KR102497484B1 - Cvd film for cutting tool with excellent peel resistance - Google Patents

Abstract

An object of the present invention is to provide a hard coating for a cutting tool having excellent adhesion and improved wear resistance and toughness.
A film for a cutting tool according to the present invention is formed by the CVD method, and the film includes a first layer and a second layer formed on top of the first layer, and the first layer is TiC _x N _y (x + y = 1, x>0, y>0) as a main phase, and is oriented so that the peak intensity of the (311) plane and / or (422) plane is the largest in X-ray diffraction analysis, and the second layer contains Ti _1-x Al _x C _1-y N _y (0.6≤x<1.0, 0≤y≤1) as a main phase, and has the highest peak intensity on the (111) plane during X-ray diffraction analysis It is characterized by being oriented.

Description

Coating for CVD cutting tools with excellent exfoliation resistance {CVD FILM FOR CUTTING TOOL WITH EXCELLENT PEEL RESISTANCE}

The present invention relates to a coating for a cutting tool, which is formed by chemical vapor deposition as a coating for a cutting tool, includes an AlTiN layer having a high Al content, and has excellent oxidation resistance, wear resistance, and peeling resistance.

In order to improve cutting performance and life, a method of depositing a thin film such as TiN, TiAlN, AlTiN, Al ₂ O ₃ which is a hard film on a hard substrate such as cemented carbide, cermet, end mill, drill, etc. is used.

Until the 1980s, cutting tools were coated with TiN to improve cutting performance and lifespan, but since heat of about 600 ~ 700℃ is generated during general cutting, in the late 1980s, TiN has higher hardness and oxidation resistance than TiN. The coating technology was changed to TiAlN, and an AlTiN thin film with more Al was developed to further improve wear resistance and oxidation resistance. The AlTiN thin film has an effect of improving high-temperature oxidation resistance and wear resistance by forming an Al ₂ O ₃ oxide layer, but has a problem in that it has a weak bonding force with a hard substrate.

In recent years, workpieces have become increasingly hard, and cutting operations for difficult-to-cut materials that have low thermal conductivity and severe adhesion to tools are increasing. It is important to have excellent oxidation resistance and wear resistance in order to obtain excellent cutting performance and lifespan during high-speed cutting of such high-hardness workpieces and high-speed cutting of difficult-to-cut materials.

In response to this demand, an AlTiN thin film formed by a CVD method with excellent oxidation resistance and wear resistance by increasing the Al content by 0.7 or more in terms of molar ratio among Al and Ti has emerged as a new alternative, but low exfoliation resistance and toughness have become a problem. The scope of application is limited.

For example, the following patent literature discloses a hard coating having improved wear resistance through an AlTiN thin film having a lamellar structure and a texture preferentially oriented in a specific crystal plane. However, the technology for improving the bonding force with the hard substrate, which is the most problematic for the application of the AlTiN thin film, is not disclosed.

Republic of Korea Patent Publication No. 2016-0130752

An object of the present invention is to provide a coating for a cutting tool having excellent peeling resistance and improved abrasion resistance and toughness.

In order to achieve the above object, the present invention is a film formed by a CVD method, wherein the film includes a first layer and a second layer formed on top of the first layer, wherein the first layer is TiC _x It includes N _y (x+y=1, x>0, y>0) as a main phase, and is oriented so that the peak intensity of the (311) plane and / or (422) plane is the greatest in X-ray diffraction analysis And, the second layer includes Ti _1-x Al _x C _1-y N _y (0.6≤x<1.0, 0≤y≤1) as a main phase, and at the time of X-ray diffraction analysis, the (111) plane Provided is a coating for a cutting tool that is oriented to have the highest peak intensity.

The film according to the present invention has excellent oxidation resistance because it includes an AlTiN layer having a high Al content, and has excellent toughness because AlTiN having a lamellar structure is used as the main phase.

In particular, the film according to the present invention is oriented to improve the bonding force with the AlTiN layer and has excellent wear resistance under the AlTiN layer, thereby improving the peeling resistance and wear resistance of the film, thereby extending the life of the cutting tool.

1 is a schematic view of the structure of a hard coating according to an embodiment of the present invention.
2 is a scanning electron microscope image of a cross-section of a film prepared according to an embodiment of the present invention.
3 is a result of X-ray diffraction analysis of a film prepared according to an embodiment of the present invention, and shows peaks (red dotted line boxes) of crystal planes with high intensity among the peaks of the TiCN layer.
FIG. 4 is a result of X-ray diffraction analysis of a film prepared according to an embodiment of the present invention, and shows a crystal plane peak (red dotted line box) with the highest intensity among peaks of an AlTiN layer.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

However, the embodiments of the present invention exemplified below may be modified in many different forms, and the scope of the present invention is not limited to the embodiments described below. The embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

A film for a cutting tool according to the present invention is formed by the CVD method, and the film includes a first layer and a second layer formed on top of the first layer, and the first layer is TiC _x N _y (x + y = 1, x>0, y>0) as a main phase, and is oriented so that the peak intensity of the (311) plane and / or (422) plane is the largest in X-ray diffraction analysis, and the second layer contains Ti _1-x Al _x C _1-y N _y (0.6≤x<1.0, 0≤y≤1) as a main phase, and has the highest peak intensity on the (111) plane during X-ray diffraction analysis It is characterized by being oriented.

As shown in FIG. 1, the film according to the present invention is formed and used on a base material 100 used for cutting tools such as cemented carbide or cermet, and is in contact with or adjacent to the base material to TiC _x N A first layer 200 having _y (x+y=1, x>0, y>0, hereinafter referred to as 'TiCN') as a main phase is formed, and Ti _1-x Al _x C _1-y is formed thereon. It has a structure in which a second layer 300 having N _y (0.6≤x<1.0, 0≤y≤1, hereinafter referred to as 'AlTiN') as a main phase is formed.

In the present invention, the term 'main phase' is a phase that constitutes 80% or more, preferably 90% or more, more preferably 95% or more, and most preferably 99% or more in volume fraction constituting the first or second layer. (phase) means.

As described above, the second layer 300 in which Al is contained more than Ti at a molar ratio of 0.6 or more has excellent oxidation resistance, but has low exfoliation resistance. In the present invention, the TiCN layer is placed on the first layer formed under the AlTiN layer, and the TiCN layer is first oriented so that the strongest peaks appear on the (311) plane and / or (422) plane during X-ray diffraction analysis. By doing so, the bonding force between the TiCN layer and the AlTiN layer is improved, and since the TiCN layer has excellent wear resistance, an effect of further extending the life of the cutting tool can be obtained.

In the TiCN layer, when the (311) plane is the strongest peak in X-ray diffraction analysis, the (422) plane is in the second strongest peak state, or if the (422) plane is the strongest peak, the (311) plane is the strongest peak. The second strongest peak state is preferred.

If the thickness of the first layer is less than 0.5 μm, it is difficult to obtain the above-mentioned effect, and if it exceeds 15 μm, the bonding force between the TiCN layer and AlTiN decreases.

The first layer is preferably formed of fine grains having an average crystal grain size of 0.9 μm or less in microstructure to improve bonding strength with the second layer having AlTiN as a main phase formed thereon and improving wear resistance of the entire film.

The second layer has a lamellar structure in which regions having different contents of Ti and Al are alternately and repeatedly formed along the thickness direction of the film, and the average thickness of the regions may be 150 nm or less.

In general, AlTiN coatings have low impact resistance due to weak toughness, but coatings having a lamellar structure have a toughness improvement effect because they have a structure that can improve such toughness. In order to obtain the effect of improving toughness, the average thickness of the region (ie, the average spacing between the microlayers constituting the lamella) is preferably 150 nm or less, more preferably 100 nm or less, and most preferably 50 nm or less.

The lamellar structure may be an alternating repetition of regions having different compositions and different crystal structures, such as a face-centered cubic (fcc) structure and a hexagonal structure (hcp) structure, or the same crystal structure, for example, a face-centered cubic (fcc) structure. While having, different composition regions may be alternately repeated. The lamellar structure is effective in extending the life of the cutting tool by increasing resistance to load when using it. In particular, it may be preferable that the two alternating regions have the same face-centered cubic (fcc) structure and have different compositional regions.

In addition, the AlTiN Considering bonding force and wear resistance, the aluminum content (x) is preferably 0.6 or more and less than 0.95, and more preferably 0.7 or more and 0.93 or less in a rich range.

In addition, the volume fraction of tissue having a face centered cubic structure (fcc) in the second layer may be 90 vol% or more. AlTiN Hard coatings with a main phase can have a face-centered cubic structure (fcc) and a dense hexagonal structure (hcp) depending on the film formation conditions. A face-centered cubic structure is more advantageous in terms of abrasion resistance and impact resistance, % or more, the characteristics according to the face-centered cubic structure can be sufficiently expressed. Therefore, the crystal structure of the second layer preferably has a face-centered cubic structure of 90 vol% or more.

In addition, the second layer is preferentially oriented so that the peak intensity of the (111) plane, (200) plane, (220) plane, or (311) plane is the largest in X-ray diffraction analysis to improve cutting performance such as wear resistance. it is desirable to do Among them, it is most preferable that the (111) plane is preferentially oriented.

In addition, it is preferable that the thickness of the second layer is 2 to 6 μm, which means that when the thickness of the second layer is less than 2 μm, wear resistance and oxidation resistance may not be sufficient, and when the thickness exceeds 6 μm, resistance due to internal stress It is because peelability may fall.

In addition, a TiN layer may be further included between the first layer 200 and the base material 100 to increase bonding strength between the base material and the coating. At this time, the thickness of the TiN layer is preferably formed to 2 μm or less, and more preferably to 1 μm or less.

Hereinafter, in order to explain the present invention in more detail, a preferred embodiment according to the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein.

[Example 1]

First, the cemented carbide base material is mixed for 13 hours by adding 7% by weight of Co, which acts as a binder of cemented carbide, and 5% by weight of carbides or carbonitrides containing elements of Groups 4, 5, or 6. After pulverization, a mixed powder is obtained using a spray drying method. With the obtained mixed powder, a molded article was manufactured by performing a press at a pressure of 2 ton/cm 2 to manufacture the SNMX1206ANN-MM model.

Subsequently, a dewaxing process is performed at 600 ° C to remove the organic binder component introduced in the molded product manufacturing process, and then sintering is performed in an inert gas atmosphere for 1 to 2 hours, followed by predetermined cooling in an inert gas atmosphere up to 600 ° C. After the rate cooling, a sintering process was performed by a natural cooling method to prepare a base material for forming a hard film.

A film was formed on the prepared base material using a thermal CVD method.

First, a method of introducing 8ml/min of TiCl ₄ , 12ml/min of N ₂ , and 100ml/min of H ₂ gas at 850° C. under a pressure of 5 mbar using a hot-wall CVD reactor Through this, a TiN layer having a thickness of 1 μm or less was formed.

Next, at 800° C., under a pressure of 50 mbar, a mixed gas of 4 ml/min TiCl ₄ , 0.5 ml/min CH ₃ CN, 15 ml/min N ₂ , and 2000 ml/min H ₂ was introduced to obtain a thickness of about 9 μm. An MT-TiCN layer (first layer) was formed.

Then, at 800° C., under a pressure of 5 mbar, 4 ml/min of TiCl ₄ , 20 ml/min of AlCl ₃ , and 1200 ml/min of H ₂ mixed gas were introduced, and 80 ml/min of NH ₃ and 160 ml/min of N ₂ , 0.5 ml /min of the CH ₃ CN mixture was passed into the reactor as the second gas feed. After a coating time of 25 minutes, a black gray AlTiN layer having a thickness of 4 μm was formed. The aluminum content (x) of the resulting AlTiN layer was 0.91.

2 shows a cross-sectional microstructure of a hard film according to Example 1 of the present invention. As confirmed in FIG. 2, while the AlTiN layer of the hard film according to Example 1 grows into a columnar crystal, it is observed that a lamellar structure, which is a nano-multilayer structure that is spontaneously generated horizontally inside the columnar crystal, is formed. A TiCN layer, which is a film directly above the base material, is formed.

3 and 4 show the results of X-ray diffraction analysis of the hard coating according to Example 1 of the present invention. As confirmed in FIG. 3, the peak representing the maximum intensity of the TiCN layer of the hard film prepared according to Example 1 is the (311) plane, and the second strongest (422) peak is formed.

In addition, as confirmed in FIG. 4, the peak representing the maximum intensity of the AlTiN layer of the hard film prepared according to Example 1 is the (111) plane.

That is, in the hard film according to Example 1 of the present invention, an AlTiN layer oriented in the (111) plane is formed after forming a TiCN layer oriented in the (311) plane and the (422) plane on the surface of a hard substrate (base material). By doing so, the bonding force between the two layers is improved due to the similarity of the crystal structure.

[Comparative Example 1]

After manufacturing the MT-TiCN layer in the same process as the cemented carbide base material as in Example 1, when forming the AlTiN layer, the input amount of AlCl ₃ , one of the raw material gases, was set to 10 ml / min, less than in Example 1, An AlTiN layer was formed.

[Comparative Example 2]

When the MT-TiCN layer was formed in the same process on the same cemented carbide base material as in Example 1, the input amount of TiCl ₄ was set higher than that of Example 1 at 8 ml/min.

[Comparative Example 3]

After manufacturing the MT-TiCN layer in the same process as in Example 1 on the same cemented carbide base material, when forming the AlTiN layer, the input amount of AlCl3, one of the raw material gases, was increased to 5 ml/min and the input amount of TiCl ₄ was increased to 2 ml/min. set up and formed.

[Comparative Example 4]

After manufacturing the MT-TiCN layer in the same process as in Example 1 on the same cemented carbide base material, when forming the AlTiN layer, the AlTiN layer formation time was set to 120 min, significantly higher than in Example 1, to form an AlTiN layer.

Table 1 below shows conditions for forming each layer when the films of Example 1 and Comparative Examples 1 to 4 were formed by the CVD method.

Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 TiCN
(1st floor) hour min 50 50 50 50 50 TiCN temperature ℃ 800 800 800 800 800 TiCN enter mbar 50 50 50 50 50 TiCN TiCl ₄ ml/min 4 4 8 4 4 TiCN N ₂ ml/min 15 15 15 15 15 TiCN _H2 ml/min bal bal bal bal bal TiCN CH ₃ CN ml/min 0.5 0.5 0.5 0.5 0.5 AlTiN
(2nd floor) hour min 25 25 25 25 125 AlTiN temperature ℃ 800 800 800 800 800 AlTiN enter mbar 5 5 5 5 5 AlTiN TiCl ₄ ml/min 4 4 4 2 4 AlTiN N ₂ ml/min 160 160 160 160 160 AlTiN _H2 ml/min bal bal bal bal bal AlTiN CH ₃ CN ml/min 0.5 0.5 0.5 0.5 0.5 AlTiN AlCl ₃ ml/min 20 10 20 5 20 AlTiN NH ₃ ml/min 80 80 80 80 80

Table 2 below shows the C content of the TiCN layer and preferentially grown crystal planes among the films of Example 1 and Comparative Examples 1 to 4. In Table 2, two preferentially grown crystal planes are described when the intensity of peaks appearing in X-ray diffraction analysis is similar. 1st floor Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 C content 0.7 or higher 0.7 or higher less than 0.5 0.7 or higher 0.7 or higher priority growth
crystal plane (311), (422) (311), (422) (222) (311), (422) (311), (422)

Table 3 below shows the Al content (molar ratio) of the TiAlN layer, preferentially grown crystal plane and thickness among the films of Example 1 and Comparative Examples 1 to 4. 2nd floor Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Al content 0.92 0.65 0.91 0.44 0.92 priority growth
crystal plane (111) (111) (111) (111) (111) Thickness (㎛) 4 3.5 5 3 20

Cutting performance evaluation

The wear resistance and chipping resistance of cutting tools having coatings prepared according to Example 1 and Comparative Examples 1 to 4 of the present invention were evaluated under the following evaluation conditions.

(1) Evaluation of wear resistance: wear on the insert flank, rake and crater

Work material: SCM440

Sample model number: SNMX1206ANN-MM

Cutting speed: 250m/min

Cutting feed: 0.15mm/tooth

Cutting Depth: 1.5mm

Coolant: none (dry)

(2) Evaluation of chipping resistance: Breakage of the cutting edge of the insert

Work material: SCM440

Sample model number: SNMX1206ANN-MM

Cutting speed: 180m/min

Cutting feed: 0.15mm/tooth

Cutting Depth: 2.0mm

Coolant: none (dry)

Table 4 below shows the samples and results evaluated for wear resistance and chipping resistance under the above conditions.

Example Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Wear resistance Machining time 23min 13min 20min 10min 30min Chipping resistance Machining time 43min 40min 35min 41min 15min

As confirmed in Table 4 above, the coating according to Example 1 of the present invention has improved bonding strength through crystal orientation and thickness control between the TiCN layer and the AlTiN layer, and the tool life was significantly improved compared to comparative examples.

100: parent material
200: first layer
300: second layer

Claims (5)

As a film formed by the CVD method,
The film includes a first layer and a second layer formed on top of the first layer,
The first layer includes TiC _x N _y (x + y = 1, x>0, y>0) as a main phase, and has a peak of (311) plane and/or (422) plane in X-ray diffraction analysis Oriented to have the greatest strength,
The second layer includes Ti _1-x Al _x C _1-y N _y (0.6≤x<1.0, 0≤y≤1) as a main phase, and peak intensity of (111) plane in X-ray diffraction analysis Coating for cutting tools, oriented so that is the largest. According to claim 1,
The second layer has a lamellar structure in which regions having different Ti and Al contents are alternately and repeatedly formed along the thickness direction of the coating, and the average thickness of the region is 150 nm or less. According to claim 1,
The second layer has a volume fraction of a tissue having a face centered cubic structure (fcc) of 90 vol% or more, a coating for a cutting tool. According to claim 1,
A base layer is further included under the first layer, and the base layer includes TiN as a main phase. According to claim 1,
The first layer has an average crystal grain size of 0.9 μm or less on a microstructure, a coating for a cutting tool.

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