WO2015105274A1 - Hard coating for cutting tool - Google Patents

Abstract

The present invention relates to a hard coating in which an MT-TiCN layer, a binding layer, and an alumina (Al₂O₃) layer are sequentially laminated on a base material, wherein the hard coating can improve mechanical properties of the MT-TiCN layer and enhance the adhesion with the alumina (Al₂O₃) layer positioned above the MT-TiCN layer by controlling the microstructure of the MT-TiCN layer, and thus, the hard coating formed on a surface of the cutting tool can increase the lifespan of the cutting tool and reduce the delamination of an edge portion of the cutting tool. The hard coating according to the present invention is formed on a base material made of cemented carbide or cermet, and has a multilayer structure including a TiC_xN_y (x+y=1, x＞0, y＞0) layer with a thickness of 1 to 20 μm, wherein, in the TiC_xN_y (x+y=1, x＞0, y＞0) layer measured by EBSD, the length of Σ3 grain boundaries accounts for 70% or more of a sum of the lengths of Σ3, Σ5, Σ7, Σ9, Σ11, Σ15, and Σ23 grain boundaries.

Description

Hard Film for Cutting Tools

The present invention relates to a hard film for cutting tools formed on a cutting tool based on a cemented carbide or cermet, more specifically, an MT-TiCN layer, a bonding layer, and alumina (Al ₂ O ₃ ) on the base material. This is a hard film laminated in the order of) layer, by controlling the bonding relationship between the grain boundaries of the grains forming the MT-TiCN layer by improving the adhesion to the alumina (Al ₂ O ₃ ) layer located on the MT-TiCN layer. In addition, the present invention relates to a hard coating which can reduce the peeling of the edge portion of the hard coating during cutting, thereby extending the life of the cutting tool.

The TiCN thin film, which has been widely used in hard coatings for cutting tools based on cemented carbide or cermet, is formed by reacting at a high temperature of about 1000 ° C. using reaction gases such as TiCl ₄ , CH ₄ and N ₂ . Carbon (C) diffuses from the cemented carbide base material into the TiCN thin film, and a brittle hard phase such as Co ₃ W ₃ C or Co ₆ W ₆ C is formed at the interface between the base material and the TiCN thin film, thereby reducing the toughness of the cutting tool. .

In order to solve this problem, a method of forming a TiCN layer (hereinafter referred to as an 'MT-TiCN layer') using MTCVD (hereinafter referred to as 'MTCVD') has been proposed. Diffusion of carbon from the cemented carbide substrate when the TiCN thin film is formed by lowering the deposition temperature to about 750-850 ° C. using CH ₃ CN as a source of TiCl ₄ , carbon (C) and nitrogen (N). By suppressing the formation of hard phases such as Co ₃ W ₃ C or Co ₆ W ₆ C, which are brittle, the TiCN thin film formed after coating is characterized by having not only wear resistance but also toughness.

The MT-TiCN layer is commercially available in a multi-layered structure in which an oxide such as an alumina layer is formed after forming a bonding layer thereon, and is widely used in cutting tools for turning and milling.

On the other hand, during cutting, heat is generated along with wear of the thin film due to friction between the cutting tool (insert) and the workpiece, and the laminated structure in the same order as the MT-TiCN layer, the bonding layer, and the alumina (Al ₂ O ₃ ) layer from the base material. After the alumina (Al ₂ O ₃ ), which is the uppermost layer in the multilayer thin film having abrasion, is completely worn through the cutting process, the wear resistance of the MT-TiCN layer is poor, so that the tool life is short.

Many studies have been conducted to solve this problem. For example, US Patent No. 6,652,913 discloses a crystal grain size (particle size) of a TiCN thin film having a columnar crystal structure by doping CO gas during MTCVD TiCN thin film formation. ) Is proposed to refine the hardness to about 0.5 μm level to improve hardness.

According to the method, it improves the mechanical properties due to the miniaturization of the TiCN layer, but improve the wear resistance of the cutting tool, of the bonding force between the top layer of alumina (Al ₂ O ₃₎ and MT-TiCN layer away, cutting the alumina layer There is a problem in that the tool life is reduced due to partial peeling, and there is a certain limit to improving the tool life only by atomizing the MT-TiCN layer.

An object of the present invention in forming the MT-TiCN layer, by forming a fine MT-TiCN layer to improve the mechanical properties of the MT-TiCN layer and at the same time to control the binding relationship of the grain boundary constituting the MT-TiCN layer, MT- It is to provide a hard film for cutting tools that can improve the bonding strength with the α-Al ₂ O ₃ layer, which is the upper layer of the TiCN layer, and improve the life of the cutting tool.

In order to solve the above problems, the present invention is formed on a base material of cemented carbide or cermet, and includes a layer of MT-TiC _x N _y (x + y = 1, x> 0, y> 0) having a thickness of 1 to 20 µm. The multilayer structure, wherein the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer has a length of Σ 3 type grain boundary measured by EBSD, Σ 3 type, Σ 5 type, Σ 7 type, Provided are hard coatings for cutting tools, which occupy 70% or more of the sum of Σ9 type, Σ11 type, Σ15 type, and Σ23 type grain boundary lengths.

Preferably, the grain size of the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer may be 1 μm or less, more preferably 0.7 μm or less.

In addition, the hard film is formed on the innermost side and has an equiaxed crystal structure and has a thickness of 0.5 ~ 2㎛ TiC _x N _y O _z (x + y + z = 1, x ≥ 0, y ≥ 0, z ≥ 0) layer and Ti (Al) C _x N _y O _z (formed on the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer and having a thickness of 1.5 μm or less). x + y + z = 1, x ≧ 0, y ≧ 0, z> 0) layers, and an α-Al ₂ O ₃ layer formed thereon.

The α-Al ₂ O ₃ layer may have a thickness of about 1 μm to about 15 μm.

The grain boundaries of the particulate MT-TiCN layer constituting the hard coating according to the present invention are controlled so that Σ3 type is the main, and the grain-bound MT-TiCN layer with the grain boundaries controlled as described above not only improves mechanical properties due to grain refinement, The bonding force with the α-Al ₂ O ₃ layer formed thereon is improved, and the life of the cutting tool can be extended.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure for demonstrating the grain boundary type by EBSD analysis.

2 is a photograph after evaluation of cutting performance of the insert with the hard film according to the comparative example.

3 is a photograph after evaluation of cutting performance of the insert with the hard film according to the embodiment.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention illustrated in the following may be modified in many different forms, the scope of the present invention is not limited to the embodiments described in the following. Embodiments of the present invention are provided to more completely explain the present invention to those skilled in the art.

In the following description, the following terms are defined as follows.

The “carbide alloy” means a sintered body sintered including a WC powder and a binding metal powder such as Co and Ni, and may include other components other than the above components.

"Cermet" means a sintered body sintered including TiCN powder and a binding metal powder such as Co, Ni, and other components other than the above components may also be included.

'MT-TiCN layer' is a TiCN layer formed by using MTCVD (Moderate Temperature Chemical Vapor Deposition). When TiCN layer is formed, it is deposited temperature using CH ₃ CN as a source of TiCl ₄ , carbon (C) and nitrogen (N). It refers to a thin film formed by lowering to about 750 ~ 850 ℃ level.

'Σn + 1 type (where n = 2,4,6,8,10,14,22) grain boundary' means that each of the constituent atoms consisting of Ti, C, and N at the grain boundary is determined by EBSD analysis. When calculating the distribution of lattice points (constituent atom shared lattice points) that share one constituent atom between grains, as shown in FIG. 1, lattice points that do not share constituent atoms between the constituent atom shared lattice points, as shown in FIG. 1. It means a grain boundary having the form of n constituent atomic covalent lattice points.

The present inventors have studied to improve the mechanical properties of the MT-TiCN layer and at the same time improve the bonding strength with the α-Al ₂ O ₃ layer formed on the top, applying the conventional atomization technology of the MT-TiCN layer and At the same time, when the Σ3 type of grain boundary is adjusted to 70% or more of the total grain boundary, the bonding strength between the fine MT-TiCN layer and the α-Al ₂ O ₃ layer formed on the upper side is improved, which can extend the life of the cutting tool even more. It has been found that the present invention can be achieved.

The hard film according to the present invention is formed on a base material made of cemented carbide or cermet, and the hard film is MT-TiC _x N _y (x + y = 1, x> 0, y having a thickness of 1 to 20 μm. > 0) layer, wherein the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer has a length of? 3 type grain boundary measured by EBSD. It is characterized by occupying 70% or more of the sum of Σ5, Σ7, Σ9, Σ11, Σ15 and Σ23 type grain boundary lengths.

When the thickness of the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer is less than 1 μm, the wear resistance is lowered. As for the thickness, 1-20 micrometers is preferable.

In addition, the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer has a columnar structure, and the average particle diameter is 1 μm or less, more preferably 0.8 μm or less. It is preferable.

TiC _x N _y O _z (x + y) having an equiaxed crystal structure and a thickness of 0.5 to 2 μm between the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer and the base material + z = 1, x≥0, y≥0, z≥0) layer can be formed, when the thickness of the TiC _x N _y O _z layer is less than 0.5㎛ thin film adhesion due to decarburization of the base material interface is reduced In the case of more than 2 µm, 0.5 to 2 µm is preferable because the proportion of the entire thin film increases and the wear resistance decreases.

In order to form an alumina layer on the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer, Ti (Al) C _x N _y O _z ( x + y + z = 1, x ≧ 0, y ≧ 0, z> 0) layers may be formed.

An α-Al ₂ O ₃ layer, which is a wear resistant layer, is formed on the Ti (Al) C _x N _y O _z (x + y + z = 1, x≥0, y≥0, z> 0) layer. When the thickness of the α-Al ₂ O ₃ layer is less than 1 μm, the wear resistance is not sufficient, and when the thickness of the α-Al ₂ O ₃ layer is less than 15 μm, peeling easily occurs, 1 to 15 μm is preferable.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments.

EXAMPLE

The hard coating according to the present invention may be applied to a base material made of a cemented carbide, cermet, or ceramic. In an embodiment of the present invention, an insert made of cemented carbide is used.

In the embodiment of the present invention, first, using the LPCVD method on the surface of the base material made of cemented carbide, at a process temperature of 900 ℃, deposition pressure 100 ~ 200 mbar, about 60 ~ 70vol% H ₂ , 10 ~ 20vol% N ₂ , A TiN layer having a thickness of 0.5 to 3 μm was formed in an innermost equiaxed structure under the condition of 0 to 5 vol% CH ₄ and 5 to 15 vol% TiCl ₄ .

Next, fine MT-TiCN consisting of columnar crystals is deposited on the TiN layer. Conditions for forming the particulate columnar MT-TiCN layer include 0-10vol% N ₂ , 7-10vol% TiCl ₄ , 1-3vol% CH ₃ CN, 1-3vol% HCl, 1-3vol% BCl ₃ , Reaction gas consisting of the remaining H ₂ was deposited at a temperature of 830 ~ 900 ℃ at a pressure of 70 mbar to form an MT-TiCN layer of about 7㎛ thickness.

On the MT-TiCN layer to form a bonding layer for forming an alumina layer, the bonding layer is composed of 75vol% H ₂ , 19vol% N ₂ , 3.0vol% CH ₄ , 2.0vol% CO, 1.5vol% TiCl ₄ Using the reaction gas at about 1000 ℃ deposition pressure is formed under the conditions of 100 ~ 150mbar, as a result of forming a TiCNO layer of about 0.5㎛ thickness.

On the TiCNO layer to form an alpha-alumina layer, the deposition temperature is 1000 ~ 1010 ℃, deposition pressure 50 ~ 75mbar process conditions, about 78vol% H ₂ , 3.5vol% CO ₂ , 0.3vol% H ₂ S, A reaction layer consisting of 3 to 5 vol% HCl and 2.5 vol% AlCl ₃ was introduced to form an alumina layer having a columnar structure and an alpha phase with a thickness of 4 μm.

And in order to easily check the wear of the insert on the upper part, in the process conditions of the deposition temperature 900 ~ 1000 ℃, deposition pressure 100 ~ 600mbar, about 60 ~ 70vol% H ₂ , 20 ~ 35vol% N ₂ , 0 ~ 5vol TiN layer of 1 μm or less was formed under% CH ₄ , 6˜10 vol% TiCl ₄ .

[Comparative Example]

The hard coating according to the comparative example was prepared in the same manner as in Example, except for the composition and process conditions of MT-TiCN. The formation of MT-TiCN used a method of forming a general MT-TiCN layer. Specifically, the reaction gas consisting of 10 ~ 40vol% N ₂ , 5 ~ 7vol% TiCl ₄ , 1 ~ 3vol% CH ₃ CN, the remaining H ₂ at a pressure of 100mbar at this time deposition temperature is 850 ~ 900 ℃ thickness 7 A μm MT-TiCN layer was formed.

Microstructure of MT-TiCN Layer

Since the hard coatings prepared according to the Examples and Comparative Examples of the present invention were formed in the same manner except for the MT-TiCN layer, the types of grain boundaries constituting the MT-TiCN layer were analyzed by EBSD analysis. It was as Table 1.

Table 1

Psalter	Percentage of the length of the Σ3 type grain boundary in the sum of the lengths of Σ3, Σ5, Σ7, Σ9, Σ11, Σ15, and Σ23 type grain boundaries.
Example	72
Comparative example	38

As shown in Table 1, in the case of the MT-TiCN layer of the hard film according to the embodiment of the present invention, the ratio of the grain size of the Σ3 type grain boundary occupies more than 70%, the comparative example In the MT-TiCN layer of the hard coating, the ratio of the grain length of the Σ3 type grains to the total sum was less than 50%.

Evaluation of Cutting Performance of Hard Films

In order to confirm the effect of the type of grain boundary of the MT-TiCN layer as described above on the cutting performance of the hard film, the following cutting test was performed.

Workpiece: SCM440 (alloy steel)

Cutting speed: 280m / min

Feed (feed): 0.25 mm / rev

-Depth of cut: 2.0 mm

Cutting insert geometry: CNMG120408-VM

-Evaluation method: After cutting for 6 minutes under the above conditions, evaluating whether the edge portion peeled

2 and 3 are photographs showing the results of the cutting test by forming the hard film according to the comparative example and the hard film according to the embodiment, respectively.

As shown in FIG. 2, in the case of the hard film having the existing MT-TiCN layer, a part of the thin film on the upper surface of the edge line was peeled off after 6 minutes of processing. On the other hand, as shown in FIG. 3, in the case of the hard film having the MT-TiCN layer according to the embodiment of the present invention, no phenomenon of peeling the thin film on the upper surface of the edge line was observed even after 6 minutes of processing.

That is, the MT-TiCN layer according to the embodiment of the present invention can improve the bonding strength with the α-Al ₂ O ₃ layer formed on the upper side, by the improved bonding strength, the hard film according to the present invention is conventional The life of the cutting tool can be extended compared to the film.

Claims (4)

1. Hard coating formed on the base material consisting of cemented carbide or cermet,

   The hard film is made of a multi-layered structure including a layer of MT-TiC _x N _y (x + y = 1, x> 0, y> 0) having a thickness of 1 ~ 20㎛,

   The MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer has a length of Σ3 type grain boundaries measured by EBSD of Σ3, Σ5, Σ7, Σ9, Σ11, Σ15 and Σ23 type grain boundaries. Hard coating for cutting tools, which accounts for more than 70% of the total length.
2. The method of claim 1,

   The hard coating, the _{MT-TiC x N y (x} + y = 1, x> 0, y> 0) is formed on the lower layer of TiC _x N _y has a thickness of 0.5 ~ 2㎛ it has a polygonal normal structure O _z (x + y + z = 1, x≥0, y≥0, z≥0) layer,

   Ti (Al) C _x N _y O _z (x + y +) formed on top of the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer and having a thickness of 1.5 μm or less z = 1, x≥0, y≥0, z> 0) layer,

   And an α-Al ₂ O ₃ layer formed on top of the Ti (Al) C _x N _y O _z (x + y + z = 1, x ≧ 0, y ≧ 0, z> 0) layer. Cutting tool film.
3. The method of claim 2,

   The α-Al ₂ O ₃ layer has a columnar top structure, the thickness of the cutting tool film, characterized in that 1 to 15㎛.
4. The method of claim 1,

   The grain size of the cutting tool, characterized in that the grain size of the MT-TiC _x N _y (x + y = 1, x> 0, y> 0) layer is 1㎛ or less.

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