COATED CUTTING TOOL

Abstract

A coated cutting tool includes a substrate and a coating, wherein the coating has a (Ti,Al)N multilayer of alternating cubic Ti.sub.1-xAl.sub.xN sub-layers, 0.60≤x≤0.75, and cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layers, 0.60≤y≤0.75. The average cubic Ti.sub.1-xAl.sub.xN sub-layer thickness is from 75 to 450 nm and the average cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layer thickness is from 50 to 300 nm. The number of each of the cubic Ti.sub.1-xAl.sub.xN sub-layers and cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layers is from 2 to 50.

Claims

1. A coated cutting tool for metal machining comprising a substrate and a coating, wherein the coating includes a (Ti,Al)N multilayer of alternating cubic Ti.sub.1-xAl.sub.xN sub-layers, 0.60≤x≤0.75, and cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layers, 0.60≤y≤0.75, an average cubic Ti.sub.1-xAl.sub.xN sub-layer thickness being from 75 to 450 nm and an average cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layer thickness being from 50 to 300 nm, a number each of cubic Ti.sub.1-xAl.sub.xN sub-layers and cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layers being from 2 to 50.

2. The coated cutting tool according to claim 1, wherein the average cubic Ti.sub.1-xAl.sub.xN sub-layer thickness is from 150 to 400 nm.

3. The coated cutting tool according to claim 1, wherein the average cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layer thickness is from 70 to 250 nm.

4. The coated cutting tool according to claim 1, wherein a thickness ratio of the cubic Ti.sub.1-xAl.sub.xN sub-layer to the cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layer is from 5:1 to 1:1.

5. The coated cutting tool according to claim 1, wherein for the cubic Ti.sub.1-xAl.sub.xN sub-layer, 0.64≤x≤0.70.

6. The coated cutting tool according to claim 1, wherein for the cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layer, 0.64≤y≤0.70.

7. The coated cutting tool according to claim 1, wherein the number each of cubic Ti.sub.1-xAl.sub.xN sub-layers and cubic+hexagonal Ti.sub.1-y Al.sub.yN sub-layers is from 3 to 40.

8. The coated cutting tool according to claim 1, wherein the difference between x in the cubic Ti.sub.1-xAl.sub.xN sub-layer and y in the cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layer is less than 0.09.

9. The coated cutting tool according to claim 1, wherein x substantially equals y.

10. The coated cutting tool according to claim 1, wherein a total thickness of the (Ti,Al)N multilayer is from 0.5 to 10 μm.

11. The coated cutting tool according to claim 1, wherein in 2theta XRD of a whole (Ti,Al)N multilayer I(0 0-1 0)/I(2 0 0), is from 0.05 to 0.75.

12. The coated cutting tool according to claim 1, wherein the cubic Ti.sub.1-xAl.sub.xN sub-layer and the cubic+hexagonal Ti.sub.1-yAl.sub.yN sub-layer are cathodic arc evaporation deposited layers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows a schematic illustration of a substrate with a coating according to one embodiment of the invention.

[0026] FIG. 2 shows an electron diffraction pattern of the cubic+hexagonal sub-layer.

[0027] FIG. 3 shows an electron diffraction pattern of the cubic sub-layer.

[0028] FIG. 4 shows an X-ray diffractogram of a cubic layer.

[0029] FIG. 5 shows an X-ray diffractogram of a cubic+hexagonal layer.

[0030] FIG. 6 shows an X-ray diffractogram of the (Ti,AI)N multilayer.

EXAMPLES

Example 1

[0031] Different coatings of Ti.sub.0.33Al.sub.0.67N, both according to the present invention and outside the present invention, were deposited on sintered cemented carbide cutting tool insert blanks of the geometry CNMG120804-MM. 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—Al were mounted in all of the flanges.

[0032] The uncoated blanks were mounted on pins that undergo a three-fold rotation in the PVD chamber.

[0033] For making a cubic Ti.sub.0.33Al.sub.0.67N layer the chamber was pumped down to high vacuum (less than 10.sup.−2 Pa) and heated to about 450° C. by heaters located inside the chamber. If the layer was to be deposited as a first layer on the substrate then the blanks were etched for 60 minutes in an Ar plasma. The chamber pressure (reaction pressure) was set to 10 Pa of N.sub.2 gas, and a unipolar DC bias voltage of −300 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).

[0034] For making a cubic+hexagonal Ti.sub.0.33Al.sub.0.67N layer the chamber was pumped down to high vacuum (less than 10.sup.−2 Pa) and heated to about 450° C. by heaters located inside the chamber. If the layer was to be deposited as a first layer on the substrate then the blanks were etched for 60 minutes in an Ar plasma. The chamber pressure (reaction pressure) was set to 4 Pa of N.sub.2 gas, and a unipolar pulsed bias voltage of −50V (relative to the chamber walls) at a pulsed bias frequency of 2 kHz and a duty cycle of 10% was applied to the blank assembly. The cathodes were run in an arc discharge mode at a current of 150 A (each).

[0035] Layers of 3 μm total thickness were deposited.

[0036] The samples made, single layers and combinations of layers, are seen in Table 1. The sub-layer thicknesses are average values.

TABLE-US-00001 TABLE 1 No. of No. of total cubic cubic + Sample thickness sub- hexagonal No. Coating (μm) layers sub-layers Comment 1 3 μm cubic Ti.sub.0.33Al.sub.0.67N 3 comparative 2 3 μm multilayer: 500 nm cubic 3  4  4 comparative Ti.sub.0.33Al.sub.0.67N + 250 nm cubic + hexagonal Ti.sub.0.33Al.sub.0.67N 3 3 μm multilayer: 300 nm cubic 3 6-7 6-7 invention Ti.sub.0.33Al.sub.0.67N + 150 nm cubic + hexagonal Ti.sub.0.33Al.sub.0.67N 4 3 μm multilayer: 200 nm cubic 3 10 10 invention Ti.sub.0.33Al.sub.0.67N + 100 nm cubic + hexagonal Ti.sub.0.33Al.sub.0.67N 5 3 μm multilayer: 30 nm cubic 3 60-65 60-65 comparative Ti.sub.0.33Al.sub.0.67N + 15 nm cubic + hexagonal Ti.sub.0.33Al.sub.0.67N

[0037] Selected area electron diffraction (SAED) analysis by transmission electron microscopy (TEM) was performed on sample 4. FIG. 2 shows the diffraction image of the cubic+hexagonal sub-layer and FIG. 3 shows the diffraction image of the cubic sub-layer. 300 kV FEG TEM was used, beam in parallel illumination mode, using a selected area aperture which had a projected size of approximately 150 nm in the objective plane (i.e., a size directly comparable to features in the sample).

[0038] The sample was a cross-section sample produced by focused Ion Beam lift-out and polishing using Ga+ ions.

[0039] FIG. 2 shows the results from the first type of sub-layer where clear point-shaped diffraction spots from cubic the crystallographic planes (2 2 0), (2 0 0) and (1 1 1) are seen together with clear point-shaped diffraction spots from the hexagonal crystallographic plane (1 0-1 0). Thus, the layer is a mixed cubic+hexagonal layer.

[0040] FIG. 3 shows the results from the second type of sub-layer where clear point-shaped diffraction spots from the cubic crystallographic planes (2 2 0), (2 0 0) and (1 1 1) are seen also here. However, there are no point-shaped diffraction spots from any hexagonal crystallographic planes. It is only seen a weak fuzzy ring-shaped reflection from the (1 0-1 0) plane. Thus, the layer contains no substantial crystalline hexagonal phase and is considered to be a single phase cubic layer.

[0041] As a further investigation XRD analysis was made on the cubic and cubic+hexagonal layers. Since XRD on a specific sub-layer present as part of a multilayered structure is difficult to make XRD measurement was made on Sample 1 being a cubic monolayer and a further sample was made according to the process parameters used for making the cubic+hexagonal sub-layer.

[0042] The X-ray diffraction (XRD) analysis was conducted on the flank face of the coated inserts using a PANalytical CubiX3 diffractometer equipped with a PIXcel detector. 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. Cu—K.sub.a radiation was used for the measurements, with a voltage of 45 kV and a current of 40 mA. Anti-scatter slit of ½ degree and divergence slit of ¼ degree were used. The diffracted intensity from the coated cutting tool was measured around 2θ angles where relevant peaks occur.

[0043] FIGS. 4 and 5 show the diffractograms. FIG. 4 shows a diffractogram of Sample 1 with no signs of any hexagonal (h) peaks. FIG. 5 shows a diffractogram from the other type of layer containing both cubic (c) and hexagonal (h) peaks.

[0044] Thus, also the XRD analysis concludes that the cubic layer present can indeed be considered to be a single phase cubic layer.

[0045] XRD analysis was further made on the whole (Ti,AI)N multilayer. Sample 4 was used. The same XRD analysis method as described above was used.

[0046] FIG. 6 shows the diffractogram. Table 2 below shows the values of peak intensities:

TABLE-US-00002 TABLE 2 Peak Area intensity I(200) 7234 I(10-10) 797

[0047] The ratio l(1 0-1 0)/l(2 0 0) was thus 0.11.

Explanations to Terms Used in Examples 2-3:

[0048] The following expressions/terms are commonly used in metal cutting, but nevertheless explained in the table below:

V.sub.c (m/min): cutting speed in meters per minute
f.sub.n (mm/rev) feed rate per revolution (in turning)
a.sub.p (mm): axial depth of cut in millimeter

[0049] Inserts from Example 1 were tested for flank wear and crater wear.

Example 2

Flank Wear Test:

[0050] Longitudinal turning
Work piece material: Uddeholm Sverker 21 (tool steel), Hardness˜210HB, D=180,

L=700 mm,

[0051] V.sub.c=125 m/min
f.sub.n=0.072 mm/rev
a.sub.p=2 mm
without cutting fluid

[0052] The cut-off criteria for tool life is a flank wear VB of 0.15 mm.

Example 3

Crater Wear Test:

[0053] Longitudinal turning
Work piece material: Ovako 825B, ball bearing steel. Hot rolled and annealed,

Hardness ˜200HB, D=160, L=700 mm,

[0054] V.sub.c=160 m/min
f.sub.n=0.3 mm/rev
a.sub.p=2 mm
with cutting fluid The criteria for end of tool life is a crater area of 0.8 mm.sup.2.

[0055] The results from the testings according to Examples 2-3 are seen in Table 3 below.

TABLE-US-00003 TABLE 3 Flank wear Crater wear Sample Tool life Tool life No. Coating Comment (min) (min) 1 3 μm cubic Ti.sub.0.33Al.sub.0.67N comparative 9.5 8.0 2 3 μm multilayer: 500 nm cubic + comparative 15.4 6.8 250 nm cubic + hexagonal 3 3 μm multilayer: 300 nm cubic + invention 20.8 7.1 150 nm cubic + hexagonal 4 3 μm multilayer: 200 nm cubic + invention 21.1 7.5 100 nm cubic + hexagonal 5 3 μm multilayer: 30 nm cubic + comparative 8.3 6.0 15 nm cubic + hexagonal

[0056] It is concluded that the samples according to the invention (No. 3 and No. 4) have exceptional flank wear resistance while their crater wear resistance remains at about the same level as for a single layer cubic (Ti,AI)N layer.