JPS61186276A - Coated silicon nitride sintered body - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a tough silicon nitride sintered body having extremely high wear resistance and suitably used as cutting tool parts.

Conventional technology Silicon nitride sintered bodies are used in so-called ceramic tool parts such as conventional aluminum oxide, aluminum oxide/titanium carbide sintered bodies, etc.
In addition to the significantly high bending strength at , +c has also been greatly improved.

In addition, regarding thermal shock, which is the biggest drawback of ceramic tools, the thermal shock resistance value, which is a guideline, is not only much higher than 16 for silicon nitride and 6.5 for aluminum oxide l, but also higher than that of cemented carbide. It's even more than 13.

However, silicon nitride sintered bodies have poor fracture resistance, which is the biggest drawback of ceramic tool parts, so there is still room for improvement as a cutting tool material.

Furthermore, since the silicon nitride sintered body reacts with steel, the life of the silicon nitride sintered body was extremely short when actually turning the steel.

Taking these drawbacks into account, we cut castings and non-ferrous metals where reaction with the work material is not a problem. Although silicon nitride demonstrated its chipping resistance as expected, it , conventionally used aluminum oxide/
Compared to titanium carbide sintered bodies (hereinafter referred to as black ceramics), they have poorer wear resistance and have a relatively narrower range of use.

As an improvement on this, various coated silicon nitride sintered bodies in which the surface of the silicon nitride sintered body is coated with a thin layer of aluminum oxide or the like, which is harder than silicon nitride, have been proposed and put into practical use.

When we actually cut a casting using coated silicon nitride, which is a silicon nitride sintered body coated with a thin layer of aluminum oxide, we found that it was 1μ
The coating coated with aluminum oxide with a film thickness of There was a shortage. Therefore, based on the expectation that the wear resistance would be improved if the aluminum oxide film was made thicker than 1 μm, we increased the aluminum oxide film thickness to 2 μm and 3 μm. It peeled off and had a shorter lifespan than the untreated one. This was thought to be due to insufficient adhesive strength between the coating film and silicon nitride.

Problems to be Solved by the Invention The purpose of the present invention is to increase the thickness of the aluminum oxide coating by improving the adhesive strength between the aluminum oxide coating and nitrogen and silicon oxide, thereby creating a long-life cutting tool tip. An object of the present invention is to provide coated silicon nitride that can be suitably used.

Measures to solve the problem When we actually coated the surfaces of various ceramic materials with aluminum oxide using the chemical vapor deposition method and investigated the adhesive strength, we found that the materials that had good adhesion to aluminum oxide were:
It has been found that titanium compounds such as titanium carbide and titanium nitride are extremely preferable.

Therefore, when we coated the surface of silicon nitride with titanium carbide and titanium nitride and investigated their adhesive strength with silicon nitride, we found that although it was slightly improved compared to aluminum oxide, it was not sufficient for use. I wanted to.

Tables 1 and 2 show measurement data of adhesive strength using a scratch tester Revtest/Automatic manufactured by LSRH.

In addition, it is considered that the adhesive strength is stronger as the critical load becomes larger.

As is clear from Tables 1 and 2, although the adhesive strength between aluminum oxide and titanium carbide and titanium nitride has been greatly improved, the adhesive strength between silicon nitride and these coating materials is Although it has been improved compared to , it is still not enough.

Here, 1 μm of silicon nitride was applied to the silicon nitride sintered body by chemical vapor deposition.
When the adhesive strength of the coated sample was measured, it was found that the critical load was extremely high at 58.2 N.

Considering these technical findings comprehensively, we have reached the conclusion that a mixture of silicon nitride and titanium nitride is optimal as a material that has good adhesion to aluminum oxide and silicon nitride. (Titanium carbide is judged to be undesirable based on the results shown in Table 2.) When we actually tried making a coated silicon nitride with this structure based on the above idea, we obtained experimental results as expected.
This completes the present invention.

That is, according to the present invention, a composite of silicon nitride and titanium nitride containing 5 to 95% by weight of titanium nitride is added to the surface of a silicon nitride sintered body containing 60 to 99% by weight of silicon nitride from the gas phase. A coated silicon nitride sintered body is provided, which is characterized in that a thin film is coated with a thickness of 0.1 to 10μ, and then aluminum oxide is coated with a thickness of 0.1 to 10μ.

Furthermore, according to the present invention, between the thin film of the composite of silicon nitride and titanium nitride and the thin film of aluminum oxide, Ti and one weight selected from the group consisting of O, N, and C are disposed.
One or more layers of compounds with the elements, the total film thickness is 0.
．． A coated silicon nitride sintered body characterized by being coated with a coating of 1 to 10μ is provided.

Examples of methods for forming a thin film of a composite of silicon nitride and titanium nitride and a thin film of aluminum oxide of the coated silicon nitride sintered body of the present invention include chemical vapor deposition (CVD) and chemical transport (CVT). be.

Function The reason for limiting the chemical composition and film thickness of each part of the coated silicon nitride sintered body of the present invention will be explained below.

■ Content of silicon nitride in silicon nitride sintered body Silicon nitride is extremely difficult to sinter, so oxides such as aluminum oxide, zirconium oxide, yttrium oxide, and magnesium oxide, and nitrides such as titanium nitride and aluminum nitride are used. A sintering aid consisting of is essential. If the content of silicon nitride is less than 60% by weight, characteristics specific to a silicon nitride sintered body cannot be obtained, and if the content is more than 90% by weight, sintering becomes insufficient.

■ Content of titanium nitride in a composite of titanium nitride and silicon nitride If the content of titanium nitride is less than 5% by weight, the adhesive strength with aluminum oxide will be insufficient, and if it is more than 95% by weight, silicon nitride sintering will occur. This is not preferable because the adhesion strength to the body becomes insufficient.

■ If the film thickness of the composite of titanium nitride and silicon nitride is less than 0.1 μm, it is difficult to see the effect of improving the adhesive strength between aluminum oxide and silicon nitride sintered body, whereas the coating with a film thickness of 10 μm or more is not effective. A coating thicker than this is economically undesirable as the silicon nitride becomes saturated and the properties of the silicon nitride are impaired.

(2) Film Thickness of Aluminum Oxide As mentioned above, the purpose of the present invention is to improve the performance of the aluminum oxide-coated silicon nitride sintered body according to the prior art. The coated silicon nitride sintered body of the present invention has significantly improved adhesion strength between aluminum oxide and silicon nitride sintered body compared to conventional products, so that the film thickness of aluminum oxide is 0.5 mm.
If the thickness is 1μ, the coating effect is sufficiently recognized. On the other hand, if the aluminum oxide film has a thickness of 10 μm or more, it is not preferable because destruction occurs within the aluminum oxide film during cutting.

Furthermore, the strength increasing effect in the coated silicon nitride sintered body of the present invention is achieved by adding at least one material selected from the group consisting of titanium, C, N, and O between the titanium nitride/silicon nitride composite film and the aluminum oxide film. If one layer or two or more layers of a compound with one type of element are sandwiched between them, the improvement will be further improved. If the thickness of the intermediate layer is less than 0.1 μm, the effect will not be achieved, and if the thickness is more than 10 μm, destruction will occur within the intermediate film during cutting, which is not preferable.

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

Example 1 A mixed powder of 85% by weight of silicon nitride, 5% by weight of Ulam, and 10% by weight of zirconium oxide was heated to a nitrogen pressure of 1.5.
Sintered by hot pressing at 1800 °C under atmospheric pressure and a load of 400 Kg/cd. The obtained sintered body was cut and ground to obtain a cutting tip having a model number SN GN432.

These sample chips were placed in a quartz vacuum container, and the carbon material in the vacuum container was heated to 1400° C. by high-frequency induction heating from the outside. On the other hand, in this quartz container, 5i
The mixed air flow of C1, TiC1, N2, B2 is I
After flowing for 3 hours under a pressure of 0'Pa, AlC1,,12,
A mixed gas flow of C02 was passed under a pressure of IXIO' Pa for 30 minutes.

After cooling, the sample was cut and the cross section was examined using EPMA.
A composite film consisting of 70% by weight of silicon nitride and 30% by weight of titanium nitride was coated with 2μ, and a thin aluminum oxide film of 3μ was formed thereon.

The sample obtained in this manner is designated as A, and for comparison, a commercially available aluminum oxide/titanium carbide sintered body sample (N B90 S manufactured by Sumiya Electric Industry Co., Ltd.) is designated as B1, a commercially available silicon nitride sintered body sample (Sumiden Electric Industry Co., Ltd.). C1 commercially available aluminum oxide coated silicon nitride sintered body sample (manufactured by Nippon Tokushu Toku Kogyo 5)
P4) was designated as D, and a cutting test was conducted under the following conditions (1).

Cutting conditions (1) Work material FC25 holder
F NIIR-44A Cutting speed 500m/min Feed 0.36mm/rev Depth of cut 2mm (no cutting agent used) Sample A (invention) had 0 flank wear after cutting for 20 minutes.
．． Compared to this, B had flank wear of 0.15 mm after 20 minutes of cutting, and flank wear of C had 0.32 mm of 5 minutes of cutting, beyond which it was no longer possible to cut. D has flank wear of 0.29 after cutting for 20 minutes.
It was mm.

Next, a cutting test was conducted under the following conditions (2).

Cutting conditions (2) Work material FC25 holder
FNIIR-44A Cutting speed: 500 m/min Feed: 0.36 mm/rev Depth of cut: 2 mm (using water-soluble cutting agent) Sample Δ was cut for 20 minutes and flank wear was 0.14 mm.
On the other hand, B broke in 2 minutes due to thermal shock. C was cut for 5 minutes, flank wear was 0.29 mm, and cutting was impossible beyond that, and D was cut for 15 minutes, flank wear was 0.34 mm, and cutting was impossible. This is considered to be because the coating film peeled off.

Next, a cutting test was conducted under the following cutting conditions (3).

Cutting conditions (3) Work material F C251010
0mmX200 cutter DNF4160R (12 blades) Cutting speed 500m/min Feed 2500m/min (0,209mm
/l) (using water-soluble cutting) Sample A had an average flank wear (average of 12 tips) of 0.28 mm after 10 minutes of cutting, while B had an average flank wear of 4.
C was unusable due to breakage in 2 seconds, average flank wear was 0.42 mm after cutting for 10 minutes, and average flank wear of D was 0.45 mm due to peeling of the coating film.

Example 2 A mixed powder of 80% by weight silicon nitride, 14% by weight titanium nitride, and 6% by weight yttrium oxide was embossed, sintered at 1900°C under a nitrogen pressure of 9.5 atm, and then ground. , a cutting tip with model number SNGN432 was created.

This chip was coated with 2μ of a composite film of titanium nitride and silicon nitride in the same manner as in Example 1, and then taken out after cooling.

After that, it was charged into a stainless steel vacuum container and heated to 950℃.
At H2, AlCl2, CO2 mixed gas flow I XIO3P
Under a pressure of a, the film thickness of aluminum oxide is 0.02
Samples of μ, 0.2μ, 2μ, and 20μ were prepared. A cutting test was conducted using the chips E, F, G, and H under the cutting conditions (1) of Example 1.
It could be cut for 14 minutes, G for 19 minutes, but H could only be cut for 48 seconds due to peeling of the coating layer.

Example 3 The same silicon nitride sintered body as in Example 2 was coated with various intermediate layers shown in Table 3, and then coated with 3μ of aluminum oxide. Table 3 shows the results of a cutting test conducted on these chips under the cutting conditions (1) of Example 1.

G Example 4 A silicon nitride sintered body similar to Example 2 was coated with 2μ of a composite film of silicon nitride and titanium nitride similar to Example 1, and then coated with 2μ of titanium carbide, 2μ of titanium nitride, and titanium carbonitride. 2μ,
Chips coated with 2μ of titanium oxycarbide and then coated with 1.5μ of aluminum oxide were designated S, T, U, and V, respectively, and cutting tests were conducted under the cutting conditions 3) of Example 1.

S has an average flank wear of 0.19 mm after cutting for 5 minutes.
T was cut for 5 minutes and the average flank wear was 0.16 mm.
U was cut for 5 minutes and the average flank wear was 0.22 mm.
■ Average flank wear after cutting for 5 minutes, 14n+
It was m.

As explained above, the present invention aims to improve the adhesive strength between silicon nitride and aluminum oxide coating of an aluminum oxide-coated silicon nitride sintered body, and to improve the adhesive strength between silicon nitride and titanium nitride between them. This was achieved by interposing a composite film.

To provide a coated silicon nitride sintered body that has significantly improved adhesive strength of the surface coating of the silicon nitride sintered body, has excellent chipping resistance and wear resistance, and can be suitably used as a long-life cutting tip. It was a success.

Furthermore, as shown in Example 4, Ti was added between the composite film of silicon nitride and titanium nitride and the aluminum oxide coating.
By forming a thin film of a compound of and one or more elements selected from the group consisting of O, N, and C, the wear resistance is further improved.

Claims (6)

[Claims] (1) A silicon nitride sintered body containing 60 to 99% by weight of silicon nitride, and a composite of silicon nitride and titanium nitride formed on the surface of the 0.1 sintered body containing 5 to 95% by weight of titanium nitride.
A coated silicon nitride sintered body comprising a thin film having a thickness of ~10μ and a thin film of aluminum oxide having a thickness of 0.1 to 10μ formed on the composite thin film. (2) The silicon nitride sintered body further includes aluminum oxide,
The coated silicon nitride sintered body according to claim 1, characterized in that it contains at least one of oxides such as zirconium oxide, yttrium oxide, and magnesium oxide, and nitrides such as titanium nitride and aluminum nitride. (3) Claims 1 or 2, characterized in that the thin film of the composite of silicon nitride and titanium nitride and the thin film of aluminum oxide are formed by a chemical vapor deposition method or a chemical transport method. The coated silicon nitride sintered body described above. (4) A silicon nitride sintered body containing 60 to 99% by weight of silicon nitride and a composite of silicon nitride and titanium nitride formed on the surface of the sintered body containing 5 to 95% by weight of titanium nitride.
A thin film with a thickness of ~10μ, and one or more layers of a compound of Ti and one or more elements selected from the group consisting of O, N, and C formed on the composite thin film. There it is,
A coated silicon nitride sintered body characterized by having a thin film having a total thickness of 0.1 to 10 μm and a thin film of aluminum oxide having a thickness of 0.1 to 10 μm formed thereon. (5) The silicon nitride sintered body further includes aluminum oxide,
The coated silicon nitride sintered body according to claim 4, which contains at least one of oxides such as zirconium oxide, yttrium oxide, and magnesium oxide, and nitrides such as titanium nitride and aluminum nitride. (6) a thin film of the above-mentioned composite of silicon nitride and titanium nitride;
The thin film of a compound of Ti and one or more elements selected from the group consisting of O, N, and C and the thin film of aluminum oxide are
The coated silicon nitride sintered body according to claim 4 or 5, characterized in that it is formed by a chemical vapor deposition method or a chemical transport method.