CVD coated cutting tool

Abstract

A coated cutting tool includes a substrate and a coating of one of more layers. The coating includes a layer of α-Al.sub.2O.sub.3 of a thickness of 1-20 μm deposited by chemical vapour deposition (CVD). The α-Al.sub.2O.sub.3 layer exhibits an X-ray diffraction pattern and wherein the texture coefficient TC(h k 1) is defined according to the Harris formula, wherein 1<TC(0 2 4)<4 and 3<TC(0 0 12)<6.

Claims

1. A coated cutting tool comprising: a substrate; and a coating, wherein the coating includes at least one layer of α-Al.sub.2O.sub.3with a thickness of 1-20 μm deposited by chemical vapour deposition (CVD), wherein said α-Al.sub.2O.sub.3layer exhibits an X-ray diffraction pattern, wherein a texture coefficient TC(h k l) is defined according to Harris formula $TC\left(hkl\right)={\frac{I\left(\mathrm{hk}l\right)}{\mathrm{I0}\left(hkl\right)}\left[\frac{1}{n}\underset{i=0}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hk}l\right)}{\mathrm{I0}\left(hkl\right)}\right]}^{-1}$ wherein the (h k l) reflections used are (1 0 4), (1 10), (1 13), (0 2 4), (1 1 6), (2 1 4), (300) and (0 0 12), I(h k l)=measured intensity of the (h k l) reflection, I.sub.0(h k l)=standard intensity according to ICDD's PDF-card No. 00-10-0173, n=8, wherein 1<TC(0 2 4)<4 and 3<TC(0 0 12)<6, and wherein the sum of the TC(0 0 12) and TC(0 2 4) for said α-Al.sub.2O.sub.3layer is >6.5.

2. The coated cutting tool of claim 1, wherein said α-Al.sub.2O.sub.3layer exhibits 1<TC(0 2 4)<3 and 3.5<TC(0 0 12)<5.5.

3. The coated cutting tool of claim 1, wherein said α-Al.sub.2O.sub.3layer exhibits 1.5<TC(0 2 4)<2.5 and 4<TC(0 0 12)<5.

4. The coated cutting tool of claim 1, wherein the third strongest TC(h k l) of said α-Al.sub.2O.sub.3layer is TC(1 1 0).

5. The coated cutting tool of claim 1, wherein said α-Al.sub.2O.sub.3layer exhibits a {0 0 1} pole figure as measured by EBSD in a portion of the α-Al.sub.2O.sub.3layer parallel to the outer surface of the coating, wherein a pole plot based on the data of the pole figure, with a bin size of 0.25° over a tilt angle range of 0°≤β≤90° from a normal of an outer surface of the coating has a ratio of intensity within β<15° tilt angle to the intensity within 0°≤β≤90° of ≥40%, and wherein said α-Al.sub.2O.sub.3layer exhibits a {0 1 2} pole figure as measured by EBSD in a portion of the α-Al.sub.2O.sub.3layer parallel to the outer surface of the coating, wherein a pole plot based on the data of the pole figure, with a bin size of 0.25° over a tilt angle range of 0°≤β≤90° from the normal of the outer surface of the coating shows a ratio of intensity within β<15° tilt angle to the intensity within 0°<β<90° of >40%.

6. The coated cutting tool of claim 5, wherein the {0 0 1} pole figure and the {0 1 2} pole figure are from a same portion of the α-Al.sub.2O.sub.3layer.

7. The coated cutting tool of claim 1, wherein said α-Al.sub.2O.sub.3layer includes columnar grains.

8. The coated cutting tool of claim 1, wherein the α-Al.sub.2O.sub.3layer includes columnar α-Al.sub.2O.sub.3layer grains and wherein an average width of said columnar grains is 0.5-2 μm as measured along a line parallel to a surface of the substrate in the middle of said α-Al.sub.2O.sub.3layer.

9. The coated cutting tool of claim 1, wherein the thickness of the α-Al.sub.2O.sub.3layer is 2-10 μm.

10. The coated cutting tool of claim 1, wherein the coating further includes a layer of one or more of TiN, TiCN, TiC, TiCO, TiCNO.

11. The coated cutting tool of claim 1, wherein the coating includes layers in the following order from the surface of the substrate: TiN, TiCN, TiCNO and α-Al.sub.2O.sub.3.

12. The coated cutting tool of claim 1, wherein the coating includes an outermost wear indication color layer.

13. The coated cutting tool of claim 1, wherein the substrate is cemented carbide with a surface zone extending from the substrate surface to a depth of about 15-35 μm into the body, said surface zone being binder phase enriched and essentially free from cubic carbides.

14. The coated cutting tool of claim 1, wherein the substrate is cemented carbide with a Co content of 6-12 wt %.

15. The coated cutting tool of claim 1, wherein the cutting tool is a cutting insert and where an inscribed circle of said cutting insert has a diameter of ≥15 mm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1. XRD diffraction graph of Sample 1. The graph is based on raw data and no corrections have been applied. The (0 0 6) peak and the (0 0 12) peak of the α-A.sub.2O.sub.3 layer are visible at about 41.7° and 90.7°, respectively. The (0 1 2) peak and the (0 2 4) peak are visible at about 25.6° and 52.6°, respectively.

(2) FIG. 2. SEM image of a cross section of the α-Al.sub.2O.sub.3 layer of Sample 1.

(3) FIG. 3. EBSD image of the area of the α-Al.sub.2O.sub.3 layer of Sample 1 as indicated with a black box in FIG. 2.

(4) FIG. 4. SEM image of a cross section of the α-Al.sub.2O.sub.3 layer of Sample 1.

(5) FIG. 5. EBSD image of the area of the α-Al.sub.2O.sub.3 layer of Sample 1 as indicated with a black box in FIG. 4.

(6) FIG. 6. Pole plot of {0 0 1} from EBSD pole figure data of Sample 1 with a bin size of 0.25 over a tilt angle range of 0°≤β≤90°. The x-label indicates the angle β and ranges from 0° to 90°. The y-label indicates intensity and is indicated M.U.D.

(7) FIG. 7. Pole plot of {0 1 2} from EBSD pole figure data of Sample 1 with a bin size of 0.25 over a tilt angle range of 0°≤β≤90°. The x-label indicates the angle β and ranges from 0° to 90°. The y-label indicates intensity and is indicated M.U.D.

EXAMPLES

(8) Embodiments of the present invention will be disclosed in more detail in connection with the following examples. The examples are to be considered as illustrative and not limiting embodiments. In the following examples coated cutting tools (inserts) were manufactured, analyzed and evaluated in cutting tests.

Example 1

Sample Preparation

(9) Sample 1 (invention)

(10) Cemented carbide substrates of ISO-type CNMG120408 for turning were manufactured from 7.2 wt-% Co, 2.7 wt % Ta, 1.8 wt % Ti, 0.4 wt % Nb, 0.1 wt % N and balance WC, comprising a Co enriched surface zone of about 25 μm from the substrate surface and to a depth into the body being essentially free from cubic carbides. The composition of the cemented carbide is thus about 7.2 wt % Co, 2.9 wt % TaC, 1.9 wt % TiC, 0.4 wt % TiN, 0.4 wt % NbC and 86.9 wt % WC.

(11) The substrates were first coated with a thin approximately 0.4 μm TiN-layer then with an approximately 7 μm TiCN layer by employing the well-known MTCVD technique using TiCl.sub.4, CH.sub.3CN, N.sub.2, HCl and H.sub.2 at 885° C. The volume ratio of TiCl.sub.4/CH.sub.3CN in an initial part of the MTCVD deposition of the TiCN layer was 6.6, followed by a period using a ratio of TiCl.sub.4/CH.sub.3CN of 3.7.

(12) On top of the MTCVD TiCN layer was a 1-2 μm thick bonding layer deposited at 1000° C. by a process consisting of four separate reaction steps. First a HTCVD TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step (TiCNO-1) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2, HCl and H.sub.2 at 70 mbar, then a third step (TiCNO-2) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar and finally a fourth step (TiCNO-3) using TiCl.sub.4, CO, N.sub.2 and H.sub.2 at 70 mbar. 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 H2.

(13) On top of the bonding layer an α-Al.sub.2O.sub.3 layer was 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 μm α-Al.sub.2O.sub.3 and a second step using 2.2 vol-% AlCl.sub.3, 4.4 vol-% CO.sub.2, 5.5 vol-% HCl, 0.33 vol-% H.sub.25 and balance H.sub.2 giving a total α-Al.sub.2O.sub.3 layer thickness of about 4 μm.

(14) Sample 2 (Reference)

(15) Cemented carbide substrates of ISO-type CNMG120408 for turning were manufactured from: 7.5 wt-% Co, 2.7 wt % Ta, 1.8 wt % Ti, 0.4 wt % Nb, 0.1 wt % N and balance WC. The substrates comprise a Co enriched surface zone of about 25 μm from the substrate surface and to a depth into the body being essentially free from cubic carbides.

(16) The substrates were first coated with a thin approximately 0.4 μm TiN-layer then with an approximately 7 μm TiCN layer by employing the well-known MTCVD technique using TiCl.sub.4, CH.sub.3CN, N.sub.2, HCl and H.sub.2 at 885° C. The volume ratio of TiCl.sub.4/CH.sub.3CN of the MTCVD deposition of the TiCN layer was 2.2.

(17) On top of the MTCVD TiCN layer was a 1-2 μm thick bonding layer deposited at 1000° C. by a process consisting of two separate reaction steps. First a HTCVD TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, and H.sub.2 at 55 mbar, then a second step using TiCl.sub.4, CO and H.sub.2 at 55 mbar and thereby producing a bonding layer. Prior to the start of the α-Al.sub.2O.sub.3 nucleation, the bonding layer was oxidized for 2 minutes in a mixture of CO.sub.2, HCl and H.sub.2.

(18) Thereafter an α-Al.sub.2O.sub.3 layer was deposited at 1000° C. and 55 mbar in three steps. The first step using 2.3 vol-% AlCl.sub.3, 4.6 vol-% CO2, 1.7 vol-% HCl and balance H.sub.2 giving about 0.1 μm α-Al.sub.2O.sub.3 and a second step using 2.2% AlCl.sub.3, 4.4% CO.sub.2, 5.5% HCl, 0.33% H.sub.2S and balance H.sub.2 and thereafter a third step using 2.2% AlCl.sub.3, 8.8% CO.sub.2, 5.5% HCI, 0.55% H.sub.2S and balance H.sub.2 giving a total α-Al.sub.2O.sub.3 layer thickness of about 5 μm.

(19) The coating also comprises an outermost layer of about 1 μm thick TiN.

(20) Sample 3 (Reference)

(21) Cemented carbide substrates of ISO-type CNMG120408 for turning were manufactured with a composition of 7.2 wt-% Co, 2.7 wt % Ta, 1.8 wt % Ti, 0.4 wt % Nb, 0.1 wt % N and balance WC. The substrates comprise a Co enriched surface zone of about 25 μm from the substrate surface and to a depth into the body being essentially free from cubic carbides.

(22) The substrates were first coated with a thin approximately 0.4 μm TiN-layer then with an approximately 7 μm TiCN layer by employing the well-known MTCVD technique using TiCl.sub.4, CH.sub.3CN, N.sub.2, HCl and H.sub.2 at 885° C. The volume ratio of TiCl.sub.4/CH.sub.3CN in an initial part of the MTCVD deposition of the TiCN layer was 3.7, followed by a period using a ratio of TiCl.sub.4/CH.sub.3CN of 2.2.

(23) On top of the MTCVD TiCN layer was a 1-2 μm thick bonding layer deposited at 1000° C. by a process consisting of four separate reaction steps. First a HTCVD TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step (TiCNO-1) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2, HCl and H.sub.2 at 70 mbar, then a third step (TiCNO-2) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar and finally a fourth step (TiCNO-3) using TiCl.sub.4, CO, N.sub.2 and H.sub.2 at 70 mbar. 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 H2.

(24) Thereafter an α-Al.sub.2O.sub.3 layer was deposited at 1000° C. and 55 mbar in two steps. The first step using 1.2 vol-% Al.sub.2O.sub.3, 4.7 vol-% CO.sub.2, 1.8 vol-% HCl and balance H.sub.2 giving about 0.1 μm α-A.sub.2O.sub.3 and a second step using 1.2% Al.sub.3, 4.7% CO.sub.2, 2.9% HCl, 0.58% H.sub.2S and balance H.sub.2 giving a total α-Al.sub.2O.sub.3 layer thickness of about 5 μm.

(25) The coating also comprises an outermost layer of about 1 μm thick TiN.

(26) The layer thicknesses were analyzed in a light optical microscope by studying a cross section of each coating at 1000× magnification and both the bonding layer and the initial TiN layer are included in the TiCN layer thickness given in Table 1.

(27) TABLE-US-00001 TABLE 1 TiCN thickness Al.sub.2O.sub.3 thickness TiN thickness Sample (μm) (μm) (μm) Sample 1 9.3 4.0 — Sample 2 8.5 4.5 1 Sample 3 9.0 5.0 1

(28) The texture coefficients were studied with the XRD method as disclosed above. The results are presented in Table 2.

(29) TABLE-US-00002 TABLE 2 Sample TC(1 0 4) TC(1 1 0) TC(1 1 3) TC(0 2 4) TC(1 1 6) TC(2 1 4) TC(3 0 0) TC(0 0 12) Sample 1 0.13 0.79 0.17 1.87 0.2 0.17 0 4.67 Sample 2 1.49 0.61 0.35 0.8 2.06 0.38 2.31 0 Sample 3 0.42 0.13 0.06 0.15 0.26 0.1 0.04 6.85

(30) The widths of the columnar α-Al.sub.2O.sub.3-grains were studied and the average width for Sample 1 was about 1 μm.

(31) Pole figures were measured by EBSD in a portion of the α-Al.sub.2O.sub.3 layer parallel to the outer surface of the coating.

(32) Crystallographic orientation data extraction of the acquired EBSD data was made using Oxford Instruments “HKL Tango” software version 5.12.60.0 (64-bit) and Oxford Instruments “HKL Mambo” software version 5.12.60.0 (64-bit). Pole figures using equal area projection and upper hemisphere projection were retrieved from the acquired EBSD data using the “HKL Mambo” software. The retrieved pole figures were for both the {0 0 1} and {0 1 2} poles with the Z direction being perpendicular to the outer surface of the coatings. Pole figures for both the {0 0 1} and the {0 1 2} pole were generated from the same EBSD data and thereby from data originating from the same portion of the α-Al.sub.2O.sub.3 layer. Pole plots of both the {0 0 1} and {0 1 2} pole figures were extracted using a class width of 0.25° for the bin size in the pole plot and for an angular measuring range β from β=0° to β≤90°. The intensity in the pole plot ranging from β=0 to β≤15° was related to the total intensity in the pole plot ranging from β=0° to β≤90°. The pole plots of {0 0 1} and {0 1 2} of Sample 1 are shown in FIG. 6 and FIG. 7, respectively. The relative intensity for 0°-15° in the measurement 0°-90° was in the pole plot {0 0 1} was about 66% and the relative intensity for 0°-15° in the measurement 0°-90° was in the pole plot {0 1 2} about 52%.

(33) Prior to cutting wear tests the inserts were blasted on the rake faces in a wet blasting equipment using a slurry of alumina in water and the angle between the rake face of the cutting insert and the direction of the blaster slurry was about 90°. The alumina grits were F220, the pressure of slurry to the gun was 1.8 bar, the pressure of air to the gun was 2.2 bar, the average time for blasting per area unit was 4.4 seconds and the distance from the gun nozzle to the surface of the insert was about 145 mm. The aim of the blasting is to influence the residual stress in the coating and the surface roughness and thereby improve the properties of the inserts in the subsequent turning test.

Example 2

Crater Wear Test

(34) The coated cutting tools, i.e. Samples 1, 2 and 3 were tested in longitudinal turning in ball bearing steel (Ovako 825B) using the following cutting data;

(35) Cutting speed v.sub.c: 220 m/min

(36) Cutting feed, f: 0.3 mm/revolution

(37) Depth of cut, a.sub.p: 2 mm

(38) Insert style: CNMG120408-PM

(39) Water miscible metal working fluid was used.

(40) One cutting edge per cutting tool was evaluated.

(41) In analyzing the crater wear, the area of exposed substrate was measured, using a light optical microscope. When the surface area of the exposed substrate exceeded 0.2 mm.sup.2 the life time of the tool was considered to be reached. The wear of each cutting tool was evaluated after 2 minutes cutting in the light optical microscope. The cutting process was then continued with a measurement after each 2 minutes run, until the tool life criterion was reached. When the size of the crater area exceeded 0.2 mm.sup.2 the time until the tool life criterion was met was estimated based on an assumed constant wear rate between the two last measurements. Beside crater wear, flank wear was also observed, but did not in this test influence the tool life. The average results of two parallel tests are shown in Table 3.

(42) TABLE-US-00003 TABLE 3 Sample Sample 1 Sample 2 Sample 3 Life time (min) 30 17 32

Example 3

Plastic Deformation Depression Test

(43) The coated cutting tools, i.e. Samples 1, 2 and 3, were tested in a test aimed to evaluate the resistance against flaking at plastic deformation of the cutting edge.

(44) The work piece material consisted of low-alloyed steel (SS2541-03). Longitudinal turning of this work piece was performed and evaluated at two different cutting speeds.

(45) The following cutting data was used;

(46) Cutting speed v.sub.c: 105 or 115 m/min

(47) Depth of cut a.sub.p: 2 mm

(48) Feed f: 0.7 mm/rev

(49) Time in cut: 0.5 min

(50) No metal working fluid was used.

(51) Two cutting edges were tested in parallel tests for each cutting speed. The cutting was performed during 0.5 minutes and the cutting edge was then evaluated in a light optical microscope. The flaking due to plastic deformation of the cutting edge was classified as follows: 0=no flaking, 1=minor flaking, 2=large flaking. The flaking was also classified regarding the depth of the flaking such that AC=flaking of the alumina layer, GAC=flaking down to the substrate. In table 4 the AC/GAC values are given for each tested cutting edge.

(52) TABLE-US-00004 TABLE 4 Sample 105 m/min 115 m/min Sample 1 0/0 2/2 0/0 0/0 Sample 2 1/0 2/2 1/1 0/0 Sample 3 2/0 2/1 2/0 2/2

Example 4

Thermal Intermittence Test

(53) The coated cutting tools, i.e. Samples 1, 2 and 3, were tested in a test aimed to evaluate the resistance against thermal cracks and edge line chipping.

(54) The work piece material consisted of steel (SS1672), a “balk” with a square cross section. Longitudinal turning of this work piece was performed and evaluated. The pre-determined number of 10 cycles was run and thereafter each cutting edge was evaluated in a light optical microscope. Three parallel tests were performed and the average is presented in Table 5.

(55) The following cutting data was used;

(56) Cutting speed v.sub.c: 220 m/min

(57) Depth of cut a.sub.p: 3 mm

(58) Feed f: 0.3 mm/rev

(59) Length of cut: 19 mm

(60) No metal working fluid was used.

(61) TABLE-US-00005 TABLE 5 Sample Sample 1 Sample 2 Sample 3 Edge line chipping Minor chipping Major chipping Minor chipping

(62) From the cutting tests it can be concluded that the Sample 1 shows improved wear performance in the combination of high resistance against flaking at plastic deformation of the cutting edge and high resistance against both crater wear at the rake face and resistance against thermal cracks and edge line chipping. In the cutting tests of Example 2 and 4, Sample 1 (invention) and Sample 3 (reference) outperforms Sample 2 (reference), while in the cutting test of Example 3, Sample 1 and Sample 2 outperforms Sample 3.

(63) While the invention has been described in connection with the above 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.