Coated cutting tool and a method for coating the cutting tool

Abstract

A coated cutting tool and a hard and wear resistant coating for a body include at least one metal based nitride layer. The layer is (ZrxCrl-x-y-zAlyMez)Na with 0.55<x<0.85, 0.05<y<0.45, 0z<0.20, 0.95<a<1.10, and Me is one or more of the elements: Y, Ti, V, Nb, Ta, Mo, W, Mn or Si. The layer can have a thickness between 0.5 m and 15 m and be comprisied of a single cubic phase or a single hexagonal phase or a mixture thereof. In an exemplary embodiment, the layer is a cubic phase of a sodium chloride structure. The layer can be deposited using cathodic arc evaporation and is useful for metal cutting applications generating high temperatures.

Claims

1. A coated cutting tool comprising: a body; and a hard and wear resistant coating on the body, the coating comprising at least one metal based nitride layer, wherein said layer is (Zr.sub.xCr.sub.1-x-yAl.sub.y)N.sub.a with 0.60<x<0.80, 0.05<y<0.20, 0.95<a<1.10, and that the layer has a single cubic phase or a single hexagonal phase or a mixture thereof or a cubic phase of a sodium chloride structure, and that the layer has a thickness between 0.5 m and 15 m.

2. The coated cutting tool according to claim 1, wherein 0.65<x<0.75.

3. The coated cutting tool according to claim 1, wherein said at least one metal based nitride layer has a thickness between 0.5 m and 10 m.

4. The coated cutting tool according to claim 1, wherein said at least one metal based nitride layer has a nanohardness >20 GPa.

5. The coated cutting tool according to claim 4, wherein said at least one metal based nitride layer has a nanohardness between 25 GPa and 40 GPa.

6. The coated cutting tool according to claim 1, wherein said coating includes an innermost single layer of TiN, and the coating has a total coating thickness between 1 m and 20 m.

7. The coated cutting tool according to claim 1, wherein said coated cutting tool is a cutting insert for machining by chip removal, the body being selected from a group of hard alloy of cemented carbide, cermet, ceramics, cubic boron nitride and high speed steel.

8. The coated cutting tool according to claim 1, wherein said coated cutting tool is a drill or end-mill for machining by chip removal, the body being selected from a group of hard alloy of cemented carbide, cermet, ceramics, cubic boron nitride and high speed steel.

9. The coated cutting tool according to claim 1, wherein said coating includes a multilayer comprising, TiN, TiC, Ti(C,N) or (Ti,Al)N, and the coating has a total coating thickness between 1 m and 20 m.

10. The coated cutting tool according to claim 1, wherein said coating includes a multilayer comprising preferably a single layer of (Ti,Al)N, followed by the (Zr,Cr,A1)N layer and an outer single layer of TiN, the coating has a total coating thickness between 1 m and 20 m.

11. A method of making a coated cutting tool, comprising the steps of: growing a metal based nitride layer on a body by cathodic arc evaporation with an evaporation current between 50 A and 200 A using composite and/or alloyed cathodes, wherein said layer is (Zr.sub.xCr.sub.1-x-yAl.sub.y)Na with 0.60<x<0.80, 0.05<y0.20, 0.95<a<1.10, in a reactive atmosphere containing N.sub.2 and optionally with a carrier gas such as, e.g., Ar at a total gas pressure between 1.0 Pa and 7.0 Pa, with a negative substrate bias between 0 V and 300 V, and at a temperature between 200 C. and 800 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic view of a cross-section of part of a cutting tool comprising a body and a (Zr,Cr,Al,Me)N layer.

(2) FIG. 2 is a schematic view of a cross-section of part of a cutting tool comprising a body and a coating consisting of an innermost single layer and/or multilayer, a (Zr,Cr,Al,Me)N layer and an outermost single layer and/or multilayer

(3) FIG. 3 is a diagram of the nanohardness, H, as a function of post heat treatment, T, of (Zr.sub.0.75Cr.sub.0.14Al.sub.0.11)N.sub.1.03 layer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(4) According to one embodiment of the present invention, there is provided a body 1 onto which a hard and wear resistant coating is deposited comprising at least one metal based nitride layer 3 as shown in FIG. 1. The metal based nitride layer 3 is (Zr.sub.xCr.sub.1-x-y-zAl.sub.yMe.sub.z)N.sub.a with 0.55<x<0.85, 0.05 <y<0.45, 0z<0.20, 0.95<a<1.10 and Me is one or more of the elements selected from the group consisting of Y, Ti, V, Nb, Ta, Mo, W, Mn and Si, and the layer comprises a single cubic phase or a single hexagonal phase or a mixture thereof, preferably with a cubic sodium chloride structure, as determined by X-ray diffraction. The metal based nitride layer has a thickness between 0.5 m and 15 m, preferably between 0.5 m and 10 m, most preferably between 0.5 m and 5 m. Additionally, the layer contains a sum of oxygen (O) and carbon (C) concentration between 0 and 2 at %, preferably between 0 and 1 at %.

(5) The elemental composition of said layer, x, y and z including 0 and C, is estimated from measurements by, e.g., EDS or WDS techniques and is, within the measurement accuracy, essentially constant all through the layer thickness with a variation less than 10%, including the influence of normal process variations such as, e.g., rotation of the inserts during growth.

(6) Said layer has a columnar microstructure with an average column width of <1 m, preferably <0.6 m, 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.

(7) Said layer has a compressive stress level of 6.0 GPa<<0.5 GPa, preferably of 3.0 GPa <<1.0 GPa. The residual stress is evaluated by XRD using the sin.sup.2-method with a Poisson's ratio of =0.23 and a Young's modulus of E =379 GPa.

(8) Said layer has a nanohardness >20 GPa, as measured by nanoindentation measurements. Nanohardness data were estimated by the nanoindentation technique of the layers after mechanical polishing of the surface using a UMIS 2000 nanoindentation system with a Berkovich diamond tip with a maximum tip load of 25 mN.

(9) According to one embodiment of the invention, z =0, and said layer is (Zr.sub.xCr.sub.1-x-yAl.sub.y)N.sub.a with 0.55<x<0.85, preferably 0.60<x<0.80, most preferably 0.65<x<0.75, 0.05<y<0.45, preferably 0.05<y<0.35, most preferably 0.05<y<0.25, 0z<0.20 and 0.95<a<1.10.

(10) It is evident that said (Zr,Cr,Al,Me)N layer can be part of a complex coating design and used as an inner, middle and/or an outer layer of said complex coating.

(11) FIG. 2 shows an embodiment of the invention, where the cutting tool 1 comprises a body 1, also called substrate, provided with a coating consisting of an innermost single layer and/or multilayer 2 comprising, e.g., TiN, TiC, Ti(C,N) or (Ti,Al)N, preferably a single layer of (Ti,Al)N, followed by said (Zr,Cr,Al,Me)N layer 3 and an outermost single layer and/or multilayer 4 comprising, e.g., TiN, TiC, Ti(C,N) or (Ti,Al)N, preferably a single layer of TiN, with a total coating thickness between 1 m and 20 m, preferably between 1 m and 15 m, and most preferably between 1 m and 7 m.

(12) According to one embodiment of the invention, said body is a cutting insert for machining by chip removal comprising a body of a hard alloy of cemented carbide, cermet, ceramics, cubic boron nitride based material or high speed steel. It is, however, obvious that said body can be other metal cutting tools, e.g., drills and end mills.

(13) The deposition method for said layer is based on PVD techniques, e.g., cathodic arc evaporation or magnetron sputtering using one or more pure, composite and/or alloyed (Zr,Cr,Al, Me) cathodes/targets.

(14) In the case of cathodic arc evaporation, the metal based nitride layer is grown with an evaporation current between 50 A and 200 A depending on the cathode size, and said layer is (Zr.sub.xCr.sub.1-x-y-zAl.sub.yMe.sub.z)N.sub.a with 0.55<x<0.85, 0.05<y<0.45, 0z<0.20 and 0.95<a<1.10. A higher evaporation current is needed for larger cathodes in order to achieve comparable deposition conditions. The layers are grown using one or more composite and/or alloyed cathodes. The desired layer composition is obtained by selecting appropriate composition of the (Zr,Cr,Al,Me) cathode and gas atmosphere, where Me, when present in the layer, is one or more of the elements selected from the group consisting of Y, Ti, V, Nb, Ta, Mo, W, Mn and Si in a reactive atmosphere containing N.sub.2 and optionally with a carrier gas such as, e.g., Ar at a total gas pressure between 1.0 Pa and 7.0 Pa, preferably between 1.5 Pa and 4.0 Pa. The negative substrate bias is between 0 V and 300 V, preferably between 10 V and 150 V, most preferably between 15 V and 60 V. The deposition temperature is between 200 C. and 800 C., preferably between 300 C. and 600 C.

(15) In the case of magnetron sputtering, (Zr,Cr,Al,Me)N layers may be grown with a power density applied to the sputter target between 0.5 W/cm.sup.2 and 15 W/cm.sup.2, preferably between 1 W/cm.sup.2 and 5 W/cm.sup.2, from co-sputtering of pure elemental targets by altering the power to the respective targets (alter the deposition rate for each target) or from a composite and/or alloyed target, where Me, when present, is one or more of the elements selected from the group consisting of Y, Ti, V, Nb, Ta, Mo, W, Mn and Si in a reactive atmosphere containing N.sub.2 and optionally with a carrier gas such as, e.g., Ar at a total pressure between 0.1 Pa and 5.0 Pa, preferably between 0.1 Pa and 2.5 Pa. The desired layer composition is obtained by selecting appropriate composition of the (Zr,Cr,Al,Me) target, target power density and gas atmosphere. The negative substrate bias is between 0 V and 300 V, preferably between 10 V and 150 V, most preferably between 10 V and 80 V. The deposition temperature is between 200 C. and 800 C., preferably between 300 C. and 600 C.

(16) The invention also relates to the use of coated cutting tool insert according to the above for machining at cutting speeds of 50-400 m/min, preferably 75-300 m/min, with an average feed, per tooth in the case of milling, of 0.08-0.5 mm, preferably 0.1-0.4 mm, depending on cutting speed and insert geometry.

EXAMPLE 1

(17) Cemented carbide inserts with composition 94 wt % WC-6 wt % Co were used as a body for the layer depositions by cathodic arc evaporation.

(18) Before deposition, the inserts were cleaned in ultrasonic baths of an alkali solution and alcohol. The system was evacuated to a pressure of less than 2.010.sup.3 Pa, after which the inserts were sputter cleaned with Ar ions. (Zr.sub.xCr.sub.1-x-y-zAl.sub.yMe.sub.z)N.sub.a layers, 0.43<x<0.85, 0.05<y<0.45, z =0 and 1.00 21 a<1.09, coatings 1-18 in Table 1, were grown using (Zr,Cr,Al) cathodes, with compositions according to coatings 1-18 in Table 2. The layers were deposited at 450 C. in a pure N.sub.2 atmosphere, a process pressure of 3 Pa, a bias of 30 V and an evaporation current of 60 A to a total thickness of about 3 m.

(19) TABLE-US-00001 TABLE 1 Coating composition (at %) Coating Description Zr Cr Al Me N 1 ZrCrAlN 0.43 0.31 0.25 1.02 2 ZrCrAlN 0.50 0.22 0.28 1.04 3 ZrCrAlN 0.55 0.40 0.05 0.97 4 ZrCrAlN 0.53 0.33 0.14 1.04 5 ZrCrAlN 0.54 0.23 0.23 1.02 6 ZrCrAlN 0.55 0.11 0.34 1.02 7 ZrCrAlN 0.56 0.00 0.45 1.02 8 ZrCrAlN 0.64 0.31 0.05 1.06 9 ZrCrAlN 0.64 0.21 0.15 1.08 10 ZrCrAlN 0.65 0.09 0.26 1.09 11 ZrCrAlN 0.63 0.03 0.34 1.00 12 ZrCrAlN 0.72 0.24 0.04 1.01 13 ZrCrAlN 0.75 0.14 0.11 1.03 14 ZrCrAlN 0.74 0.13 0.13 1.04 15 ZrCrAlN 0.76 0.00 0.24 1.06 16 ZrCrAlN 0.81 0.08 0.11 1.03 17 ZrCrAlN 0.85 0.09 0.06 1.01 18 ZrCrAlN 0.85 0.00 0.14 1.03 19 ZrCrAlTiN 0.57 0.19 0.16 0.08 1.04 20 ZrCrAlNbN 0.58 0.22 0.15 0.05 1.02 21 ZrCrAlNbN 0.60 0.10 0.16 0.14 1.02 22 ZiCrAlTaN 0.62 0.12 0.17 0.09 1.02 23 ZrCrAlSiN 0.56 0.15 0.23 0.06 1.06 24 ZrCrAlSiN 0.55 0.12 0.25 0.08 1.00

(20) TABLE-US-00002 TABLE 2 Cathode composition (at %) Coating Description Zr Cr Al Me 1 ZrCrAlN 0.40 0.35 0.25 2 ZrCrAlN 0.50 0.20 0.30 3 ZrCrAlN 0.55 0.35 0.10 4 ZrCrAlN 0.55 0.30 0.15 5 ZrCrAlN 0.60 0.20 0.20 6 ZrCrAlN 0.60 0.05 0.35 7 ZrCrAlN 0.60 0.40 8 ZrCrAlN 0.65 0.25 0.10 9 ZrCrAlN 0.65 0.20 0.15 10 ZrCrAlN 0.65 0.10 0.25 11 ZrCrAlN 0.65 0.35 12 ZrCrAlN 0.75 0.20 0.05 13 ZrCrAlN 0.75 0.15 0.10 14 ZrCrAlN 0.75 0.10 0.15 15 ZrCrAlN 0.75 0.25 16 ZrCrAlN 0.80 0.10 0.10 17 ZrCrAlN 0.85 0.05 0.10 18 ZrCrAlN 0.85 0.15 19 ZrCrAlTiN 0.60 0.15 0.15 0.10 20 ZrCrAlNbN 0.60 0.20 0.15 0.05 21 ZrCrAlNbN 0.60 0.10 0.15 0.15 22 ZiCrAlTaN 0.65 0.10 0.15 0.10 23 ZrCrAlSiN 0.55 0.15 0.25 0.05 24 ZrCrAlSiN 0.55 0.10 0.25 0.10

EXAMPLE 2

(21) Example 1 was repeated using (Zr,Cr,Al,Me) cathodes for the deposition of the (Zr.sub.xCr.sub.1-x-y-zAl.sub.yMe.sub.z)N.sub.a layers, coatings 19-24 in Table 1 using cathodes as specified for coatings 19-24 in Table 2.

EXAMPLE 3

(22) The composition x, y, z and a, of the (Zr.sub.xCr.sub.1-x-y-zAl.sub.yMe.sub.z)N.sub.a layers was estimated by energy dispersive spectroscopy (EDS) analysis using a LEO Ultra 55 scanning electron microscope operated at 10 kV and equipped with a Thermo Noran EDS detector. The data were evaluated using the Noran System Six (NSS ver 2) software.

(23) The phase structure of as-deposited (Zr.sub.xCr.sub.1-x-y-zAl.sub.yMe.sub.z)N.sub.a layers where characterized by X-ray diffraction (XRD) using Cu K alpha radiation and a -2 configuration in a Bruker AXS D8 Advance diffractometer.

(24) The residual stresses, , of the (Zr.sub.1-x-zSi.sub.xMe.sub.z)N.sub.y layers were evaluated by XRD measurements using the sin.sup.2 method (see e.g. I.C. Noyan, J.B. Cohen, Residual Stress Measurement by Diffraction and Interpretation, Springer-Verlag, New York, 1987). The measurements were performed using CuK-radiation on the (311)-reflection. The residual stress values were within 5.0 GPa<<1.0 GPa for the different layers as evaluated using a Poisson's ratio of =0.23 and Young's modulus of E =379 GPa.

(25) Hardness data were estimated by the nanoindentation technique of the layers after mechanical polishing of the surface using a UMIS 2000 nanoindentation system with a Berkovich diamond tip with a maximum tip load of 25 mN. FIG. 2 shows the nanohardness, H, of (Zr.sub.0.75Cr.sub.0.14Al.sub.0.11)N.sub.1.03 layer as a function of post heat treatment, demonstrating its typical age hardening behavior.

EXAMPLE 4

(26) For a cutting test using the coatings from Table 1 (example 1) in a turning operation with the following data:

(27) Geometry: CNMG120408-MF1

(28) Application: Facing

(29) Work piece material: 100Cr6

(30) Cutting speed: 200 m/min

(31) Feed: 0.25 mm/rev.

(32) Depth of cut: 2 mm

(33) Performance criterion: Crater wear resistance

(34) the following relative cutting results, as shown in Table 3, are expected. Coatings 12-15 of the invention are expected with improved crater wear performance with a stop criteria of 1 mm.sup.2 crater area, and compared to the reference materials according to prior art.

(35) TABLE-US-00003 TABLE 3 Coating Relative performance Coatings according to embodiments of the invention coating 1 80-90 coating 2 80-90 coating 3 80-90 coating 4 80-90 coating 5 80-90 coating 6 80-90 coating 7 90-100 coating 8 90-100 coating 9 90-100 coating 10 90-100 coating 11 90-100 coating 12 100-110 coating 13 110-120 coating 14 110-120 coating 15 100-110 coating 16 90-100 coating 17 90-100 coating 18 90-100 coating 19 70-80 coating 20 90-100 coating 21 90-100 coating 22 70-80 coating 23 80-90 coating 24 80-90 Reference coatings according prior art Ti.sub.0.34Al.sub.0.66N (ref) 70-80 Al.sub.0.68Cr.sub.0.32N (ref) 60-70 TiN (ref) 50-60