Coated Cutting Tools

Abstract

The present invention relates to a coated cutting tool. The cutting tool is CVD-coated, the substrate is a cemented carbide, and the metal binder in the cemented carbide contains Ni. The CVD coating includes an inner TiN layer followed by a TiCN layer.

Description

[Technical Field]

[0001] The present invention relates to a coated cutting tool having a substrate and a coating, wherein the substrate is a cemented carbide and a metal binder in the cemented carbide contains Ni. The coating is a CVD coating including a TiN inner layer and a TiCN layer. [Background technology]

[0002] CVD (Chemical Vapor Deposition) and PVD (Physical Vapor Deposition) coated hardmetals are widely used in the market for cutting tools for chip-forming metal cutting operations; hardmetals are typically made of WC in a Co metallic binder. Alternative metal binders with Co-free or reduced amounts have been developed, but products on the market are still rare or non-existent. As well as the production of the hardmetal itself, the coating of the hardmetal is also demanding, especially in the case of chemical vapor deposition, which is carried out using reactive gases at high temperatures, due to the interaction that occurs between the gas phase and the hardmetal.

[0003] Among alternative metal binders, Ni is a promising candidate. Ni is the element next to Co in the periodic table. Ni exhibits high reactivity with Ti, and high Ni content in cemented carbides poses a problem in the chemical vapor deposition of Ti-containing coatings because it leads to the formation of intermetallic phases such as Ni3Ti at the interface between the cemented carbide and the coating and within the coating. Intermetallic phases such as Ni3Ti at the interface or within the Ti-containing coating adversely affect the wear resistance of coatings deposited after the Ti-containing coating.

[0004] The problem of Ni3Ti formation when depositing TiN coatings on Ni metal substrates has been analyzed in "Chemical vapor deposition of TiN on transition metal substrates" by L. von Fieandt et al., Surface and Coatings Technology 334 (2018) 373-383. It was concluded that excessive N2 partial pressure and low H2 partial pressure during the CVD process can reduce Ni3Ti formation.

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

[0006] At least one of the above mentioned objects is achieved by a cutting tool according to claim 1. Preferred embodiments are disclosed in the dependent claims.

[0007] The present invention relates to a coated cutting tool comprising a cemented carbide substrate and a coating, wherein the cemented carbide is composed of hard constituents in a metal binder, the metal binder containing 55-80 mol% Ni, 0.1035 mol% Co, and 4-15 mol% W, the coating comprising, in this order from the substrate, a TiN inner layer and a TiCN layer, the C activity (carbon activity) of the metal binder relative to graphite is lower than 0.15, the average d-electron value of the metal binder is 7.0-7.43, and no Ti-containing intermetallic compound phase is present at the contact surface between the substrate and the TiN inner layer.

[0008] It has surprisingly been found that high-quality TiN and TiCN can be deposited on a cemented carbide substrate with a high Ni content in the metallic binder, provided that the average d-electron value in the metallic binder is between 7.0 and 7.43 and the carbon activity relative to graphite is less than 0.15. The coated cutting tool according to the present invention surprisingly exhibits minimal porosity within the coating, making it a promising wear-resistant coating for metalcutting applications. The TiN inner layer and TiCN layer exhibit improved characteristics with respect to intermetallic phase formation, porosity, and orientation-related defects in the layer and subsequently deposited layers. The technical effect can be improved flank wear resistance and / or improved spalling resistance and / or improved crater wear resistance, for example, in metalcutting operations of steel.

[0009] The composition of the metallic binder in a cemented carbide affects the quality of layers deposited on the cemented carbide by CVD, at least when a Ti-containing layer is deposited. TiN is a very common initial layer in cutting tool coatings. Without being bound by any theory, the inventors concluded that during CVD deposition of a TiN layer, N molecules dissociate into N atoms and N radicals before they can react to form TiN. However, Ni on the surface passivates N and prevents the dissociation of N atoms and radicals at the surface, increasing the recombination rate of N from the N atoms and radicals. Without N atoms and radicals, TiN would not form. Instead, as mentioned above, Ti may react with Ni to form NiTi3. The reactivity of Ni in a metallic binder is affected by the composition of the metallic binder. Furthermore, the number of d-electrons and carbon activity in the metallic binder have been found to be important.

[0010] The average d-electron number of the metal binder is not only determined by the components Co, Ni, and / or Fe, but also by other metal elements contained in the alloy. For example, the W content has a relatively large effect on the average d-electron number in the metal binder. The W content in the binder is strongly affected by the C content; excessive C in the metal binder reduces the W content, while reduced C increases the W content.

[0011] Carbon activity is a thermodynamic index that indicates how readily carbon reacts with other elements. It is expressed as a dimensionless quantity between 0 and 1. Carbon activity is related to concentration, but properly takes into account all physical interactions that limit the reaction of the total amount of carbon. Carbon activity is defined as follows: C activity=exp((μ-μ graf ) / RT) [where μ is the chemical potential of carbon in the material, μ graf is the chemical potential of carbon in pure graphite, R is the gas constant, and T is the temperature] Carbon activity is a good indicator of position in the phase diagram; an activity close to 1 means that the cemented carbide is close to having free carbon in the microstructure, while a low value close to 0.1 means that the cemented carbide has η phase (MeC and Me 12 This means that the crystalline structure is likely to have a phase C.

[0012] As used herein, cemented carbide refers to a material containing hard constituents distributed in a continuous metal binder phase. This type of material combines high hardness due to the hard constituents with high toughness due to the metal binder phase, making it suitable as a substrate material for metal cutting tools. As used herein, "hardmetal" refers to a material containing at least 50% by weight of WC, and optionally other hard constituents and metal binders common in the art of producing cemented carbides.

[0013] The metal binder of a cemented carbide can contain elements that dissolve into the metal binder during sintering, such as W and C from WC, and other elements may also dissolve into the binder depending on what hard constituents are present.

[0014] As used herein, "cutting tool" refers to a cutting tool for cutting metal, such as an insert, an end mill, a drill, etc. Applications may include turning, milling, or drilling.

[0015] In this specification, the term "intermetallic compound phase" refers to a metal alloy consisting of two or more metal elements. The term "Ti-containing intermetallic compound phase" refers to an alloy in which one of the metal elements is Ti. In one embodiment of the present invention, the Ti-containing intermetallic compound phase is Ni3Ti.

[0016] The presence of Ti-containing intermetallic phases in the interface layer and / or in the portion of the TiN layer adjacent to the substrate affects the growth of the TiN layer, and likewise the growth of subsequent layers. The intermetallic phases hinder columnar growth, and pores are commonly found in association with the intermetallic phases. Normally, TiN and subsequently TiCN grow with columnar grains, but SEM analysis of samples with intermetallic phases reveals disordered growth.

[0017] In one embodiment of the present invention, the carbon activity in the metal binder is 0.095 to 0.12.

[0018] In one embodiment of the present invention, the interface between the substrate and the coating is free of Ti and Ni containing intermetallic phases.

[0019] In one embodiment of the present invention, the average d electron value is 7.20 to 7.43.

[0020] In one embodiment of the present invention, the average d electron value is 7.30 to 7.43.

[0021] In one embodiment of the present invention, the metal binder contains 65 to 80 mol % of Ni, 10 to 25 mol % of Co, and 8 to 13 mol % of W.

[0022] In one embodiment of the present invention, the content of the metal binder in the cemented carbide is 3-20 wt %, preferably 5-15 wt %, and most preferably 7-12 wt %.

[0023] In one embodiment of the present invention, the total thickness of the coating is between 2 and 20 μm. The coating is preferably a CVD coating.

[0024] In one embodiment of the present invention, the TiN layer has a thickness of 0.1-1 μm and is preferably deposited on a cemented carbide substrate.

[0025] In one embodiment of the present invention, the thickness of the TiCN layer is 6 to 12 μm.

[0026] In one embodiment of the present invention, the coating includes an α-Al 2 O 3 layer located between the TiCN layer and the outermost surface of the coated cutting tool.

[0027] In one embodiment of the present invention, the thickness of the Al2O3 layer located between the TiCN layer and the outermost surface of the coated cutting tool is 4-8 μm.

[0028] In one embodiment of the present invention, the α-Al2O3 layer is measured by X-ray diffraction using CuKα radiation and a θ-2θ scan, according to the Harris equation: TIFF0007733733000001.tif12170 [where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection; I0(hkl) is the standard intensity according to ICDD PDF-card No. 00-010-0173, n is the number of reflections used in the calculation, the (hkl) reflections used are (1 0 4), (1 1 0), (1 1 3), (024), (1 1 6), (2 1 4), (3 0 0) and (0 0 12), and TC(0 0 12) is ≥ 6, preferably ≥ 7]. The texture coefficient TC(hkl) is defined as follows:

[0029] In one embodiment of the present invention, the coating further comprises one or more layers selected from TiN, TiCN, AlTiN, ZrCN, TiB2, Al2O3, or multiple layers comprising α-Al2O3 and / or κ-Al2O3.

[0030] In one embodiment of the present invention, the cemented carbide substrate comprises an η phase. In this specification, the η phase is defined as MeC and Me 12 C, where Me is selected from W and one or more binder phase metals. Common carbides are WCoC, WCoC, WNiC, WNiC, WFeC, WFeC.

[0031] In one embodiment, the cemented carbide substrate comprises a carbide, carbonitride, or nitride of one or more of Ti, Ta, Nb, Cr, Mo, Zr, or V.

[0032] Embodiments of the present invention and references will now be described with reference to the accompanying drawings. [Brief explanation of the drawings]

[0033] [Figure 1] 1 is a cross-sectional SEM micrograph showing the substrate-coated contact surface of a coated cutting tool NC60e (invention) coated by CVD process 1. [Figure 2] 1 is a cross-sectional SEM micrograph showing the substrate-coated contact surface of a coated cutting tool NC70e (invention) coated by CVD process 1. [Figure 3] 1 is a cross-sectional SEM micrograph showing the substrate-coated contact surface of a coated cutting tool NC70e (invention) coated by CVD process 2. [Figure 4] 1 is a cross-sectional SEM micrograph showing the substrate-coat contact surface of a coated cutting tool NC80e (reference) coated by CVD process 1. [Figure 5]1 is a cross-sectional SEM micrograph showing the substrate-coated contact surface of a coated cutting tool NC80e (invention) coated by CVD process 2. [Figure 6] 1 is a cross-sectional SEM micrograph showing the substrate-coat contact surface of coated cutting tool N100e (reference) coated by CVD process 1. [Figure 7] 1 is a top view SEM micrograph showing the outer surface of a coated cutting tool, substrate NC70e (invention), with a CVD process 2 coating. [Figure 8] 1 is a top-view SEM micrograph showing the outer surface of a coated cutting tool, substrate N100e (reference), coated with CVD Process 2. DETAILED DESCRIPTION OF THE INVENTION

[0034] method The cemented carbide substrate of the present invention can be produced according to the following steps. - Preparing powders of W, Ta, Cr, C, WC, TiC, etc. that form or are hard constituents - Preparing powders such as Co, Ni, etc. to form metal binders - Preparing the grinding liquid - Crushing, drying, pressing, and sintering the powder into a cemented carbide substrate.

[0035] During sintering, oxygen reacts with carbon and leaves the substrate as CO or CO. The amount of carbon lost during sintering varies depending on the raw materials and manufacturing techniques used, and it is up to the skilled artisan to adjust the amounts of each component to obtain the desired sintered body.

[0036] The carbon content in the cemented carbide was analyzed by carbon combustion analysis using a LECO 844 series instrument. The carbon content in the cemented carbide was measured in the sintered substrate. Some of the carbon mixed into the powder during cemented carbide production is consumed during sintering. Some of the carbon dissolves in the metal binder, and some of the carbon may form carbides.

[0037] This study focuses on the composition of the metal binder, but because preparing samples is expensive and complicated, the composition was calculated using software called Thermo-Calc. Alternatively, the composition of the metal binder can be measured using XRF (X-ray fluorescence).

[0038] Thermo-Calc is a software package used worldwide by materials scientists, researchers and in industry in the field of materials engineering for the development and production of both materials and components. Development of Thermo-Calc software began already in the mid-70s at the Department for Physical Metallurgy at the Royal Institute of Technology in Stockholm, Sweden, and Thermo-Calc Software AB was founded in 1997. More information can be found at www.thermocalc.com. Thermo-Calc provides, for example, thermodynamic calculations of the amounts of phases and their composition, as well as phase diagrams (binary, ternary and multicomponent systems).

[0039] Thermo-Calc calculations are based on thermodynamic data provided in high-quality databases for various purposes, including many different materials. These databases are created by expert assessment and systematic evaluation of experimental and theoretical data, according to the well-established so-called CALPHAD technique. The databases provided by Thermo-Calc Software AB are validated against experimental data to assess their accuracy in computational predictions.

[0040] The database used for the Thermo-Calc calculations herein was "TCFE7," commercially available from Thermo-Calc Software AB. TCFE7 is a thermodynamic database for various types of steels, Fe-based alloys (stainless steels, high-speed steels, tool steels, HSLA steels, cast irons, corrosion-resistant high-strength steels, etc.), and cemented carbides. The TCFE7 database has been validated against experimental data and has shown accurate predictions, particularly for cemented carbides, particularly in predicting the correct phases and fractions, phase compositions, and solid-liquid equilibrium temperatures.

[0041] The composition of the metal binder in the present invention was determined using Thermo-Calc software, as 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):273312].

[0042] The Thermo-Calc calculation of the present invention was performed under the following criteria: atmospheric pressure, temperature 1000°C, 1 mol of substance, Ni, Fe, Co composition, crushed Co added and weighed, C level by chemical analysis, balance W.

[0043] If the composition of the metal binder is known in mol%, the average d-electron count is calculated as follows: d-electrons are counted as the number of electrons in the highest d orbital for each element, e.g., Fe is 6, Co is 7, Ni is 8, C is 0, and W is 4.

[0044] The coatings in the following examples were deposited in a Radial Bernex™ CVD reactor, size 530, manufactured by Ionbond, which has a capacity of 10,000 half-inch cutting inserts.

[0045] To investigate the layer structure, X-ray diffraction was performed on the flank and rake faces of the cutting tool inserts using an Xpert-Pro diffractometer system equipped with an X'Celerator RTMS detector. The coated cutting tool inserts were mounted in a specimen holder, ensuring that the surface of the cutting tool insert was parallel to the reference plane of the specimen holder and that the cutting tool surface was at the appropriate height. Measurements were performed using Cu-Kα radiation at 45 kV and 40 mA. A 0.02 radian Soller slit and a 0.25° divergence slit were used for the incident beam path. A 0.25° anti-scatter slit and a 0.02 radian Soller slit were used for the diffracted beam. The nickel beta filter had a thickness of 0.020 mm. The diffraction intensity from the coated cutting tool was measured over the 15° to 140° 2θ range, i.e., over an incidence angle θ range of 10° to 70°.

[0046] Data analysis, including background subtraction, Cu-Kα stripping, and profile fitting of the data, was performed using PANalytical's X'Pert HighScore Plus software. The fitting process is outlined below. The output from this program (integrated peak areas of the profile fitting curve) was then used to calculate the layer's texture coefficient by comparing the ratio of the measured intensity data to the standard intensity data from the α-Al2O3 PDF-card using the Harris equation (1), as disclosed above. Because the layer has a finite thickness, the relative intensities of peaks at different 2θ angles will differ from those of the bulk sample due to differences in path length through the layer. Therefore, a thin-film correction was applied to the integrated peak area intensities obtained from the profile fitting curve, and the TC value was calculated by taking into account the linear absorption coefficients of the layer. Since additional layers on top of the α-Al2O3 layer affect the X-ray intensity entering the α-Al2O3 layer and exiting the entire coating, corrections for these must also be made, taking into account the linear absorption coefficients of each compound within the layer. Alternatively, the additional layer, such as TiN, on top of the alumina layer can be removed by a method that does not substantially affect the XRD measurements, such as chemical etching.

[0047] To investigate the texture of the α-Al2O3 layer, X-ray diffraction was performed using CuKα radiation, and the texture coefficient TC(hkl) for the columnar grains in the α-Al2O3 layer with different growth directions was calculated according to the Harris equation (1), where I(hkl) = the measured (integrated area) intensity of the (hkl) reflection, I0(hkl) = the standard intensity according to ICDD PDF-card No. 00-010-0173, and n = the number of reflections used in the calculation. In this case, 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).

[0048] It should be noted that peak overlap is a possible phenomenon in X-ray diffraction analysis of, for example, coatings containing multiple crystalline layers and / or coatings deposited on substrates containing crystalline phases, and that peak overlap must be considered and corrected for. The overlap of peaks from the α-Al2O3 layer with peaks from the TiCN layer may affect the measurement and must be taken into account. It should also be noted that, for example, WC in the substrate may have diffraction peaks close to the relevant peaks of the present invention. [Example]

[0049] An exemplary embodiment of the present invention will now be disclosed in more detail and compared with a reference embodiment. Coated cutting tools (inserts) were manufactured and analyzed.

[0050] Cemented carbide substrates were manufactured according to ISO classification SNUN120408. The cemented carbide substrates were made of WC in a metal binder, with the metal binder content being approximately 10 wt%. The cemented carbide substrates were manufactured from a powder mixture. The powder mixture was milled, dried, pressed, and sintered at 1450°C. WC / Co milling bodies were used during the milling and mixing process. The carbon content in the powder was approximately 6.07 wt%. The carbon content determined by chemical analysis of the sintered cemented carbide is shown in Tables 1A and 1B. The sintered cemented carbide contained approximately 0.4 wt% Co, primarily derived from the milling bodies worn during the milling process. SEM micrographs of the cross-sections of the cemented carbide substrates showed no visible free graphite.

[0051] The C levels of the substrates were measured by LECO carbon combustion. The compositions of the cemented carbide substrates are listed in wt. % for the so-called e-samples in Table 1A and for the so-called f-samples in Table 1B. Table 1A. Overview of cemented carbide substrates, e-samples TIFF0007733733000002.tif68170Table 1B. Overview of cemented carbide substrates, f-specimen TIFF0007733733000003.tif68170

[0052] The composition of the metal binder was calculated using Thermo-Calc using the following conditions: atmospheric pressure, temperature 1000 °C, 1 mol of material, Ni, Fe, Co composition plus ground Co weighed, C level by chemical analysis, and the remainder W. The resulting binder composition, excluding carbides, is listed in mol% in Table 2A (e-sample) and Table 2B (f-sample).

[0053] The calculated composition of the metal binder is used to calculate the average number of d electrons in the binder. d electrons are counted as the number of electrons in the highest d orbital for each element, e.g., Co is 7, Ni is 8, C is 0, and W is 4. The average number of d electrons for the binder is shown in Tables 2A and 2B.

[0054] To calculate the carbon activity of a cemented carbide, the chemical composition must first be known. In this example, the C activity calculation is based on the values ​​shown in Tables 1A and 1B. For unknown samples, the C activity can be measured, for example, by XRF.

[0055] A Thermo-Calc calculation of thermodynamic equilibrium is performed at atmospheric pressure, a temperature of 1000°C, 1 mole of material, with a composition of Ni, Fe, Co, C from chemical analysis, and the balance W. The carbon activity relative to graphite at this equilibrium is then extracted as an output parameter from Thermo-Calc. See Tables 2A and 2B. Table 2A. Metal binder overview, e-samples TIFF0007733733000004.tif68170Table 2B. Metal binder overview, f-sample TIFF0007733733000005.tif68170

[0056] CVD coatings were deposited on the cemented carbide compositions shown in Tables 2A and 2B. A summary of the CVD coatings is shown in Table 3. Prior to coating deposition, the rake face was polished to remove the outermost metal from the surface, while the flank face was left unpolished. Polishing was performed in two steps: each SNUN120408 specimen was mounted in black conductive phenolic resin from AKASEL, then ground off approximately 1 mm, followed by coarse polishing (9 μm) and fine polishing (1 μm) using a diamond slurry solution. After polishing, the SNUN120408 specimens were removed from the black conductive phenolic resin and washed with ethanol before coating. Table 3. CVD process overview TIFF0007733733000006.tif66170

[0057] Before starting the CVD deposition, the CVD chamber was heated to reach 885° C. The preheating step was carried out in 1000 mbar, 100% by volume H 2 for both process CVD1 and process CVD2.

[0058] In Process CVD-1, the substrate was first coated with a TiN layer approximately 0.2–0.3 μm thick at 885°C (Process TiN-2). Process CVD-2 involved two alternate TiN depositions: an initial TiN-1 step followed by a subsequent TiN-2 step. The purpose of the TiN-1 step was to prevent the formation of intermetallic phases such as Ni3Ti within the CVD coating and at the interface between the substrate and coating. Compared to the TiN-2 deposition step, which was performed without HCl and with a 50 / 50 H2 / N2 gas mixture, the N2 partial pressure was higher and the H2 partial pressure was lower during TiN-1 deposition, and HCl was added. Once TiN-1 was deposited, the subsequent TiN-2 deposition time was adjusted to achieve a total TiN layer thickness of 0.7 μm. The TiN-1 deposition lasted for 150 minutes.

[0059] An approximately 8 μm TiCN layer was then deposited at 885 °C using the well-known MTCVD method using TiCl, CH, N, HCl, and H. The volume ratio of TiCl / CH was 6.6 at the beginning of the MTCVD deposition of the TiCN layer, followed by a period in which the ratio was increased to 3.7. The details of the TiN and TiCN deposition are shown in Table 4. Table 4. MTCVD of TiN and TiCN TIFF0007733733000007.tif77170

[0060] In process CVD1, after depositing the TiCN outer layer, the temperature was increased from 885°C to 1000°C in an atmosphere of 75% H2 by volume, 25% N2 by volume, and 55 mbar. In process CVD2, after depositing the TiCN outer layer, the temperature was increased from 885°C to 1000°C in an atmosphere of 100% N2 by volume, and 1000 mbar.

[0061] A 1-2 μm thick bond layer was deposited on the MTCVD TiCN layer at 1000 °C in a process consisting of four separate reaction steps: first, an HTCVD TiCN step using TiCl4, CH4, N2, HCl, and H2 at 400 mbar; then, a second step (TiCNO-1) using TiCl4, CH3CN, CO, N2, and H2 at 70 mbar; then, a third step (TiCNO-2) using TiCl4, CH3CN, CO, N2, and H2 at 70 mbar; and finally, a fourth step (TiN-3) using TiCl4, N2, and H2 at 70 mbar. The bond layer was oxidized in a mixture of CO2, CO, N2, and H2 for 4 minutes before the onset of active Al2O3 nucleation.

[0062] The details of the tie layer deposition are given in Table 5. Table 5. Bond layer deposition TIFF0007733733000008.tif98170

[0063] An α-Al2O3 layer was deposited on top of the tie layer. All α-Al2O3 layers were deposited in two steps at 1000 °C and 55 mbar. The first step, using 1.2 vol% AlCl3, 4.7 vol% CO2, 1.8 vol% HCl, and the remainder H2, yielded an α-Al2O3 thickness of approximately 0.1 μm, while the second step, disclosed below, yielded an α-Al2O3 layer with a total thickness of approximately 5 μm. The α-Al2O3 layer in the second step was deposited using 1.2% AlCl3, 4.7% CO2, 3.0% HCl, 0.58% H2S, and the remainder H2.

[0064] XRD was used to analyze the texture coefficient (TC) values ​​of the α-Al2O3 according to the method disclosed above. The layer thickness was analyzed by examining a cross section of each coating at 12,000x magnification on a Carl Zeiss AG-Supra 40 SEM (Scanning Electron Microscope). The TiCN layer thickness includes both the bond layer and the first TiN layer. See Table 1. Both the polished rake face and the unpolished flank face were examined. The results from the XRD are shown in Tables 6A and 6B. Table 6A. XRD results (e-sample) TIFF0007733733000009.tif52170Table 6B. XRD results (f-sample) TIFF0007733733000010.tif60170

[0065] The coating was also analyzed using SEM to check for the presence of any Ni compounds, such as intermetallic phases, at the interface between the substrate and the first TiN layer.

[0066] The top-view images of the coated samples showed that the outer alumina surface was uneven and had a high surface roughness. The unexpectedly rough surface indicated the formation of an intermetallic phase at the interface, leading to the conclusion that examining the outer alumina surface could confirm the formation of an intermetallic phase at the interface.

[0067] To determine whether the diffusion of binder elements (Ni compounds) hindered the growth of the coating, cross-sectional images were mainly focused on the interface between the substrate and the first TiN layer. The formation of Ti-containing intermetallic phases (e.g., Ni3Ti) depended on the binder composition.

[0068] The quality of the coatings deposited on the Ni-rich binder by Process CVD1 and Process CVD2 was determined by analyzing both the outer surface and morphology of the Al2O3, as well as the interface between the substrate and the first TiN layer. The irregularities on the Al2O3 surface can be attributed to the growth of coarse grains and correlate with the formation of intermetallic phases, such as Ni3Ti, at the interface between the substrate and the coating. When the Al2O3 irregularities were difficult to determine, the interface between the substrate and the coating was analyzed to determine the quality of the coating. For this investigation, a SEM was used at 12,000x magnification, and three parallel images were taken from three locations on the sample, approximately 10 μm apart along the substrate surface, to detect the presence of intermetallic phases. The results of the analysis are shown in Tables 7A and 7B. Table 7A SEM analysis of e-sample TIFF0007733733000011.tif77170Table 7B f-SEM analysis of sample TIFF0007733733000012.tif77170

[0069] Surface and cross-sectional analysis revealed that samples with visible irregularities or large surface roughness on the outer (top) alumina surface also exhibited Ti-containing intermetallic phases at the interface (cross-section). It is unexpected that Ti-containing intermetallic phases or obstructive pores do not appear at the interface of the CVD coating when the carbon activity is low (less than 0.15) and the average d-electron number is between 7.0 and 7.43. See Table 8. Table 8 Results summary TIFF0007733733000013.tif69170* No Ti-containing intermetallic compound phase exists on the contact surface ** CVD process 1: Ti-containing intermetallic compound phase present on the contact surface, CVD process 2: Ti-containing intermetallic compound phase not present on the contact surface *** Ti-containing intermetallic compound phase exists on the contact surface

[0070] While the invention has been described in connection with various exemplary embodiments, it is understood that the invention is not limited to the disclosed exemplary embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements within the scope of the appended claims.

Claims

1. 1. A coated cutting tool comprising a cemented carbide substrate and a coating, wherein the cemented carbide is composed of hard constituents in a metal binder, the metal binder containing 55-80 mol % of Ni, 10-35 mol % of Co, and 4-15 mol % of W, the coating comprising, in order from the substrate, a TiN inner layer and a TiCN layer, the carbon activity of the metal binder relative to graphite being lower than 0.15, the average d-electron value of the metal binder being 7.00-7.43, and no Ti-containing intermetallic compound phase being present at the interface between the substrate and the TiN inner layer.

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

120.

3. 3. The coated cutting tool according to claim 1, wherein the contact surface between the substrate and the TiN inner layer is free of Ti and Ni-containing intermetallic compound phases.

4. The coated cutting tool according to any one of claims 1 to 3, wherein the average d electron value is from 7.20 to 7.

43.

5. The coated cutting tool according to any one of claims 1 to 4, wherein the average d electron value is from 7.30 to 7.

43.

6. 6. The coated cutting tool according to claim 1, wherein the metallic binder comprises 65-80 mol% Ni, 10-25 mol% Co, and 8-13 mol% W.

7. The coated cutting tool according to any one of claims 1 to 6, wherein the content of the metal binder in the cemented carbide is 3 to 20 wt%.

8. The coated cutting tool according to any one of claims 1 to 7, wherein the total thickness of the coating is from 2 to 20 µm.

9. 9. The coated cutting tool of claim 1, wherein the coating is a CVD coating.

10. The coated cutting tool according to any one of claims 1 to 9, wherein the thickness of the TiN inner layer is 0.1 to 1 µm.

11. The coated cutting tool according to any one of claims 1 to 10, wherein the thickness of the TiCN layer is 6 to 12 µm.

12. The coating is an α-Al layer located between the TiCN layer and the outermost surface of the coated cutting tool. ２ O ３ The coated cutting tool of claim 1 , comprising a layer.

13. α-Al located between the TiCN layer and the outermost surface of the coated cutting tool ２ O ３ A coated cutting tool according to any one of claims 1 to 12, wherein the layer has a thickness of 4 to 8 µm.

14. The α-Al ２ O ３ The layer was measured by X-ray diffraction using CuKα radiation and θ-2θ scan and was found to be in accordance with the Harris equation: where I(h k l) is the measured intensity (integrated area) of the (h k l) reflection; I ０ (h k l) is the standard intensity according to ICDD PDF-card No. 00-010-0173, n is the number of reflections used in the calculation, and the (h k l) 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), and TC(0 0 12) is ≥ 6.

14. The coated cutting tool according to claim 12 or 13, exhibiting a texture coefficient TC(h k l) defined according to:

15. The coating is a CVD coating, CVD coatings include TiN, TiCN, AlTiN, ZrCN, TiB ２ , Al ２ O ３ or one or more layers selected from α-Al ２ O ３ and / or κ-Al ２ O ３ 15. The coated cutting tool of claim 1, further comprising a multilayer comprising:

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