JPH11335168A - Highly tough ceramic-based sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a ceramic sintered compact having a high hardness and a high toughness and capable of manifesting high abrasion and high fracture resistances especially for cutting cast iron at a high speed. SOLUTION: This highly tough ceramic sintered compact is obtained by including Al in an amount of 1.5-10 mol.% expressed in terms of Al2 O3 , a carbide, a nitride and a carbonitride of Ti in an amount of 30-80 mol.% and the balance of silicon nitride and a group 3a element (RE) of the periodic table in an amount of 1-10 mol.% expressed in terms of RE2 O3 and based on the silicon nitride. Furthermore, the ratio of the peak intensity ITi CN of the (200) face in an X-ray diffraction(XRD) of TiCx Ny [(x)+(y)]<=1; 0<=(x) and (y)<=1} and the peak intensity ISN of the (200) face of the silicon nitride is 0.5<=ITi CN/ ISN<=3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic sintered body having excellent thermal shock resistance, fracture resistance, and wear resistance for cutting tools, and more particularly to a high-toughness ceramic sintered body suitable for cutting cast iron. It is about the body.

[0002]

2. Description of the Related Art In recent years, ceramic sintered bodies used as cutting tools include alumina, alumina with ZrO ₂ , Ti
There are ceramics to which C and the like are added and those obtained by adding various sintering aids to silicon nitride. Among them, silicon nitride ceramics has the highest toughness among ceramics, and is particularly often used as a cutting tool.

As a sintering aid for silicon nitride, Y ₂ O ₃
For example, a system containing an oxide of an element belonging to Group 3a of the periodic table and aluminum oxide, and a system containing magnesium oxide, silicon oxide, and aluminum oxide are mainly used.

Recently, a silicon nitride based sintered body using these sintering aids coated with a thin film of titanium nitride or aluminum oxide to improve wear resistance has also been disclosed in JP-B-62-13430. It is proposed in Japanese Patent Application Laid-Open No. 2-116401.

[0005]

In recent years, demands for heavy cutting such as high-speed machining and high-feed machining have been increasing in order to improve productivity in various cutting fields, and the use conditions of cutting tools have been increasing year by year. And high feed rate are progressing.
For this reason, cutting tools are required to have even higher wear resistance and chipping resistance.

However, a conventional silicon nitride sintered body is
In the case of a tool material in which a hard layer is adhered only to the surface using a technique such as PVD, high-speed and high-feed cutting of cast iron is performed, specifically, at a speed of 400 m / min or more and a feed of 0.5 mm / rev.
(Mm / blade) When cutting under the above conditions, the coating peels off and does not have sufficient wear resistance and chipping resistance, resulting in chipping, chipping, abnormal wear, etc. of the cutting edge, resulting in a short life. Was something.

Further, when these methods are used, there is a problem that a coating step is required in the production of a tool, so that the cost is increased.

Accordingly, an object of the present invention is to provide a ceramic sintered body having high hardness and high toughness, and particularly, capable of exhibiting high wear resistance and chipping resistance for high-speed cutting of cast iron. Is what you do.

[0009]

Means for Solving the Problems The present inventor has conducted various studies on such problems and found that the hardness and toughness of the sintered body can be increased by dispersing Ti compound particles in the sintered body. I got When a Ti compound is added in an amount of about 30 to 80 mol%, an oxide of RE ₃ O element (RE) of the periodic table, RE ₂ O
It has been found that the wear resistance as a tool can be improved even when additives such as ₃ and Al ₂ O ₃ are added in a relatively large amount. As a result of further study, Al was converted to Al ₂ O ₃ in the range of 1.5 to 10
Mol%, Ti carbide, nitride, carbonitride 30-80mol%,
The remainder is composed of silicon nitride and Group 3a element (RE) of the periodic table.
It has been found that by setting the content to 1 to 10 mol% based on silicon nitride in terms of E ₂ O ₃ , the fracture toughness value of the sintered body is dramatically improved, and the present invention has been achieved. Furthermore, in such a sintered body, the XR of TiCxNy (x + y ≦ 1, 0 ≦ x, y ≦ 1)
(200) plane peak intensity I _TiCN and silicon nitride (200)
It has been found that the peak intensity I _{SN of the} surface is particularly preferably 0.5 ≦ I _TiCN / _ISN ≦ 3.

That is, it has been found that the high toughness ceramic-based sintered body of the present invention improves the hardness and toughness of the sintered body by dispersing particles of the Ti compound in the sintered body. As a result of further extensive studies, 1.5 to 1 of Al in terms of Al ₂ O ₃
0 mol%, 30 to 80 mol of Ti carbide, nitride and carbonitride
%, With the balance being silicon nitride and Group 3a elements of the periodic table (RE)
Is 1 to 10 mol% based on silicon nitride in terms of RE ₂ O _3.
The XRD of TiCxNy (x + y ≦ 1, 0 ≦ x, y ≦ 1) is (200)
The peak intensity I _{TiCN of the} plane and the peak intensity I _SN of the (200) plane of silicon nitride _satisfy 0.5 ≦ I _TiCN / _{IS N} ≦ 3.

As a manufacturing method, after firing, Al is changed to Al ₂ O ₃
1.5 to 10 mol% in terms of a carbide of Ti, a nitride, 30～80Mol% carbonitride, and the balance silicon nitride silicon nitride and the periodic table group 3a elements of the (RE) in terms _of RE ₂ O ₃ 1 to
10 mol%, X of TiCxNy (x + y ≦ 1, 0 ≦ x, y ≦ 1)
(200) plane peak intensity I _TiCN and silicon nitride (200)
A high-toughness ceramic sintered body characterized by being obtained by firing in a nitrogen atmosphere a molded product blended so that the surface peak intensity I _SN becomes a composition of 0.15 ≦ I _TiCN / _{IS N} ≦ 3. is there.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The high-toughness ceramic sintered body according to the present invention contains 1.5 to 10 mol%, particularly 2 to 8 mol%, of Al in terms of oxide, and the balance is silicon nitride and group 3a of the periodic table. Element is 1 to 10 mol% based on silicon nitride in terms of oxide,
In particular, a composition containing 2 to 8 mol% is desirable.

Here, the reason why the composition of the sintered body is limited as described above is that if Al is less than 1.5 mol%, a dense body cannot be obtained when a Ti compound is added, and if Al is more than 10 mol%, the sintered body is not formed. This is because the high-temperature strength and the reaction resistance are deteriorated, and the performance as a tool is inferior. In addition, Ti carbides, nitrides and carbonitrides
~ 80 mol%, the hard particles are dispersed on the surface hardness,
This is for improving toughness and improving wear resistance and fracture resistance as a tool, and is particularly preferably 35 to 75 mol%. This is because if Ti carbide, nitride, carbonitride is less than 30 mol%, the effect of particle dispersion hardens the sintered body, the effect of toughening is small, and if it is more than 80 mol%, a dense sintered body cannot be obtained. This is because the characteristics as a tool are lacking. If the Group 3a element of the periodic table is more than 10 mol% in terms of oxide oxide, the hardness of the sintered body is reduced, and the wear resistance as a tool is deteriorated. If the content is less than 1 mol% with respect to silicon nitride, a dense body cannot be obtained and the strength of the sintered body decreases.

According to the present invention, the development of cracks can be suppressed and the particles harder than the matrix are dispersed by dispersing and containing Ti carbide, nitride and carbonitride hard particles. So high hardness.

Further, according to the present invention, Ti carbides, nitrides, and carbonitride hard particles are dispersed and composed of silicon nitride crystals and a grain boundary phase existing between the crystals.
It contains at least an element of Group 3a of the periodic table. The grain boundary phase may be amorphous, but is preferably crystallized, and the crystal phase may be apatite, YA
It is preferable that at least one of M, wollastonite, disilicate and monosilicate is mainly used.

In the present invention, the periodic table 3
Group a elements include Y, Sc, Yb, Er, Dy, H
o, Lu and the like. Among them, Er, Y
b and Lu are good.

Next, as a production method of the present invention, a powder of a Group 3a element (RE) oxide of the periodic table and Al ₂ O ₃ are added as additional components to a silicon nitride powder. And mix. These additional components are prepared so that the final sintered body composition falls within the above-mentioned range. As the silicon nitride powder to be used, any of α-type and β-type manufactured by a reduction nitriding method, a direct nitriding method, or the like may be used. The BET specific surface area is 5 m ² / g or more, and the amount of impurity oxygen is 0.7 to ² % by weight.
Is suitable. The mixture mixed as described above is formed into a desired shape by a desired forming means, for example, a die press, a cold isostatic press, an extrusion molding, a casting molding, an injection molding or the like.

The firing is performed in a non-oxidizing atmosphere at 1600 to 2000 ° C. If the firing temperature at this time is lower than 1600 ° C., it is difficult to sufficiently densify. If the firing temperature is higher than 2000 ° C., problems such as abnormal grain growth of crystals and decomposition of silicon nitride and roughening of the surface occur.

The firing method includes normal pressure firing, nitrogen gas pressure firing at 2 atm or more of nitrogen gas, hot press firing, and the like under a pressure of 1,000 atm after these firings so that silicon nitride is not decomposed. It can be further densified by hot isostatic firing. Especially 1700-19
It is preferable to perform firing in a non-oxidizing atmosphere containing nitrogen gas at 50 ° C. and 2 atm or more.

[0020]

EXAMPLE 1 Silicon nitride powder (BET specific surface area: 10 m ² / g, impurity oxygen content: 1.0% by weight) as raw material powder and Table 1
The mixture was prepared at a ratio shown in Table 1 using an oxide of an element belonging to Group 3a of the Periodic Table shown in Table 2 and SiO2, and a binder for molding was added thereto and mixed using a silicon nitride ball.
Press molding was performed at a pressure of ² .

Further, cold isostatic pressing was performed at 3 ton / cm ² to obtain a molded product. The molded body was fired at a nitrogen gas pressure of 30 atm at a temperature shown in Table 1 for 3 hours to obtain a sintered body.

The obtained sintered body was analyzed by ICP emission spectroscopy to determine Si, Group 3a element of the periodic table (RE),
The amounts of Al and Ti were determined, Si was converted to Si ₃ N ₄ , RE was converted to RE ₂ O ₃ , Al was converted to Al ₂ O ₃ , and Ti was converted to Ti carbides, nitrides and carbonitrides, and the composition ratio was calculated. I asked. Further, the strength was measured by X-ray diffraction measurement of Ti carbides, nitrides, and carbonitrides, and was compared with the strength of silicon nitride similarly obtained by X-ray diffraction.

Further, as the characteristics of the sintered body, JIS R16
Vickers hardness according to No. 10 and fracture toughness according to the IF method according to JIS R1607 were determined, and the results are shown in Table 1.

Further, as a cutting test, a cutting tool produced by shaping and firing into a CNGN160412 tool shape in the same manner as described above was used. The following cutting conditions were used. Work material FC250 Cutting speed 600 m / min Feed 0.5 mm / rev Depth of cut Dry turning was performed at 2.0 mm 2, and the wear width after cutting for 20 minutes was measured.

As a cutting test, a face milling test was performed using a cutting tool machined into the shape of SNGN120408 under the following conditions.

Work Material FCD 450 (shape of 125 × 300 mm) Cutting speed 600 m / min Feed 0.5 mm / blade Cutting 2.0 mm Face milling was performed under the above conditions, and the cutting time up to chipping is shown in Table 1.

[0027]

[Table 1]

As is clear from Table 1, in Samples Nos. 8 to 13 whose sintered body compositions deviate from the range of the present invention, the hardness is 1 unit.
It was lower than 4.0 GPa and the fracture toughness was lower than 8 MPam ^0.5 . In the cutting test, the wear width was set to 0.
It became 2 mm or more, or chipping occurred within 20 passes, resulting in the tool life.

On the other hand, all of the samples of the present invention show high mechanical properties with a hardness of 15 GPa or more and a fracture toughness of 8.0 MPam ^0.5 or more, and even in a high-speed cutting test of cast iron, a wear width of 0.15 mm or less and a wear width of 20 pass. Undeleted performance was shown. As described above, the silicon nitride sintered body of the present invention has high wear resistance and chipping resistance in cutting cast iron, and can extend the life of the tool.

[0030]

As described above in detail, the ceramic sintered body of the present invention has high hardness and high toughness by dispersing Ti compound hard particles in the sintered body.
Particularly in cutting cast iron, it has excellent wear resistance and high fracture resistance. Thereby, a long-life cast iron cutting tool can be provided at low cost.

[Brief description of the drawings]

FIG. 1 shows an example of an X-ray diffraction result of a ceramic sintered body of the present invention.

Claims (2)

[Claims] 1. Al is 1.5 to 10 mol% in terms of Al ₂ O ₃ , 30 to 80 mol% of carbides, nitrides and carbonitrides of Ti, and the remainder is silicon nitride and a group 3a element of the periodic table (RE ) To RE ₂
High toughness ceramic sintered body characterized in that it is 1 to 10 mol% based on silicon nitride in terms of O ₃ . 2. The XR of TiCxNy (x + y ≦ 1, 0 ≦ x, y ≦ 1)
(200) plane peak intensity I _TiCN and silicon nitride (200)
2. The high toughness ceramic sintered body according to claim 1, wherein the peak intensity I _{SN of the} surface is 0.5 ≦ I _TiCN / _{IS N} ≦ 3.