JP2012115967A - Surface coated cutting tool in which hard covering layer exhibits superior peeling resistance and superior chipping resistance in intermittently cutting hard difficult-to-cut material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface coated cutting tool in which a hard covering layer exhibits superior peeling resistance and superior chipping resistance in intermittently cutting a hard difficult-to-cut material.SOLUTION: The cutting tool is formed by coating an uppermost surface of a tool substrate constituted of a tungsten carbide based cemented carbide or titanium carbonitride based cermet with at least an Nb boride layer with an average layer thickness of 0.5-5 μm. In the cutting tool, the Nb boride layer is constituted as a composition structure of a crystalline grain structure with multiple average grain sizes. The composition structure is constituted of: a secondary crystalline grain constituted of an aggregate of a primary crystalline grain with an average grain size of 5-20 nm and having an average grain size of 40-80 nm; and a tertiary crystalline grain constituted of an aggregate of the secondary crystalline grain and having an average grain size of 150-800 nm.

Description

  In the present invention, the hard coating layer is constituted by a surface layer having excellent adhesion resistance and excellent adhesion, and therefore, intermittent cutting of hard difficult-to-cut materials such as various Ni-based alloys and Ti-based alloys is performed. In this case, it also relates to a surface-coated cutting tool (hereinafter referred to as a coated tool) that suppresses peeling of the hard coating layer due to the occurrence of welding and exhibits excellent peeling resistance and chipping resistance over a long period of time. is there.

  In general, for coated tools, throwaway inserts that are detachably attached to the tip of the cutting tool for turning and planing of various steel and cast iron materials, drilling of the work material, etc. Drills and miniature drills, and solid type end mills used for chamfering, grooving and shouldering of the work material, etc. A slow-away end mill tool that performs cutting work in the same manner as an end mill is known.

Further, the surface of a tool base made of tungsten carbide (hereinafter referred to as WC) -based cemented carbide or titanium carbonitride (hereinafter referred to as TiCN) -based cermet has a hexagonal crystal structure, and X-ray A cutting tool coated with NbB ₂ having the strongest diffraction intensity in diffraction on the (001) plane and having a residual compressive stress of 0.1 GPa or more is known.

Further, in the conventional coated tool, the above-mentioned tool base is placed in a film forming apparatus in which an NbB ₂ target is mounted on a sputtering evaporation source, and an independent anode is installed at a position facing the evaporation source, and the substrate is heated by heating. After the temperature was set to 500 ° C., the exhaust was performed, and the internal pressure of the container reached 4 × 10 ⁻³ Pa, Ar gas was introduced into the vacuum container, and a bias voltage of −400 V was applied to the tool base to apply the ion base. After cleaning the material for 30 minutes, the cathode power starts discharging at 4 kW, and the ionization rate during film formation is increased by optimizing the film formation conditions such as bias voltage and Ar flow rate applied to the tool base. It is also known that the film is manufactured by controlling the crystal orientation of the film and simultaneously applying a bias voltage to the tool substrate to coat the boride film.

As means for forming a hard coating layer, not only arc ion plating and direct current sputtering but also film formation using high-power pulse sputtering has been proposed. For example, as shown in Patent Documents 2 and 3 (Al, M) ₂ O ₃ (where M is Mg, by applying high power pulse sputtering under the condition that the instantaneous applied power of the pulse is 200 W / cm ² or more and the one wavelength length of the pulse is 100 μsec or less. It is also known that Zn, Mn, Fe, etc.) or α-Al ₂ O ₃ can be deposited at a high deposition rate.

JP 2008-238281 A International Publication No. 2008/148673 International Publication No. 2009/010330

  The performance and automation of cutting machines in recent years have been remarkable. On the other hand, there are strong demands for labor saving and energy saving and further cost reduction for cutting. Accordingly, cutting speed has been increased and types of work materials have been increased. There is a tendency that a general-purpose coated tool that is not limited to the above is strongly desired. However, in the conventional coated tool, when a hard difficult-to-cut material such as an Al-Si alloy is cut, a long life is obtained. Although shown, this occurs during cutting when intermittent cutting of hard difficult-to-cut materials such as various Ni-based alloys and Ti-based alloys that have low thermal conductivity and heat tends to stay at the tool tip during cutting. As a result, welding to the tool edge occurs due to extremely high heat generation, and the hard coating layer peels off along with the welding because the work material and the coated tool are separated several times, leading to a service life in a relatively short time. Is the current situation.

In view of the above, the present inventors have conducted intensive research in order to develop a coated tool that exhibits excellent welding resistance and peeling resistance in which the hard layer is excellent in intermittent cutting of the hard difficult-to-cut material. As a result, the following knowledge was obtained.
First, in the conventional coated tool (Patent Document 1), the NbB ₂ layer is formed by direct current sputtering, and when this is used for cutting hard difficult-to-cut materials such as Al-Si alloys, it is special. However, when this is used for intermittent cutting of hard difficult-to-cut materials such as various Ni-based alloys and Ti-based alloys, the contact with the work material due to the dense surface structure. It has been found that the hard coating layer is peeled off due to the welding because the area is large, the heat generation is caused by extremely high heat generation, and the bonds between the crystal grains of the NbB _two layers are weak.
Accordingly, the present inventors have welding occurs hardly occurs, and, as a result of research by focusing on high NbB ₂ layer tissue binding strength of the crystal grains mutually, when forming the NbB ₂ layers, Patent Document 1 By adopting high-power pulse sputtering under specific conditions instead of the direct current sputtering shown in Fig. 4, the surface structure is porous even in intermittent cutting of hard difficult-to-cut materials such as various Ni-based alloys and Ti-based alloys. In addition, since the contact area with the work material is small, it is difficult to generate heat and welding, and the NbB ₂ layer is less likely to be peeled off due to the strong bond strength between the crystal grains of the NbB ₂ layer. It was found that a film can be formed.

More specifically, FIG. 1 shows a schematic plan view of a high-power pulse sputtering apparatus. In the high-power pulse sputtering apparatus, a sintered body of Nb boride (hereinafter referred to as NbB ₂ ) powder (hereinafter referred to as NbB). ₍ Sintered ₂ ) Target is placed, the atmosphere in the apparatus is Ar atmosphere, high power pulse sputtering is performed with a high average input power of 6 kW or more, and NbB ₂ layer is deposited on the surface of the tool base. NbB has excellent welding resistance, strong bond strength between crystal grains, and high film hardness (for example, a nanoindentation hardness of 3700 kgf / mm ² or more when measured at a load of 200 mg). It was found that _two layers were formed.
As a result, the resulting coated tool has excellent welding resistance, bonding strength between grains, hard hardness, especially in intermittent cutting of hard difficult-to-cut materials such as various Ni-based alloys and Ti-based alloys that generate significant heat. By the surface layer comprising the NbB ₂ layer having a thickness, particularly, the peeling of the hard coating layer caused by the welding is suppressed, so that excellent peeling resistance and wear resistance are exhibited over a long period of time. I found out.

The present invention has been made based on the above findings,
A cutting tool in which an Nb boride layer having an average layer thickness of at least 0.5 to 5 μm is coated on the outermost surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet,
The Nb boride layer is configured as a composite structure of a crystal grain structure having a plurality of average grain sizes, and the composite structure has an average grain size of 40 composed of an aggregate of primary crystal grains having an average grain size of 5 to 20 nm. A surface-coated cutting tool comprising secondary crystal grains of ˜80 nm and tertiary crystal grains having an average grain size of 150 to 800 nm composed of aggregates of the secondary crystal grains. "
It has the characteristics.

  Next, the coated tool of the present invention will be described in detail.

Average layer thickness of hard coating layer The Nb boride layer formed on the outermost surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet is self-tangled when the average layer thickness is less than 0.5 μm. On the other hand, if the average layer thickness exceeds 5 μm, the intermittent cutting of hard difficult-to-cut materials such as Ni-based alloys and Ti-based alloys is caused by welding. Peeling can be suppressed, but chipping is likely to occur at the cutting edge due to a large compressive residual stress caused by a high driving effect on the film of high power pulse sputtering, so the average layer thickness is 0.5 to It was set to 5 μm.

The effect of the composite structure and the average grain size of the crystal grains The effect of the composite structure is that the bonding force between the secondary crystal grains as well as the primary crystal grains can be used by forming an aggregate of crystal grains. It is. The average grain size of the primary crystal grains constituting the composite structure is difficult to form a film having crystal grains of less than 5 nm. On the other hand, when the average grain size exceeds 20 nm, there is a grain boundary that inhibits dislocation movement. Since it decreases, it cannot maintain high hardness. Further, when the average grain size of the secondary crystal grains composed of the aggregate of the primary crystal grains is less than 40 nm, the primary crystal grains constituting the secondary crystal grains for obtaining a strong bonding force between the crystal grains, which is an advantage of the composite structure The number of crystal grains is not sufficient, and if it exceeds 80 nm, the number of secondary crystal grains constituting the tertiary crystal grains is not sufficient. Furthermore, if the average grain size of the tertiary crystal grains composed of the aggregate of secondary crystal grains is less than 150 nm, the area in contact with the work material at the time of cutting becomes large, so that welding easily occurs, and the entire composite structure peels off. On the other hand, if it exceeds 800 nm, it becomes impossible to withstand the load during cutting.

Next, a method for manufacturing the coated tool of the present invention will be described.
FIG. 1 shows a high-power pulse sputtering apparatus as an example of an apparatus for producing the coated tool of the present invention.
That is, in the high-power pulse sputtering apparatus shown in FIG. 1, a tool base mounting rotary table is provided at the center of the high-power pulse sputtering apparatus, and the NbB ₂ powder is sintered at two locations facing each other across the rotary table. A body (NbB ₂ sintered body) target is arranged, and a plurality of tool bases are mounted in a ring shape along the outer peripheral portion at a predetermined distance in the radial direction from the central axis on the rotary table. While rotating the rotary table with an Ar atmosphere as the inner atmosphere and rotating the tool base itself for the purpose of uniforming the thickness of the wear-resistant hard layer formed by vapor deposition, 6 kW or more with respect to the NbB ₂ sintered body target perform high output pulse sputtering at a high average input power, it is prepared by the NbB ₂ layer with an average layer thickness of 0.5~5μm deposited film Kill.
It is also effective to coat a (Ti, Al) N layer which is a wear-resistant layer as an underlayer of the NbB _two layers.
For example, in the manufacturing method in this case, a Ti—Al alloy target having a predetermined composition is arranged at two locations facing each other across the rotary table, and the position is shifted by 90 degrees from the Ti—Al alloy target. Thus, NbB ₂ powder sintered bodies (NbB ₂ sintered body) targets are arranged at two locations facing each other across the rotary table. Then, while rotating the rotary table with the atmosphere inside the apparatus as a nitrogen atmosphere, and rotating the tool base itself for the purpose of uniforming the thickness of the wear-resistant hard layer formed by vapor deposition, 6 kW or more with respect to the Ti—Al alloy target High-power pulse sputtering with a high average input power is performed, and a (Ti, Al) N layer is vapor-deposited as an abrasion-resistant hard layer with an average layer thickness of 0.8 to 5 μm on the surface of the tool base. The inner atmosphere can be substantially changed to an Ar atmosphere, and the NbB ₂ layer can be formed by vapor deposition.

Furthermore, in the high-power pulse sputtering, the sputtering conditions are preferably such that the generated plasma density at the time of applying the pulse is 10 ¹⁸ m ⁻³ or more, and the length of one wavelength of the pulse is 200 μsec or more. In addition, it is preferable to perform sputtering under sputtering conditions in which the pulse non-application time for each cycle is 10 μsec or more.

In high-power pulse sputtering using a rectangular pulse with an increased energy level, it is possible to reduce the thermal load on the target, and thus it is possible to suppress an unnecessary temperature increase of the target.
Further, the (Ti, Al) N layer and the NbB ₂ layer formed by the high-power pulse sputtering both have high adhesion strength and high hardness.

The coated tool of the present invention is a composite structure of a crystal grain structure having a porous surface structure with a small contact area with a work material and a strong bond strength between crystal grains as a hard coating layer, and has a high hardness. Since it consists of _two NbB layers, it is possible to suppress the peeling of the hard coating layer due to welding, especially when intermittent cutting of hard difficult-to-cut materials such as various Ni-based alloys and Ti-based alloys is performed. It exhibits excellent wear resistance over use.

It is a schematic plan view of the high-power pulse sputtering apparatus used for forming the surface coating layer of the coated tool of the present invention. The scanning electron micrograph (magnification: 100,000 times) of the horizontal cross section of the Nb boride layer of this invention covering insert 9 is shown. The scanning electron micrograph (magnification: 100,000 times) of the horizontal section of the Nb boride layer of the conventional covering insert 9 is shown. The horizontal cross-section schematic diagram of the Nb boride layer which consists of a composite structure of this invention covering insert is shown.

  Next, the coated tool and the manufacturing method thereof according to the present invention will be specifically described with reference to examples.

WC powder, TiC powder, ZrC powder, VC powder, TaC powder, NbC powder, Cr ₃ C ₂ powder, TiN powder, TaN powder, and Co powder all having an average particle diameter of 1 to 3 μm are prepared as raw material powders. These raw material powders are blended in the composition shown in Table 1, wet mixed by a ball mill for 72 hours, dried, and then pressed into a green compact at a pressure of 100 MPa. Medium, sintered at 1400 ° C for 1 hour, after sintering, WC-based carbide with honing of R: 0.03 on the cutting edge and ISO standard / CNMG120408 insert shape Alloy tool bases A-1 to A-10 were formed.

In addition, as raw material powders, all of TiCN (weight ratio TiC / TiN = 50/50) powder, Mo ₂ C powder, ZrC powder, NbC powder, TaC powder, WC powder having an average particle diameter of 0.5 to 2 μm Co powder and Ni powder are prepared, and these raw material powders are blended in the blending composition shown in Table 2, wet mixed by a ball mill for 24 hours, dried, and then pressed into a compact at a pressure of 100 MPa. The green compact was sintered in a nitrogen atmosphere of 2 kPa at a temperature of 1500 ° C. for 1 hour, and after sintering, the cutting edge portion was subjected to a honing process of R: 0.03 to obtain ISO standard / CNMG120408. The tool bases B-1 to B-6 made of TiCN base cermet having the insert shape were formed.

(A) Next, each of the tool bases A-1 to A-8 is ultrasonically cleaned in acetone and dried, and the center axis on the rotary table in the high-power pulse sputtering apparatus shown in FIG. The NbB ₂ sintered body target is disposed at four positions facing each other across the rotary table in the high-power pulse sputtering apparatus, while being mounted along the outer peripheral portion at a predetermined distance away from the radial direction from
(B) First, the inside of the apparatus is evacuated and kept at a vacuum of 0.1 Pa or less, and the inside of the apparatus is heated to 400 ° C. with a heater, and then the tool base that rotates while rotating on the rotary table is −200V. The tool substrate is treated with Ar bombardment for 1 hour by applying a DC bias voltage,
(C) Ar gas is introduced as a reaction gas into the apparatus, the atmosphere in the apparatus is set to 0.5 Pa, sputtering is performed for a time corresponding to the layer thickness under the predetermined pulse sputtering conditions shown in Table 3, and Table 4 The NbB ₂ layer having the target layer thickness shown in FIG. 1 is formed as a surface layer of the hard coating layer, thereby manufacturing the surface coating inserts of the present invention (hereinafter referred to as the present coating inserts) 1 to 8 as the coating tools of the present invention. did.
(D) Moreover, this invention covering insert 9-16 which introduce | transduced the (Ti, Al) N layer as a base layer is made to each said tool base | substrate A-9-A-10 and B-1 to B-6 with acetone. In the ultrasonically cleaned and dried state, mounted along the outer peripheral portion at a predetermined distance in the radial direction from the central axis on the rotary table in the high-power pulse sputtering apparatus shown in FIG. In the high-power pulse sputtering apparatus, a Ti—Al alloy target and an NbB ₂ sintered body target having a predetermined composition are arranged at four locations facing each other across the rotary table,
(E) First, the inside of the apparatus is evacuated and kept at a vacuum of 0.1 Pa or less, and the inside of the apparatus is heated to 400 ° C. with a heater, and then the tool base that rotates while rotating on the rotary table is −200V. By applying a DC bias voltage, the tool base was subjected to Ar bombardment treatment for 1 hour, nitrogen gas was introduced into the apparatus as a reaction gas to make a reaction atmosphere of 0.6 Pa, and the Ti-Al alloy target was exposed to the Ti-Al alloy target. The high power pulse sputtering is performed under the predetermined pulse sputtering conditions indicated by the condition symbol a in FIG. 3, and the (Ti, Al) N layer having the target composition and target layer thickness shown in Table 4 is hardened on the surface of the tool base. Deposited as a wear-resistant hard layer of the coating layer,
(F) High-power pulse sputtering was performed on the NbB ₂ sintered compact target under the predetermined pulse sputtering conditions shown in Table 3, the gas introduced into the apparatus was switched from nitrogen gas to Ar gas, and the atmosphere in the apparatus was set to 0. Sputtering was performed for 5 Pa under the conditions corresponding to the layer thickness, and the NbB ₂ layer having the target layer thickness shown in Table 4 was formed as a surface layer of the hard coating layer.

For comparison purposes, these tool bases A-1 to A-10 and B-1 to B-6 were ultrasonically cleaned in acetone and dried, and the distance between the base and the target was 50 mm. Yes, a sputtering apparatus provided with an independent anode at a position facing the evaporation source, and an NbB ₂ sintered body target mounted in the apparatus,
First, while the inside of the apparatus is evacuated and kept at a vacuum of 4 × 10 ⁻³ Pa or less, the inside of the apparatus is heated to 500 ° C. with a heater, and then Ar gas is introduced into the apparatus and rotates on the rotary table. While applying a DC bias voltage of −400 V to the rotating tool base, the tool base was subjected to Ar bombardment for 30 minutes, and the direct current of the NbB ₂ sintered body arranged as the cathode electrode (evaporation source) of the DC sputtering apparatus. A conventional surface-coated insert (hereinafter referred to as a conventional coated tool) as a conventional coated tool by depositing NbB ₂ layers having an average layer thickness shown in Table 6 under the predetermined direct current sputtering condition or pulse sputtering condition shown in Table 5 at the same time when the sputtering is started. 1 to 16 were manufactured.

  For reference, in the same apparatus as the apparatus for manufacturing the present invention coated inserts 1-16 shown in FIG. 1, by forming a film with a composition, film thickness, and sputtering conditions different from those of the present invention coated inserts 1-16, Reference surface-coated inserts (hereinafter referred to as reference coated inserts) 1 to 4 as reference coated tools shown in Table 6 were produced.

About the NbB ₂ layers of the present invention coated inserts 1-16, the conventional coated inserts 1-16, and the reference coated inserts 1-4, the crystal grain structure of the NbB _two layers is 100,000 times by a scanning electron microscope (Carl Zeiss, ultra55). Observation with a visual field, the result is assumed to be a plane, and the area of the crystal grain is calculated as the area of the grain cross section. Furthermore, the average diameter of primary crystal grains, secondary crystal grains, and tertiary crystal grains was measured at 10 points when the cross-sectional area of the crystal grains was calculated as the area of a circle, and the average value was obtained.
Tables 4 and 6 show the measured values.
2 shows a scanning electron micrograph (magnification: 100,000 times) of the horizontal section of the NbB ₂ layer of the coated insert 9 of the present invention, and FIG. 3 shows a scan of the horizontal section of the NbB ₂ layer of the conventional coated insert 9. A scanning electron micrograph (magnification: 100,000 times) is shown in FIG. 4, and a horizontal cross-sectional schematic diagram of an Nb boride layer made of a composite structure of the coated insert of the present invention is shown.

For the NbB _two layers of the present invention coated inserts 1-16, the conventional coated inserts 1-16 and the reference coated inserts 1-4, the surface hardness was measured by an ultra-fine indentation hardness tester (ENTIONX Corporation, ENT-1100a). It was measured by.
Tables 4 and 6 show the measured values.

In addition, the composition of the wear-resistant hard layers constituting the hard coating layers of the present invention coated inserts 1 to 16, the conventional coated inserts 1 to 16 and the reference coated inserts 1 to 4 is expressed by energy dispersion X using a transmission electron microscope. When measured by the line analysis method, each showed substantially the same composition as the target composition.
Further, when the average layer thicknesses of the NbB ₂ layer and the wear-resistant hard layer of the hard coating layer were measured by cross-section using a scanning electron microscope, the average value was substantially the same as the target layer thickness (average value of 5 locations). )showed that.

Next, in the state where all the above-mentioned various coated inserts are screwed to the tip of the tool steel tool with a fixing jig, the present coated inserts 1-16, the conventional coated inserts 1-16, and the reference coated insert 1 About ~ 4
Work material: Ti-6% Al-4% V alloy round bar by mass%,
Cutting speed: 120 m / min. ,
Cutting depth: 1.0 mm,
Feed: 0.2 mm / rev. ,
Cutting time: 5 minutes
A dry interrupted cutting test of a Ti-based alloy under the above conditions (referred to as cutting condition A) was performed, and the flank wear width of the cutting edge was measured.
The measurement results are shown in Table 7.

As raw material powder, WC powder having an average particle size of 5.5 μm, 0.8 μm fine WC powder, 1.3 μm TaC powder, 1.2 μm NbC powder, 1.2 μm ZrC powder, 2.3 μm Cr ₃ C ₂ powder, 1.5 μm VC powder, 1.0 μm (Ti, W) C [by mass ratio, TiC / WC = 50/50] powder, and 1.8 μm Co powder was prepared, and these raw material powders were blended in the blending composition shown in Table 8 respectively. Further, wax was added, ball milled in acetone for 24 hours, dried under reduced pressure, and then dried into various shapes at a pressure of 100 MPa. The green compact was press-molded, and these green compacts were heated to a predetermined temperature in the range of 1370 to 1470 ° C. at a temperature increase rate of 7 ° C./min in a 6 Pa vacuum atmosphere. After holding time, sintering under furnace cooling conditions, A tool bar forming round bar sintered body having a diameter of 6 mm is formed, and further, the diameter x length of the cutting edge portion is 6 mm x 12 mm and the helix angle 30 by grinding from the round bar sintered body. Tool bases (end mills) C-1 to C-8 having a two-blade square shape were manufactured.

Subsequently, the surfaces of these tool bases (end mills) C-1 to C-8 were ultrasonically cleaned in acetone and dried, and then charged into the vapor deposition apparatus shown in FIG. Under the same conditions, a hard coating layer composed of a surface layer composed of _two NbB layers having the target layer thickness shown in Table 9 in C-1 to C-4 is formed by vapor deposition. Inventive surface-coated end mills (hereinafter referred to as the present invention-coated end mills) 1 to 4 are composed of (Ti, Al) N layers having the target composition and target layer thickness shown in Table 9 in C-5 to C-8. The coated end mills 5 to 8 according to the present invention were manufactured by vapor-depositing a layer and a hard coating layer composed of a surface layer composed of NbB ₂ layers having the target layer thicknesses similarly shown in Table 9.

Further, for comparison purposes, the surfaces of the tool bases (end mills) C-1 to C-8 were ultrasonically cleaned in acetone and dried under the same conditions as in Example 1 and also in Table 10. Conventional surface-coated end mills (hereinafter referred to as conventional coated end mills) 1 to 8 as conventional coated tools are manufactured by vapor-depositing and forming a hard coating layer composed of a surface layer composed of _two NbB layers having the target layer thicknesses shown. did.
Further, for reference, the surfaces of the tool bases (end mills) C-1, C-3, C-5, and C-7 are ultrasonically cleaned in acetone and dried. The reference surface coating end mill (hereinafter referred to as a reference coating end mill) 1 to 1 as a reference coating tool shown in Table 10 by forming a film with a composition, film thickness, and sputtering conditions different from those of the present invention coated end mills 1 to 8 4 were produced respectively.

About the NbB ₂ layers of the present invention coated end mills 1-8, the conventional coated end mills 1-8, and the reference coated end mills 1-4, the crystal grain structure of the NbB _two layers is 100,000 times by a scanning electron microscope (made by Curl Zeiss, ultra 55). Observation with a visual field, the result is assumed to be a plane, and the area of the crystal grain is calculated as the area of the grain cross section. Furthermore, the average diameter of primary crystal grains, secondary crystal grains, and tertiary crystal grains was measured at 10 points when the cross-sectional area of the crystal grains was calculated as the area of a circle, and the average value was obtained.
Tables 9 and 10 show the measured values.

For the NbB _two layers of the present invention coated end mills 1 to 8, the conventional coated end mills 1 to 8 and the reference coated end mills 1 to 4, the surface hardness is measured by an ultra-fine indentation hardness tester (ENT-1100a, manufactured by Elionix). It was measured by.
Tables 9 and 10 show the measured values.

Further, the composition of the hard coating layer constituting the hard coating layers of the present invention coated end mills 1 to 8, the conventional coated end mills 1 to 8 and the reference coated end mills 1 to 4 is expressed by energy dispersion X using a transmission electron microscope. When measured by the line analysis method, each showed substantially the same composition as the target composition.
Further, when the average layer thicknesses of the NbB ₂ layer and the wear-resistant hard layer of the hard coating layer were measured by cross-section using a scanning electron microscope, the average value was substantially the same as the target layer thickness (average value of 5 locations). )showed that.

Next, for the present invention coated end mills 1-8, conventional coated end mills 1-8 and reference coated end mills 1-4,
Work material-plane: 100 mm × 250 mm, thickness: 50 mm Ti-based alloy (mass%, Ti-6% Al-4% V alloy) plate material,
Cutting speed: 160 m / min. ,
Groove depth (cut): 3 mm,
Table feed: 960 mm / min,
The dry grooving test of the Ti-based alloy under the above conditions (referred to as cutting condition B) is performed, and the flank wear width of the outer peripheral edge of the cutting edge in the grooving test is 0.1 mm, which is a guide for the service life The length of the cutting groove was measured.
The measurement results are shown in Table 11, respectively.

From the results shown in Tables 3-11, the coated tool of the present invention having excellent NbB ₂ layer welding resistance and hardness is accompanied by high heat generation of hard difficult-to-cut materials such as various Ni-based alloys and Ti-based alloys. Exhibits excellent peeling and wear resistance by intermittent cutting.
On the other hand, as shown in Tables 6 and 10, in the conventional coated tool, the composite structure is not formed, so that the welding resistance is inferior, and the hard tool is hard under intermittent cutting conditions accompanied by high heat generation. Since peeling of the coating layer cannot be suppressed and the hardness is not sufficient, the wear resistance is poor. In addition, in the reference coated tool having the NbB ₂ layer that is out of the range specified in the present invention, in the intermittent cutting process with the high heat generation of the hard difficult-to-cut material, the progress of wear of the cutting edge is fast, and the service life is relatively short. It is clear that

  As described above, according to the coated tool of the present invention and the manufacturing method thereof, not only cutting under normal cutting conditions such as various types of steel and cast iron, but also the discontinuity of the hard difficult-to-cut material with particularly high heat generation. Since it exhibits excellent peeling resistance and wear resistance even in cutting processing, and exhibits excellent cutting performance over a long period of time, higher performance and automation of cutting equipment, and labor saving and energy saving of cutting processing In addition, it can cope with the cost reduction sufficiently satisfactorily.

Claims (1)

A cutting tool formed by coating an outermost surface of a tool base made of a tungsten carbide-based cemented carbide or a titanium carbonitride-based cermet with an Nb boride layer having an average layer thickness of at least 0.5 to 5 μm,
The Nb boride layer is configured as a composite structure of a crystal grain structure having a plurality of average grain sizes, and the composite structure has an average grain size of 40 composed of an aggregate of primary crystal grains having an average grain size of 5 to 20 nm. A surface-coated cutting tool comprising secondary crystal grains of ˜80 nm and tertiary crystal grains having an average grain size of 150 to 800 nm composed of aggregates of the secondary crystal grains.

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