COATED CUTTING TOOL

Abstract

A cutting tool including a substrate at least partially coated with a coating is provided. The coating includes a ?-Al.sub.2O.sub.3 layer, wherein the ?-Al.sub.2O.sub.3 layer in a portion O1 of the ?-Al.sub.2O.sub.3 layer within 1 ?m from the bonding layer, as measured with EBSD, exhibits Schmid factors calculated for the {0001} <11-20> slip system with the normal force applied at a 45? angle to the surface normal of the ?-Al.sub.2O.sub.3 layer, wherein the Schmid factor distribution was determined and wherein >90% of the analyzed area had a Schmid factor between 0.4 and 0.5, preferably >97% of the analyzed area had a Schmid factor between 0.4 and 0.5.

Claims

1. A cutting tool comprising a substrate at least partially coated with a coating, said coating including a ?-Al.sub.2O.sub.3 layer, wherein said ?-Al.sub.2O.sub.3 layer in a portion O1 of the ?-Al.sub.2O.sub.3 layer within 1 ?m from the bonding layer, as measured with EBSD, exhibits Schmid factors calculated for the {0001} <11-20> slip system with the normal force applied at a 45? angle to a surface normal of the ?-Al.sub.2O.sub.3 layer, wherein the Schmid factor distribution was determined and wherein >90%, of an analyzed area had a Schmid factor between 0.4 and 0.5.

2. The cutting tool according to claim 1, wherein said coating includes a layer of Ti(C,N), a layer of ?-Al.sub.2O.sub.3 and there between a bonding layer, wherein said Ti(C,N) layer has a thickness of 3-25 ?m and is composed of columnar grains, wherein an average grain size D.sub.422 of the Ti(C,N) layer is 25-50 nm, as measured with X-ray diffraction with CuK? radiation, wherein the average grain size D.sub.422 is calculated from the full width at half maximum (FWHM) of the peak according to Scherrer's equation $D_{422}=\frac{K?}{B_{422}\cos ?}$ wherein D.sub.422 is an average grain size of the Ti(C,N), K is a shape factor here set at 0.9, ? is a wave length for the CuK? radiation here set at 1.5405 ?, B.sub.422 is a FWHM value for the reflection and ? is the Bragg angle, wherein the Ti(C,N) layer includes a portion B1 that is adjacent to the bonding layer, and wherein an average grain size of the Ti(C,N) grains in portion B1 is larger than the average grain size D.sub.422 over a whole thickness of the Ti(C,N) layer, in the portion B1 of Ti(C,N) layer the Ti(C,N) grains has an average grain size of 130 nm-165 nm as measured with Transmission Kikuchi Diffraction (TKD) on a plane view of the portion B1 of the Ti(C,N) layer extending in parallel with a substrate surface.

3. The cutting tool according to claim 1, wherein said ?-Al.sub.2O.sub.3 layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuK? radiation and ?-2? scan, defined according to Harris formula: $TC\left(\mathrm{hkl}\right)={\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\left[\frac{1}{n}\underset{n=1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\right]}^{-1}$ where I(hkl) is a measured intensity (integrated area) of the (hkl) reflection, I.sub.0(hkl) is a standard intensity according to ICDD's PDF-card No. 00-010-0173, n is a number of reflections used in the calculation, and where the (hkl) reflections used are (1 0 4), (1 1 0), (1 1 3), (0 2 4), (1 1 6), (2 1 4), (3 0 0) and (0 0 12), wherein TC(0 0 12)?7.5.

4. The cutting tool according to claim 1, wherein said ?-Al.sub.2O.sub.3 layer exhibits a texture coefficient TC(110)?0.2.

5. The cutting tool according to claim 1, wherein an average thickness of the ?-Al.sub.2O.sub.3 layer is 1 ?m-15 ?m.

6. The cutting tool according to claim 1, wherein said Ti(C,N) layer in the portion B1 of the Ti(C,N) layer exhibits an orientation as measured with Transmission Kikuchi Diffraction (TKD) on a plan view extending in parallel with the substrate surface, wherein a surface normal of the Ti(C,N) layer is parallel to a surface normal of a substrate surface, wherein ?93%, of the analysed area has a <211> direction within 15 degrees from the surface normal of the Ti(C,N) layer.

7. The cutting tool according to claim 1, wherein a thickness of the portion B1 of the Ti(C,N) layer is 0.5-1.5 ?m.

8. The cutting tool according to claim 1, wherein the Ti(C,N) layer exhibits an X-ray diffraction pattern, as measured using CuK? radiation and ?-2? scan, wherein the TC(hkl) is defined according to Harris formula where I(hkl) is a measured intensity (integrated area) of the (hkl) reflection, I.sub.0(hkl) is a standard intensity according to ICDD's PDF-card No. 42-1489, n is a number of reflections, wherein the reflections used in the calculation are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 2 0) and (4 2 2), wherein TC(422)?3.

9. The cutting tool according to claim 1, wherein the grain size D.sub.422 of Ti(C,N) is 25-40 nm.

10. The cutting tool according to claim 1, wherein an average thickness of the Ti(C,N) layer is 4-20 ?m.

11. The cutting tool according to claim 1, wherein the bonding layer at least one compound selected from the group of titanium carboxide, titanium oxynitride and titanium carboxynitride.

12. The cutting tool according to claim 1, wherein an average thickness of the bonding layer is 0.25-2.5 ?m.

13. The cutting tool according to claim 1, wherein an average thickness of the coating is 5 ?m-30 ?m.

14. The cutting tool according to claim 1, wherein said substrate is a cemented carbide, cermet or ceramic.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0053] Embodiments of the invention will be described with reference to the accompanying drawings, wherein:

[0054] FIG. 1 shows a Scanning Electron Microscope (SEM) image of a cross section of an example of the inventive coating, Sample D, where the portion B1 of the Ti(C,N) layer (1), the bonding layer (2) and the portion O1 of the ?-Al.sub.2O.sub.3 layer (3) are indicated,

[0055] FIG. 2 shows a Scanning Electron Microscope (SEM) image of a cross section of an example of a reference coating, Sample A, where the uppermost Ti(C,N) (1), the bonding layer (2) and the lowermost ?-Al.sub.2O.sub.3 (3) is visible,

[0056] FIG. 3 shows a Scanning Electron Microscope (SEM) image of a cross section of an example of a comparative coating, Sample G, where the portion B1 of the Ti(C,N) layer (1), the bonding layer (2) and the portion O1 of the ?-Al.sub.2O.sub.3 layer (3) are indicated,

[0057] FIG. 4 shows a Scanning Electron Microscope (SEM) image of a cross section of an example of a reference coating, Sample B, where the uppermost Ti(C,N) (1), the bonding layer (2) and the lowermost ?-Al.sub.2O.sub.3 (3) is visible,

[0058] FIG. 5 shows a Scanning Electron Microscope (SEM) image of a top surface of portion B1 of a sample provided with a Ti(C,N) layer corresponding to the Ti(C,N) in sample D where the morphology of the outermost surface of the portion B1 is visible,

[0059] FIG. 6 shows a Scanning Electron Microscope (SEM) image of a top surface of the Ti(C,N) layer of a sample provided with a Ti(C,N) layer corresponding to the Ti(C,N) in sample B where the morphology of the outermost surface of the very fine grained Ti(C,N) is visible,

[0060] FIG. 7 shows a Scanning Electron Microscope (SEM) image of a top surface of the Ti(C,N) layer of a sample provided with a Ti(C,N) layer corresponding to the Ti(C,N) in the reference sample A where the morphology of the outermost surface of the coarse grained Ti(C,N) is visible,

[0061] FIG. 8 is a schematic overview showing the position of the layers and portions of the present invention, the Ti(C,N) layer (1), the portion B1 of the Ti(C,N) layer (1), the bonding layer (2), the ?-Al.sub.2O.sub.3 layer (3), the portion O1 of the ?-Al.sub.2O.sub.3 layer (3) and the substrate (4),

[0062] FIG. 9 is a band contrast TKD image of a plan view of sample D where Ti(C,N) grains in the B1 portion are visible,

[0063] FIG. 10 shows the Schmid factor distribution of sample D, where the normal load was applied 45? to the coating/sample normal,

[0064] FIG. 11 shows the Schmid factor distribution of sample F, where the normal load is applied 45? to the coating/sample normal, and

[0065] FIG. 12 shows the Schmid factor distribution of sample A, where the normal load is applied 45? to the coating/sample normal.

EXAMPLES

[0066] Exemplifying embodiments of the present invention will now be disclosed in more detail and compared to reference embodiments. Coated cutting tools (inserts) were manufactured, analysed and tested in cutting tests.

[0067] Cemented carbide substrates were manufactured utilizing conventional processes including milling, mixing, spray drying, pressing and sintering. The ISO-type geometry of the cemented carbide substrates (inserts) was CNMG-120408-PM. The composition of the cemented carbide was 7.2 wt % Co, 2.9 wt % TaC, 0.5 wt % NbC, 1.9 wt % TiC, 0.4 wt % TiN and the rest WC.

[0068] Before the coating depositions the substrates were exposed to a mild blasting treatment to remove any residuals on the substrate surfaces from the sintering process.

CVD Depositions

[0069] The sintered substrates were CVD coated in a radial CVD reactor of lonbond Type size 530 capable of housing 10.000 half inch size cutting inserts. The samples to be tested and analysed further were selected from the middle of the chamber and at a position along half the radius of the plate between the center and the periphery of the plate. Mass flow controllers were chosen so that the high flow of for example CH.sub.3CN could be set.

[0070] A first innermost coating of about 0.2 ?m TiN was deposited on all substrates in a process at 400 mbar and 885? C. A gas mixture of 48.8 vol % H.sub.2, 48.8 vol % N.sub.2 and 2.4 vol % TiCl.sub.4 was used.

[0071] Thereafter followed the Ti(C,N) layer deposition, and all samples A-G were deposited with different Ti(C,N) in accordance with the following. The reference sample A was deposited with the process steps V and W as shown in Table 1. The temperature adjustment from 885? C. to 870? C. before starting with process step X for the samples B-G was made in 50 vol % H.sub.2 and 50 vol % N.sub.2 at 80 mbar. The Ti(C,N) layer of reference sample B was deposited with the process step X as shown in Table 1. On samples C-G the Ti(C,N) layers were deposited with the process steps X, Y and Z using the deposition times as indicated in Tables 1 and 2. The process times were adjusted to reach about the same total Ti(C,N) layer thickness for all the samples.

TABLE-US-00001 TABLE 1 Process Process Process Process Process Parameter step X step Y step Z step V step W H.sub.2 Balance Balance Balance Balance Balance N.sub.2 42.97% 7.76% 37.57% 7.76% TiCl.sub.4 2.95% 1.17% 2.38% 2.95% 2.38% CH.sub.3CN 0.45% 2.08% 0.65% 0.45% 0.65% HCl 10.82% 7.76% 7.76% Total gas 5600 3421 7734 5590 7734 flow [l/h] Pressure 80 70 70 55 55 [mbar] Temperature 870 870 870 885 885 [? C.] Process See Table 2 15 10 270 time [min]

TABLE-US-00002 TABLE 2 Process step X Process step Y Sample [minutes] [minutes] B 260 C 243 5 D 240 15 E 238 20 F 235 30 G 230 45

[0072] A 0.7-0.9 ?m thick bonding layer was deposited at 100000 on top of the Ti(C,N) layer by a process consisting of four separate reaction steps. First a 8 minutes HTCVD Ti(C,N) step using TiCl.sub.4, OH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step (Ti(C,N,O)-1) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar for 7 minutes, then a third step (Ti(C,N,O)-2) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar for 5 minutes and finally a fourth step (TiN) using TiCl.sub.4, N.sub.2 and H.sub.2 at 70 mbar for 6 minutes. During the third deposition step the CO gas flow was continuously linearly increased from a start value to a stop value as shown in Table 3. All other gas flows were kept constant, but since the overall gas flow is increased, the concentration of all gases were somewhat influenced due to this. Prior to the start of the subsequent Al.sub.2O.sub.3 nucleation, the bonding layer was oxidized for 4 minutes in a mixture of CO.sub.2, CO, N.sub.2 and H.sub.2.

[0073] The details of the bonding layer deposition are shown in Table 3.

TABLE-US-00003 TABLE 3 Bonding layer deposition Bonding H.sub.2 N.sub.2 CH.sub.4 HCl CO TiCl.sub.4 CH.sub.3CN CO.sub.2 layer Pressure[mbar] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] Temp. 55 Balance 25 increase HTCVD 400 Balance 25.5 3.4 1.7 1.55 Ti(C,N) Ti(C,N,O)-1 70 Balance 12.0 1.2 1.2 1.5 0.40 Ti(C,N,O)-2 70 Balance 31.5-30.6 1.6-4.6 3.15-3.06 0.65-0.63 TiN 70 Balance 32.3 3.23 Oxidation 55 Balance 30 12.5 3.7

[0074] On top of the bonding layer an ?-Al.sub.2O.sub.3 layer was deposited. All the ?-Al.sub.2O.sub.3 layers were deposited at 1000? C. and 55 mbar in two steps. The first step using 1.2 vol-% AlCl.sub.3, 4.7 vol-% CO.sub.2, 1.8 vol-% HCl and balance H.sub.2 giving about 0.1 ?m ?-Al.sub.2O.sub.3 and a second step as disclosed below giving a total ?-Al.sub.2O.sub.3 layer thickness of about 5 ?m. The second step of the ?-Al.sub.2O.sub.3 layer was deposited using 1.16% AlCl.sub.3, 4.65% CO.sub.2, 2.91% HCl, 0.58% H.sub.2S and balance H.sub.2.

Coating Analysis

[0075] The layer thicknesses were measured on the rake face of the cutting tool samples using a Scanning Electron Microscope. The layer thicknesses of the coating the samples A-G are shown in Table 4.

TABLE-US-00004 TABLE 4 Layer thicknesses TiN + Ti(C,N) + Thickness Thickness bonding Process portion portion layer times of from step from step Thickness Al.sub.2O.sub.3 thickness steps Y/Z Y Z portion B1 thickness Sample [?m] [min/min] [?m] [?m] [?m] [?m] A 10.4 0/0 5.0 B 8.7 0/0 4.5 C 9.4 5/15 ?0.1 ?0.4 ?0.5 4.3 D 9.2 15/15 ?0.2 ?0.5 ?0.7 4.6 E 8.7 20/15 ?0.3 ?0.4 ?0.7 4.8 F 9.4 30/15 ?0.5 ?0.4 ?0.9 5.3 G 8.7 45/15 ?0.5 ?0.4 ?0.9 4.2

[0076] The grain size of the Ti(C,N) layers were analysed both as an average in the whole Ti(C,N) layer and in the portion B1 close to the bonding layer. The results are presented in Table 5.

[0077] The orientation of the Ti(C,N) grains in the portion ye of the Ti(C,N) layer and the Schmid factors of the ?-Al.sub.2O.sub.3 grains in the O1 portion of the ?-Al.sub.2O.sub.3 layer were analysed. The results are presented in Table 5.

[0078] The grain size of the Ti(C,N) layer in the reference sample A was too large to be analysed with XRD, and the Scherrer's equation is not considered valid for grain sizes larger than about 0.2 ?m. The average grain size of this layer is larger than 200 nm as measured in a cross section SEM image

TABLE-US-00005 TABLE 5 Grain sizes and orientations of the portions 01 and B1. Schmid factor Orientation in frequency Average grain Average grain portion B1 in within 0.4-0.5 size D.sub.422 in size in B1 of Ti(C, N), ?15? for 45? load Sam- Ti(C, N) layer Ti(C, N) from <211> of O1 portion ple [nm] [nm] [%] [%] A n.a no B1 portion no B1 portion 78.9% B 31 no B1 portion no B1 portion 96.8% C 28 115 91.7% 97.8 D 27 146 98.5% 97.6 E 27 157 96.6% 94.8 F 29 208 76.6% 83.1 G 27 168 85.3% 87.4 (n.a. = not analysed)

[0079] Texture coefficients of the Ti(C,N) and the ?-Al.sub.2O.sub.3 layers were analysed using X-ray diffraction and the results are presented in Table 6 and Table 7.

TABLE-US-00006 TABLE 6 Texture coefficients for the ?-Al.sub.2O.sub.3 layer in the samples Sample TC(104) TC(110) TC(113) TC(024) TC(116) TC(214) TC(300) TC(0012) A 0.02 0.25 0.01 0.07 0.01 0.03 0.00 7.61 B 0.00 0.01 0.00 0.00 0.00 0.00 0.00 7.99 C 0.02 0.03 0.00 0.01 0.01 0.00 0.00 7.94 D 0.01 0.07 0.00 0.02 0.00 0.00 0.00 7.89 E 0.01 0.08 0.00 0.02 0.01 0.00 0.00 7.89 F 0.09 0.09 0.00 0.03 0.06 0.01 0.01 7.70 G 0.03 0.17 0.00 0.05 0.03 0.01 0.00 7.72

TABLE-US-00007 TABLE 7 Texture coefficient TC(422) for the Ti(C, N) layer in the samples Sample TC(422) A 3.94 B 3.95 C 3.43 D 4.14 E 4.06 F 3.19 G 3.74

Performance Tests

[0080] The as coated cutting tools were tested in two parallel cutting tests, Cutting test 1 and Cutting test 2, in a longitudinal turning operation in a work piece material Ovako 825B (100CrMo7-3), a high alloyed steel. The cutting speed, Vc, was 220 m/min, the feed, fn, was 0.3 mm/revolution, the depth of cut was 2 mm and water miscible cutting fluid was used. The machining was continued until the end of lifetime criterion was reached. One cutting edge per cutting tool was evaluated.

[0081] The tool life criterion was considered reached when the primary or secondary flank wear was >0.3 mm or when the crater area (exposed substrate) was >0.2 mm.sup.2. As soon as any of these criteria were met the lifetime of the sample was considered reached. The result of the cutting test is presented in Table 8 and 9.

TABLE-US-00008 TABLE 8 Cutting test 1 Flank wear after 30 minutes Crater wear after Primary flank Secondary flank 40 minutes wear wear Crater area Sample [mm] [mm] [mm.sup.2] A 0.26 0.25 0.13 C 0.25 0.24 0 D 0.27 0.22 0 E 0.24 0.21 0 F 0.29 0.27 0.04 G 0.28 0.24 0.07

TABLE-US-00009 TABLE 9 Cutting test 2 Time in cut until lifetime Sample [min.] Lifetime reached due to A 54 Crater wear >0.2 D 86 Crater wear >0.2 E 82 Crater wear >0.2

[0082] As can be seen in the table 8 all the inventive samples D and E, showed a high wear resistance whereas samples A, F and G shows a forming crater as a result of the lower Schmid factor value in portion O1. As shown in table 9 the inventive samples D and E shows a high resistance to both flank and crater wear in metal cutting of steel, also compared with the reference sample A which is a very high performing reference sample.

[0083] The cutting tools were also evaluated by being exposed to an abrasive wet blasting. The blasting was performed on the rake faces of the cutting tools. The blaster slurry consisted of 20 vol-% alumina in water and an angle of 90? between the rake face of the cutting insert and the direction of the blaster slurry. The distance between the gun nozzle and the surface of the insert was about 145 mm. The pressure of the slurry to the gun was 1.8 bar for all samples, while the pressure of air to the gun was 2.2 bar. The alumina grits were F230 mesh (FEPA 42-2:2006). The average time for blasting per area unit was 4.4 seconds. Samples B and C could not withstand the wet blasting, the coating of sample B showed severe flaking, the sample C showed spot wise flaking. All the other samples did withstand the wet blasting without destroying the coatings.

[0084] While the invention has been described in connection with various exemplary embodiments, it is to be understood that the invention is not to be limited to the disclosed exemplary embodiments, on the contrary, it is intended to cover various modifications and equivalent arrangements within the appended claims. Furthermore, it should be recognized that any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the appended claims appended hereto.