Coated cutting tool

Abstract

To provide a surface coated cutting tool which is excellent in abrasion resistance without degrading defect resistance.SOLUTION: A surface coated cutting tool comprises: a lower layer with TiCN layer; and an upper layer with Al2O3 layer which contacts with the lower layer. Average thickness of the lower layer is 3.0-20.0 μm and average thickness of the upper layer is 2.0-12.0 μm. In a region A of the Al2O3 layer where it is 1 μm from a boundary face with the lower layer to a tool surface side in a thickness direction of a coating layer, a ratio of random grain boundary length that is a coincidence boundary more than Σ49 to total grain boundary length is 70-95%, and Σ3 / Σ(3-49) that is a ratio of Σ3 coincidence boundary length obtained by a coincidence boundary distribution graph to the sum total of coincidence boundary length which is Σ3 or more and Σ49 or less, is 30-80%. In the Al2O3 layer other than the region A, Σ3 has a maximum peak in the coincidence boundary distribution graph, the Σ3 / Σ(3-49) is 80% or more, and the ratio of the random grain boundary length to the total grain boundary length is 10-50%.SELECTED DRAWING: Figure 1

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] Conventionally, there has been a coated tool in which a coating layer such as a Ti compound is formed by vapor deposition on the surface of a substrate such as a tungsten carbide (hereinafter referred to as WC)-based cemented carbide for the purpose of improving the cutting performance of the cutting tool. This exhibits excellent wear resistance, and various proposals have been made for further improvement of the coating layer.

[0003] For example, Patent Document 1 describes a coated tool having a two-layer structure including a lower layer composed of a Ti compound layer and a TiCN layer and an upper layer composed of an α-Al 2 O 3 layer, and the coated tool is said to have excellent wear resistance as shown by a specific compositional atomic shared lattice point distribution graph.

[0004] Also, for example, Patent Document 2 describes a coated tool in which the coating layer is an aluminum oxide multilayer film having a structure in which two or more unit layers composed of aluminum oxide containing an additive element are included and the two or more unit layers are periodically repeated and laminated, and each of the unit layers has a different type or combination of the additive elements, and the additive element is at least one element selected from the group consisting of elements of Groups 4, 5, and 6 of the periodic table, Y, Ca, Mg, B, and Si, and the coated tool is said to have improved wear resistance.

[0005] Furthermore, for example, Patent Document 3 describes a plurality of α-Al 2 O 3The crystal grains thereof exhibit a (001) orientation, and the grain boundaries of the crystal grains include CSL grain boundaries and general grain boundaries. The length of the Σ3 type grain boundary among the CSL grain boundaries is more than 80% of the length of the Σ(3-29) type grain boundary, and is 10% or more and 50% or less of the total length of all grain boundaries, which is the sum of the length of the Σ(3-29) type grain boundary and the length of the general grain boundary. A coated tool is described, and the coated tool is said to have a long service life.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above circumstances and the above proposal, and an object thereof is to provide a coated tool that exhibits more excellent wear resistance and chipping resistance.

Means for Solving the Problems

[0008] A surface-coated cutting tool according to an embodiment of the present invention has a substrate and a coating layer on the surface of the substrate, (a) The coating layer has a lower layer containing a TiCN layer and an upper layer containing an α-Al 2 O 3 layer, (b) The average thickness of the lower layer is 3.0 to 20.0 μm, (c) The average thickness of the upper layer is 2.0 to 12.0 μm, which is in contact with the lower layer, (d) In the α-Al 2 O 3 layer, In the region A up to 1 μm toward the tool surface side in the thickness direction of the coating layer from the interface with the lower layer, the ratio of the random grain boundary length, which is the corresponding grain boundary exceeding Σ49, to the total grain boundary length is 70 to 95%, and Σ3 / Σ(3 - 49), which is the ratio of the Σ3 corresponding grain boundary length obtained from the corresponding grain boundary distribution graph to the sum of the Σ3 or more and Σ49 or less corresponding grain boundary lengths, is 30 to 80%. In the region of the α-Al 2 O 3 layer excluding the region A, there is a highest peak at Σ3 in the corresponding grain boundary distribution graph, and the ratio Σ3 / Σ(3 - 49) is 80% or more, and the ratio of the random grain boundary length to the total grain boundary length is 10 to 50%.

Advantages of the Invention

[0009] The surface-coated cutting tool according to the above embodiment is excellent in wear resistance and chipping resistance.

Brief Description of the Drawings

[0010]

Figure 1

Modes for Carrying Out the Invention

[0011] The present inventor earnestly studied to obtain a surface-coated cutting tool excellent in wear resistance and chipping resistance. As a result, when the coating layer is a lower layer which is a Ti compound layer containing a TiCN layer in order from the substrate side, and an α-Al 2 O 3 layer exists as an upper layer in contact with this lower layer, when the crystal grains in a predetermined region in contact with the lower layer of this α-Al 2 O 3 layer are refined, the adhesion between the α-Al 2 O 3 layer and the lower layer is enhanced and the chipping resistance is improved, and it was found that the degree of refinement of the crystal grains of this α-Al 2 O 3 layer can be defined by the corresponding grain boundary distribution.

[0012] Hereinafter, the coating tool according to the embodiment of the present invention will be described in detail. In the present specification and claims, when a numerical range is expressed as "L to M" (both L and M are numerical values), the range includes the upper limit value (M) and the lower limit value (L). When only the unit is described for the upper limit value (M), the units of the upper limit value (M) and the lower limit value (L) are the same.

[0013] 1. Coating layer In the coating tool of the present embodiment, the coating layer on the surface of the substrate (1) has a lower layer (2) and an upper layer (3) that is in contact with the lower layer (2) directly above it, as shown in FIG. 1. Further, an outermost layer (4) may be selectively provided on the upper part of the upper layer (3). Hereinafter, the layers constituting the coating layer will be described. Note that the composition of the compounds constituting each layer described below is not limited to the stoichiometric composition.

[0014] (1) Lower layer The Ti compound layer on the substrate side, which is the lower layer, may be only a TiCN layer, or in addition to the TiCN layer, it may have other Ti compound layers, that is, one or more of Ti carbides, nitrides, carbonates, and carbonitride layers. That is, it may have a Ti compound layer in addition to the TiCN layer. And the ratio of the average thickness of the TiCN layer to the other Ti compound layers is not particularly restricted, but it is preferable that the TiCN layer occupies 80% or more of the thickness of the lower layer.

[0015] The lower layer preferably has an average layer thickness of 3.0 to 20.0 μm. The reason is that if it is less than 3.0 μm, the excellent wear resistance of the lower layer cannot be fully exhibited, while if it exceeds 20.0 μm, peeling in the coating layer is likely to occur. The average thickness of the lower layer is more preferably 5.0 to 17.0 μm.

[0016] (2) Upper layer The upper layer is α-Al 2 O 3It is a layer containing a layer with improved wear resistance and chipping resistance. Its average layer thickness is preferably 2.0 to 12.0 μm. The reason is that if it is less than 2.0 μm, the functions of improving the thermal stability and wear resistance exerted by the upper layer cannot be fully exerted. On the other hand, if it exceeds 12.0 μm, peeling in the coating layer is likely to occur. The average thickness of the upper layer is more preferably 3.0 to 10.0 μm.

[0017] Also, α-Al contained in the upper layer 2 O 3 In the region A up to 1 μm from the interface between the lower layer of the layer and the tool surface in the thickness direction of the coating layer, the ratio of the random grain boundary length, which is the corresponding grain boundary exceeding Σ49, to the total grain boundary length is 70 to 95%, more preferably 80 to 90%. The ratio Σ3 / Σ(3-49), which is the ratio of the Σ3 corresponding grain boundary length to the sum of the corresponding grain boundary lengths of Σ3 or more and Σ49 or less obtained by measuring the corresponding grain boundary length, is 30 to 80%, more preferably 50 to 80%. And In the region of the α-Al 2 O 3 layer excluding the region A, there is a highest peak at Σ3 in the corresponding grain boundary distribution graph, and Σ3 / Σ(3-49) is 80% or more. The ratio of the random grain boundary length to the total grain boundary length is 10 to 50%, more preferably 10 to 35%.

[0018] In this way, the adhesion between the α-Al 2 O 3 layer contained in the upper layer and the lower layer is improved, showing excellent defect resistance and chipping resistance. Furthermore, the coarsening of the α-Al 2 O 3 crystallites can be prevented, giving excellent defect resistance.

[0019] Here, the corresponding grain boundary distribution of the α-Al 2 O 3 layer contained in the upper layer can be measured by the following procedure. 1) For the coated tool, its longitudinal section (a section perpendicular to the substrate) is used as the polished surface. 2) Using a field emission scanning electron microscope and an electron backscatter diffraction device, an electron beam was irradiated onto each crystal grain having a random hexagonal crystal lattice existing within the measurement range of the cross-section polished surface, and the crystal orientation of each crystal grain was identified by EBSD (Electron BackScatter Diffraction). The measurement range is preferably 30×50 μm, but is not limited thereto. 3) From this measurement result, the crystal orientation relationship between adjacent crystal lattices was calculated, and the distribution of lattice points (referred to as "constituent atom sharing lattice points") where each of the constituent atoms constituting the crystal lattice interface shares one constituent atom between the crystal lattices was calculated.

[0020] Here, the constituent atom sharing lattice point form is represented by ΣN + 1 when there are N lattice points (where N is an even number of 2 or more but some even numbers do not exist due to the crystal structure of the random hexagonal crystal lattice) that do not share constituent atoms between the constituent atom sharing lattice points. By calculating the respective distribution ratios of the constituent atom sharing lattice points represented above and creating a corresponding grain boundary distribution graph (with the vertical axis representing the existence ratio and the horizontal axis taking ΣN + 1) showing the ratio in the total distribution ratio of all corresponding grain boundary lengths of Σ3 or more, the presence of the peak of Σ3 and the ratio of the corresponding grain boundary lengths of Σ3 / Σ(3 - 49) can be obtained. The calculation method for the distribution ratio exceeding Σ49 was obtained as the distribution ratio of the random grain boundary length exceeding Σ49 using the value obtained by calculating the respective corresponding grain boundary lengths of Σ3 to Σ49 from the obtained measurement results and subtracting the sum of these corresponding grain boundary lengths from the total grain boundary length.

[0021] Also, α-Al 2 O 3 Region A up to 1 μm from the substrate side of the α-Al 1) Observe the longitudinal section of the polished coating layer with a scanning electron microscope. The observation magnification is 5000 times or more, and the observed field of view is 10 μm or more in the direction parallel to the substrate surface. 2) From the difference in contrast, the boundary between the lower layer and the α-Al 2 O 3 layer was visually recognized, and every 0.2 μm in the direction parallel to the substrate surface, α-Al 2 O3 Identify the points where the layer and the lower layer are in contact, and connect the adjacent points with a straight line. 3) Using the line created here as the boundary line, add a line obtained by moving this boundary line 1 μm toward the tool surface side, and define the area sandwiched between the boundary line and the added line as Area A.

[0022] (3) Outermost layer The outermost layer is provided selectively. That is, the outermost layer may or may not be provided. As the outermost layer, it is preferable to provide an outermost layer having a total average layer thickness of 0.1 to 3.0 μm including one or two or more Ti compound layers among a Ti carbide layer, a nitride layer, and an oxide layer. In this case, if the total average layer thickness of these layers is less than 0.1 μm, the effect of providing the outermost layer is not sufficiently exhibited. On the other hand, if it exceeds 3.0 μm, chipping is likely to occur.

[0023] (4) Other layers At the time of switching the film-forming gas, layers different from the TiCN layer, the Ti carbide, nitride, carbon oxide, and carbonitride oxide layers, and the α-Al 2 O 3 layer are produced although they are very few.

[0024] 2. Tool substrate (1) Material As long as the tool substrate is a conventionally known base material for this type of tool substrate and does not inhibit the achievement of the object of the present invention, any one can be used. For example, it is preferably any one of cemented carbide (WC-based cemented carbide, including those containing Co in addition to WC and further adding carbonitrides such as Ti, Ta, Nb, etc.), cermet (those mainly composed of TiC, TiN, TiCN, etc.), ceramics (titanium carbide, silicon carbide, silicon nitride, aluminum nitride, aluminum oxide, etc.), cBN sintered body, or diamond sintered body.

[0025] (2) Shape The shape of the substrate is not particularly limited as long as it is a shape used as a cutting tool, and examples thereof include the shape of an insert and the shape of a drill.

[0026] 3. Measurement of average thickness Here, the average thickness of each layer constituting the coating layer can be obtained, for example, by using a focused ion beam system (FIB), a cross section polisher (CP), etc. to process a sample at an arbitrary position of the coating layer to prepare a longitudinal section for observation, and observing the longitudinal section at a plurality of locations (for example, 5 locations) using a scanning electron microscope (SEM), a transmission electron microscope (TEM), a scanning transmission electron microscope (STEM), or an energy dispersive X-ray spectrometry (EDX) device attached to SEM or TEM, and then averaging.

[0027] 4. Manufacturing method The coated tool of the present embodiment can be manufactured, for example, by the following method.

[0028] (1) Lower layer and outermost layer Since the lower layer and the outermost layer can be manufactured using a known chemical vapor deposition method (CVD method), the description thereof is omitted.

[0029] (2) Upper layer containing α - Al 2 O 3 layer α - Al 2 O 3 The upper layer containing the α - Al 1) Lower layer surface treatment step The lower layer surface treatment step is to use CO gas and CO 2This is a process carried out using gas. This treatment improves the adhesion between the bottom layer's outermost surface layer and the upper layer. The gas used, reaction ambient temperature, reaction ambient pressure, and reaction time are, for example, as follows. Reaction gas: CO 2 1.0 - 5.0 vol%, CO 1.0 - 10.0 vol%, Ar 5.0 - 10.0 vol%, H 2 The balance Reaction ambient temperature: 900 - 1000 °C Reaction ambient pressure: 5.0 - 10.0 kPa Reaction time: 10 - 20 minutes

[0030] 2) Primary process The primary process is the manufacturing condition for increasing the random grain boundaries of α - Al 2 O 3 crystallites. The gas used, reaction ambient temperature, reaction ambient pressure, and reaction time are, for example, as follows. The reaction time is adjusted so that the α - Al 2 O 3 film thickness formed in this process becomes 1 μm. Reaction gas: AlCl 3 1.5 - 3.5 vol%, CO 2 2.0 - 4.0 vol%, HCl 1.0 - 2.0 vol%, H 2 S 0.0 - 0.1 vol%, H 2 The balance Reaction ambient temperature: 900 - 1000 °C Reaction ambient pressure: 5.0 - 10.0 kPa Reaction time: 30 - 60 minutes

[0031] 2) Secondary process The secondary process is the manufacturing condition for increasing the ratio of Σ3 - corresponding grain boundaries of α - Al 2 O 3 crystallites. The gas used, reaction ambient temperature, and reaction ambient pressure are, for example, as follows. The reaction time is adjusted in combination with the primary process to achieve the target film thickness. Reaction gas: AlCl 3 1.0 - 3.0 vol%, CO 25.0 to 10.0 vol%, HCl 4.0 to 6.0 vol%, H 2 S 0.6 to 1.0 vol%, H 2 the balance Reaction atmosphere temperature: 900 to 1000 °C Reaction atmosphere pressure: 5.0 to 10.0 kPa

Examples

[0032] Next, examples will be described. Here, as an example of the coated tool of the present invention, an insert cutting tool using a WC-based cemented carbide as a substrate will be described. However, the material of the substrate may be any of the above-mentioned materials, and the same applies when applied to a drill, an end mill, etc. as a tool.

[0033] As raw material powders, WC powder, TiC powder, TiN powder, TaC powder, NbC powder, Cr 3 C 2 powder and Co powder having an average particle size of 1 to 3 μm were prepared. These raw material powders were blended as shown in Table 1. Further, wax was added and ball milled in acetone for 24 hours, dried under reduced pressure, and then press-molded into a green compact of a predetermined shape at a pressure of 98 MPa. This green compact was vacuum sintered in a vacuum of 5 Pa under the condition of holding at a predetermined temperature in the range of 1370 to 1470 °C for 1 hour, and then honing with R: 0.06 mm was performed on the cutting edge portion to produce substrates α and β made of WC-based cemented carbide having an insert shape defined in ISO·CNMG120408.

[0034] Next, a lower layer was formed on the surfaces of these substrates α and β under the conditions shown in Table 2, and an upper layer (α-Al 2 O 3 layer) was formed under the conditions shown in Table 3, and the outermost layer was selectively formed under the conditions shown in Table 2 to produce Examples 1 to 8 having the lower layer, upper layer, and outermost layer shown in Tables 4 and 5. The average thickness, corresponding grain boundary ratio, etc. of the formed coating layer are shown in Table 5.

[0035] On the one hand, for comparison, a lower layer was formed on the surfaces of these substrates α and β under the conditions shown in Table 2, and an upper layer (α-Al 2 O 3 layer) was formed under the conditions shown in Table 3, and the outermost layer was selectively formed under the conditions shown in Table 2, and Comparative Examples 1 to 8 having the lower layer, upper layer, and outermost layer shown in Tables 4 and 5 were produced. The average layer thickness, corresponding grain boundary ratio, etc. of the formed coating layer are shown in Table 6.

[0036]

Table 1

[0037]

Table 2

[0038]

Table 3

[0039]

Table 4

[0040]

Table 5

[0041]

Table 6

[0042] Next, Cutting Tests 1 and 2 were carried out on Examples 1 to 8 and Comparative Examples 1 to 8 under the following cutting conditions.

[0043] Cutting Test 1 (S45C 2-slit material interrupted outside diameter machining test) Cutting speed: 300 m / min Depth of cut: 2.0 mm Feed per revolution: 0.35 mm Cutting time: 7 minutes Wet cutting

[0044] Cutting test 2 (Intermittent outer diameter machining of SCM440 4-slit material) Cutting speed: 250 m / min Depth of cut: 2.0 mm Feed per revolution: 0.4 mm Cutting time: 8 minutes Wet cutting

[0045] The results of Cutting tests 1 and 2 are shown in Tables 7 and 8 respectively.

[0046]

Table 7

[0047]

Table 8

[0048] As is clear from the results of Tables 7 and 8, the examples show good cutting performance, while in the comparative examples, the coating layer peeled off in a short time, or chipping occurred, or wear progressed, resulting in a short lifespan.

Explanation of reference numerals

[0049] 1 Substrate 2 Lower layer 3 Upper layer 4 Outermost layer 5 Region A

Claims

【Claim 1】 A surface-coated cutting tool having a substrate and a coating layer on the surface of the substrate, (a) The coating layer has a lower layer containing a TiCN layer and an upper layer containing an α-Al ２ O ３ layer, and (b) the average thickness of the lower layer is 3.0 to 20.0 μm, (c) the average thickness of the upper layer is 2.0 to 12.0 μm, in contact with the lower layer, (d) said α-Al ２ O ３ layer, In the region A up to 1 μm from the interface with the lower layer toward the tool surface side in the thickness direction of the coating layer, the ratio of the random grain boundary length, which is the corresponding grain boundary exceeding Σ49, to the total grain boundary length is 70 to 95%, and Σ3 / Σ(3-49), which is the ratio of the Σ3 corresponding grain boundary length obtained from the corresponding grain boundary distribution graph to the sum of the Σ3 or more and Σ49 or less corresponding grain boundary lengths, is 30 to 80%, The α-Al excluding the region A ２ O ３ In the region of the layer, the highest peak exists at Σ3 in the corresponding grain boundary distribution graph, and the ratio Σ3 / Σ(3 - 49) is 80% or more, and the ratio of the random grain boundary length to the total grain boundary length is 10 to 50%. A surface-coated cutting tool characterized by the above.

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