JP2000044352A - High toughness ceramic sintered body - Google Patents

Abstract

(57) Abstract: Provided is 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. SOLUTION: Al is 1.5 to 10 mol in terms of Al ₂ O _3.
%, Any of Ti carbide, nitride, carbonitride 30 ~ 80
mol%, the balance being silicon nitride and Group 3a element (RE) in the periodic table
Is 1 to 10 mol% with respect to silicon nitride in terms of RE ₂ O ₃ ,
Compressive residual stress applied to silicon nitride is 100MPa ~ 1000MPa, Vickers hardness is 15 ~ 18GPa, fracture toughness value is 8 ~ 15MPam
A high-toughness ceramic sintered body characterized in that it is ^1/2 .

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, chipping resistance, and wear resistance, and more particularly to a high-toughness sintered body suitable for cutting cast iron. Things.

[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 often used particularly as a cutting tool.

As a sintering aid for silicon nitride, a system containing an oxide of an element of Group 3a of the periodic table such as Y ₂ O ₃ and aluminum oxide, and a system containing magnesium oxide, silicon oxide, and aluminum oxide are given. 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.

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

[0008]

Means for Solving the Problems The present inventors have conducted various studies on such problems and found that the hardness and toughness of the sintered body can be increased by dispersing particles of the Ti compound in the sintered body. I got When about 40 mol% of a Ti compound is added, RE ₂ O ₃ or Al ₂ O ₃ element (RE) oxide of the periodic table can be used.
It has been found that the wear resistance as a tool can be improved even when additives such as ₂ O ₃ are added in a large amount to some extent. As a result of further study, 1.5 to 10 mol of Al was converted to Al ₂ O _3.
%, Any of Ti carbide, nitride, carbonitride to 30%
80 mol%, with the balance being silicon nitride and group 3a elements of the periodic table (R
E) is 1 to 10 mol% based on silicon nitride in terms of RE ₂ O _3.
By adding and baking at 1500 ° C or more, it is dense and 100MPa
It has been found that a compressive residual stress of up to 1000 MPa can be generated and the fracture toughness value and hardness of the sintered body are drastically improved. Further, when the sintered body of the present invention is coated with a hard phase composed of at least one selected from carbides, nitrides, carbonitrides and Al ₂ O _{3 of} Groups 4a, 5a and 6a of the periodic table, the resistance as a tool is improved. The inventors have found that the abrasion property is further improved, and have reached the present invention.

That is, the high-toughness ceramic sintered body of the present invention contains 1.5 to 10 mol% of Al in terms of Al ₂ O ₃ , and 30 to 80 mol% of any of carbides, nitrides and carbonitrides of Ti.
The remainder is silicon nitride and RE of the Periodic Table Group 3a (RE).
It is characterized in that the content is 1 to 10 mol% with respect to silicon nitride in terms of ₂ O ₃ and the compressive residual stress applied to the silicon nitride particles is 100 to 1000 MPa. The fracture toughness of the sintered body is 8 to 15MPa.
am ^1/2 , Vickers hardness is 15-18 GPa. Further, the surface of the sintered body is coated with a hard phase composed of at least one selected from carbides, nitrides, carbonitrides, and Al ₂ O _{3 of} Groups 4a, 5a, and 6a of the periodic table.

As a manufacturing method, after firing, Al is changed to Al ₂ O ₃
1.5 to 10 mol% in conversion, 30 to 80 mol% of carbides, nitrides, and carbonitrides of Ti, and the balance of silicon nitride and Group 3a element (RE) of the periodic table, 1 to 1 in terms of RE ₂ O _3. -10
mol%, the compressive residual stress on silicon nitride after firing is 20 ~ 10
It can be obtained by firing a molded article blended to have a pressure of 00 MPa in a nitrogen atmosphere. For the coating of the surface hard phase, a CVD method or a PVD method is used.

[0011]

Embodiments of the present invention will be described below.

In the high-toughness ceramic sintered body of the present invention, Al is 1.5 to 10 mol% in terms of oxide, particularly 2 to 8 mol%.
mol%, 30 of Ti carbide, nitride or carbonitride
A composition in which hard particles are dispersed in an amount of about 80 mol%, and the remainder contains silicon nitride and a Group 3a element of the periodic table in an amount of 1 to 10 mol%, particularly 2 to 8 mol%, of silicon nitride in terms of oxide. It is desirable that it is a thing. In addition, carbides, nitrides, carbonitrides and Al ₂ O ₃ of the periodic table 4a, 5a, 6a group
It is desirable to coat with at least one hard phase selected from the group consisting of:

Here, the composition of the sintered body is limited as described above. If Al is less than 1.5 mol%, a dense body cannot be obtained when a Ti compound is added. This is because high-temperature strength and reaction resistance are deteriorated, and performance as a tool is inferior. Dispersing 30 to 80 mol% of hard particles of any one of Ti carbide, nitride and carbonitride causes residual stress due to the difference in thermal expansion coefficient between the silicon nitride matrix and the Ti compound. To make it happen. As a result, the fracture toughness is improved, and the wear resistance and fracture resistance of the tool are improved. It is particularly desirable that the amount of the Ti compound is 35 to 75 mol%. This is because Ti carbide, nitride, carbonitride is 30 mol%
Below this, the residual stress is small, so that the effect of toughening is small and the hardness is low. On the other hand, if the content is 80 mol% or more, a dense sintered body cannot be obtained, and the properties as a tool are lacking. Periodic Table 3
When the group a element is more than 10 mol% in terms of oxide oxide,
The hardness of the sintered body decreases, the wear resistance as a tool deteriorates,
Group 3a element of the periodic table is 1 equivalent to silicon nitride in terms of oxide.
If the amount is less than mol%, a dense body cannot be obtained, and the strength of the sintered body decreases.

The reason why the surface coating layer is limited to coating with a hard phase composed of at least one selected from the group consisting of carbides, nitrides, carbonitrides and Al ₂ O _{3 of} Groups 4a, 5a and 6a of the periodic table is as follows. Since carbides, nitrides, carbonitrides and Al ₂ O _{3 of} the Periodic Table 4a, 5a, 6a group have high hardness, excellent reactivity with the work material and excellent wear resistance can be achieved. is there.

According to the present invention, by dispersing and containing Ti carbides, nitrides, and carbonitride hard particles, a compressive residual stress is generated and generated, so that the progress of cracks can be suppressed, and The hardness is also high because hard particles are dispersed.

Further, according to the present invention, Ti carbides, nitrides, and carbonitride hard particles are dispersed and constituted by 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 No. 3 used in the present invention is used.
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 the silicon nitride powder, and a ball mill or the like is used. Mix with. These additional components are prepared so that the final sintered body composition falls within the above-mentioned range. The silicon nitride powder used, reduction nitriding method, a direct nitriding method manufactured α-type by like, may be either β-type, BET specific surface area of 5 m ² / g or more, the amount of oxygen 0.7 to 2 wt% impurities Powders are suitable. The mixture mixed as described above is formed into an arbitrary shape by desired molding means, for example, a die press, a cold isostatic press, an extrusion molding, a casting molding, an injection molding and the like. The firing is performed in a non-oxidizing atmosphere at 1600 to 2000 ° C. The firing temperature at this time is 160
If the temperature is lower than 0 ° C., it is difficult to sufficiently densify,
If the temperature exceeds 00 ° C., problems such as abnormal grain growth of crystals and decomposition of silicon nitride to roughen the surface will 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.

It is desirable to use the CVD and PVD methods for the surface coating.

[0021]

EXAMPLE A silicon nitride powder (BET specific surface area: 10 m ² / g, impurity oxygen content: 1.0% by weight) and various group 3a element oxides of the periodic table shown in Table 1 and SiO ₂ were used as raw material powders. The mixture was prepared at the ratio shown in Table 1, and a molding binder was added thereto and mixed using a silicon nitride ball, and ² ton / cm ²
Press molding.

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, a Group 3a element (RE) of the periodic table,
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 residual stress was determined by an X-ray residual stress measuring method.

Further, as the characteristics of the sintered body, JISR 16
Vickers hardness according to 10, IF of JISR 1607
The fracture toughness was determined by the method, and the results are shown in Table 1.

The surface of the sintered body was coated, and the results are shown in Table 2.
It was shown to.

Further, as a cutting test, a cutting tool produced by shaping into a CNGN160412 tool shape and firing in the same manner as described above was used under the following cutting conditions Work material FC250 Cutting speed 600 m / min Feed 0.5 mm / rev 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 test was performed by face milling under the following conditions using a cutting tool machined into the shape of SNGN120408.

Workpiece FCD 450 (125 × 300 mm shape) Cutting speed 600 m / min Feed 0.5 mm / tooth Cutting depth 2.0 mm Face milling is performed under the above conditions, and the cutting time until chipping is shown in Tables 1 and 2. did.

[0030]

[Table 1]

According to the results shown in Table 1, in Samples Nos. 8 to 13 whose sintered body composition deviates from the range of the present invention, the hardness is 14.3.
It was lower than 0 GPa and the fracture toughness was lower than 8 MPam ^1/2 . In the cutting test, wear width 0.2m
m or a defect occurred within 20 passes, resulting in the tool life.

On the other hand, each of the samples of the present invention had a hardness of 15 GPa or more and a fracture toughness of 8. It exhibited high mechanical properties of 0 MPam ^1/2 or more, and even in a high-speed cutting test of cast iron, it exhibited non-destructive performance even at a wear width of 0.15 mm or less and 20 pass. 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.

[0033]

[Table 2]

According to the results shown in Table 2, carbides, nitrides, carbonitrides and Al ₂ Os belonging to groups 4a, 5a and 6a of the periodic table were added to the sintered body of the present invention.
Abrasion resistance could also be improved by coating with at least one hard phase selected from ₃ above.

[0035]

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

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C04B 35/58 101 C23C 16/30 C23C 16/30 C04B 35/56 SF term (Reference) 3C046 FF02 FF04 FF09 FF11 FF13 FF33 FF37 FF40 FF42 FF47 4G001 BA03 BA08 BA25 BA32 BA38 BA57 BA73 BB03 BB08 BB25 BB32 BB38 BB57 BB73 BC13 BC23 BC42 BC43 BD12 BD16 BD18 BE26 4K030 BA02 BA18 BA36 BA38 BA41 BA42 BA55 CA05 LA04

Claims (2)

[Claims] (1) Al is 1.5 to 10 mol in terms of Al ₂ O _3.
%, Any of Ti carbide, nitride, carbonitride 30 ~ 80
mol%, with the balance being silicon nitride and Group 3a elements of the periodic table (R
E) is 1 to 10 mol% based on silicon nitride in terms of RE ₂ O _3.
The compressive residual stress applied to silicon nitride is 100 MPa to 1000 MPa
, Vickers hardness is 15-18GPa, fracture toughness value is 8-15M
A high-toughness ceramic sintered body characterized by being Pam ^1/2 . 2. Carbides, nitrides of groups 4a, 5a, 6a of the periodic table,
_2. The high-toughness ceramic sintered body according to claim 1, wherein the sintered body is coated with a hard phase comprising at least one selected from carbonitrides and Al ₂ O ₃ .