Patent Application
20230286056
This application claims priority to Korean Patent Application No. 10-2022-0029266 filed on Mar. 8, 2022, and all the benefits accruing therefrom under 35 U.S.C. § 119, the contents of which are incorporated by reference in their entirety.
The present disclosure herein relates to a coated cutting tool in which a coating layer including an α-Al2O3 layer is formed, and a method for making the coating layer.
A coating requires an excellent adhesion to a base material in conjunction with the mechanical excellence of a coating material. In order to secure excellent adhesion, a method of depositing a plurality of coating layers by overlapping them has been conventionally used. α-Al2O3, which is one of the coating materials, is a material having good chemical stability and thermal properties, and an α-Al2O3 texture control technology may be used to improve mechanical properties of the α-Al2O3 thin film by controlling a crystallographic direction for growing the α-Al2O3 texture. Conventionally, the α-Al2O3 thin film technology has been well-known in which the texture is controlled in the plane directions of (006), (012), (104), (110), (113), (116), and the like. Among them, the (006) crystallographic orientation has texture characteristics that are mechanically superior to other orientations, and Korean Patent No. 10-1314504 discloses an example of a technique for the orientation.
A method for making an α-Al2O3 thin film on the surface of a substrate is conventionally known, which is formed by sequentially stacking a TiN layer on a base material, an MT-TiCN layer, an HT-TiCN bonding layer, and a TiCNO bonding layer, and then depositing an α-Al2O3 layer on the TiCNO bonding layer. The HT-TiCN layer, which is a bonding layer provided between the α-Al2O3 layer and the MT-TiCN layer, is a dense equiaxed crystal structure and is deposited at a high temperature of 1,000° C. or higher using mainly N2 and CH4 gases as a source. Although the HT-TiCN bonding layer provides excellent adhesion between the MT-TiCN layer and the α-Al2O3 layer, there is a limitation in that the HT-TiCN bonding layer has a side effect of inducing the texture of the α-Al2O3 layer to the (104) plane orientation, and thus interferes with the (006) plane orientation of the α-Al2O3 layer. Therefore, in order to suppress the side effect of interfering the orientation of the plane with the (006) plane orientation, the thickness of the TiCNO bonding layer is increased in the related art, and when the TiCNO bonding layer becomes thick, the adhesiveness of the HT-TiCN bonding layer to the α-Al2O3 layer deteriorates, resulting in poor performance and life of the tool.
The present disclosure provides a coated cutting tool in which a coating layer including an α-Al2O3 layer in a strong (006) plane orientation is formed, and a method for making the coating layer which can deposit an α-Al2O3 layer with excellent adhesion.
In accordance with an exemplary embodiment of the present invention, a cutting tool includes a substrate, a coating layer formed on the upper portion of the substrate, wherein the coating layer includes: an MT-TiCN layer formed by an MTCVD technique; a TiCNO layer, which is a bonding layer directly deposited on the surface of the MT-TiCN layer; and an α-Al2O3 layer, which are sequentially formed from the substrate side. Therefore, there does not exist an HT-TiCN layer between the MT-TiCN layer and the α-Al2O3 layer.
The MT-TiCN layer has a columnar structure and has texture coefficients of TC(311)>1.5 and TC(422)>1.5, and the α-Al2O3 layer has a texture coefficient of TC(006)>4 and is formed of columnar grains. Here, the TC (311), TC (422), and TC (006) are defined according to the Equation below which is Harris formula.
I(hkl) above is the reflection or diffraction intensity of the measured (hkl) plane, and I0(hkl) above is the standard intensity according to the PDF of ICDD. The standard intensity according to the PDF Card No. 42-1489 of ICDD is used to calculate the texture coefficient of the MT-TiCN layer, and the standard intensity according to the PDF Card No. 42-1212 of ICDD is used to calculate the texture coefficient of the α-Al2O3 layer.
n is the number of reflecting planes used in the calculation of the texture coefficients, the (hkl) reflecting planes used in the calculation of the texture coefficient of the MT-TiCN layer are (111), (200), (220), (311), and (422) and the (hkl) reflecting planes used in the calculation of the texture coefficient of the α-Al2O3 layer are (012), (104), (110), (006), (113), and (116).
According to an embodiment, the MT-TiCN layer includes an upper layer and a lower layer thereof, and thus the TiCNO layer is directly deposited on the surface of the upper layer. The deposition temperature of the upper layer is 1.11-1.15 times higher than that of the lower layer. The lower layer is deposited by a chemical vapor deposition (CVD) method using H2, TiCl4, and CH3CN as a source at 850° C. at an initial stage, and using H2, N2, TiCl4, and CH3CN as a source at 850° C. at a middle stage, and the upper layer is deposited by the CVD method using H2, N2, TiCl4, CH3CN, and HCl as a source at 950° C.
According to an embodiment, the thickness of the TiCNO bonding layer is preferably 0.2 μm to 1.3 μm, the thickness of the α-Al2O3 layer is preferably 1.5 μm to 10 μm, and the thickness of the MT-TiCN layer is preferably 2 μm to 12 μm.
According to another embodiment, the coating layer of the present disclosure may further include a TiN layer formed on the upper surface of the α-Al2O3 layer by using a mixed gas of H2, N2, and TiCl4 as a source.
Meanwhile, the surface of the coating layer may be subjected to a brushing process using a paste containing diamond powder.
Method for Making a Coating Layer
The present disclosure pertains to a method for making a coating layer on the whole or part of a substrate of a cutting tool. The method for making a coating layer according to the present disclosure includes: depositing a TiN layer on the upper surface of the substrate; depositing an MT-TiCN layer which has texture coefficients of TC(311)>1.5 and TC(422)>1.5 and is formed of columnar grains of TiCN deposited on the TiN layer by a chemical vapor deposition method within the range of 800° C. to 950° C.; depositing a TiCNO bonding layer on the upper surface of the MT-TiCN layer, and then oxidizing the TiCNO bonding layer for a predetermined time using H2, N2, CO, and CO2; and depositing, on the oxidized TiCNO bonding layer, an α-Al2O3 layer which has a texture coefficient of TC(006)>4 and is formed of columnar grains.
Exemplary embodiments can be understood in more detail from the following description taken in conjunction with the accompanying drawings, in which:
Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.
Referring to
The substrate 101 may be formed of a material such as a superhard material, such as ceramic or cubic boron nitride (CBN), or a cemented carbide, and a cemented carbide, which is generally widely used, is preferable. The cemented carbide includes 4-15 wt % of Co (preferably 6-10 wt % of Co) and 5-12 vol % of cubic carbides of metals from groups IV, V and VI of the periodic table (preferably Ti, Nb, and Ta).
The coating layer 110 is formed on the substrate 101, and a TiN layer 103, an MT-TiCN layer 105, a TiCNO bonding layer 107, and an α-Al2O3 layer 109 are deposited in this order using a chemical vapor deposition (CVD) method.
The TiN layer 103 is provided on the upper portion of the substrate 101 using a mixed gas of H2, N2, and TiCl4 as source.
The MT-TiCN layer 105 is formed by being coated on the upper surface of the TiN layer 103 with a gas selectively mixed with H2, N2, TiCl4, CH3CN and HCl as source using a medium temperature chemical vapor deposition (MTCVD) technique.
Here, the MTCVD is a chemical vapor deposition method within a temperature range of 800° C. to 950° C., and the TiCN coating film coated with the MTCVD technique is referred to as the MT-TiCN layer 105. The thickness of the MT-TiCN layer 105 is 2 μm to 12 μm, preferably 3 μm to 9 μm. When the MT-TiCN layer 105 is thinner than 2 μm, the crystallographic characteristics of the columnar are not sufficiently met, and thus the chipping resistance or resistance against flank wear of the tool may be deteriorated, and when the thickness of the layer 105 exceeds 12 μm, the coating may be flaked off and the chipping resistance thereof may be weakened, and thus the tool life may be reduced. The MT-TiCN layer 105 includes a lower layer 401 and an upper layer 403 deposited under different temperature conditions as shown in
The TiCNO bonding layer 107 is formed on the upper surface of the MT-TiCN layer 105 using a mixed gas of H2, N2, TiCl4, CH3CN, and CO as source. The TiCNO bonding layer 107 is a bonding layer that bonds the MT-TiCN layer 105 and the α-Al2O3 layer 109, and bonds the MT-TiCN layer 105 and the α-Al2O3 layer 109 without using the HT-TiCN layer unlike the related art. The TiCNO bonding layer 107 is formed to be a thickness of 0.2 μm to 1.3 μm. When the TiCNO bonding layer 107 is thinner than 0.2 μm, it is difficult to obtain a high (006) T.C value of α-Al2O3, and when the TiCNO bonding layer 107 exceeds 1.3 μm, the adhesiveness with the underlying layer is inhibited to cause flaking between the MT-TiCN 105 and the α-Al2O3 layer 109, and thus the tool life may be reduced.
The α-Al2O3 layer 109 is formed on the upper surface of the TiCNO bonding layer 107 using a gas selectively mixed with H2, HCl, AlCl3, CO2 and H2S as source. The α-Al2O3 layer 109 is deposited to be a thickness of 1.5 μm to 10 μm. When the α-Al2O3 layer 109 is thinner than 1.5 μm, it is difficult to prevent plastic deformation due to high temperatures generated during cutting, and it is difficult to have sufficient wear-resistance, thereby reducing the tool life, and when the α-Al2O3 layer 109 exceeds 10 μm, the flaking resistance and chipping resistance of the coating are weakened, thereby causing an unexpected end-of-life. In the present disclosure, the MT-TiCN layer 105 and the α-Al2O3 layer 109 are formed of columnar grains.
Crystallographic Characteristics of MT-TiCN Layer 105 and α-Al2O3 Layer 109
Hereinafter, the crystallographic characteristics of the MT-TiCN layer 105 and the α-Al2O3 layer 109 of the present disclosure are defined by using a texture coefficient (TC) obtained according to the Harris formula using an X-ray diffraction analysis (XRD) diffraction pattern. When defined as the texture coefficient obtained according to the Harris formula, the MT-TiCN layer 105 has characteristics of TC(311)>1.5 and TC(422)>1.5, and the α-Al2O3 layer 109 has characteristics of TC(006)>4. The Harris formula is as shown in Equation 1 below:
In Equation 1, I(hkl) is the reflection or diffraction intensity of the measured (hkl) plane, and I0(hkl) is the standard intensity according to the powder diffraction file (PDF) of International Centre for Diffraction Data (ICDD). The standard intensity according to the PDF Card No. 42-1489 of ICDD is used for the calculation of the texture coefficient of the MT-TiCN layer 105, and the standard intensity according to the PDF Card No. 42-1212 of ICDD is used for the calculation of the texture coefficient of the α-Al2O3 layer 109. The PDF of ICDD is data on the basis of a standard powder, and is an organic and inorganic diffraction database for phase identification and material characterization by powder diffraction.
In Equation 1, n is a natural number n>0, which is the number of reflecting planes used to calculate the texture coefficient.
The (hkl) reflecting planes used to calculate the texture coefficient of the MT-TiCN layer 105 are (111), (200), (220), (311) and (422), and under this condition, the MT-TiCN layer 105 of the present disclosure should satisfy TC(311)>1.5 and TC(422)>1.5. By satisfying this, the orientation of the MT-TiCN layer 105 may strongly facilitate the (006) plane orientation of the α-Al2O3 layer 109. As described above, the thickness of the MT-TiCN layer 105 is 2 μm to 12 μm, preferably 3 μm to 9 μm.
The (hkl) reflecting planes used to calculate the texture coefficients of the α-Al2O3 layer 109 are (012), (104), (110), (006), (113) and (116), and the α-Al2O3 layer 109 of the present disclosure should satisfy TC(006)>4. The fact that TC (006) is greater than 4 means that the crystallographic orientation of the α-Al2O3 layer 109 has been made strongly in the <001> direction because if the texture coefficient TC(hkl) according to the Harris formula is greater than 1, it means that the orientation of the crystalline material is present parallel to the surface of the substrate at least more frequently than the random orientation of the standard powder. The strong (006) plane orientation of the α-Al2O3 layer 109 means that the orientation of the crystal in the <001> crystallographic direction has been achieved, and the (006) plane orientation has grown to a (006) crystallographic plane that is more frequently parallel to the surface of the substrate than other crystallographic planes of the α-Al2O3 layer that are parallel to the surface of the substrate.
The coating layer (110) of the present disclosure, which is formed as the composite layers as described above, has strong resistance against crater wear and flank wear, and has an excellent bonding force between the MT-TiCN layer 105 and the α-Al2O3 layer 109 so that the chipping resistance is improved. Above all, since the coating layer 110 of the present disclosure does not use the HT-TiCN layer, the limitation, in which the (006) plane orientation of the α-Al2O3 layer 109 is disturbed by using the HT-TiCN layer as described in the background art, is eliminated.
Method for Producing Coating (Coating Layer)
Hereinafter, referring to
<Production of TiN Layer: S201>
In the chamber, a substrate 101 is disposed as a target, a mixed gas of H2, N2, and TiCl4 is used as source in the chamber, and a TiN layer 103 is deposited.
<Deposition of MT-TiCN Layer: S203>
The MT-TiCN layer 105 is deposited on the upper surface of the TiN layer 103 using a gas selectively mixed with H2, N2, TiCl4, CH3CN, and HCl as source by means of an MTCVD technique. For the MT-TiCN layer 105, a lower layer 401 is deposited using H2, TiCl4 and CH3CN as source at 850° C. at an initial stage and using H2, N2, TiCl4 and CH3CN as source at 850° C. at a middle stage, and then at the end stage of the deposition, an upper layer 403 is deposited using H2, N2, TiCl4, CH3CN and HCl as source at 950° C. By such adjustment of the deposition temperature, the MT-TiCN layer 105 includes the lower layer 401 deposited at 850° C. and the upper layer 403 deposited at 950° C. as shown in
<Deposition of TiCNO Layer: S205, S207>
When the MT-TiCN layer 105 has been deposited, a thin TiCNO bonding layer 107 is deposited on the upper surface of the MT-TiCN layer 105 by using a mixed gas of H2, N2, TiCl4, CH3CN, and CO as source (S205). When the TiCNO bonding layer 107 has been deposited, oxidation is performed for approximately 2 minutes by using H2, N2, CO, and CO2 (S207).
<Deposition of α-Al2O3 Layer: S209>
A gas selectively mixed with H2, HCl, AlCl3, CO2, and H2S is used as source to deposit the α-Al2O3 layer 109 on the upper surface of the oxidized TiCNO bonding layer 107.
<Polishing: S211>
According to an example, after the α-Al2O3 layer 109 is deposited, the surface of the α-Al2O3 layer 109 may be polished by brushing the surface thereof using a paste including diamond powder. The production of the coating (coating layer) of the present disclosure is performed by the above method.
Referring to
The TiN layer 301 further improves the wear-resistance of the thin film, and at the same time, acts as a wear-recognition layer which displays the wear state of the coating layer because the TiN layer is yellow.
In order to evaluate the performance of the coating layer 110 formed by the present disclosure, an evaluation sample obtained by coating an insert according to the present disclosure, and first and second comparative samples using the HT-TiCN bonding layer were produced, respectively, and compared as follows. The HT-TiCN layer was used for each of the first and second comparative samples.
<Evaluation Sample>
On the upper portion of the substrate of a cemented carbide cutting tool with an ISO P15 grade, a TiN layer having about 0.5 μm was deposited using H2, N2 and TiCl4, and an MT-TiCN layer having about 8 μm was deposited on the upper surface of the TiN layer using H2, N2, TiCl4, CH3CN and HCl as source. At the initial stage of deposition of the MT-TiCN layer, H2, TiCl4 and CH3CN were used as source at 850° C., at the middle stage, H2, N2, TiCl4 and CH3CN were used as source at 850° C., and at the end stage of deposition, H2, N2, TiCl4, CH3CN and HCl were used as source, and the deposition temperature was controlled at 950° C., and thus the MT-TiCN layer was maintained, and an HTCVD method for depositing the HT-TiCN layer was not used. Table 1 shows the detailed deposition conditions of TiN and MT-TiCN of the evaluation sample.
Under the deposition conditions of 1,000° C. and 55 mbar, a TiCNO bonding layer 107 having a thickness of 0.3 μm to 1 μm was deposited on the upper surface of the MT-TiCN layer 105 using H2, N2, TiCl4, CH3CN, and CO, and oxidized for 2 minutes using H2, N2, CO, and CO2. After oxidation, the α-Al2O3 layer 109 was deposited in two steps under the deposition conditions of 1,000° C. and 65 mbar. First, an initial α-Al2O3 was deposited to be a thickness of about 0.2 μm using H2, HCl, AlCl3, and CO2, and an end α-Al2O3 layer was deposited to be a thickness of about 8 μm using H2, HCl, AlCl3, CO2, and H2S as source, thereby producing an evaluation sample of the present disclosure. Table 2 shows the detailed deposition conditions of the TiCNO layer and the α-Al2O3 layer of the evaluation sample.
<First Comparative Sample>
On the upper portion of the same substrate as the evaluation sample, a TiN layer and an MT-TiCN layer were deposited by a conventional method, and an HT-TiCN bonding layer having about 1 μm was deposited by the HTCVD technique. A TiN layer having about 0.5 μm was deposited on the substrate using H2, N2, and TiCl4, and an MT-TiCN layer having about 8 μm and an HT-TiCN layer having about 1 μm were sequentially deposited on the upper surface of the TiN layer. In the case of the MT-TiCN layer, H2, TiCl4, and CH3CN were used as an initial-stage source at 850° C., and H2, N2, TiCl4, and CH3CN were used as a middle-stage source. At the end stage of the TiCN deposition, an HT-TiCN bonding layer having about 1 μm was deposited on the upper surface of the MT-TiCN layer under conditions of 1,000° C. and 160 mbar according to the HTCVD method using H2, N2, TiCl4, and CH4 as source. Table 3 shows the detailed deposition conditions of TiN, MT-TiCN and HT-TiCN of the first comparative sample.
Under the deposition conditions of 1,000° C. and 55 mbar, a TiCNO layer having a thickness of 0.3 μm to 1 μm was deposited on the upper surface of the HT-TiCN layer using H2, N2, TiCl4, CH3CN, and CO, and oxidized for 2 minutes using H2, N2, CO, and CO2. After oxidation, in the same manner as in the evaluation sample, an α-Al2O3 layer was deposited in two steps under deposition conditions of 1,000° C. and 65 mbar. First, an initial α-Al2O3 was deposited to be a thickness of about 0.2 μm using H2, HCl, AlCl3, and CO2, and an end α-Al2O3 layer was deposited to be a thickness of about 8 μm using H2, HCl, AlCl3, CO2, and H2S as source, thereby producing a first comparative sample. Table 4 shows the detailed deposition conditions of the TiCNO layer and the α-Al2O3 layer of the first comparative sample.
<Second Comparative Sample>
On the upper portion of the same substrate as the evaluation sample, a TiN layer and an MT-TiCN layer were deposited by a conventional method, and an HT-TiCN bonding layer having about 1 μm was deposited by the HTCVD technique. A TiN layer having about 0.5 μm was deposited on the substrate using H2, N2, and TiCl4, and an MT-TiCN layer having about 8 μm and an HT-TiCN layer having about 1 μm were sequentially deposited on the upper surface of the TiN layer. In the case of the MT-TiCN layer, H2, TiCl4, and CH3CN were used as an initial-stage source at 850° C., and H2, N2, TiCl4, and CH3CN were used as a middle-stage source. At the end stage of the TiCN deposition, an HT-TiCN bonding layer having about 1 μm was deposited on the upper surface of the MT-TiCN layer under conditions of 1,000° C. and 160 mbar according to the HTCVD method using H2, N2, TiCl4, and CH4 as source. Table 5 shows the detailed deposition conditions of TiN, MT-TiCN and HT-TiCN of the second comparative sample.
The detailed deposition conditions of the TiCNO layer and the α-Al2O3 layer of the second comparative sample are the same as those of the first comparative sample. However, the TiCNO layer of the second comparative sample was deposited to be a thickness of 1 μm to 3 μm, being thicker than the thickness of the first comparative sample. Table 6 shows the detailed deposition conditions of the TiCNO layer and the α-Al2O3 layer of the second comparative sample.
<Analysis of Texture Coefficients>
The X-ray diffraction equipment (model X'pert) made by PANalytical was utilized to analyze the texture of the coating layer, and the analysis was performed using a detector equipped with Bragg Brentano HD (hereinafter, BBHD) and PIXcel 3D. The XRD electrode material is copper (Cu), and for the analysis, a voltage of 45 kV and a wavelength of Cu-Kα of 40 mA were used. For the analysis, the BBHD equipped with a 1/20 anti-scatter slit and a ⅛° divergence and 10 mm-mask were used, and the detector, to which a ½ solar slit was fastened, was used. The analysis was performed on 2θ angles of 20° to 145° by the θ-2θ method. The analysis was performed on the flank plane of the sample while the appropriate height and balance of the sample were adjusted. The analysis, including background subtraction, Cu-Kα2 stripping and profile fitting of the data, was performed using PANalytical's HighScore Plus program. The texture coefficients were calculated by applying the data derived through the program to the Harris formula (Equation 1).
Since the length of the path through which the X-ray penetrates is different depending on the 20 angle of the thin film, unlike the bulk sample, the linear absorption coefficient of the thin film should be taken into account when calculating the texture coefficient, and thus the thin film correction was applied to the integrated peak area intensities for the profile fitted curve. If the α-Al2O3 layer is not the uppermost layer, the upper layer of the α-Al2O3 layer may be removed by methods such as chemical etching and blasting that do not influence the XRD measurement, and then the analysis may be performed.
According to the above-described analysis method, the texture coefficients of the α-Al2O3 layer and the MT-TiCN layer of the evaluation sample of the present disclosure, the first comparative sample, and the second comparative sample are shown in Table 7.
Referring to Table 7, it may be seen that the MT-TiCN layer of the evaluation sample satisfies TC(311)>1.5 and TC(422)>1.5, and the α-Al2O3 layer also satisfies TC(006)>4. Thus, it may be seen that by using the method of the present disclosure, the α-Al2O3 layer with a strong (006) plane orientation may be obtained.
<Thickness Analysis>
The cross-sectional textures of the evaluation sample, the first comparative sample, and the second comparative sample were analyzed with an optical microscope at 1000× magnification to measure the thickness of each coating layer. Table 8 shows the thickness of each coating layer measured with an optical microscope at 1000× magnification. Referring to Table 8, it may be seen that the HT-TiCN layer was not formed in the evaluation sample, and the α-Al2O3 layer 109 was deposited to be a sufficient thickness.
<Performance Comparison of Evaluation Sample and Comparative Sample>
(1) Cutting Performance Evaluation: Wear Resistance Evaluation
Table 9 below is a table for comparing the lives of the tools measured when the end-of-life criterion is Vb>0.25 mm at the main cutting edge, and it may be seen that the tool life of the evaluation sample measured on the basis of the resistance against the flank wear is longer than those of the first and second comparative samples, and thus the mechanical stiffness is more excellent than those of the first and second comparative samples. Here, Vb is the flank wear.
(2) Cutting Performance Evaluation: Chipping Resistance Evaluation
Table 10 below shows the tool life measured on the basis of the occurrence of chipping without separate damage or wear, and the tool life of the evaluation sample is similar to that of the first comparative sample and longer than that of the second comparison sample. Therefore, it may be seen that the coating layer 110 produced according to the present disclosure has excellent bonding force between the MT-TiCN layer 105 and the α-Al2O3 layer 109, thereby improving the chipping resistance.
According to the present disclosure, a thin film for a cutting tool having improved wear-resistance and chipping resistance can be achieved by depositing an α-Al2O3 layer having a strong (006) plane orientation in the <001> crystallographic direction with excellent adhesion, and a cutting tool having a predictable tool life may be provided.
The present disclosure presents a method for manufacturing a cutting tool in which a coating of α-Al2O3 material is formed without using an HT-TiCN bonding layer, thereby providing a thin film having excellent mechanical properties and a cutting tool coated with the thin film in a simpler and more efficient manner as compared to conventional methods.
Although the preferred embodiments of the present invention have been illustrated and described above, the present invention is not limited to the above-described specific embodiments, and various modifications can be made by those skilled in the art without departing from the spirit and scope of the present invention defined by the appended claims, and such modifications should not be individually understood from the technical spirit or the scope of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0029266 | Mar 2022 | KR | national |
