KR960016069B1 - Silicon nitride base sintered body - Google Patents

Abstract

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Description

Sintered Body Based on Silicon Nitride

1 is a graph showing the relationship between the Si reduction rate of the surface portion and the wear resistance.

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

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

4 is a partial cross-sectional view showing the shape of the workpiece to be used in the method 3. FIG.

5 is a state diagram of atmospheric gas pressure and temperature and Si ₂ N ₄ .

* Explanation of symbols for main parts of the drawings

1: Insulation material 2: Silicon nitride-based sintered body tip

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 abrasion resistance without degrading essential properties such as toughness.

動)부품 등에 이용될 수 있다.The present invention is a cutting tool, wear-resistant parts and perturbation (

It can be used for parts and the like.

As a conventional silicon nitride sintered body, in order to improve abrasion resistance, it is known to coat a ceramic material of high hardness or excellent abrasion resistance (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 (see Japanese Patent Application Laid-Open No. 58-185484).

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, furthermore, the cost is considerably high, and the economical problem also occurs. It is hardly put into 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, only the balance and the intermediate performance are 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 body, which is different from the conventional one, in which a surface portion is improved to form a surface portion excellent in wear resistance and exhibits sufficient surface portion and material properties therein. For the purpose of

MEANS TO SOLVE THE PROBLEM As a result of investigating the cause which abrasion resistance of silicon nitride is bad, the present inventors discovered the following fact and completed this invention.

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, whereas Si, which is a major member of silicon nitride, has a high chemical affinity, and thus has poor wear resistance.

By the way, in the sintering of silicon nitride, efforts to prevent decomposition volatilization of silicon nitride have been made conventionally.

In the present invention, on the contrary, using such decomposition volatilization, a sintered body based on silicon nitride having a reduction ratio with respect to the inside of the Si content of the silicon nitride component at the surface portion of not less than 20% by weight (hereinafter simply referred to as "%") is tough. It has been found that wear resistance can be improved without lowering the back.

The sintered compact based on the silicon nitride of this invention is characterized by the fact that Si content which comprises this differs in a surface part and inside.

Here, such a Si reduction rate of a surface part is computed by the following formula especially as described also in a claim column.

This reduction rate is set to 20% because the effect is not sufficient when it is less than 20%, and when it is more than that, the wear resistance can be improved without deteriorating the internal characteristics of excellent toughness.

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

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

Moreover, even if the Si content of a surface part disappears substantially, in this case, although abrasion resistance further improves, since surface roughness falls, it is preferable to set it as the range which a weak compound does not produce.

That is, the Si reduction rate is preferably 25-61%, more preferably in the range 50-60%.

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-Al-O-N (sialon).

Such silicon nitride or Si-Al-ON can be selected depending on the purpose and use regardless of the α- and β types, and may be a mixture of such silicon nitride and Si-Al-ON or a mixture of α- and β types. Do.

As components other than silicon nitride and the like, it is also known as boundary phase forming components (Boundary phase forming componants) or third components other than the 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 transition metals of group IVa, Va, and VIa of the periodic table, and one or two or more of two or more solid solutions thereof can be used.

Moreover, since this compound does not reduce the toughness of a sintered compact, 30 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.

In this interior, since Si ₃ N ₄ is not decomposed and volatilized (hereinafter referred to as "vaporization"), the above-mentioned silicon nitride and the grain boundary component, or the above-mentioned third component, are configured as it is.

The surface portion is a portion in which Si ₃ N ₄ is vaporized to decrease Si content, and components other than Si ₃ N ₄ remain, 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., it is about several micrometers-0.1 mm normally.

Moreover, in the sintered compact of this invention, when the above-mentioned composition ratio does not change suddenly in the boundary between a surface part and an inside, ie, it changes continuously, the surface part which has at least predetermined composition ratio in this way, and predetermined composition ratio It is good to have an internal vortex with.

Since this sintered compact is normally used as the baked surface which vaporized the Si ₃ N ₄ component of the surface, it is necessary to be careful about the deterioration of the surface roughness by vaporization.

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

In particular, when used for applications in which surface roughness is important, it is desirable to allow grain boundary components to remain and cover the surface.

Although this sintered compact is normally manufactured by normal atmospheric pressure sintering, it can also manufacture also by a gas pressure sintering method or a hot hydrostatic sintering method (HIP method, Heat Isostatic Pressing Method).

The firing atmosphere basically needs to be carried out in an atmosphere containing nitrogen, and the pressure may be a condition in which silicon nitride vaporizes in an appropriate amount, and can be varied widely from reduced pressure to thousands of atmospheres.

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

In the manufacturing method of this sintered compact, a silicon nitride powder, a predetermined | prescribed sintering aid, etc. are mix | blended with a predetermined composition, for example, first, and it grind | mixes and grinds.

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

As such, for example there may be mentioned _{Al 2 O 3, Y 2 O} 3, AIN, MgO, CaO, AlON, YN or once-earth oxide.

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

In during the sintering, a method of vaporizing the Si ₃ N ₄ on the surface is, for example, the lower the nitrogen partial pressure or partial pressure of Si, there may be mentioned a method of or using a reducing atmosphere.

Usually, the composition of a raw material can be as follows.

Si ₃ N ₄ : 50-95% 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.

(The above sintering aids are Al ₂ O ₃ , AIN, Y ₂ O ₃ , MgO, CaO, AlON, YN, rare earth oxide, and the third component is periodic table IVa (Ti, Zr, Hf), Va Compounds such as oxides, carbides, or nitrides of group (V, Nb, Ta) or group VIa (Cr, Mo, W).

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

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

(a) preparation of raw materials of predetermined qualitative components, including mixing (usually at the same time as grinding);

(b) forming into a predetermined shape;

(c) The above-mentioned molding is sintered at a predetermined temperature under conditions such that Si ₃ N ₄ on the surface of the sintered body is vaporized to form a surface portion with reduced Si content.

Firing is carried out for a time sufficient to sinter the molded article, preferably 0.5-5 hours, more preferably 1-3 hours.

The firing conditions are set by a specific atmosphere for sintering, such as a reduced partial pressure of nitrogen and / or silicon, or a reducing atmosphere containing CO ₂ and / or Co (particularly in addition to the reduced partial pressure).

Typically, firing conditions vary with composition and firing temperature.

That is, the atmosphere is set to a partial pressure of N ₂ and / or Si which is slightly lower than the pressure deemed to be suitable for the plastic component in proportion to the temperature as shown in FIG. 5, for example.

In such a manner, the appropriate amounts of Si and N decompose and volatilize at the surface portion to such an extent that the surface roughness is not compromised.

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 compounds (or including a 3rd component).

The amount of Si ₃ N ₄ and / or Si-Al-ON in the surface portion is relatively small compared to the inside (preferably in the range of 20% by volume to 100% by volume).

Through vaporization of Si and N, the grain boundary phase and the third component remaining in the surface portion are increased compared with the inside, thereby resulting in a change in density and hardness (hardness is improved).

EXAMPLE

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

First, as raw material powder, Si ₃ N ₄ (α volatilization rate 90% or more) powder having an average particle diameter of 0.6 mu m,

Al ₂ O ₃ or MgO, with an average particle diameter of 0.5 μm,

AIN powder having an average particle diameter of 1.3 μm,

Y ₂ O ₃ powder having an average particle diameter of 1.2 μm,

ZrO ₂ powder having an average particle diameter of 0.4 μm,

TiN powder having an average particle diameter of 1.2 μm,

HfN powder having an average particle diameter of 1.7 μm,

WC powder with an average particle diameter of 2.0 µm

Each was formulated in a formulation as shown in the following table, and mixed with a wet ball mill for 48 hours, after which 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, the thickness of the surface part was measured by surface removal by grinding and micro area X-ray diffraction, and all of them 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 was left as it 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 performed by the three methods shown below (particularly, method 1 and 2 were abrasion resistance, method 3 was strength), and the results are shown in the following table and FIG.

[table]

Each condition of the method 1,2,3 is as follows.

Method 2 is shown in small parentheses "()" and method 3 is in middle parentheses "[]".

In addition, the lifetime in the method 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.

Material to be cut: Inconel 718, (FC 20), [FC 23]

Cutting speed (m / min): 250, (600), [150]

Depth of cut (mm): 1, (0.5), [2]

Feedrate (mm / revolution): 0.25, (0.2), [0.6]

Cutting oil: Water-soluble oil (none), [none]

Cutting time (seconds): to defect, (330), [to defect]

Life judgment: seconds, (mm), [number of acids]

Work piece (symbol 1 in the drawing) shape: donor shape having an outer diameter of 300 mm ψ and inner diameter of 200 mm ψ as shown in FIG. 2, (rod shape having an outer diameter of 240 mm ψ as shown in FIG. 3), [as shown in FIG. Ring-shaped grooved rod shape with the same outer diameter 240mmψ and the width of the mountain 15mm]

Reference numeral 3 in the figure denotes a holder.

The life judgment of the method 2 was performed by abrasion of the side surface.

The composition of Si ₃ N ₄ (including Si-Al-ON) is determined depending on the purpose of use.

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

For example, the comparative examples described above are those of a relatively hard type (Comparative Example 1), those of a type relatively suitable for Ni alloys (Comparative Example 2), and those of a type relatively suitable for castings (Comparative Example 3). The comparison between the different types is not significant, and the comparison within each type is meaningful.

Therefore, the table 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 1 and 3, each of Examples 1 and 6 was ground and removed by about 0.2 mm or more from the surface thereof, and the surface part was completely removed to expose the inside.

In Comparative Example 2, the composition of Example 3 had a state in which the surface Si hardly decreased, that is, the surface state as it was baked.

When each Example which reduced Si content of the surface part is compared with each comparative example (Example 1, Comparative Example 1, Example 3, Comparative Example 2, Example 6-8, and Comparative Example 3), all of them are abrasion-resistant This is improved.

In this case, none of them is slightly problematic, although the strength slightly decreases.

Furthermore, in Example 608 and Comparative Example 3, as shown in FIG. 1, the relationship between Si reduction rate and wear resistance is increased, the wear resistance is improved as the reduction rate is increased, and the effect is particularly excellent at the reduction rate of 20% or more.

In addition, the compound (HfN, WC, TiN) of the transition metals of the group IVa, VIa (Examples 2, 4, 6) is not wear-resistant (Examples 1, 3, 5). This has been improved.

However, if this blending amount is too large, it is necessary to pay attention because the strength may decrease considerably as in Example 9.

As described above, in Example 1-9, since the Si reduction rate of the surface portion is 25-61%, all of them have improved wear resistance while maintaining the strength, and the characteristics of the material constituting the surface portion and the interior are sufficiently satisfied. Exerted.

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

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

의 값으로 정의된다.α rate was measured by X-ray Peak Intensity Ratio Method.

It is defined as the value of.

In the α-Si-Al-ON, a part of the Si elements in the α-Si ₃ N ₄ structure is substituted with Al, and a part of the N elements in the structure is substituted with O, and moreover, Li, Na, Mg, Ca, Y or a rare earth element is a substitution / intrusion solid solution in which a solid solution is formed by infiltrating into the interstitial space between (Si, Al) and (O, N).

In general, such α-Si-Al-O-N is represented by the following formula.

M _X (Si, Al) ₁₂ (O, N) ₁₆

(Wherein Mt = Li, Na, Mg, Ca, Y or a rare earth element and 0 <X ≦ 2).

On the other hand, in β-Si-Al-ON, a part of each of Si element and N element in β-silicon nitride is substituted with Al and O, and solid solution of Al ₂ O ₃ , AlN and SiO ₂ is formed in β-silicon nitride. Substituted solid solution.

Such β-Si-Al-O-N is represented by the following formula.

Si ₆ - _z Al _z O _z N _8-z

(Where 0 <z≤4)

The sintered compact based on the silicon nitride of the present invention has a property that the Si content of the surface portion thereof is reduced by 20% or more compared to the inside, and the inside thereof is excellent in wear resistance of the surface portion because the inside thereof is free from vaporization of Si ₃ N ₄ , Essential properties such as high toughness inside are sufficiently exhibited.

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

In this sintered compact, its surface modification improves abrasion resistance without lowering the intrinsic properties of the interior.

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

Moreover, as can be seen from the above embodiment, the effect of improvement is excellent.

Furthermore, the sintered compact of the present invention may further coat a coating layer or coating layers formed of Al ₂ O ₃ , TiC, TiN, AlON, or the like with a thickness of 0.5-10 μm.

Claims (15)

A silicon nitride-based sintered body, wherein a reduction rate of the Si content of the surface portion with respect to the internal Si content of the calculated content is 20% by weight or more.

The silicon nitride based sintered body according to claim 1, wherein a surface portion having a reduced Si content is produced by sintering. The silicon nitride-based sintered body according to claim 1, wherein the Si reduction rate is 25-61 wt%. The silicon nitride-based sintered body according to claim 3, wherein the Si reduction rate is 50-60 wt%. The silicon nitride-based sintered body according to claim 1, wherein the inside of the sintered body is made of either or both of Si-Al-O-N and silicon nitride having mainly grain boundaries. 6. The group according to claim 5, wherein the sintered body further includes a third component of 30% by weight or less based on the total weight of the sintered body, wherein the third component is composed of a compound of a transition metal of Groups IVa, Va, and VIa of the periodic table. Sintered body based on silicon nitride, characterized in that at least one component selected from. The silicon nitride-based sintered body according to claim 6, wherein the compounds are oxides, carbides, nitrides and solid solutions thereof. 8. A silicon nitride-based sintered body according to claim 7, wherein said compound is ZrO ₂ , WC and TiN. The silicon nitride-based sintered body according to claim 5, wherein the grain boundary phase is formed of a sintering aid. 10. The silicon nitride based sintered body according to claim 9, wherein said sintering aid is at least one component selected from the group consisting of Al ₂ O ₃ , Y ₂ O ₃ , AIN, MgO, CaO, YN and rare earth oxides. The silicon nitride-based sintered body according to claim 1, wherein the thickness of the surface portion of the sintered body is 0.1 mm or less. The silicon nitride-based sintered body according to claim 11, wherein the thickness of the surface portion of the sintered body is several micrometers or more. The said sintered compact is manufactured by baking the raw material of the composition based on (alpha)-silicon nitride at the temperature of 1550-1800 degreeC on the conditions which the vaporization of the silicon nitride which exists in the surface part of a raw material is permissible. Sintered body based on silicon nitride. The silicon nitride-based sintered compact according to claim 13, wherein the firing step is performed under either a reduced partial pressure atmosphere or a reduced atmosphere of both nitrogen and silicon. The silicon nitride-based sintered body according to claim 1, wherein the surface portion of the sintered body has either or both of silicon nitride and Si-Al-O-N in an amount reduced by at least 20% by volume relative to the inside.

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