KR101215463B1 - Thin film for cutting tools - Google Patents

Abstract

An object of the present invention is to provide a cutting tool thin film manufactured by the LPCVD method which is improved in cutting performance and excellent in heat resistance at a high temperature, compared to the Al _x Ti _1-x N thin film formed by the PVD method.
The cutting tool thin film according to the present invention for achieving the above object,
It has a composition represented by the following [Formula 1] prepared by LPCVD method,
Thin film with residual stress of 1GPa ~ -2GPa.
[Formula 1]
Al _x Ti _y Si _z Cr _w N
(Where x + y + z + w = 1, x≥0.75, y≥0.1, 0 <z≤0.06, 0.01≤w≤0.06)

Description

Thin Films for Cutting Tools {THIN FILM FOR CUTTING TOOLS}

The present invention relates to a thin film coated on the surface of a cutting tool, and more particularly, to the LPCVD method, which has improved cutting performance and excellent thermal resistance at high temperature, compared to an Al _x Ti _1-x N thin film formed by the PVD method. It relates to an Al _x Ti _y Si _z Cr _w N thin film produced by.

Al _x Ti _{1 - x} N thin films manufactured by physical vapor deposition (PVD) include aluminum (hereinafter referred to as 'Al') in the composition of the thin film, so that high temperature and oxidizing atmosphere such as cutting is performed. Since Al combines with oxygen in the air to form alumina (Al ₂ O ₃ ) on the surface of the thin film to block oxidation of the thin film, the content of conventional TiN, TiCN and titanium (hereinafter 'Ti') Compared to many TiAlN coatings, it is usefully used as a cutting insert for high speed milling and a thin film for tools.

However, as the content of Al increases, the hardness and oxidation resistance of the thin film formed by the above-described effects are improved, and the maximum content (x) of the solid solution can be found to be about 0.65 by the PVD method. This means that when the Al content (x) is greater than or equal to 0.64, the phase structure of fcc-Al _x Ti _{1 - x} N is TiN + h-AlN, and phase decomposition occurs, and in general, the h-AlN phase is crystallized. Because of its low hardness, the h-AlN phase is not suitable for cutting tool thin films because of its low hardness.

On the other hand, German Patent Publication DE102007000512, by using a Low Pressure Chemical Vapor Deposition (LPCVD) to increase the content of Al which was the limit of the Al _x Ti _{1 - x} N thin film manufactured by conventional PVD A method has been proposed. According to this method, the main reaction gases are H ₂ , Ar, NH ₃ , TiCl ₄ , AlCl ₃ AlCl ₃ is produced by the reaction of H ₂ and Al chip, and the deposition pressure is about 100 mbar and the deposition temperature is about 800 ~ 850 ℃ to form an Al _x Ti _{1 - x} N thin film. When using this method, the content of Al in the Al _x Ti _{1 - x} N thin film (x) is improved to about 0.8 to 0.9, which occurs when the content of Al in PVD (x) exceeds 0.65. The phase separation phenomenon was not observed, and Al-riched Al _x Ti _{1 - x} N thin films manufactured by LPCVD had a cutting performance of about 20 to 30% compared to Al _x Ti _{1 - x} N thin films prepared by PVD. Improvements are reported to be identified.

However, when Al-riched Al _x Ti _{1 - x} N thin films by LPCVD are exposed for a long time in a high temperature atmosphere, Al or Ti bonds with oxygen atoms, causing Al ₂ O ₃ , TiO ₂ And the like, thereby gradually causing phase separation in the pure fcc crystal structure, resulting in a problem of deterioration in hardness.

The present invention is manufactured by, PVD method serves to improve the problems of the Al _x Ti _1-x N thin films to be coated for the purpose of improving the cutting performance on the surface of the above-described conventional cutting tool Al _x Ti _1-x It is an object of the present invention to provide a cutting tool thin film having excellent high temperature oxidation resistance and high temperature hardness, in which cutting performance is greatly improved compared to N thin film, and at the same time, hardness reduction due to phase separation does not occur even when used for a long time in a high temperature atmosphere.

As a means for solving the above problems, the present invention provides a thin film having a composition represented by the following [Formula 1] prepared by LPCVD method as a thin film coated on the base material for cutting tools.

[Formula 1]

Al _x Ti _y Si _z Cr _w N

Where x + y + z + w = 1, x≥0.75, y≥0.1, 0 <z≤0.06, 0≤w≤0.08

The thin film according to the present invention, by containing the Al content of 0.75 or more through the LPCVD method, compared to the AlTiN thin film prepared by the conventional PVD method to maintain a high content of Al to improve the cutting performance, and at the same time Si and The addition of Cr prevents phase separation of Al or Ti components from the fcc crystal structure even when used for a long time at high temperature, so that high temperature hardness can be maintained.

Here, since the content of Al is less than 0.75, sufficient cutting performance improvement cannot be expected, It is preferable to set it as 0.75 or more.

In addition, Si is a component that improves room temperature hardness and high temperature hardness. When Si is added to a TiAlN-based thin film, Si is phase-separated into nanoscale Si ₃ N ₄ in TiAlN, resulting in a large number of interfaces. By the effect, the room temperature hardness is improved, and the effect of improving the high temperature hardness by forming Si ₃ N ₄ occurs. When the content of Si exhibiting such an effect exceeds 0.06, Si having lower physical properties compared to Si ₃ N ₄ may be present alone, and the amount of amorphous Si ₃ N ₄ is excessively increased, thereby decreasing the physical properties. It is preferable that a predetermined effect can be expected even if a small amount is added, but in order to sufficiently obtain the above-mentioned effect, it is more preferably added at 0.01 or more.

In addition, Cr is added to TiAlN-based like Si to improve the hardness due to the solid solution strengthening effect and to reduce the tensile residual stress that may occur in the CVD manufacturing process, and to convert to compressive stress. In the case of addition, since Cr is not present in the lattice, it is preferably added at 0.08 or less, and more preferably at 0.01 to 0.06.

In addition, the present invention provides a thin film coated on the base material for cutting tools, a thin film having a composition represented by the following formula [2] and a thin film of the composition represented by the following [Formula 3] alternately laminated.

[Formula 2]

Al _a Ti _{1 - a} N

(Where 0.75 ≦ a ≦ 0.8)

(3)

Al _x Ti _y Si _z Cr _w N

Where x + y + z + w = 1, x≥0.75, y≥0.1, 0 <z≤0.06, 0≤w≤0.08

When Al-rich AlTiN thin film and Al-rich AlTiSiCrN thin film containing Si and Cr are alternately laminated, Al _x Ti _y Si _z Cr _w N thin film is coated alone. Cutting performance is improved as compared to the case. This is presumed to be an effect due to particle minimization that occurs while laminating in a multilayer structure.

In addition, the stacking structure of the thin film is preferably a thickness of 1 ~ 10㎛ with a stacking period of 100 ~ 700nm thickness, it is difficult to form a uniform thin film when the stacking thickness is less than 100nm, when it exceeds 700nm to contrast with a single thin film This is because the difference in physical properties is not large.

In addition, an underlayer may be further formed between the thin film or the laminated thin film and the base material. As the base layer to be formed, a thin film of Ti (B, C, N) is preferable.

In addition, the thin film according to the present invention is characterized in that its crystal structure is Face Centered Cubic (FCC).

In addition, the thin film according to the present invention is characterized in that its residual stress is 1 to -2 GPa. It is preferable that the thin film to be formed has a compressive stress state rather than a tensile stress state, which is chipped by numerous vibrations and shocks generated during cutting when the state of the stress existing in the thin film is the tensile residual stress. This is because it is easy to occur and, on the contrary, the compression residual stress can suppress the generation and progress of chipping. In the present invention, to prevent the phase separation at high temperature and at the same time to add Cr to the compressive stress residual stress state of the thin film formed, when the tensile residual stress exceeds 1 GPa, chipping is likely to occur, -2 GPa If it is less than the thin film is spontaneous peeling due to excessive compression residual stress, it is preferable to maintain in the above range.

The cutting tool thin film according to the present invention has the following effects.

First, since it is higher than the Al _x Ti _1-x N thin film produced by the PVD method, the cutting performance is greatly improved.

Second, compared to the Al _x Ti _1-x N thin film manufactured by the conventional LPCVD method by the addition of Si and Cr can prevent the hardness decrease due to long-term use, it is possible to improve the durability of the cutting tool.

Third, the Al _x Ti _1-x N thin film and the Al _x Ti _y Si _z Cr _w N thin film are alternately stacked to increase the hardness compared to the Al _x Ti _{1 - x} N thin film. It can improve more.

Fourth, the residual stress of the thin film formed through the addition of Cr can be maintained in a low tensile stress state or a compressive stress state, and it is effective to suppress chipping generation.

1 is a graph showing a result of a cutting test after forming a thin film according to an embodiment of the present invention and a comparative example on a surface of a cutting insert.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, embodiments of the present invention illustrated 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. In addition, the size or thickness of the film or regions in the drawings is exaggerated for clarity.

Example 1

In the embodiment of the present invention, the LPCVD method was used as a method of coating the Al _x Ti _y Si _z Cr _w N thin film on the base material. As the base material, a hard base material made of cemented carbide, cermet, or ceramic may be used. In the embodiment of the present invention, an insert made of cermet was used.

In forming the thin film, H ₂ , NH ₃ , TiCl ₄ and AlCl ₃ were used as reaction gases for forming AlTiN. AlCl ₃ was prepared by the chemical reaction of H ₂ , HCl, Al chip using a separate generating device.

In addition, Si added to improve high temperature hardness and oxidation resistance was added to the thin film by vaporizing the SiCl ₄ solution and introducing it into the LPCVD reactor.

In addition, Cr added selectively to improve the high temperature hardness was formed in a thin film through a method of introducing CrCl ₄ through a chemical reaction between Cr chips, H ₂ and HCl in a separate generator, and then introduced into the LPCVD reactor. .

In the embodiment of the present invention, when the Al-riched Al _x Ti _y Si _z Cr _w N thin film was formed, the deposition temperature was 750 to 850 ° C., the deposition pressure was maintained at 20 to 150 mbar, and the thickness of the thin film was 1 to 10 μm. It was set as the range.

On the other hand, the thin film according to an embodiment of the present invention can be applied to turning as well as milling when formed on a 3-10 μm thick TiCN layer formed by a medium temperature deposition method (hereinafter referred to as MTCVD) as a base layer on a hard base material. have.

The high temperature hardness, high temperature oxidation resistance, and cutting performance of the thin film prepared as described above were applied to the insert or the cutting tool.

High temperature hardness test

First, the high temperature hardness test was carried out at 900 ℃ in consideration of the temperature generated during the actual cutting, the test object was Al _x Ti _{1 - x} N thin film manufactured by PVD method and Al _x TiSi _1-x N manufactured by PVD method thin film, a Ti _x Al ₁ made of a LPCVD method _- a _x N thin film, and Al-riched 4 kinds of _{Al x Ti y Si z Cr w} N in the embodiment;

The four types of samples were deteriorated in a temperature of 900 ° C. and in the air, and then cooled again to measure the micro hardness, thereby comparing the hardness before and after degradation. The instrument used for the micro hardness measurement was Fischer scope HM2000 (Ficsher scope HM2000) and the load used for hardness measurement was 30mN and the composition of the measured thin film was analyzed using the GDS850 equipment, the results are shown in Table 1 below.

No. Thin film type Manufacturing method Degradation War (GPa) After deterioration (GPa) Remarks One Al _{0 .64} Ti _{0 .35} N PVD 36 30 Comparative example 2 _{Al 0 .60 Ti 0 .30 Si 0} .04 N PVD 37 37 Comparative example 3 Al _{0 .82} Ti _{0 .18} N LPCVD 36 34 Comparative example 4 _{Al 0 .86 Ti 0 .12 Si 0} .02 N LPCVD 40 39 Example 5 _{Al 0 .84 Ti 0 .30 Si 0} .04 N LPCVD 42 42 Example 6 _{Al 0 .80 Ti 0 .30 Si 0} .08 N LPCVD 36 32 Example 7 _{Al 0 .84 Ti 0 .12 Si 0} .02 Cr 0 .02 N LPCVD 42 40 Example 8 Al _{0 .80} T _{0 .12} iSi _{0 .02} Cr _{0 .06} N LPCVD 44 42 Example

As confirmed in Table 1, the Al _x Ti _y Si _z Cr _w N thin film according to an embodiment of the present invention is A _x lTi _1-x N, Al _x Ti _y Si _1-xy prepared by commercialized PVD method Compared with Al _x Ti _1-x N prepared by N and LPCVD method, it can be seen that even after the high temperature deterioration treatment, hardness deterioration hardly occurs and high temperature stability is very excellent. In addition, it can be seen that the thin film according to the embodiments (Nos. 4 to 8) of the present invention has a substantially high hardness as compared with the comparative example.

High temperature Oxidation resistance  Test and Residual stress  analysis

Next, the high temperature oxidation resistance test of the thin film according to the embodiment of the present invention was carried out for 1 hour in the atmosphere of 900 ℃, the same temperature and atmosphere as the measurement of the deterioration hardness, and the comparison was the same as in Table 1.

The oxidation resistance evaluation was confirmed by measuring the thickness of the oxide layer formed on the surface of a thin film after high temperature heat processing. In this case, in order to facilitate the comparison between the samples, the thin film thicknesses of the four types of samples were equally deposited at 4 μm, and after the oxidation resistance evaluation, the evaluation results are shown in Table 2 below.

At the same time, the residual stress according to the change of the composition of the thin film was analyzed. The instrument used for this analysis was Xpert Pro MRD by Panalytical, and the sinψ ² method was used.

No. Thin film type Manufacturing method Oxide layer thickness
(Μm) Residual stress
(GPa) Remarks One Al _0.64 Ti _0.35 N PVD 2.8 -1.13 Comparative example 2 Al _0.60 Ti _0.30 Si _0.04 N PVD 0.5 -1.35 Comparative example 3 Al _0.82 Ti _0.18 N LPCVD 0.4 +0.31 Comparative example 4 Al _0.86 Ti _0.12 Si _0.02 N LPCVD 0.1 +0.23 Example 5 Al _0.84 Ti _0.30 Si _0.04 N LPCVD 0.04 +0.11 Example 6 Al _0.80 Ti _0.30 Si _0.08 N LPCVD 1.1 +0.02 Example 7 Al _0.84 Ti _0.12 Si _0.02 Cr _0.02 N LPCVD 0.09 -0.51 Example 8 Al _0.80 T _0.12 iSi _0.02 Cr _0.06 N LPCVD 0.08 -1.27 Example

As shown in Table 2, in the case of the thin film according to the embodiment of the present invention, the thickness of the oxide layer oxidized at high temperature is less than about 0.1 ~ 0.08㎛ oxidized amount, in the comparative example, No. 1 is 2.8㎛ The oxidation resistance is very low at a high temperature, and in the case of No. 2 to which Si is added, the oxidation resistance is considerably improved compared to that in which Si is not added, but also oxidation resistance is inferior to the embodiment of the present invention. In addition, in the case of No. 3 produced by the LPCVD method, the oxidation resistance is inferior to that of the embodiment of the present invention.

In general, when CVD coating is performed on a cemented carbide base material and the residual stress of the thin film is analyzed, tensile residual stress exists at a level of 1 GPa or less. It is desirable to keep the stress as low as possible or to keep the residual stress in a compressive stress state as it easily propagates.

However, in the case of the Al _x Ti _y Si _z Cr _w N thin film manufactured according to the embodiment of the present invention, the tensile residual stress gradually decreases as silicon (Si) is added, and the compressive residual stress as chromium (Cr) is simultaneously added. It can be seen in Table 2 that the conversion to the state.

The change of the residual stress state is believed to occur due to the formation of a substituted solid solution of chromium (Cr) having a larger atomic radius than that of Ti or Al.

Cutting test

In order to confirm the actual cutting characteristics of the Al _x Ti _y Si _z Cr _w N thin film according to an embodiment of the present invention, the cutting performance was evaluated through two cutting methods, milling and turning.

First, milling processability was performed on the thin films of Nos. 1 to 4 in Table 1 above, in consideration of the characteristics of the milling process, the thicknesses of the thin films were all equally deposited at 5 μm, and the milling conditions were Vc = It was set as 350m / min, fz = 0.16mm / tooth, ap = 2.0mm, dry type, and SCM440.

As a result of measuring the VB wear after cutting performance evaluation, as shown in FIG. 1, the Al _x Ti _y Si _z Cr _w N thin film (No. 4) according to the embodiment of the present invention is a thin film (No. 1) according to a comparative example. Compared to 3), it can be seen that the tool life is significantly improved.

Further, the turning test in the present embodiment Al _{0 .84} Ti _{0 .30} Si ₀ in accordance with the invention in order to confirm whether or not there is the _{Al x Ti y Si z Cr w} N thin film according to the present invention can also be used in for _{turning. 04} N thin film (No. 4) was deposited to have a composition of 93% WC-1.5% TaC-5.5% Co so that the MTCVD TiCN thin film was about 5 μm thick on a cemented carbide base material having about 8 to 10 μm formed thereon.

For the comparison, Al ₂ O ₃ was deposited on the same base material by CVD to a thickness of 5 μm.

Two types of samples were evaluated under cutting conditions of Vc = 450 m / min, fn = 0.35 mm / rev, ap = 2.0 mm, wet, and GC250. As a result, Al _x Ti _y Si _z Cr _w N thin films according to the present invention exhibited comparable performance to turning thin films having commercially available thin film structure of MTCVD TiCN / Al ₂ O ₃ when MTCVD TiCN was used as the underlying layer. It was confirmed that. In other words, as a result of checking the required time until the side wear amount (V _B ), which is a criterion for tool life, became 0.2mm, MTCVD TiCN / commercialized with a thin film having a MTCVD TiCN-Al _x Ti _y Si _z Cr _w N structure The tool life of the thin film having the Al ₂ O ₃ structure was found to be 30 minutes.

In view of this, it can be seen that the thin film according to the present invention has sufficient effect of improvement by itself and can replace an oxide thin film such as Al ₂ O ₃ .

[Example 2]

The Al-riched Al _x Ti _y Si _z Cr _w N thin film according to the embodiment of the present invention may be formed as a single layer, but may be alternately stacked in multiple layers to further improve the high temperature hardness, and the laminated structure may be formed on the base material. Al _x Ti _{1 - x} N thin film ⇒ Al _x Ti _y Si _z Cr _w N thin film ⇒ Al _x Ti _{1 - x} N thin film ⇒ Al _x Ti _y Si _z Cr _w N thin film 100-700 nm of thickness is preferable for hardness improvement.

In order to confirm the effect of improving the high temperature deterioration hardness when the Al _x Ti _y Si _z Cr _w N thin film according to the present invention was applied in multiple layers, hardness measurements were performed on the single layer and the multilayer thin film.

The multi-layered thin film sample was configured such that Al _x Ti _{1 - x} N / Al _x Ti _y Si _z Cr _w N thin films were alternately laminated, and each layer had a thickness of about 300 nm, 600 nm, and 1 μm, respectively. The thickness was confirmed using a TEM (transmission electron microscope, FEI-20, philips), the results are shown in Table 3 below.

_{Al 0 .86 Ti 0 .12 Si 0} .02 N fault Each layer thickness
1㎛ Each layer thickness
600 nm Each layer thickness
300 nm Laminated structure _{Al 0 .86 Ti 0 .12 Si 0} .02 N Al _{0 .82} Ti _{0 .18} N /
_{Al 0 .86 Ti 0 .12 Si 0} .02 N Al _{0 .82} Ti _{0 .18} N /
_{Al 0 .86 Ti 0 .12 Si 0} .02 N Al _{0 .82} Ti _{0 .18} N /
_{Al 0 .86 Ti 0 .12 Si 0} .02 N Thin film thickness 5㎛ 5.1 μm 4.8㎛ 4.9 μm Deterioration 40.0GPa 41.2GPa 43.0GPa 45.3GPa After deterioration 39.2GPa 40.3GPa 42.3GPa 44.9GPa

As confirmed in Table 3, the Al _x Ti _{1 - x} N / Al _x Ti _y Si _z Cr _w N thin film structure to be alternately stacked with each other than when formed in a single layer, the hardness is 5 ~ 10% It can be seen that further improvement.

Claims (8)

As a thin film coated on a cutting tool base material,
It has a composition represented by the following [Formula 1] prepared by LPCVD method,
Thin film with residual stress of 1GPa ~ -2GPa.
[Formula 1]
Al _x Ti _y Si _z Cr _w N
(Where x + y + z + w = 1, x≥0.75, y≥0.1, 0 <z≤0.06, 0.01≤w≤0.06) As a thin film coated on a cutting tool base material,
A thin film having a structure in which a thin film having a composition represented by the following [Formula 2] and a thin film having a composition represented by the following [Formula 3] are alternately stacked.
(2)
Al _a Ti _1-a N
(Where 0.75 ≦ a ≦ 0.8)
(3)
Al _x Ti _y Si _z Cr _w N
Where x + y + z + w = 1, x≥0.75, y≥0.1, 0 <z≤0.06, 0≤w≤0.08 delete The method according to claim 1 or 2,
Thin film, characterized in that the base layer is further formed between the base material and the thin film. The method of claim 2,
The lamination cycle of the laminated structure is 300nm to 700nm, the thickness of the thin film, characterized in that 1㎛ ~ 10㎛. The thin film of claim 4, wherein the base layer is a Ti (B, C, N) thin film. The method according to claim 1 or 2,
The thin film is a thin film, characterized in that the crystal structure of the FCC. delete

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