JP3394021B2 - Coated cutting tool - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated cutting tool used for cutting metal materials and the like.

[0002]

2. Description of the Related Art In recent years, in high-efficiency and high-precision cutting, the phenomenon of adhesion and welding between a wear-resistant coating on the surface of a cutting tool and a work material has a great influence on the cutting performance. That is, in the case of high hardness coatings that pursue high temperature characteristics and abrasive wear resistance, such as the TiAlN coatings that are currently the mainstream, a sufficient cutting life can be obtained due to the increase in frictional resistance due to the adhesion with the work material and the welding phenomenon. Not only not
There are problems such as deterioration of processing accuracy due to the peeling phenomenon of the cutting surface. By the way, it is known that in the surface treatment of a mold or the like, the CrN film has excellent sliding characteristics and affinity with the object to be treated, and as a result, has a lubricating action and exhibits excellent characteristics. Therefore, as an attempt to solve the above problems, examples of applying the lubricity of this CrN coating to a cutting tool are disclosed in JP-A-11-156992 and JP-A-11-505573. Also, as an example of improving the wear resistance of the CrN coating by mixing BN, there is JP-A-7-150337.

[0003]

However, since the CrN film has insufficient film hardness and the compressive stress remaining in the film is extremely low, it does not have sufficient wear resistance in a severe cutting environment, and the heat resistance Film peeling due to cracks will occur. In particular, in wet cutting, the resistance to heat cracking is extremely poor and film breakage or peeling due to heat cracking occurs. In view of these circumstances, the present invention employs an anti-adhesion coating that suppresses an increase in frictional resistance due to adhesion with a work material and a welding phenomenon, and does not cause abnormal wear due to film peeling and thermal cracking. An object is to provide a coated cutting tool.

[0004]

The gist of the present invention is a coated cutting tool in which a cutting tool substrate is coated with a coating layer consisting of one layer or multiple layers, and at least one of the coating layers is (Cr _a
Si _1-a ) (N _x B _{1 -x} ), where 0.7 ≦ a <1,
0.4 ≦ x ≦ 1, and has a chemical composition represented by:
CrSi containing Si nitride phase and / or B nitride phase
It is a coated cutting tool characterized by being a system film.

[0005]

By adopting such a structure, the performance of the cutting tool becomes extremely good without causing film peeling even under a severe cutting environment such as high-speed cutting and the accuracy of the work piece is improved. Proved to be significantly improved,
The problems of the prior art have been solved. C of CrSi-based film
Although an appropriate amount of additive element to the r-nitride exhibits excellent performance, the Cr content is 70 at% in terms of atomic ratio of metal component.
If the amount is less than the above, not only the cutting characteristics are not sufficiently obtained, but also Si or B is excessively dissolved in the Cr nitride, so that the coating becomes very brittle and the adhesion resistance is deteriorated. From this, the addition of Si to the CrSi-based film is 30
It must be at% or less. In addition, the amount of B added to the Cr nitride needs to be 60 at% or less of the non-metal component from the viewpoints of low friction and wear resistance. In this specification, B is treated as a non-metal component.

As a means for improving the wear resistance and heat crack resistance of Cr nitride, Si and / or
Alternatively, it is extremely effective to add B and interpose the Si nitride phase or the B nitride phase in the Cr nitride. As a result of observing the CrSi-based film according to the present invention in detail with a transmission electron microscope, the Si nitride phase or the B nitride phase is a nanocrystal of about 20 nm, and has a fcc structure and grows into a columnar CrN phase. It was confirmed that the nanocrystals were dispersed inside. The nanocrystals generate lattice strain, and the dispersion strengthening mechanism moderately increases the residual compressive stress in the coating, making the coating highly hard without deteriorating the adhesion resistance and significantly improving the wear resistance. It is considered to be a thing.
Further, this moderate residual compressive stress effectively suppresses thermal cracks in wet cutting, and also works effectively in a more severe cutting environment such as high-speed cutting, thus enabling stable cutting. In particular, the intervening Si nitride phase greatly contributes to improvement in wet cutting. Furthermore, the nitride of B contributes to the further reduction of the friction of Cr nitride, suppresses the peeling phenomenon of the machined surface or the re-adhesion of the workpiece, and has significantly improved the machined surface.

Although the CrSi-based film has excellent adhesion and low friction under static and dynamic conditions, a single film is sufficient for a work material having high hardness such as a temper material. It may not show cutting performance. Therefore, it is necessary to use a film having excellent wear resistance and oxidation resistance in combination, but the most suitable film for this film is at least Ti as a metal element.
TiA containing Al and Al, and containing a small amount of N as a non-metal element
It is an l-based film. By adopting this, it becomes possible to obtain a coated cutting tool compatible with high-speed cutting. By alternately laminating one or more layers of the TiAl-based film and the CrSi-based film, it is possible to obtain a coated cutting tool compatible with high-speed cutting. The TiAl-based film not only has a good balance of oxidation resistance and wear resistance, but also has excellent adhesion to the CrSi-based film by the adhesion-improving method according to claim 3, so that the characteristics of the CrSi-based film are complemented, It maximizes its performance. At this time, the CrSi-based film is preferably on the uppermost layer of the hard film, but the effect is not limited to the uppermost layer, and the effect is sufficiently exhibited.

Further, by setting the ratio of lattice constants calculated from the X-ray diffraction of the (111) planes of the TiAl-based film and the CrSi-based film to 0.98 to 1.02, Cr
The lattice mismatch between atoms of the Si-based film and the TiAl-based film is reduced, and as a result, the adhesiveness is remarkably improved. This value is T
The lattice constant calculated from the (111) plane of the iAl-based film is
Usually, a (111) CrSi-based film formed immediately above
It is a value divided by the lattice constant calculated from the plane. More specifically, if the lattice constants calculated from the (111) planes of the TiAl-based film and the CrSi-based film are in the range of 0.412 nm to 0.420 nm, respectively, the value of the lattice constant ratio is satisfied, This reduces the lattice mismatch between the atoms of the CrSi-based film and the TiAl-based film, and reduces the TiAl-based film and the Cr-based film.
The interfacial strength of the Si-based film was remarkably improved, and interfacial peeling did not occur. As a result, the adhesion was remarkably improved. Since the method of adjusting the lattice constant also depends largely on the film forming conditions, it is necessary to appropriately adjust the lattice constant so that the desired lattice constant is obtained. Although the bias voltage is the main influential parameter, the side of relatively low energy is preferable directly above the TiAl-based film. More specifically, the bias voltage is preferably -30 to -200V. That is, high adhesion can be obtained by applying this bias before and after switching the film type in the film forming process.

Since the CrSi-based film in the present invention may not exhibit sufficient performance as a tool even if it is used alone as described above, it is necessary to separately provide a film for supplementing wear resistance and oxidation resistance and use together. is there. At this point in time, a known TiAl-based film is considered to be the most suitable, so the following description will be made using this film, but it is not always necessary to use a TiAl-based film together in the practice of the invention according to claim 1 of the present application.

[0010]

EXAMPLES As a method of forming the CrSi-based film according to the present invention on the surface of a substrate, there is a PVD method typified by an ion plating method and a sputtering method.
For example, in the film formation by the arc ion plating method, the following method may be used. First, in the furnace 3 × 1
After evacuation to 0 ⁵ Pa, the substrate is cleaned and activated with Ar. After that, Cr, Si, and B ionized from the cathode, which is the evaporation source by arc discharge, are obtained by ion plating in an N ₂ atmosphere. Further, if a target whose composition is adjusted according to the target film composition is used, the target film composition can be stably obtained.

The formation of the CrSi-based film in which the Si nitride phase or the B nitride phase is dispersed, which is extremely important in the present invention, largely depends on the coating conditions during film formation. That is, the present inventors consider that the energy released by the ions involved in film formation (hereinafter referred to as ion energy) is extremely important. Since the magnitude of the ion energy during coating depends on the bias voltage applied to the substrate, the setting of the bias voltage is important in the present invention. That is, in the case of a relatively low bias voltage of −50 V, f of Cr nitride is
Cr atoms in the cc structure are replaced with Si atoms or B atoms, and independent Si nitride phase and B in Cr nitride
No nitride phase was identified. That is, in order to interpose the Si nitride phase and the B nitride phase in the Cr nitride, it is necessary to form a film with extremely high ion energy. The ion energy also depends on the pressure in the reaction vessel, the ion species, etc., but these are limited by the target coating composition and the performance of the ion source, so there is little room for change. Therefore, the bias voltage is the most effective parameter for increasing the ion energy, and −2
A voltage of about 00 to -500 V is preferable, and within this range, a CrSi-based film having extremely excellent characteristics in which the Si nitride phase or the B nitride phase is dispersed in nano units is easily obtained. In addition, as a means for increasing the ion energy, it is also effective to add a small amount of an active gas component such as oxygen to the atmosphere to activate the plasma during arc discharge.

1 to 3 show the C by X-ray photoelectron spectroscopy.
The result of having measured the binding energy of the compound which exists inside a rSi type | system | group film is shown. FIG. 1 shows the binding energy of N in the 1S orbit, but shows the existence of a nitride composed of CrN. Figure 2 shows Si 2
It shows the binding energy in P orbital, but S
Binding of i ₃ N ₄ is confirmed. FIG. 3 shows the binding energy of the 1S orbital of B, but the binding of BN is confirmed. The binding energy represented by the peak is shown in the figure. It is apparent from FIGS. 1 to 3 that there is a bond of Si nitride and B nitride phase in the CrSi-based film. That is, the binding energy of Cr nitride, Si nitride, and B nitride was confirmed, and Si and B were contained in the Cr nitride.
Has been revealed to exist as a nitride.

When the bias voltage is increased, the substrate temperature also tends to rise. When the temperature is limited due to the requirements of the substrate material, a cooling means for the substrate may be required. Also,
The production amounts of the Si nitride phase and the B nitride phase change depending on the substrate temperature. According to the research conducted by the present inventor, the production amount decreases as the temperature rises, and the Si nitride phase and the B nitride phase may not be detected at 700 ° C. or higher in some cases. Therefore, it is considered that the preferable substrate temperature is 500 ° C. or lower, and more preferably 350 ° C. or lower. The coated cutting tool of the present invention is not particularly limited in its coating method, but when considering the thermal influence on the coating base material, the fatigue strength of the tool, the adhesion of the coating, etc., at a relatively low temperature. A physical vapor deposition method that applies a bias voltage to the side of a coated substrate such as an arc discharge type ion plating that can be coated, has a compressive stress remaining in the coated film, and has excellent adhesion is preferable. Hereinafter, the present invention will be described based on examples.

[0014]

[Example] Using an arc ion plating apparatus, using various alloy targets which are evaporation sources of metal components and N ₂ gas which is a reaction gas, the coated substrate temperature is 400 ° C.
The reaction gas pressure was adjusted to 1 × 10 ^{−1 to} 7 × 10 ⁰ Pa and the bias voltage was appropriately adjusted to form a target film under the conditions of −30 to −500 V. For the coated substrate, cemented carbide 2-flute scare end mill with an outer diameter of 10 mm, R5
A 2-blade ball end mill made of cemented carbide having a thickness of 4 mm was used to form a film having a total thickness of 4 to 5 μm. The order of film formation was such that a TiAl-based film was 2.5 μm first, and then a CrSi-based film was 1.5 μm. Composition of CrSi-based film and TiAl-based film of each sample, nitride and boride contained in the CrSi-based film, and lattice constants calculated from the (111) planes of the TiAl-based film and CrSi-based film and their ratios. The values of are shown in Table 1.

[0015]

[Table 1]

The composition and lattice constants shown in Table 1 were also adjusted under the film forming conditions of the comparative example. In addition, in Table 1, the compositional representation is expressed by atomic ratio so that the total of the metal component and the non-metal component is 100, but this means that the atomic ratio of the metal component and the non-metal component is 1: 1. It does not mean. A cutting test was conducted using the obtained coated end mill. The tool life was defined as the cutting length when the tool could not be cut due to chipping or wear of the cutting edge, or when the accuracy of the machined surface after cutting was significantly deteriorated. The cutting specifications are shown below.

The cutting specifications of the two-flute cemented carbide scare end mill are side cutting, down cutting, and work material S50C (H
B220), cutting amount Ad10 mm × Rd1 mm, cutting speed 250 m / min, feed 0.06 mm / blade, air blow used.

The cutting specifications of the two-blade cemented carbide ball end mill are downcut, work material S50C (HB22
0), depth of cut Ad 0.2mm × Pick Feed
0.2 mm, rotation speed 10000 min ⁻¹ , table feed rate 4000 mm / min, and water-soluble cutting fluid used.

Inventive Example 2 is a case where B is not added to the CrSi-based film, but the cutting length is longer than that of Comparative Example 11. It can be seen that the present invention example 3 shows excellent cutting performance as compared with the comparative example 14, although Si is a very small amount of 0.5 atom%. Inventive Example 5 was prepared by adding 50 atomic% of B. The cutting length was the same as the amount of B was increased, but in Comparative Example 12 in which 70 atomic% was added, defects were generated. Inventive Example 6 has 20 atomic% of Si added, but has a longer life than the inventive example. Inventive Examples 8 and 9 have TiAlN film with N
This is an example of the present invention when b or Y is added, and excellent cutting performance was obtained as compared with the example of the present invention. Invention Example 10
Is a value obtained by dividing the lattice constant calculated from the (111) plane of the TiAl-based film by the lattice constant calculated from the (111) plane of the CrSi-based film, which is outside the range of 1.08 to 0.98, and C
An example of the coating composition and detection compound of the rSi-based film is shown in the case of being within the range of the present invention. The cutting length is somewhat shorter than that of sample samples 1 to 9 of the present invention, but it is smaller than the conventional coating. A significantly longer cutting length was obtained.

From the above, Examples 1 to 10 of the present invention use a CrSi-based film and a TiAl-based film in combination in which the resistance to friction during cutting is significantly reduced and the adhesion with the hard film and the balance between hardness and toughness are taken into consideration. As a result, abnormal wear due to adhesion and welding phenomena does not progress, and it exhibits excellent properties against thermal cracks, and overall tool life is significantly improved. We have succeeded in greatly improving the conventional problems by suppressing the deterioration of the machining accuracy of the machined surface. The coating film of the present invention is suitable for a ball end mill, particularly for a wet ball end mill. Among the various cutting tools, ball end mills that have strong discontinuity and a small machining allowance for finishing, and that require finishing accuracy of the work piece, require adhesion and welding on the tool surface and during cutting. Cutting performance is greatly affected by thermal cracks. Further, in a shape such as a ball end mill in which the cutting speed changes continuously, in addition to the thermal cracks at the time of cutting, the cutting margin becomes minute near zero cutting speed, and sliding characteristics are required. As described above, it is clear that these characteristics are the characteristics particularly required in the end mill.

On the other hand, in Comparative Examples 11 and 12, Cr is
When the amount of Si and B added in the Si-based film is larger than the claimed range, the adhesion resistance and the welding resistance are not sufficient,
Abnormal wear occurred due to adhesion. Comparative Example 13: Film composition and CrSi-based film in the present claims, is a ratio of the lattice constant of the TiAl-based film, _Si 3 _N 4 in CrSi system within the membrane, BN
This is a comparative example in which the compound of 1 is not present, and has a shorter life than the example of the present invention. Comparative Example 14 is a case where an element is not added to Cr, but film peeling due to thermal cracking occurs and sufficient characteristics cannot be exhibited. Comparative Examples, 15, 16, 17, 1
Nos. 8, 19, 20, and 21 show the cutting performance of conventional hard coatings, but all of them are significantly inferior to the examples of the present invention.

[0022]

As described above, the coated cutting tool of the present invention is
Since it has excellent adhesion and low friction compared to conventional coated cutting tools, it can achieve a significantly longer tool life in further high-speed cutting and is extremely effective in improving productivity in cutting.

[Brief description of drawings]

FIG. 1 shows an X-ray photoelectron spectroscopy spectrum showing the binding energy of CrN in a CrSi-based film.

FIG. 2 shows an X-ray photoelectron spectroscopy spectrum showing the binding energy of Si ₃ N ₄ in a CrSi-based film.

FIG. 3 shows an X-ray photoelectron spectroscopy spectrum showing the binding energy of BN in a CrSi-based film.

Claims (3)

(57) [Claims] 1. A coated cutting tool comprising a cutting tool substrate coated with a coating layer comprising one layer or multiple layers, wherein at least one layer of the coating layer is (CraSi1-a) (NxB1-x),
However, a CrSi system having a chemical composition represented by 0.7 ≦ a <1 and 0.4 ≦ x ≦ 1 and including a Si nitride phase and / or a B nitride phase in a Cr nitride. A coated cutting tool characterized by being a film. 2. The coated cutting tool according to claim 1, wherein at least one of the coating layers contains at least Ti and Al as metal elements and at least N as a non-metal element.
A coated cutting tool comprising a TiAl-based film containing: 3. The coated cutting tool according to claim 2, wherein each of the TiAl-based film and the CrSi-based film (11
1) When the lattice constants calculated from the X-ray diffraction of the plane are dT and dC, respectively, the value of dT / dC is 0.98 or more,
A coated cutting tool, which is 1.02 or less.