JPH06226509A - Coating cutting tool - Google Patents

Abstract

PURPOSE:To provide a coating cutting tool having a coating layer constructed to be excellent in a breakage resistance and antiwear property compared with a coating layer coated by a chemical deposition method or coating layer processed after coating. CONSTITUTION:In a coated cutting tool provided with a hard coating layer on the surface of a base body 1 made of a cemented carbide member or ceramic member, the density of cracks 4 in the coating layer is discontinuously changed in the sectional direction of the coating layer and the concentration of the cracks in the outer layer part 3 is made smaller than that in the inner layer part 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a cutting tool using a cemented carbide member for a cutting tool or a ceramic member for a cutting tool, which is mainly used for cutting, and has a hard coating layer on the surface.
The present invention relates to a coated cutting tool adapted to withstand high-speed, high-efficiency severe cutting conditions where the cutting temperature easily rises.

[0002]

2. Description of the Related Art It is known that the cutting edge temperature of a cutting tool during cutting is about 800 ° C. or higher. Furthermore, in recent years, due to the popularization of NC machine tools, efforts to reduce production costs, and shortening of working hours, in order to improve productivity per unit time, the development of cutting tools that can cut at higher speeds and higher feed rates than before has been developed. It is required mainly by automobile manufacturers. Under such cutting conditions, the tool edge temperature exceeds 1000 ° C., which is a very severe cutting condition for the material of the tool.

When the temperature of the cutting edge becomes high, the cutting edge of the cutting tool is deformed by heat, and the flank wear resistance decreases. In order to improve the damage caused by such cutting, a coated cutting tool made of coated cemented carbide or coated ceramic coated with various hard coating layers by chemical vapor deposition or physical vapor deposition is used, which results in wear resistance. It is possible to improve the sex.

By the way, when the coating is carried out by the chemical vapor deposition method, the adhesion between the coating and the cemented carbide or ceramic which is the substrate is so high that the mutual adhesion strength is very high, and therefore the wear resistance is greatly improved. On the other hand, with respect to chipping resistance, there is a drawback that the cutting edge strength is lower than that of the cemented carbide or ceramic of the substrate, and the tool is easily chipped. The reason for this is that defects in cutting occur when cracks originating from the surface of the coating film propagate to the base cemented carbide and ceramics, but when coating by chemical vapor deposition, the coating temperature is usually Since the temperature is as high as about 1000 ° C, if the substrate is cooled to room temperature (about 20 ° C), residual tensile stress acts on the coating film due to the difference in thermal expansion coefficient between the cemented carbide or ceramic of the substrate and the coating layer. This is because this residual stress promotes the propagation of cracks.

The coating film thickness of a cutting tool which is generally used at present is from several μm to about 10 μm because the wear resistance is improved as the coating film thickness is increased. This is due to the decrease in fracture resistance. Therefore, if the fracture resistance of the coating film can be improved, a thick film can be coated, and a tool with excellent wear resistance that can be cut under high-speed and high-efficiency cutting conditions where the cutting temperature rises can be obtained. Is possible.

Usually, a coating film of several μm is formed by a chemical vapor deposition method.
When coated to about 10 μm, the coated film surface is cooled to room temperature and the surface of the coated film has a coefficient of thermal expansion of the base cemented carbide (about 5.5 * 10 ^-6 K ^-1 ) and thermal expansion of the ceramic. The coefficient (about 3.0 * 10 ⁻⁶ K ^{−1 for} silicon nitride) is the coefficient of thermal expansion of the coating film (for example, about 7.6 * 10 for TiC).
^-6 K ^-1 and Al ₂ O ₃ are smaller than 7.9 * 10 ^-6 K ^-1 ), this difference causes tensile stress in the coating film, and this stress exceeds the breaking strength of the coating layer. Therefore, when the coating film thickness is about 2 to 15 μm, cracks having an average gap between the cracks of 100 to 400 μm occur and some stress is released. However, T which is usually coated by chemical vapor deposition
The coating film of iC, Al ₂ O ₃ , TiCN, TiN, TiBN, etc. still has an elastic strain of about 0.5 to 1.0 GPa remaining, which promotes the propagation of cracks during cutting. The cutting edge strength of the tool has decreased.

In order to prevent the reduction of the cutting edge strength of the tool when the coating is performed by the chemical vapor deposition method, heretofore, only the film thickness of the coating layer of the cutting edge portion of the tool after coating is made thinner than the flat portion (JP-A-2- No. 48103), a method of releasing stress remaining in the coating layer by shot peening after coating (JP-A-2-254144), and the like have been tried. In addition, blasting using media of iron powder, GC abrasive grains and ceramic grains such as Al ₂ O ₃ and mechanical treatment with a barrel using media containing GC grains or treatment for applying thermal shock by quenching gives elasticity. A method of releasing the distortion (Japanese Patent Application No. 3-357570) has been proposed.

Although the cutting edge strength of the tool was slightly improved by these treatments, since cracks were generated in the coating film, in high-speed, high-feed cutting where the cutting edge temperature was 1000 ° C. or higher,
Oxygen penetrates through these cracks, and Ti, which is the constituent material of the film
Non-oxides such as C, TiCN, TiN, and TiBN, and cemented carbide and ceramics that are the coating base material oxidize and become brittle, which reduces wear resistance and chipping resistance, resulting in severe cutting. It could not be used under conditions.

[0009]

Means for Solving the Problems The present inventors have conducted various studies, and compared with a coating layer coated by the conventional chemical vapor deposition method described above and a coating layer subjected to the above-mentioned treatment after coating, The structure of the coating layer having excellent chipping property and abrasion resistance was found.

First, by increasing the average spacing of cracks to a range of 60 μm or less, and treating the average length of cracks in the coating film thickness direction to a coating film thickness of −2 μm or more. , Reduce the residual stress in the coating. At this time, if the average distance between cracks is 5 μm or less, the wear resistance in cutting is reduced, and the average value of the length of cracks is the coating film thickness + 5.
If the thickness is more than μm, the fracture resistance in cutting is reduced, so the average value of the crack spacing is 5 μm to 60 μm, and the average length of the cracks in the coating film thickness direction is the coating film thickness-2 μm or more. It is preferably +5 μm or less.

Further, TiC, Al ₂ O ₃ , HfO ₂ and TiC whose tensile residual stress is reduced to the above-mentioned range.
After coating a single layer or multiple layers of N, TiN, TiBN, etc. by a chemical vapor deposition method, then by a chemical vapor deposition method
A single layer or two or more layers of a group IVa metal carbide, nitride, carbonitride, carbon oxide, boronitride, or group IVa metal oxide and having a crack spacing of the coating layer surface. By coating a film having an average value of 100 μm or more and an average value of the crack length in the coating film thickness direction from the coating film thickness −2 μm to the coating film thickness +2 μm, a coating film having a small crack density can be obtained. It was attempted to improve the wear resistance and the chipping resistance by providing it on a high inner layer coating film to suppress the penetration of oxygen into the inner layer coating film.

As a result, carbides, nitrides of Group IVa metals,
A single layer or two or more layers of carbonitride, carbon oxide, boronitride or group IVa metal oxide, and having an average crack spacing of 5 μm to 60 μm in the coating layer,
The average value of the crack lengths in the coating film thickness direction constitutes the inner layer portion of the coating film having a coating film thickness of −2 μm to the coating film thickness of +5 μm, and the outer layer portion thereof is made of a Group IVa metal by chemical vapor deposition. Carbide, nitride, carbonitride, carbon oxide, boronitride, or oxide of Group IVa metal, which is a single layer or two or more layers and the average value of the crack spacing in the coating layer is 100 μm. Above, the average value of the crack length in the coating film thickness direction is the coating film thickness-2μ
By coating a coating film having a coating film thickness of m to a coating film thickness of +2 μm, it is possible to remove the coating layer and the coating base material when performing cutting under high-speed and high-feed cutting conditions such that the cutting temperature is 1000 ° C. or higher. Oxidation can be suppressed, wear resistance,
It has been clarified that both the characteristics of chipping resistance can be significantly improved as compared with the conventional product.

Further, if the coating thickness of the inner layer portion is 5 μm or less, the effect of improving wear resistance is small, and if it is more than 60 μm, the chipping resistance is remarkably reduced. Good cutting performance with high film thickness and high feed cutting. Regarding the film thickness of the outer layer,
If the thickness is 0.2 μm or less, the effect is small, and if the thickness is 10 μm or more, the fracture resistance decreases. Therefore, the thickness of the outer layer portion is 0.2 to 10 μm, preferably 0.2 to 3 μm. Further, when the ceramic base material of the coated ceramic member is a silicon nitride ceramic, a non-oxide whisker reinforced ceramic, or a titanium carbide ceramic, the effect of the present invention is great. The non-oxide whiskers mentioned here refer to silicon carbide, titanium carbide, titanium carbonitride, titanium nitride, boron nitride, boron carbide whiskers and the like.

FIG. 1 shows a conceptual diagram of the structure of the coating layer of the coated cutting tool of the present invention. A coating layer composed of an inner layer portion 2 and an outer layer portion 3 is formed on the surface of a base 1 which is a hard alloy or ceramic for a cutting tool. Since the coating layer has cracks 4, the residual stress between the substrate 1 and the coating layer is released, the propagation of cracks is not promoted during cutting, and the fracture resistance is improved. In addition, since the crack density of the outer layer portion 3 is smaller than the crack density of the inner layer portion 2, the penetration of oxygen from the cracks 4 at the time of cutting under high temperature is suppressed and the embrittlement due to the oxidation of the coating layer and the substrate 1 is suppressed. can do.

[0015]

EXAMPLES The present invention will be described below with reference to examples.

Example 1. By the known chemical vapor deposition method, Table 1
Prepare a tool material that combines the base material and coating layer shown in
The cutting performance was evaluated under the cutting conditions shown in Table 2, and the results are shown in Table 1. In Table 2, only the abrasion resistance test is performed by wet cutting, and the cross-sectional view of the four-groove material used in the fracture resistance test is as shown in FIG. Further, the crack interval and the crack length were obtained by observing the lapping surface or fracture surface of an arbitrary cross section with a SEM (scanning electron microscope). The visual field was set to 5 arbitrary visual fields, 10 cracks were selected in each visual field, and the average values of the crack interval and the crack length were calculated and used.

[0017]

[Table 1]

[0018]

[Table 2]

Comparison of Nos. 1 and 6 with No. 9 and No.
From the comparison between No. 3 and No. 15, it can be seen that the cutting performance of the coating alloy having a coating layer with a crack density smaller than that of the inner layer on the outer layer is superior to the conventional coating alloy without such a structure. . Also, No. 3 and No. 11, 16, 17, 18
From the comparison of No. 3 and No. 1, it is preferable that the crack spacing of the coating layer of the inner layer is 5 μm to 60 μm from the viewpoint of fracture resistance.
From the comparison of Nos. 3 and 19, from the viewpoint of wear resistance, the crack spacing of the coating layer of the outer layer portion is preferably 100 μm or more, No. 3,
From the comparison of Nos. 1, 7, 10, 22, and 23, it is preferable that the average value of the crack length of the inner layer portion is from the coating film thickness −2 μm to the coating film thickness +5 μm from the comparison of Nos. 5, 7, 20, 22, and 23 , No. 1 that the thickness of the inner layer is preferably 5 to 60 μm
It can be understood from the comparison between No. 4 and No. 4 that it is better to have an oxide layer in the outer layer.

Example 2. Tool materials were prepared by combining various ceramic base materials with the coating layers shown in Table 3, and the cutting performance was evaluated under the cutting conditions shown in Table 4. The results are shown in Table 3.
Described inside. All the tests in Table 4 were performed by dry cutting, and the cross-sectional view of the four-groove material used in the fracture resistance test is as shown in FIG.

[0021]

[Table 3]

[0022]

[Table 4]

From Table 3, even in the coated cutting tool using ceramic as a base material, the coated cutting tool having a structure in which the crack density of the coating layer changes discontinuously and the crack density of the outer layer portion is smaller than that of the inner layer portion is excellent. It can be seen that it has abrasion resistance.

[0024]

As described above, according to the present invention, the hard coating layer is provided on the surface of the cemented carbide member or the ceramic member, and the crack density in the coating layer changes discontinuously in the cross-sectional direction of the coating layer. However, since the crack density of the outer layer portion is smaller than the crack density of the inner layer portion, the cutting edge temperature is 1000
Even during high-speed, high-feed cutting at temperatures above ℃, oxygen is suppressed from entering from the outside through cracks, and embrittlement due to oxidation of the non-oxide forming the coating layer or the cemented carbide or ceramic of the coating base material Since it is suppressed, it is possible to obtain a coated cutting tool excellent in fracture resistance and wear resistance.

[Brief description of drawings]

FIG. 1 is a conceptual diagram of a structure of a coating layer in a coated cutting tool of the present invention.

FIG. 2 is a diagram showing a cross-sectional shape of a grooved material used for evaluation of a defect rate in Examples 1 and 2 of the present invention.

[Explanation of symbols]

 1 base 2 inner layer 3 outer layer 4 cracks

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[Procedure amendment]

[Submission date] September 29, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

[0017]

[Table 1]

Claims (5)

[Claims] 1. In a coated cutting tool comprising a coated cemented carbide member or a coated ceramic member having a hard coating layer on its surface, the crack density in the coating layer changes discontinuously in the cross-sectional direction of the coating layer, and the outer layer portion The coated cutting tool is characterized in that the crack density of is smaller than the crack density of the inner layer portion. 2. The coated cutting tool according to claim 1, wherein
IV produced by chemical vapor deposition on the inner layer as a coating layer
It is a single layer or two or more layers of a group a metal carbide, nitride, carbonitride, carbon oxide, boronitride or group IVa metal oxide, and the crack spacing in the coating layer Of the coating film having an average value of 5 μm to 60 μm and an average value of the crack length in the coating film thickness direction from the coating film thickness −2 μm to the coating film thickness +5 μm, and the outer layer portion of the coating film is formed. A single layer or two or more layers of a group IVa metal carbide, nitride, carbonitride, carbooxide, boronitride or group IVa metal oxide, which is obtained by chemical vapor deposition, and The average value of crack intervals in the coating layer is 100 μm or more, and the average value of crack lengths in the coating film thickness direction is from coating film thickness −2 μm to coating film thickness +2.
A coated cutting tool having a structure coated with a coating film having a thickness of μm. 3. The coated cutting tool according to claim 1, wherein the film of the inner layer coated by the chemical vapor deposition method has a film thickness of 5 μm to 60 μm, and the outer layer is coated by the chemical vapor deposition method. The thickness of the formed film is 0.2 μm to 1
A coated cutting tool having a thickness of 0 μm. 4. The coated cutting tool according to claim 1, claim 2 or claim 3, comprising a coated ceramic member based on a silicon nitride ceramic, a non-oxide whisker reinforced ceramic or a titanium carbide ceramic. Cutting tools. 5. The coated cutting tool according to claim 1, claim 2, claim 3 or claim 4, wherein the outer layer portion and the inner layer portion are provided.
A coated cutting tool having at least one single layer selected from Group IVa oxides or two or more multi-layers.