Surface-coated cutting tools

Abstract

To provide a surface-coated cutting tool having excellent durability.SOLUTION: In a surface-coated cutting tool, a coating layer has a layer A2, a layer B3, and a layer C4 that come in contact with each other in this order, the sum of the average thickness of the three layers is 1.05-21.00 μm, the layer A2 has the average thickness of 0.05-2.00 μm and is a nitride or a carbonitride of Ti, the layer B3 has the average thickness of 0.50-13.50 μm and has the average composition of (AlXBTi1-XB)(CYBN1-YB)(0.53≤XB≤0.80, 0.00≤YB<0.05), where 80 area% or more is occupied by crystal grains having a NaCl type face-centered cubic structure, and the layer C4 has the average layer thickness of 0.50-7.00 μm and has the average composition of (AlXCTi1-XC)(CYCN1-YC)(0.50≤XC≤0.75, 0.00≤YC<0.05), where 80 area% or more is occupied by crystal grains having a NaCl type face-centered cubic structure, and 0.03≤XB-XC≤0.10.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 technology]

[0002] Conventionally, in order to extend the life of cutting tools, there are coated tools in which a coating layer is applied to the surface of a substrate such as a tungsten carbide (hereinafter sometimes referred to as WC)-based cemented carbide, and these coated tools have improved wear resistance, etc. In order to further improve the cutting performance of coated tools, various proposals have been made regarding the composition and structure of the coating layer.

[0003] For example, Patent Document 1 describes a tool having a single-layer or multi-layer wear protection coating having a thickness of 2 μm to 25 μm, The wear protection coating has a thickness in the range of 1 μm to 16 μm, and has greater than 85% by volume of a face-centered cubic crystal structure, and is at least one of Ti, 0.40≦x≦0.95, 0≦y≦0.10, and 0.85≦z≦1.15. 1-x Al x C y N z The Ti layer 1-x Al x C y N z The layer has a higher Al content than the inside of the crystal. 1-x Al x C y N z Ti at the grain boundaries 1-o Al o C p N q 0.95≦o≦1.00, 0≦p≦0.10, 0.85≦q≦1.15 and (0−x)≧0.05; and 1-x Al x C y N z Coated tools are described in which the TC(111) of the layer is greater than 1.5, and the coated tools are said to exhibit improved wear resistance and resistance to comb cracking.

[0004] Furthermore, for example, Patent Document 2 discloses a coating layer having, from the side closer to the substrate, a lower layer containing a compound having a composition represented by the following formula (1), and an upper layer formed on the lower layer and containing a compound having a composition represented by the following formula (2): (Al x Ti 1-x )N(0.60≦x≦0.95)(1) (Al y Ti 1-y )N(0.50≦y≦0.85)(2) the average thickness of the lower layer is 1.0 μm or more and 10.0 μm or less, and the average thickness of the upper layer is 1.0 μm or more and 10.0 μm or less, The area ratio of crystal grains in the lower layer that have a GOS value of 1 degree or less GOS i and the area ratio GOS of crystal grains in the upper layer having a GOS value of 1 degree or less s But, GOS i <GOS s The coated tool is said to be capable of extending the tool life even under cutting conditions in which a load acts at a high speed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2018-522748 [Patent Document 2] Patent Publication No. 2021-16934 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in consideration of the above circumstances and proposals, and has an object to provide a surface-coated cutting tool having excellent durability. [Means for solving the problem]

[0007] The surface-coated cutting tool according to an embodiment of the present invention comprises: A substrate and a coating layer on the surface of the substrate are included. (a) the coating layer has, in order from the surface of the substrate toward the surface of the tool, a layer A, a layer B, and a layer C that are in contact with each other, and the sum of the average thicknesses of these three layers is 1.05 to 21.00 μm; (b) the average thickness of the layer A is 0.05 to 2.00 μm and is a nitride or carbonitride of Ti; (c) the average thickness of the layer B is 0.50 to 13.50 μm; (Al XB Ti 1-XB )(C YB N 1-YB )( 0.68 ≦XB≦0.80, 0.00≦YB<0.05), and crystal grains having a NaCl-type face-centered cubic structure account for 80% or more by area; (d) the average thickness of the layer C is 0.50 to 7.00 μm; (Al XC Ti 1-XC )(C YC N 1-YC )( 0.65 ≦XC≦0.75, 0.00≦YC<0.05), and crystal grains having a NaCl-type face-centered cubic structure account for 80% or more by area; (e) The XB and XC are in the range of 0.03≦XB−XC≦0.10 is.

[0008] Furthermore, the surface-coated cutting tool according to the above embodiment may satisfy the following requirements.

[0009] In the layers B and C, the diffraction line intensity value I(200) of the crystal grains (200) of the NaCl-type face-centered cubic crystal structure and the diffraction line intensity value I(111) of the crystal grains (111) are: The relationship 1.0≦I(200) / I(111) must be satisfied. [Effects of the Invention]

[0010] The surface-coated cutting tool according to the embodiment has excellent durability. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic cross-sectional view of a surface-coated cutting tool according to an embodiment of the present invention. [Figure 2] FIG. 3 is a schematic diagram showing crystals at the interface between Layer B and Layer C in a surface-coated cutting tool according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present inventors have conducted extensive research into methods for suppressing adhesion of workpiece materials to the coating layer and cracks that propagate into the substrate in coated tools having a coating layer of composite carbide and nitride of Al and Ti (hereinafter, sometimes referred to as (AlTi)CN). As a result, they discovered that crack propagation can be suppressed by providing an (AlTi)CN layer of a predetermined average thickness on the surface side of the coated tool, the layer having a composition excellent in wear resistance and welding resistance, and providing an (AlTi)CN layer of a predetermined average thickness below the layer (on the substrate side), the layer having a composition that suppresses crack propagation toward the substrate. Furthermore, it was found that continuous crystal growth between the two layers can be achieved by setting the difference in Al content between the two layers within a predetermined range.

[0013] Hereinafter, a coated tool according to an embodiment of the present invention will be described in detail. In this specification and claims, when a numerical range is expressed as "L to M" (where L and M are both numerical values), the range includes an upper limit (M) and a lower limit (L), and when a unit is stated only for the upper limit (M), the unit of the lower limit is also the same.

[0014] Figure 1 shows a schematic cross-sectional view of a coated tool according to one embodiment of the present invention (a cross-section perpendicular to the substrate surface, with the substrate surface treated as a horizontal plane, ignoring minute irregularities on the substrate surface). As is clear from Figure 1, the coated tool according to this embodiment has a layer A (2) in contact with the surface of a substrate (1), a layer B (3) in contact with layer A (2) on the tool surface side of layer A (2), and a layer C (4) in contact with layer B (3) on the tool surface side of layer B (3). The sum of the average thicknesses of layers A (2), B (3), and C (4) is 1.05 to 21.00 µm, constituting a coating layer (6). Each layer will be described in turn below.

[0015] 1.Coating layer The coating layer preferably has an average thickness of 1.05 to 21.00 μm and includes Layer A, Layer B, and Layer C. If the average thickness is thinner than 1.05 μm, the abrasion resistance is insufficient, while if it is thicker than 21.00 μm, peeling or chipping of the coating occurs due to internal defects.

[0016] 2. Layer A Layer A in contact with the substrate surface is made of a nitride or carbonitride of Ti, and acts as a layer (adhesion layer) that provides adhesion between the substrate and Layer B.

[0017] (1) Average composition There are no particular restrictions on the composition of layer A, as long as it is a nitride or carbonitride of Ti. For example, the composition formula is TiC Z N 1-Z (0.00≦Z≦0.05) Here, if Z is contained in an amount greater than 0.05, the hardness of Layer A increases excessively, and Layer A may become more susceptible to peeling from the interface with the substrate.

[0018] (2) Average thickness The average thickness of Layer A is preferably 0.05 to 2.00 μm. This is because if it is thinner than 0.05 μm, it will not function adequately as an adhesive layer, and if it exceeds 2.00 μm, the thickness of the adhesive layer will be too large in the coating layer, making it difficult to obtain sufficient abrasion resistance. The average thickness of Layer A is more preferably 0.10 to 1.50 μm.

[0019] 3. Layer B Layer B, which is provided in contact with the surface of Layer A, is an (AlTi)CN layer, which acts as a layer for suppressing the propagation of cracks that propagate toward the substrate.

[0020] (1) Average composition The average composition of layer B is (Al XB Ti 1-XB )(C YB N 1-YB ) it is preferable that 0.53≦XB≦0.80 and 0.00≦YB<0.05. The reason is that if XB is less than 0.53, the inherent high oxidation resistance of the (AlTi)CN layer cannot be fully obtained, while if XB exceeds 0.80, it becomes difficult to obtain good adhesion with the adjacent layer C, which makes the C layer more susceptible to peeling and reduces durability. The C component in (AlTi)CN may be contained because it has the effect of improving hardness. However, if YB is 0.05 or more, the high-temperature strength of Layer B decreases, so it is preferable that 0.00≦YB<0.05. It is more preferable that XB is 0.70≦XB≦0.80, and within this range, the oxidation resistance is significantly exhibited.

[0021] Also, (Al XB Ti 1-XB ) and (C YB N 1-YB The ratio of Al to Al is not particularly limited. XB Ti 1-XB ) is set to 1, then (C YB N 1-YB ) is preferably 0.8 to 1.2, because the object of the present invention can be reliably achieved within this range. This means that the (Al XC Ti 1-XC )(C YC N 1-YC ) is also the same.

[0022] (2) NaCl-type face-centered cubic crystal grains In Layer B, the proportion of crystal grains having an NaCl-type face-centered cubic structure is preferably 80% by area or more. The reason is that if the proportion is less than 80% by area, the proportion of the soft wurtzite-type hexagonal structure, which is the inherent stable phase of (AlTi)CN, increases in Layer B, and the coated tool does not have sufficient durability.

[0023] (3) Average thickness The average thickness of Layer B is preferably 0.50 to 13.50 μm. The reason is that if it is less than 0.50 μm, the aforementioned crack propagation cannot be sufficiently suppressed, while if it exceeds 13.50 μm, the crystal grains of Layer B become coarse, and although wear resistance is obtained, damage accompanied by the detachment of crystal grains in Layer B due to processing impacts is likely to occur, leading to abnormal damage to the coated tool. The average thickness of Layer B is more preferably 2.00 to 7.00 μm.

[0024] 4. Layer C Layer C, which is provided in contact with the surface of layer B, is an (AlTi)CN layer, which acts as a wear-resistant layer during cutting and as a layer that suppresses adhesion of deposits resulting from the work material.

[0025] (1) Average composition The average composition of layer C is (Al XC Ti 1-XC )(C YC N 1-YC ) it is preferable that 0.50≦XC≦0.75 and 0.00≦YC<0.05. The reason is that if XC is less than 0.50, the high oxidation resistance of (AlTi)CN cannot be fully obtained, while if XC exceeds 0.75, the desired wear resistance and adhesion suppression cannot be obtained. It is more preferable that XC be 0.65≦XC≦0.75. The C component in (AlTi)CN has the effect of improving hardness, so it may be contained. However, if YC is 0.05 or more, high-temperature strength decreases, so it is preferable that 0.00≦YC<0.05.

[0026] (2) NaCl-type face-centered cubic crystal grains In Layer C, the proportion of crystal grains having an NaCl-type face-centered cubic structure is preferably 80% by area or more. The reason is that if the proportion is less than 80% by area, the proportion of the soft wurtzite-type hexagonal structure, which is the inherent stable phase of (AlTi)CN, increases in Layer C, and sufficient durability of the coated tool cannot be obtained.

[0027] (3) Average thickness The average thickness of Layer C is preferably 0.50 to 7.00 μm. The reason is that if it is less than 0.50 μm, sufficient wear resistance and suppression of adhesion cannot be obtained, while if it exceeds 7.00 μm, damage in Layer C originating from cracks that propagate toward the substrate during cutting processing becomes large, which may cause abnormal damage to the tool. The average thickness of Layer C is more preferably 2.00 to 5.00 μm.

[0028] 5. Difference in Al content between layers B and C In this embodiment, the difference in Al content between layers B and C is set within a predetermined range, thereby promoting continuous crystal growth in layers B and C, and further, layer C grows while accumulating crystal lattice distortion, thereby improving the mechanical properties of layer C itself. Here, continuous crystal growth between layers B and C refers to a state in which the crystal grains of layer C grow as if the crystal grains (7) of layer C are fitted into the tips of the crystal grains (6) of layer B at the interface (8) between layers B and C, as shown in Figure 2.

[0029] That is, The difference between the Al content XB of layer B and the Al content XC of layer C is It is preferable that 0.03≦XB−XC≦0.10. The reason for this is that if this difference is less than 0.03, the mechanical properties (wear resistance) of Layer C itself due to the crystal lattice strain accumulated in Layer C will not be sufficiently improved, while if it exceeds 0.10, it will be difficult to achieve continuous crystal growth between Layer B and Layer C. It is more preferable that this difference be 0.05≦XB−XC≦0.10.

[0030] 6. Diffraction line intensity of layers B and C In Layers B and C, it is more preferable that the diffraction line intensity value I(200) of the crystal grains (200) of the NaCl-type face-centered cubic crystal structure and the diffraction line intensity value I(111) of the same (111) satisfy the relationship 1.0≦I(200) / I(111). The reason is that the C layer grows as a crystal on the B layer as a base, and if the I(200) / I(111) ratio is less than 1.0, the desired crack propagation suppression in the B layer and continuous crystal growth from the B layer to the C layer may not be achieved. Here, "in layers B and C" refers to the X-ray diffraction peaks obtained by measuring the X-ray diffraction peaks of layers B and C in an overlapping state rather than individually when performing X-ray diffraction on layers B and C.

[0031] 7. Other layers (1) Outermost layer In this embodiment, an outermost layer consisting of one or more Ti compound layers selected from Ti nitride layers, carbide layers, and carbonitride layers and having a total average layer thickness of 0.10 to 4.00 μm may be provided on top of layer C as part of the coating layer (the outermost layer may be omitted). The distinct color of these layers makes it easy to identify corners (used portions) after cutting when the coated tool is an insert. If the total average layer thickness is less than 0.1 μm, the effect of providing the outermost layer is not fully realized, while if it exceeds 4.00 μm, chipping is likely to occur.

[0032] (2) Unintended demographic When the deposition gas is switched, a TiCN layer, a Ti carbide, nitride, carbonate, and carbonitride oxide layer, and a layer different from the (AlTi)CN layer may be unintentionally produced, although only slightly.

[0033] 8.Base In this embodiment, the substrate may be made of cemented carbide (WC-based cemented carbide: containing Co in addition to WC, and further including carbonitrides of Ti, Ta, Nb, etc.), cermet (mainly composed of TiC, TiN, TiCN, etc.), ceramics (silicon nitride, sialon, aluminum oxide, etc.), or cBN sintered body, but is not limited to these.

[0034] 9. Composition Measurement The average Al content XB and XC of the TiAlCN layer was determined by Auger electron spectroscopy (AES), which irradiated a polished cross-section of a sample with an electron beam and averaged the Auger electron analysis results obtained by performing five line analyses along the thickness of the coating layer. The average C content YB and YC was determined by secondary ion mass spectroscopy (SIMS). Specifically, an ion beam was irradiated from the surface of a polished sample to a 70 μm × 70 μm area of ​​the (AlTi)CN layer, and the depth distribution was measured by alternating ion beam area analysis and sputter ion beam etching. Measurements were performed from the outermost surface of the sample to the substrate surface at intervals of 0.05 μm or less. The average thickness of each layer was then determined using the method described below, and the average C content YB and YC of each layer was calculated.

[0035] 10. Measurement of the proportion of crystal grains with NaCl-type face-centered cubic structure The area ratio of crystal grains with an NaCl-type face-centered cubic crystal structure was measured as follows. The measurement range was 100 μm in the thickness direction of the (AlTi)CN layer in layers B and C, spanning the average thickness of the layers. This measurement range was polished, and an electron backscatter diffraction image was obtained by irradiating the polished surface with an electron beam at an incident angle of 70°, an accelerating voltage of 15 kV, a probe current of 1 nA, and 0.01 μm intervals. The crystal structure of each crystal grain with an NaCl-type face-centered cubic crystal structure was analyzed based on the electron backscatter diffraction image. Specifically, if there is an orientation difference of 5° or more between adjacent measurement points (pixels), this point is defined as a grain boundary, and the area surrounded by the grain boundary is defined as a single crystal grain. However, a single pixel with an orientation difference of 5° or more from all adjacent pixels is not considered a crystal grain; a group of two or more connected pixels is considered a crystal grain. Then, in each of Layers B and C, the area ratio occupied by crystal grains having this NaCl-type face-centered cubic structure is determined for each layer.

[0036] 11. Measurement of average layer thickness The average thickness of each layer constituting the coating layer can be obtained by, for example, using a focused ion beam system (FIB), a cross section polisher (CP), or the like to prepare a sample for observing a longitudinal cross section of the coating layer at any position, and then observing the longitudinal cross section at multiple locations (e.g., five 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) attached to the SEM or TEM, determining the thickness, and averaging these values.

[0037] 12. Measurement of I(111) and I(200) Using an X-ray diffractometer, CuKα1 radiation is irradiated onto the coating layer to measure I(111) and I(200), and the I(200) / I(111) value is obtained. This value is determined as follows: X-ray diffraction is performed on the coating layer surface parallel to the substrate surface using Cu-Kα1 radiation as the X-ray source under the following conditions: measurement range (2θ): 20 to 120 degrees, scan step: 0.013 degrees, and measurement time per step: 0.48 seconds / step. X-ray diffraction peaks appearing between the diffraction angles of the same crystal planes shown for JCPDS00-038-1420 cubic TiN and JCPDS00-046-1200 cubic AlN (e.g., 36.66 to 38.53°, 43.59 to 44.77°, 61.81 to 65.18°), respectively, are confirmed. Then, the X-ray diffraction peak intensities of the (200) diffraction line and the (111) diffraction line are measured to obtain I(200) / I(111), which is the ratio of the intensity I(200) of the 200 diffraction line to the intensity I(111) of the 111 diffraction line.

[0038] 13. Manufacturing method The coating layer of the coated tool of this embodiment can be produced by chemical vapor deposition under the following production conditions, for example.

[0039] (1) Manufacturing of Layer A For example, the following production conditions 1) or 2) can be exemplified. 1) Manufacturing conditions 1 Deposition of TiN layer Reactant gas composition (volume %) TiCl4: 3.0~6.0%, N2: 25.0~35.0%, H2: remainder Reaction atmosphere pressure: 4.0 to 12.0 kPa Reaction atmosphere temperature: 780-900℃

[0040] 2) Manufacturing conditions 2 Deposition of TiCN layer Reactant gas composition (volume %) TiCl4:3.0~6.0%, N2:15.0~30.0% CH4 or CH3CN: 0.6-2.0%, H2: balance Reaction atmosphere pressure: 7.0 to 12.0 kPa Reaction atmosphere temperature: 780-900℃

[0041] (2) Manufacturing of Layer B Reactant gas composition (volume %) Gas group B1: TiCl4: 0.01 to 0.04%, AlCl3: 0.01 to 0.05%, N2:0.0~10.0%, C2H4:0.0~0.5%, H2:Remaining Gas group B2: NH3: 0.1-0.8%, H2: 25.0-35.0% Reaction atmosphere pressure: 4.0 to 5.0 kPa Reaction atmosphere temperature: 700-850℃ Supply cycle: 1~5 seconds, Gas supply time per cycle: 0.15 to 0.25 seconds Phase difference between the supply of gas group B1 and the supply of gas group B2: 0.10 to 0.20 seconds Preheat temperature of gas group B2: 300 to 450°C

[0042] (3) Fabrication of Layer C Reactant gas composition (volume %) Gas group C1: TiCl4: 0.01 to 0.04%, AlCl3: 0.01 to 0.05%, N2:0.0~10.0%, C2H4:0.0~0.5%, H2:Remaining Gas group C2: NH3: 0.1-0.8%, H2: 25.0-35.0% Reaction atmosphere pressure: 4.0 to 5.0 kPa, Reaction atmosphere temperature: 700-850℃ Supply cycle: 1~5 seconds, Gas supply time per cycle: 0.15 to 0.25 seconds, Phase difference between supply of gas group C1 and supply of gas group C2: 0.10 to 0.20 seconds Preheat temperature of gas group C2: 50 to 250°C [Example]

[0043] Next, an example will be described. Here, as an example, we will describe an application to an insert cutting tool using a WC-based cemented carbide as the substrate, but the same applies when the above-mentioned substrate is used, and also when applied to drills and end mills.

[0044] WC powder, TiC powder, TaC powder, NbC powder, Cr3C2 powder, and Co powder, all with an average particle size of 1 to 3 μm, were prepared as raw material powders and blended as shown in Table 1. Wax was added and the mixture was mixed in a ball mill in acetone for 24 hours, dried under reduced pressure, and then pressed into a green compact of the specified shape at a pressure of 98 MPa. This green compact was then vacuum sintered in a vacuum of 5 Pa at a specified temperature in the range of 1370 to 1470°C, holding the temperature for 1 hour, to produce WC-based cemented carbide substrates A to C, each with an ISO standard RCMX1204M0 shape.

[0045] Next, layers A, B, and C were formed on the surfaces of these substrates A to C in this order according to the manufacturing conditions shown in Tables 2 to 4, respectively, to form coated tools 1 to 8 of the examples shown in Table 5 (hereinafter referred to as Examples 1 to 8). However, Examples 1, 4, 6 and 7 are reference examples. ) was obtained.

[0046] On the other hand, for comparison, layers A, B, and C were formed in sequence on the surfaces of substrates A to C according to the manufacturing conditions shown in Tables 2 to 4, respectively, to obtain comparative coated tools 1 to 8 (hereinafter, Comparative Examples 1 to 8) shown in Table 6.

[0047] [Table 1]

[0048] [Table 2]

[0049] [Table 3]

[0050] [Table 4]

[0051] [Table 5]

[0052] [Table 6]

[0053] The following cutting tests were carried out on the thus obtained Examples 1 to 8 and Comparative Examples 1 to 8. The results are shown in Table 7.

[0054] Cutting test: Wet turning outer diameter intermittent cutting test Work material: Ti-6Al-4V slit material Outer diameter 200 mm, length 400 mm (grooved round bar material) (4mm wide slits are evenly spaced at 50mm intervals) Rotation speed: 80 min -1 Cutting speed: 50m / sec. Cutting depth: 0.5mm, Feed rate: 0.3 mm / rev Cutting time: Processing until the cutting edge is chipped

[0055] [Table 7]

[0056] As is clear from Table 7, the maximum machining time, which is the time until the cutting edge breaks, was long in all of the examples, and they had excellent durability. In contrast, the comparative examples reached the end of their life in a short time. [Explanation of symbols]

[0057] 1 Base 2 layer A 3 layer B 4 layer C 5 Covering layer 6. Grains of Layer B 7. Grains of layer C 8 Interface between Layer B and Layer C

Claims

1. A surface-coated cutting tool having a substrate and a coating layer on a surface of the substrate, (a) the coating layer has, in order from the surface of the substrate toward the surface of the tool, a layer A, a layer B, and a layer C that are in contact with each other, and the sum of the average thicknesses of these three layers is 1.05 to 21.00 μm; (b) the average thickness of the layer A is 0.05 to 2.00 μm and is a nitride or carbonitride of Ti; (c) the average thickness of the layer B is 0.50 to 13.50 μm; (Al ＸＢ Ti １－ＸＢ ) (C ＹＢ N １－ＹＢ ) (0.68≦XB≦0.80, 0.00≦YB<0.05), and crystal grains having a NaCl-type face-centered cubic structure account for 80% or more by area, (d) the average thickness of the layer C is 0.50 to 7.00 μm; (Al ＸＣ Ti １－ＸＣ ) (C ＹＣ N １－ＹＣ ) (0.65≦XC≦0.75, 0.00≦YC<0.05), and crystal grains having a NaCl-type face-centered cubic structure account for 80% or more by area, (e) the XB and the XC satisfy the relationship 0.03≦XB−XC≦0.10; A surface-coated cutting tool characterized by:

2. 2. The surface-coated cutting tool according to claim 1, wherein in the layers B and C, a diffraction line intensity value I(200) of the crystal grains (200) of the NaCl-type face-centered cubic crystal structure and a diffraction line intensity value I(111) of the crystal grains (111) satisfy the relationship 1.0≦I(200) / I(111).

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