Surface coated cutting tools

Abstract

A surface-coated cutting tool has a hard coating layer on a tool substrate, wherein the hard coating layer has an inner layer, a lower intermediate layer, an upper intermediate layer, a bonding auxiliary layer and an outer layer in sequence from the tool substrate toward the surface, wherein the inner layer is a Ti carbonitride layer with an average layer thickness of 4.0 to 20.0 μm, the lower intermediate layer is a Ti nitride layer with an average layer thickness of 0.1 to 2.0 μm, the upper intermediate layer is a Ti carbonitride layer with an average layer thickness of 0.1 to 2.5 μm, and the The grain boundaries of the Ti nitride in the lower middle layer and the Ti carbonitride in the upper middle layer are continuous with the grain boundaries of the Ti carbonitride in the inner layer, the bonding auxiliary layer is a Ti carbonitride oxide layer with an average layer thickness of 3 to 80 nm, the outer layer is an α-type aluminum oxide layer with an average layer thickness of 2.0 to 20.0 μm, the texture coefficient TC (422) of the Ti carbonitride in the inner layer and the upper middle layer is greater than 3.0, and the texture coefficient TC (0 0 12) of the α-type aluminum oxide in the outer layer is greater than 5.0.

Description

Technical Field

[0001] The present invention relates to a surface-coated cutting tool (hereinafter, sometimes referred to as a coated tool). Background Art

[0002] In order to improve the cutting performance of cutting tools, it has been known in the past to have a coated tool having a hard coating layer formed by vapor deposition on the surface of a tool substrate such as tungsten carbide (hereinafter referred to as WC)-based cemented carbide, which exhibits excellent wear resistance.

[0003] Although the conventional coated tool formed with the hard coating layer described above is excellent in wear resistance, various proposals have been made for further improvement of the hard coating layer.

[0004] For example, Patent Document 1 describes a coated tool having a hard coating layer, wherein the hard coating layer has a TiCN layer, a bonding layer, an α-type Al 2 O 3 The average thickness of the TiCN layer is 4 to 20 μm, the texture coefficient TC(220) (hereinafter, sometimes simply represented by TC) is 0.5 or less, TC(422) is 3 or more, and the sum of TC(311) and TC(422) is 4 or more, the bonding layer is at least one layer of TiN, TiCN, TiCO and TiCNO and has an average thickness of 0.5 to 2 μm, and the α-type Al 2 O 3 The average thickness of the layer is 2 to 20 μm, TC(0 0 12) is 7.2 or more, and I(0 0 12) / I(0 0 14) is 1 or more.

[0005] In addition, for example, Patent Document 2 describes a coated tool having a hard coating layer, wherein the hard coating layer has a TiCN layer, a bonding layer, an α-type Al 2 O 3 The average thickness of the TiCN layer is 2 to 20 μm, the bonding layer is a needle-shaped TiCNO or TiBN, and the α-type Al 2 O 3 The average thickness of the layer is 1 to 15 μm, and TC(006) is greater than 5.

[0006] Patent Document 1: Japanese Patent Publication No. 2016-137564

[0007] Patent Document 2: Japanese Patent No. 5872746

[0008] In recent years, there has been a strong demand for labor-saving and energy-saving in cutting processing. Along with this, cutting processing has a tendency to become further faster and more efficient. The hard coating layer of the coated tool is further required to have resistance to abnormal damage such as chipping resistance, defect resistance, and peeling resistance, and is required to have excellent wear resistance during long-term use.

[0009] However, according to the research conducted by the present inventors, the coated tools described in Patent Documents 1 and 2 do not have sufficient durability in cutting processes in which a large load is placed on the cutting edge. Summary of the invention

[0010] The present invention has been made in view of the above situation, and an object of the present invention is to provide a covered tool having sufficient durability in cutting processing in which a cutting edge is subjected to a large load.

[0011] A surface-coated cutting tool according to one embodiment of the present invention is characterized in that:

[0012] A tool substrate and a hard coating layer on the tool substrate are provided.

[0013] The hard coating layer comprises an inner layer, a lower middle layer, an upper middle layer, a bonding auxiliary layer and an outer layer in sequence from the tool base toward the surface.

[0014] The inner layer is a Ti carbonitride layer with an average layer thickness of 4.0 to 20.0 μm.

[0015] The lower intermediate layer is a Ti nitride layer with an average layer thickness of 0.1 to 2.0 μm.

[0016] The upper intermediate layer is a Ti carbonitride layer with an average layer thickness of 0.1 to 2.5 μm, the grain boundaries of the Ti nitride in the lower intermediate layer and the Ti carbonitride in the upper intermediate layer are continuous with the grain boundaries of the Ti carbonitride in the inner layer,

[0017] The bonding auxiliary layer is a Ti carbonitride oxide layer with an average layer thickness of 3 to 80 nm.

[0018] The outer layer is an α-aluminum oxide layer with an average layer thickness of 2.0 to 20.0 μm.

[0019] The texture coefficient TC(422) of the Ti carbonitride of the inner layer and the upper intermediate layer is 3.0 or more, and the texture coefficient TC(0 0 12) of the α-alumina of the outer layer is 5.0 or more.

[0020] As described above, the blade has sufficient durability even in cutting processing where a large load is placed on the blade edge. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1Schematic diagram showing an inner layer, a lower intermediate layer, an upper intermediate layer, a bonding auxiliary layer, and an outer layer of a coated tool according to an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The inventors of the present invention have conducted intensive studies focusing on the α-alumina layer and the bonding auxiliary layer (adhesive layer) to improve the durability of coated tools including an α-alumina layer as a hard coating layer. As a result, they have found that the needle-like structure of the adhesive layer has an adverse effect on durability.

[0023] That is, the adhesive layer described in Patent Document 1 has a needle-like structure similar to the adhesive layer in Patent Document 2 in order to obtain an anchor effect for strengthening the bond with the α-alumina layer, although it is not explicitly described in the document.

[0024] However, according to the research of the present inventors, it is clear that the needle-like structure is the cause of the voids in the interface region between the α-alumina layer and the bonding layer. That is, it is found that the raw material gas used to form the α-alumina layer is not fully supplied to the gap formed by the needle-like structure, thereby generating voids and making it difficult to obtain the anchoring effect brought by the needle-like structure. In addition, it is also found that the chipping resistance is improved by setting the Ti carbonitride layer described in the above-mentioned patent documents 1 and 2 to three layers of Ti carbonitride layer-Ti nitride layer-Ti carbonitride layer.

[0025] Below, one embodiment of the present invention is described in detail. In addition, in this specification and claims, when "A to B" (A and B are both numerical values) is used to represent a numerical range, the range includes an upper limit (B) and a lower limit (A), and the upper limit (B) and the lower limit (A) have the same unit. In addition, the numerical value includes a tolerance.

[0026] The compositions of each layer of Ti nitride, Ti carbonitride, Ti oxycarbonitride, Ti oxide, and the α-aluminum oxide layer are not limited to stoichiometric compositions, but include compositions of all conventionally known atomic ratios.

[0027] like Figure 1As schematically shown, the coated tool of one embodiment of the present invention has an inner layer 2, a lower intermediate layer 3, an upper intermediate layer 4, a bonding auxiliary layer 5 and an outer layer 6 in a hard coating layer 1 on a tool substrate 8. Moreover, the inner layer 2, the lower intermediate layer 3, the upper intermediate layer 4, and the bonding auxiliary layer 5 (hereinafter, these layers are collectively referred to as main layers) are epitaxially grown by adjusting the gas composition of the film-forming gas and the reaction atmosphere pressure. Therefore, when observed in a longitudinal section (a section perpendicular to the surface of the tool substrate 8), the grain boundaries of the Ti nitride of the lower intermediate layer 3 and the grain boundaries of the Ti carbonitride of the upper intermediate layer 4 are continuous with the grain boundaries of the Ti carbonitride having the columnar particles 7 in the inner layer, and when they are regarded as a whole, they can be regarded as a structure that is just like a part of a larger columnar particle. Moreover, the bonding auxiliary layer 5 is not a needle-shaped structure. That is, the bonding auxiliary layer 5 is a non-needle-shaped structure, for example, composed of equiaxed crystals.

[0028] The term "grain boundary continuity" refers to a state in which the grain boundary can be visually recognized as continuous when an arbitrary longitudinal cross section of the hard coating layer described later is observed with a scanning electron microscope (SEM: Scanning Electron Microscope).

[0029] In this way, the reason why the grain boundaries can be visually distinguished as continuous can be considered to be the following: since the lattice constants of the epitaxially grown Ti nitride and Ti carbonitride can be considered to be substantially the same, the Ti nitride of the lower intermediate layer is the Ti carbonitride of the inner layer, and in addition, the Ti carbonitride of the upper intermediate layer and the Ti nitride of the lower intermediate layer are respectively grown in a direction parallel to the surface of the tool substrate in such a way that the lattice spacing (plane spacing) is consistent, and this lattice spacing can be maintained even after cooling after film formation, so that the plane spacing of the Ti carbonitride of the inner layer is directly inherited by the Ti nitride of the lower intermediate layer and the Ti carbonitride of the upper intermediate layer.

[0030] Each layer is described below.

[0031] Inner Layer:

[0032] The inner layer is a Ti carbonitride layer having columnar particles adjacent to the tool substrate or the innermost layer described later, and its average layer thickness is preferably 4.0 to 20.0 μm. The reason for setting the average layer thickness to this range is that when it is less than 4.0 μm, the wear resistance is reduced, and on the other hand, when it is greater than 20.0 μm, the defect resistance is reduced. The average layer thickness is more preferably 5.0 to 15.0 μm, and further preferably 8.0 to 12.0 μm.

[0033] Lower middle layer:

[0034] The lower intermediate layer is arranged between the inner layer and the upper intermediate layer, and the lower intermediate layer is a Ti nitride layer, and the average layer thickness is preferably 0.1 to 2.0 μm. Since the Ti nitride layer is softer than other main layers and has a lower Young's modulus, the toughness of the hard coating layer is improved, thereby improving the chipping resistance. That is, as described later, although when the Ti carbonitride layer as a bonding auxiliary layer and the α-alumina layer of the outer layer are firmly attached, due to the difference in physical properties such as the thermal expansion coefficient of these substances, a large deformation occurs in the upper intermediate layer adjacent to the bonding auxiliary layer, it is believed that the deformation will be alleviated by the Ti nitride layer with a low Young's modulus. In addition, since the aforementioned grain boundary continuity is damaged when the average layer thickness of the lower intermediate layer is greater than 2.0 μm, the average layer thickness of the lower intermediate layer is preferably 0.1 to 2.0 μm, more preferably 0.3 to 1.5 μm, and further preferably 0.5 to 1.0 μm.

[0035] In addition, the lower middle layer also plays a role in firmly bonding the upper middle layer and the inner layer.

[0036] Upper middle layer:

[0037] The upper intermediate layer is a Ti carbonitride layer disposed between the lower intermediate layer and the bonding auxiliary layer. The reason for setting it as a Ti carbonitride layer is that since the bonding auxiliary layer described later is a Ti carbonitride oxide layer and has oxygen, it has a higher chemical affinity with the outer α-alumina layer, and the crystallographic affinity is higher when considering the inclination of the (422) plane of the Ti carbonitride and the inclination of the (0 0 12) plane of the α-alumina. When the average layer thickness of the upper intermediate layer is less than 0.1 μm, the effect of the affinity is not sufficient. On the other hand, when it is greater than 2.5 μm, the toughness improvement effect of the aforementioned lower intermediate layer on the hard coating layer cannot be exerted. The average layer thickness is more preferably 0.3 to 2.0 μm, and more preferably 0.5 to 1.5 μm.

[0038] The texture coefficient TC(422) of the Ti carbonitride in the inner layer and the upper intermediate layer:

[0039] As described above, in the inner layer, the lower middle layer, and the upper middle layer, which can be regarded as a large columnar particle in the main layer, the TC (422) of the Ti carbonitride, which is the main constituent phase of these layers, is preferably 3.0 or more. The reason is that when it is 3.0 or more, the TC (0 0 12) of the α-alumina of the outer layer described later becomes 5.0 or more due to the aforementioned epitaxial growth, thereby improving the wear resistance. Here, TC (texture coefficient TC) is measured by X-ray diffraction using a 2θ / θ converging optical system of CuKα, and is a parameter defined by the Harris formula described below.

[0040] [Mathematical formula 1]

[0041]

[0042] Here, I(hkl) is the diffraction intensity of the (hkl) plane, I 0 (hkl) is the standard intensity recorded in ICDD file number 00-042-1489 on the same surface, and n is the total number of reflective surfaces. The surfaces to be considered as reflective surfaces are (111), (200), (220), (311), (331), (420), (422), and (511).

[0043] Combined auxiliary layer:

[0044] The bonding auxiliary layer is a layer that is in contact with the outer α-alumina layer, and is a Ti carbonitride oxide layer corresponding to the bonding layer of the above-mentioned Patent Documents 1 and 2, and having an average layer thickness of 3 to 80 nm. Since this layer contains oxygen, it has the characteristic of being firmly attached to the outer α-alumina layer, and this characteristic can be exerted when the average layer thickness is 3 to 80 nm. In addition, from the perspective of exerting this characteristic, the average layer thickness is more preferably 3 to 50 nm, and more preferably 3 to 30 nm.

[0045] The bonding auxiliary layer is formed into a thin layer with an average thickness of 3 to 80 nm by adjusting the composition of the film-forming gas and the reaction time, and its structure is not a needle-shaped structure. Therefore, when the outer α-alumina layer is formed, the α-alumina layer will not produce gaps in the vicinity of the bonding auxiliary layer, and the outer α-alumina layer can be firmly bonded to the inner layer, the lower intermediate layer and the upper intermediate layer through the bonding auxiliary layer.

[0046] Outer Layer:

[0047] The outer layer is preferably an α-alumina layer with an average layer thickness of 2.0 to 20.0 μm and a TC (0 0 12) of 5 or more. When the average layer thickness is less than 2.0 μm, the durability cannot be fully ensured in long-term use due to its thinness. On the other hand, when the average layer thickness is greater than 20.0 μm, the grains of the α-alumina layer become larger, and chipping is likely to occur. When TC (00 12) is 5.0 or more, high wear resistance is exerted.

[0048] Here, when calculating TC(0 0 12), the standard strengths of the (104) plane, (110) plane, (113) plane, (024) plane, (116) plane, (214) plane, (300) plane, and (0 0 12) plane described in ICDD file number 00-010-0173 are used.

[0049] Other layers:

[0050] In this embodiment, the other layer is composed of one or more Ti compound layers among the Ti carbide layer and the Ti nitride layer, and the innermost layer having a total average layer thickness of 0.1 to 2.0 μm can be disposed between the tool substrate and the inner layer in a manner adjacent to the tool substrate. When the innermost layer is disposed, the durability of the coated tool is further exerted. Here, when the total average layer thickness of the innermost layer is less than 0.1 μm, the effect of disposing the innermost layer cannot be fully achieved. On the other hand, when the total average layer thickness of the innermost layer is greater than 2.0 μm, the grains are easily coarsened, and chipping is easily caused.

[0051] In addition, in the present embodiment, the other layers are composed of one or more Ti compound layers among Ti nitride layers, Ti carbide layers, and Ti carbonitride layers, and the outermost layer having a total average layer thickness of 0.1 to 4.0 μm can be set on the upper part of the outer layer. When the outermost layer is set, due to the obvious color and other effects, when the coated tool is a blade, it is easy to identify the corner after cutting (corner identification, identification of the used part). Here, when the total average layer thickness is less than 0.1 μm, the effect of setting the outermost layer cannot be fully exerted. On the other hand, when it is greater than 4.0 μm, chipping is likely to occur.

[0052] Tool base:

[0053] In this embodiment, the tool substrate can use cemented carbide (WC-based cemented carbide: in addition to WC, it also includes Co, and further includes alloys of substances formed by adding carbonitrides of Ti, Ta, Nb, etc.), metal ceramics (ceramics with TiC, TiN, TiCN, etc. as main components, etc.), ceramics (silicon nitride, sialon, alumina, etc.) or cBN sintered body, but is not limited to these.

[0054] Determination of average layer thickness:

[0055] Here, for example, a focused ion beam device (FIB: Focused Ion Beam system), a cross section polisher (CP: Cross section Polisher), etc. can be used to prepare a sample for observing a longitudinal section (a cross section cut using a surface perpendicular to the surface of the tool substrate) at any position of the hard coating layer, and a scanning electron microscope (SEM) or a transmission electron microscope (TEM: Transmission Electron Microscope), a scanning transmission electron microscope (STEM: Scanning Transmission Electron Microscope), or an energy dispersive X-ray analysis (EDX: Energy Dispersive X-ray spectrometer) device with a SEM or TEM is used to observe multiple parts (for example, five parts) of the longitudinal section and take an average value to obtain the average layer thickness of each layer constituting the hard coating layer.

[0056] Example

[0057] Next, examples are described.

[0058] Here, although the case where the embodiment is applied to a blade cutting tool using WC-based cemented carbide as a tool base is described, the same is true for the case where the aforementioned tool base is used as the tool base, and the same is true for the case where the embodiment is applied to a drill or an end mill.

[0059] As raw material powders, WC powder, TiC powder, TiN powder, NbC powder, Cr powder, etc., each having an average particle size of 1 to 3 μm, were prepared. 3 C 2 Powder and Co powder are formulated according to the composition shown in Table 1, and wax is further added. The raw material powders are ball-milled in acetone for 24 hours. After reduced pressure drying, the powder is pressed into a compact of a specified shape at a pressure of 98 MPa. The compact is vacuum sintered in a vacuum of 5 Pa at a specified temperature in the range of 1370 to 1470°C for 1 hour. After sintering, WC-based cemented carbide tool substrates A to B with a blade shape of CNMG120412 of ISO specification are manufactured respectively.

[0060] Next, the outer layer and the main layer were formed on the surface of these tool substrates A to B. Of the outer layer and the main layer, the inner layer was formed according to the film forming conditions shown in Table 2, and the lower intermediate layer, the upper intermediate layer and the bonding auxiliary layer in the main layer were formed according to the film forming conditions shown in Table 3, and then the oxidation treatment shown in Table 3 was performed to produce the coated tools 1 to 6 of the present invention shown in Table 6. In addition, except for the example tools 1 and 4, the innermost layer and / or the outermost layer (Ti nitride layer) were formed according to the film forming conditions shown in Table 4.

[0061] For comparison, the hard coating layer was formed on the surface of these tool substrates A to B according to the film forming conditions shown in Table 2, Table 3 or Table 5 based on the film forming conditions described in the above-mentioned patent document 1, and comparative example tools 1 to 6 shown in Table 6 were prepared. The comparative coated tools are: coated tools without a lower intermediate layer or a coating tool in which the average layer thickness of the lower intermediate layer does not meet the range specified in one embodiment of the present invention although the film forming conditions of the coated tool of the present invention are used; coated tools without an upper intermediate layer or whose average layer thickness does not meet the range specified in one embodiment of the present invention; and coated tools in which the average layer thickness of the bonding auxiliary layer does not meet the range specified in one embodiment of the present invention. In addition, observation was performed using SEM (magnification 500 to 5000 times), and the results showed that the TiCNO layer equivalent to the bonding auxiliary layer of one embodiment of the present invention all had a needle-like structure. In addition, as in the examples, except for comparative example tools 1 and 4, the innermost layer and / or the outermost layer (Ti nitride layer) were formed according to the film forming conditions shown in Table 4.

[0062] [Table 1]

[0063]

[0064] *“-” indicates not contained.

[0065] [Table 2]

[0066]

[0067] [Table 3]

[0068]

[0069] α: From film formation to 10 minutes

[0070] β: 10 minutes after film formation [Table 4]

[0071]

[0072] [Table 5]

[0073]

[0074]

[0075] Next, the Example Tools 1 to 6 and the Comparative Example Tools 1 to 6 were clamped to the tip of a tool steel turning tool by a fixing fixture, and then subjected to a dry lathe cutting test 1 and a cutting test 2 of ductile iron and alloy steel to evaluate the cutting performance. The cutting test was as follows.

[0076] Cutting test 1

[0077] Subject: Example tools 1 to 3 and comparative example tools 1 to 3

[0078] Workpiece: FCD700

[0079] Cutting speed: 400m / min

[0080] Feed rate: 0.3mm / rev

[0081] Cutting depth: 1.5mm

[0082] Cutting time: 1 minute per pass

[0083] Evaluation: The cutting edge was observed with a magnifying glass having a magnification of 2 times for every 1 minute of cutting time, and the time until the peeling of the α-alumina layer was confirmed was measured.

[0084] The results are shown in Table 7.

[0085] Cutting test 2

[0086] Target: Example tools 4 to 6 and comparative example tools 4 to 6

[0087] Workpiece: SNCM439

[0088] Cutting speed: 200m / min

[0089] Feed rate: 0.55mm / rev

[0090] Cutting depth: 4mm

[0091] Cutting time: 2 minutes

[0092] Evaluation: Observe the chipping after 2 minutes of cutting.

[0093] Five corners were evaluated for each tool, and the number of corners at which chipping occurred was evaluated.

[0094] The results are shown in Table 8.

[0095] [Table 7]

[0096]

[0097] [Table 8]

[0098]

[0099] It is clear from the results in Tables 7 and 8 that the Example tool exhibits good cutting performance even when used in cutting of ductile iron and alloy steel, where the blade tip bears a heavy load. However, the Comparative Example tool loses its cutting performance in a short period of time. 2 O 3 ) layer peeling or more chipping occurs, and the service life reaches its limit in a short time.

[0100] The embodiments disclosed above are merely illustrative in all aspects and are not restrictive. The scope of the present invention is expressed by the claims rather than the embodiments described above, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0101] Description of Reference Numerals

[0102] 1 Hard coating

[0103] 2 Inner layer (Ti carbonitride layer)

[0104] 3 Lower intermediate layer (Ti nitride layer)

[0105] 4 Upper intermediate layer (Ti carbonitride layer)

[0106] 5. Bonding auxiliary layer (Ti carbonitride oxide layer)

[0107] 6 Outer layer (α-alumina layer)

[0108] 7 Columnar particles

[0109] 8 Tool base

Claims

1. A surface-coated cutting tool comprising a tool base and a hard coating layer on the tool base, It is characterized in that The hard coating layer comprises an inner layer, a lower intermediate layer, an upper intermediate layer, a bonding auxiliary layer and an outer layer in sequence from the tool base toward the surface of the surface-coated cutting tool, The inner layer is a Ti carbonitride layer with an average layer thickness of 4.0 to 20.0 μm. The lower intermediate layer is a Ti nitride layer with an average layer thickness of 0.1 to 2.0 μm. The upper intermediate layer is a Ti carbonitride layer with an average layer thickness of 0.1 to 2.5 μm. The grain boundary of the Ti nitride of the lower intermediate layer and the grain boundary of the Ti carbonitride of the upper intermediate layer are continuous with the grain boundary of the Ti carbonitride of the inner layer, The bonding auxiliary layer is a Ti carbonitride oxide layer with an average layer thickness of 3 to 80 nm. The outer layer is an α-aluminum oxide layer with an average layer thickness of 2.0 to 20.0 μm. The texture coefficient TC(422) of the Ti carbonitride of the inner layer and the upper intermediate layer is greater than 3.0, and the texture coefficient TC(0 0 12) of the α-alumina of the outer layer is greater than 5.

0. The texture coefficient TC(422) and the texture coefficient TC(0 0 12) are measured by X-ray diffraction using a 2θ / θ converging optical system of CuKα.

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