nitride powder having an average particle diameter of 0.7 μm (purity of silicon nitride: 99.1% by weight) and Y ₂ O ₃ powder having an average particle diameter of 1.5 μm were used. 3% by weight, Al ₂ O ₃ powder having an average particle diameter of 1 μm 3% by weight
Is mixed and pulverized with water using a ball mill.
This was performed for 0 hour, and dried using the apparatus shown in FIG. 1 to obtain a base powder. Next, the base powder was molded by the rolling granulation method shown in FIG. The number of rotations of the granulation container 32 is 5 to 5 depending on the size of the sphere.
It was changed in the range of 30 rpm. In addition, 100 compacts were prepared for each condition, but 10% (10
Pieces), a stainless steel piece of about 200 μm and 5
Resin beads having a size of about 00 μm were embedded, and foreign substances were intentionally introduced.

The obtained molded body was placed under one atmosphere of nitrogen gas.
After primary firing at 1700 ° C., the density was measured by the Archimedes method. Then, carbon powder (product name: EG-
Using a paste obtained by mixing and kneading 900 ml of ethyl alcohol with 700 g of 120 (manufactured by Toyo Tanso Co., Ltd.),
The surface of the sintered body after the primary firing was coated so as to have various coating amounts, and this was housed in a carbon sheath, and then fired at 1750 ° C. under 75 atm of nitrogen gas. When the density of the obtained sintered body was measured again by the Archimedes method, it was found to be 99% or more in all cases.

Next, the surface of the sintered body was mirror-polished, and pore observation was performed with a microscope and a scanning electron microscope (SEM), and the diameter of the maximum pore per 1 mm ² was measured at 10 places. When the maximum pore size was 3 μm or more, it was judged as unacceptable (x), and when it was less than 3 μm, it was judged as acceptable (o). On the other hand, the surface of the sintered body after polishing is treated with a Raman spectrometer (Labr, manufactured by ISA of France, Labr.
am, an Ar laser (wavelength: 514.5 nm), spot diameter 10 μm), a peak intensity (β-silicon nitride-based peak intensity) X1 of 206 ± 10 cm ⁻¹ and 1584.
The ratio (X2 / X1) to the peak intensity (graphite peak intensity) X2 of ± 20 cm ⁻¹ was determined.

FIG. 8A shows the profile of the Raman scattering spectrum of Sample No. 5, and FIG.
The peak near ± 10 cm ⁻¹ (β-silicon nitride-based peak) and the peak near 1584 ± 20 cm ⁻¹ (graphite-based peak) are enlarged and shown, respectively. Note that the peak height and the obtained spectrum profile were converted to a wavelength of 300 by digital low-pass filter processing.
A component below cm ⁻¹ is cut to generate a background curve, and the height is calculated from the height of protrusion from the background curve.

The appearance color of the polished surface of each sintered body was determined by JI
Hue, lightness, and chroma were measured by visual comparison with a standard color chart prepared based on S-Z8721. Further, the polished surface of each sintered body was observed with a stereoscopic microscope and a metallographic microscope at a magnification of 10 to 200 times, and the ratio of intentionally introduced foreign matter was accurately confirmed (10% if all 10 were confirmed).
0%). As for the pores, the proportion of the pores that could be visually confirmed in all the quantities was determined. Table 3 shows the above results.

[0067]

[Table 3]

As described above, when the Raman intensity ratio X2 / X1 is in the range of 0.001 to 0.5, the brightness VS of the polished surface of the sintered body becomes 3.0 to 9.0, and the detection of foreign matter or pores It can be seen that the operation can be performed accurately.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view conceptually showing an example of an apparatus for producing a raw material powder.

FIG. 2 is a diagram for explaining the operation of the apparatus shown in FIG. 1;

FIG. 3 is an operation explanatory view following FIG. 2;

FIG. 4 is a perspective view and an operation explanatory view of a rolling granulator.

FIG. 5 is a schematic view of a ball bearing using the ceramic ball of the present invention.

FIG. 6 is a front view showing an example of a tappet using a ceramic plate configured as a silicon nitride-based sintered body of the present invention.

FIG. 7 is an enlarged photograph of metal foreign matter and internal pores observed on the polished surface of Sample No. 5 of Experimental Example 1;
The enlarged photograph showing the appearance color of 5, 8, 10, and 12 sintered compacts.

FIG. 8 is a profile of a Raman scattering spectrum of Sample No. 5 in Experimental Example 2.

FIG. 9 is a process explanatory view showing an example of a method for producing a spherical molded body by pressing.

[Description of References] 40 Ball bearing 43 Ceramic ball (silicon nitride sintered member) 50 Tappet 53 Ceramic plate (silicon nitride sintered member)

Claims (12)

[Claims] 1. A semiconductor comprising silicon nitride as a main component and JI
A silicon nitride based sintered member characterized in that at least the surface appearance lightness VS is 3.0 to 9.0 when the lightness in the color display method defined in S-Z8721 is VS. 2. The silicon nitride material according to claim 1, wherein, when the saturation in the color display method defined in JIS-Z8721 is CS, at least the surface appearance saturation CS is 3.0 or less. Sintered members. 3. The silicon nitride based sintered member according to claim 1, wherein the member surface is a mirror-polished surface. 4. The silicon nitride sintered member according to claim 3, wherein said mirror-polished surface has an arithmetic average roughness Ra of 0.10 μm or less. 5. The silicon nitride based sintered member according to claim 1, wherein at least a surface layer portion contains transition metal cations in a range of 0.1 to 3% by weight. 6. The transition metal cation is Ta, Co,
6. The silicon nitride based sintered member according to claim 5, wherein the silicon nitride based sintered member contains one or more ions selected from Ti and Fe. 7. One or more kinds selected from Ta, Co, Ti and Fe, and Ta is Co in terms of Ta ₂ O _5.
Is converted to CoO, Ti is converted to TiO ₂ , and Fe is F
At e ₂ O ₃ in terms of, silicon nitride sintered member according to claim 6 wherein the content in the range of 0.1 to 3 wt% in total. 8. The silicon nitride based sintered member according to claim 1, further comprising titanium nitride as a coloring component. 9. The silicon nitride-based sintered member according to claim 1, wherein a carbon-enriched layer having a higher carbon concentration than the inner layer is formed on the surface layer of the sintered body. 10. When Raman spectroscopic analysis of the member surface is performed, the intensity of a peak existing at 206 ± 10 cm ⁻¹ is defined as X1, and the intensity of a peak existing at 1584 ± 20 cm ⁻¹ is defined as X2, where X2 / X1. The peak ratio expressed is 0.0
The silicon nitride-based sintered member according to any one of claims 1 to 9, wherein the number is from 01 to 0.5. 11. A ceramic ball formed as the silicon nitride-based sintered member according to any one of claims 1 to 10. 12. A ball bearing wherein the ceramic ball according to claim 11 is incorporated between an inner ring and an outer ring made of metal or ceramic.