KR970005888B1 - Process for the preparation of sintered body of silicon nitride - Google Patents

Abstract

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Description

Sintered Body Based on Silicon Nitride

1 is a graph showing the relationship between the reduction rate of Si3N4 and Si-A1-O-N particles and the wear resistance of the surface portion.

2 is an explanatory cross-sectional view showing the shape of the workpiece to be used in Test 1. FIG.

3 is an explanatory cross-sectional view showing the shape of the fracture cutting material used in the test 2. FIG.

4 is a partial cross-sectional view showing the shape of the fracture cutting material used in the test 3.

FIG. 5 is a graph of a confusion showing the relationship between the Si 3 N 4 phase and the partial pressure of the sintering atmosphere.

6 is a graph showing the relationship between the [surface portion / internal] ratio R2 of the content of merrillite and the wear resistance.

7 is a graph showing the relationship between the [meryllite / silicon nitride] content ratio (R1) of the surface portion and wear resistance.

8 is a graph showing the results of X-ray diffraction at the surface portion of the sintered body of Sample No. 28.

9 is a graph showing the results of X-ray diffraction inside the sintered body of Sample No. 28.

10 is a schematic view of the tissues of the surface portions (a) and (b).

11 is a known SiO 2 -Si 3 N 4 -Y 2 O 3 ternary diagram obtained by a hot press sample at 1600-1750 ° C.

* Explanation of symbols for main parts of the drawings

1: Cutting material 2: Sintered body team based on silicon nitride

3: holder

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sintered compact based on silicon nitride, and more particularly to a sintered compact based on silicon nitride having improved wear resistance without deteriorating essential properties such as toughness.

The present invention can be used for cutting tools, wear-resistant parts, perturbation parts, and the like.

As a conventional silicon nitride sintered body, in order to improve abrasion resistance, a coating of a ceramic material having high hardness or excellent abrasion resistance is known (see Japanese Patent Application Laid-Open No. 63-1278).

In another silicon nitride sintered body, it is also known to disperse high hardness α-silicon nitride particles in tough β-silicon nitride particles as an improvement of the base material.

However, in the former sintered body, due to the problem that the thermal expansion or chemical affinity between the coated ceramic material and the silicon nitride base material is different, sufficient adhesive strength is difficult to be obtained, and furthermore, the cost is considerably high and economical problems are caused. There is almost no practical use.

In addition, since the latter sintered compact contains the phase uniformly as a whole, the performance changes depending on the ratio, and the respective performances thereof cannot be sufficiently exhibited.

In other words, if one of the performances is sufficiently high, the performance of the other must be sacrificed. Therefore, the medium performance is generally only shown.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described aspects, and provides an excellent silicon nitride-based sintered compact, which is different from the conventional one, in which the surface is modified to form a surface having excellent abrasion resistance and exhibits sufficient surface properties and material properties therein. For the purpose of

MEANS TO SOLVE THE PROBLEM As a means of improving the wear resistance of a sintered compact, this inventor discovered the following fact and completed this invention, as a result of various examination of surface modification.

According to a first aspect of the present invention, a silicon nitride and Si-A1-ON (sialon) crystal grains are formed in an integrally formed surface portion and the inside, and the surface portion is less than 30% by volume. The problem of the above prior art is solved by the sintered compact based on this.

According to the second aspect of the present invention, the content of the internal to the surface portion of the crystalline compound which forms part or all of the grain boundary phase in the sintered body based on silicon nitride composed of the surface portion formed integrally with the interior The above-mentioned problem of the prior art is solved by the ratio being less than 0.5 by the X-ray peak intensity contrast method.

According to the third aspect of the present invention, the crystalline compound which forms part or all of the grain boundary phase is contained 0.3 or more by the maximum X-ray strength comparison method with respect to the content of silicon nitride and Si-A1-ON particles in the surface portion. As a result, the above-described first and second aspects are further improved.

According to the fourth aspect of the present invention, in the second aspect of the present invention, the crystalline compound that forms the grain boundary phase of the surface portion is Mellilite.

According to the fifth aspect of the present invention, in the third aspect of the present invention, the crystalline compound that forms the grain boundary phase of the surface portion is meryllite.

In the following preferable embodiment, the effect of this invention is exhibited well.

In a 1st viewpoint, when a grain boundary phase is a glass phase or one part or all part of a grain boundary phase may crystallize.

In the case of not containing (or slightly) Y2O3, the grain boundary phase of the surface portion is mainly a glass phase except the third phase.

Even when the crystallization treatment is not performed, the glass phase remains in the grain boundary phase of the surface portion.

The compound (Si3N4-nY203-mX) of the crystalline Si3N4-Y2O3 group included in this grain boundary phase is a merillite phase (abbreviated as Mellilite phase or M phase) J phase, K phase, H phase, A phase or these It is a mixed phase.

These phases mean the following compounds.

M phase (mellite): Si3Y203N4 (Si3N4-Y203)

J phase (wohlerite): Si2Y407N2 (Si2N20-2Y203)

K phase (wollastonite): SiY02N (Si3N4-2Y203-Si02)

H phase (apatite): S17Y10023N4 (Si3N4-5Y203-4Si02)

A phase (-): Si3Y10A12010N4 (Si3N4-5Y203-A1203)

These are summarized as a general formula as follows.

Si3N4-nY203-mX (where n = 1-5, X = Si02, A1203, m = 0-4)

That is, it has been found that almost all of the material to be cut or the counterpart material is an alloy of an iron system. On the other hand, Si, which is a major component of silicon nitride, has a high chemical affinity, and thus has a poor wear resistance.

On the other hand, in sintering of silicon nitride, efforts have been made to prevent decomposition volatilization of silicon nitride.

The present invention conversely utilizes such decomposition volatilization so that a silicon nitride-based sintered body having a reduction ratio of 20% by weight or more of the Si content of the silicon nitride component in the surface portion can improve wear resistance without lowering toughness or the like. Find out the facts and start from there.

According to the present invention, the sintered compact based on silicon nitride of the first viewpoint is characterized in that, in the surface portion and the inside, the Si content constituting this is different, and the proportion of grain boundaries in the surface portion is increased. It is done.

Here, this Si reduction rate of a surface part is computed by the following formula.

The sintered compact based on the silicon nitride of the first oligopolitan has a reduction ratio of Si 3 N 4 and Si-A 1 -ON particles at the surface portion thereof of 30 vol% or more compared to the inside, and the inside thereof is excellent in wear resistance because it is in a state without evaporation of Si 3 N 4. Essential properties such as high properties and toughness inside are sufficiently exhibited.

That is, this sintered compact does not show intermediate characteristics of both properties as in the prior art.

In other words, the present sintered body can improve wear resistance without deteriorating the internal essential characteristics by the surface modification thereof.

Moreover, since the surface part and the inside are integrated, the bonding strength between them is high and there is no peeling.

The Si3N4 and Si-A1-ON particle reduction rate of 30% by volume or more is less than 30% by volume, and the effect is not sufficient, and when it is higher than that, the wear resistance is improved without degrading the internal properties of excellent toughness. Because you can.

Moreover, this reduction rate is preferably 50 vol% or more.

This is because wear resistance is further improved in this case.

In addition, although the surface area of Si3N4 and Si-A1-ON particle | grains may disappear substantially, in this case, even if abrasion resistance further improves, surface roughness may fall, and a range where a weak compound is not produced | generated It is preferable to set it as.

The sintered compact based on the silicon nitride of the present invention is mainly composed of silicon nitride, but is not limited thereto, and may be Si-A1-O-N.

Such silicon nitride or Si-A1-ON may be selected depending on the purpose and use regardless of the α- or β type, and may be a mixture of such silicon nitride and Si-A1-ON, or an α- or β type mixture. .

As components other than silicon nitride etc., it can also be set as boundary phase forming components or a third component other than a grain boundary phase.

The grain boundary phase component may be only a glass phase or may include various crystal phases in addition to the glass phase.

As a 3rd component, it can be made a component which is effective in abrasion resistance and toughness improvement, for example.

As such, for example, carbides, nitrides and oxides of the periodic table IVa, Va, and VIa transition metals, and one or two or more of two or more solid solutions thereof can be used.

These third components may be in the form of particles, or may be in the form of needles (eg whiskey) or fibers. Generally, the particulate dispersed particles are effective in improving the hardness or improving the toughness resulting from the particle growth suppression effect.

In addition, the needle-like or fibrous dispersion component is remarkably effective in improving toughness.

Moreover, since this third component compound does not lower the toughness of the sintered compact, 30% by weight or less is preferable.

Inside is a part except the surface part, and becomes a main part of the sintered compact based on the silicon nitride of this invention, and is a part which shows the essential characteristic of this sintered compact.

Since Si 3 N 4 is not decomposed and volatilized (hereinafter referred to as vaporization), the inside is composed of the above-mentioned silicon nitride and grain boundary components, or the third component as it is.

As the Si 3 N 4 vaporizes and the Si content decreases, the surface portion is a component other than Si 3 N 4 and Si-A 1 -O-N, and the relative content of the component is improved.

Although the thickness of a surface part changes with an objective, a use, a manufacturing method, etc., although it is about several micrometers -0.1 mm normally, it may reach about 1 mm depending on a case.

In addition, in the sintered compact of the present invention, the surface portion having at least a predetermined composition ratio and the predetermined composition ratio, including the case where the above-described composition ratio does not change suddenly at the boundary between the surface portion and the inside, that is, continuously. What is necessary is to have an inside which has.

)으로 통상 사용되기 때문에, 기화에 다른 면조도의 악화에는 주의할 필요가 있다.This sintered compact has a baked surface obtained by vaporizing a surface Si3N4 component.

Since it is usually used for), it is necessary to pay attention to deterioration of surface roughness different from vaporization.

Therefore, this surface roughness is preferably 12.5 S (JIS B 0601) or less.

In particular, when it is used for the application which emphasizes surface roughness, it is preferable to make the grain boundary formation component remain and to cover the surface.

Common to all aspects of the invention, the following holds true.

That is, in (1) surface part, there are substantially more grain boundary phases than an inside. (2) Since the crystallinity of the grain boundary phase is higher in the surface portion (except when the grain boundary phase is the glass phase) than inside, the wear resistance is greatly improved by the synergistic effect of both.

The range effective for improving the wear resistance is determined by the features defined in the first and third aspects of the present invention.

On the other hand, in the case where the grain boundary phase contains a crystalline substance, among the crystalline compounds forming the surface grain boundary phase, merrill is preferable.

In other words, when the grain boundary phase of the surface portion is mainly crystallized by Si 3 N 4 .Y203 tetragonal compound (hereinafter referred to as < RTI ID = 0.0 > meryllite), < / RTI >

Moreover, almost all of the material to be cut or the counterpart material is often an iron-based alloy. On the other hand, Si, which is a major member of silicon nitride, has a high chemical affinity, and thus has low wear resistance, and therefore, Si is less than Si 3 N 4. The reaction is less, the chemical stability is improved, and further wear resistance is improved.

However, when the above-mentioned grain boundary crystalline Si 3 N 4 -Y 203 group compounds such as meryllite are also crystallized largely inside, the toughness at room temperature decreases. It is important to let them go.

In view of the above, the present invention has been made, and in the first point of view, the Si3N4 and Si-A1-ON crystal grains are less than 30% by volume or less in the surface portion, and the difference between them is less than 30% by volume. Effect (abrasion resistance increase) does not occur

In the second aspect, when the grain boundary phase crystalline compound is present at the surface portion and the content ratio to the inside thereof is 0.5 or more by the X-ray peak intensity comparison method, a sufficient surface modification effect does not appear.

In the third point of view, when the grain boundary phase crystalline compound is 0.3 or more in the surface portion at the highest X-ray strength comparison method compared to the content of Si 3 N 4 and Si-A 1 -ON crystal grains, the wear resistance is improved in the second point of view. It becomes more preferable.

Although the sintered compact used as a base body is normally manufactured by the normal atmospheric pressure sintering method, it can also be manufactured by the gas pressure sintering method or the hot hydrostatic sintering method (HIP method, Heat Isostatic Pressing Method).

The sintering atmosphere basically needs to be performed in an atmosphere containing nitrogen, and as an example of a method of reducing Si 3 N 4 and / or Si-A 1 -ON crystal grains on the surface portion, the pressure may be a condition in which silicon nitride is vaporized in an appropriate amount, It can vary widely from decompression to thousands of atmospheres.

The sintering temperature is usually in the range of 1550 to 1800 ° C, but preferably 1600-1750 ° C.

The manufacturing method of this sintered compact can be performed as follows, for example.

First, silicon nitride powder, a predetermined sintering aid, and the like are blended in a predetermined composition and mixed and ground.

The sintering aid may be an auxiliary agent for atmospheric sintering of silicon nitride (including gas pressure sintering and HIP sintering), and preferably, no Si element is contained.

As such a thing, rare earth oxides, such as A1203, Y203, A1N, MgO, CaO, Y203, etc. are mentioned, for example.

These raw materials are press-molded into a required shape and sintered.

At the time of this sintering, as a method of vaporizing Si3N4 of a surface, the method of reducing nitrogen partial rock, Si partial pressure, or using a reducing atmosphere is mentioned, for example.

As a typical example, the composition to the starting raw material powder material can be prepared as follows.

Si 3 N 4: 50-50% by weight, preferably 60-90% by weight, more preferably 64-86% by weight

Sintering aid: 5-30% by weight, preferably 7-20% by weight, more preferably 10-20% by weight;

Third component: 30% by weight or less, preferably 25% by weight or less.

Said sintering aid is A1203, A1N, Y203, MgO, CaO, A10N, YN, rare earth oxide, and the 3rd component is periodic table IVa (Ti, Zr, Hf), Va (V, Nb, Ta) or VIa Compounds of the (Cr, Mo, W) group (oxides, carbides, or nitrides) include needle-like (whisca) or fibrous crystals.

The average particle size of these starting material powder materials (mixtures) is preferably 5 µm or less, more preferably 2 µm.

The manufacturing method of the sintered compact is summarized as follows.

(a) preparation of starting material powder material of predetermined qualitative components, including mixing (usually at the same time as grinding);

(b) forming into a predetermined shape;

(c) The step of sintering the above-mentioned molded body at a predetermined temperature under the conditions in which silicon nitride is vaporized on the surface so that Si does not occur on the surface of the sintered body.

Sintering is carried out for a time sufficient for the molded body to be sintered (preferably 0.5-5 hours, more preferably 1-3 hours).

Sintering conditions are achieved by a special atmosphere for sintering, such as a predetermined reduced pressure nitrogen and / or silicon partial pressure, or (in particular in addition to these reduced pressure partial pressures) an atmosphere containing 0.02 and / or CO.

In general, the sintering conditions vary with composition and sintering temperature.

That is, the sintering atmosphere is set to a partial pressure slightly lower than the N2 and / or Si partial pressure, which is recognized as appropriate for the predetermined composition, for example, as shown in FIG. 5.

In this way, an appropriate amount of Si and N is decomposed and vaporized within the range of not forming a rough surface from the surface portion Si3N4.

The surface part of the sintered compact obtained in this way consists mainly of the sintering adjuvant which contains Si and / or N in solid solution, and / or these reaction products (compounds) (or including a 3rd component).

By evaporation of Si and N, the ratio of the grain boundary phase and the third component remaining in the surface portion becomes higher than that inside, thereby causing a change in density and hardness (hardness is improved).

The amount of silicon nitride and / or Si-A1-O-N in the surface portion is less than 30% by volume or less (up to 100% by volume) in comparison with the inside.

In a fourth aspect, the surface portion and the inside are characterized in that the content ratio (the X-ray peak intensity ratio) of the merlite constituting them is different.

When the [internal / surface portion] ratio is less than 0.5, the effect is insufficient when it is 0.5 or more, and even when it is less, the internal characteristics of excellent toughness and the like can be improved, and wear resistance can be improved. Because.

In addition, from a 5th viewpoint, the maximum X-ray intensity ratio of a merlite content is 0.3 or more with respect to silicon nitride and Si-A1-O-N content in a surface part.

In this case, it is possible to secure an increase in the content of the merrillite and to reduce the Si content, thereby ensuring the improvement of the wear resistance and ensuring this further.

The sintered compact based on the silicon nitride of the present invention is usually composed of silicon nitride, but in the present invention, in order to perform surface modification such that a grain boundary crystalline compound such as merrillite is contained in the surface portion rather than the inside, the above-described modification is carried out. As described above, it is not limited to silicon nitride and may be Si-A1-ON or a mixture of both.

The silicon nitride or Si-A1-O-N can be selected depending on the purpose and use regardless of the α- and β-forms, and may be mixed.

In the present invention, when the crystalline compound is contained in the grain boundary, the composition component amount (compounding amount) of Y203 is usually 1-20% by weight, preferably 1-15% by weight, more preferably 1-10% by weight. to be.

In order to supply Y, which is a member of grain boundary crystalline compounds such as meryllite, V 2 O 3 is most preferable, and more than 1% by weight is required. However, when the amount is increased, high temperature characteristics decrease due to the increase of the grain boundary phase. Because.

Moreover, Y may be added with other compounds, such as nitrides and silicides other than an oxide.

At this time, the amount added in terms of Y203 is applied.

Moreover, A1203 and A1N can also be mix | blended simultaneously with Y203, and these are Si3N4 and Y203, such as a merilite, play an important role in crystallization of a compound.

It is preferable to add 1-10 weight% of A1203 and 1-10 weight% of A1N.

In this case, when A1N is added more than A1203, more preferable results are obtained.

In addition, at least one of ordinary auxiliary sintering agents for normal pressure sintering of Si 3 N 4, for example, MgO, SiO 2, Zro 2, rare earth oxide, or the like may be used.

A part of the silicon nitride may be replaced with a component (third component) effective for improving wear resistance and defect resistance, for example.

For example, carbides, nitrides and oxides of the periodic table IVa, Va, Via family transition metals, and one or two or more of these solid solutions may be used.

In addition, in order for this substitution compound not to reduce toughness etc. of a sintered compact, 30 weight% or less of the whole is preferable.

The inside is a portion excluding the surface portion, which forms the main part of the silicon nitride-based sintered body of the present invention, and is a part showing the essential characteristics of the sintered body.

The surface part in the 2nd viewpoint of this invention is a part in which the relative content of Si3N4-Y203 group compounds, such as a merilite, improved.

Although the thickness of a surface part changes with an objective, a use, a manufacturing method, etc., it is usually about 1 mm or less from several micrometers-0.1 mm.

In the case where the Sin 3 N 4 -Y 203 crystalline compound is crystallized in a large amount on the surface to cover the entire surface, the layer covering the surface contains almost no Si 3 N 4 and / or Si-A 1 -ON particles (a third component = (Dispersed phase is included), and the volume is reduced by 100% by volume, and the thickness thereof (the volume by which the volume is reduced by 100%) is preferably 5 µm or less in order to prevent a decrease in strength of the entire sintered body.

In addition, in the present sintered body, the above-described composition ratio does not change rapidly at the boundary between the surface portion and the inside, that is, the case of continuously changing, and thus the surface portion having at least the predetermined composition ratio and the predetermined composition ratio What is necessary is just to have the inside which has.

The manufacturing method of the sintered compact of the 4th viewpoint of this invention is as having already demonstrated.

Moreover, although it is preferable to sinter under the appropriate amount of vaporization conditions of the silicon nitride in a surface part, it is not necessarily limited to this.

This minor component atmosphere is basically carried out in a nitrogen-containing atmosphere, and this pressure is a nitrogen partial pressure (thousands of pressures from reduced pressures) used for ordinary firing.

At the time of this sintering, in order to form the surface of the above-mentioned sintered compact of this invention, it is preferable to crystallize a grain boundary phase as Si3N4-Y203 group compounds, such as a merilite.

For this purpose, a method such as maintaining at a constant time at 1400-1700 ° C., preferably 1500-1650 ° C. at the time of sintering, or slowing down the cooling rate, is performed.

Moreover, this predetermined temperature sintering may be reheated to the said temperature after normal baking (refer 1st viewpoint) once, and may be performed continuously.

At the time of this determination, since Si3N4-Y203 group compounds, such as a merrillite, crystallize not only in the surface but also in the internal phase inside, care should be taken at the time of excessive heat treatment.

As a method of increasing the crystallization of the merrillite at the surface portion more than the inside, a method of controlling the atmosphere during firing, that is, controlling the nitrogen partial pressure and the oxygen partial pressure, or coating the composition with a composition material which is likely to crystallize on the surface. Can be used.

In addition, the crystallization status of M, J, K, H, and A phases at the surface portion is basically affected by the amount of Y203 component and the sintering time.

In the case of the present invention, a complicated composition fluctuation occurs due to the vaporization of the component in the surface portion, and the produced crystal phase is also affected by the change of the atmosphere or by the segregation of components in the cooling process.

Locally, however, the SiO2-Si3N4-Y203 ternary state diagram [Figure 11, F.F. Lange et al. J.AM. Ceram. Soc. 60 (5-6), P249-252 (1977) and the relations described in the literature powders of Lim, Yang, etc., and powder metallurgy 34 (1), Fig. 3 of P26-31]. .

Example

Hereinafter, the present invention will be described in more detail with reference to examples.

Example 1 (point of view 1-3)

The Si content of the surface portion was reduced from the inside, and further, the grain boundary phase crystalline compound (Si 3 N 4 -Y 203 group compound) was crystallized in the surface portion to examine the effect.

First, as a raw material powder, Si3N4 powder having an average site diameter of 0.6 µm (more than 90 vol% of α conversion), A1203 or MgO having an average particle diameter of 0.5 µm, AIN powder having an average particle diameter of 1.3 µm, and an average particle diameter The Y203 powder of 1.2 μm, Zr02 powder of 0.4 μm in average particle diameter, TiN powder of 1.2 μm in average particle diameter, HfN powder of 1.7 μm in average particle diameter, and WC powder of 2.0 μm in average particle diameter are respectively shown in the following table. After blending in the formulation as shown and mixing for 48 hours in a wet ball mill, a molding aid was added and dried.

Using this powder, the mold was molded and fired in an atmosphere of 1650-1750 占 폚, 0.7-10 atmospheres of nitrogen pressure, and in some examples to produce a sintered compact.

In addition, when the thickness of the surface part was measured by surface erase by grinding and microregion X-ray diffraction, all were about 0.01-0.1 mm.

This sintered compact was post-treated by the method of SNMN 432 (JIS B4103).

However, this post-processing process grind | polished only the upper and lower surfaces, and the side surface was baked, and it was set as the test piece (tip) (2).

The dimension of the test piece was adjusted at the time of press molding.

Evaluation was carried out by the three methods shown below (in particular, tests 1 and 2 were abrasion resistance, test 3 was strength), and the results are shown in Tables 1 and 1 below.

Each condition of test 1, 2, 3 is as follows.

For convenience, test 2 is shown in small parentheses () and test 3 in middle parentheses [].

In addition, the lifetime in test 1 takes time until a defect, as described next.

In this case, the main cause of the defect is not merely mechanical strength, but the result of the increase in cutting resistance due to wear, and is used as a standard of wear resistance.

Work piece (symbol 1 in the drawing) Shape: Detective Donors with an outer diameter of 300 mm Φ and an inner diameter of 200 mm Φ as shown in Fig. 2, (rod shape having an outer diameter of 240 mm Φ as shown in Fig. 3), [ A ring-shaped grooved rod shape having an outer diameter of 240 mm Φ and a peak width of 150 mm as shown in FIG. 4]

Reference numeral 3 in the figure denotes a holder.

The life of the test 2 was determined by wear on the side.

Sample No. 1-8 of Table 1 relates to the 1st department of this invention, and Sample No. 9 relates to a 2nd viewpoint, and Sample No. 10-13 relates to 3rd department, respectively.

Sample No. 9 is crystallized by heat treatment of the sample of Sample No. 3 after heating to 1500 ℃ X 4 hours.

Sample No. 12-14 was prepared by varying the firing temperature, firing time, and firing atmosphere (composition position, for example, the position on the pit, the position in the firing furnace, etc.) of the feed of Sample No. 11.

The composition of Si 3 N 4 (including Si-A 1 -O-N) is determined depending on the purpose of use.

Therefore, it is difficult to compare all these examples under the same conditions.

For example, in the comparative example described above, a relatively hard type (Comparative Example C1), a relatively suitable Ni alloy type (Comparative Example C2), a relatively suitable type of casting (Comparative Example C3) It is meaningless to compare these different types with each other, and the comparison within each type is meaningful.

Therefore, Table 1 was arranged to compare the performance between the same or similar raw material composition, the results are described as follows.

That is, in Comparative Examples C1 and C3, each of Sample Nos. 1 and 6 of the Example of the present invention was ground, and removed by 0.2 mm or more from the surface thereof, and the surface part was completely removed to expose the inside. Check with line)

In Comparative Example C2, the composition of Sample No. 3 had a state in which Si on the surface was hardly reduced, that is, a surface state as it was baked.

In the sample numbers 1 and 2, the grain boundary phase of the surface portion, which has not been subjected to a special surface crystallization treatment, is mainly composed of a glass phase except for the third phase (HfN).

When the samples in which the Si3N4 and Si-A1-ON particle contents of the surface portion were reduced were compared with the respective comparative examples (Sample No. 1 and Comparative Example C1, Sample No. 3 and Comparative Example C2, and Sample No. 6-8 and Comparative Example C3). ), Both have improved wear resistance.

In this case, none of them is slightly deteriorated, but there is almost no sign of trouble.

In addition, in Sample No. 6-8 and Comparative Example C3, as shown in FIG. 1, the relationship between Si3N4 and Si-A1-O-N particle reduction rate and abrasion resistance is increased, the wear resistance is improved and the effect is excellent.

In addition, the compound (HfN, WC, TiN) of the transition metals of group IVa and group VIa (Sample Nos. 2, 4, 6) was added to the ones that were not blended (Sample Nos. 1, 3, 5). Wear resistance is improved.

However, if this blending amount is too large, it is necessary to pay attention because the strength as in Comparative Example C4 may be considerably lowered.

As mentioned above, in feed No. 1-8, since the reduction rate of silicon nitride and Si-A1-ON particle | grains of a surface part is 30 volume% or more, both are improved in abrasion resistance, maintaining strength, and the surface part and an inside are improved. The characteristics of the material to be formed are sufficiently exhibited.

On the other hand, in the sample No. 9-13, various Si3N4-Y203 group crystal phases were crystallized out in the surface part by the crystallization process of the surface, and the improvement of the test 1 was excellent, and the test 3 also showed the satisfactory result.

In all the above examples, the density was 99.5% or more with respect to the theoretical density.

The interior consisting of Si-A1-ON showed β-type in Example 3, Comparative Example 2 and Example 4, (β-type + α-type) in Example 5-9 and Comparative Example 3 The α conversion rates at this time were 0.33, 0.28, 0.34, 0.42, 0.36 and 0.22, respectively.

Example 2 (4th, 5th viewpoint)

The crystalline grain boundary phase was made into a merlite phase, and the effect thereof was examined. The composition and the baking conditions which can make a sample into a merlite phase were examined and created.

As the raw material powder, Si3N4, the same powder as in Example 1, A1203 powder or MgO powder, AIN powder, Y203 powder, ZrO2 powder, TiN powder were used, and the average particle diameter was 5.1 μm Yb203 powder, respectively, After blending with the formulation shown in Figure 4 and mixing with a wet bowl mill for 4 hours, a molding aid is added and dried.

Molding was carried out using this powder, and at various temperatures of 1650-1750 ° C., the resultant was calcined for about 2 hours or more in various atmospheres at 0.7-10 atmospheres of nitrogen rock to produce respective sintered bodies having various meryl content. Table 2 shows.

The reduction rate of Si3N4 / Si-A1-O-N particles at the surface portion of Sample Nos. 27-29 was 100% by volume.

In addition, the thickness of the surface part of sample number 27 was about 3.5 micrometers.

On the other hand, the thickness of the surface portion of Sample No. 28 was about 1 µm, and the X-ray diffraction result of the surface portion thereof was shown in FIG. 8, the X-ray diffraction result thereof in FIG. 8, and the X-ray diffraction result thereof in FIG. It is shown in the figure.

The thickness of the surface portion was measured by surface portion deletion by grinding and microregion X-ray diffraction.

[Marylite / silicon nitride] content ratio (R1) of the surface portion is represented by the formula R1 = I / Is, as shown in FIG. 8, and the [inner / surface portion] ratio (R2) of the merylene content is shown in FIG. It is computed by the ratio of I and I in FIG. 9, ie, R2 = I / I.

This sintered compact was post-processed according to the method of SNMN432 (JIS B 4103).

However, in the post-treatment processing, only the upper and lower surfaces were ground, and the side surfaces were fired in the same state as the test piece (tip) 2.

The dimension of the test piece was adjusted at the time of press molding. (Same as Example 1 above)

It evaluated by the two methods described below, and the result is shown to Table 2 and FIG. 5-FIG.

Each condition of test 4 and 5 is as follows.

For convenience, Test 5 is listed in the title. In addition, the life in Test 4 is the amount of wear (mm), and the life of Test 5 takes the number of phases up to the defect.

Test 4 (Test 5)

Material to be cut: FC 20 (FC 23)

Cutting speed (m / min): 600, (150)

Depth of cut (mm): 0.5, (2)

Feedrate (mm / revolution): 0.2 (0.6)

Coolant: None, (None)

Cutting time (sec): 330, (to defect)

Horizontal Judgment: ㎜, (Number of Acids)

Workpiece (sign 1 in the drawing) Shape:

Rod shape with outer diameter 240 mm Φ as shown in FIG. 3, (ring shape with a ring groove with outer diameter 240 mm Φ and width of 150 mm as shown in FIG. 4)

The composition of Si 3 N 4 and / or (Si-A 1 -O-N) depends on the purpose of use.

Therefore, it is difficult to compare these examples under the same conditions.

That is, it does not make much sense to compare series which differs in composition component ratios according to the objective, and the comparison in each thing of the same series is meaningful.

Therefore, Table 2 is arranged to compare the performance between the same or similar raw material composition, and the results are as follows.

On the other hand, in comparison, C21 and C24 ground the surface by 0.5 mm or more, completely removed the surface part, and indicated the inside, and indicated by * in Table 2.

Compared with Comparative Example C21, Sample Nos. 21 and 22 of the present invention also had a smaller amount of abrasion than both Comparative Examples C22-24 and abrasion resistance, and improved acid resistance to defects. The same or more of them, the defect resistance is also maintained.

Sample Nos. 23, 24, and 25, 26 also have excellent wear resistance.

In FIG. 5 and FIG. 6, the test result, such as the amount of abrasion with respect to sample numbers 27-30 and comparative examples C22 and C23, is shown.

As shown in FIG. 5, in each sample in which the [internal / surface portion] ratio of merilite is less than 0.5, the amount of wear is smaller than that of the comparative example in which the ratio is higher.

Moreover, also in the comparison of sample numbers 21 and 22 with comparative examples C21, sample numbers 23 and 24, and sample numbers 25 and 26, the amount of electrons having a small ratio is small.

Therefore, it shows that the abrasion resistance is excellent when the ratio is small, that is, when the amount of the surface portion and the meryllite is larger than the inside.

In addition, as shown in Fig. 6, the larger the amount of merrillite in the surface portion is, the smaller the amount of wear is, indicating that the wear resistance is excellent.

This is also demonstrated from the fact that the wear amount of the electron with a large ratio is small also in the comparative example of the sample numbers 21 and 22 which are other series, the comparative examples C21, the sample numbers 23 and 24, and the sample numbers 25 and 26.

In addition, as shown in FIG. 7, the sum of the ratios R1 and R2 increases inversely, and the number of cutting acids decreases when the content of meryllite in the internal system increases (for example, sample numbers 27 and 28). , Defect resistance decreases.

In addition, the commercially available Si-A1-O-N tool of Comparative Example C25 has a particularly large amount of abrasion, and the commercially available coated silicon nitride tool of Comparative Example C26 is likely to be remarkably missing.

As described above, in the sample No. 21-30, all of the defects were defects because the [meryllite / silicon nitride] ratio of the surface portion was 0.36-4.5 and the [inner / surface portion] ratio of the merryllite was 0.02-0.31. Wear resistance is improved while maintaining the properties, and the properties of the material constituting the surface portion and the interior are sufficiently exhibited.

The reduction rate of Si 3 N 4 / Si-A 1 -O-N particles indicates that the grain boundary phase is larger in the surface portion than in the interior (1), but it is not necessarily correlated with R 2.

In the surface part, it is recognized that it is more easy to crystallize than inside (2). Therefore, R2 is considered to be determined by the synergistic effect of (1) and (2).

Since the sintered compact based on the silicon nitride by the 4th and 5th viewpoint of this invention by this Example has more mercurite content in the surface part compared with the inside, it is excellent in the abrasion resistance of the surface part, internal toughness, etc. The essential characteristic of this high is fully exhibited.

That is, this sintered compact does not exhibit intermediate characteristics of both properties as in the prior art.

Therefore, in this sintered compact, the surface modification does not reduce the intrinsic characteristic internally, and wear resistance can be improved.

Moreover, since the surface part and the inside are integrated, the bonding strength between them is high, so that they do not peel off.

In the sintered compact based on silicon nitride according to the fifth aspect of the present invention according to the present embodiment, moreover, the merrillite content of the surface portion is higher than that of silicon nitride, and thus the wear resistance is reliably ensured.

Note: C: Comparative Example

*: Remove surface

* *: 100% means that there are no Si3N4-Si-A1-O-N particles.

* * *: Sample Nos. 27 and 28 each have a surface portion having a thickness of 3 µm and 1.5 µm, respectively, and the surface portion is composed of TiN (third phase) and grain boundary phase.

Claims (11)

A sintered body based on silicon nitride, wherein the surface portion is formed integrally with the inside, and the surface portion is less than 30% by volume of silicon nitride and Si-A1-O-N crystal grains. The silicon nitride-based sintered body according to claim 1, wherein part or all of the grain boundary phase is crystallized at the surface portion. The silicon nitride-based sintered body according to claim 2, wherein an internal content ratio of the crystalline compound forming part or all of the grain boundary phase is less than 0.5 by an X-ray peak intensity method. The crystalline compound which forms part or all of the grain boundary phase contains 0.3 or more by the maximum X-ray intensity comparison method compared with content of the silicon nitride and Si-A1-ON crystal grain in a surface part. A sintered body based on silicon nitride characterized by the above-mentioned. The silicon nitride-based sintered body according to any one of claims 2 to 4, wherein the crystalline grain boundary phase at the surface portion is a merlite phase, a J phase, a K phase, an H phase, an A phase, or a mixed phase thereof. 3. The silicon nitride-based sintered compact according to claim 2, wherein the ratio of the content of the internal merlite to the content of the merryllite in the surface portion is less than 0.5 by an X-ray park strength comparison method. 7. The silicon nitride-based sintered compact according to claim 6, wherein the ratio of the content of meryllite to the content of silicon nitride and Si-A1-O-N in the surface portion is 0.3 or more by the maximum X-ray strength comparison method. The silicon nitride-based sintered body according to claim 5, wherein the crystalline grain boundary phase at the surface portion is substantially made of meryllite. The silicon nitride-based sintered compact according to claim 8, wherein the ratio of the content of meryllite to the content of silicon nitride and Si-A1-O-N in the surface portion is 0.3 or more in terms of the maximum X-ray strength comparison method. The sintered compact based on surface-modified silicon nitride characterized by the ratio of the content of the internal merlite to the content of the merlite in the surface portion is less than 0.5 by the X-ray peak intensity comparison method. The silicon nitride-based sintered body according to claim 10, wherein the ratio of the content of meryllite to the content of silicon nitride and Si-A1-O-N in the surface portion is 0.3 or more by the maximum X-ray strength comparison method.

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