Coated cutting tool

Abstract

This invention relates to a coated cutting tool. The cutting tool is CVD coated, and the substrate is a cemented carbide, wherein the metal binder in the cemented carbide comprises Ni. The CVD coating comprises an inner layer of TiN and a subsequent layer of TiCN.

Description

Technical Field

[0001] This invention relates to a coated cutting tool comprising a substrate and a coating, wherein the substrate is a cemented carbide, and the metal binder in the cemented carbide comprises Ni. The coating is a CVD coating comprising a TiN inner layer and a TiCN layer. Background Technology

[0002] The market for cutting tools used in chip-forming metal cutting operations is dominated by cemented carbide coated by CVD (chemical vapor deposition) and PVD (physical vapor deposition), which is typically made of WC in a Co metal binder. Alternative metal binders without Co or with reduced Co content are being developed, but such products remain scarce or nonexistent in the market. Particularly during CVD using reactive gases at high temperatures, the interaction between the gas phase and the cemented carbide places high demands not only on the manufacturing of the cemented carbide itself but also on the coating process.

[0003] Among alternative metal binders, mixtures of Ni and Fe are promising candidates: these two elements are located on either side of Co in the periodic table. Ni exhibits high reactivity with Ti, and high Ni content in cemented carbides can cause problems in chemical vapor deposition of Ti-containing coatings due to the formation of intermetallic phases such as Ni3Ti at the interface between the cemented carbide and the coating, as well as within the coating itself. Intermetallic phases such as Ni3Ti at the interface or within the Ti-containing coating can negatively impact the wear resistance of coatings subsequently deposited on top of the Ti-containing coating.

[0004] In their paper "Chemical Vapor Deposition of TiN on Transition Metal Substrates" published in Surface & Coating Technology 334(2018)373-383, L. von Fieandt et al. analyzed the problem of Ni3Ti formation during TiN coating deposition on Ni metal substrates. They concluded that Ni3Ti formation can be reduced during the CVD process by using an excess N2 partial pressure and a low H2 partial pressure.

[0005] One object of the present invention is to provide a coated cutting tool for metal cutting having a Ni-containing cemented carbide substrate and a high-performance wear-resistant CVD coating. Another object is to provide a wear-resistant coating on a Ni-containing cemented carbide substrate, particularly a substrate containing a metal binder having more than 60% by weight of Ni, comprising a TiN layer, a TiCN layer and 001-oriented α-Al2O3. Summary of the Invention

[0006] At least one of the above-mentioned objectives is achieved by the cutting tool according to item 1. Preferred embodiments are disclosed in the dependent items.

[0007] This invention relates to a coated cutting tool comprising a cemented carbide substrate and a coating, wherein the cemented carbide is composed of a hard component in a metal binder, and wherein the metal binder comprises 68 mol% to 80 mol% Ni, 5 mol% to 25 mol% Fe, 0 mol% to 10 mol% Co, and 4 mol% to 15 mol% W, and wherein the coating comprises, from the substrate, a TiN inner layer and a TiCN layer, wherein the C activity (carbon activity) of the metal binder relative to graphite is less than 0.15, and the average d-electron value of the metal binder is 7.0 to 7.43, and wherein the interface between the substrate and the TiN inner layer does not contain a Ti-containing intermetallic phase.

[0008] Surprisingly, high-quality TiN and TiCN were found to be deposited on cemented carbide substrates with high Ni content in the metal binder when the average d-electron value in the metal binder was 7.0 to 7.43 and the C activity relative to graphite was less than 0.15. The coated cutting tools according to the invention unexpectedly exhibit fewer pores within the coating, which is promising for wear-resistant coatings for metal cutting applications. The TiN inner layer and the TiCN layer exhibit improved properties related to intermetallic phase formation, pores, and interferences related to the orientation of the layers and subsequently deposited layers. Technical effects could include increased flank wear resistance and / or increased flaking resistance and / or increased crater wear resistance in metal cutting operations, such as steel.

[0009] At least when depositing Ti-containing layers, the composition of the metal binder in the cemented carbide has an impact on the quality of the layer deposited thereon via CVD. TiN is a very common initial layer in cutting tool coatings. Without being bound by any theory, the inventors have concluded that during the CVD deposition of TiN layers, N2 molecules are thought to dissociate into N atoms / N radicals, which can then react to form TiN. However, Ni in the surface increases the recombination rate of N2 from N atoms / radicals, thereby passivating N and preventing the dissociation of N atoms / radicals on the surface. TiN cannot form in the absence of N atoms / radicals. Instead, Ti may react with Ni to form NiTi3 as described above. The reactivity of Ni in the metal binder is affected by the composition of the metal binder. Furthermore, the number of d electrons and the C activity in the metal binder have been found to be important.

[0010] The average number of d electrons in the metal binder is determined not only by the components Co, Ni, and / or Fe, but also by other metallic elements present in the alloy serving as the metal binder. For example, the W content in the metal binder has a relatively high impact on the average number of d electrons. The W content in the binder is highly influenced by the C content, such that excess C in the metal binder leads to a lower W content, while less C leads to a higher W content.

[0011] Carbon reactivity is a thermodynamic measure of how easily carbon can react with other elements. It is expressed as a dimensionless quantity between 0 and 1. It is concentration-dependent, but properly accounts for all physical interactions that limit the total amount of carbon that can react. The definition of carbon reactivity is...

[0012] C activity = exp((μ-μ 石墨 ) / RT)

[0013] Where μ is the chemical potential of carbon in the material, μ 石墨 R is the chemical potential of carbon in pure graphite, T is the gas constant, and T is the temperature. The carbon activity is a good measure of its position in the phase diagram; an activity close to 1 indicates that the cemented carbide is close to having free carbon in its microstructure, while a low value close to 0.1 indicates that the cemented carbide tends to have the η phase (Me6C and Me) in its microstructure. 12 (C phase).

[0014] In this document, "carbide" refers to a material comprising a hard component distributed in a continuous metallic binder phase. This material possesses the properties of combining high hardness from the hard component with high toughness from the metallic binder phase, and is suitable as a base material for metal cutting tools. In this document, "carbide" refers to a material comprising at least 50% by weight WC (or possibly other hard components commonly found in the carbide manufacturing industry) and a metallic binder.

[0015] The metal binder of the cemented carbide may contain elements dissolved in the metal binder during sintering, such as W and C derived from WC. Depending on the type of cementing component present, other elements may also be dissolved in the binder.

[0016] In this article, "cutting tools" refers to cutting tools used for metal cutting, such as inserts, end mills, or drills. Applications may include turning, milling, or drilling.

[0017] In this document, intermetallic phase refers to a metal alloy of two or more metallic elements. A Ti-containing intermetallic phase refers to one of these metallic elements being Ti. In one embodiment of the present invention, the Ti-containing intermetallic phase is Ni3Ti.

[0018] The presence of Ti-containing intermetallic phases at the interface and / or in the portion of the TiN layer adjacent to the substrate can affect the growth of the TiN layer and subsequent layers. These intermetallic phases interfere with columnar growth, and pores are typically found to be bonded to the intermetallic phases. Typically, TiN and subsequent TiCN grow as columnar grains, and interference with growth is observed in SEM analysis of samples containing intermetallic phases.

[0019] In one embodiment of the invention, the C activity in the metal binder is 0.095 to 0.12.

[0020] In one embodiment of the present invention, the interface between the substrate and the coating does not contain intermetallic phases containing Ti and Ni.

[0021] In one embodiment of the present invention, the interface between the substrate and the coating does not contain intermetallic phases containing Ti, Fe and Ni.

[0022] In one embodiment of the invention, the average d-electron value is 7.25 to 7.43.

[0023] In one embodiment of the invention, the average d-electron value is 7.36 to 7.43.

[0024] In one embodiment of the invention, the metal binder comprises 73 mol% to 80 mol% Ni, 5 mol% to 15 mol% Fe, 1 mol% to 5 mol% Co, and 8 mol% to 13 mol% W.

[0025] In one embodiment of the invention, the content of the metal binder in the cemented carbide is 3% to 20% by weight, preferably 5% to 15% by weight, and most preferably 7% to 12% by weight.

[0026] In one embodiment of the present invention, the total thickness of the coating is 2 μm to 20 μm. The coating is preferably a CVD coating.

[0027] In one embodiment of the invention, the thickness of the TiN layer is 0.1 μm to 1 μm, and it is preferably deposited on the cemented carbide substrate.

[0028] In one embodiment of the present invention, the thickness of the TiCN layer is 6 μm to 12 μm.

[0029] In one embodiment of the invention, the coating comprises an α-Al2O3 layer located between the TiCN layer and the outermost surface of the coated cutting tool.

[0030] In one embodiment of the invention, the thickness of the Al2O3 layer located between the TiCN layer and the outermost surface of the coated cutting tool is 4 to 8 μm.

[0031] In one embodiment of the invention, the α-Al₂O₃ layer exhibits a texture coefficient TC(hkl) as defined by the Harris formula, which is measured using CuKα radiation and θ-2θ scanning X-ray diffraction.

[0032]

[0033] Where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I0(hkl) is the standard intensity according to the ICDD PDF card 00-010-0173, n is the number of reflections used in the calculation, where the (hkl) reflections used are (1 0 4), (1 1 0), (1 1 3), (0 2 4), (1 1 6), (2 1 4), (3 0 0) and (0 0 12), where TC(00 12)≥6, preferably≥7.

[0034] In one embodiment of the invention, the coating further comprises one or more layers selected from: TiN, TiCN, AlTiN, ZrCN, TiB2, Al2O3, or a multilayer comprising α-Al2O3 and / or κ-Al2O3.

[0035] In one embodiment of the invention, the cemented carbide substrate comprises an η phase. Hereinafter, the η phase refers to a phase selected from Me6C and Me. 12 C carbides, wherein Me is selected from W and one or more binder phase metals. Common carbides are W6Co6C, W3Co3C, W6Ni6C, W3Ni3C, W6Fe6C, and W3Fe3C.

[0036] In one embodiment, the cemented carbide substrate comprises one or more carbides, carbonitrides, or nitrides selected from Ti, Ta, Nb, Cr, Mo, Zr, or V. Attached Figure Description

[0037] Embodiments of the present invention will be described with reference to the accompanying drawings, wherein:

[0038] Figure 1 This is a cross-sectional SEM micrograph of the substrate coating interface of the coating cutting tool, i.e., the NF70e (in this invention) with the coating of CVD process 1.

[0039] Figure 2This is a cross-sectional SEM micrograph of the substrate coating interface of the NF70e (of the present invention) with the coating of the coating cutting tool, i.e., the coating of the CVD process 2.

[0040] Figure 3 This is a cross-sectional SEM micrograph of the substrate coating interface of the NF80e (in this invention) with the coating of the coating cutting tool, i.e., the coating of the CVD process 1.

[0041] Figure 4 This is a cross-sectional SEM micrograph of the substrate coating interface of the NF80e (in this invention) with the coating of the coating cutting tool, i.e., the coating of the CVD process 2.

[0042] Figure 5 This is a cross-sectional SEM micrograph of the substrate coating interface of the coating cutting tool, i.e., the NF85e (in this invention) with the coating of CVD process 1.

[0043] Figure 6 This is a cross-sectional SEM micrograph of the substrate coating interface of the NF85e (in this invention) substrate with the coating of the coating cutting tool, i.e., the coating of the CVD process 2.

[0044] Figure 7 This is a cross-sectional SEM micrograph of the substrate coating interface of the coating cutting tool, i.e., the coating with CVD process 1, NF90e (reference).

[0045] Figure 8 This is a top-view SEM micrograph of the outer surface of the substrate NF90e (reference) with the coating of the coating cutting tool, i.e., the coating of CVD process 1.

[0046] Figure 9 This is a top-view SEM micrograph of the outer surface of the substrate NF90e (of the present invention) with the coating of the coating cutting tool, i.e., the coating having CVD process 2.

[0047] Figure 10 This is a top-view SEM micrograph of the outer surface of the substrate NF90f (reference) with the coating of the coating cutting tool, i.e., the coating of the substrate with CVD process 2.

[0048] Figure 11 This is a top-view SEM micrograph of the outer surface of the substrate N100f (reference) with the coating of the coating cutting tool, i.e., the coating of the substrate with CVD process 2.

[0049] method

[0050] The cemented carbide substrate of the present invention can be manufactured according to the following steps:

[0051] - Provides powders such as W, Ta, Cr, C, WC, TiC, etc., that form or become hard components.

[0052] - Provide powders such as Co, Fe, Ni to form metal binders

[0053] - Provide grinding fluid

[0054] - The powder is ground, dried, pressed and sintered into a cemented carbide substrate.

[0055] During sintering, oxygen reacts with carbon and leaves the substrate as CO or CO2. The exact amount of carbon lost during sintering depends on the raw materials and manufacturing techniques used, and is adjusted by those skilled in the art to achieve the desired sintered material.

[0056] The carbon content in the cemented carbide was analyzed using carbon combustion analysis in a LECO 844 series instrument. The carbon content in the cemented carbide was measured in the sintered substrate. Some of the carbon mixed in the powder during the manufacture of the cemented carbide is consumed during sintering, some carbon can dissolve in the metal binder, and some carbon may form carbides.

[0057] This invention relates to the composition of the metal binder, and because sample fabrication is expensive and complex, the composition is calculated using software called Thermo-Calc. Alternatively, the composition of the metal binder can be measured using XRF (X-ray fluorescence).

[0058] Thermo-Calc is a software package used by materials scientists, researchers, and manufacturers worldwide in the field of materials engineering for the development and fabrication of materials and components. Development of Thermo-Calc software began in the mid-1970s at the Department of Physical Metallurgy of the Royal Institute of Technology in Stockholm, Sweden, and Thermo-Calc Software Company was founded in 1997. More information can be found at www.thermocalc.com. Thermo-Calc provides thermodynamic calculations, such as the amount and composition of phases, as well as phase diagrams (binary, ternary, and multicomponent).

[0059] Calculations performed using Thermo-Calc are based on thermodynamic data provided in a high-quality database encompassing many different materials for various purposes. This database was generated by experts through evaluation and systematic review of experimental and theoretical data, following the widely accepted CALPHAD technique. The database provided by Thermo-Calc software company was validated against experimental data to evaluate its accuracy in computational predictions.

[0060] The database used in this Thermo-Calc calculation is "TCFE7," commercially available from Thermo-Calc software company. TCFE7 is a thermodynamic database for various types of steel, ferrous alloys (stainless steel, high-speed steel, tool steel, HSLA steel, cast iron, corrosion-resistant high-strength steel, etc.), and cemented carbides. The TCFE7 database was validated against experimental data, demonstrating accurate predictions, particularly for cemented carbides, in terms of correct phase and fraction, phase composition, and solid / liquid equilibrium temperature.

[0061] The composition of the metal binder in this invention was determined using Thermo-Calc software, and is further described in [J.-O. Andersson, T. Helander, L. Hoglund, P. Shi and B. Sundman, Thermo-Calc & DICTRA, Computational Tools for Materials Science, Calphad, 2002:26(2):2273312].

[0062] The Thermo-Calc calculations of this invention are performed using the following standards: atmospheric pressure, temperature of 1000°C, 1 mole of material weighed with the composition of Ni, Fe and Co, wherein Co is added to the grinding material, the C level is derived from chemical analysis, and the balance is W.

[0063] When the composition of the metal binder is known (in mole %), the average number of d electrons is calculated as follows: d electrons are counted as the number of electrons in the highest d orbital of each element, for example, 6 for Fe, 7 for Co, 8 for Ni, 0 for C, and 4 for W.

[0064] The coatings in the following examples were deposited in a radial Ionbond Bernex™ CVD unit 530, which is capable of accommodating 10,000 half-inch cutting blades.

[0065] To investigate the texture of the layer, X-ray diffraction was performed on the flank and rake faces of the cutting tool insert using an Xpert-Pro diffractometer system equipped with an X′Celerator RTMS detector. The coated cutting tool insert was mounted in a sample holder, ensuring that the surface of the cutting tool insert was parallel to a reference surface of the sample holder and that the cutting tool surface was at an appropriate height. Measurements were performed using Cu-Kα radiation at a voltage of 45 kV and a current of 40 mA. A 0.02 radian Soler slit and a 0.25-degree divergence slit were used for the incident beam path. For the diffracted beam, a 0.25-degree antiscattering slit and a 0.02 radian Soler slit were used. The β-filter nickel thickness was 0.020 mm. The diffraction intensity from the coated cutting tool was measured in the 2θ range of 15° to 140°, i.e., within the range of incident angle θ of 10° to 70°.

[0066] Data analysis was performed using PANalytical's X'Pert HighScore Plus software, including background subtraction and Cu-K resizing. α2 Stripping and pattern fitting. The fitting is described in general below. The texture factor of the layer is then calculated using the output from the program (the integral peak area of ​​the pattern fitting curve) and Harris's formula (1) as described above, by comparing the measured intensity data with the standard intensity data according to the PDF card of α-Al2O3. Because the layer is of finite thickness, the relative intensity of a pair of peaks at different 2θ angles differs from that of the bulk sample due to the difference in path length through the layer. Therefore, thin film correction is applied to the integral peak area intensity of the extracted pattern fitting curve, and the linear absorption coefficient of the layer is also considered when calculating the TC value. Since possible other layers above the α-Al2O3 layer will affect the X-ray intensity entering the α-Al2O3 layer and leaving the entire coating, these also need to be corrected for considering the linear absorption coefficient of the corresponding compounds in the layer. Alternatively, other layers above the alumina layer, such as TiN, can be removed by methods that do not substantially affect the XRD measurement results (e.g., chemical etching).

[0067] To study the texture of the α-Al2O3 layer, CuK was used. α X-ray diffraction was performed on the radiation, and the texture coefficient TC(hkl) of the columnar grains of the α-Al2O3 layer was calculated according to Harris's formula (1) for different growth directions, where I(hkl) = the measured (integrated area) intensity of the (hkl) reflection, I0(hkl) = the standard intensity according to the PDF card 00-010-0173 of ICDD, and n = the number of reflections used in the calculation. In this case, the (hkl) reflections used are: (1 0 4), (1 1 0), (113), (0 2 4), (1 1 6), (2 1 4), (3 0 0), and (0 0 12).

[0068] It should be noted that peak overlap is a phenomenon that can occur in X-ray diffraction analysis of coatings containing, for example, several crystalline layers and / or coatings deposited on a substrate containing a crystalline phase, and this must be taken into account and compensated for. The overlap of peaks from the α-Al₂O₃ layer with peaks from the TiCN layer may affect the measurement and needs to be considered. It should also be noted that, for example, WC in the substrate may have diffraction peaks close to the relevant peaks of this invention. Example

[0069] Exemplary embodiments of the present invention will now be disclosed in more detail and compared with reference embodiments. Manufacturing and analysis of coated cutting tools (blades).

[0070] A cemented carbide substrate of ISO type SNUN120408 was manufactured. The cemented carbide substrate was manufactured using WC in a metal binder, wherein the metal binder content was approximately 10% by weight. The cemented carbide substrate was manufactured from a powder mixture. The powder mixture was ground, dried, pressed, and sintered at 1450°C. WC / Co abrasive media were used during the grinding and mixing steps. The carbon content in the powder was approximately 6.07% by weight, and the carbon content measured in the chemical analysis of the sintered cemented carbide is presented in Tables 1A and 1B. The sintered cemented carbide contained approximately 0.4% by weight Co, which mainly originated from the abrasive media worn during the grinding steps. No free graphite was observed in the SEM micrograph of the cross-section of the cemented carbide substrate.

[0071] The carbon level of the substrate was measured using the LECO carbon combustion method. The composition of the cemented carbide substrate is listed in weight percent in Table 1A, referred to as e-sample, and in Table 1B, referred to as f-sample.

[0072] Table 1A Overview of cemented carbide substrates (e-samples)

[0073]

[0074] Table 1B Overview of cemented carbide substrates (f-samples)

[0075]

[0076] The composition of the metal binder was calculated using Thermo-Calc under the following conditions: atmospheric pressure, temperature of 1000°C, 1 mole of material weighed as Ni, Fe, and Co, with Co added to the grinding media, C level from chemical analysis, and balance W. The composition of the resulting binder, excluding carbides, is listed in mol% in Tables 2A (e-sample) and 2B (f-sample).

[0077] To calculate the average number of d electrons in the binder, the calculated composition of the metal binder is used. d electrons are counted as the number of electrons in the highest d orbitals of each element, for example, 6 for Fe, 7 for Co, 8 for Ni, 0 for C, and 4 for W. The average number of d electrons in the binder is shown in Tables 2A and 2B.

[0078] To calculate the carbon activity of the cemented carbide, its chemical composition must first be known. In this example, the C activity is calculated based on the values ​​shown in Tables 1A and 1B. In unknown samples, this can be measured, for example, by XRF.

[0079] Thermo-Calc calculations were performed at atmospheric pressure, 1000°C, with 1 mole of material, and the composition of Ni, Fe, Co, and C from chemical analysis, and the balance of W, under thermodynamic equilibrium. The carbon activity relative to graphite at this equilibrium was then extracted from Thermo-Calc as an output parameter, as shown in Tables 2A and 2B.

[0080] Table 2A Overview of Metal Binders (e-sample)

[0081]

[0082] Table 2B Overview of Metal Binders (f-sample)

[0083]

[0084] CVD coatings were deposited on the cemented carbide compositions shown in Tables 2A and 2B, and an overview of the CVD coatings is given in Table 3. Prior to coating deposition, the rake face was polished to remove the outermost metal from the surface; the flank face was not polished. Polishing was performed as follows: each SNUN120408 sample was mounted in black conductive phenolic resin from AKASL and ground down approximately 1 mm, followed by polishing in two steps: coarse polishing (9 μm) and fine polishing (1 μm) using a diamond slurry solution. After polishing, the SNUN120408 samples were removed from the black conductive phenolic resin and washed in ethanol before coating.

[0085] Table 3 Overview of CVD Processes

[0086]

[0087] Prior to the commencement of the CVD deposition, the CVD chamber is heated to 885°C. For both CVD 1 and CVD 2 processes, the preheating step is performed at 1000 mbar and 100 vol% H2.

[0088] In the CVD 1 process, the substrate is first coated with a TiN layer of approximately 0.2 μm to 0.3 μm thickness at 885 °C, i.e., the TiN-2 process. In the CVD 2 process, two alternative TiN deposition methods are performed: an initial TiN-1 step followed by the TiN-2 process. The purpose of the TiN-1 step is to prevent the formation of intermetallic phases such as Ni3Ti at the interface between the CVD coating and the substrate coating. Compared to the TiN-2 deposition step performed without HCl and with a 50 / 50 H2 gas ratio, the TiN-1 deposition process involves a higher N2 partial pressure, a lower H2 partial pressure, and the addition of HCl. After the TiN-1 deposition, the subsequent TiN-2 deposition time is adjusted until the total TiN layer thickness reaches 0.7 μm. The TiN-1 deposition process lasts for 150 minutes.

[0089] Subsequently, an approximately 8 μm TiCN layer was deposited at 885 °C using a known MTCVD technique employing TiCl4, CH3CN, N2, HCl, and H2. The initial portion of the TiCN layer MTCVD deposition had a TiCl4 / CH3CN volume ratio of 6.6, followed by a period where the TiCl4 / CH3CN ratio was 3.7. Details of the TiN and TiCN depositions are presented in Table 4.

[0090] Table 4 MTCVD of TiN and TiCN

[0091]

[0092] After depositing the TiCN outer layer, CVD step 1 was performed by raising the temperature from 885°C to 1000°C in an atmosphere of 75 vol% H2 and 25 vol% N2 at 55 mbar. After depositing the TiCN outer layer, CVD step 2 was performed by raising the temperature from 885°C to 1000°C in an atmosphere of 100 vol% N2 at 1000 mbar.

[0093] A 1-2 μm thick binder layer was deposited on top of the MTCVD TiCN layer at 1000 °C through a process consisting of four separate reaction steps. First, the MTCVD TiCN step was carried out at 400 mbar using TiCl4, CH4, N2, HCl, and H2. Then, the second step (TiCNO-1) was carried out at 70 mbar using TiCl4, CH3CN, CO, N2, and H2. Next, the third step (TiCNO-2) was carried out at 70 mbar using TiCl4, CH3CN, CO, N2, and H2. Finally, the fourth step (TiN-3) was carried out at 70 mbar using TiCl4, N2, and H2. Prior to the subsequent Al2O3 nucleation, the binder layer was oxidized for 4 minutes in a mixture of CO2, CO, N2, and H2.

[0094] Details of the adhesive layer deposition are shown in Table 5.

[0095] Table 5 Adhesive layer deposition

[0096]

[0097] An α-Al₂O₃ layer was deposited on top of the adhesive layer. All α-Al₂O₃ layers were deposited in two steps at 1000 °C and 55 mbar. The first step used 1.2 vol% AlCl₃, 4.7 vol% CO₂, 1.8 vol% HCl, and the balance H₂ to obtain an α-Al₂O₃ layer of approximately 0.1 μm thickness. The second step, as described below, yielded a total α-Al₂O₃ layer thickness of approximately 5 μm. The second step used 1.2% AlCl₃, 4.7% CO₂, 3.0% HCl, 0.58% H₂S, and the balance H₂ to deposit the α-Al₂O₃ layer.

[0098] The texture factor (TC) of α-Al₂O₃ was analyzed using XRD according to the method disclosed above. Layer thickness was analyzed by studying the cross-sections of each coating at 12000x magnification using a Carl Zeiss AG-Supra 40 SEM (scanning electron microscope), with both the adhesive layer and the initial TiN layer included in the TiCN layer thickness (see Table 1). Both polished rake faces and unpolished flank faces were investigated. The XRD results are shown in Tables 6A and 6B.

[0099] Table 6A XRD results (e-sample)

[0100]

[0101] Table 6B XRD results (f-sample)

[0102]

[0103] In addition, SEM analysis was used to investigate the presence of any Ni and Fe compounds at the interface between the substrate and the first TiN layer.

[0104] The top view of the coated sample revealed inhomogeneity or high surface roughness on the outer surface of the alumina. The conclusion is that the unexpectedly rough surface indicates intermetallic phases at the interface, and the formation of these intermetallic phases at the interface can be determined by studying the outer surface of the alumina.

[0105] Cross-sectional views are primarily focused on the interface between the substrate and the first TiN layer to determine whether the diffusion of binder elements (Ni and Fe compounds) interferes with the growth of the coating. The formation of Ti-containing intermetallic phases (e.g., Ni3Ti) depends on the binder composition.

[0106] The coating quality deposited on the Ni-rich binder in the CVD 1 and CVD 2 processes was determined by analyzing the outer surface and morphology of Al2O3, as well as the interface between the substrate and the first TiN layer. Surface inhomogeneity of Al2O3 can be caused by the growth of coarse grains and is associated with the formation of intermetallic phases such as Ni3Ti at the interface between the substrate and the coating. When the inhomogeneity of Al2O3 is difficult to determine, the interface between the substrate and the coating is analyzed to determine the coating quality. For this study, SEM was used at 12000X magnification, and three parallel images were studied from three locations approximately 10 μm apart along the substrate surface on the sample to detect the presence of intermetallic phases. The analytical results are shown in Tables 7A and 7B.

[0107] Table 7A SEM analysis of e-samples

[0108]

[0109] Table 7B SEM analysis of f-samples

[0110]

[0111] The surface and cross-sectional analyses clearly show that samples exhibiting visual inhomogeneity or high surface roughness on the outer surface (top view) of the alumina also show Ti-containing intermetallic phases in the interface (cross-section). Surprisingly, when C activity is low (below 0.15) and the average number of d electrons is 7.0 to 7.43, no Ti-containing intermetallic phases or interfering pores appear at the interface of the CVD coating, see Table 8.

[0112] Table 8 Summary of Results

[0113]

[0114] *No Ti-containing intermetallic phase is present at the interface.

[0115] **CVD process 1: Ti-containing intermetallic phase is present at the interface; CVD process 2: No Ti-containing intermetallic phase is present at the interface.**

[0116] ***There is a Ti-containing intermetallic phase at the interface.

[0117] While the invention has been described in conjunction with various exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments; rather, the invention is intended to cover various modifications and equivalent arrangements within the scope of the claims.

Claims

1. A coated cutting tool comprising a cemented carbide substrate and a coating, wherein the cemented carbide is composed of a metal binder and a hard component in the metal binder. The metal binder comprises 68 mol% to 80 mol% Ni, 5 mol% to 25 mol% Fe, 0 mol% to 10 mol% Co, and 4 mol% to 15 mol% W, and The coating comprises, from the substrate, a TiN inner layer and a TiCN layer, wherein the C activity of the metal binder relative to graphite is less than 0.15, and the average d-electron value of the metal binder is 7.00 to 7.

43. The interface between the substrate and the TiN inner layer does not contain Ti-containing intermetallic phases.

2. The coated cutting tool according to claim 1, wherein the C activity in the metal binder is 0.095 to 0.

120.

3. The coated cutting tool according to claim 1 or 2, wherein the interface between the substrate and the TiN inner layer does not contain intermetallic phases containing Ti and Ni.

4. The coated cutting tool according to claim 1 or 2, wherein the interface between the substrate and the TiN inner layer does not contain intermetallic phases containing Ti, Fe and Ni.

5. The coated cutting tool according to claim 1 or 2, wherein the average d-electron value is 7.25 to 7.

43.

6. The coated cutting tool according to claim 1 or 2, wherein the average d-electron value is 7.36 to 7.

43.

7. The coated cutting tool according to claim 1 or 2, wherein the metal binder comprises 73 mol% to 80 mol% Ni, 5 mol% to 15 mol% Fe, 1 mol% to 5 mol% Co, and 8 mol% to 13 mol% W.

8. The coated cutting tool according to claim 1 or 2, wherein the content of the metal binder in the cemented carbide is from 3% to 20% by weight.

9. The coated cutting tool according to claim 1 or 2, wherein the total thickness of the coating is from 2 μm to 20 μm.

10. The coated cutting tool according to claim 1 or 2, wherein the coating is a CVD coating.

11. The coated cutting tool according to claim 1 or 2, wherein the thickness of the TiN inner layer is 0.1 μm to 1 μm, and it is deposited on the cemented carbide substrate.

12. The coated cutting tool according to claim 1 or 2, wherein the thickness of the TiCN layer is 6 μm to 12 μm.

13. The coated cutting tool according to claim 1 or 2, wherein the coating comprises an α-Al2O3 layer located between the TiCN layer and the outermost surface of the coated cutting tool.

14. The coated cutting tool according to claim 13, wherein the thickness of the α-Al2O3 layer located between the TiCN layer and the outermost surface of the coated cutting tool is 4 μm to 8 μm.

15. The coated cutting tool according to claim 13, wherein the α-Al₂O₃ layer exhibits a texture coefficient TC(hkl) defined according to the Harris formula, said texture coefficient TC(hkl) being measured by X-ray diffraction using CuKα radiation and θ-2θ scanning. Where I(hkl) is the measured intensity of (hkl) reflection, I0(hkl) is the standard intensity according to the ICDD PDF card 00-010-0173, and n is the number of reflections used in the calculation, where the (hkl) reflections used are (1 0 4), (1 10), (1 1 3), (0 2 4), (1 1 6), (2 1 4), (3 0 0), and (0 0 12), where TC(0 0 12)≥6.

16. The coated cutting tool according to claim 10, wherein the CVD coating further comprises one or more layers selected from the group consisting of TiN, TiCN, AlTiN, ZrCN, TiB2, and Al2O3.

17. The coated cutting tool according to claim 10, wherein the CVD coating further comprises a multilayer containing α-Al2O3 and / or κ-Al2O3.

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