Coated cutting tool

Abstract

The invention relates to a coated cutting tool (1) comprising a matrix (5) of cemented carbide comprising WC grains and eta-phase grains and a metal binder comprising Co and Cr, the content of Co in the cemented carbide being 6-14 wt%, the content of Cr being 0.5-10 wt%, and the content of WC in the matrix (5) being 0.5-10 wt%. The [eta] phase content in the cemented carbide is 1-10 vol% and the [eta] phase grains have an average grain size of 0.5-5 m, the Cr / Co weight ratio in the cemented carbide is 0.005-0.025, and wherein the coating (6) comprises a nanomultilayer (8) of alternating layers of a first nanolayer (9) of Ti1-xAlxN, 0.35 < = x < = 0.70, and a second nanolayer (10) of Ti1-ySiyN, 0.12 < = y < = 0.25.

Description

[0001] The present invention relates to a coated cutting tool comprising a nanolaminate of (Ti,Si)N and (Ti,Al)N. The coating is deposited on a cemented carbide substrate comprising eta phase grains distributed in a binder comprising cobalt and chromium. BACKGROUND

[0002] Metal machining operations include, for example, turning, milling and drilling.

[0003] In order to provide long tool life, a coated cutting tool, such as an insert, should have high resistance to different types of wear, such as resistance to flank wear, resistance to crater wear, resistance to chipping and resistance to spalling.

[0004] Different metal machining operations affect the coated cutting tool in different ways. For example, turning is a continuous metal machining operation, whereas milling is essentially more intermittent. In milling, thermal and mechanical loads vary over time. Thermal loads induce thermal tensions, which can lead to so-called thermal cracks, herein referred to as "comb cracks". Mechanical loads can induce fatigue in the cutting edge, leading to chipping, i.e. small pieces of the cutting edge loosening from the rest of the substrate. Thus, common wear types in milling of coated cutting tools are cracks and chipping. High levels of toughness of the coating, particularly at the cutting edge, can reduce such chipping. Therefore, to improve tool life, it is of great importance to improve comb crack resistance and edge line toughness.

[0005] Heat resistant superalloys (HRSA) and titanium, i.e. ISO-S materials, are important materials in, for example, the aerospace industry. Machining of ISO-S materials is challenging due to the properties of the workpiece material. These materials are hard and smearing, putting special demands on the cutting tool. For example, ISO-S materials are poor conductors of heat, leading to high temperatures, formation of wear during machining.

[0006] There is a continuous need for coated cutting tools, wherein the coating has excellent properties in terms of wear resistance.

[0007] It is an object of the present invention to provide a coated cutting tool that at least shows high resistance to chipping and high toughness, particularly in ISO-S milling applications. SUMMARY

[0008] There is now provided a combination of a cemented carbide substrate comprising WC and eta phase uniformly distributed in a metallic binder comprising Co and Cr, the substrate further having a coating deposited thereon, the coating comprising a nanolaminate coating of alternating (Ti,Si)N layers and (Ti,Al)N layers.

[0009] The coated cutting tool according to the present invention shows surprisingly high toughness behaviour in the metal machining of titanium.

[0010] The present invention relates to a coated cutting tool comprising a cemented carbide and a coating, wherein the cemented carbide comprises WC grains and eta phase grains and a metallic binder, wherein the metallic binder comprises Co and Cr, the Co content in the cemented carbide is 6-14 wt%, the eta phase content in the cemented carbide is 1-10 vol% and the average grain size of the eta phase grains is 0.5-5 pm, the Cr / Co weight ratio in the cemented carbide is 0.005-0.025, and wherein the coating comprises a nanolayered nanomultilayer of alternating layers of a first nanolayer of Ti 1-x Al x N, wherein 0.35≤x≤0.70, and a second nanolayer of Ti 1-y Si y N, wherein 0.12≤y≤0.25, the sequence of one first nanolayer and one second nanolayer forms a layer period, the average layer period thickness in the nanomultilayer is < 10 nm.

[0011] The cemented carbide of the present invention comprises WC grains and eta phase grains embedded in a metallic binder. The metallic binder comprises Co and Cr, and also W dissolved from the WC grains into the metallic binder during sintering of the cemented carbide.

[0012] The Co content in the cemented carbide of the present invention is suitably 7-13 wt% Co, preferably 8-12 wt% Co.

[0013] The Cr content in the cemented carbide of the present invention is suitably such that the Cr / Co weight ratio is 0.010-0.020.

[0014] The cemented carbide with the Cr / Co weight ratio range of the present invention is highly solution strengthened. The work hardening properties of Co are improved, the hot hardness properties are improved, and also the chemical resistance, i.e. corrosion resistance, is improved. By adding Cr to the cemented carbide, the eta phase grains will contain some Cr. The Cr will also be retained to some extent as a solid solution in the metallic binder phase comprising Co. The Cr will also act as a grain growth inhibitor during sintering and limit the continued growth and coarsening of the WC grains. If the Cr content is too low, the Cr still influences the WC grain size growth, but the above-mentioned solution effect is limited. If the Cr is too high, the cemented carbide is too hard and too brittle to be used in ISO-S milling applications.

[0015] The eta phase content in the cemented carbide of the invention is 1-8 vol%, suitably 2-8 vol%, preferably 3-6 vol%. If the eta phase content is too high, most of the Co content in the metal binder is consumed into the eta phase grains, which makes the cemented carbide too brittle. If the eta phase content is too low, the risk of clusters of eta phase grains increases, and these clusters are brittle, rather than well-distributed eta grains. The amount of eta phase in the cemented carbide can be determined by image analysis of LOM (light optical microscope). It is believed that the area fraction in the image corresponds to the volume fraction in the cemented carbide.

[0016] The cemented carbide according to the invention has a low carbon content, such that eta phase grains are formed. Eta phase in this context means carbides selected from Me 12 C and Me6C, where Me is one or more metals selected from W and the binder phase metals, such that the carbide can be, for example, (W,Co,Cr)6C and / or (W,Co,Cr) 12 C.

[0017] In the invention, the cemented carbide comprises finely dispersed eta phase grains. The average grain size of the eta phase grains in the cemented carbide of the invention is 0.5-5 pm, suitably 1-4 pm. The average grain size of the eta phase grains is defined in this context as the average of the largest Feret diameter of the eta phase grains. This value can be determined by, for example, image analysis of light optical microscope (LOM) images.

[0018] The eta phase grains are suitably uniformly distributed within the cemented carbide.

[0019] The distributed eta phase grains of the invention are formed during the sintering process, and control of carbon defects and balancing temperature is required in the process to achieve the desired eta phase grain size and content. The eta phase grains themselves are often present in an undesirable form as very large grains, which can be agglomerates of smaller grains, leading to brittle cemented carbide. Such undesirable forms of eta phase grains typically have a grain size of more than 50 pm, or even more than 100 pm.

[0020] The difference between achieving the undesirable large grains or agglomerates of eta phase and achieving the targeted distributed small eta phase grains can be very small. Approaching this limit requires monitoring of the formation of the microstructure, ensuring that the undesirable large grains or agglomerates are avoided. Careful adjustment of the carbon content and then monitoring the results in terms of the obtained microstructure is a process known to the person skilled in the art.

[0021] In one embodiment, the average WC grain size in the cemented carbide is 0.6-1.2 pm, preferably 0.7-1.0 pm.

[0022] In one embodiment of the present application, the cemented carbide comprises 70-90 vol% WC, preferably 75-85 vol% WC. The amount of WC in the cemented carbide can be determined by image analysis of LOM (light optical microscopy). It is believed that the area fraction in the image corresponds to the volume fraction in the cemented carbide.

[0023] In one embodiment of the present application, the content of eta phase in the part of the matrix adjacent to the surface of the matrix corresponds to the content in the innermost part of the matrix. In one embodiment of the present application, the distribution of eta phase is constant throughout the entire cemented carbide matrix, i.e. the cemented carbide does not comprise any gradient of eta phase or regions without eta phase, such as in US 4,843,039. The distribution of eta phase is preferably as uniform as possible.

[0024] In one embodiment of the present application, the cemented carbide comprises 8-28 vol% metallic binder, preferably 13-23 vol% metallic binder.

[0025] In one embodiment, the cemented carbide comprises metallic binder, eta phase and balance WC.

[0026] The metallic binder comprises Co and Cr. In addition, some amount of W is dissolved in the metallic binder. W will inevitably dissolve in the metallic binder during sintering, the exact amount depending on several factors, such as the overall composition of the cemented carbide, the exact carbon content, etc.

[0027] The cemented carbide in the present application has a substoichiometric carbon content SCC within a certain range. The substoichiometric carbon content is a measure of the carbon content in relation to the stoichiometric value of carbon.

[0028] The stoichiometric carbon content can be calculated by assuming that WC is completely stoichiometric, i.e. the atomic ratio W:C is 1 : 1. Since there are other carbide forming elements, it is also assumed that their carbides are stoichiometric.

[0029] This means that the term substoichiometric carbon content SCC as used herein is the total carbon content (in wt%) determined from chemical analysis minus the stoichiometric carbon content (in wt%) calculated based on WC and other carbides that can be present in the cemented carbide.

[0030] As an example, if the stoichiometric carbon content of a particular cemented carbide is 5.60 wt% and the carbon content when the same cemented carbide is made is 5.30 wt%, the substoichiometric carbon is -0.30 wt%.

[0031] To achieve the correct carbon content in the final sintered cemented carbide, W and / or W2C is added in an amount such that the substoichiometric carbon content, SCC, in the sintered cemented carbide is -0.40 wt% < SCC < -0.16 wt%, or -0.35 wt% < SCC < -0.17 wt%.

[0032] The cemented carbide has a low carbon content which enables the formation of eta phase. However, the formed eta phase does not exist as large grains or agglomerates, but has a fine grain size and is well distributed. The desired eta phase form is provided by careful control of the carbon balance during manufacturing.

[0033] If the carbon content in the sintered cemented carbide is too low, i.e. below a substoichiometric carbon content of -0.40 wt%, the amount of eta phase becomes too large and the grain size increases significantly such that the cemented carbide is brittle. On the other hand, if the carbon content is higher than a substoichiometric carbon content of -0.16 wt%, but still within the eta phase formation region, the formed eta phase is unevenly distributed in the form of large agglomerates, resulting in a reduced toughness of the cemented carbide.

[0034] The cemented carbide within the scope of the present invention can be made according to the following steps:

[0035] - providing raw materials,

[0036] - providing a milling liquid,

[0037] - milling, drying, pressing and sintering the powder into a cemented carbide.

[0038] Due to the presence of oxygen, some carbon is typically lost during sintering. The oxygen will react with the carbon and escape as CO or CO2 during sintering, thereby deviating from the carbon balance, and the amount of one or more of W and W2C must therefore be adjusted. How much carbon is exactly lost during sintering depends on the raw materials used and the manufacturing technique, and the addition of W and / or W2C is adjusted by the person skilled in the art such that the target eta phase properties are achieved in the sintered material.

[0039] The substoichiometric carbon value in the sintered material is slightly different from that in the powder. This is due to some carbon reacting with oxygen and escaping as CO or CO2 gas during sintering, which reduces the total final C content of the cemented carbide. The substoichiometric carbon value in the sintered material is typically about 5-25% lower than the substoichiometric carbon value in the powder composition. For example, a substoichiometric carbon value of -0.20 wt% in the powder composition can result in a substoichiometric carbon value of from about -0.21 wt% to about -0.25 wt% in the sintered material.

[0040] The stoichiometric carbon content in cemented carbide can be determined by first measuring the total carbon content in the sample by using for example a LECO CS 844 instrument. Also the cobalt content is measured by for example X-ray fluorescence analysis. The tungsten content is derived by subtracting the cobalt amount and the carbon amount from the total weight of the sample and is then used to calculate the stoichiometric carbon content (assuming WC has a 1 : 1 ratio).

[0041] The grain size of the WC powder used is selected to provide the desired WC grain size in the final cemented carbide, taking into account the effect of all ingredients in the raw material powder mixture, also any milling procedure used. Suitably the grain size (FSSS) of the WC powder is between 2 and 7 pm.

[0042] The powder forming the binder phase is Co and is added in the desired amount. In addition, Cr is added in the desired amount (suitably in the form of Cr3C2) and in the final cemented carbide, partly contained in the eta phase and partly dissolved in the binder phase.

[0043] The slurry comprising the powders forming the hard constituents and the powder forming the binder phase is suitably mixed by a milling operation in a ball mill or a vertical mill. Any liquid commonly used as a milling liquid in conventional cemented carbide manufacturing can be used. The slurry containing the powdered materials is then dried, suitably forming agglomerated particles.

[0044] Subsequently, a green body is formed from the dried powder / particles by a pressing operation, for example uniaxial pressing, multi-axial pressing, etc.

[0045] Subsequently, the green body formed from the powder / particles manufactured is sintered according to any conventional sintering method, for example vacuum sintering, Sinter HIP, spark plasma sintering, gas pressure sintering (GPS), etc.

[0046] The sintering temperature is typically between 1300 and 1580 °C, or between 1360 and 1450 °C.

[0047] The coating comprises a nanolayer of Ti 1-x Al x N, 0.35 < x < 0.70, and a second nanolayer of Ti 1-y Si y N, 0.12 < y < 0.25.

[0048] For the first nanolayer Ti 1-x Al x N, suitably 0.45 < x < 0.70, preferably 0.55 < x < 0.65.

[0049] For the second nanolayer Ti1-y Si y N, suitably 0.14 < y < 0.23, preferably 0.17 < y < 0.21.

[0050] The average layer period thickness of the nanomultilayer is suitably from 2 to 7 nm, preferably from 3 to 6 nm.

[0051] In one embodiment, the nanomultilayer has a columnar organization with an average column width of < 100 nm or < 70 nm. In one embodiment, the average column width of the nanomultilayer is from 5 to 100 nm, or from 10 to 70 nm, or from 25 to 70 nm.

[0052] The thickness of the nanomultilayer is suitably from about 0.5 to about 10 pm, preferably from about 0.5 to about 5 pm, more preferably from about 1 to about 3 pm.

[0053] The nanomultilayer is suitably a cathodic arc evaporation deposited layer.

[0054] In one embodiment, the coating comprises a layer of TiN, (Ti,AI)N or (Cr,AI)N between the substrate and the nanomultilayer, preferably as the innermost layer of the coating. Preferably, the layer is (Ti,AI)N. If (Ti,AI)N is used, the (Ti,AI)N is suitably Ti 1-z Al z N, 0.35 < z < 0.70, preferably 0.45 < z < 0.70, most preferably 0.50 < z < 0.65. In one preferred embodiment, the Ti-AI relationship in the (Ti,AI)N is the same as in the first nanolayer of the nanomultilayer. The thickness of this layer can be from about 0.1 to about 2 pm, preferably from about 0.5 to about 1.5 pm.

[0055] In one embodiment, the coating comprises a top layer of (Ti,Si)N. The (Ti,Si)N is suitably Ti 1-v Si v N, 0.12 < v < 0.25, or 0.14 < v < 0.23, or 0.17 < v < 0.21. In one preferred embodiment, the Ti-Si relationship in this (Ti,Si)N top layer is the same as in the second nanolayer of the nanomultilayer. The thickness of this top layer can be from about 0.02 to about 0.5 pm, preferably from about 0.05 to about 0.2 pm.

[0056] In one preferred embodiment, the coating comprises a nanomultilayer of alternating layers of a first nanolayer and a second nanolayer, the first nanolayer being Ti 1-x Alx N, 0.55 < x < 0.65, the second nanolayer being Ti 1-y Si y N, 0.17 < y < 0.21, the nanomultilayer having an average layer period thickness from 3 to 6 nm, an average column width in the nanomultilayer from 25 to 70 nm, a thickness of the nanomultilayer from about 1 to about 3 pm, the nanomultilayer being underlain by an innermost layer (Ti, Al)N, closest to the substrate, having a thickness from about 0.5 to about 1.5 pm.

[0057] The coated cutting tool is suitably a cutting tool insert, drill or solid end mill for metal machining. Preferably, the cutting tool insert is a milling insert or a solid end mill. BRIEF DESCRIPTION OF DRAWINGS

[0058] Figure 1 Schematic drawing showing one embodiment of a cutting tool as a milling insert.

[0059] Figure 2 Schematic drawing showing one embodiment of a cross section of a coated cutting tool of the invention, showing the substrate and the coating comprising different layers.

[0060] Figure 3 LOM (light optical microscope) image showing one embodiment of a cross section of a substrate used in the invention.

[0061] Figure 4 LOM image showing Figure 3 a zoom in on the lower right corner. DETAILED DESCRIPTION

[0062] Figure 1 Schematic drawing showing one embodiment of a cutting tool (1) having a rake face (2) and a flank face (3) and a cutting edge (4). In this embodiment the cutting tool (1) is a milling insert. Figure 2 Schematic drawing showing one embodiment of a cross section of a coated cutting tool of the invention, the coated cutting tool having a substrate body (5) and a coating (6). The coating (6) consists of a (Ti, Al)N inner layer (7), followed by a nanomultilayer (8) of nanolayers of Ti 1-x Al x N (9) and Ti 1-y Si y N (10). Figure 3 LOM (light optical microscope) showing one embodiment of a cross section of a cemented carbide substrate used in the invention. The cemented carbide comprises eta phase grains (dark), WC grains (grey) and metallic binder (light greyish). Figure 4 LOM image showing Figure 3Enlarged view of the lower right corner of a LOM image of the cemented carbide. The cemented carbide comprises eta phase grains (11), WC grains (12) and metallic binder (13).

[0063] Definitions and methods

[0064] The amount of eta phase in the cemented carbide was determined by image analysis using LOM (light optical microscope) using the "Analyze Particles" function in the software Image J with "Include holes" and "0-Infinity" filter settings. Prior to the measurement, the colour LOM image was converted to an 8-bit black and white image using the automatic threshold setting. The magnification of the image was 1000X and 2000X, two measurements were made at each magnification, and the values in Table 2 are the average of these. Thus, the values in the table are the average of four image analyses, two images, two measurements on each image. The area fraction in the image is considered to correspond to the volume fraction in the cemented carbide. The volume fraction of WC could be determined in a corresponding manner to the volume fraction of eta phase.

[0065] The average grain size of the eta phase grains is herein defined as the average of the maximum Feret diameter of the eta phase grains. This value is herein determined by image analysis on light optical microscope (LOM) images using the "Analyze Particles" function in the software Image J with "Include holes" and "0-Infinity" filter settings. The Feret diameter option "Exclude edges" was additionally enabled in the "Analyze Particles" function. Prior to the measurement, the colour LOM image was converted to an 8-bit black and white image using the automatic threshold setting. The image used for the analysis was a LOM image with a magnification of 1000X, and 10 images were processed, the maximum Feret diameter was obtained for each image, and the overall average of the maximum Feret diameter was calculated.

[0066] The stoichiometric carbon content in the sintered cemented carbide can be calculated by first measuring the total carbon content in the sintered cemented carbide. A suitable instrument is used, such as a LECO CS 844 instrument. The sample is crushed prior to analysis. The W, Co and Cr content is measured, for example, by using a Panalytical Axios Max Advanced instrument with XRF (X-ray fluorescence). The W content is obtained by subtracting the cobalt amount, the chromium amount and the carbon amount from the total weight of the sample, which is then used to calculate the stoichiometric carbon content (assuming WC has a 1 : 1 ratio). The sub-stoichiometric carbon value is obtained by subtracting the stoichiometric carbon content from the total carbon content that has been measured.

[0067] The grain size d of WC is determined in this document by the value of the magnetic coercivity. The relationship between the coercivity of WC and the grain size is described for example in Roebuck et al., Measurement Good Practice No. 20, National Physical Laboratory, ISSN 1368-6550, November 1999, revised February 2009, section 3.4.3, pages 19-20. For the purpose of this application, the grain size d of WC is determined according to equation (8) on page 20 in the above-mentioned document:

[0068] K = (c1+d1W Co ) + (c2+d2W Co ) / d. Rearranging gives:

[0069] d = (c2+d2W Co ) / (K-(c1+d1W Co )) where

[0070] d = WC grain size of the cemented carbide body, K = coercivity of the cemented carbide body in kA / m, measured according to standard DIN IEC 60404-7, W Co = wt% Co in the cemented carbide body, c1 = 1.44, c2 = 12.47, d1 = 0.04, d2 = -0.37.

[0071] The layer thickness of the coating is measured in a polished cross-section in a SEM image.

[0072] The term "average layer period thickness" refers to the average thickness of the combination A-B in a nanolaminate coating of the first nanolayer A and the second nanolayer B in a nanolaminate A-B-A-B-A... If the deposition sequence is known, it can be calculated by dividing the total thickness of the nanolaminate by the number of A-B depositions (corresponding to the number of revolutions when depositing the substrate in a rotating manner).

[0073] Alternatively, it is calculated by TEM analysis of a cross-section of the nanolaminate, counting the number of consecutive A-B nanolayer combinations within a length of at least 250 nm and calculating the average.

[0074] The term "average column width" in a nanolaminate refers to the average value of crystalline columns or "grains" in a nanolaminate. A length of at least 500 nm perpendicular to the growth direction of the layers is considered and the column width is measured at at least 4 different locations within this length at a distance of 500 nm from the lower interface of the nanolaminate.

[0075] If the total thickness of the nanomultilayer is only 0.5 pm, the measurement position is located just below the outer surface of the nanomultilayer. Suitable methods for the analysis include transmission electron microscopy (TEM).

[0076] Examples

[0077] Example 1:

[0078] A coated cutting tool was manufactured. A sintered cemented carbide cutting tool insert blank with geometry R390-11 was used.

[0079] The first cemented carbide had a composition of 10.40 wt% Co, 0.15 wt% Cr and the rest WC-matrix 1 (inventive part). The reference cemented carbide had a composition of 11.2 wt% Co, 1.12 wt% Cr and the rest WC-matrix 2 (reference).

[0080] The cemented carbide was made from raw material powders according to Table 1.

[0081]

[0082] The powders were milled in a ball mill together with a milling liquid (water / ethanol, ratio 9 / 91) and an organic binder 2 wt% PEG. The amount of PEG is not included in the dry powder weights presented in Table 1. After milling, the slurry was dried. The dried agglomerates were then pressed into green bodies. The green bodies were sintered at 1410 °C in Ar and CO at 40 mbar.

[0083] The chemical composition of the sintered cemented carbide was measured using XRF (X-ray fluorescence) using a Panalytical Axios Max Advanced instrument.

[0084] The carbon in the powders was adjusted to achieve the desired microstructure in the sintered cemented carbide.

[0085] The content of Co and Cr in the sintered cemented carbide matrix is given in Table 2. In addition, values for the coercivity and the calculated average WC grain size are given.

[0086]

[0087] The content of eta phase and the average grain size of the eta phase grains were measured according to the methods disclosed herein. Table 3 shows the results. The eta phase grains in the samples containing eta phase were evenly distributed throughout the entire matrix bulk, no gradient in the content of eta phase was observed in the samples. No gamma phase grains, no very large eta phase grains and no graphite were found in the cemented carbides.

[0088]

[0089] The hard metal blanks are coated by cathodic arc evaporation in a vacuum chamber comprising an arc flange.

[0090] A target of Ti 0.80 Si 0.20 is mounted in two flanges opposite to each other. A target of Ti 0.40 Al 0.60 is mounted in two flanges opposite to each other. The Ti target is mounted in 1 flange. The targets are circular and face-like with a diameter of 100 mm and are available on the open market. A suitable arc source to be used is the arc source from Kobelco (Kobe Steel Ltd.) called Super Fine Cathode (SFC).

[0091] The uncoated blanks of both matrix 1 and matrix 2 are mounted on pins which are subjected to a triple rotation in the PVD chamber.

[0092] The chamber is pumped down to high vacuum (less than 10 -2 Pa) and heated to 550-650°C by a heater located inside the chamber. Then the blanks are etched in an Ar plasma for 60 minutes.

[0093] Then, in order to enhance the adhesion of the coating to the matrix, the matrix is subjected to an etching treatment with Ti ions. This treatment is performed for 4 minutes at a DC bias voltage of -200 V, at an arc current (applied to the Ti target) of 150 A, and at an Ar pressure of 0.7 Pa.

[0094] Then, a Ti 0.40 Al 0.60 N innermost layer of about 0.8 pm thick is first deposited. The chamber pressure (reaction pressure) is set to 4 Pa of N2 gas and a DC bias voltage of -30 V (relative to the chamber wall) is applied to the blank assembly. The cathode of the Ti-Al target is operated in arc discharge mode for 40 minutes at a current of 150 A (each).

[0095] Then a nanolaminate of (Ti,Si)N and (Ti,Al)N is deposited on the Ti 0.40 Al 0.60 N innermost layer.

[0096] The chamber pressure (reaction pressure) was set to 4 Pa of N2 gas and a DC bias voltage of -40 V (relative to the chamber wall) was applied to the blank assembly. The cathodes of the Ti-Al and Ti-Si targets were operated in arc discharge mode for 30 minutes (4 flanges) at an arc current of 150 A (each). A nanomultilayer coating with a thickness of about 1.3 pm was deposited on the blank. Due to the target setup, two nanolayer periods were formed per revolution of the base. The rotational speed of the base was adjusted to provide an average nanolayer period thickness of about 4 nm.

[0097] Finally, a Ti 0.80 Al 0.20 N top layer was deposited. The chamber pressure (reaction pressure) was set to 4 Pa of N2 gas and a DC bias voltage of -70 V (relative to the chamber wall) was applied to the blank assembly. The cathodes of the Ti-Al and Ti-Si targets were operated in arc discharge mode for 5 minutes (2 flanges) at an arc current of 150 A (each).

[0098] The substrate 1 of the coated cutting tool with a nanomultilayer coating comprising Ti 0.40 Al 0.60 N / Ti 0.80 Si 0.20 N nanolayers was denoted “Sample 1 (invention)”.

[0099] The substrate 2 (reference) of the coated cutting tool with a nanomultilayer coating comprising Ti 0.40 Al 0.60 N / Ti 0.80 Si 0.20 N nanolayers was denoted “Sample 2 (comparison)”.

[0100] As another reference sample included in the performance test, a coated cutting tool was made by depositing a (Ti,Al)N layer of about 2 pm in thickness consisting of targets of Ti 0.33 Al 0.67 N in a separate deposition run.

[0101] The (Ti,Al)N layer was deposited on a sintered cemented carbide cutting tool insert blank of the substrate 2 (reference) type of geometry R390-11T308M-PM. By using this reference TiAlN layer, any kind of possible differences between the performance test runs were compensated and results from different test runs could be compared. The cemented carbide blank was coated by cathodic arc evaporation in a PVD vacuum chamber comprising several arc flanges, each flange comprising several cathode evaporators.

[0102] The Ti 0.33 Al 0.67The target installation in the evaporator. Suitable target technology packages for arc evaporation are commercially available from market suppliers such as IHI Hauzer Techno Coating B.V., Kobelco (Kobe Steel Ltd.) and Oerlikon Balzers.

[0103] The PVD chamber comprises a circular base and the uncoated cutting tool insert blanks are mounted on pins. The inserts are mounted such that the relief of the inserts directly faces the target during rotation.

[0104] The chamber pressure (reaction pressure) is set to 1 Pa of N2gas and a DC bias voltage of -100 V (relative to the chamber wall) is applied to the blank assembly. The cathodes are operated in arc discharge mode at a current of 140 A (each). The substrates 2 (reference) of Al 0.33 Al 0.67 The inserts of the substrate 2 (reference) of N are denoted as "sample 3 (reference)".

[0105] To confirm the actual elemental composition in the nanolayers, the average composition of some samples was analyzed by using energy dispersive X-ray spectroscopy (EDS). The EDS measurements were performed in SEM on cross sections of the coatings over a distance comprising multiple nanolayers.

[0106] As a result, a deviation from the theoretical composition of only 1-2 percentage units was observed. This is within the accuracy of the EDS method. It is therefore concluded that the exact elemental composition of Ti, Al and Si in the layers of the nanolayers corresponds substantially well to the respective target composition used. For the innermost layer of TiAlN and the top layer of TiSiN, it is considered that the respective target composition corresponds to the composition in the deposited layer.

[0107] Example 2

[0108] Cutting tests were performed to determine the performance of the manufactured samples.

[0109] Explanation of terms used:

[0110] The following expressions / terms are commonly used in metal cutting, but are still explained:

[0111] Vc (m / min): cutting speed in meters per minute

[0112] fz (mm / tooth): feed rate in millimeters per tooth

[0113] a e (mm): radial depth of cut in millimeters

[0114] a p (mm): axial depth of cut in millimeters

[0115] z: (number) number of teeth in the tool

[0116] Toughness test in titanium:

[0117] The test evaluates the resistance to large cracks. The test is a plunge test, run by reverse milling, with the tool positioned at 0° entry, i.e. half the tool diameter engages (ae). Under these conditions, the chip thickness is maximized outside the workpiece material. These conditions make the operation demanding on toughness. The test is run in the y-direction of the test workpiece and the number of plunges until the cut-off criterion is recorded. During the test, the wear of the variants is measured continuously. In order to obtain the same conditions during the test, a "clean tool" is used to clean the surface when the number of plunges per row is reached. Due to the different conditions for the first plunge, a "clean tool" is also used for the first plunge of each row (right-hand x-direction).

[0118] Workpiece material: Ti6AI4V

[0119] Charge: 04696

[0120] MC S4.2.Z.AN

[0121] Dim: 600x200x50mm

[0122] Hardness: 330 HB

[0123] Tool: R390-32mm (R390-032A32-11M)

[0124] Tool length: 132 mm

[0125] Coolant: Internal 10 bar

[0126] Vc = 35 m / min

[0127] fz = 0.20 mm

[0128] a e = 16 mm

[0129] Plunge depth = 27 mm

[0130] a p = 2.0 mm

[0131] z = 1

[0132] Insert type: R390-11T308M-MM

[0133] Cut-off criterion: crack / chip breakage measured on the rake or flank face > 1.0 mm.

[0134] Tool life report is the number of cuts to achieve the cut-off criteria.

[0135] The uncoated cutting tool blanks (see example 1) of substrates 1 and 2 with geometry R390-11 were tested in the toughness test in titanium. See table 4 for the results.

[0136]

[0137] Thus, substrate 1 showed about four times longer tool life in the toughness test.

[0138] Furthermore, the coated cutting tools of example 1 were tested in the toughness test in titanium. Since two different test runs were performed, the reference samples (sample 2 and sample 4) were tested together with sample 1 (invention) and sample 3 (comparison), respectively, so that a comparison between the performance of sample 1 and sample 3 could be made.

[0139] See table 6 for the results.

[0140]

[0141] Thus, sample 1 (substrate 1 with the combination of a Ti 0.40 Al 0.60 N / Ti 0.80 Si 0.20 N nanolaminate coating) showed about seven times longer tool life in the toughness test than the reference sample 3 (substrate 2 + reference coating Ti 0.33 Al 0.67 N).

[0142] The comparative sample 2 (substrate 2 with the combination of a Ti 0.40 Al 0.60 N / Ti 0.80 Si 0.20 N nanolaminate coating) showed not more or equal performance in the toughness test than the reference sample 3 (substrate 2 + reference coating Ti 0.33 Al 0.67 N).

Claims

1. A coated cutting tool (1) comprising: a cemented carbide substrate (5) and a coating (6), wherein The cemented carbide comprises WC grains and η-phase grains, and a metal binder, wherein the metal binder comprises Co and Cr, the Co content in the cemented carbide is 6-14 wt%, the η-phase content in the cemented carbide is 1-10 vol%, and the average grain size of the η-phase grains is 0.5-5 µm, the Cr / Co weight ratio in the cemented carbide is 0.005-0.025, and wherein... - The coating (6) comprises a nanolayer (8) consisting of alternating layers of a first nanolayer (9) and a second nanolayer (10), wherein the first nanolayer (9) is Ti 1-x Al x N, where 0.35≤x≤0.70, and the second nanolayer (10) is Ti. 1-y Si y N, where 0.12≤y≤0.25, a sequence of a first nanolayer (9) and a second nanolayer (10) forms a layer period, wherein the average layer period thickness in the nanolayer (8) is ≤10 nm.

2. The coated cutting tool according to claim 1, wherein the Co content in the cemented carbide is 7-13 wt%.

3. The coated cutting tool according to any one of claims 1-2, wherein the Cr / Co ratio in the cemented carbide is 0.010-0.

020.

4. The coated cutting tool according to any one of claims 1-3, wherein the η phase content in the cemented carbide is 2-8 vol.

5. The coated cutting tool according to any one of claims 1-4, wherein the content of the η phase in the portion of the substrate adjacent to the surface of the substrate corresponds to the content of the η phase in the innermost portion of the substrate.

6. The coated cutting tool (1) according to any one of claims 1-5, wherein for the first nanolayer (9) Ti 1-x Al x N, 0.45≤x≤0.

70.

7. The coated cutting tool (1) according to any one of claims 1-6, wherein for the second nanolayer (10) Ti 1-y Si y N, 0.14≤y≤0.

23.

8. The coated cutting tool (1) according to any one of claims 1-7, wherein the average layer period thickness in the nanomultilayer (8) is from 2 to 7 nm.

9. The coated cutting tool (1) according to any one of claims 1-8, wherein the nanolayer (8) has a columnar structure with an average column width of ≤100 nm.

10. The coated cutting tool (1) according to any one of claims 1-9, wherein the thickness of the nanolayer (8) is from about 0.5 to about 15 µm.

11. The coated cutting tool (1) according to any one of claims 1-10, wherein the thickness of the nanolayer (8) is from about 0.5 to about 5 µm.

12. The coated cutting tool (1) according to any one of claims 1-11, wherein the coating (6) comprises a layer (7) of TiN, (Ti,Al)N or (Cr,Al)N located between the substrate and the nanolayer (8), the thickness of the layer (7) being from about 0.1 to about 2 µm.

13. The coated cutting tool (1) according to claim 12, wherein the innermost layer (7) is Ti 1-z Al z N, 0.35≤z≤0.

70.

14. The coated cutting tool (1) according to any one of claims 1-13, wherein the coated cutting tool (1) is a cutting tool insert, drill bit or solid end mill for metal machining.

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