JP2012139795A - Surface coated cutting tool with hard coating layer exhibiting superior resistance against peeling and chipping in high speed cutting of soft hard-to-cut material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface coated cutting tool with a hard coating layer exhibiting a superior resistance against peeling and chipping in high speed cutting of a soft hard-to-cut material.SOLUTION: The cutting tool constituted by coating the outermost surface of a tool base body comprising tungsten carbide base cemented carbide or titanium carbide nitride base cermet with a titanium boride layer with an average layer thickness of 0.5 to 5 ηm, the titanium boride layer is constituted as a complex tissue of a crystalline particles tissue having a plurality of average particle sizes, the complex tissue is constituted of secondary crystalline particles having an average particle size of 40 to 70 nm comprising the aggregate of primary crystalline particles having an average particle size of 10 to 15 nm and tertiary crystalline particles having an average particle side of 300 to 600 nm comprising the aggregate of the secondary crystalline particles.

Description

  In the present invention, the hard coating layer is constituted by a surface layer having excellent adhesion resistance and excellent adhesion, and therefore, particularly when cutting difficult hard-to-cut materials such as various Al-based alloys, peeling and chipping occur more. Surface-coated cutting tool (hereinafter referred to as coating) that suppresses the 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 even when performed under easy high-speed cutting conditions. Tool).

  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.

A cutting tool insert comprising a tool base and a coating comprising at least one TiB ₂ (titanium boride) layer having a fibrous microstructure, wherein the cylindrical grains have a diameter of 5 to 50 nm, Cutting tool insert characterized in that the ratio l / d of length to diameter is> 2 and has a length of 250 nm or more, and the fibrous grains are oriented perpendicular to the surface of the substrate ( Hereinafter, conventional coated tools) are known, and this conventional coated tool is also used when cutting hard hard-to-cut materials such as Ti-based alloys and die steel under high-speed cutting conditions with high heat generation. It is known to exhibit excellent wear resistance over a long period of time.

Furthermore, the conventional coated tool is charged with a tool substrate in a commercially available deposition apparatus for thin film deposition equipped with a direct current magnetron sputtering source having a TiB ₂ target. Resistance heating is performed, and immediately after heating, the tool base is subjected to Ar etching with a base bias of −200 V for 30 minutes, and then the TiB ₂ target is sputtered for a predetermined time while maintaining the atmosphere in the apparatus in an Ar atmosphere. It is also known that it is manufactured by forming a hard coating layer comprising a TiB ₂ layer.

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 2002-355704 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 versatile coated tool that is not limited to the above is strongly desired. However, in the conventional coated tool, the cutting of a hard difficult-to-cut material such as a Ti-based alloy or die steel is performed at high speed with high heat generation Although it exhibits excellent wear resistance when performed with, extremely high heat generation that occurs during cutting is performed when cutting soft difficult-to-cut materials such as various Al alloys under high-speed cutting conditions. Due to this, welding is likely to occur, and due to this, the hard coating layer is peeled off and the service life is reached in a relatively short time.

  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 high-speed cutting of the soft difficult-to-cut material. As a result, the following knowledge was obtained.

First, in the conventional coated tool (Patent Document 1), the TiB ₂ layer is formed by direct current magnetron sputtering, and this is used for high-speed cutting of hard difficult-to-cut materials such as Ti-based alloys and die steel. However, when this is used to cut soft difficult-to-cut materials such as various Al-based alloys under high-speed cutting conditions, the surface structure is dense. It was found that the hard coating layer peeled off due to the welding because the contact area with the cutting material was large, welding was caused by extremely high heat generation, and the bond between the crystal grains of the TiB ₂ layer was weak.

Accordingly, the present inventors have welding occurs hardly occurs, and, as a result of research by focusing on high TiB ₂ layer tissue binding strength of the crystal grains mutually, when forming the TiB ₂ layer, Patent Document 1 By adopting high-power pulse sputtering with specific conditions instead of the DC magnetron sputtering shown in Fig. 4, the surface structure is porous even in cutting of soft difficult-to-cut materials such as various Al alloys under high-speed cutting conditions. Therefore, since the contact area with the work material is small, it is difficult to generate heat and welding, and the TiB ₂ layer has a strong bond strength between the crystal grains of the TiB ₂ layer. It was found that a film can be formed.

Specifically, FIG. 1 shows a schematic plan view of a high-power pulse sputtering apparatus. A sintered body of Ti boride (hereinafter referred to as TiB ₂ ) powder (hereinafter referred to as TiB ₂ ) is used in the high-power pulse sputtering apparatus. ₍ 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 a TiB ₂ layer is deposited on the surface of the tool base. TiB has excellent welding resistance, strong bond strength between crystal grains, and high film hardness (for example, nanoindentation hardness measured at a load of 200 mg is 3700 kgf / mm ² or more), TiB It was found that _two layers were formed.

As a result, the resulting coated tool is a TiB having excellent welding resistance, bond strength between grains, and hardness in high-speed cutting of soft difficult-to-cut materials such as various Al-based alloys with particularly high heat generation. _{It has} been found that the surface layer composed of _two layers suppresses the peeling of the hard coating layer caused by welding, and thereby exhibits excellent peeling resistance and wear resistance over a long period of time. It was.

The present invention has been made based on the above findings,
A surface-coated cutting tool in which a Ti 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. And
The Ti 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 consisting of an aggregate of primary crystal grains having an average grain size of 10 to 15 nm. A surface-coated cutting tool comprising secondary crystal grains of ˜70 nm and tertiary crystal grains having an average grain size of 300 to 600 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 thickness of hard coating layer Ti boride layer formed on the outermost surface of a tool substrate made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet, if the average layer thickness is less than 0.5 μm, it is tangled. On the other hand, if the average layer thickness exceeds 5 μm, the high-speed cutting of soft difficult-to-cut materials such as Al-based alloys suppresses peeling due to welding. However, chipping is likely to occur at the cutting edge due to the large compressive residual stress resulting from the high driving effect on the coating of high-power pulse sputtering, so the average layer thickness was determined to be 0.5 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 utilized 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 10 nm. On the other hand, when the average grain size exceeds 15 nm, there is a grain boundary that inhibits dislocation motion. 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 70 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 300 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 600 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 TiB ₂ powder is sintered at two locations facing each other across the rotary table. A body (TiB ₂ sintered body) target is disposed, 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 TiB ₂ sintered body target. perform high output pulse sputtering at a high average input power, it is produced by a TiB 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 the underlying layer of the TiB ₂ layer.

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. Then, a sintered body (TiB ₂ sintered body) target of TiB ₂ powder is 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 TiB ₂ layer can be formed by vapor deposition.

In particular, the TiB ₂ layer formed by high-power pulse sputtering under the specific conditions has excellent adhesion strength to the (Ti, Al) N layer, and the film hardness is further increased.

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.

The (Ti, Al) N layer and TiB 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 layers of TiB, it is possible to suppress the peeling of the soft coating layer due to welding when performing high-speed cutting condition processing accompanied by high heat generation of a soft difficult-to-cut material, which is excellent over a long period of use. Demonstrate wear resistance.

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 section of the Ti boride layer of this invention covering insert 9 is shown. The scanning electron micrograph (magnification: 100,000 times) of the horizontal section of the Ti boride layer of the conventional covering insert 9 is shown. The horizontal cross-section schematic diagram of the Ti 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 into 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. Is mounted along the outer periphery at a position that is a predetermined distance away from the radial direction, while in the high-power pulse sputtering apparatus, TiB ₂ sintered body targets are arranged at four locations facing each other across the rotary table,
(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 present surface coated inserts (hereinafter referred to as the present invention coated inserts) 1 to 8 as the present invention coated tools are produced by forming the TiB ₂ layer having the target layer thickness shown in FIG. did.
(D) Further, the coated inserts 9 to 16 of the present invention in which a (Ti, Al) N layer is introduced as an underlayer are used for each of the tool bases A-9 to A-10 and B-1 to B-6. 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 a TiB 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) The TiB ₂ sintered body target is subjected to high-power pulse sputtering under the predetermined pulse sputtering conditions shown in Table 3, the gas introduced into the apparatus is switched from nitrogen gas to Ar gas, and the atmosphere in the apparatus is set to 0. Sputtering was performed for 5 Pa under the conditions corresponding to the layer thickness, and the TiB 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, each of the tool bases A-1 to A-8 is ultrasonically cleaned in acetone and dried, and a physical vapor deposition apparatus provided with a high-power pulse sputtering apparatus and a DC sputtering apparatus, respectively. In the apparatus, a Ti-Al alloy target having various component compositions and a TiB ₂ sintered body target are mounted,
First, the inside of the apparatus is evacuated and kept at a vacuum of 0.1 Pa or less, the inside of the apparatus is heated to 400 ° C. with a heater, and then a DC bias voltage of −200 V is applied to the tool base that rotates while rotating on the rotary table. By applying, the tool base is subjected to Ar bombardment treatment for 1 hour, and the inside of the apparatus is heated to 500 ° C. with a heater, and then the atmosphere in the apparatus is set to an Ar atmosphere to serve as a cathode electrode (evaporation source) of the DC sputtering apparatus. Conventional surface-coated insert as a conventional coated tool by starting DC sputtering of the arranged TiB ₂ sintered body and simultaneously applying a bias voltage of +60 V to the tool base and depositing a TiB ₂ layer having an average layer thickness shown in Table 6 Conventional coated inserts 1 to 8 (hereinafter referred to as conventional coated inserts) were produced. Further, each of the tool bases A-9 to A-10 and B-1 to B-6 is first evacuated from the apparatus and kept at a vacuum of 0.1 Pa or less, and the interior of the apparatus is heated to 400 ° C. with a heater. After heating, a DC bias voltage of −200 V is applied to the tool base that rotates while rotating on the rotary table, whereby the tool base is subjected to Ar bombardment for 1 hour, and nitrogen gas is introduced into the apparatus as a reactive gas. The reaction atmosphere is 0.6 Pa and the inside of the apparatus is heated to 500 ° C. with a heater, and then the high-power pulse sputtering is performed on the Ti—Al alloy target under predetermined pulse sputtering conditions indicated by the condition symbol a in Table 3. Then, a (Ti, Al) N layer having the target composition and target layer thickness shown in Table 6 is formed on the surface of the tool base as a hard-wearing hard layer of the hard coating layer. The atmosphere in the DC sputtering apparatus as an Ar atmosphere, applying a cathode electrode bias voltage of + 60V to TiB ₂ sintered at the same time tool substrate when starting the DC sputtering arranged as (evaporation source) of the DC sputtering device, with by the Conventional coated inserts 9 to 16 are manufactured by depositing TiB ₂ layers having an average layer thickness shown in Table 6 under the predetermined DC sputtering conditions shown in Table 5 as upper layers on top of the (Ti, Al) N layer. did.

  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 TiB ₂ 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, the crystal grain structure of the TiB _two layers is 100,000 times by a scanning electron microscope (Carl 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 4 and 6 show the measured values.

FIG. 2 shows a scanning electron micrograph (magnification: 100,000 times) of the horizontal section of the TiB ₂ layer of the coated insert 9 of the present invention, and FIG. 3 shows the scanning of the horizontal section of the TiB 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 view of a Ti boride layer made of a composite structure of the coated insert of the present invention is shown.

For the TiB ₂ layers of the inventive 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 (manufactured by Elionix, 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 thickness of the TiB ₂ layer and the wear-resistant hard layer of the hard coating layer was 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: Al-based alloy JIS A7075 (mass%, Si: 0.25%, Fe: 0.4%, Cu: 2.0%, Mn: 0.3%, Mg: 2.9%, Round bars of Cr: 0.28%, Zn: 5.1%, Ti: 0.2%, Al and impurities: the rest)
Cutting speed: 600 m / min. ,
Incision: 1.5mm,
Feed: 0.6 mm / rev. ,
Cutting time: 90 minutes
Dry-type high-speed cutting test (normal feed is 0.4 m / min.) Of an Al-based alloy under the following conditions (referred to as cutting condition A),
The flank wear width of the cutting blade 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 10 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 TiB ₂ layers having target layer thicknesses 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 of the present invention were produced by vapor-depositing a layer and a hard coating layer composed of a surface layer composed of a TiB ₂ layer having a target layer thickness 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. A conventional surface-coated end mill (hereinafter referred to as a conventional coating tool) as a conventional coating tool is formed by depositing a wear-resistant hard layer comprising a (Ti, Al) N layer and a TiB ₂ layer having a target composition and target layer thickness as a hard coating layer. 1-8) (referred to as end mills) were produced.

  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 TiB ₂ 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 crystal grain structure of the TiB ₂ layers was 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 TiB ₂ 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 was measured by an ultra-fine indentation hardness tester (manufactured by Elionix, ENT-1100a). 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 thickness of the TiB ₂ layer and the wear-resistant hard layer of the hard coating layer was 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 Al-based alloy JIS A7075 (mass%, Si: 0.25%, Fe: 0.4%, Cu: 2.0% Mn: 0.3%, Mg: 2.9%, Cr: 0.28%, Zn: 5.1%, Ti: 0.2%, Al and impurities: remaining)
Cutting speed: 188.4 m / min. (Rotation speed: 10,000 times / min),
Groove depth (cut): 10 mm,
Table feed: 2000 to 6000 mm / min,
Cutting time: Al type alloy wet high-speed grooving test under the condition of 5 minutes (referred to as cutting condition B) (normal table feed is 1000 mm / min),
Was gradually increased from a table feed of 1000 mm / min to 500 mm / min to confirm whether normal cutting could be performed without causing welding or chip clogging. The measurement results are shown in Table 11, respectively.

表３〜１１に示される結果から、ＴｉＢ_２層がすぐれた耐溶着性と硬さを有する本発明被覆工具は、各種のＡｌ系合金などの軟質難削材の高熱発生を伴う高速切削で、すぐれた耐剥離性と耐摩耗性を発揮する。

From the results shown in Tables 3 to 11, the present coated tool having excellent welding resistance and hardness with the TiB ₂ layer is high-speed cutting accompanied by high heat generation of soft difficult-to-cut materials such as various Al alloys, Excellent peel resistance and wear resistance.

On the other hand, as shown in Tables 6 and 10, in the conventional coated tool, since the composite structure is not formed, the welding resistance is inferior, and it is hard under high-speed cutting conditions with high heat generation of a soft difficult-to-cut material. Since peeling of the coating layer cannot be suppressed and the hardness is not sufficient, the wear resistance is poor. In the case of a reference coated tool having a TiB ₂ layer that is out of the range specified in the present invention, the wear of the cutting edge portion is fast in high-speed cutting with high heat generation of a soft difficult-to-cut material, 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 high speed of the soft 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 is possible to sufficiently satisfy the cost reduction.

Claims (1)

A surface-coated cutting tool formed by coating a Ti boride layer having an average layer thickness of at least 0.5 to 5 μm on the outermost surface of a tool base made of tungsten carbide-based cemented carbide or titanium carbonitride-based cermet. ,
The Ti 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 consisting of an aggregate of primary crystal grains having an average grain size of 10 to 15 nm. A surface-coated cutting tool comprising secondary crystal grains of ˜70 nm and tertiary crystal grains having an average grain size of 300 to 600 nm composed of aggregates of the secondary crystal grains.

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