KR20160080609A - Hard coated layer for cutting tools - Google Patents

Abstract

The present invention relates to a hard coating comprising an alumina layer which is formed by a CVD method and has different crystal orientations across a lower layer, a middle layer, and an upper layer in a thickness direction to improve wear resistance of a crater of an upper surface during a high speed and a high transport process to extend tool life. According to the present invention, the hard coating is formed on a surface of base metal of a cutting tool containing a cemented carbide alloy, cermet, ceramic, or cBN, and comprises one or more alumina layers formed by CVD. The alumina layers are formed in an alpha phase from a nucleation step. Crystal grains of a lower layer adjacent to the base metal form an angle of 27-37° and 57-67° between a normal line to (006) surface and a normal line to the surface of the base metal. Crystal grains of a middle layer of the alumina layers form an angle of 0-7° and 40-50° between a normal line to (110) surface and the normal line to the surface of the base metal. Crystal grains of an upper layer of the alumina layers form an angle of 0-7° and 43-53° between a normal line to (012) surface and the normal line to the surface of the base metal.

Description

HARD COATED LAYER FOR CUTTING TOOLS [0001]

The present invention relates to a hard coating for a cutting tool, and more particularly to a hard coating for a cutting tool, wherein the coating comprises an alumina layer formed by a CVD method, the alumina layer having a crystal orientation different from the lower layer to the intermediate layer The present invention relates to a hard film capable of improving the wear resistance of a top surface crater during high-speed and high-feed machining, thereby increasing tool life.

Generally, a cemented carbide used as a cutting tool is used after forming a hard thin film layer on its surface in order to increase abrasion resistance. The hard thin film can be formed by chemical vapor deposition (hereinafter referred to as' CVD ') or physical vapor deposition (hereinafter referred to as' PVD ').

On the other hand, when cutting a high-hardness material at high speed, the cutting tool is exposed to a high-temperature environment of about 1000 캜, and friction and oxidation due to contact with the workpiece are caused, and mechanical shock such as interruption is also received. Therefore, cutting tools are required to have toughness with adequate wear resistance.

In general, the hard thin film is composed of a single layer or a multilayer non-oxide thin film (e.g., TiN, TiC, TiCN), an oxide thin film having excellent oxidation resistance (e.g., Al ₂ O ₃ ), or a mixed layer thereof, Examples of the carrier-type thin film include carbides, nitrides, and carbonitrides of Group 4, 5, and 6 metal elements on the periodic table such as TiN, TiC, and TiCN. Examples of the oxide-based thin film include α-Al ₂ O ₃ or κ- Al ₂ O ₃ .

Among the oxide thin films, κ-Al ₂ O ₃ is excellent in adhesion to non-oxide thin films and can be formed at a relatively low temperature (1000~1020 ° C.), but due to the high temperature generated during cutting, κ- And the phase transformation causes volume shrinkage and cracking of about 6 to 8%, which may cause peeling of the Al ₂ O ₃ thin film.

On the other hand, α-Al ₂ O ₃ is a stable phase at high temperature, so phase transformation does not occur during machining and relatively abrasion resistance is exhibited, which is widely used for cutting tool coatings.

Factor influences the wear resistance of such α-Al ₂ O ₃ is known as anisotropy (anisotropy) of the α-Al ₂ O ₃ grain size and the α-Al ₂ O ₃ grains of. In this connection, European Patent Publication No. 0603144 (Patent Document 1) discloses that α-Al ₂ O ₃ having a (012) face first grown and having excellent surface roughness shows excellent performance in gray cast iron and spheroidal graphite cast iron processing, European Patent Publication No. 0659903 (Patent Document 2) discloses that α-Al ₂ O ₃ having a (110) plane firstly grown and having no cracking and having a plate shape exhibits improved tool life in cutting of steel and cast iron. In EP-A-0738336 (Patent Document 3), when α-Al ₂ O ₃ is first grown on the (104) plane, the surface roughness of α-Al ₂ O ₃ is excellent and the abrasion resistance and toughness of the tool are improved Lt; / RTI > In _{addition, Enhanced performance of alpha Al 2 O} 3 coatings by control of crystal orientation, Surface & Coatings Technology 202 (2008) 4257-4269 ( Non-Patent Document 1), when the surface (006) of the α-Al ₂ O ₃ growth priority , it has been introduced that the ductile fracture of α-Al ₂ O ₃ is suppressed and the plastic deformation resistance is improved, and the crater wear (K _T wear) of the insert is reduced during the machining of the steel and the tool life is greatly improved.

However, as shown in the above patent documents or non-patent documents, even if a texture structure in which anisotropy of? -Al ₂ O ₃ is controlled is made, it is difficult to obtain sufficient abrasion resistance under specific cutting conditions Lt; / RTI >

1. European Patent Publication No. 0603144 2. European Patent Publication No. 0659903 3. European Patent Publication No. 0738336

1. Enhanced performance of alpha Al2O3 coatings by control of crystal orientation, Surface & Coatings Technology 202 (2008) 4257-4269

An object of the present invention is to provide a hard coating comprising an alpha-alumina layer which is excellent in resistance to crater wear generated on the upper surface during high-speed and high-feed processing and can improve tool life.

In order to solve the above problems, the present invention provides a hard coating formed on a surface of a base material of a cutting tool comprising a cemented carbide, cermet, ceramic or cBN, wherein the hard coating comprises an alumina layer formed by more than one layer of CVD, And the crystal grains of the lower layer portion adjacent to the base material side have an angle formed by the normal line of the (006) plane with the normal line of the surface of the base material is 27 to 37 ° and 57 to 67 °, The angle formed between the normal line of the (110) plane and the normal line of the surface of the base material is 0 to 7 degrees and the angle of 40 to 50 degrees, and the crystal grain of the upper layer of the alumina layer is And an angle formed by the normal to the surface of the base material is 0 to 7 ° and 43 to 53 °.

INDUSTRIAL APPLICABILITY The cutting tool having a hard coating according to the present invention is excellent in resistance to crater wear caused during high-speed and high-feed machining, and can improve tool life.

FIG. 1 shows psi rocking analysis results for the (006) surface of the lower layer of the alumina layer according to an embodiment of the present invention.
Figure 2 shows the psi rocking analysis results for the (110) plane of the middle layer of the alumina layer according to an embodiment of the present invention.
3 is a psi rocking analysis result for the (012) surface of the upper layer of the alumina layer according to an embodiment of the present invention.
4 is a psi rocking analysis result for the (110) plane of the middle layer of the alumina layer according to the comparative example.
FIG. 5 shows psi rocking analysis results for the (012) surface of the upper layer of the alumina layer according to the comparative example.
FIG. 6 shows a state of wear of a top surface after evaluation of a cutting performance of an insert having a hard coating according to the present invention.
FIG. 7 shows a state of wear of the upper surface after evaluation of the cutting performance of the insert having the hard coating according to the comparative example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the following embodiments of the present invention may be modified into various other forms, and the scope of the present invention is not limited to the embodiments described below. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

In the present invention, the 'lower layer' of the alumina layer means that the incident angle of X-rays in the psi rocking analysis using XRD analysis equipment is 20.860 ° from the surface of the alumina coating when the surface direction of the hard coating is defined upward in the base material side The "middle layer" of the alumina layer is defined as the portion of the alumina layer to be measured when incident, and the "middle layer" of the alumina layer refers to the direction of the surface of the hard coating on the base material side in the upward direction. In the psi rocking analysis using XRD analysis equipment When the angle of incidence of X-rays is 18.908 ° from the surface of the alumina coating, the portion of the alumina layer to be measured is defined as an intermediate layer and the 'upper layer' of the alumina layer is defined as the upward direction of the surface of the hard coating In the psi rocking analysis using XRD analysis equipment, when the incident angle of X-ray is incident at 12.799 ° from the surface of the alumina coating, This is defined as.

The angle formed by the normal line of the (006) plane of the crystal grain with the normal line of the surface of the base material means the angle formed by the normal line of the (006) crystal plane inside the alumina layer with the normal line of the base material surface on which the alumina layer is formed. This angle can be measured by psi rocking analysis of the XRD equipment, and since the angle between the normal of the (006) plane and the normal of the surface of the base material is measured, the angle at which the (006) plane is detected is 41.720 °, Is fixed at 20.860 ° and the sample is scanned in the psi direction and measured.

The angle formed by the normal line of the (110) plane of the crystal grain with the normal line of the surface of the base material means the angle formed by the normal line of the (110) crystal plane inside the alumina layer with the normal line of the base material surface on which the alumina layer is formed. Since this angle can be measured by psi rocking analysis of the XRD equipment and the angle between the normal of the (110) plane and the normal of the surface of the base material is measured, the 2θ at which the (110) plane is detected is 37.816 °, Is fixed at 18.908 [deg.] And the sample is measured by scanning in the psi direction.

The angle formed by the normal line of the (012) plane of the crystal grain with the normal line of the surface of the base material means the angle formed by the normal line of the (012) crystal plane inside the alumina layer with the normal line of the base material surface on which the alumina layer is formed. Since this angle can be measured by psi rocking analysis of XRD equipment and the angle between the normal of the (012) plane and the normal of the surface of the base material is measured, the angle at which the (012) plane is detected is 25.598 °, Is fixed at 12.799 ° and the sample is scanned in the psi direction.

The hard coating according to the present invention comprises an alumina layer formed by one or more layers of CVD, wherein the alumina layer is formed from the nucleation step to the alpha phase, and the crystal grains of the lower layer portion adjacent to the base material have a Wherein the angle formed by the normal of the (110) plane with the normal of the surface of the base material is 0 to 7 degrees and the angle formed by the normal to the surface of the base material is And an angle formed by the normal of the (012) plane and the normal of the surface of the base material is 0 to 7 degrees and 43 to 53 degrees.

The hard coating according to the present invention is characterized in that the crystal grains constituting the lower layer have an aggregate structure having anisotropy in a specific direction with respect to the (006) plane, the middle layer has an aggregate structure having anisotropy in a specific direction with respect to the (110) (012) plane, it is possible to obtain an alumina layer having excellent resistance to crater wear, which occurs during high-speed and high-feed processing.

Further, the hard coating according to the present invention is applicable to various base materials including cemented carbide, cermet, ceramic or cBN. Preferably, the cutting tool base material comprises 1.5 to 8 wt% of a carbide or carbonitride containing at least one of Ta, Nb and Ti, and 5 to 10 wt% of Co, and the cubic carbide And a non-existent CFL (Cubic Carbide Free Layer) layer may be formed to a thickness of 10 to 40 탆.

The alumina layer included in the hard coating according to the present invention has a TC (012) of at least 2 but less than 3 and a TC (110) of at least 1 and at most 2, in view of the texture coefficient (TC) (006), TC (311), TC (104), and TC (116) are all preferably less than 1.3. This is because when the aggregate coefficient of the crystal plane is out of the above range, It is impossible to obtain sufficient resistance to crater wear.

[Formula 1]

TC (hkl) = I (hkl ) / I o (hkl) × {(1 / n) × ΣI (hkl) / I o (hkl)} -1

I (hkl): diffraction intensity of crystal plane

I _o (hkl): Standard diffraction intensity of ASTM standard powder diffraction data

n: number of crystal faces used in calculation

(hkl): (012), (104), (110), (311), (006), (116)

Further, a TiC _x N _y O _z (x + y + z = 1) layer having a multi-layered structure of two or more layers may be additionally provided between the base material and the alumina layer. The TiC _x N _y O _z (x + y + z = 1) layer may contain elements such as Al, Zr, and B.

[Example]

In the embodiment of the present invention, the hard coating was formed on the cemented carbide base material of the ISO P20-25 grade in the following order.

As a first step, a TiCN layer was formed to a thickness of about 7 to 8 탆 using TiCl ₄ and CH ₃ CN at a temperature of 880 캜 and a pressure of 70 mbar.

In order to suppress the diffusion of Co from the base material to the alumina layer while maintaining the deposition temperature at 1000 ° C in the second step and maintaining the deposition pressure at 500 mbar, a reaction gas containing H ₂ and N ₂ , TiCl ₄ and CH ₄ Was used to form TiCN to a thickness of about 1 to 2 mu m.

The TiAlCNO layer, which can improve the adhesion to the alumina layer by using a reaction gas containing CO and AlCl ₃ , is formed on the TiCN layer to a thickness of about 0.5 to 1 μm while reducing the deposition pressure from about 300 mbar to 120 mbar in the third step .

The surface of the coating was oxidized using CO and CO ₂ gas with the pressure in the furnace being reduced to 60 mbar in the step 4, and then the surface of the coating was oxidized in 5 steps, and the reaction gas containing AlCl ₃ , CO ₂ , CO, H ₂ and H ₂ S Was used to form the alpha-alumina layer.

Table 1 below shows specific process conditions of each of the above processes.

coating Step 5 Al ₂ O ₃ nucleation
And growth 1000 to 1010 < 0 > C, 65 mbar
1 to 5AlCl ₃ + 1 to 5CO ₂ + 0 to 3CO + Bal.H ₂ + 0 to 0.5H ₂ S Step 4 TiAlCNO oxidation 1000 to 1010 C, 60 mbar
_{1 ~ 5CO 2 + 0 ~ 3CO} + Bal.H 2 Step 3 TiAlCNO 1000 to 1010 < 0 > C, 120 to 300 mbar
1 to 5 TiCl ₄ + 1 to 3 CH ₄ + 1 to 10 CO + Bal.H ₂ + 1 to 5 N ₂ + 0.5 to 10 AlCl ₃ Step 2 TiCN 1000 C, 500 mbar
2 to 5 TiCl ₄ + 1 to 15 CH ₄ + Bal.H ₂ + 1 to 40 N ₂ Stage 1 MT-CVD TiCN 880 DEG C, 70 mbar
2 to 10 TiCl ₄ + 0.1 to ₅ CH ₃ CN + Bal.H ₂ + 20 to 40 N ₂ Base material Grade: ISO P20-25 grade
Model number: CNMG120408-HM 86WC-2.5TiCN-4TaNbC-7.5Co
Cubic carbide Free layer; 20 ~ 25㎛

In Table 1, the numerals shown in the base material represent weight%, and the numerals shown in the gas component represent volume%.

In order to evaluate the orientation of the α-alumina layer formed through the above process, psi rocking analysis was performed after the X-ray incident angles were entered at 12.799 °, 18.908 ° and 20.860 °, respectively.

Figure 1 shows psi rocking analysis results for the (006) surface of the lower layer of the alumina layer formed according to an embodiment of the present invention. As shown in FIG. 1, in the lower layer of the alumina layer according to the embodiment of the present invention, the psi rocking analysis of the (006) plane revealed that the center of the first peak having the highest intensity was located between 27 and 37 degrees, The center of the second peak is observed at 57-67 °. In the lower layer of the alumina layer formed according to the embodiment of the present invention, a large number of crystal grains having an angle of about 30 ° with respect to the surface of the base material and a normal line to the (006) plane are formed, Means that a crystal grain is formed. That is, the lower layer portion of the alumina layer coexisted with the (006) plane inclined at about 30 ° to the normal direction of the surface of the base material and inclined at about 60 °.

Figure 2 shows psi rocking analysis results for the (110) plane of the middle layer of the alumina layer formed in accordance with an embodiment of the present invention. As shown in FIG. 2, in the case of the middle layer of the alumina layer according to the embodiment of the present invention, the psi rocking analysis for the (110) plane shows that the center of the first peak having the greatest intensity is located between 0 and 7 degrees, The center of the second peak is observed at 40-50 °. In the case of the middle layer of the alumina layer formed according to the embodiment of the present invention, a large number of crystal grains having an angle of about 3 DEG with respect to the normal line of the surface of the base material and the normal line of the (110) plane are formed, Means that a crystal grain forming an angle is formed. That is, the middle layer of the alumina layer coexisted with the normal of the (110) plane perpendicular to the surface of the base material and about 45 degrees inclined.

3 shows psi rocking analysis results for the (012) surface of the upper layer of the alumina layer formed according to an embodiment of the present invention. 3, in the case of the upper layer of the alumina layer according to the embodiment of the present invention, the center of a peak having a high strength in peaks as a result of psi rocking analysis for the (012) plane is located between 0 and 7 degrees, The center of the second peak is observed at 43-53 °. In the upper layer of the alumina layer formed according to the embodiment of the present invention, a large number of grains having an angle of about 2 to 3 degrees with respect to the normal to the surface of the base material and the normal to the (012) plane are formed, (012) plane is formed in a direction perpendicular to the surface of the base material because the intensity of the second peak is very low.

Also, the result of calculation of the texture coefficient (TC) according to the formula 1 for the alpha-alumina layer formed according to the embodiment of the present invention was as follows.

- TC (012): 2.9

- TC (110): 1.1

- TC (006): 1.2

- TC (311): 0.3

- TC (104): 0.2

- TC (116): 0.3

[Comparative Example]

For comparison with the hard coating according to the embodiment of the present invention, a hard coating having different orientation of the alpha-alumina layer of the upper layer was formed. The specific manufacturing process of the hard coating according to the comparative example is shown in Table 2 below.

coating Step 4
Al ₂ O ₃ nucleation
And growth 1000 to 1010 < 0 > C, 65 mbar
1 to 5AlCl ₃ + 1 to 5CO ₂ + 0 to 3CO + Bal.H ₂ + 0 to 0.5H ₂ S Step 3 TiAlCNO 1000 to 1010 < 0 > C, 120 to 300 mbar
1 to 5 TiCl ₄ + 1 to 3 CH ₄ + 1 to 10 CO + Bal.H ₂ + 1 to 5 N ₂ + 0.5 to 10 AlCl ₃ Step 2 TiCN 1000 C, 500 mbar
2 to 5 TiCl ₄ + 1 to 15 CH ₄ + Bal.H ₂ + 1 to 40 N ₂ Stage 1 MT-CVD TiCN 880 DEG C, 70 mbar
2 to 10 TiCl ₄ + 0.1 to ₅ CH ₃ CN + Bal.H ₂ + 20 to 40 N ₂ Base material Grade: ISO P20-25 grade
Model number: CNMG120408-HM 86WC-2.5TiCN-4TaNbC-7.5Co
Cubic carbide Free layer; 20 ~ 25㎛

In Table 2, the numerals in the base material mean% by weight, and the numerals in the gas components mean volume%.

As shown in Table 2, the hard coating according to the comparative example differs from the hard coating according to the embodiment of the present invention in that the four-step process is omitted and the five-step process is performed.

In order to evaluate the orientation properties of the alpha-alumina layer formed through the above process, in order to evaluate anisotropy according to the layer thicknesses of the formed alpha-alumina layer, the X-ray incident angles were entered at 12.799 °, 18.908 °, and 20.860 °, respectively, psi rocking analysis was performed.

However, in the case of the comparative example, psi rocking analysis results for the (006) plane of the lower layer portion could not be obtained, which means that the orientation to the (006) plane was not observed.

FIG. 4 shows psi rocking analysis results for the (110) plane of the middle layer of the alumina layer according to the comparative example. As shown in FIG. 4, in the middle layer of the alumina layer according to the comparative example, only one peak is observed as a result of psi rocking analysis, and the center of the peak is located at 50 to 60 degrees. This means that the intermediate layer of the alumina layer according to the comparative example is oriented in a shape in which the normal line of the (110) plane is inclined by about 55 ° with respect to the normal line of the surface of the base material.

FIG. 5 shows psi rocking analysis results for the (012) surface of the upper layer of the alumina layer according to the comparative example. As shown in FIG. 5, in the upper layer of the alumina layer according to the comparative example, only one peak is observed as a result of psi rocking analysis, and the center of the peak is located at 0 to 10 degrees. This means that the upper part of the alumina layer according to the comparative example is oriented perpendicular to the surface of the base material.

As is apparent from the above description, the upper layer of the alumina layer according to the comparative example is oriented in a manner substantially similar to the embodiment of the present invention, but the intermediate layer and the lower layer portion are oriented in a different form from the embodiment of the present invention have.

In addition, the result of calculating the texture coefficient (TC) according to Equation 1 for the α-alumina layer formed according to the comparative example is as follows.

- TC (012): 1.4

- TC (110): 0.8

- TC (006): 0.6

- TC (311): 1.2

- TC (104): 0.4

- TC (116): 1.6

Cutting performance evaluation result

Using the insert having the hard coating prepared according to the example of the present invention and the comparative example, the surface abrasion resistance was evaluated under the following conditions.

- Workpiece: S45C

- Rotation speed (Vc): 350m / min

- Feed rate (fn): 0.35mm / rev

- Infeed depth (ap): 2 mm

- Coolant: Application

The measurement intervals for the examples and the comparative examples were 5 minutes. After 30 minutes in total, the surface wear of the inserts of the examples and the comparative examples was compared and observed in FIGS. 6 and 7.

As shown in FIG. 7, in the case of the hard coating having the alumina layer according to the comparative example, large wear occurred on the upper surface of the insert, but in the case of the hard coating having the alumina layer according to the present invention under the same cutting conditions, Of the wearer's wear was greatly reduced. That is, the wear resistance of the hard coating having alumina according to the embodiment of the present invention is significantly improved as compared with the comparative example.

Claims (4)

A hard coating formed on the surface of a cutting tool base material comprising cemented carbide, cermet, ceramic or cBN,
Wherein the hard coating comprises an alumina layer formed by more than one layer of CVD,
Wherein the alumina layer consists of nucleation to alpha phases,
The crystal grains in the lower layer portion adjacent to the base material side have an angle formed by the normal to the (006) plane and the normal to the surface of the base material is 27 to 37 degrees and 57 to 67 degrees,
The crystal grains of the intermediate layer of the alumina layer are such that the angle formed by the normal to the (110) plane and the normal to the surface of the base material is 0 to 7 ° and 40 to 50 °,
Wherein an angle formed between a normal to the (012) plane and a normal to the surface of the base material is 0 to 7 degrees and 43 to 53 degrees. The method according to claim 1,
Wherein the alumina layer has a TC (012) of 2 or more and less than 3,
TC 110 is 1 or more and less than 2,
Wherein the TC (006), TC (311), TC (104) and TC (116) are all less than 1.3.
[Formula 1]
TC (hkl) = I (hkl) / Io (hkl) x {(1 / n) x I (hkl) / Io (hkl)} ^-1
I (hkl): diffraction intensity of crystal plane
Io (hkl): Standard diffraction intensity of ASTM standard powder diffraction data
n: number of crystal faces used in calculation
(hkl): (012), (104), (110), (311), (006), (116) The method according to claim 1,
Wherein the cutting tool base material comprises 1.5 to 8 wt% of carbide or carbonitride containing at least one of Ta, Nb, and Ti, the content of Co is 5 to 10 wt%, and the cubic carbide Wherein a non-existent CFL (Cubic Carbide Free Layer) layer is formed to a thickness of 10 to 40 탆. The method according to claim 1,
Hard coating film for the cutting tool comprises a base material and the layer of aluminum oxide added to one layer or more of _{TiC x N y O z (x} + y + z = 1) in between.

Images