JP5624067B2 - Silicon nitride sintered body - Google Patents

Description

  The present invention relates to a silicon nitride sintered body.

  Conventionally, silicon nitride-based sintered bodies have excellent wear resistance, heat resistance, thermal shock resistance or oxidation resistance, so machine sliding parts such as bearing balls, tools, tappets, turbo rotors, piston pins and engine valves Application to automotive parts such as automobiles and heat-resistant structural members such as turbine blades is also being made.

JP 11-045771 A

  A silicon nitride sintered body is generally composed of silicon nitride main phase particles and a grain boundary phase mainly composed of a sintering aid component. For example, as a method for improving wear resistance and sliding characteristics. Attempts have been made to crystallize the grain boundary phase and to add different kinds of particles. However, crystallization is difficult to process, and depending on the composition, it may be impossible to form a crystal phase precipitate. In addition, the grain boundary phase is a phase that plays an important role in bonding and holding the silicon nitride main phase, but it is structurally a qualitative approach based on whether it is simply crystallized or not. Is just made. In particular, in the case of a grain boundary phase vitrified (hereinafter also referred to as a glass phase), since it has an amorphous structure in which atoms or ions are randomly arranged, a state inconvenient for bonding the silicon nitride main phase is local. However, it is virtually impossible to deduce what the inconvenience is caused based on crystallographic analysis information such as X-ray diffraction. For example, even if a situation occurs where the wear resistance and sliding properties of the sintered body vary or are insufficient due to amorphous structural non-uniformity, etc. In the first place, it was not possible to find the specific structural means for solving the problems.

  An object of the present invention is to provide a silicon nitride-based sintered body that can improve wear resistance and can effectively suppress variations thereof.

Means and actions / effects for solving the problems

In order to solve the above problems, the first of the silicon nitride sintered bodies of the present invention is:
A main body crystal particle mainly composed of silicon nitride is a sintered body bonded with a glassy binder phase, and contains Al as a sintering aid component constituting the binder phase, and a sintering aid. The component is 1 to 5% by weight in terms of oxide, and the rare earth component in the sintering aid component is 1 to 3% by weight in terms of oxide, and the carbon / oxygen wt% ratio is 0.1. in 5 below der Ru sintered body, beam intensity as the intensity Xk of the strongest scattering peaks appearing in 500～530Cm ^-1 is 2400 ± 200 counts when subjected to Raman spectroscopic analysis of the silicon single crystal sample Obtained by performing Raman spectroscopic analysis of the sintered body with the scattering intensity at 1200 cm ⁻¹ when the Raman spectroscopic analysis is performed on the silicon single crystal sample under the conditions as the reference scattering intensity level X0. Of the spectral profile The scattering intensity X1 at 200 cm ^-1, the incremental scattering intensity expressed in increments from a reference scattering intensity level X0 Y1 = X1-X0 is characterized in that has a 1500 count or more. In the present invention, the term “main component” (also synonymous with “main component” or “mainly”) means that the content of the material of interest is 50% by weight or more unless otherwise specified. To do.

  In the present invention, Raman spectroscopic analysis is used as a means for detecting material structure information that could not be traced by crystallographic analysis information, and in a silicon nitride sintered body, a Raman active substance other than β silicon nitride is used. The purpose is to improve wear resistance and suppress variation of the silicon nitride sintered body by defining the relative amount. Here, a Raman-active substance is a substance that causes a change in polarizability when the lattice vibration in the substance changes, and in particular, a substance in which optical phonons are induced by electromagnetic waves in the visible light region. You can also. The energy level of an optical phonon is specific to the material structure. Absorption of an electromagnetic wave with a specific wavelength induces an optical phonon with a frequency specific to the material, and the wavelength of the energy used for phonon induction. Electromagnetic waves are scattered in such a way that becomes longer (so-called Raman shift).

In the present invention, a Raman scattering spectrum profile of a silicon single crystal sample is used in order to estimate the relative amount of a Raman active substance. The silicon single crystal sample shows a very sharp Raman scattering peak (hereinafter referred to as a standard peak) in the vicinity of 500 to 530 cm ⁻¹ , specifically 520 cm ⁻¹ , while almost Raman scattering occurs in other wavelength bands. Not having a stable background level at a low level. Therefore, whether or not a Raman-active substance is present in the sample to be measured is determined based on the background level of the sample in the scattering spectrum profile (in the present invention, the scattering intensity at 1200 cm ⁻¹ is used as a reference). It can be determined whether or not a higher scattering intensity level is found, and the higher the scattering intensity, the greater the relative amount of Raman-active substance.

As a result of intensive studies by the present inventors, in a silicon nitride sintered body containing a sintering aid component, for example, as shown in FIG. 16, a sharp scattering peak derived from β silicon nitride at 206 ± 10 cm ^−1. (Hereinafter referred to as β silicon nitride peak), a very broad scattering peak (hereinafter referred to as glassy peak) appears at a position different from the β silicon nitride, and by changing the firing conditions, It was found that the scattering intensity level of the glassy peak changed. Since the glassy peak has a very wide half-value width, it looks like a background part when the peak apex position is not clear, but the scattering intensity level is clearly higher than the background part of the silicon single crystal sample, It clearly indicates the presence of Raman-active substances.

  The glassy peak is considered to be derived from a substance other than the silicon nitride main phase, in this case, a binder phase mainly composed of a sintering aid component. For example, when an X-ray diffractometer analysis is performed, a diffraction peak that reflects a specific crystal structure does not appear, and instead a halo pattern is observed (the grain boundary phase is a glass phase or disorder close to it). The glassy peak appears particularly clearly when the target phase is formed). And considering the experimental facts such that the height of the glassy peak changes depending on the firing conditions and the peak height and peak position change depending on the blending composition of the sintering aid component, the glassy peak The height and peak position can be considered as parameters reflecting the bonding state of the glassy grain boundary phase structure. The reason why broad glassy peaks are formed in the spectrum profile is that the binder phase is in a short-range ordered glassy state, and the glassy state is essentially metastable and local structural fluctuations, etc. It is thought that it is easy to produce. In addition to this, the binder phase is basically composed of ions derived from the sintering aid component, and the arrangement thereof is basically random except for the short-range ordered structure. As a result of complex superposition of long-distance Coulomb fields of ions, various factors can be assumed, such as local coexistence of various Raman active structures. In any case, since it is a metastable state, the local structure at the atomic level of the bonded phase changes variously depending on what thermodynamic history is received by firing or the like, and as a result, the phase itself The mechanical properties are also affected considerably, and it is presumed that the level and variation of wear resistance and the like will vary.

And according to the 1st of the silicon nitride sintered body of this invention, when the scattering intensity in 1200cm < ^-1 > of the spectrum profile obtained when performing Raman spectroscopic analysis of a sintered compact is set to X1, By adjusting the glassy peak level so that the incremental scattering intensity Y1 = X1-X0 from the reference scattering intensity level X0 is 1500 counts or more, the wear resistance of the silicon nitride sintered body can be improved. In addition, the variation can be suppressed. This is considered to suggest that the grain boundary phase becomes stronger and more homogeneous as the amount of the Raman-active substance contained in the grain boundary phase increases. When Y1 is less than 1500 counts, the effect is not significant. On the other hand, if Y1 exceeds 30000 counts, the amount of glassy grain boundary phase increases too much, and the wear resistance may decrease instead. Y1 is more preferably 2000 to 20000 counts.

In the spectrum profile, the integrated intensity of the scattered light varies depending on the wavelength, intensity, spot diameter, or integrated irradiation time of the laser incident light serving as the probe. Therefore, in the present invention, the laser light used is an argon laser having a wavelength of 514.5 nm. The spot diameter of the laser beam is about 10 μm, and the integrated irradiation time for the laser beam sample is about 5 seconds (the count number representing the scattering peak intensity is the integrated count number for 5 seconds). Furthermore, the silicon single crystal sample is stable for scattering peak intensity, the strongest scattering peaks appearing in 500~530cm ^-1 (approximately 520 cm ^-1 is a peak position: hereinafter also referred to as standard peak) height Xk As a reference, the beam intensity is determined so that this is approximately 2400 ± 200 counts (± 200 count is a range set in consideration of an error in beam intensity setting, but when performing Raman spectroscopic analysis of a plurality of samples. (It is desirable to make the conditions as close as possible to 2400 counts). Further, the reason why the scattering intensity at 1200 cm ⁻¹ in the spectrum profile is adopted is that it is difficult to strictly determine the point where the intensity of the broad peak is maximum, or the point where the intensity is maximum is the measurement of the scattering wavelength. This is because the scattering intensity level of the glassy peak can be uniquely determined even when it does not appear within the range.

  On the other hand, as the laser beam irradiation position on the sintered body, an area having a depth of 100 ± 10 μm from the surface of the sintered body is selected as the surface area of the sintered body contributing to wear resistance. In this case, the laser beam may be irradiated at a position of 100 ± 10 μm in the depth direction from the surface in the cross section of the sintered body. In addition, when distribution has arisen in the peak intensity in the direction along the sintered compact surface, the average value of the peak intensity in that direction shall be adopted.

In the first aspect of the present invention, when the laser beam condition is set such that the standard peak height Xk is a constant value, the glassy peak is determined by the number of scattered light counts at a specific wave number (1200 cm ⁻² ). Although the scattering intensity level has been quantified, it can be quantified by other methods, for example, it can be quantified not by the number of counts but also by an intensity ratio with respect to a specific scattering peak.

For example, in the second of the silicon nitride sintered body of the present invention, the main phase crystal particles mainly composed of silicon nitride are bonded with a glassy binder phase, and the binder phase is formed. 1-3 weight by containing Al as a sintering aid component, 1 to 5% by weight in terms of oxide of the sintering aid components, and in terms of oxide of the rare earth component of該焼Yuisuke component that % contained in the sintered body Ru der 0.5 or less wt% ratio of carbon content / oxygen content, when subjected to Raman spectroscopic analysis of the silicon single crystal sample, the strongest appearing in 500～530Cm ^-1 Similarly, the intensity of the scattering peak is Xk, and the intensity of the strongest scattering peak appearing at 780 to 790 cm ⁻¹ when Raman spectroscopic analysis of the SiC single crystal sample is performed is Wk, and Xk / Wk is 0.10 ± 0.00. Set the beam intensity so that it becomes 01. The scattering intensity at 1200 cm ^-1 when performing Raman spectroscopy as a reference scattering intensity level X0 for single crystal sample, expressed in increments scattering intensity from the reference scattering intensity X0, appearing 500～530Cm ^-1 Yk is the height of the strongest scattering peak, and the ratio of Y1 to Yk is the incremental scattering intensity Y1 from the reference scattering intensity X0 at 1200 cm ⁻¹ in the Raman profile of the sintered body. Y1 / Yk is 0.4 or more (see FIG. 16).

For example, the absolute value (count number) of the standard peak height Xk of a silicon single crystal sample may slightly vary due to disturbances, variations in the measurement system, particularly variations in specifications of the light receiving unit such as a photosensor. Further, in the above configuration, the strongest appearing at 500 to 530 cm ⁻¹ when two types of silicon single crystal and SiC single crystal are used as the standard sample and Raman spectroscopic analysis of the silicon single crystal sample is performed. The ratio Xk / Wk between the intensity Xk of the scattering peak and the intensity Wk of the strongest scattering peak appearing at 780 to 790 cm ⁻¹ when the Raman spectroscopic analysis of the SiC single crystal sample is performed is 0.10 ± 0.01. (± 0.01 is a range that is set in anticipation of an error in beam intensity setting. However, when performing Raman spectroscopic analysis of a plurality of samples as much as possible, Xk / Wk = 0.11 is desirable) As a result, there is an advantage that the scattering intensity level of the glassy peak can always be accurately evaluated without being affected by disturbances and variations in the measurement system.

Then, under the above measurement conditions, the incremental scattering intensity Y1 from the reference scattering intensity X0 at 1200 cm ⁻¹ of the spectral profile when the Raman spectroscopic analysis is performed in the region of depth of 100 ± 10 μm from the sintered body surface. In addition, by making the ratio Y1 / Yk to the reference peak height Yk to be 0.4 or more, the wear resistance of the silicon nitride sintered body can be improved, and variations thereof are also suppressed. be able to. Y1 / Yk is preferably 35 or less, more preferably 0.1 to 20 so that the grain boundary phase does not become excessive.

The third of the silicon nitride sintered bodies of the present invention employs the same measurement conditions as those of the second of the present invention, and is scattered at 1200 cm ⁻¹ when Raman spectroscopic analysis is performed on a silicon single crystal sample. Yk is the height of the strongest scattering peak appearing at 500 to 530 cm ⁻¹ , expressed as the incremental scattering intensity from the reference scattering intensity X0, with the intensity as the reference scattering intensity level X0, and the Raman of the sintered body Z2 is the strongest scattering peak height that appears at 206 ± 10 cm ⁻¹ expressed by the height of the spectral profile protruding from the base curve when the spectral analysis is performed, and the wave number of 750 to 750 of the spectral profile of the sintered body the half-value width 300 cm ^-1 or more broad peak appearing in the 2500 cm ^-1, a peak height Y3 expressed in increments scattering intensity from a reference scattering intensity X0, Y3 of Over click strength 1330 or more, and the ratio Y3 / Z2 and Y3 and Z2 is equal to or not less than 0.5.

The scattering peak Z2 corresponds to the β silicon nitride peak, but at the peak position, the skirt of a broad glassy peak (half-value width is usually much larger than 300 cm ⁻¹ ) is often superimposed. In order to extract the scattering component derived from the silicon main phase, the amount of protrusion from the base curve is displayed. The base curve can be determined by applying a low-pass filter process to the spectrum profile to cut components having a profile wavelength cm ⁻¹ or less.

  That is, when the peak position of the glassy peak can be specified, the peak height is Y3, and the ratio Y3 / Z2 to the β silicon nitride peak height Z2 is 0.5 or more, so that the silicon nitride quality The wear resistance of the sintered body can be improved, and variations thereof can also be suppressed. Y3 / Z2 should be 40 or less, and preferably 0.5 to 30 so that the grain boundary phase does not become excessive.

The position of the glassy peak varies depending on the composition of the sintering aid used. For example, when ZrO ₂ is added to the sintering aid, the peak position may shift to the high wavenumber side.

The fourth aspect of the silicon nitride sintered body of the present invention is a sintered body containing silicon nitride as a main component and containing a sintering aid component, and a laser is cut in the depth direction from the surface of the sintered body in the cross section of the sintered body. When the Raman spectroscopic analysis is performed while changing the irradiation position of the beam spot, the scattering intensity at 1200 cm ⁻¹ appearing in the Raman scattering spectrum is different between the surface layer portion and the inner layer portion of the sintered body.

As already explained, the scattering intensity at 1200 cm ⁻¹ appearing in the Raman scattering spectrum reflects the intensity of the glassy peak described above and reflects the amount of glassy grain boundary phase having Raman activity in the sintered body. It is what. The fact that the scattering intensity differs between the sintered body surface layer portion and the inner layer portion means that the amount of the glassy grain boundary phase having Raman activity differs between the sintered body surface layer portion and the inner layer portion. In other words, depending on the purpose of use of the sintered body, by varying the amount of the glassy grain boundary phase between the surface layer portion and the inner layer portion of the sintered body, the sintered body characteristics that meet various purposes can be freely adjusted. It becomes possible. In the case where the glass peak position can be specifically identified, i.e., as described above, appears in the Raman scattering spectrum, the half width 300 cm ^-1 or more broad intensity of scattering peak appearing in the wavenumber 750～2500Cm ^-1 certain If possible, the intensity of the broad scattering peak, that is, the intensity of the glassy peak, differs between the surface layer portion and the inner layer portion of the sintered body.

For example, the scattering intensity at 1200 cm ⁻¹ (or the intensity of the glassy peak) can be made higher in the surface layer portion of the sintered body than in the inner layer portion. As described above, the present inventors have intensively studied, and as described above, by keeping the glassy peak low in the sintered body and actively generating the glassy peak in the surface layer part, cutting tools and other It has been found that the wear resistance and fracture resistance required for sliding parts can be achieved at a higher level. In other words, by forming a lot of glassy grain boundary phases having Raman activity in the surface layer of the sintered body and reducing this inside, a sliding member excellent in both wear resistance and fracture resistance can be obtained. It is effective in obtaining. The mechanism is presumed as follows. That is, in the surface layer portion, the formation amount of the glassy grain boundary phase contributing to the wear resistance is increased, while in the inner layer portion having a small glassy grain boundary phase, a portion having a weak grain boundary phase is locally generated. As a result, cracks that propagate in a straight line are deflected in the part where the bonding force is weak, and as a result of the increase in crack extension until breakage, the toughness is improved and the fracture resistance is also improved. It is done.

  On the other hand, depending on the intended use of the sintered body, it may be more convenient for the inner layer portion to have a higher glassy peak strength than the sintered body surface layer portion. For example, in a member where the lubricity on the surface is more prioritized, it may be advantageous that the glassy grain boundary phase having Raman activity is reduced in the surface layer portion, and conversely the inside is a glassy grain boundary phase. It is effective to increase the strength and rigidity of the entire member by increasing the number.

Next, when the strength of the glassy peak is made higher than the inner layer portion in the sintered body surface layer portion, the following standard measurement conditions, that is,
When subjected to Raman spectroscopic analysis of the silicon single crystal sample, the intensity of the strongest scattering peaks appearing in 500~530cm-1 and Xk, of also when subjected to Raman spectroscopic analysis of the SiC single crystal sample 780～790Cm ^- Where the intensity of the strongest scattering peak appearing in ¹ is Wk, the beam intensity is set so that Xk / Wk is 0.10 ± 0.01,
The scattering intensity at 1200 cm ⁻¹ when the Raman spectroscopic analysis is performed on the silicon single crystal sample under the conditions is defined as the reference scattering intensity level X 0, and Raman spectroscopic analysis is performed at each position in the depth direction of the cross section of the sintered body. Xa is the scattering intensity level at each position, and Ya = Xa-X0,
Ymax / Ymin is 2 or more, where Ymax is the maximum value of Ya appearing on the surface layer side of the sintered body, and Ymin is the minimum value of Ya appearing on the inner layer side. This maintains good fracture resistance. However, it is desirable from the viewpoint of further improving the wear resistance. When Ymax / Ymin is 2 or less, the improvement in wear resistance is not so remarkable. The value of Ymax / Ymin is more desirably 10 or more, and when it is applied to a cutting tool or the like, its life is greatly improved. The maximum value of Ymax / Ymin confirmed by the present inventors is about 37.5.

  In the sintered inner layer portion, a region having a substantially constant glassy peak intensity (hereinafter referred to as a steady region) can be formed, and the surface layer portion of the sintered body has a glassy peak strength, A region that is higher than the average value of the steady region (hereinafter referred to as a Raman enhancement region) can be formed. With the value of Ya in the standard measurement conditions described above, the average glassy peak intensity in the Raman-enhanced region is at least twice, preferably at least 10 times the average glassy peak intensity in the steady region. It is desirable for achieving both higher wear resistance and fracture resistance at a higher level. Further, the thickness of the Raman strengthened region measured in the depth direction from the surface of the sintered body is 2 mm or less, preferably 1 mm or less. When the thickness of the Raman strengthened region exceeds 2 mm, the surface of the sintered body becomes brittle, and microcracks and breakage occur, which is not desirable.

  In addition, when the Raman strengthening region as described above is formed, a difference in thermal expansion coefficient is generated between the steady region and residual stress may be generated in the sintered body. Specifically, the coefficient of thermal expansion becomes small in the Raman strengthened region, and compressive residual stress may be generated on the surface of the sintered body. By generating such residual stress, the apparent strength and toughness of the sintered body are improved, and more excellent wear resistance can be obtained. Further, the presence of a unique bonding state of the grain boundary phase in the surface layer portion of the sintered body, such as the above-mentioned Raman active glass grain boundary phase, increases the hardness of the Raman strengthened region and improves the wear resistance. These effects become more prominent as the thickness of the Raman-enhanced region increases. However, an optimum thickness exists in view of the aforementioned fragility.

Next, a Raman inclined region in which the scattering intensity at 1200 cm ⁻¹ in the Raman scattering spectrum monotonously decreases in the depth direction from the surface of the sintered body can be formed on the surface layer portion of the sintered body. By forming such a Raman inclined region, the effect of improving wear resistance and chipping resistance becomes more remarkable. Also in this case, by viewing the Raman inclined region as the above-described Raman enhancement region, it is possible to form a steady region in which the scattering intensity at 1200 cm ⁻¹ is substantially constant in the sintered body layer portion. When the difference in thermal expansion coefficient between the Raman strengthened region and the steady region becomes a problem, the thermal strengthening resistance can be improved by forming the Raman strengthened region as a Raman inclined region so that local concentration of thermal stress can be avoided. In addition, it is possible to achieve a long life even in applications such as cutting tools in which a thermal cycle is frequently applied. In this case, assuming that the maximum value of Ya on the surface side of the sintered body in the Raman inclined region is Ymax and the value of Ya that is substantially constant in the sintered body layer portion is Ymin, Ymax / Ymin is preferably 2 or more, preferably 10 The above is desirable for enhancing the above effect.

  The silicon nitride sintered body of the present invention can be used, for example, in sliding parts (in addition to general mechanical sliding parts, a ceramic tool is also included in the concept by considering a contact surface with a workpiece as a sliding surface). Can be applied. In addition, the silicon nitride based sintered body of the present invention can be applied to other wear resistant members, corrosion resistant members, heat resistant members, and other structural members. Specific examples include bearing balls and ceramic hydrodynamic bearing parts (these are used as rotating sliding members for precision electronic devices such as hard disk drives and polygon mirror drive parts of polygon scanners, such as computers and laser printers. Cutting parts, drawing rolls, tappets, turbo rotors, automotive parts such as piston pins and engine valves, and heat-resistant structural materials such as turbine blades, but are not limited to these. Absent.

  The first to third silicon nitride sintered bodies of the present invention as described above can be manufactured by the first to third methods for manufacturing a silicon nitride sintered body described below, for example. The first method for producing the silicon nitride sintered body is to oxidize 1 to 5% by weight of a sintering aid powder in terms of oxides and oxidize a rare earth component in the sintering aid component. 1 to 3% by weight in terms of product, forming a green powder for molding, molding this into the desired shape, and then firing the molded body at normal pressure or under a pressurized nitrogen atmosphere, and molding And a heat treatment step of holding the body or sintered body in a vacuum atmosphere of 50 kPa or less at 1200 to 1500 ° C. for 10 minutes or more. Note that when the treatment is performed at a relatively low vacuum with an atmospheric pressure exceeding 10 kPa, the firing atmosphere is preferably a low-oxidizing atmosphere such as nitrogen or an inert gas.

  By performing the heat treatment step as described above, the scattering intensity level of the glassy peak can be effectively increased in the Raman spectrum profile of the obtained silicon nitride sintered body. As a result, the first to third silicon nitride sintered bodies of the present invention having excellent wear resistance can be easily produced. The increase in the scattering intensity level of the glassy peak by the vacuum heat treatment means that the Raman active substance (or structure) occupying in the grain boundary phase increases at least in the surface layer portion of the sintered body to be subjected to Raman spectroscopic analysis. I guess that. The reason is considered that a part of the grain boundary phase constituent components volatilizes from the surface of the sintered body (or the formed body during sintering) by vacuum decompression at a high temperature, and the ionic bond state is changed.

  In the heat treatment step, when the degree of vacuum of the atmosphere exceeds 50 kPa or the holding time is less than 10 minutes, the effect of increasing the scattering intensity level of the glassy peak becomes insufficient. Moreover, there is no restriction | limiting in particular in the lower limit of a vacuum degree, It is possible to employ | adopt as high a vacuum degree as possible, as long as it does not cause the unnecessary cost increase in terms of equipment or manufacturing efficiency. The holding time is preferably 30 minutes or longer. On the other hand, although there is no particular limitation on the upper limit value of the holding time, about 60 minutes is a good guideline from the viewpoint of avoiding unnecessary cost increase in terms of manufacturing efficiency.

  Moreover, if the temperature of heat processing is less than 1200 degreeC, the effect which raises the scattering intensity level of a glassy peak will become inadequate, and when it exceeds 1500 degreeC, component volatilization will advance too much and it will lead to fall of abrasion resistance etc. The temperature of the heat treatment is desirably 1400 to 1450 ° C.

On the other hand, when the temperature of the heat treatment is further increased, if the component volatilization is suppressed by slightly increasing the pressure of the atmosphere, it is possible to achieve the same object as the first of the above production method. That is, in the second method for producing a silicon nitride sintered body, 1 to 5% by weight of a sintering aid powder in terms of oxide is added to silicon nitride powder, and a rare earth component is included in the sintering aid component. After forming 1 to 3% by weight in terms of oxide and forming a green powder for molding, and molding this into the desired shape, the firing step of firing the molded body in a normal pressure or pressurized nitrogen atmosphere, And a heat treatment step of holding the compact or its sintered body at the following pressure P (unit: Pa).
If heat treatment step of 1 5 00 to 2,000 ° C., it expresses at ^{1 × 10 -68 × T 22.3 ≦} P ≦ 5 × 10 -20 × T 7.65.

In the formula that gives the processing pressure P, by setting the upper and lower limits of the pressure in a form that is proportional to the power of the temperature, the processing pressure is increased as the temperature becomes higher, so that excessive increase in component volatilization accompanying the temperature rise is suppressed. It is aimed at. Below the lower limit of the pressure, component volatilization proceeds too much, leading to a decrease in wear resistance and the like. When the upper limit is exceeded, the effect of increasing the scattering intensity level of the glassy peak becomes insufficient. On the other hand, when the temperature exceeds 2000 ° C., strength reduction due to abnormal grain growth of the ceramic or melting of the ceramic itself becomes a problem. Moreover, about holding time, it is good that it is 10 minutes or more, for example.
Note that the range of pressure P at typical temperatures is as follows:
1500 ° C .: 670 to 106620 Pa
1800 ° C .: 39130-430880 Pa
2000 ° C .: 410170 to 965740 Pa.

  Next, the firing temperature and pressure are appropriately set according to the use of the sintered body. For example, when performing the two-step firing of primary firing and secondary firing, the primary firing is 1 to 10 atm or less including nitrogen. It is desirable to carry out at 1900 ° C. or less under the atmosphere of the above, so that the sintered body relative density after the primary firing is 78% or more, preferably 90% or more. The secondary firing can be performed at 1600 to 1950 ° C. in an atmosphere of 10 to 1000 atmospheres containing nitrogen. However, one-step firing may be used as long as sufficient performance such as strength, toughness, wear resistance, heat resistance, or sliding characteristics is guaranteed. And it is efficient to perform the above-mentioned vacuum heat treatment process in the middle of the above-mentioned baking process or after the end of the baking process.

  Moreover, when it is desired to obtain a sintered body structure in which the strength of the glassy peak is higher in the surface layer portion of the sintered body than in the inner layer portion, the primary firing is performed in a non-oxidizing atmosphere (for example, nitrogen atmosphere) of 1 to 3 atmospheres. It is desirable to do so. This is because if the pressure exceeds 3 atm, the intensity of the glassy peak may be as high as that of the surface layer portion in the inner layer portion. Further, when it is desired to form the above-described inclined Raman region, it is desirable that the molded body before firing is not coated with a release agent or the like as much as possible in the primary firing. However, in order to prevent adhesion between the sintered body and the sintering container composed of graphite or the like, it is possible to apply a release agent such as a small amount of BN. On the other hand, in the secondary firing, since firing is performed at a high temperature and high pressure, it is desirable not to apply a release agent or the like as much as possible in order to secure an inclined structure.

  In the present invention, the raw material powder for the sintered body is preferably prepared as follows. That is, a predetermined amount of raw material powder and an organic binder (binder) are blended and mixed with a ball mill or the like using water as a dispersion medium. At this time, it is desirable to grind in as short a time as possible so that the powder does not react with water and increase the amount of oxygen. In order to perform pulverization in a short time, it is effective to employ a planetary ball mill that combines mill pot rotation and revolution. In this case, it is desirable to maintain the pulverization acceleration of the planetary ball mill at 5 to 10 G (G is gravitational acceleration), and the pulverization time is preferably within 5 hours.

Next, the structure of the silicon nitride-based sintered member is in a form in which main phase crystal particles mainly composed of silicon nitride are bonded by vitreous and / or crystalline binder phases. The main phase is preferably composed mainly of a Si ₃ N ₄ phase having a β conversion rate of 70% by volume or more (preferably 90% by volume or more). In this case, the Si ₃ N ₄ phase is one in which a part of Si or N is replaced with Al or oxygen, and further, a metal atom such as Li, Ca, Mg, or Y is dissolved in the phase. There may be. For example, sialon represented by the following general formula can be exemplified;
β-sialon: Si _6-z Al _z O _z N _8-z (z = 0 to 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).

  As the sintering aid component, at least one selected from the group of elements of each group of 3A, 4A, 5A, 3B (for example, Al) and 4B (for example, Si) of the periodic table and Mg can be used. Can be added in the form.

  The sintering aid component can be contained, for example, in the range of 2 to 30% by weight in terms of oxide. Correspondingly, silicon nitride can be contained in the range of 70 to 98% by weight. If the sintering aid component is less than 2% by weight, it becomes difficult to obtain a dense sintered body. However, in order to effectively bring out the effects of the present invention, the upper limit value is desirably about 5% by weight lower than the addition level of a general silicon nitride sintered body. When there are too many sintering aid components, the precipitation of Si particles is hindered, making it difficult to obtain a silicon nitride sintered body having the structure of the present invention, and consequently the strength, toughness and wear resistance at the level intended by the present invention. This is because of insufficiency or heat resistance, or in the case of sliding parts, it leads to a decrease in wear resistance. The content of the sintering aid component is more preferably 1 to 5% by weight in terms of oxide (95 to 99% by weight for the content of silicon nitride).

In addition, as a sintering aid component of group 3A (rare earth), Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu are common. Used for. The content of these element R, Ce only RO _2, others are translated by _R 2 _{O 3} type oxide. Among these, oxides of heavy rare earth elements of Y, Tb, Dy, Ho, Er, Tm, and Yb are preferable because they have the effect of improving the strength, toughness, and wear resistance of the silicon nitride sintered body. used. In particular, the use of Yb and Al in combination is effective in promoting the formation of the aforementioned Raman active glass-like peak layer and improving the wear resistance.

  When the sintering aid component contains a rare earth component, the content of the rare earth component in the sintered body is 1 to 4% by weight, preferably 1 to 3% by weight in terms of oxide. . If the content of the rare earth component is excessive, the wear resistance of the resulting silicon nitride sintered body may be impaired. If it is less than 1% by weight, the effect of improving the strength, toughness and wear resistance of the silicon nitride sintered body due to the use of rare earth element oxide cannot be sufficiently expected.

The sintering aid component mainly constitutes the binder phase, but a part thereof may be incorporated into the main phase. In addition to the components intentionally added as a sintering aid, the binder phase contains inevitable impurities such as silicon oxide (eg, SiO ₂ ) contained in the silicon nitride raw material powder. There is.

  The silicon nitride sintered body of the present invention can be suitably used for various silicon nitride parts that require a high level of wear resistance, in particular, machine sliding parts such as bearing balls. In addition, high-speed bearings used as bearings for precision electronic equipment, such as computer hard disk drives, require a particularly high precision finish so that no abnormal noise or the like is generated. The finished bearing ball can be easily obtained, and the problem of abnormal noise and vibration is less likely to occur.

  Next, a reference technique that is more advantageous in the case of manufacturing a small-sized bearing ball of 5 mm or less will be described. However, it goes without saying that the technology does not constitute an essential requirement of the present invention, and may be implemented in combination with the present invention or may be implemented independently of the present invention. Therefore, the present invention is naturally not limited. However, in combination with the present invention, it is possible to realize a small-diameter bearing ball that is further excellent in sliding characteristics or wear resistance.

In the case of bearing balls of small diameter and high grade that are premised on application to bearings for electronic precision equipment, etc., the HIP method (for example, firing pressure of 200 atm or more, usually 1000 to 2000 atm) is effective in increasing the density of the sintered body. However, since the surface of the sintered body is easily hardened, polishing becomes somewhat difficult, which may affect the securing of high precision sphericity or non-uniform diameter. Therefore, when considering the production of silicon nitride ceramic balls by firing at normal pressure or gas pressure, where the surface is difficult to harden, the density of the bearing balls is reduced due to the inhibition of sinterability, and the performance degradation such as wear resistance is significantly reduced. It was found that the dimension range was a dimension range in which the ratio A / W of the surface area A (unit: mm ² ) to the weight W (unit: g) was 300 or more. Specifically, a molding base powder mainly composed of silicon nitride powder and sintering aid powder is obtained by using a ratio A ′ of a surface area A ′ (unit: mm ² ) and a weight W ′ (unit: g). / W ′ is 350 or more, and is molded into a spherical shape so that the density is 2.0 to 2.5 g / cm ^3, and the spherical molded body (hereinafter also simply referred to as a molded body) is obtained by firing at normal pressure or gas pressure. It is effective to sinter. In consideration of molding the green powder for molding so that the density becomes 2.0 to 2.5 g / cm ³ at the stage of the molded body before firing, the surface area A ′ (unit: mm ² ) and the weight W The ratio A ′ / W ′ to “(unit: g)” corresponds to 350 or more.

Further, by molding the green powder for molding so that the density (density) of the green body before firing is in the range of 2.0 to 2.5 g / cm ³ , the small diameter is such that A / W becomes 300 or more. Even the above bearing balls can be sintered at a sufficiently high density by firing at normal pressure or gas pressure. Further, the hardened bearing balls obtained by firing are hard to be hardened, and precise polishing can be performed very easily and efficiently. As a result, the A / W is 300 or more, the density is increased to 3.2 g / cm ³ or more, and the sphericity and the difference in diameter are both 0.10 μm or less. High performance and high precision small diameter silicon nitride ceramic bearing balls can be realized. For example, in a precision electronic device such as a computer hard disk drive, even if it is used at a high speed (for example, 5400 to 12000 rpm), its life can be ensured over a long period of time without generating sound or vibration.

  In the present specification, the sphericity means the maximum value of the distance in the radial direction between the minimum spherical surface circumscribing the surface of the bearing ball and each point on the surface of the bearing ball. Also, the diameter unequal means the difference between the maximum value and the minimum value of the diameter of one bearing ball.

  Further, in the present specification, gas pressure firing means firing in an atmosphere containing at least nitrogen of more than 1 atm and not more than 200 atm, and normal pressure firing means firing in an atmosphere containing at least nitrogen of not more than 1 atm. To do. By setting the upper limit of the atmospheric pressure of the gas pressure firing to 200 atm, it is possible to effectively prevent the surface of the sintered body from being excessively hardened. It becomes easy to secure.

  The above effects are more effectively exhibited when A / W exceeds 500. On the other hand, when the A / W exceeds 5000, it becomes difficult to produce a high-density spherical molded body. Therefore, it is possible to target a bearing ball having an A / W of less than that, more preferably an A / W of 2000 or less. desirable. The above A / W range corresponds to a ball diameter of 0.5 to 6 mm (preferably 1 to 6 mm) in consideration of the density of the silicon nitride ceramic.

Also, if the density of the bearing ball is less than 3.2 g / cm ^{3, the} wear resistance and strength are insufficient, and it is sufficient when applied to bearings for precision electronic devices such as computer hard disks that require high-speed rotation. High performance and longevity cannot be secured. On the other hand, the upper limit of the density of silicon nitride ceramic is the theoretical density value determined for each ceramic composition. The closer to the theoretical density value as much as possible by selection of firing conditions, etc., is advantageous in improving wear resistance or strength. It is.

  When the theoretical density value can be actually measured or estimated, the density of the bearing ball can be expressed by the ratio of the apparent density to the theoretical density, that is, the relative density. In this case, the relative density is preferably 99.0% or more, more preferably 99.5% or more. Moreover, the relative density being less than 100% means that fine voids remain in the sintered body structure and the density of the sintered body is reduced. Therefore, the abundance ratio of the voids in the sintered body can be a parameter reflecting the relative density of the sintered body.

  When the sphericity and diameter difference of the bearing balls are set to 0.10 μm or less, they are incorporated into bearings for precision electronic devices such as computer hard disks and used at high speed rotation (for example, 5400 to 10,000 rpm). And the occurrence of abnormal vibration can be remarkably suppressed. The sphericity of the bearing ball is more preferably 0.03 μm or less, and the non-uniform diameter is more preferably 0.07 μm or less.

When the ratio A ′ / W ′ between the surface area A ′ (unit: mm ² ) and the weight W ′ (unit: g) of the spherical molded body in producing the bearing ball is less than 350, the bearing finally obtained It becomes impossible to make the A / W value of the ball 300 or more (strictly speaking, there is a difference in size between the bearing ball and the bearing ball by the grinding allowance, but the grinding allowance depends on the diameter of the ball. The A / W value is not so much affected). The upper limit value of A ′ / W ′ is about 2560 (preferably 1650) correspondingly when the upper limit value of the A / W value of the obtained ceramic ball is 5000 (preferably 2000).

On the other hand, when the density of the spherical molded body is less than 2.0 g / cm ³ , densification does not proceed at the time of sintering by gas pressure sintering or atmospheric pressure sintering, resulting in performance deterioration such as wear resistance or pores. It is impossible to achieve a sphericity of 0.10 μm or less or a diameter difference due to the remaining of slag. On the other hand, if the density of the molded body exceeds 2.5 g / cm ³ , the stress remaining in the molded body after molding becomes too high, leading to the collapse of the molded body, or promoting cracking and cracking during firing. This causes problems that lead to a decrease in yield. The density of the spherical molded body is more preferably 2.15 to 2.38 g / cm ³ .

The schematic diagram which shows an example of the ball bearing which comprised the bearing ball as the silicon nitride sintered body of this invention. The figure explaining the concept of a primary particle diameter and a secondary particle diameter. Explanatory drawing which shows the concept of a relative cumulative frequency. The longitudinal cross-sectional view which shows notionally an example of the manufacturing apparatus of the base powder for shaping | molding. FIG. 5 is an operation explanatory diagram of the apparatus of FIG. 4. Action explanatory drawing following FIG. Process explanatory drawing of rolling granulation. Process explanatory drawing following FIG. The figure explaining the progress process of a rolling granulation shaping | molding process. The schematic diagram which shows an example of the cross-sectional structure of the bearing element ball manufactured by the rolling granulation method. The front view which shows an example of the ceramic tappet using the silicon nitride-type sintered compact of this invention. Sectional drawing explaining and illustrating some powder molding methods by die press. The top view of the tool comprised as a silicon nitride-type sintered compact of this invention, a side view, and the side surface enlarged view of the edge part. Explanatory drawing which shows the outline | summary of a cutting test. Explanatory drawing which shows the positional relationship of the test piece and workpiece in a cutting test. The figure which shows an example of the spectrum profile of a Raman spectroscopic analysis. The schematic diagram which shows the various embodiment of a vacuum heat processing. The figure which shows an example of the Raman scattering spectrum profile of a SiC single crystal sample. The value of Ya of each test product of Nos. 5, 6, and 11 in Table 3 (however, it is expressed as a ratio to the scattering intensity (reference scattering intensity level) X0 at 1200 cm ⁻¹ of the silicon single crystal sample). The graph which showed the measurement result in relation to the depth direction distance from the sintered compact surface.

  Hereinafter, embodiments of the silicon nitride sintered member of the present invention will be described.

  FIG. 1 shows a ball bearing 40 in which a bearing ball 43 which is an embodiment of the silicon nitride sintered body of the present invention is incorporated between an inner ring 42 and an outer ring 41 made of metal or ceramic. If the shaft SH is fixed to the inner surface of the inner ring 42 of the ball bearing 40, the bearing ball 43 is held so as to be rotatable or slidable with respect to the outer ring 41 or the inner ring 42. As already described in detail, the ceramic constituting the bearing ball 43 contains silicon nitride as a main component, contains a sintering aid component, and an average observed in the cross-sectional structure in the whole or part of the sintered body. It is a silicon nitride ceramic in which single crystal Si particles having a size of 0.1 to 10 μm are dispersed.

  Hereinafter, although an example of the manufacturing method of the ceramic ball | bowl 43 is demonstrated, it is not limited to this manufacturing method. First, it is desirable to use a silicon nitride powder as a raw material having an α ratio of 70% or more, and the sintering aid is selected from a group of rare earth elements, 3A, 4A, 5A, 3B and 4B elements. At least one of these is mixed in an amount of 2 to 8% by weight, preferably 2 to 4% by weight in terms of oxide. In addition to the oxides of these elements, the raw materials may be compounded in the form of a compound that can be converted into an oxide by sintering, for example, carbonate or hydroxide.

The green powder for molding is suitable for, for example, the rolling granulation method described later, and the average particle size measured by a laser diffraction particle size meter is 0.3-2 μm, and the 90% particle size is 0.4- It is preferable to employ one having a thickness of 3.5 μm (preferably 0.7 to 2.0 μm) and a BET specific surface area value of 5 to 13 m ² / g. However, this is not the case when a molding method other than the rolling granulation method is adopted.

  The powder particle diameter measured by the laser diffraction particle size reflects the secondary particle diameter D shown in FIG. In addition, as shown in FIG. 3, the relative cumulative frequency from the small particle size side of the particles is arranged in the order of the particle size, and the frequency of the particles from the small particle size side is arranged on the array. When counting, the relative frequency nrc represented by nrc = (Nc / N0) × 100 (%), where Nc is the cumulative frequency up to the particle size of interest and N0 is the total frequency of the particles to be evaluated. Say. The X% particle diameter means a particle diameter corresponding to nrc = X (%) in the above-described arrangement. That is, the 90% particle diameter means a particle diameter corresponding to nrc = 90 (%).

On the other hand, the specific surface area value of the green powder for molding is measured by an adsorption method. Specifically, the specific surface area value can be obtained from the amount of gas adsorbed on the powder surface. In general, an adsorption curve showing the relationship between the pressure of the measurement gas and the amount of adsorption is measured, and the known BET formula for polymolecular adsorption (collecting the initials of the inventors Brunauer, Emett, Teller) By applying, the adsorption amount vm when the monomolecular layer is completed is obtained, and the BET specific surface area value calculated from the adsorption amount vm is used. However, if approximately the same result can be obtained, a simple method that does not use the BET equation, for example, a method of directly reading the monomolecular layer adsorption amount vm from the adsorption curve may be employed. For example, when a section where the amount of adsorption is approximately proportional to the gas pressure appears in the adsorption curve, there is a method of reading the amount of adsorption corresponding to the end point on the low pressure side of that section as vm (The
(See the article by Brunauer and Emett, Journal of American Chemical Society, 57 (1935), 1754). In any case, in the measurement of the specific surface area value by the adsorption method, the adsorbed gas molecules penetrate into the secondary particles and cover the surface of the individual primary particles constituting this, so that the specific surface area value is It reflects the specific surface area of the primary particles, and thus the average value of the primary particle diameter d in FIG.

  Hereinafter, an example of a method convenient for the preparation of the green powder for molding as described above will be described. FIG. 4 shows an embodiment of an apparatus used in the forming base powder preparation process. In the apparatus, the hot air flow passage 1 is formed to include a hot air duct 4 arranged vertically, and in the middle of the hot air duct 4, a gas flow body that allows passage of hot air and does not allow passage of the drying medium 2, For example, a media holding unit 5 made of a net, a perforated plate, or the like is formed. On the media holding unit 5, the dry media 2 made of ceramic spheres mainly composed of alumina, zirconia, or a mixed ceramic thereof is accumulated to form a layered dry media aggregate 3. .

On the other hand, the raw material is prepared in the form of a slurry obtained by adding an aqueous solvent to a blend of silicon nitride powder and sintering aid powder and wet mixing (or wet mixing / pulverizing) with a ball mill or attritor. . 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. 5, hot air is circulated through the dry media aggregate 3 so as to escape upward from the lower side of the media holding unit 5 while moving the dry media 2 in the hot air duct 4. On the other hand, as shown in FIG. 4, the slurry 6 is pumped up from the slurry tank 20 by the pump P, and is dropped and supplied to the dry media stack 3 from above. As a result, as shown in FIG. 6, the slurry is dried by hot air and adheres to the surface of the drying medium 2 in the form of a powder aggregate layer PL.

  The dry media 2 repeatedly vibrates and falls due to the circulation of hot air, and hits each other. Further, the powder agglomerated layer PL is pulverized into the green powder particles 9 for molding by rubbing due to the hits. The pulverized molding base powder particles 9 include those in the form of isolated primary particles, but most are secondary particles in which primary particles are aggregated. The molding base powder particles 9 having a particle size of a certain size or less flow downstream along with hot air (FIG. 4). On the other hand, the pulverized particles larger than a certain level are not blown away by hot air but fall again to the dry media aggregate 3 and further crushed between the media. In this way, the molding base powder particles 9 that have flowed downstream along with the hot air are recovered as the molding base powder 10 in the recovery unit 21 via the cyclone S.

  In FIG. 6, the diameter of the drying medium 2 is appropriately set according to the flow cross-sectional area of the hot air duct 4. If the diameter is insufficient, the striking force on the powder agglomerated layer formed on the medium is insufficient, and a green powder for molding having a particle diameter in a desired range may not be obtained. On the other hand, if the diameter becomes too large, even if hot air is circulated, it is difficult for the dry media 2 to vibrate, so that the striking force is similarly insufficient, and a green powder with a particle diameter in the expected range cannot be obtained. There is. In addition, it is desirable to use the dry media 2 having a uniform size as much as possible in order to form an appropriate gap between the media and to promote the movement of the media during hot air circulation.

  Moreover, the filling depth t1 of the dry media 2 in the dry media aggregate 3 is appropriately set in a range where the flow of the media 2 occurs without excess or deficiency according to the flow velocity of the hot air. If the filling depth t1 becomes too large, the flow of the dry medium 2 becomes difficult, and the striking force may be insufficient, so that a forming powder with a particle diameter in a desired range may not be obtained. On the other hand, if the filling depth t1 becomes too small, the dry media 2 is too small and the striking frequency decreases, leading to a reduction in processing efficiency.

  Next, the temperature of the hot air is appropriately set within a range where the drying of the slurry progresses sufficiently and the powder does not suffer from problems such as thermal alteration. For example, when the slurry solvent is mainly water, when the hot air temperature is less than 100 ° C., drying of the supplied slurry does not proceed sufficiently, and the moisture content of the resulting green powder for molding becomes too high. Aggregation is likely to occur, and a powder having a desired particle size may not be obtained. Furthermore, the flow rate of the hot air is appropriately set within a range where the dry media 3 is not blown to the collection unit 21. If the flow rate becomes too small, the flow of the dry media 2 becomes difficult, and the striking force may be insufficient to obtain a green powder for molding having a particle diameter in a desired range. On the other hand, if the flow velocity becomes too high, the dry media 2 will rise so much that the collision frequency decreases, leading to a reduction in processing efficiency.

  The green base powder 10 thus obtained can be formed into a spherical shape by a rolling granulation molding method. That is, as shown in FIG. 7, the green powder 10 for molding is put into the granulation container 132, and as shown in FIG. 8, the granulation container 132 is rotationally driven at a constant peripheral speed. In addition, moisture W is supplied to the green base powder 10 in the granulation container 132 by, for example, spraying. As shown in FIG. 9, the charged green powder for forming is aggregated into a spherical shape while rolling on the inclined powder layer 10k formed in the rotating granulation container to form a compact. The operating conditions of the rolling granulator are adjusted so that the relative density of the obtained molded body is 61% or more. Specifically, the rotation speed of the granulation container is adjusted at 10 to 200 rpm, and the moisture supply amount is adjusted so that the moisture content in the finally obtained molded body is, for example, 10 to 20% by weight. The As shown in FIG. 9 (e), by supplying moisture, the moisture penetrates between the powder particles, and the densification of the molded body is further promoted.

By adopting the rolling granulation method as described above, for example, a high-density spherical molded body having a diameter of up to about 10 mm can be produced with extremely high efficiency. In addition, for a small diameter having a ratio A ′ / W ′ of the surface area A ′ and the weight W ′ of the obtained molded body G of 350 or more (for example, the diameter is 6.73 mm or less), the density of the molded body is A level of about 2.0 to 2.5 g / cm ^3, which is impossible with a normal pressing method, can be sufficiently secured.

  When performing rolling granulation, it is desirable to put the forming core 50 into the granulating container 132 as shown in FIG. In this way, as shown in FIG. 9 (a), the forming core 50 rolls on the forming base powder layer 10k, and as shown in FIG. 9 (b), the forming core 50 is formed around the forming core 50. The base powder 10 adheres and aggregates in a spherical shape to form a spherical molded body 80 (rolling granulation step). By sintering the molded body 80, a spherical silicon nitride sintered body 90 is obtained as shown in FIG.

  The forming core 50 is mainly composed of ceramic powder, for example, composed of a material having a composition similar to that of the forming base powder 10 (however, the ceramic powder (inorganic material powder) forming the main body of the forming base powder). However, it is desirable that the core does not act as an impurity source for the spherical silicon nitride sintered body 90 finally obtained. However, if there is no concern of reaching the surface layer portion of the spherical silicon nitride sintered body 90 where the diffusion of the nucleus component can be obtained, the nucleus can be a metal nucleus or a glass nucleus. It is also possible to form the core with a material that disappears by pyrolysis or evaporation during firing, for example, a polymer material such as wax or resin. The shaped core may have a shape other than a spherical shape, but it goes without saying that the use of a spherical shape is desirable in order to increase the sphericity of the obtained shaped body.

  The method for producing the molded core is not particularly limited, but when the ceramic powder is mainly used, there is a method of obtaining the core by compression molding with a ceramic powder die press or the like. In addition, the powder is dispersed in a molten thermoplastic binder to obtain a molten compound, and this is spray solidified to obtain a spherical core, or the molten compound is injected into a spherical cavity of an injection mold to form a spherical core. There is also a method of shaping the body. On the other hand, in FIG. 7, only the molding base powder 10 is put into the granulation vessel 132, and the agglomerates of the powder are generated by rotating the vessel at a lower speed than when the molded body is grown. If the aggregate is formed, the rotational speed of the container 132 is then increased, and the molded body 80 may be grown in such a manner that the aggregate is used as the core 50. In this case, it is not necessary to dare to put the core manufactured in the separate process as described above into the container 132 together with the green powder 10 for molding.

  The molding core 50 obtained as described above can be stably maintained in shape without collapsing even when some external force is applied. As a result, as shown in FIG. 9A, the reaction due to its own weight can be reliably received even when it rolls on the green powder layer 10k for molding. Further, as shown in FIG. 9 (c), the powder particles entrained when rolled can be firmly pressed against the surface, so that it is considered that the powder is moderately compressed to grow a dense aggregate layer 10a. . On the other hand, as shown in FIG. 9 (d), when the nucleus is not used, the aggregate 100 corresponding to the nucleus is generated only by an accidental factor, and therefore it takes a long time to grow the compact. There is.

  It should be noted that the minimum size of the core 50 is preferably about 40 μm (preferably about 80 μm). If the nucleus 50 is too small, the growth of the aggregate layer 10a may be incomplete. Further, if the core is too large, the thickness of the aggregated layer to be formed is insufficient, and defects or the like are likely to occur in the sintered body. Therefore, the dimension is preferably set to 1 mm or less, for example.

  As the forming core, it is possible to use an agglomerate obtained by agglomerating ceramic powder at a density higher than the bulk density of the forming base powder (for example, the apparent density defined in JIS-Z2504 (1979)). It is desirable to receive the pressing force with certainty and promote the growth of the aggregated layer 10a. Specifically, it is preferable to use a powder aggregated to 1.5 times the bulk density of the green powder for molding. In this case, it is sufficient that the agglomerates are aggregated to such an extent that they do not collapse due to the rolling impact on the forming base powder layer 10k.

  In order to perform more stable growth of the molded body, it is desirable to set the dimensions of the core 50 as follows according to the dimensions of the molded body to be obtained. That is, as shown in FIG. 9 (b), the dimension of the forming core 50 is represented by the diameter dc of a sphere having the same volume as this, but (of course, if the core 50 is spherical, the diameter thereof is Is equivalent to the dimension itself), and dc is set so that dc / dg satisfies 1/100 to 1/2, where dg is the diameter of the finally obtained spherical molded body. If dc / dg is less than 1/100, there is a concern that the nucleus is too small and the growth of the agglomerated layer 10a may be incomplete, or only those having many defects may be obtained. On the other hand, when it exceeds 1/2, for example, when the density of the core 50 is not so high, the strength of the obtained sintered body may be insufficient. It should be noted that dc / dg is preferably adjusted within a range of 1/50 to 1/5, more preferably 1/20 to 1/10. Further, the dimension dc of the forming core is preferably set to 20 to 200 times the average particle diameter when the average particle diameter of the forming base powder is taken as a scale. On the other hand, the absolute value of the dimension dc is preferably adjusted to, for example, 50 to 500 μm.

  Incidentally, as a molding method other than the rolling granulation method, as shown in FIG. 12B, a hemispherical shape is formed on each tip surface of the upper and lower press punches 103, 103 inserted into the die hole 102 of the molding die 101. A spherical ceramic molded body 104 can be obtained by forming the recesses 103a and 103a and compressing the powder between the punches 103 and 103, respectively. In the die press method as described above, it is desirable to adopt 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 region, but in this method, the press punches 103, 103 are adopted. Corresponding to the flattened portions 103b and 103b, the molded body 104 inevitably has a bowl-shaped unnecessary portion 104a. This unnecessary portion 104a needs to be removed by polishing or the like before or after firing.

  In addition to a die press, a cold isostatic press (CIP) method can be employed. Specifically, it is temporarily formed into a spherical shape by the die press method as described above, and the temporary formed body is sealed in a rubber tube, and hydrostatic pressure is applied to the tube by a liquid forming medium such as oil or water. Apply approximately pressure. In addition, when the density of a molded object is not sufficiently improved by one cold isostatic pressing, a cycle CIP method in which the cold isostatic pressing is repeated may be employed.

  In addition to the mold forming method, a molding base powder is dispersed in a thermoplastic binder to form a slurry, and the slurry is freely dropped from a nozzle and made spherical by surface tension, and then cooled and solidified in air (for example, (Disclosed in JP-A-63-229137), or a slurry comprising a green powder for molding, a monomer (or prepolymer), and a dispersion solvent, is dispersed as droplets in a liquid immiscible with the slurry, Examples thereof include a method for obtaining a spherical molded body by polymerizing a monomer or a prepolymer in that state (for example, disclosed in JP-A-8-52712).

  Firing of the molded body obtained as described above can be performed, for example, 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 sintered body density after the primary firing is 78% or more, preferably 90% or more. Is desirable. If the primary firing density is less than 78%, many defects such as pores are likely to remain after the secondary firing. Moreover, secondary baking can be performed at 1600-1950 degreeC in the non-oxidizing atmosphere of 10-1000 atmospheres containing nitrogen (a concept of a hot isostatic pressing method is also included). When the firing pressure is less than 10 atm, the decomposition of silicon nitride cannot be suppressed, and even if this pressure exceeds 1000 atm, the effect is not changed, and the cost is disadvantageous. On the other hand, if the firing temperature is less than 1600 ° C., defects such as pores cannot be eliminated, and the strength tends to decrease. However, when the density can be sufficiently increased by the firing conditions corresponding to the above-described secondary firing and defects and the like can be reduced, the primary firing can be omitted and the one-step firing can be performed. Moreover, when performing secondary baking, the excessive increase in the surface hardness of the obtained sintered compact (bearing element ball) is suppressed by performing this by the atmospheric pressure or gas pressure below 200 atmospheres containing nitrogen. be able to. Thereby, processing such as polishing can be performed more smoothly, and as a result, it becomes easy to ensure the dimensional accuracy of the bearing ball after polishing, such as sphericity and non-uniform diameter.

  And the heat processing hold | maintained for 10 minutes or more at 1200-1500 degreeC in the vacuum atmosphere of 50 kPa or less in the middle of the said baking process or after completion | finish of a baking process is performed. This treatment is performed in order to increase the scattering intensity level of the glassy peak appearing in the spectrum profile and to improve the wear resistance of the sintered body when the Raman spectrum analysis of the sintered body obtained as described above is performed. It is what is said. And as long as the effect is not impaired, the heat treatment temperature can be set regardless of the firing temperature, but it changes the quasi-stable bonding state of the constituent ions and atoms of the bonded phase of the finally obtained sintered body. From the viewpoint, it is preferable to set the temperature lower than the firing temperature. It should be noted that firing of the molded body may proceed simultaneously during the heat treatment, and in this case, it can be considered that the heat treatment process is also used as part of the firing process.

  The heat treatment can be performed at various timings. FIG. 17 shows some examples. In (a), the temperature period of heat treatment is set in the temperature raising process before firing, and then the temperature is raised to a firing temperature set higher than the heat treatment temperature. This is an example of heating and introducing a gas having a predetermined pressure to perform firing. Further, (b) is an example in which a vacuum heat treatment is performed by setting a vacuum decompression period at the initial stage of the firing step, and the firing temperature and the heat treatment temperature are set almost the same. (C) and (d) are examples in which heat treatment is performed by setting a vacuum decompression period during or at the end of the firing step. Further, (e) shows an example in which after the firing is once finished, the temperature is raised again to perform the heat treatment. In the case of performing the two-stage firing, the above heat treatment can be performed corresponding to one or both of the primary firing and the secondary firing, but the more effective is corresponding to the secondary firing (that is, It is desirable to carry out during or after the secondary firing.

The heat treatment is performed at a temperature T of 1500 to 2000 ° C. and a pressure P (unit: Pa) represented by 1 × 10 ⁻⁶⁸ × T ^22.3 ≦ P ≦ 5 × 10 ⁻²⁰ × T ^7.65. For example, you may perform as a process hold | maintained for 10 minutes or more.

  The surface of the sintered body (bearing element ball) thus obtained is precisely polished to form the bearing ball 43 of FIG. 1 as the silicon nitride sintered body of the present invention. For example, a glassy peak as shown in FIG. 16 appears in the spectrum profile obtained when the Raman spectroscopic analysis is performed at a position of 100 ± 10 μm from the surface of the bearing ball 43. The scattering intensity level of the glassy peak satisfies the relationships shown in the first to third aspects of the present invention. Thereby, the wear resistance of the bearing ball 43 is improved.

  In addition, if the spherical molded body 80 (FIG. 9) obtained by the rolling granulation method is fired, the obtained sintered body 90 is obtained by polishing a cross section passing through a substantially center as shown in FIG. When magnified, the core 91 derived from the forming core may be formed at the center of the core 91 so as to be distinguishable from the outer layer 92 having a high density and few defects. In the polished cross section, the core portion 91 often exhibits a visually distinguishable contrast in at least one of brightness and color tone with the outer layer portion 92. This is presumed to be because the density ρe of the ceramic constituting the outer layer portion 92 is different from the density ρc of the ceramic constituting the core portion 91. For example, when the forming core 50 (FIG. 9) has a lower density than the agglomerated layer 10a, the density ρe of the ceramic composing the outer layer portion 92 is higher than the density ρc of the ceramic composing the core portion 91. In many cases, the outer layer portion 92 appears in a lighter tone than the core portion 91. Note that the relative density of the outer layer portion 92 is 95% or more, preferably 99% or more, from the viewpoint of ensuring the strength and durability of the ceramic. In any case, by using a sintered body structure in which the above structure appears in the polished cross section, the defect formation rate of the outer layer portion 92, which is the key to improving the performance of bearings and the like, is small (for example, no pore is confirmed). High-density and high-strength bearing balls are realized. However, the sintered body may exhibit a substantially uniform density in the radial direction from the surface layer portion to the center portion when firing proceeds uniformly. Further, even if there is a difference in color tone or brightness between the core portion and the outer layer portion, there may be little difference in density. Furthermore, when the sintering proceeds more uniformly, it may be difficult to visually confirm the concentric contrast (described later) in the core portion 91 or the outer layer portion 92.

  Here, as shown in FIG. 9B, the diameter dc of the molding core 50 is 1/100 to 1/2 (desirably 1/50 to 1 / 5, more preferably 1/20 to 1/5), the cross section of the sintered body 90 in FIG. 10 is the same as the diameter Dc of the circle having the same area as that of the core 91. On the other hand, when the diameter of the ceramic sintered body is Dg, Dc / Dg is 1/100 to 1/2 (preferably 1/50 to 1/5, more preferably 1/20 to 1/10). Presents a satisfactory organization. If Dc / Dg is less than 1/50, defects tend to occur in the aggregated layer 10a (FIG. 9) that is the basis of the outer layer portion 92, which may lead to insufficient strength. On the other hand, when it exceeds 1/5, for example, when the density of the core 50 is not so high, the strength of the sintered body may be insufficient. Dc / Dg is more preferably adjusted within a range of 1/20 to 1/10.

  As a state in which a visually distinguishable contrast occurs between the core portion 91 and the outer layer portion 92 in the sintered body 90, for example, a difference in brightness or color tone is formed in the radial direction of the sphere and formed in the circumferential direction. It can be illustrated as a state without. As a specific aspect, a layered pattern 93 surrounding the core 91 may be formed concentrically on the outer layer 92 in the polished cross section. This is a characteristic structure observed when the rolling granulation method is employed, and the cause of formation can be estimated as follows. That is, as shown in FIG. 9 (a), the molded body 80 grows the agglomerated layer 10a while rolling on the molding base powder layer 10k. It does not exist on the green powder layer 10k for molding. In other words, due to the avalanche flow of the powder accompanying the rotation of the granulation container, when it reaches the lower side of the molding base powder layer 10k, it sinks into the molding base powder layer 10k and is lifted to the wall surface of the granulation container. It is carried to the upper side of the green powder layer 10k and rolls down again on the green powder layer 10k. When submerged into the molding base powder layer 10k, the periphery is pressed down with powder, and the impact due to rolling and falling is relatively difficult to apply, and the powder particles adhere relatively loosely. On the other hand, when rolling on the forming base powder layer 10k, an impact due to rolling and dropping is applied, and the liquid spray medium W such as moisture is easily sprayed, so that the powder is firmly and easily tightened. Then, the rolling form on the molding base powder layer 10k and the submergence into the molding base powder layer 10k are periodically repeated, so that the powder adhesion form also changes periodically. It is considered that a layered pattern 93 is formed as a result of the occurrence of radial densification in the layer 10a, which appears as a subtle difference in density after firing (when the difference in densification is very small). In fact, it is possible that the actual density is not confirmed by the normal density measurement accuracy level). For example, the layered pattern 93 is considered to be formed by alternately stacking concentric arc-shaped portions and higher-density remaining portions in the radial direction.

  Next, the silicon nitride based sintered body of the present invention is not limited to the ball bearing, but can be applied to other sliding parts such as a ceramic tappet 150 as shown in FIG. Here, it has a structure in which a ceramic plate 53 configured as a silicon nitride sintered body of the present invention is joined to an end face of a metal main body 51 via a brazing filler metal layer 52. A sliding surface 53 a is formed on the side opposite to the bonding surface of the ceramic plate 53. As shown in FIG. 12 (a), the ceramic plate 53 can be manufactured by making a plate-like molded body 104 by press-molding a green powder for molding and firing it. In this case, since the particle size distribution or the BET specific surface area of the molding base powder does not necessarily satisfy the above-mentioned conditions suitable for the rolling granulation method, the preparation method is also shown in FIG. Not only the thing using this but a well-known thing, such as a spray dry method, is employable.

  Further, the silicon nitride sintered body of the present invention can be applied to a tool. FIG. 13 shows an example of a throw-away tip for cutting which is configured entirely as a silicon nitride sintered body of the present invention. The throwaway tip 301 has a flat prismatic shape with a substantially square cross section, and as shown in FIG. 14 (a), the workpiece W is rotated around the axis, and the throwaway tip 301 is rotated with respect to the outer peripheral surface. As shown in FIG. 14 (b), the outer peripheral cutting of the work material W is performed by using one of the main surfaces 301c as a rake face (hereinafter, the rake face is indicated as 301c ') and the side face 301e as a flank face. It can be performed. As shown in FIG. 13, the corner portion 301a of the throw-away tip 301 is rounded, and the edge portion 301b is formed with a chamfered portion (chamfer) having a predetermined width t and a predetermined angle θ.

  The throw-away tip 301 as described above can also be manufactured by forming a molded body 104 by press-molding a green powder for molding as in FIG.

Experimental example

In order to confirm the effect of the present invention, the following experiment was conducted.
(Experimental example 1)
First, as a raw material powder, silicon nitride powder (α conversion rate of 97% or more, O ₂ content level: 1.2% by weight in terms of SiO ₂ , average particle size 0.7 μm), Y ₂ O ₃ powder (average particle size) 1.3 μm), Al ₂ O ₃ powder (average particle size 1.2 μm), basic magnesium carbonate powder (average particle size 0.5 μm), ZrO ₂ powder (average particle size 1.1 μm), Si powder (average particle) (Diameter 3 μm) was prepared. These powders were blended in various compositions shown in Table 2, and after adding an appropriate amount of a solvent and an organic binder and mixing using a ball mill, the powder was granulated by drying by a spray drying method. A green powder for molding was obtained. The reason why ZrO ₂ powder is added in this example is to improve the sinterability and toughness of the obtained sintered body.

And after carrying out temporary shaping | molding of said base powder for shaping | molding by the die-press method, CIP was performed with the pressure of 2 ton / cm < ² >, and the powder compact was obtained. In addition, the shape of the powder compact prepared two types, one for cutting tool test pieces (throw away tip shape) and one for fatigue life test pieces. The obtained molded body was subjected to binder removal treatment at a predetermined temperature not higher than the firing temperature, and then fired. Firing is performed by the following two-stage process. First, a calcined body having a relative density of 90 to 94% was obtained by performing primary pressure primary firing in a nitrogen atmosphere of 1 atm at 1700 ° C. for 2 hours. Subsequently, this calcined body was subjected to gas pressure secondary firing under various conditions to obtain a spherical sintered body. The condition settings are as shown in Table 2. Then, after the firing, heat treatment was performed under various conditions shown in Table 2 (the atmosphere used nitrogen).

  The density of the obtained sintered body was measured by the Archimedes method. Moreover, the cutting test was done on the following conditions using the cutting tool test piece. First, the shape of the test piece is as shown in FIG. 13 (specified as SNGN120408 in the lSO standard). That is, the test piece 301 has a flat rectangular column shape with a substantially square cross section with a thickness of about 4.76 mm and a side of about 12.7 mm, and the radius R of the corner portion 301a is about 0.8 mm. It was. Further, as shown in FIG. 13B, the chamfered portion (chamfer) applied to the edge portion 301b has a width t on the main surface 301c side of about 0.15 mm and an inclination angle θ with respect to the main surface 301c of about 25 °. It formed so that it might become.

The evaluation conditions for the cutting performance of each tool are as follows. That is, the bar-shaped work material W having the shape shown in FIG. 14A is rotated around the axis, and the test piece 301 shown in FIG. 20 is brought into contact with the outer peripheral surface thereof as shown in FIG. 14B. By using one of the main surfaces 301c as a rake face (hereinafter, the rake face is denoted as 301c ') and the side face 301e as a flank, the outer peripheral surface of the work material was continuously cut dry by the following conditions.
Work material: Cast iron (FC230), round bar form (outer diameter φ240mm, length 100mm)
Cutting speed V: 500 m / min Feed amount f: 0.34 mm / 1 rotation Cutting d: 1.5 mm
Cutting oil: None Cutting length: 500 mm
A more detailed positional relationship between the test piece 1 and the work material is as shown in FIG. In the figure, 1g indicates a side clearance surface, and 1f indicates a front clearance surface. The meanings of the other symbols are shown in the drawing. After cutting, the average value of the flank wear amount Vn (the wear height in the turning direction on the side flank 1g side: see FIG. 14C) and the variation (the number of test pieces 5) were measured. The results are shown in Table 1.

  Further, the fatigue life test was performed by a rolling fatigue life test described below by using a fatigue life test piece. The test piece is a square with a main surface of 50 mm in length and width and a square plate shape with a thickness of 10 mm, and the main surface is mirror-finished so that the arithmetic average roughness Ra (according to JIS-B0601; the same shall apply hereinafter) is 0.01 μm. Polished. The fatigue life was detected by vibration using a 6-ball thrust bearing tester. The test was performed up to 2000 hours while supplying a lubricating oil at 60 ° C. with a bearing load of 180 kgf and a rotation speed of 3000 rpm. The results are shown in Table 1.

  And after said various measurement was complete | finished, the Raman spectroscopic analysis was performed as follows. First, a mirror-polished silicon single crystal wafer not doped with impurities was prepared as a silicon single crystal sample. In addition, the sample was subjected to mirror polishing so that a cross-section orthogonal to the region that was not used for cutting the main surface of the cutting test piece appeared, and a sintered body measurement sample was obtained.

Moreover, as a Raman spectroscopic analyzer, a French ISA company make, Labram, Ar laser (wave number: 514.5 nm) was used, and the measurement conditions were defined as follows. First, the spot diameter of the laser beam was about 10 μm, and the integrated irradiation time for the laser beam sample was about 5 seconds. And the laser beam intensity | strength was defined as follows with respect to each sample. That is, measurement is performed on a silicon single crystal sample, and the scattering intensity at 1200 cm ⁻¹ in the spectrum profile is set as a reference scattering intensity level X 0, and is expressed by an incremental scattering intensity from the reference scattering intensity X 0, 500 to 530 cm ^−1. Let Yk be the height of the strongest scattering peak (standard peak) appearing at. Further, the same measurement is performed on the SiC single crystal sample, and the intensity of the strongest scattering peak appearing at 780 to 790 cm ⁻¹ is defined as Wk. The laser beam intensity was set to be Yk / Wk = 0.10. Scattered light was detected by a CCD sensor. The scattering peak intensities Yk and Wk were Yk = 2400 counts (FIG. 16) and Wk = 24000 counts in terms of photoelectron conversion counts (FIG. 18 shows the Raman scattering spectrum profile of the SiC single crystal sample).

Then, measurement is performed in a region of a depth of 100 ± 10 μm from the surface of the sintered body sample, and a base curve is generated by performing low-pass filter processing on the spectrum profile to cut components having a profile wavelength of 300 cm ⁻¹ or less. Then, the height of the strongest scattering peak appearing at 206 ± 10 cm ⁻¹ of the spectrum profile, expressed by the protruding height from the base curve, was determined as the β silicon nitride peak height Z2. Moreover, the incremental scattering intensity Y1 = X1−X0 expressed in increments from the reference scattering intensity level X0 of the scattering intensity X1 at 1200 cm ⁻¹ , the ratio Y1 / Yk of the incremental scattering intensity Y1 and the standard peak height Yk, and wavenumber 750~2500cm FWHM 300 cm ^-1 or more broad peak appearing ^-1 (glass peak), reference scattering intensity peaks expressed in increments scattering intensity from X0 height Y3 and β silicon nitride peak Z2 The ratio Y3 / Z2 was also determined. Moreover, the peak position of the glassy peak was read from the spectrum profile. The results are shown in Table 1. FIG. 16 shows the spectrum profile of Sample No. 5.

  From the results shown in Table 1, when Y1, Y1 / Yk or Y3 / Z2 satisfies the numerical values described in the claims, good results are obtained in both the cutting wear test and the fatigue test, It can be seen that the variation is small.

(Experimental example 2)
First, as a raw material powder, silicon nitride powder (α conversion rate of 97% or more, O ₂ content level: 1.2% by weight in terms of SiO ₂ , average particle size 0.5 μm), Y ₂ O ₃ powder (average particle size) 1.5 μm), Yb ₂ O ₃ powder (average particle size 1.5 μm), Al ₂ O ₃ powder (average particle size 1.0 μm), and basic magnesium carbonate powder (average particle size 0.5 μm) were prepared. These powders are blended in various compositions shown in Table 3, added with an appropriate amount of solvent and organic binder, mixed using a planetary ball mill, and then granulated by drying by spray drying. A green powder for molding was obtained.

Then, after the above molding powder was temporarily formed into a test piece shape by a die press method, CIP was performed at a pressure of 2 ton / cm ² to obtain a powder compact. The obtained molded body was coated with a release agent in which 30% by mass of BN powder was dispersed in ethanol. This is subjected to a binder removal treatment at a predetermined temperature equal to or lower than the firing temperature, and then subjected to a primary pressure firing at 1700 ° C. for 2 hours in a nitrogen atmosphere at 1 atm to obtain a calcined body having a relative density of 90 to 94%. It was. Next, the calcined body was subjected to secondary firing at various temperatures in a nitrogen atmosphere of 100 atm without a release agent coating or the like to obtain a sintered body. For comparison, a test product that was subjected to secondary firing by applying the same release agent as in the primary firing was also prepared (Table 3: No. 11). In addition, as a test piece, as a test piece for Raman spectroscopic analysis, a plate shape having a width of 10 mm, a length of 30 mm, and a thickness of 3 mm, and as a test piece for cutting test, a tool shape defined by ISO as SNGN120408 Two types of were produced.

  The density of the obtained sintered body was measured by the Archimedes method. Moreover, the Raman spectroscopic analysis of the sintered compact was performed as follows. First, a mirror-polished silicon single crystal wafer not doped with impurities was prepared as a silicon single crystal sample. Further, the sintered body was cut so that a cross section perpendicular to the main surface appeared and mirror-polished to obtain a sintered body measuring sample. As a Raman spectroscopic analysis apparatus, a Labram, Ar laser (wave number: 514.5 nm) manufactured by France ISA was used, and measurement conditions were determined in the same manner as in Experimental Example 1.

On the polished surface, the Raman scattering spectrum is measured while changing the laser beam irradiation position (measurement position) at 10 μm intervals in the depth direction from the surface of the sintered body sample, and 1200 cm ^{− in} the spectrum profile at each position. ^1. Incremental scattering intensity Ya = X1-X0 expressed in increments from the reference scattering intensity level X0 of the scattering intensity X1 at ¹ , and further, the maximum value Ymax of Ya appearing on the sintered body surface layer side, and the inner layer side The minimum value Ymin of Ya appearing in Fig. 5 and the ratio Ymax / Ymin of both were determined.

  The raw material powder of each sintered body is heated to 600 ° C. and treated to remove the binder, and then the amount of oxygen is measured by non-dispersive infrared spectroscopy, and further contained in the blended sintering aid. The amount of excess oxygen was calculated by subtracting the estimated amount of oxygen. On the other hand, carbon content was also analyzed by the same non-dispersive infrared spectroscopy.

  Further, a cutting test was performed under exactly the same conditions as in Experimental Example 1 using a tool test piece. The above results are shown in Table 3.

As is clear from this result, by adjusting the firing conditions, a glassy peak (1200 cm ⁻¹ peak) observed in the Raman spectrum profile is observed at the sintered body surface layer (Ymax). It can be seen that it can be higher than (Ymin), and by setting Ymax / Ymin to 2 or more, particularly good wear resistance is realized. FIG. 19 shows the ratio of Ya to each of the test products of Nos. 5, 6, and 11 in Table 3 (where the silicon single crystal sample has a scattering intensity (reference scattering intensity level) X0 at 1200 cm ⁻¹ ). The measurement results are shown in relation to the depth direction distance from the sintered body surface.

40 Ball bearing (ceramic sliding member)
43 Bearing ball (Silicon nitride sintered body)
150 Tappet (Ceramic sliding member)
301 Ceramic tool (silicon nitride sintered body)

Claims (13)

A main body crystal particle mainly composed of silicon nitride is a sintered body bonded with a glassy binder phase, and contains Al as a sintering aid component constituting the binder phase, and a sintering aid. The component is 1 to 5% by weight in terms of oxide, and the rare earth component in the sintering aid component is 1 to 3% by weight in terms of oxide, and the carbon / oxygen wt% ratio is 0.1. in 5 below der Ru sintered body, beam intensity as the intensity Xk of the strongest scattering peaks appearing in 500～530Cm ^-1 is 2400 ± 200 counts when subjected to Raman spectroscopic analysis of the silicon single crystal sample Set
The spectral profile obtained when the Raman spectral analysis of the sintered body was performed with the scattering intensity at 1200 cm ⁻¹ when the Raman spectral analysis was performed on the silicon single crystal sample under the conditions as the reference scattering intensity level X0. Silicon nitride based sintering characterized in that an incremental scattering intensity Y1 = X1−X0 expressed by an increment from the reference scattering intensity level X0 of the scattering intensity X1 at 1200 cm ⁻¹ is 1500 counts or more. body. A main body crystal particle mainly composed of silicon nitride is a sintered body bonded with a glassy binder phase, and contains Al as a sintering aid component constituting the binder phase, and a sintering aid. The component is 1 to 5% by weight in terms of oxide, and the rare earth component in the sintering aid component is 1 to 3% by weight in terms of oxide, and the carbon / oxygen wt% ratio is 0.1. in 5 below der Ru sintered body, when subjected to Raman spectroscopic analysis of the silicon single crystal sample, the intensity of the strongest scattering peak and Xk appearing in 500～530Cm ^-1, likewise Raman spectroscopy of SiC single crystal sample The intensity of the strongest scattering peak appearing at 780 to 790 cm ⁻¹ at the time of analysis is set as Wk, and the beam intensity is set so that Xk / Wk is 0.10 ± 0.01,
The scattering intensity at 1200 cm ⁻¹ when Raman spectroscopic analysis was performed on the silicon single crystal sample under the conditions was set as a reference scattering intensity level X 0, which was expressed as an incremental scattering intensity from the reference scattering intensity X 0, 500 to the intensity of the strongest scattering peaks appearing in 530 cm ^-1 and Yk, also, the spectral profile when subjected to Raman spectroscopic analysis of the sintered body, as an incremental scattering intensity Y1 from the reference scattering intensity X0 at 1200 cm ^-1 A silicon nitride sintered body, wherein the ratio Y1 / Yk of Y1 to Yk is 0.4 or more. A main body crystal particle mainly composed of silicon nitride is a sintered body bonded with a glassy binder phase, and contains Al as a sintering aid component constituting the binder phase, and a sintering aid. The component is 1 to 5% by weight in terms of oxide, and the rare earth component in the sintering aid component is 1 to 3% by weight in terms of oxide, and the carbon / oxygen wt% ratio is 0.1. in 5 below der Ru sintered body, when subjected to Raman spectroscopic analysis of the silicon single crystal sample, the intensity of the strongest scattering peak and Xk appearing in 500～530Cm ^-1, likewise Raman spectroscopy of SiC single crystal sample The intensity of the strongest scattering peak appearing at 780 to 790 cm ⁻¹ at the time of analysis is set as Wk, and the beam intensity is set so that Xk / Wk is 0.10 ± 0.01,
The scattering intensity at 1200 cm ⁻¹ when Raman spectroscopic analysis was performed on the silicon single crystal sample under the conditions was set as a reference scattering intensity level X 0, which was expressed as an incremental scattering intensity from the reference scattering intensity X 0, 500 to Yk is the intensity of the strongest scattering peak appearing at 530 cm ⁻¹ ,
Further, the strongest scattering peak intensity appearing at 206 ± 10 cm ⁻¹ of the spectral profile obtained by performing Raman spectroscopic analysis of the sintered body, expressed by the height of protrusion from the base curve, is Z2,
The spectral profile obtained when subjected to Raman spectroscopic analysis of the sintered body, the half width 300 cm ^-1 or more broad peak appearing in the wavenumber 750～2500Cm ^-1, incremental scattering intensity from the reference scattering intensity X0 The peak intensity expressed as
A silicon nitride-based sintered body having a peak intensity of Y3 of 1330 or more and a ratio Y3 / Z2 of Y3 and Z2 of 0.5 or more. When a Raman spectroscopic analysis is performed while changing the irradiation position of the laser beam spot in the depth direction from the surface of the sintered body in the cross section of the sintered body in a sintered body containing silicon nitride as a main component and a sintering aid component The silicon nitride based sintered body according to any one of claims 1 to 3, wherein the scattering intensity at 1200 cm ^-1 appearing in the Raman scattering spectrum is different between the surface layer portion and the inner layer portion of the sintered body. The appearing in the Raman scattering spectrum, the half width 300 cm ^-1 or more broad intensity of scattering peak appearing in the wavenumber 750～2500Cm ^-1 is silicon nitride according to different claims 4 and sintered surface layer portion and inner layer portion Sintered material. The silicon nitride based sintered body according to claim 4 or 5, wherein the scattering intensity at 1200 cm ^-1 is higher in the surface layer portion of the sintered body than in the inner layer portion. Xk is the intensity of the strongest scattering peak appearing at 500 to 530 cm ⁻¹ when performing Raman spectroscopic analysis of a silicon single crystal sample, and 780 to 790 cm ⁻ when performing Raman spectroscopic analysis of a SiC single crystal sample. The intensity of the strongest scattering peak appearing in ¹ is Wk, and the beam intensity is set so that Xk / Wk is 0.10 ± 0.01,
Under the conditions, the scattering intensity at 1200 cm ⁻¹ when Raman spectroscopy analysis is performed on the silicon single crystal sample is defined as a reference scattering intensity level X 0, and at each position in the depth direction of the cross section of the sintered body. When the Raman spectroscopic analysis is performed, the scattering intensity level at each position is set to Xa, and further, Ya = Xa-X0, and the maximum value of Ya appearing on the surface layer side of the sintered body is Ymax, and Ya appearsing on the inner layer side as well. The silicon nitride based sintered body according to any one of claims 4 to 6, wherein Ymin / Ymin is 2 or more, where Ymin is the minimum value. 8. The Raman slope region in which the scattering intensity at the 1200 cm ⁻¹ in the Raman scattering spectrum monotonously decreases in the depth direction from the sintered body surface is formed in the sintered body surface layer portion. The silicon nitride based sintered body according to any one of the above. The silicon nitride based sintered body according to claim 8, wherein the scattering intensity at 1200 cm ⁻¹ is substantially constant in the sintered body layer portion.   The maximum value of Ya on the surface side of the sintered body in the Raman inclined region is Ymax, and the value of Ya that is substantially constant in the sintered body layer portion is Ymin, and Ymax / Ymin is 2 or more. 9. The silicon nitride sintered body according to 9. The sintered body of silicon nitride sintered body according to any one of claims 1 to 10 containing Yb Ingredient.   A silicon nitride-based sliding component comprising the silicon nitride-based sintered body according to any one of claims 1 to 11, wherein at least a part of the surface of the sintered body is used as a sliding surface.   The silicon nitride-based sliding component according to claim 12, wherein a surface corresponding to a surface layer portion forming the Raman inclined region is used as the sliding surface.

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