COATED CUTTING TOOL

Abstract

A coated cutting tool including a substrate and a coating is provided. The coating includes a nano-multilayer of alternating layers of a first nanolayer being Ti.sub.1-xAl.sub.xN, 0.35≤x≤0.70, and a second nanolayer being Ti.sub.1-yAl.sub.yN, 0.12≤y≤0.25. A sequence of one first nanolayer and one second nanolayer forms a layer period. The average layer period thickness in the nano-multilayer is ≤7 nm. The nanomultilayer has a columnar structure with an average column width of ≤70 nm.

Claims

1. A coated cutting tool comprising: a substrate; and a coating, wherein the coating comprises a nano-multilayer of alternating layers of a first nanolayer being Ti.sub.1-xAl.sub.xN, 0.35≤x≤0.70, and a second nanolayer being Ti.sub.1-yAl.sub.yN, 0.12≤y≤0.25, a sequence of one first nanolayer and one second nanolayer forming a layer period, and wherein an average layer period thickness in the nano-multilayer is ≤7 nm, the nano-multilayer having a columnar structure with an average column width of ≤70 nm.

2. The coated cutting tool according to claim 1, wherein for the first nanolayer Ti.sub.1-xAl.sub.xN, 0.45≤x≤0.70.

3. The coated cutting tool according to claim 1, wherein for the second nanolayer Ti.sub.1-yAl.sub.yN, 0.14≤y≤0.23.

4. The coated cutting tool according to claim 1, wherein the average layer period thickness in the nano-multilayer is from 2 to 7 nm.

5. The coated cutting tool according to claim 1, wherein the nano-multilayer has an average column width of ≤55 nm.

6. The coated cutting tool according to claim 1, wherein the nano-multilayer has an average column width of 30 to 45 nm.

7. The coated cutting tool according to claim 1, wherein a FWHM value for a cubic peak in X-ray diffraction is from 0.8 to 1.2 degrees (2theta).

8. The coated cutting tool according to claim 1, wherein a thickness of the nano-multilayer is from about 0.5 to about 15 μm.

9. The coated cutting tool according to claim 1, wherein a thickness of the nano-multilayer is from about 1 to about 7 μm.

10. The coated cutting tool according to claim 1, wherein the coating includes an innermost layer of TiN, (Ti,Al)N or (Cr,Al)N below the nano-multilayer closest to the substrate having a thickness of from about 0.1 to about 2 μm.

11. The coated cutting tool according to claim 10, wherein the innermost layer is Ti.sub.1-zAl.sub.zN, 0.35≤z≤0.70.

12. The coated cutting tool according to claim 1, wherein the nano-multilayer is a cathodic arc evaporation deposited layer.

13. The coated cutting tool according to claim 1, wherein the substrate of the coated cutting tool is selected from the group of cemented carbide, cermet, ceramic, cubic boron nitride and high speed steel.

14. The coated cutting tool according to claim 1, wherein the coated cutting tool is a cutting tool insert, a drill, or a solid end-mill, for metal machining.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0030] FIG. 1 shows a schematic view of one embodiment of a cutting tool being a milling insert.

[0031] FIG. 2 shows a schematic view of a cross section of an embodiment of the coated cutting tool of the present invention showing a substrate and a coating comprising different layers.

[0032] Detailed description of embodiments in drawings FIG. 1 shows a schematic view of one embodiment of a cutting tool (1) having a rake face (2) and flank faces (3) and a cutting edge (4). The cutting tool (1) is in this embodiment a milling insert. FIG. 2 shows a schematic view of a cross section of an embodiment of the coated cutting tool of the present invention having a substrate body (5) and a coating (6). The coating consisting of a first (Ti,Al)N innermost layer (7) followed by a nano-multilayer (8) of alternating nanolayers being Ti.sub.1-xAl.sub.xN (9) and nanolayers being Ti.sub.1-xAl.sub.xN (10).

EXAMPLES

Example 1

[0033] Different nano-multilayers of (Ti,Si)N and (Ti,Al)N were deposited on sintered cemented carbide cutting tool insert blanks of the geometries SNMA120408, CNMG120408MM and R390-11. The composition of the cemented carbide was 10 wt % Co, 0.4 wt % Cr and rest WC. The cemented carbide blanks were coated by cathodic arc evaporation in a vacuum chamber comprising four arc flanges. Targets of Ti—Si were mounted in two of the flanges opposite each other. Targets of Ti—Al were mounted in the two remaining flanges opposite each other. The targets were circular and planar with a diameter of 100 mm available on the open market. Suitable target technology packages for arc evaporation are available from suppliers on the market such as IHI Hauzer Techno Coating B. V., Kobelco (Kobe Steel Ltd.) and Oerlikon Balzers.

[0034] The uncoated blanks were mounted on pins that undergo a three-fold rotation in the PVD chamber.

[0035] Samples 1-9:

[0036] The chamber was pumped down to high vacuum (less than 10.sup.−2 Pa) and heated to 450-550° C. by heaters located inside the chamber. The blanks were then etched for 60 minutes in an Ar plasma.

[0037] The chamber pressure (reaction pressure) was set to 4 Pa of N.sub.2 gas, and a DC bias voltage of −50 V (relative to the chamber walls) was applied to the blank assembly. The cathodes were run in an arc discharge mode at a current of 150 A (each) for 75 minutes (4 flanges). A nano-multilayer coating having a thickness of about 3 μm was deposited on the blanks.

[0038] Depositions were made with combinations of Ti—Si targets being Ti.sub.0.80Si.sub.0.20, Ti.sub.0.85Si.sub.0.15 and Ti.sub.0.90Si.sub.0.10, and Ti—Al targets being Ti.sub.0.75Al.sub.0.25, Ti.sub.0.60Al.sub.0.40, Ti.sub.0.50Al.sub.0.50, and Ti.sub.0.40Al.sub.0.60. The total thickness of the deposited nano-multilayers were 3 μm. The rotational speed correlates to a certain period thickness. In order to investigate the effect of the layer period thickness in the nano-multilayer a series of depositions of blanks were made using different table rotational speeds.

[0039] Due to the target set-up two nanolayer periods are formed per revolution of the substrate table. In the equipment used the correlation between table rotational speed and nanolayer period thickness is shown in Table 1.

TABLE-US-00001 TABLE 1 Table rotational speed Estimated nanolayer period thickness* 1 rpm 20 nm 2 rpm 10 nm 2.4 rpm 8 nm 3 rpm 7 nm 4 rpm 5 nm 5 rpm 4 nm *sum of thickness of one nanolayer (Ti, Al)N and one nanolayer (Ti, Si)N

[0040] In most samples an innermost, about 1 μm thick, layer of (Ti,Al)N was deposited. In all such cases the (Ti,Al)N layer was deposited using the same content of Ti and Al in the targets as when making the (Ti,Al)N nanolayer in the above-deposited nano-multilayer. The process conditions when depositing the innermost (Ti,Al)N layer were: a chamber pressure (reaction pressure) of 4 Pa of N.sub.2 gas, and a DC bias voltage of −70 V (relative to the chamber walls) applied to the blank assembly. The cathodes were run in an arc discharge mode at a current of 150 A (each).

[0041] The samples 1-12 made are listed in Table 2.

TABLE-US-00002 TABLE 2 First Second Layer Innermost Sample nanolayer nanolayer period layer 1 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm — 2 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm — 3 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 20 nm — 4 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm Ti.sub.0.40Al.sub.0.60N, 1 μm 5 Ti.sub.0.50Al.sub.0.50N Ti.sub.0.80Si.sub.0.20N 4 nm Ti.sub.0.50Al.sub.0.50N, 1 μm 6 Ti.sub.0.60Al.sub.0.40N Ti.sub.0.80Si.sub.0.20N 4 nm Ti.sub.0.60Al.sub.0.40N, 1 μm 7 Ti.sub.0.75Al.sub.0.25N Ti.sub.0.80Si.sub.0.20N 4 nm Ti.sub.0.75Al.sub.0.25N, 1 μm 8 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.85Si.sub.0.15N 4 nm Ti.sub.0.40Al.sub.0.60N, 1 μm 9 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.90Si.sub.0.10N 4 nm Ti.sub.0.40Al.sub.0.60N, 1 μm 10 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm Ti.sub.0.40Al.sub.0.60N, 0.2 μm 11 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm Ti.sub.0.40Al.sub.0.60N, 0.4 μm 12 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm Ti.sub.0.40Al.sub.0.60N, 0.8 μm (~1 μm)

[0042] Samples 13-17:

[0043] Samples were further made using DC bias voltage and N.sub.2 pressure combinations other than −50 V/4 Pa.

[0044] The chamber was pumped down to high vacuum (less than 10.sup.−2 Pa) and heated to 450-550° C. by heaters located inside the chamber. The blanks were then etched for 60 minutes in an Ar plasma.

[0045] An about 1 μm thick innermost layer of Ti.sub.0.40Al.sub.0.60 was first deposited. The process conditions were: a chamber pressure (reaction pressure) of 4 Pa of N.sub.2 gas, and a DC bias voltage of −70 V (relative to the chamber walls) applied to the blank assembly. The cathodes were run in an arc discharge mode at a current of 150 A (each).

[0046] Then for the deposition of nano-multilayers of (Ti,Si)N and (Ti,Al)N different chamber pressures (reaction pressure) of between 2 and 6 Pa of N.sub.2 gas were used, and different unipolar DC bias voltages of between −30 V and −100 V (relative to the chamber walls) were applied to the blank assembly for the different samples. The cathodes were run in an arc discharge mode at a current of 150 A (each). Nano-multilayers having a thickness of about 2 μm were deposited on the blanks, i.e., a total coating thickness of about 3 μm was provided on each insert.

[0047] Depositions were made with a combination of Ti—Si targets being Ti.sub.0.80Al.sub.0.20and Ti—Al targets being Ti.sub.0.40Al.sub.0.60. The depositions were made using a table rotational speed of 5 rpm, i.e., giving a layer period thickness of about 4 nm in the nano-multilayer.

[0048] The samples 13-17 made are listed in Table 3.

TABLE-US-00003 TABLE 3 First Second Layer DC bias Sample nanolayer nanolayer period voltage N.sub.2 pressure 13 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm −30 V 4 Pa 14 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm −70 V 4 Pa 15 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm −100 V 4 Pa 16 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm −50 V 2 Pa 17 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm −50 V 6 Pa

[0049] In order to confirm the actual elemental composition in the nano-multilayer the average composition was analysed by using energy-dispersive X-ray spectroscopy (EDS) for some samples. The EDS measurements were made over a distance comprising a number of nanolayers in SEM on a cross-section of the coating.

[0050] The result was that deviations of only 1-2 percentage units from the theoretical composition were seen. This is within the accuracy of the EDS method. It is therefore concluded that the actual elemental composition of Ti, Al and Si in the layers substantially correspond well to the respective target compositions used.

[0051] X-ray diffraction (XRD) analysis was conducted on the flank face of coated inserts using a Bruker D8 Discover diffractometer equipped with a 2D detector (VANTEC-500) and a IμS X-ray source (Cu-K.sub.a, 50.0 kV, 1.0 mA) with an integrated parallel beam Montel mirror. The coated cutting tool inserts were mounted in sample holders that ensure that the flank face of the samples were parallel to the reference surface of the sample holder and also that the flank face was at appropriate height. The diffracted intensity from the coated cutting tool was measured around 20 angles where relevant peaks occur, so that at least 35° to 50° is included. Data analysis, including background subtraction and Cu-K.sub.a2 stripping, was performed using PANalytical's X′Pert HighScore Plus software. A Pseudo-Voigt-Fit function was used for peak analysis. No thin film correction was applied to the obtained peak intensities. Possible peak overlap of a (200) peak with any diffraction peak not belonging to the PVD layer, e.g., a substrate reflection like WC, was compensated for by the software (deconvolution of combined peaks) when determining the peak intensities and peak widths. The full width at half maximum (FWHM) value for the (200) peak of the samples was calculated. The results are shown in Table 4.

TABLE-US-00004 TABLE 4 DC N.sub.2 FWHM Sam- First Second Layer bias pres- I(200), ple nanolayer nanolayer period voltage sure [º2θ] 1 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm  −50 V 4 Pa 0.7 2 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm  −50 V 4 Pa — 3 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 20 nm  −50 V 4 Pa — 4 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm  −50 V 4 Pa 0.6 5 Ti.sub.0.50Al.sub.0.50N Ti.sub.0.80Si.sub.0.20N 4 nm  −50 V 4 Pa — 6 Ti.sub.0.60Al.sub.0.40N Ti.sub.0.80Si.sub.0.20N 4 nm  −50 V 4 Pa — 7 Ti.sub.0.75Al.sub.0.25N Ti.sub.0.80Si.sub.0.20N 4 nm  −50 V 4 Pa — 8 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.85Si.sub.0.15N 4 nm  −50 V 4 Pa — 9 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.90Si.sub.0.10N 4 nm  −50 V 4 Pa — 10 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm  −50 V 4 Pa — 11 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm  −50 V 4 Pa — 12 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 8 nm  −50 V 4 Pa — 13 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm  −30 V 4 Pa 0.6 14 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm  −70 V 4 Pa 0.7 15 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm −100 V 4 Pa 1.0 16 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm  −50 V 2 Pa 0.7 17 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 4 nm  −50 V 6 Pa 0.6

Example 2

[0052] Cutting tests were made in order to determine the performance of the samples made.

[0053] Explanations to Terms Used:

[0054] The following expressions/terms are commonly used in metal cutting, but nevertheless explained in the table below: [0055] Vc (m/min): cutting speed in meters per minute [0056] fz (mm/tooth): feed rate in millimeter per tooth (in milling) [0057] fn (mm/rev) feed rate per revolution (in turning) [0058] z: (number) number of teeth in the cutter [0059] a.sub.e (mm): radial depth of cut in millimeter [0060] a.sub.p (mm): axial depth of cut in millimeter

[0061] Comb Crack Resistance: [0062] Operation: Shoulder milling [0063] Tool holder: R245-080027-12M, Dc=80 mm [0064] Work piece material: Toolox 33 (tool steel), L=600 mm, 1=200 mm, h=100 mm, [0065] Insert type: R390-11 [0066] Cutting speed V.sub.c=320 m/min [0067] Feed rate f.sub.z=0.3 mm/rev [0068] Depth of cut a.sub.p=2 mm [0069] Radial engagement a.sub.e=15 mm [0070] with cutting fluid

[0071] The criteria for end of tool life is a max. chipped height VB>0.3 mm.

[0072] Edge Line Toughness: [0073] Work piece material: Dievar unhardened, P3. 0.Z.AN, [0074] z=1 [0075] V.sub.c=200 m/min [0076] f.sub.z=0.20 mm [0077] a.sub.e=12 mm [0078] a.sub.p=3.0 [0079] length of cut=12 mm [0080] without cutting fluid

[0081] The cut-off criteria are chipping of at least 0.5 mm of the edge line or a measured depth of 0.2 mm at either the flank- or the rake phase. Tool life is presented as the number of cut entrances in order to achieve these criteria.

[0082] Flank Wear Test: [0083] Longitudinal turning [0084] Work piece material: Sverker 21 (tool steel), Hardness ˜210HB, D=180, L=700 mm, [0085] V.sub.c=125 m/min [0086] f.sub.n=0.072 mm/rev [0087] a.sub.p=2 mm [0088] without cutting fluid

[0089] The cut-off criteria for tool life is a flank wear VB of 0.15 mm.

[0090] Flaking Resistance:

[0091] The evaluation was made through turning test in austenitic steel. In order to provoke adhesive wear and flaking of the coating the depth of cut a.sub.p was varied between 4 to 0 and 0 to 4 mm (in one run during radial facing). The inserts were evaluated through SEM analysis. [0092] Operation: Facing (turning) [0093] Work piece material: Bar of austenitic stainless steel Sanmac 316L, L=200 mm, D=100 mm, ˜215 HB [0094] Insert type: CNMG 120408-MM [0095] Cooling: yes [0096] Depth of cut a.sub.p=4 to 0, 0 to 4 mm [0097] Cutting speed V.sub.c=140 m/min [0098] Feed rate f.sub.z=0.36 mm/rev

[0099] Layer Period Thickness:

TABLE-US-00005 TABLE 5 Comb crack resistance Flaking resistance Sample Layer period (No. cuts) (flaked area, mm.sup.2) 1 4 nm 30 0.06 2 8 nm 23 0.06 3 20 nm 21 0.09

[0100] Table 5 shows that in terms of flaking resistance the thickest layer period, 20 nm, showed the worst performance.

[0101] Furthermore, from the test results (sample 1, sample 2, sample 3) it is seen that out of the tested layer periods 4 nm (5 rpm), 8 nm (2.4 rpm) and 20 nm (1 rpm), the best result in comb crack resistance, 30 cuts until cut-off criteria is seen for the layer period 4 nm. When the layer period is 8 nm the comb crack resistance result is 23 cuts and when the layer period is 20 nm the comb crack resistance result is 21 cuts. A result of less than 25 minutes is considered insufficient. Thus, the lower the layer period the better the result. Thus, a suitable range of an average layer period of the nano-multilayer is considered to be from 2 to 7 nm, preferably from 3 to 6 nm.

[0102] Effect of innermost layer:

[0103] Samples having a deposited nano-multilayer of Ti.sub.0.40Al.sub.0.60N/Ti.sub.0.80Al.sub.0.20 (target composition) were tested with or without any additional innermost layer directly on the substrate.

TABLE-US-00006 TABLE 6 Comb crack Edge line resistance toughness Sample Innermost layer Layer period (No. cuts) (No. cuts) 1 — 4 nm 30 not tested 4 Ti.sub.0.40Al.sub.0.60N, 4 nm 39 43 1 μm

[0104] The result in comb crack resistance is improved by the presence of an innermost additional (Ti,Al)N layer.

[0105] Even though there was no ELT testing for the sample without any additional innermost layer, table 7 shows at least the effect of the thickness of an additional innermost layer in terms of ELT. The samples in table 7 are outside the invention in terms of layer period thickness 8 nm. However, the impact on ELT for a variation in layer thickness on the innermost layer is regarded to follow the same direction also for a layer period lower than 8 nm, i.e., within the present invention.

TABLE-US-00007 TABLE 7 Edge line toughness Sample Innermost layer Layer period (No. cuts) 10 Ti.sub.0.40Al.sub.0.60N, 8 nm 11 0.2 μm 11 Ti.sub.0.40Al.sub.0.60N, 8 nm 15 0.4 μm 12 Ti.sub.0.40Al.sub.0.60N, 8 nm 29 0.8 μm (~1 μm)

[0106] ELT is considered to improve by the presence of an innermost additional (Ti,Al)N layer. When comparing innermost layers of 0.2, 0.4 and 0.8 μm thickness, 0.8 μm thickness gave better performance than the thinner ones.

[0107] Ti/Al Relation in (Ti,Al)N Nanolayer:

TABLE-US-00008 TABLE 8 Comb crack Edge line First Second resistance toughness Sample nanolayer nanolayer (No. cuts) (No. cuts) 4 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 39 43 5 Ti.sub.0.50Al.sub.0.50N Ti.sub.0.80Si.sub.0.20N 36 19 6 Ti.sub.0.60Al.sub.0.40N Ti.sub.0.80Si.sub.0.20N 33 9 7 Ti.sub.0.75Al.sub.0.25N Ti.sub.0.80Si.sub.0.20N 19 12

[0108] From the test results it is seen that the best result in comb crack resistance, 39 cuts until cut-off criteria is seen for sample 4 (Ti.sub.0.40Al.sub.0.25). For sample 7 (Ti.sub.0.75Al.sub.0.25) the comb crack resistance result is only 19 cuts. A result of less than 25 cuts is considered insufficient. Thus, all of sample 4 (Ti.sub.0.40Al.sub.0.60), sample 5 (Ti.sub.0.50Al.sub.0.50) and sample 6 (Ti.sub.0.60Al.sub.0.40) showed good performance in the comb crack resistance test. Thus, a required range of Al the (Ti,Al)N sublayer composition in the nano-multilayer is considered to be Ti.sub.1-xAl.sub.xN, 0.35≤x≤0.70 in terms of good comb crack resistance.

[0109] However, when ELT performance is taken into account sample 6 with Ti.sub.0.60Al.sub.0.40N/Ti.sub.0.40Si.sub.0.20N performs bad. The best performance in both of comb crack resistance and edge line toughness was sample 4 with Ti.sub.0.40Al.sub.0.60N/Ti.sub.0.40Al.sub.0.20.

[0110] A suitable Al content range is therefore 0.45≤x≤0.70 and a preferred one 0.55≤x≤0.65.

[0111] Ti/Si Relation in (Ti,Si)N Nanolayer:

TABLE-US-00009 TABLE 9 Comb crack Edge line Flank wear First Second resistance toughness resistance Sample nanolayer nanolayer (No. cuts) (No. cuts) (minutes) 4 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.80Si.sub.0.20N 39 43 21.3 8 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.85Si.sub.0.15N 27 11 17.7 9 Ti.sub.0.40Al.sub.0.60N Ti.sub.0.90Si.sub.0.10N 25 15 13.5

[0112] Regarding comb crack resistance, sample 8 (Ti.sub.0.40Al.sub.0.60N/Ti.sub.0.85Al.sub.0.15N), run at 5 rpm, 50 V, 4 Pa, shows a quite good result in comb crack resistance, 27 cuts until cut-off criteria. Also, the flank wear resistance is good (17.7 minutes). However, in terms of edge line toughness the result is unsatisfactory. Sample 9 (Ti.sub.0.40Al.sub.0.60N/Ti.sub.0.90Al.sub.0.10N), run at 5 rpm, 50 V, 4 Pa) also shows a quite good result in comb crack resistance, 25 cuts until cut-off criteria. However, the flank wear resistance is completely unsatisfactory (13.5 minutes) and also the edge line toughness (15 cuts) is unsatisfactory.

[0113] The best performance in all of comb crack resistance, edge line toughness and flank wear was sample 4 with (Ti.sub.0.40Al.sub.0.60N/Ti.sub.0.60Si.sub.0.20N). The second best is sample 8 with (Ti.sub.0.40Al.sub.0.60N/Ti.sub.0.85Si.sub.0.15N) while sample 9 with (Ti.sub.0.40Al.sub.0.60N/Ti.sub.0.90Si.sub.0.10N) is regarded as unsatisfactory.

[0114] Thus, a required working range of Si content in the (Ti,Si)N sublayer in the nano-multilayer is considered to be Ti.sub.1-ySi.sub.yN, 0.12≤y≤0.25. Suitably 0.14≤y≤0.23 and preferably 0.17≤y≤0.21.

[0115] A too high Si content in the (Ti,Si)N sublayer is expected to decrease the toughness (ELT) of the nano-multilayer.

[0116] Grain size, FWHM:

[0117] Exceptional results in an edge line toughness (ELT) test (number of cuts) are seen for samples in which the nano-multilayer has been deposited using a certain level of DC bias voltage and/or N.sub.2 pressure. From the test results of sample 4 (−50 V, 4 Pa), sample 13 (−30 V, 4 Pa), sample 14 (−70 V, 4 Pa), sample 15 (−100 V, 4 Pa), sample 16 (−50 V, 2 Pa), and sample 17 (−50 V, 6 Pa) it is seen that coatings deposited at 4 Pa N.sub.2 pressure give very excellent ELT results for DC bias voltage levels used of at least −70 V, with −100 V even better (sample 14 and sample 15). For coatings deposited at 2 Pa N.sub.2 pressure excellent ELT results are provided for DC bias voltages used already at −50 V (sample 16). Startlayer about 1 μm. Thickness of nano-multilayer about 2 μm.

TABLE-US-00010 TABLE 10 Edge line Comb FWHM, tough- crack TiAIN DC N.sub.2 ness resistance Column [200] bias pres- (No. (No. width (degrees voltage sure cuts) cuts) (nm) 2theta) 4  −50 V 4 Pa 43 39 54 0.6 13  −30 V 4 Pa 34 37 — 0.6 14  −70 V 4 Pa 83 29 50 0.7 15 −100 V 4 Pa 99 31 37 1.0 16  −50 V 2 Pa 94 34 — 0.7 17   50 V 6 Pa 39 39 — 0.6

[0118] For the samples having excellent ELT results, (sample 14 (−70 V, 4 Pa), sample 15 (−100 V, 4 Pa), and sample 16 (−50 V, 2 Pa), the comb crack test results were excellent as well (29, 31 and 34 cuts, respectively).

[0119] Thus, in order to provide coatings with the best edge line toughness the bias voltage-pressure relation in the deposition process is concluded to be either using a DC bias voltage of from −65 to −125 V at a N.sub.2 pressure of from 3 to 6 Pa, or, using a DC bias voltage of from −30 to −75 V at a N.sub.2 pressure of from 1 to 3 Pa.

[0120] It is seen from sample 4 (−50 V, 4 Pa), sample 13 (−70 V, 4 Pa), and sample 15 (−100 V, 4 Pa), that a higher DC bias voltage used gives a lower grain size (average column width) in the nano-multilayer (−50V gives 54 nm, −70 V gives 50 nm and −100 V gives 37 nm). The lower grain size is also reflected in a higher FWHM value. Thus, a range of an average column width in the nano-multilayer is considered to be suitably s 70 nm, preferably s 55 nm. The lower limit is considered to be suitably 5 nm, preferably 10 nm, more preferably 25 nm. A most preferred range is considered to be from 30 to 45 nm.