Coated Cutting Tools

Abstract

The present invention relates to a coated cutting tool (1) comprising a substrate (5) and a coating (6), the coating (6) having an average composition Ti 1-x-y Al x S y The present invention relates to a coated cutting tool (1) comprising a 0.5 to 15 μm monolithic layer (7) of (Ti,Al,Si)N having a refractive index of 0.50≦x≦0.60, and a refractive index of 0.03≦y≦0.08, the (Ti,Al,Si)N layer (7) having a structure of columnar crystal grains (9), the (Ti,Al,Si)N layer (7) containing two different cubic phases, one of which is present within the columnar crystal grains (9) and the other of which is a grain boundary phase (10) located between the columnar crystal grains (9), and the (Ti,Al,Si)N layer (7) having a plane strain elastic modulus of 425 GPa or more.

Description

[Technical field]

[0001] The present invention relates to a coated cutting tool for metal machining having a coating comprising a (Ti,Al,Si)N layer. [Background technology]

[0002] There is a continuing desire to improve cutting tools for metalworking so that they last longer and withstand higher cutting speeds and / or other increasingly demanding cutting operations.

[0003] Generally, cutting tools for metalworking include a substrate of a hard material, such as cemented carbide, cubic boron nitride, or cermet, and a wear-resistant coating deposited on the surface of the substrate. The wear-resistant coating is usually deposited by either chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0004] The coating should ideally have a high hardness, but at the same time be tough enough to withstand the harshest cutting conditions possible.

[0005] Coatings for metal cutting tools should also ideally have low thermal conductivity as this correlates to the heat resistance of the coating.

[0006] There are different methods of PVD, which give different properties of the deposited coating.

[0007] Cathodic arc evaporation uses an electric arc to vaporize material from a cathode target. The vaporized material or its compounds are then condensed on a substrate. Cathodic arc evaporation has the advantage of high deposition rates, but has drawbacks such as droplets of target material in the coating and on the surface. This can result in brittleness in the coating and a relatively rough surface. In many metal cutting applications, a smooth surface of the deposited wear-resistant coating is beneficial.

[0008] Reactive sputtering is the second method of PVD. In this method, a plasma of ionized inert gas is created that is bombarded with a target material. Atoms from the target material are ejected and accelerated towards the substrate in the presence of a reactive gas, e.g. nitrogen. Coatings with a smooth surface are generally obtained, since there are no problems with droplet formation. However, it is very difficult to obtain high metal ionization. Also, sputtering is a very slow deposition process.

[0009] High power impulse magnetron sputtering (HIPIMS) is a special type of sputtering that allows great flexibility in the power levels used (average power, peak pulse power) in combination with various process parameters, especially pulse on-time, and using high bias voltages. HIPIMS allows high metal ionization, enabling high quality coatings to be provided, and by controlling the level of metal ionization, very specialized coatings can be produced.

[0010] In severe cutting conditions, the heat resistance of the coating is particularly important. Heat resistance, in this context, means a low thermal conductivity of the coating, which protects the cutting tool body from excessive heat that is damaging to the substrate. The more thermally protective the coating, the better the wear resistance of the coated cutting tool. Better wear resistance means longer tool life.

[0011] PVD (Ti,Al)N coatings are commonly used as wear-resistant coatings on cutting tools.

[0012] Generally, a sufficiently high Al content is desirable because increasing the Al content leads to better oxidation stability of the (Ti,Al)N coating. Increasing the Al content also increases the hot hardness. However, a cubic structure is still desired to provide high hardness and high plane strain modulus.

[0013] It is known that the high temperature stability of the coating is improved by including Si within the (Ti,Al)N to provide a (Ti,Al,Si)N coating.

[0014] However, a drawback of (Ti,Al,Si)N is that already at a moderate Al content of the metallic element, with Si in an amount of only a few percent of the metallic element, further structures, either hexagonal or amorphous, such as amorphous grain boundary phases, can form. The hexagonal phase, like the amorphous phase, is responsible for poor mechanical properties such as insufficient hardness and insufficient plane strain modulus.

[0015] Therefore, it is desirable to provide a (Ti,Al,Si)N coating with a relatively high Al content that can enjoy the benefits of Si, and which has excellent mechanical properties and thermal stability.

[0016] It is an object of the present invention to provide a coated cutting tool including a layer of (Ti,Al,Si)N that has improved tool life over prior art coated cutting tools. The present invention

[0017]

[0006] Herein, a coated cutting tool is provided that includes a substrate and a coating, the coating having an average composition of Ti 1-x-y Al x S y the (Ti,Al,Si)N layer has a columnar grain structure; the (Ti,Al,Si)N layer contains two distinct cubic phases, one cubic phase is present within the columnar grains and one cubic phase is a grain boundary phase located between the columnar grains; and the (Ti,Al,Si)N layer has a plane strain elastic modulus of greater than or equal to 425 GPa.

[0018] Ti 1-x-y Al x S y In N, preferably, 0.52≦x≦0.58.

[0019] Ti 1-x-y Al x S y In N, 0.03≦y≦0.07 is preferable, and 0.04≦y≦0.06 is more preferable.

[0020] In a preferred embodiment, Ti 1-x-y Al x S y In N, 0.52≦x≦0.58 and 0.03≦y≦0.07.

[0021] In the most preferred embodiment, Ti 1-x-y Al x S y In N, 0.52≦x≦0.58 and 0.04≦y≦0.06.

[0022] The (Ti,Al,Si)N layers of the present disclosure are monolithic, i.e., their properties and elemental content are substantially uniform throughout the (Ti,Al,Si)N layer, in contrast to multi-layer (Ti,Al,Si)N layers.

[0023] Ti 1-x-y Al x S y When the aluminum content x in N is less than 0.50, the oxidation stability and high-temperature hardness are insufficient, and the metal cutting performance is reduced. 1-x-y Al x S y If the aluminum content x in N is higher than 0.60, there is a risk that hexagonal phases will be introduced within the (Ti,Al,Si)N layer, resulting in worse mechanical properties such as lower hardness and lower plane strain modulus, which reduces the metal cutting performance.

[0024] Ti 1-x-y Al x S y When the silicon content in N is less than 0.03, there is no grain boundary phase or an insufficient amount of grain boundary phase that reduces the metal cutting performance. 1-x-y Al xS y If the silicon content y in N is higher than 0.08, there is a risk that hexagonal phases will be introduced within the (Ti,Al,Si)N layer, resulting in worse mechanical properties such as lower hardness and lower plane strain modulus, which reduces the performance of metal cutting.

[0025] Determination of the crystalline structure or structures present in the (Ti,Al,Si)N-layer is suitably performed by X-ray diffraction analysis or TEM analysis.

[0026] The FWHM (full width at half maximum) of the diffraction peak in the X-ray diffraction analysis depends on both the crystallinity of the (Ti,Al,Si)N layer and the grain size of the crystallites: the smaller the FWHM value, the higher the crystallinity and / or the larger the grain size.

[0027] In one embodiment, the (Ti,Al,Si)N layer comprises a cubic crystal structure and, in X-ray diffraction using Cu k-alpha radiation, the FWHM (full width at half maximum) of the cubic (200) peak in a theta-2theta scan is between 0.4 and 1.5 degrees 2theta, preferably between 0.5 and 1.0 degrees 2theta.

[0028] The crystallinity of the (Ti,Al,Si)N layer itself can be expressed as measured by the peak-to-background ratio in X-ray diffraction analysis. At low crystallinity, the diffraction intensity of all (hkl) peaks from a particular crystal structure in the theta-2 theta scan is low and therefore has a low relationship to the background intensity. The following formula can be used: the highest peak I in the theta-2 theta scan of a particular crystal structure max From the intensity of background Subtract the background intensity I at the 2 theta position of the peak. background Divide by, i.e. Peak to background ratio = (I max -I background ) / I background .

[0029] Since the crystal structure may be of different preferred crystallographic orientations and the relationship between the intensities of the different (hkl) peaks in the crystal structure may vary, the highest peak of the crystal structure may be represented by I in the formula max Use as.

[0030] In the (Ti,Al,Si)N layers of the present invention, the cubic (200) peak is, in one embodiment, one of the cubic peaks that exhibits the highest intensity in an X-ray diffraction theta-2theta scan.

[0031] In one embodiment, the (Ti,Al,Si)N layer has a peak to background ratio in an X-ray diffraction analysis using Cu k-alpha radiation for the cubic (200) peak of 3 or more, preferably 4 or more. The peak to background ratio in an X-ray diffraction analysis using Cu k-alpha radiation for the cubic (200) peak of the (Ti,Al,Si)N layer is suitably any one combination of lower limits of 15 or less, preferably 12 or less.

[0032] The columnar grains in the (Ti,Al,Si)N layer preferably have a single phase cubic structure.

[0033] The grain boundary phase has an average composition Ti, suitably 0.40≦z≦0.55, preferably 0.43≦z≦0.52, suitably 0.06≦v≦0.13, preferably 0.07≦v≦0.12. 1-z-v Al z S v Has N.

[0034] In one embodiment, v>y.

[0035] In one embodiment, v / y is >1 but ≦3.5, or v / y is ≧1.2 but ≦3, or v / y is ≧1.5 but ≦2.5.

[0036] In one embodiment, x / z is ≧1 but ≦1.5, or x / z is ≧1.1 but ≦1.3.

[0037] In one embodiment, the average thickness of the grain boundary phase between the columnar grains is 0.5 to 10 nm, suitably 1 to 5 nm.

[0038] In one embodiment, the (Ti,Al,Si)N layer includes lattice planes that penetrate the columnar grains and grain boundary phases.

[0039] In addition to the cubic phase present within the columnar grains and the cubic phase being the grain boundary phase, small amounts of other phases such as hexagonal or amorphous phases may be present within the layers of (Ti,Al,Si)N. Such phases give a small, broad diffraction peak in theta-2theta X-ray diffraction covering a range of about 30-40 degrees 2theta. The peak to background ratio in X-ray diffraction analysis using Cu k-alpha radiation for this peak is suitably ≦0.25, preferably ≦0.2, most preferably ≦0.15.

[0040] In one embodiment, the (Ti,Al,Si)N layer has a thermal conductivity of ≦5 W / mK, preferably 2-4 W / mK. In wear resistant coatings on cutting tools, low thermal conductivity is beneficial to keep the heat load from the cutting process on the tool substrate as low as possible.

[0041] In one embodiment, the (Ti,Al,Si)N layer has a residual compressive stress of 1.5-6 GPa, preferably 2-4 GPa. If the residual compressive stress is too low, the coating may have insufficient toughness. On the other hand, if the residual compressive stress is too high, flaking of the coating may occur.

[0042] In one embodiment, an innermost layer of the coating of nitrides of one or more elements belonging to group 4, 5 or 6 of the periodic table of elements, or of nitrides of Al together with one or more elements belonging to group 4, 5 or 6 of the periodic table of elements, is directly on the substrate. This innermost layer acts as a tie layer to the substrate and enhances the adhesion of the entire coating to the substrate. Such tie layers are commonly used in the art and the skilled person will select an appropriate one. A preferred alternative for this innermost layer is TiN or (Ti,Al)N. The thickness of this innermost layer may vary and depends for example on the type of cutting tool, i.e. the coated insert may have an optimal innermost layer thickness different from the coated drill. The thickness of this innermost layer is suitably less than 2 μm. The thickness of this innermost layer is in one embodiment 5 nm to 2 μm, preferably 10 nm to 1 μm. It may also be necessary to have an innermost layer that acts as a barrier for Co diffusion into the coating, so the thickness should be at least 50 nm. Si-containing nitride layers are known to attract Co more than most other metal nitride layers. Thus, in a further embodiment, this innermost layer is between 50 nm and 2 μm, preferably between 100 nm and 1 μm.

[0043] In one embodiment, the (Ti,Al,Si)N layer has a Vickers hardness of 3500HV (15mN load) or more, preferably 3500HV to 3800HV (15mN load).

[0044] The (Ti,Al,Si)N layer suitably has a plane strain modulus of 425-540 GPa, preferably 450-530 GPa.

[0045] The thickness of the (Ti,Al,Si)N layer is suitably 0.5 to 10 μm, preferably 1 to 6 μm.

[0046] If the thickness of the (Ti,Al,Si)N layer is less than 0.5μm, the effect of the (Ti,Al,Si)N layer in metal cutting is insufficient, while if the thickness of the (Ti,Al,Si)N layer is more than 15μm, there is a risk of the coating flaking, which will reduce the performance of metal cutting.

[0047] The substrate of the coated cutting tool may be of any type common in the field of cutting tools for metalworking, suitably selected from cemented carbide, cermet, cubic boron nitride (cBN), ceramic, polycrystalline diamond (PCD) and high speed steel (HSS).

[0048] In one preferred embodiment, the substrate is a cemented carbide.

[0049] The coated cutting tool preferably has at least one rake face, at least one flank face, and a cutting edge therebetween.

[0050] The coated cutting tool is preferably in the form of an insert, drill or end mill.

[0051] The (Ti,Al,Si)N layer according to the present invention is suitably a sputter deposited layer, preferably a high power impulse magnetron sputtering (HIPIMS) deposited layer. [Brief description of the drawings]

[0052] [Figure 1] FIG. 1 shows a schematic diagram of one embodiment of a cutting tool that is a milling insert. [Diagram 2] FIG. 1 shows a schematic diagram of a cross section of one embodiment of a coated cutting tool of the present invention showing the substrate and coating. [Diagram 3] 1 shows a dark field TEM image of sample 1 (invention), with the dark areas showing the grain boundary phase visualized as being between the columnar grains. [Figure 4] High-resolution TEM (HR-TEM) dark-field image is shown, revealing lattice planes intersecting the columnar grains and the darker grain boundary phase. [Diagram 5] 1 shows X-ray diffraction patterns from theta-2 theta scans of the (Ti,Al,Si)N layer of sample 1 (invention) as deposited and after heat treatment at 950° C. [Figure 6]1 shows X-ray diffraction patterns from theta-2theta scans of the (Ti,Al,Si)N layer of sample 2 (invention) as deposited and after heat treatment at 950° C. [Figure 7] 4 shows X-ray diffraction patterns from theta-2theta scans of the (Ti,Al,Si)N layer of sample 3 (comparative) as deposited and after heat treatment at 950° C. [Figure 8] 1 shows an X-ray diffraction pattern from theta-2theta scan of the (Ti,Al,Si)N layer of as-deposited sample 4 (comparative). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0053] Figure 1 shows a schematic diagram of one embodiment of a cutting tool (1) having a rake face (2), a flank face (3) and a cutting edge (4). The cutting tool (1) is a milling insert in this embodiment. Figure 2 shows a schematic diagram of a cross section of an embodiment of a coated cutting tool of the invention having a substrate body (5) and a coating (6). The coating (6) consists of a first thin (Ti,Al)N innermost layer (8) followed by a (Ti,Al,Si)N layer (7).

[0054] Figure 3 shows a dark-field TEM image of sample 1 (invention). A structure with bright areas (9) and dark areas (10) showing different elemental compositions can be seen. The bright areas (9) are columnar grains, and the dark areas (10) are grain boundary phases.

[0055] Figure 4 shows a high resolution transmission electron microscope (HR-TEM) image of a cross section of one embodiment of a (Ti,Al,Si)N layer. The bright areas (9) are columnar grains and the dark areas (10) are grain boundary phases. A striped pattern is seen in the crystal structure of the entire (Ti,Al,Si)N layer analyzed, such that lattice planes intersect the columnar grains (9) and grain boundary phase (10). method X-ray diffraction:

[0056] X-ray diffraction patterns were acquired by grazing incidence mode (GIXRD) on a diffractometer manufactured by Panalytical (Empyrean). Cu-Kα radiation with a line focus was used for the analysis (voltage 40 kV, current 40 mA). The incident beam was defined by a 2 mm mask and a 1 / 8° divergence slit in addition to an X-ray mirror resulting in a parallel X-ray beam. The lateral spread was controlled by a Soller slit (0.04°). A 0,18° parallel plate collimator combined with a proportional counter (0D detector) was used in the diffracted beam path. The measurements were performed in grazing incidence mode (omega = 1°). The 2-theta range was approximately 20-80° with a step size of 0.03° and a counting time of 10 s. Peak analysis was performed using the software HighScore from PANalytical BV. TEM analysis:

[0057] Transmission electron microscopy data (selected area diffraction patterns and dark field images) were acquired using a Joel ARM200F transmission electron microscope. A high voltage of 300 kV was used for the analysis.

[0058] Where electron diffraction experiments are referred to herein, these are TEM measurements made with collimated illumination: a region of interest was selected with a selected area aperture.

[0059] A FIB (focused ion beam) lift-out was used for TEM sample preparation. For final polishing, the Ga ion beam was adjusted to a low voltage of about 5 kV and a low current of about 200–500 pA.

[0060] A cross section of the coating was analyzed perpendicular to the surface of the coating.

[0061] Analysis of the thickness of the grain boundary phase can be performed by image analysis by determining the change in brightness of the TEM image along the intersection lines. The grain boundary phase is dark in the image so that the thickness can be determined. A sufficient length and / or number of intersection lines are drawn to provide a reliable average value of the grain boundary phase thickness. Preferably, at least 20 grain boundaries are intersected and the average value is calculated. Elemental content:

[0062] It should be noted that the content of metal elements, nitrogen and argon in the coating can be measured by scanning transmission electron microscopy (STEM) with energy dispersive X-ray spectroscopy (EDX) on cross-sections of samples prepared by FIB. The TEM imaging and EDX analysis used in the analysis in this disclosure used a Jeol ARM System instrument equipped with a field emission gun, secondary electron detector, and a Si(Li) energy dispersive X-ray (EDX) detector manufactured by Oxford Instruments. Use a spot size small enough to probe, for example, grain boundaries, or use STEM mode to obtain elemental mapping over distances in the coating. Residual stress

[0063] Residual stress is sin 2 Measured by XRD using the Ψ method (see ME Fitzpatrick, ATFry, P. Holdway, FA Kandil, J. Shackleton and L. Suominen - A Measurement Good Practice Guide No. 52; "Determination of Residual Stresses by X-ray Diffraction - Issue 2", 2005).

[0064] The lateral tilt method (Ψ-geometry) is based on the selected sin 2Eight Ψ angles equidistant in the Ψ range have been used. An equidistant distribution of Φ angles in a Φ sector of 90° is preferred. For the calculation of the residual stress values, a Poisson's ratio of 0.20 and a Young's modulus E of 450 GPa were applied. For measurements on (Ti,Al,Si)N layers, the data were evaluated using a commercial software (RayfleX version 2.503) that locates the (200) reflection of (Ti,Al,Si)N by a Pseudo-Voigt-Fit function. For the measurement of residual stresses in a layer of a coating with further deposited layers on top of the coating itself, the coating material is removed on top of the layer to be measured. Care must be taken to select and apply a material removal method that does not significantly change the residual stresses in the remaining (Ti,Al,Si)N multilayer material. A suitable method for removing the deposited coating material may be polishing, but gentle and slow polishing using fine-grain abrasives should be applied. Aggressive polishing using coarse-grain abrasives rather increases the compressive residual stresses, as is known in the art. Other suitable methods for removing deposited coating material are ion etching and laser ablation. Thermal Conductivity

[0065] The thermal conductivity of the coatings produced in this invention was measured using the Time Domain Thermoreflectance (TDTR) method with the following characteristics:

[0066] 1. A laser pulse (Pump) is used to locally heat the sample.

[0067] 2.Depending on the thermal conductivity and heat capacity, heat energy is transferred from the sample surface to the substrate. The temperature of the surface decreases with time.

[0068] 3. The fraction of the laser that is reflected depends on the surface temperature. A second laser pulse (the probe pulse) is used to measure the temperature drop of the surface.

[0069] 4. By using a mathematical model, the thermal conductivity can be calculated using the heat capacity value of the sample as well. (See DG Cahill, Rev. Sci. Instr. 75, 5119 (2004)).

[0070] The sample should be polished to a mirror finish before the measurement. Vickers hardness:

[0071] The Vickers hardness was measured by nanoindentation (load-depth graph) using a Picodentor HM500 from Helmut Fischer GmbH, Sindelfingen, Germany. For the measurements and calculations, the Oliver and Pharr evaluation algorithm was applied, in which a Vickers diamond specimen was pressed into the layer and the force-path curve was recorded during the measurements. The maximum load used was 15 mN (HV 0.0015), the load increase and load decrease times were 20 s each, and the hold time (creep time) was 10 s. The hardness was calculated from this curve. Plane Strain Modulus:

[0072] The elastic properties of the coating samples were determined by the so-called plane strain elastic modulus E, derived by nanoindentation according to the Oliver and Pharr method. ps Nanoindentation data was obtained from indentation as described for Vickers hardness above. Thickness:

[0073] The thickness of the coating layer was determined by calotte grinding, whereby a steel ball with a diameter of 30 mm was used to grind the dome-shaped recess, and the ring diameter was measured and the layer thickness was calculated from it. The layer thickness measurements on the rake face (RF) of the cutting tool were made at a distance of 2000 μm from the corner, and the flank face (FF) measurements were made in the center of the flank face of the ground test specimen. EXAMPLES

[0074] Example 1 (present invention): Composition Ti 0.40Al 0.60 An initial layer of (Ti,Al)N was deposited on a WC-Co based substrate using three targets with the composition Ti 0.40 Al 0.55 S 0.06 A (Ti, Al, Si)N layer was further deposited using three targets with the following geometry: WC-Co based substrates were cutting tools, milling inserts of geometry ADMT 160608R-F56, ROHX1204M0-D67, and flat inserts using HIPIMS mode in an Oerlikon Balzers Ingenia machine using S3p technology (to facilitate analysis of the coating). The substrates had a composition of 8 wt.% Co and balance WC.

[0075] An uncoated insert blank was mounted and rotated in the PVD chamber during deposition of the coating.

[0076] The deposition process was carried out in HIPIMS mode using the following process parameters:

[0077] Starting layer of (Ti,Al)N: Target material: Ti 0.40 Al 0.60 (3 targets) Target size: circular, diameter 160mm Thickness: 12mm Average power per target: 9.06kW Peak pulse power: 60kW Pulse on time: 7.56ms Temperature: 430°C Total pressure: 0.6Pa (N2+Ar) Argon pressure: 0.42Pa Bias potential: -40V Repetitive Pulse Number Per cycle: 1

[0078] A layer thickness of approximately 200 nm was deposited.

[0079] (Ti,Al,Si)N layer: Target material: Ti 0.40 Al 0.54 S 0.06 Target size: circular, diameter 160mm Thickness: 12mm Average power per target: 4.8kW Peak pulse power: 60kW Pulse on time: 4ms Temperature: 430°C Total pressure: 0.6Pa Argon pressure: 0.42Pa Bias potential: -40V Repetitive Pulse Number Per cycle: 1

[0080] A (Ti,Al,Si)N layer was deposited on the milling insert with a thickness of about 2.5 μm as measured on the flank face of the insert.

[0081] The coated cutting tool provided is referred to as "Sample 1 (Invention)". Example 2 (present invention):

[0082] The target material used in the process for depositing the (Ti,Al,Si)N layer is Ti 0.40 Al 0.54 S 0.06 Instead of Ti 0.40 Al 0.56 S 0.04 Further samples within the present invention were prepared in the same manner as described in Example 1, except that:

[0083] The WC-Co based substrate was a cutting tool with a flat insert (to facilitate analysis of the coating).

[0084] A (Ti,Al,Si)N layer having a thickness of about 1.5 μm as measured on the rake face of the insert was deposited on the insert.

[0085] The coated cutting tool provided is referred to as "Sample 2 (Invention)". Example 3 (Comparative):

[0086] The target material used in the process for depositing the (Ti,Al,Si)N layer is Ti 0.40 Al 0.54 S 0.06 Instead of Ti 0.39 Al 0.59 S 0.02 Further samples within the invention were made in the same manner as described in Example 1, except that:

[0087] The WC-Co based substrate was a cutting tool with a flat insert (to facilitate analysis of the coating).

[0088] A (Ti,Al,Si)N layer having a thickness of about 1.6 μm as measured on the rake face of the insert was deposited on the insert.

[0089] The coated cutting tool provided is referred to as "Sample 3 (comparative)." Example 4 (Comparative):

[0090] Composition Ti 0.35 Al 0.55 S 0.10 (Ti,Al,Si)N layers from a target with were deposited on WC-Co based substrates of turning inserts type ADMT 160608R-F56 ​​and flat cutting inserts (to facilitate analysis of the coating). The substrates had a composition of 8 wt.% Co and balance WC. An uncoated insert blank was mounted and rotated in the PVD chamber during deposition of the coating.

[0091] The deposition was carried out using HIPIMS mode on an Oerlikon Balzers tool using S3p technology with the following process parameters: Target material 2: Ti 0.35 Al 0.55 S 0.10 Target size: circular, diameter 150mm Average power per target: 5.1kW Peak pulse power: 30kW Pulse on time: 0.2ms Pulse frequency 20Hz Temperature: 450°C Total pressure: 0.64Pa Argon pressure: 0.43Pa Bias potential: -80V Repetitive Pulse Number Per cycle: 43

[0092] A (Ti,Al,Si)N layer was deposited on the milling insert with a thickness of about 2.5 μm as measured on the flank face of the insert.

[0093] The coated cutting tool provided is referred to as "Sample 4 (comparative)." Example 5 (Comparative):

[0094] Composition Ti 0.40 Al 0.54 S 0.06 (Ti,Al,Si)N layers from a target with were deposited on WC-Co based substrates of milling inserts and flat cutting inserts with SPMW12 geometry (to facilitate analysis of the coating). The substrates had a composition of 8 wt% Co and balance WC. Uncoated insert blanks were mounted and rotated in the PVD chamber during deposition of the coating.

[0095] The deposition was carried out using cathodic arc deposition in a Hauzer HTC1000 tool using the following process parameters: Starting layer of (Ti,Al)N: Target material: Ti 0.40 Al 0.60 Target size: circular, diameter 104mm Arc current: 150A N2 pressure: 10Pa Temperature: 430°C Bias potential: -40V

[0096] A layer thickness of approximately 340 nm was deposited. (Ti, Al, Si)N layer: Target material: Ti 0.40 Al 0.54 S 0.06 Target size: circular, diameter 104mm Arc current: 150A N2 pressure: 10Pa Temperature: 430°C Bias potential: -60V

[0097] A (Ti,Al,Si)N layer was deposited on the milling insert with a thickness of about 2.5 μm as measured on the flank face of the insert.

[0098] The coated cutting tool provided is referred to as "Sample 5 (comparative)". Example 6 (Comparative):

[0099] Composition Ti 0.40 Al 0.60 A (Ti,Al)N layer from a target with was deposited on a WC-Co based substrate, a cutting tool with a turning insert type ROHX1204M0-D67 and a flat insert (to facilitate the analysis of the coating), using the HIPIMS mode in an Oerlikon Balzers device using the S3p technique. This HIPIMS deposited coating was known to give very good results in the machining of stainless steel (ISO-M) material.

[0100] The substrate had a composition by weight of 8% Co and balance WC. An uncoated insert blank was mounted and rotated in the PVD chamber during deposition of the coating.

[0101] The deposition process was carried out in HIPIMS mode using the following process parameters: Target material 1: Ti 0.40 Al0.60 Target size: circular, diameter 160mm Target thickness: 12mm Average power per target: 4.8kW Peak pulse power: 60kW Pulse on time: 4ms Temperature: 430°C Total pressure: 0.55Pa Argon pressure: 0.43Pa Bias potential: -80V Repetitive Pulse Number Per cycle: 1

[0102] A (Ti,Al,Si)N layer was deposited on the milling insert with a thickness of about 2.5 μm as measured on the flank face of the insert.

[0103] The coated cutting tool provided is referred to as "Sample 6 (comparative)." Example 7 (Analysis):

[0104] X-ray diffraction (XRD) theta-2theta analysis was carried out for samples 1-4.

[0105] 5 to 8 show XRD theta-2theta diffractograms of Sample 1 (invention), Sample 2 (invention), Sample 3 (comparison), and Sample 4 (comparison).

[0106] The diffractograms of Sample 1 (invention) and Sample 2 (invention) are seen to exhibit a cubic crystal structure. The diffractograms show significant cubic (111) and (200) peaks at about 37-38 degrees 2-theta and about 43-44 degrees 2-theta, respectively. The peaks are also very sharp, implying significant crystallinity. The most intense peak is the (200) peak. The peak-to-background ratio of the (200) peak is estimated to be about 5.0 for Sample 1 (invention) and about 8.1 for Sample 2 (invention).

[0107] The FWHM (full width at half maximum) of the cubic (200) peak is about 0.8 degrees 2-theta for sample 1 (invention) and about 0.6 degrees 2-theta for sample 2 (invention).

[0108] The diffractogram of sample 4 (comparison) shows a much less significant cubic (111) peak and a cubic (200) peak than sample 1 (invention) and sample 2 (invention). The (111) peak can hardly be distinguished from a broad basal reflection ranging from about 31 to 39 degrees 2-theta. There is also a broad basal reflection ranging from about 40 to 45 degrees 2-theta that covers the position where the cubic (200) peak is present. These broad reflections imply the presence of significant amorphous structure. A much lower degree of crystallinity can be determined from the peak-to-background ratio of the (200) peak, which is only estimated to be about 0.3.

[0109] The full width at half maximum (FWHM) of this minor cubic (200) peak is very difficult to determine but is estimated to be about 4 degrees 2-theta.

[0110] The average content of each metal element in the (Ti, Al, Si)N layer is assumed to reflect the target composition, i.e., the deposited layer is assumed to be that found in Table 1.

[0111] Table 1 TIFF2025513252000002.tif50170

[0112] Transmission electron microscopy (TEM) analysis was performed on sample 1 (invention), sample 2 (invention) and sample 3 (comparison). Columnar microstructures were found in their (Ti,Al,Si)N layers. Further observation of dark field imaging of the (Ti,Al,Si)N layers of the samples revealed the presence of grain boundary phase in sample 1 (invention) and sample 2 (invention). No grain boundary phase was found in the dark field TEM image of sample 3 (comparison). No grain boundary phase was found in the dark field TEM image of the (Ti,Al,Si)N layer of sample 5 (comparison). Figure 3 shows the dark field TEM image of the (Ti,Al,Si)N layer of sample 1 (invention). It can be seen that the grain boundary phase was visualized as dark areas are found between the columnar grains.

[0113] Furthermore, from a high-resolution TEM (HR-TEM) dark-field image of the (Ti,Al,Si)N layer of sample 1 (invention), referring to FIG. 4, lattice planes are visible that intersect the columnar grains and the darker grain boundary phase.

[0114] Electron energy loss spectroscopy (EELS) of the (Ti,Al,Si)N layer of sample 1 (invention) concluded that the grain boundary phase is a cubic (Ti,Al,Si)N phase. The EELS spectrum has no ionization edges, indicating the presence of a hexagonal phase. The EELS spectrum further shows that the elemental content of Ti, Al and Si in the grain boundary phase is different from the average elemental content in the whole (Ti,Al,Si)N layer. For the EELS analysis, the equipment Jeol ARM200F equipped with a Gatan Quantum ER spectrometer was used. The high voltage was set at 300 kV. The system was tuned more for intensity rather than resolution, which meant that the energy resolution was only 1.3 eV. The spectrum was acquired in STEM mode using Spot5, a measure of spot size.

[0115] Using STEM-EDX, measurements were taken at four different locations in the grain boundary phase, and the average element contents of Ti, Al, and Si in the grain boundary phase of sample 1 (the present invention) were Ti: 43 at%, Al: 46 at%, and Si: 11 at%.

[0116] For Sample 1 (the present invention), the thickness of the grain boundary phase was estimated to be about 2 nm from TEM analysis.

[0117] Furthermore, scanning electron microscope (SEM) analysis of sample 5 (comparative) showed a columnar microstructure of the (Ti,Al,Si)N layer.

[0118] Residual stresses were also measured for sample 1 (invention) and sample 2 (invention) and showed values ​​of -2 to -3 GPa for the deposited samples. Further heat treatment at 950°C for 1 hour did not show any significant relaxation, i.e. no reduction in residual stress, indicating no substantial formation of the hexagonal phase.

[0119] Table 2 TIFF2025513252000003.tif35170

[0120] Furthermore, phase stability was determined by XRD measurements of samples heat treated at 950°C for 1 hour. For example, the cubic (200) peak at about 42-43 degrees 2-theta for Sample 1 (invention) and Sample 2 (invention) showed only minor changes in the (200) peak shape. See Figures 5 and 6. However, Sample 3 (comparison) showed significant broadening of the (200) peak (see Figure 7), indicating reduced crystallinity and / or other changes in structure. Thus, Sample 3 (comparison) is less thermally stable than Sample 1 (invention) and Sample 2 (invention).

[0121] The thermal conductivity was determined using the time domain thermoreflectance (TDTR) method, and the results are shown in Table 3.

[0122] Table 3 TIFF2025513252000004.tif29170

[0123] The results for Sample 1 (the present invention) showed that, despite its cubic columnar structure, it had a low thermal conductivity of 3.1 W / mK, which was advantageous for metal cutting, which generates a lot of heat.

[0124] Hardness measurements (load 15 mN) were carried out on the coated tools of Samples 1 to 5 to determine the Vickers hardness and plane strain modulus. The results are shown in Table 4.

[0125] Table 4 TIFF2025513252000005.tif67170

[0126] The very high values ​​of the plane strain modulus, well above 400 GPa, reflect a high degree of cubic structure even for the samples according to the invention with 4 and 6 at% Si of Ti, Al and Si. Surprisingly, Sample 1 and Sample 2 had such high values ​​for the plane strain modulus. Example 8: Cutting test of sample 1 (invention) and sample 4 (reference):

[0127] Milling inserts of the ADMT160608R-F56 ​​type, sample 1 (invention) and sample 4 (comparison), were tested in milling tests and the average flank wear was measured. The cutting conditions are summarized in Table 5. Stainless steel ISO-M was used as the workpiece. Cutting conditions:

[0128] Table 5 TIFF2025513252000006.tif59170

[0129] Three cutting edges were tested for each sample and the average length of cut is shown in Table 6.

[0130] Table 6 TIFF2025513252000007.tif34170

[0131] Sample 1 (invention) performs better than sample 4 (comparison). Cutting test of sample 1 (invention) and sample 6 (reference):

[0132] Milling inserts of the ROHX1204M0-D67 type, sample 1 (invention) and sample 6 (comparison), were tested in milling tests and the average flank wear was measured. The cutting conditions are summarized in Table 7. Stainless steel ISO-M was used as the workpiece. Cutting conditions:

[0133] Table 7 TIFF2025513252000008.tif52170

[0134] Four cutting edges were tested for each sample and the average length of cut is shown in Table 8.

[0135] Table 8 TIFF2025513252000009.tif34170

[0136] Sample 1 (invention) performs better than sample 6 (comparison). Cutting test of sample 1 (invention) and sample 5 (comparison):

[0137] Milling inserts of the SPMW12 type, sample 1 (invention) and sample 5 (comparison), were tested in milling tests to measure the flank wear. The cutting conditions are summarized in Table 9. The stainless steel ISO-P, 42CrMo4, was used as the workpiece. Cutting conditions:

[0138] Table 9 TIFF2025513252000010.tif59170

[0139] The wear values ​​(averaged over the cutting edge) for each cutting length are shown in Table 10.

[0140] Table 10 TIFF2025513252000011.tif34170

[0141] Sample 1 (invention) performs better than sample 5 (comparison).

Claims

1. A coated cutting tool (1) comprising a substrate (5) and a coating (6), wherein the coating (6) has an average composition Ti １－ｘ－ｙ Al ｘ Si ｙ A coated cutting tool (1) comprising a 0.5 to 15 μm monolithic layer (7) of (Ti,Al,Si)N having a crystalline structure of 0.50≦x≦0.60, 0.03≦y≦0.08, wherein the (Ti,Al,Si)N layer (7) has a columnar crystal grain (9) structure, the (Ti,Al,Si)N layer (7) contains two different cubic phases, one of which is present within the columnar crystal grains (9) and the other of which is a grain boundary phase (10) located between the columnar crystal grains (9), and the (Ti,Al,Si)N layer (7) has a plane strain elastic modulus of 425 GPa or more.

2. Ti １－ｘ－ｙ Al ｘ Si ｙ 2. The coated cutting tool (1) according to claim 1, wherein, in N, 0.52≦x≦0.58 and 0.03≦y≦0.

07.

3. The grain boundary phase (10) has an average composition of Ti １－ｚ－ｖ Al ｚ Si ｖ 2. The coated cutting tool (1) according to claim 1, wherein N, 0.40≦z≦0.55 and 0.06≦v≦0.

13.

4. 4. The coated cutting tool (1) according to claim 3, wherein v>y.

5. 2. The coated cutting tool (1) according to claim 1, wherein the grain boundary phase (10) between the columnar crystal grains (9) has an average thickness of 0.5 to 10 nm.

6. 2. The coated cutting tool (1) according to claim 1, wherein the (Ti,Al,Si)N layer (7) comprises lattice planes that penetrate the columnar grains (9) and the grain boundary phase (10).

7. 2. The coated cutting tool (1) according to claim 1, wherein the (Ti,Al,Si)N layer (7) has a thermal conductivity of 5 W / mK or less.

8. The coated cutting tool (1) according to claim 1, wherein the (Ti,Al,Si)N layer (7) has a residual compressive stress of 1.5 to 6 GPa.

9. 2. The coated cutting tool (1) according to claim 1, wherein an innermost layer (8) of a coating of nitrides of one or more elements belonging to group 4, 5 or 6 of the periodic table of the elements or nitrides of Al with one or more elements belonging to group 4, 5 or 6 of the periodic table of the elements is present directly on the substrate, and the thickness of the innermost layer (8) is between 5 nm and 2 μm.

10. 2. The coated cutting tool (1) according to claim 1, wherein the (Ti,Al,Si)N layer (7) has a Vickers hardness of 3500 HV (15 mN load) or more.

11. The coated cutting tool (1) according to claim 1, wherein the (Ti,Al,Si)N layer (7) has a plane strain modulus of elasticity of 425 to 540 GPa.

12. The coated cutting tool (1) according to claim 1, wherein the (Ti,Al,Si)N layer (7) has a thickness of 0.5 to 10 μm.

13. 2. The coated cutting tool (1) according to claim 1, wherein the substrate (5) is selected from cemented carbide, cermet, cubic boron nitride (cBN), ceramic, polycrystalline diamond (PCD) and high speed steel (HSS).

14. 2. A coated cutting tool (1) according to claim 1 in the form of an insert, a drill or an end mill.

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