BACKGROUND OF THE INVENTION

The present invention relates to a cutting tool insert comprising of a body of a hard alloy of cemented carbide, cermet, ceramics and cubic boron nitride based materials and a coating designed to be used in metal cutting applications generating high tool temperatures. Said coating comprises at least one thermally stable, textured

(Ti,Al,Cr,Me) based nitride, carbonitride, oxynitride and/or oxycarbonitride layer, where Me is one or more of the elements: Zr, Hf, V, Nb, Ta, Mo, W or Si. The coating is grown by physical vapour deposition (PVD) and preferably by cathodic arc evaporation.

Since the mid 1980's, efforts have been made to improve the properties, e.g., wear resistance and hence the performance of tool coatings. At that time, the common practice was to coat cutting tools with TiN. However, TiN suffers from poor oxidation resistance. Improved heat resistance have been achieved by alloying Al in (Ti,Al)N. To further enhance the performance of tool coatings, a wide range of ternary and quaternary systems have been investigated, some with good and some with poor results. One of the most crucial parameter in this research is to achieve a good control of the solubility behavior of the alloying elements and in turn how this would yield an optimized coating performance. Recently, it has been shown that alloying Cr in (Ti,Al,Cr)N improves the coating behavior metal cutting applications.

JP 7237010 discloses a coated cutting tool at least one layer selected from

(Ti,Al,Cr)C, (Ti,Al,Cr)N or (Ti,Al,Cr)(C,N) and at least one layer of Ti, TiC, TiN or TiCN.

JP 4128363 discloses a (Tii„ _x „ _y Al _x Cr _y )N layer where x < 0.8 and 0.2 < y < 0.7.

JP 2000038653 discloses a (Tii_ _x _ _y Cr _x Al _y )N layer where 0.02 < x < 1.0 and 0.02 < y < 0.7. EP 1219723 discloses a hard coating for cutting tools composed of (Tii_ _a _b- _C - _d Al _a Cr _b Si _c B _d )(Ci_ _e Ne) where 0.5 < a < 0.8, 0.06 < b, 0 < c < 0.1, 0 < d < 0.1, 0 < c + d < 0.1, a + b + c + d < 1 and

0.5 < e < 1.

EP 1132498 discloses a hard wear resistance coating comprising one or two layers of (Al _a Ti _b Cr _c ) (N _w Oi_w) where 30 < a < 70, 30 < b < 70, 0.5 < c < 20, a + b + c = 1 0 0 and 0.7 < w < 0.9.

EP 1947209 discloses a first layer of (Cri_ _x M _x )(B _a C _b Ni_ _a -b) where 0 < x < 0.7, 0 < a < 0.2 and 0 < b < 0.5 and M is at least one of the elements W, V, Mo, Nb, Ti and Al and a second layer of (Tii_x_YCrxAlYLz)(B _B CANi_A-B) where 0 < 1-X-Y < 0.5, 0 < X < 0.5 , 0.4 < Y < 0.7, 0 < Z < 0.15, 0 < A < 0.5, and 0 < B < 0.2 and L is at least either of Si and Y.

As mentioned, the metal cutting industry is continuously looking for new hard coatings with improved high temperature wear resistance and is partly biased by the ongoing development of advanced work material as well as the need for an increased productivity. In turn, these aspects typically results in an increase of the tool temperature during a cutting operation. Hence, the problem to be solved by the present invention focuses on how to provide an alternative method for making a coated cutting tool insert, drill or endmill.

It is an object of the present invention to provide a coated cutting tool insert yielding improved performance in metal cutting applications at high tool temperatures.

Surprisingly, it has been found that by alloying Cr in (Ti,Al)N and adding small amounts of the metal elements Me: Zr, Hf, V, Nb, Ta, Mo, W and/or Si in a textured (Ti,Al,Cr,Me)(C,0,N) layer structure onto a cutting tool insert improves the tool life at machining operations generating high tool temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig 1; SEM micrograph of a fractured cross section (Tio _. i ₇ Alo.5 ₃ Cro _.3 o)N layer, marked with I, on a cemented carbide insert, marked with II. Fig 2; TEM micrograph of a (Tio _. i ₇ Alo.53Cro.3o)N layer in cross section. The image is obtained close to the middle of the layer thickness. The growth direction is marked with an arrow.

Fig 3; Grazing incidence X-ray diffraction patterns of a (Tio _. i ₇ Alo.53Cro.3o)N layer obtained with an incidence angle of 1°. The diffraction peaks are indexed as a NaCl- structure.

Fig 4; X-ray diffraction patterns of (Ti,Al,Cr)N layers with (A) a layer with { 111 } fiber texture having a Cr content of 30 at% and (B) a layer with {200} fiber textured having a Cr content of 10 at%.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, there is provided a cutting tool insert for machining by chip removal comprising a body of a hard alloy of cemented carbide, cermet, ceramics, polycrystalhne- diamond or cubic boron nitride based materials onto which is deposited a hard and wear resistant coating comprising at least one layer of a NaCl-structured (Ti _c Al _a Cr _b Me _d )(C _z O _y N _x ) with a thickness between 0.5 and 10 μπι, preferably between 1.5 and 5 μπι, where Me is one or more of the elements: Zr, Hf, V, Nb, Ta, Mo, W or Si, preferably Zr, Nb and Ta, and

0.10 < a < 0.60, preferably 0.25 < a < 0.55, most preferably 0.45 < a < 0.55, b + d > 0.20, preferably b + d > 0.25, most preferably b + d > 0.35

c > 0.05, preferably 0.05 < c < b + d,

0 < d < 0.25,

0.75 < x < 1.05, preferably 0.90 < x < 1.05,

0 < y < 0.25, preferably 0 < y < 0.15,

0 < z < 0.25, preferably 0 < z < 0.15.

Said layer has a fiber texture with texture coefficients, TC(hkl), according to:

- TC(220) < TC(111),

- TC(220) < TC(200) and

- 0.1 < TC(111)/TC(200) < 10, preferably 1 < TC( 111 )/TC(200) < 10, most preferably

4 < TC(111)/TC(200) < 10. Due to the finite layer thickness, the corrected texture coefficients, TC(hkl), are deduced as:

TC(hkl) = TC (hkl) l— where

TC _m eas(hkl) is the measured texture coefficient for a given (hkl) reflection, μ (μπι ^{" 1} ) is the linear absorption coefficient, x (μπι) is the layer thickness and QtM is half the diffraction angle for the same (hkl) reflection.

For said layers, μ vary between 0.053 and 0.11 μπ ¹ using CuKoc radiation, μ increases with an increasing Cr content of the layers. In average, μ = 0.0815 μπ ¹ is used in the TC(hkl) calculations which also is the close to the value for (Tio _. i ₇ Alo.53Cro.3o)N with μ = 0.08201.

TC _m eas(hkl) is determined from X-ray diffraction data in a θ - 2Θ configuration as:

Tc (hki) = ^{Imeas {hhl)} where

I hkl) ⁿ n=l IQ hkl)

Imeas(hkl) is the intensity of the (hkl) reflection, I ₀ (hkl) is the standard intensity for the same (hkl) reflection where I ₀ (l 11) = 72, I _o (200) = 100 and I _o (220) = 45, respectively, and n = 3, i.e., the number of (hkl) reflections used in the calculations. Here, only the first order reflections (hkl) are used, i.e., (I l l), (200) and (220), respectively.

Said layer has a columnar microstructure with an average column width of <1 μπι, preferably <0.6 μπι, as determined by cross sectional transmission electron microscopy of a middle region of the layer, i.e., a region within 30 to 70 % of the layer thickness in the growth direction, and said average columnar width is the average of at least 10 adjacent columns.

Said layer has a compressive stress level -6.0 < σ < -0.5 GPa, preferably -4.0 < σ < -1.5 GPa. The residual stress is evaluated by XRD using the sin ψ method with a Poisson's ratio of v=0.23 and a Young's modulus of E = 379 GPa. Said layer has a nanohardness >25 GPa, preferably between 25 GPa and 40 GPa, as measured by nanoindentation experiments.

In one preferred embodiment, d = y = z = 0.

In another preferred embodiment, y = z = 0.

In yet another preferred embodiment, d = y = 0.

In yet another preferred embodiment, y = 0.

In yet another preferred embodiment, d = z = 0.

In yet another preferred embodiment, z = 0.

In yet another embodiment y = z = 0 and Me = Zr.

In yet another embodiment y = z = 0 and Me = Nb.

In yet another embodiment y = z = 0 and Me = Ta.

In yet another embodiment y = 0 and Me = Zr.

In yet another embodiment y = 0 and Me = Nb.

In yet another embodiment y = 0 and Me = Ta.

In yet another embodiment z = 0 and Me = Zr.

In yet another embodiment z = 0 and Me = Nb.

In yet another embodiment z = 0 and Me = Ta.

Said layer may comprise an inner single- and/or laminated coating structure of, e.g., TiN, TiC, Ti(C,N) or (Ti,Al)N, preferably TiN or (Ti,Al)N, and/or an outer single- and/or laminated coating structure of, e.g., TiN, TiC, Ti(C,N), (Ti,Al)N or oxides, preferably TiN or (Ti,Al)N, to a total thickness of 0.7 to 20 μπι, preferably 2 to 10 μπι, and most preferably 2 to 7 μπι, according to prior art.

The deposition method for the layers of the present invention is based on PVD techniques, e.g., cathodic arc evaporation or magnetron sputtering using one or more pure and/or alloyed metal (Ti _c Al _a Cr Me _d ) cathodes/targets.

In the case of cathodic arc evaporation, the layers according to the invention are grown with an evaporation current between 50 and 200 A depending on the cathode size. A higher evaporation current is needed for larger cathodes in order to achieve comparable deposition conditions. The layers are grown using one or more pure, composite and/or alloyed metal cathodes, where Me is one or more of the elements: Zr, Hf, V, Nb, Ta, Mo, W or Si, in a reactive atmosphere containing N ₂ and optionally 0 ₂ and/or C-containing gases, with or without a carrier gas such as, e.g. Ar, at a total gas pressure between 1.0 and 7.0 Pa, preferably between 1.5 and 4.0 Pa. The C-containing gas may, e.g., be selected from CH ₄ and/or C ₂ H ₂ . The desired layer composition is obtained by selecting adequate (Ti _c Al _a Cr Me _d ) cathode compositions and gas atmosphere. The negative substrate bias is between 0 and 300 V, preferably between 10 and 150 V, most preferably between 15 and 60 V. The deposition temperature is between 200 and 800 °C, preferably between 300 and 600 °C.

In the case of magnetron sputtering, the layers according to the invention are grown with a power density applied to the sputter target between 0.5 and 15 W/cm , preferably between 1 and 5 W/cm . The layers are grown using one or more pure, composite and/or alloyed metal cathodes, where Me is one or more of the elements: Zr, Hf, V, Nb, Ta, Mo, W or Si, in a reactive atmosphere containing N ₂ and optionally 0 ₂ and/or C-containing gases, with or without a carrier gas such as, e.g. Ar, at a total pressure between 0.13 and 7.0 Pa, preferably between 0.13 and 2.5 Pa. The C-containing gas may, e.g., be selected from CH ₄ and/or C ₂ H ₂ . The desired layer composition is obtained by selecting adequate (Ti _c Al _a CrbMed) cathode compositions and gas atmosphere. The negative substrate bias is between 0 and 300 V, preferably between 10 and 150 V, most preferably between 20 and 100 V. The deposition temperature is between 200 and 800 °C, preferably between 300 and 600 °C.

The invention also relates to the use of cutting tool insert according to the above for metal machining generating high temperatures, e.g., super alloys and hardened steel at cutting speeds of 50 - 500 m/min, preferably 50 - 300 m/min, with an average feed of 0.08 - 0.5 mm/rev, preferably 0.1 - 0.4 mm/rev, depending on cutting speed and insert geometry.

The present invention has been described with reference to a cutting tool insert but it is evident that it also can be applied to other metal cutting tools, e.g., drills and endmills.

Example 1

Cemented carbide inserts with composition 90 wt% WC - 10 wt% Co (fine grain size, He = 20.5 kA/m) were used. Before deposition, the inserts were cleaned according to standard practice. The system was evacuated to a pressure of less than 0.08 Pa, after which the inserts were sputter cleaned with Ar ions. (Ti _c Al _a Cr _b )N _y layers were grown by cathodic arc evaporation using alloyed (Ti,Al,Cr) cathodes, resulting in the desired layer

compositions as shown in Table 1. The layers were grown at 400 °C, in pure N ₂ atmosphere at a total pressure of 2.5 Pa, using a substrate bias of -40 V and an

evaporation current of 75 A to a total thickness of about 3.0 μπι.

Table 1.

Layer composition (at%)

Sample TC(111) TC(200) TC(220) TC(111)/TC(200)

Ti Al Cr N

1 0,63 0,16 0,23 1 ,02 1 ,23 0,64 0,09 1 ,92

2 0,41 0,1 1 0,48 1 ,00 1 ,05 0,58 0,09 1 ,81

3 0,09 0,08 0,83 0,94 1 ,20 0,50 0,05 2,40

4 0,24 0,21 0,55 0,96 2,43 0,62 0,13 3,93

5 0,37 0,25 0,38 0,97 2,21 0,57 0,1 1 3,89

6 0,49 0,24 0,29 1 ,02 2,01 0,60 0,08 3,35

7 0,09 0,23 0,68 1 ,00 1 ,95 0,56 0,08 3,48

8 0,75 0,25 0,00 0,98 - - - -

9 0,01 0,29 0,67 0,97 - - - -

10 0,46 0,33 0,22 0,97 2,12 0,60 0,06 3,53

1 1 0,32 0,34 0,34 0,92 2,10 0,56 0,07 3,75

12 0,16 0,33 0,51 0,98 2,14 0,57 0,12 3,76

13 0,49 0,48 0,06 1 ,03 0,51 2,44 0,30 0,21

14 0,24 0,46 0,30 1 ,00 2,48 0,43 0,09 5,83

15 0,15 0,46 0,38 0,95 2,29 0,28 0,09 8,18

16 0,31 0,46 0,23 0,97 2,10 0,55 0,15 3,82

17 0,08 0,47 0,45 0,96 2,13 0,42 0,10 5,06

18 0,38 0,47 0,15 0,97 0,37 2,52 0,25 0,15

19 0,02 0,50 0,49 1 ,01 2,38 0,35 0,13 6,80

20 0,50 0,50 0,05 1 ,05 - - - -

21 0,27 0,52 0,24 1 ,03 1 ,95 0,52 0,07 3,75

22 0,08 0,53 0,39 0,95 2,13 0,25 0,07 8,37

23 0,17 0,53 0,30 0,94 2,19 0,44 0,13 4,98

24 0,24 0,54 0,23 1 ,00 2,10 0,45 0,08 4,67

25 0,17 0,55 0,28 0,97 2,02 0,50 0,14 4,05

26 0,08 0,57 0,37 1 ,02 2,14 0,42 0,15 5,1 1

27 0,13 0,56 0,31 1 ,00 2,17 0,54 0,1 1 4,01

28 0,20 0,58 0,22 0,96 2,15 0,49 0,12 4,39

29 0,04 0,60 0,36 0,93 2,08 0,42 0,08 5,00

30 0,27 0,63 0,10 0,97 0,41 2,26 0,33 0,18

31 0,26 0,74 0,03 1 ,03 - - - -

32 0,00 0,73 0,27 0,95 - - - - The as-deposited layers were characterized with respect to composition, microstructure and hardness by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and nanoindentation, respectively. The average composition of the layers was estimated by energy dispersive spectroscopy (EDS) analysis area using a LEO Ultra 55 scanning electron microscope operated at 10 kV equipped with a Thermo Noran EDS. Industrial standards and ZAF correction were used for the quantitative analysis. The metal composition was evaluated using a Noran System Six (NSS ver 2) software (see Table 1).

All layers exhibited a columnar microstructure. Figure 1 is a SEM micrograph of sample #23 in Table 1 showing a fractured cross section of the (Tio _. i ₇ Alo.53Cro.3o)N layer, marked as I, and the cemented carbide insert, marked as II. In addition to SEM, further details of the mictrostructure were obtained by cross-sectional TEM using a FEI Technai G" TF 20 UT operated at 200 kV. Samples for TEM were prepared by conventional mechanical grinding/polishing followed by ion-beam etching to electron translucency of the samples. Figure 2 shows a TEM micrograph of the (Τΐο _.17 Α1ο.53θ¾.3 ₀ )Ν layer in cross section. The image is obtained close to the middle of the layer thickness and the growth direction is marked with an arrow. Said layer has a columnar microstructure with an average columnar width of about 0.5 μπι. The average column width was determined by averaging the width of more than 10 adjacent columns.

The NaCl-structure of the layers was confirmed by XRD in both Θ-2Θ and grazing incidence (GI) configuration. XRD patterns were obtained using a Bruker AXS D8- advanced x-ray diffractometer with Cu K _a radiation. Figure 3 shows the GI pattern, 1° incidence angle, of sample #23 from which the NaCl layer structure is verified. The XRD data was also used to determine the texture relations of the samples. Figure 4 shows XRD patterns of sample #14, marked as A, with texture coefficients TC(111) = 2.48, TC(200) = 0.43 and TC(220) = 0.09, i.e., having a { 111 } fiber texture and sample #30, marked as B, with texture coefficients TC(111) = 0.41, TC(200) = 2.26 and TC(220) = 0.33, i.e., having a {200} fiber texture.

The residual stresses, σ, of the (Ti,Al,Cr)N layers were evaluated by XRD measurements using the sin ψ method. The stress measurements were obtained using the 220-reflection. Data was obtained using the side-inclination technique (Ψ-geometry) with 11, Ψ-angles (positive and negative), equidistant within a sin Ψ range of 0 to 0.82 (Ψ~65°). The residual stress values were evaluated using a Poisson's ratio of v=0.23 and Young's modulus of E=379 GPa.

Finally, hardness data was estimated by the nanoindentation technique.

Indentations were performed on mechanically polished layers using a UMIS

nanoindentation system with a Berkovich diamond tip and a maximum tip load of 30 mN. Hardness data was evaluated from the load-off segment using the UMIS software.

Example 2

Example 1 was repeated but using alloyed (Ti,Al,Cr,Me) cathodes, resulting in the desired (Ti,Al,Cr,Me)N, balanced in N content, layer compositions as shown in Table 2 for Me = Zr, Table 3 for Me = Nb and Table 4 for Me = Ta, respectively.

Table 2

Table 3

Layer composition (at%)

Sample

Ti Al Cr Nb

1 0,22 0,55 0, 18 0,05

2 0, 13 0,48 0,27 0, 12

3 0,20 0,38 0,27 0, 15 Table 4

Layer composition (at%)

Sample

Ti Al Cr Ta

1 0, 1 1 0,60 0,24 0,05

2 0, 15 0,48 0,27 0, 10

3 0,20 0,36 0,29 0, 15 Example 3

Example 1 was repeated but using an alloyed (Tio .33AI0 _.33 0¾ _.34 ) cathode for growth of samples 1-4 in, an alloyed (Tio.25Alo.45Cro.30) cathode for growth of samples 5-8 and an alloyed (Tio.15Alo.55Cro.30) cathode for growth of samples 9-12 in Table 6, respectively. Said layers were grown in a mixed reactive N2 + O2 + CH ₄ gas mixture at a total gas pressure of 2.5 Pa. The partial pressures of N ₂ , O2 and CH ₄ were individually set to yield the desired layer composition as shown in Table 5.

Table 5

Layer composition (at%)

Sample

Ti Al Cr C 0 N

1 0,32 0,34 0,34 0,06 0,45 0,49

2 0,32 0,34 0,34 0, 13 0,25 0,62

3 0,32 0,34 0,34 0,07 0, 12 0,81

4 0,32 0,34 0,34 0, 10 0,00 0,90

5 0,24 0,46 0,30 0,06 0,45 0,49

6 0,24 0,46 0,30 0, 13 0,25 0,62

7 0,24 0,46 0,30 0,07 0, 12 0,81

8 0,24 0,46 0,30 0, 10 0,00 0,90

9 0, 13 0,56 0,31 0,06 0,45 0,49

10 0, 13 0,56 0,31 0, 13 0,25 0,62

1 1 0, 13 0,56 0,31 0,07 0, 12 0,81

12 0, 13 0,56 0,31 0, 10 0,00 0,90

Example 4

Samples 2, 4, 10, 13, 14, 22, 23, 25 and 30 from example 1 were tested and compared to competitor grades under the following conditions:

Geometry: DCMT11T304-F1

Application: Longitudinal turning

Work piece material: DIN 100Cr6

Cutting speed: 250 m/min

Feed: 0.15 mm/rev

Depth of cut: a _p = 0.5 mm

Tool life criteria: Flank wear (vb) > 0.2 mm

The results are presented in Table 6.

Table 6

The test was stopped at the same maximum flank wear. An improved tool performance with improved wear characteristics scales with an increase in

TC(111)/TC(200).

Example 5

Samples 2, 4, 10, 13, 14, 22, 23, 25 and 30 from example 1 were tested and compared to competitor grades under the following conditions:

Geometry: XOEX120408-M07

Application: Shoulder milling

Cutter diameter: 32 mm

Work piece material: SSI 672

Cutting speed: 275 m/min

Feed: 0.25 mm/tooth

Depth of cut: a _p = 3 mm

Width of cut: 8.8 mm

Tool life criteria: Flank wear (vb) > 0.3 mm

The results are presented in Table 7.

Table 7

The test was stopped at the same maximum flank wear. An improved tool performance with improved wear characteristics scales with an increase in

TC(111)/TC(200).