JPH06344204A - Cutting tool made of composite ceramics and its manufacture - Google Patents

Abstract

PURPOSE:To suppress the scattering of the strength and improve the fracture toughness of the surface by executing the heat treatment of a composite sintered compact made of silicon nitride and silicon carbide, and grinding the surface. CONSTITUTION:The composite sintered compact of silicon nitride and silicon carbide in a cutting tool made of the composite sintered compact of silicon nitride and silicon carbide consists of the matrix phase made of silicon nitride and silicon carbide having fine structure where the particles of silicon carbide of <=1mum in average grain size are present in the grain boundary of the particles of silicon nitride and the particles of silicon carbide of several nm to several hundred nm in size are dispersed in the particles of silicon nitride, and the dispersed phase of the particles of silicon carbide of 5-50mum in average grain size, and/or the whisker of silicon carbide whose minor axis is 0.05-3.0mum in length and whose aspect ratio is 5-300. In addition, the oxide layer containing silica on the surface of the sintered compact and/or the layer with different hue from that of the inside part are provided. The heat treatment of this surface and the subsequent grinding suppresses the scattering of the strength of the sintered compact, the fracture toughness of the surface is improved, and similar effect to that of the coating can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride-silicon carbide composite cutting tool and a method for producing the same, and is made of silicon nitride-silicon carbide which can be used as a cutting tool for throwaway inserts for turning and milling, drills and end mills. Composite ceramic cutting tool.

[0002]

2. Description of the Related Art Silicon nitride ceramic cutting tools take advantage of higher strength and fracture toughness or heat resistance and thermal shock resistance as compared with alumina cutting tools, especially for high speed cutting of cast iron and cutting of heat resistant alloys. It has begun to be used as a tool. However, in order to speed up cutting in recent years and to cut heat-resistant alloys, conventional silicon nitride cannot obtain a sufficient life due to wear and damage, and various improvements have been added.

As one of the methods, it is known that a single layer or a multi-layer coating layer of alumina or titanium is provided on the surface of silicon nitride to improve fracture toughness and wear resistance. However, this method has drawbacks in that it does not exhibit sufficient fracture resistance and abrasion resistance due to peeling of the coating layer, and the coating process causes an increase in cost of the cutting tool.

As another method, by adding silicon carbide whiskers to silicon nitride, a conventional silicon nitride whiskers is disclosed, for example, as shown in Ceramic Industry Association, 91,491 (1983) and Japanese Patent Laid-Open No. 59-54680. More excellent fracture toughness or fracture resistance is performed.

Further, in Japanese Patent Application Laid-Open No. 1-137486, silicon carbide particles having an average particle diameter of 1 μm or less are present at the grain boundaries of silicon nitride particles, and silicon carbide particles having a diameter of several nm to several hundreds nm are contained in the silicon nitride particles. A matrix phase composed of silicon nitride-silicon carbide showing a dispersed microstructure, and a) having an average particle size of 5
-50 μm silicon carbide particles, and / or b) minor axis 0.05-3.0 μm, aspect ratio 5-300
The silicon nitride-silicon carbide composite sintered body consisting of the dispersed phase of the silicon carbide whiskers is superior to silicon nitride in both room temperature or high temperature strength and fracture toughness value, and has been shown to be useful as a wear resistant material such as a cutting tool. ing.

[0006]

However, although the silicon nitride-silicon carbide composite sintered body according to the above-mentioned invention is characterized by being excellent in strength and fracture toughness, in order to use this material as a cutting tool, It has been demanded to further improve the variation in fracture toughness, fracture toughness, wear resistance and fracture resistance.

[0007]

According to the present invention, it is possible to suppress the dispersion of strength and improve the fracture toughness of the surface by subjecting the above silicon nitride-silicon carbide composite sintered body to a heat treatment to grind the surface. As a result, they have found that they have excellent properties as a cutting tool.

That is, the present invention has a microstructure in which silicon carbide particles having an average particle size of 1 μm or less are present at the grain boundaries of silicon nitride particles, and silicon carbide particles having a particle size of several nm to several hundred nm are dispersed in the silicon nitride particles. A silicon nitride-silicon carbide matrix phase shown, and a) silicon carbide particles having an average particle size of 5 to 50 μm, and / or b) a minor axis of 0.05.
A silicon nitride-silicon carbide composite sintered body comprising a dispersed phase of silicon carbide whiskers having an aspect ratio of -300 μm and a color ratio of an oxide layer containing silica on the surface of the sintered body and / or the inside thereof. Have different layers. The present invention relates to a silicon nitride-silicon carbide composite ceramic cutting tool.

Further, the present invention has a microstructure in which silicon carbide particles having an average particle size of 1 μm or less are present at the grain boundaries of silicon nitride particles, and silicon carbide particles having a particle size of several nm to several hundred nm are dispersed in the silicon nitride particles. A silicon nitride-silicon carbide matrix phase shown, a) silicon carbide particles having an average particle size of 5 to 50 μm, and / or b) a minor axis of 0.05-
A silicon nitride-silicon carbide composite sintered body composed of a dispersed phase of silicon carbide whiskers having a thickness of 3.0 μm and an aspect ratio of 5-300 is heat-treated at 1300 to 1600 ° C. in an oxidizing atmosphere,
Then, the present invention relates to a method for manufacturing a composite ceramic cutting tool made of silicon nitride-silicon carbide, which is characterized by removing the surface by 5-2000 μm.

According to the present invention, variations in the strength of the sintered body can be suppressed by simple surface heat treatment and subsequent grinding,
Moreover, since the fracture toughness of the surface is improved and the same effect as the coating is obtained, it is possible to obtain a composite ceramics cutting tool having sufficient fracture resistance and wear resistance. As a result, the cutting tool according to the present invention can be used not only as a tool for long-lived high-speed cutting such as cast iron, but also as a cutting tool for heat-resistant alloys, a drill, an end mill, or the like.

The silicon nitride-silicon carbide composite sintered body used in the present invention comprises fine silicon carbide having an average particle size of 0.5 μm or less as a raw material of a matrix phase, as disclosed in JP-A 1-137486. The resulting amorphous silicon nitride-silicon carbide composite powder or silicon nitride-silicon carbide mixed powder is used, and the powder has an average particle size of 5-50 as a dispersed phase.
μm silicon carbide particles and / or minor axis of 0.05
It is manufactured by mixing silicon carbide whiskers with an aspect ratio of 5-300 and a molding and sintering.

The raw material powder constituting the matrix phase of the above-mentioned sintered body has a silicon carbide powder having an average particle size of at least 0.5 μm or at the time of sintering of 0.5 μm or less when the silicon carbide powder is used as a raw material. Amorphous powders that produce silicon carbide are used.

As a more preferable material for the matrix phase, a powder composed of amorphous silicon, carbon, nitrogen and oxygen obtained by the method disclosed in Japanese Patent Laid-Open No. 60-235077. Can be mentioned. Effectively, the amount of silicon carbide in the matrix phase is 3-25% by weight, preferably 5-20% by weight.

On the other hand, the raw material for the disperse phase has been conventionally marketed a) silicon carbide particles having an average particle size of 5 to 50 μm, and / or b) a short axis of 0.05 to 3.0 μm.
m, silicon carbide whiskers having an aspect ratio of 5-300 can be used. In the present invention, the amount of the dispersed phase depends on the amount of silicon carbide in the matrix phase, but is generally 5
-40% by weight, preferably 10-30% by weight is effective.

These powders are well mixed with a sintering aid which forms a liquid phase during sintering and, if necessary, a molding binder and the like. As the sintering aid, any of those conventionally used for silicon nitride and silicon carbide can be used.For example, B, C, MgO, Al ₂ O ₃ , Y ₂ O ₃ , AlN, ZrO ₂ , S
Examples thereof include iO ₂ , CrO ₂ , Sc ₂ O ₃ , HfO ₂ , and other lanthanum-based oxides. These can be added not only as a simple substance but also as a carbonate, a nitrate, an alkoxide, or an amorphous state. At least one of these sintering aids is mixed with the above-mentioned raw material powder, and the amount used is usually 0.1 to 20 weight.
It is in the range of%.

Among these sintering aids, Y ₂ O ₃ is effective in enhancing the strength characteristics of the sintered body, and in the present invention,
It is preferred to add 0.5-15% by weight, preferably 2-10% by weight. During the heat treatment process of the present invention, this Y ₂ O ₃ moves to the surface of the sintered body by diffusion, forms a solid solution with the oxidation product on the surface of the composite sintered body, and also forms grain boundaries inside the sintered body. It forms a crystal phase with high heat resistance.

The mixing method may be any conventionally used dry method or wet mixing method. In the case of hot press sintering, this mixed powder is directly filled in a die to be sintered, and in other cases, it is molded by a method such as die molding or injection molding, and the next sintering step is performed.
As the sintering method, a normal atmospheric pressure sintering, a gas pressure sintering, or a conventionally practiced method such as hot pressing or HIP can be applied as it is.

The silicon nitride-silicon carbide composite sintered body obtained as described above is heat treated according to the method of the present invention,
After that, the surface is removed by grinding. That is, the above-mentioned silicon nitride-silicon carbide composite sintered body was heat-treated at 1300 to 1600 ° C. in an oxidizing atmosphere, and then the surface was treated with 5-200
Remove 0 μm.

The heat treatment in the present invention is carried out in an oxidizing gas atmosphere such as oxygen or air, or in a gas stream. The heat treatment conditions should be appropriately selected depending on the size of the sintered body to be treated, the sintering aid used, or the treatment atmosphere, but generally the treatment temperature is 1300 to
1600 ° C, preferably 1400 to 1550 ° C, treatment time 1 to 48
Time is chosen. This heat treatment may be carried out either under normal pressure or under pressure.

When heat treatment is performed according to the present invention, the following changes occur in the sintered body. That is, inside the sintered body, a part of the sintering aid component existing in the grain boundary layer changes to a crystal phase having high heat resistance. In addition, a layer having a hue different from that of the inside is formed on the surface of the sintered body. This hue is greenish gray inside, whereas the surface is dark greenish gray or black. It is speculated that this is because silica is generated on the surface by oxidation, or the sintering aid component accompanying diffusion reacts with silica and silicon nitride components to form a complex oxide layer of crystalline or vitreous material. .

For example, Y₂O₃As a sintering aid
According to the present invention, a silicon nitride-silicon carbide composite sintered body
When heat treated, the surface of the sintered body turns black and
The crystalline yttria as a result of the diffusion of the ions of
Ummdisilicate (Y₂O₃2 SiO ₂) Is generated or silicon nitride
Crystalline cristobalite by oxidation of silicon and silicon carbide
(SiO₂) Or silica-containing glass phase is formed.

The thickness of this oxide layer is usually 5 μm or more, though it depends on the heat treatment conditions.
After heat treatment for a long time, the thickness of the oxide layer reaches about 10 μm. At this time, in a part of the surface of the sintered body, the oxidation progresses rapidly due to the non-uniform oxidation, and the surface is exposed to cause variations in strength.

Therefore, in the present invention, the surface of the heat-treated sintered body is removed by grinding. By this grinding, the roughened portion of the surface is removed, and the variation in strength can be reduced. With this grinding, the color of the surface of the sintered body gradually changes from black to dark greenish gray, and finally becomes greenish gray which is the color inside the sintered body. It is not preferred to completely remove the layers that differ. This is because the fracture toughness of the surface is higher as it is closer to the oxidized surface. That is, the fracture toughness of the surface of the sintered body decreases as the grinding amount increases, and finally becomes the same as the internal fracture toughness value.

Therefore, although the amount of grinding of the surface layer depends on the required roughness of the surface and the size of the cutting tool, it is preferable to keep the amount of grinding to the minimum level in which variations in strength are suppressed. That is, the grinding amount in the present invention is usually 5-2000 μm.
Range, preferably 10-200 μm.

The sintered body obtained by the method of the present invention as described above is a composite sintered body having an oxide layer containing silica on the surface and / or a layer having a hue different from that of the inside.
Since this sintered body has a small variation in strength and the fracture toughness of the surface is higher than that of the inside, it exhibits more excellent fracture resistance and wear resistance as a cutting tool.

As a concrete method for removing the surface of the sintered body, when the member is a flat surface, a surface grinder is used.
When the shape is complicated, NC lathe or barrel polishing is used.

The following examples show one example of the present invention, and are not limited to these as long as they do not exceed the gist of the present invention. In the present invention, the room temperature strength test piece was performed with a size of 3 × 4 ×> 36 mm, and the strength test was performed with a 4-point bending strength, an outer span of 30 mm, an inner span of 10 mm and a crosshead speed of 0.5 mm / min. For the fracture toughness of the surface of the sintered body, after polishing the surface of the sintered body with 3 μm or 1 μm diamond paste, press the indenter (load 20).
kg, holding time 20 seconds).

Examples 1-5, Comparative Examples 1 and 2 As the matrix phase, silicon containing 3.0, 5.1% by weight of carbon (corresponding to 10 vol% and 17 vol% of silicon carbide),
Amorphous powder consisting of carbon, nitrogen and oxygen and having an average particle size of 1 μm or less (Examples 1-4 and Comparative Examples 1 and 2) or an amorphous powder having a carbon content of 0.5% by weight and having an average particle size of 0.3 μm. β-S
What added iC powder in the ratio shown in Table 1 (Example 5) was made into the raw material powder. On the other hand, as the dispersed phase, silicon carbide powder or silicon carbide whiskers shown in Table 1 (diameter: 0.1-1.
0 μm, aspect ratio: 50-300) was used. As a sintering agent to produce the raw material and the liquid phase of the matrix phase and the dispersed phase, Y ₂ O ₃ after the 8 wt% was wet mixed and dried in ethanol, 1750 ° C. at a pressure of nitrogen gas 350 kg / cm ² The hot press sintering was performed for 4 hours. The obtained sintered body was heat-treated in air at 1500 ° C. for 2 hours to obtain a test piece whose surface was ground by a predetermined amount. Further, the same hot press sintering was performed to obtain a test piece that was ground without heat treatment and a test piece that was not ground after heat treatment. (Comparative examples 1 and 2)

The surface of the non-heat-treated sintered body is greenish gray, and in X-ray diffraction, in addition to silicon nitride and silicon carbide, Si ₃ Y ₂ O ₃ N which is a reaction product of yttrium oxide and silica or silicon nitride. ₄ , Si ₃ NY ₅ O ₁₂ , Y ₃ SiO ₅ , Y ₂ Si ₂ O ₇
A small amount was observed.

On the other hand, the surface of the sintered body which has been subjected to the heat treatment has a dark dark greenish gray color, and X-ray diffraction shows that yttrium disilicate (Y ₂ O ₃ 2SiO) is used in addition to silicon nitride and silicon carbide.
₂ ) and cristobalite (SiO ₂ ) crystal phases were strongly observed. In addition, the inside of this sintered body has the same hue as that of the non-heat-treated sintered body, and Si ₂ N ₂ Y ₄ O ₇ is contained in the produced phase in addition to the produced phase observed in the unheated sintered body. Admitted.

Test pieces 15 were obtained from the various sintered bodies obtained.
The room-temperature average bending strength by the measurement of the book, the Weibull coefficient (m) as an index of the variation in strength, and the fracture toughness of the surface of the sintered body were obtained. The results are shown in Table 1.

[0032]

[Table 1] Actual 1 Actual 2 Actual 3 Actual 4 Actual 5 Ratio 1 Ratio 2 ─────────────────────────────── Matrix Phase SiC amount (vol%) 10 10 17 17 17 10 17 Dispersed phase (powder) Average particle size 10 18 10 Addition amount (vol%) 20 15 20 Dispersed phase (whisker) addition amount (vol%) 20 15 15 15 ─ ────────────────────────────── With or without heat treatment With Yes With With With Without With Cutting amount (μm) 20 20 20 20 20 20 0 Sintered body properties Room temperature strength 115 121 127 120 112 103 85 (kg / mm ² ) Weibull coefficient 14.2 16.7 15.0 17.0 15.5 8.7 9.2 Fracture toughness (MPa ・ m ^1/2 ) 8.7 8.4 8.2 9.0 8.5 7.3 7.7 ── ───────────────────────────── In the table, “actual” indicates the example and “ratio” indicates the comparative example.

Examples 6 and 7, Comparative Examples 3 and 4 The sintered bodies obtained in Examples 1 and 4 and Comparative Example 2 were treated with SN.
GN 120408 shaped throw-away tip. Further, a turning test of a dry cast iron including a commercially available silicon nitride cutting tip of the same shape (Comparative Example 4) was performed under the following conditions to compare the flank wear width (VB) and the life. The results are shown in Table 2. Work Material: FC30 Cutting Speed: 400 m / min Depth of Cut: 1.5 mm Feed: 0.3 mm / min Cutting Time: <40 min

[0034]

[Table 2] Actual 6 Actual 7 Ratio 3 Ratio 4 ─────────────────────────────── Chip material Actual 1 Actual 4 ratio 2 Silicon nitride VB (mm) 0.42 0.35 − − Lifetime (min)> 40> 40 30 12 Remark Not missing Not missing Not missing ───────────────────── ───────────

Examples 8 and 9, Comparative Examples 5 and 6 Using the same throw-away inserts as those of Examples 6 and 7 and Comparative Examples 3 and 4, a wet Inconel turning test was conducted under the following conditions, and the boundary The wear width (VN) was compared. The results are shown in Table 3. Work Material: Inconel 718 Cutting Speed: 180 m / min Cutting Depth: 1.0 mm Feed: 0.1 mm / min Cutting Time: 3 min (Below Margin)

[0036]

[Table 3] Actual 8 Actual 9 Ratio 5 Ratio 6 ───────────────────────────── Chip material Actual 1 Actual 4 Ratio 2 Nitriding Silicon VN (mm) 0.55 0.42 0.80-Remark No loss No loss No loss ───────────────────────────────

[0037]

EFFECTS OF THE INVENTION The silicon nitride-silicon carbide composite cutting tool obtained by the present invention has a small variation while maintaining excellent strength and is excellent in fracture toughness. Therefore, it can be used not only for cast iron but also for a wide range of materials such as heat-resistant alloys as a cutting tool having a longer life than conventional silicon nitride tools.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C04B 35/58 X

Claims (3)

[Claims] 1. An average particle size of 1 μm at a grain boundary of silicon nitride particles.
The following silicon carbide particles are present and several nm to several hundreds n
a matrix phase composed of silicon nitride-silicon carbide having a fine structure in which m silicon carbide particles are dispersed in silicon nitride particles, and a) silicon carbide particles having an average particle size of 5 to 50 μm,
And / or b) a silicon nitride-silicon carbide composite sintered body comprising a dispersed phase of silicon carbide whiskers having a minor axis of 0.05 to 3.0 μm and an aspect ratio of 5-300, and A silicon nitride-silicon carbide composite ceramics cutting tool having an oxide layer containing silica and / or a layer having a hue different from that of the inside. 2. Yttrium oxide is 2 as a sintering aid.
The silicon nitride-silicon carbide composite ceramic cutting tool according to claim 1, wherein the cutting tool is added in an amount of not less than wt%. 3. An average particle size of 1 μm at a grain boundary of silicon nitride particles.
The following silicon carbide particles are present and several nm to several hundreds n
a matrix phase composed of silicon nitride-silicon carbide having a fine structure in which m silicon carbide particles are dispersed in silicon nitride particles, and a) silicon carbide particles having an average particle size of 5 to 50 μm,
And / or b) a silicon nitride-silicon carbide composite sintered body consisting of a dispersed phase of silicon carbide whiskers having a minor axis of 0.05-3.0 μm and an aspect ratio of 5-300 in an oxidizing atmosphere at 1300 to 1600. Heat treatment at ℃, and then the surface
A method for manufacturing a silicon nitride-silicon carbide composite ceramics cutting tool, characterized by removing 5-2000 μm.