Coated cutting tool and a method for coating the cutting tool

Abstract

A coated cutting tool includes a substrate with a coating having a total thickness of 0.25-30 μm. The coating has a first layer and a second layer, the first layer being a wear resistant PVD deposited layer having a thickness of 0.2-15 μm arranged between the substrate and the second layer, and wherein the second layer is a Cr layer.

Claims

1. A coated cutting tool comprising a substrate with a coating having a total thickness of 0.25-30 μm, wherein the coating includes a first layer and a second layer, and wherein the first layer is a wear resistant PVD deposited layer having a thickness of 0.2-15 μm, the first layer being arranged between the substrate and the second layer, the first layer being a (Ti.sub.1−xAl.sub.x)N.sub.y layer with 0.1<x<0.7 and 0.6<y<1.1, or a NaCl structured (Ti.sub.1−yAl.sub.y)N.sub.w/(Ti.sub.1−aSi.sub.a)N.sub.b nanolaminate with sublayer thickness between 5 and 50 nm, where 0.1<v<0.7, 0.7<w<1.1, 0.02<a<0.25, and 0.7<b<1.1, or a (Ti.sub.1−mSi.sub.m)N.sub.n layer, where 0≤m<0.25, and 0.7<n<1.1, or a (Cr.sub.1−cAl.sub.c)N.sub.d layer, where 0.5<c<0.9, and 0.7<d<1.1, or a (Cr.sub.1−eAl.sub.e).sub.2O.sub.3 layer, where 0.5<e<0.9, and wherein the second layer is a Cr layer, the Cr layer being an outermost layer of the coating.

2. The coated cutting tool according to claim 1, wherein a thickness of the Cr layer is 0.05-5 μm.

3. The coated cutting tool according to claim 1, wherein the Cr layer is a PVD deposited layer.

4. The coated cutting tool according to claim 1, wherein the Cr layer has a body-centered cubic structure with a crystallographic orientation relation of 0.3<R1<1, where R1=I.sub.(110)/(I.sub.(110)+I.sub.(200)+I.sub.(211), and where 1.sub.(110), 1.sub.(200), and 1.sub.(211) are the XRD peak areas as extracted from the pseudo-Voigt peak profile fitting results of θ-2θ scans obtained with CuKα radiation for the bcc structure Cr layer diffraction peaks.

5. The coated cutting tool according to claim 1, wherein the first layer is a (Ti.sub.1−xAl.sub.x)N.sub.y layer with 0.1<x<0.7 and 0.7<y<1.1.

6. The coated cutting tool according to claim 1, wherein the first layer is a NaCl structure c-(Ti.sub.1−xAl.sub.x)N.sub.y layer, where 0.1<x<0.7, and 0.7<y<1.1.

7. The coated cutting tool according to claim 5, wherein 0.5<x<0.6.

8. The coated cutting tool according to claim 1, wherein the first layer is a NaCl structured (Ti.sub.1−vAl.sub.v)N.sub.w/(Ti.sub.1−aSi.sub.a)N.sub.b nanolaminate with a sublayer thickness between 5 and 50 nm, and wherein 0.4<v<0.7 , , 0.7<w<1.1,0.02<a<0.25, and 0.7<b<1.1.

9. The coated cutting tool according to claim 1, wherein the first layer is a (Ti.sub.1−mSi.sub.m)N.sub.n layer, where 0<m<0.15, and 0.7<n<1.1.

10. The coated cutting tool according to claim 1, wherein the first layer is a (Cr.sub.1−cAl.sub.c)N.sub.d layer, where 0.5<c<0.8, and 0.7<d<1.1.

11. The coated cutting tool according to claim 1, wherein the first layer is a (Cr.sub.1−eAl.sub.e).sub.2O.sub.3 layer, where 0.5<e<0.8.

12. The coated cutting tool according to claim 1, wherein a ratio between the Cr layer thickness and the total coating thickness is between 0.01 and 2.

13. The coated cutting tool according to claim 1, wherein the first layer has a hardness H>20 GPa.

14. The coated cutting tool according to claim 1, wherein the first layer has a NaCl type structure and the Cr layer has a body-centered cubic structure, the ratio, R4, between the XRD peak intensity of the body-centered cubic Cr peak and the XRD peak intensity of the NaCl structure peak originating from the first layer is 0.05<R4<30, where XRD peak intensity is evaluated as the peak area extracted from the pseudo-Voigt peak profile fitting results of θ-2θ scans obtained with CuKα radiation.

15. The coated cutting tool according to claim 1, wherein the substrate comprises at least one of the following: cemented carbide, cermet, ceramics, steel and cubic boron nitride.

16. The coated cutting tool according to claim 15, wherein the cemented carbide includes WC and 4-15 wt % Co.

17. A method for producing of a coated cutting tool comprising the steps of: applying a substrate of cemented carbide, cermet, ceramic, steel or cubic boron nitride with a hard and wear resistant coating having a thickness of 0.25-30 μm by means of PVD (physical vapor deposition) techniques, such as cathodic arc deposition, wherein the coating includes a first layer, the first layer being a (Ti.sub.1−xAl.sub.x)N.sub.y layer with 0.1<x<0.7 and 0.6<y<1.1, or a NaCl structured (Ti.sub.1−yAl.sub.v)N.sub.w/(Ti.sub.1−aSi.sub.a)N.sub.b nanolaminate with sublayer thickness between 5 and 50 nm, where 0.1<v<0.7, 0.7<w<1.1, 0.02<a<0.25, and 0.7<b<1.1, or a (Ti.sub.1−mSi.sub.m)N.sub.n layer, where 0≤m<0.25, and 0.7<n<1.1, or a (Cr.sub.1−cAl.sub.c)N.sub.d layer, where 0.5<c<0.9, and 0.7<d<1.1, or a (Cr.sub.1−eAl.sub.e).sub.2O.sub.3 layer, where 0.5<e<0.9 and a second layer, the second layer being a Cr layer arranged as an outermost layer of the coating; and growing the Cr layer by using pure Cr cathodes applying an evaporation current between 50 A and 200 A, a gas atmosphere containing pure Ar at a total gas pressure between 1.0 Pa and 7.0 Pa, and applying a deposition temperature between room temperature and 500° C.

18. The method according to claim 17, further comprising growing a first layer being a (Ti.sub.1−xAl.sub.x)N.sub.y-layer, with 0.1<x<0.7 and 0.7<y<1.1, between the substrate and the Cr layer, by cathodic arc evaporation with an evaporation current between 50 A and 200 A using composite and/or alloyed (Ti,Al) cathodes, and in a reactive gas atmosphere containing N.sub.2 and optionally mixed with 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, at a temperature between 200° C. and 800° C.

19. A coated cutting tool comprising a substrate with a coating having a total thickness of 0.25-30 μm, wherein the coating includes a first layer and a second layer, and wherein the first layer is a wear resistant PVD deposited layer having a thickness of 0.2-15 μm, the first layer being arranged between the substrate and the second layer, and wherein the second layer is a Cr layer, the Cr layer being an outermost layer of the coating, wherein the Cr layer has a body-centered cubic structure with a crystallographic orientation relation of 0.3<R1<1, where R1=I.sub.(110)/(I.sub.(110)+I.sub.(200)+I.sub.(211)), and where I.sub.(110), 1.sub.(200), and 1.sub.(211) are the XRD peak areas as extracted from the pseudo-Voigt peak profile fitting results of θ-2θ scans obtained with CuKα radiation for the bcc structure Cr layer diffraction peaks.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows x-ray diffractograms for three coatings according to embodiments of the invention. Peaks marked “S” originate from the substrate, peaks marked “A” originate from a first layer, and peaks marked “Cr” originate from the Cr layer.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(2) According to the invention there is provided a coated cutting tool consisting of a substrate and a coating. The coating comprising a first layer and a second layer where the first layer is a wear resistant PVD deposited layer and the second layer is a Cr layer. The Cr layer is arranged as an outermost layer and it has surprisingly been found that the Cr layer gives improved performance in machining. The Cr layer is a PVD deposited layer and has a thickness between 0.05 μm and 3 μm.

(3) The average composition of the layers was estimated by energy dispersive spectroscopy (EDS) analysis area using a LEO Ultra 55 scanning electron microscope (SEM) operated at 20 kV and normal incidence to the coated surface equipped with a Thermo Noran EDS. Internal standards and ZAF correction were used for the quantitative analysis. The metal composition was evaluated using a Noran System Six (NSS ver 2) software.

(4) Coating phase detection and evaluation of preferred crystallographic orientation were performed by XRD using a Bruker AXS D8-advance x-ray diffractometer and Cu Kα radiation in Bragg-Brentano configuration. Typically, the detection limit for each phase in a polycrystalline mixed phase materials is less than 5 vol %.

(5) FIG. 1 shows 0-2θ X-ray diffractograms collected from three coatings according to embodiments of the invention. The coating phases were indexed with respect to the JCPDS cards 01-1261 (Cr) and 38-1420 (c-TiAlN), where the latter had to be shifted to match the smaller lattice parameter of c-TiAlN compared to c-TiN. Small amounts, close to or below the detection limit of the diffraction technique, of cubic phase c-TiN, cubic phase c-AlN and hexagonal phase h-AlN phases cannot be ruled out.

(6) The position and intensity (area) of the crystalline peaks in the XRD diffractograms are determined by fitting a pseudo-Voigt function to each crystalline peak. Additionally, the fitting function contains a linear term to account for residual scattering arising from the background. The XRD data peak fitting was conducted using the Bruker AXS Topas 2.1 software. The resulting peak areas are used to calculate the ratios R1, R2, R3, R4, and RA according to the embodiments of the invention.

Example 1

(7) Cemented carbide (WC—Co) cutting tools with a range of compositions comprising 6 to 13 wt % Co binder balanced with tungsten carbide (WC) and other carbides of, e.g., titanium, tantalum or niobium as well as various amounts of binder alloying elements such as iron, chromium, nickel, molybdenum or alloys of these elements were used as substrate for the layer depositions by cathodic arc evaporation.

(8) Before deposition, the cutting tools were cleaned in ultrasonic baths of an alkali solution and alcohol. The system was evacuated to a pressure of less than 2.0×10.sup.−3 Pa, after which the tools were sputter cleaned with Ar ions. Then, for coatings I1-I10, a Ti.sub.0.47Al.sub.0.53N layer was deposited at 450° C. using Ti.sub.0.45Al.sub.0.55 cathodes in a reactive N.sub.2 gas atmosphere at a total gas pressure of 4.5 Pa, applying an evaporation arc current of about 150 A and a negative substrate bias of about 50 V. Subsequently, the Cr layers were deposited in separate processes without external heating using Cr cathodes in an Ar atmosphere at a total gas pressure of 4 Pa, applying an evaporation arc current of about 150 A. The substrate bias and thickness was varied for the Cr layer to produce several coatings as shown in Table 1 and for coatings I5-I10 an additional Ar etch was introduced before Cr deposition. A reference Ti.sub.0.47Al.sub.0.53N coating, C1, without Cr layer was also produced at the same time and with same parameters as above. The first layers of coatings I11-I15 and coatings C2-C6 were also deposited by cathodic arc evaporation using similar process parameters, except coatings I15 and C6 in which the chromium aluminium oxide layer was deposited in a pure O.sub.2 atmosphere at a pressure of about 1 Pa.

(9) The XRD peak intensity ratios as defined in the embodiments of the invention are shown in table 1.

(10) TABLE-US-00001 TABLE 1 Specifications and properties of the coatings. Coating Layer A Cr layer Inventive Composition Thickness RA Thickness Bias R1 R2 R3 R4 I1 Ti.sub.0.47Al.sub.0.53N 2 μm 0.87 0.1 μm 0 0.85 0.01 0.14 0.11 I2 Ti.sub.0.47Al.sub.0.53N 2 μm 0.87 0.3 μm 0 0.87 0.01 0.12 0.68 I3 Ti.sub.0.47Al.sub.0.53N 2 μm 0.83 0.8 μm 0 0.93 0.02 0.05 4.11 I4 Ti.sub.0.47Al.sub.0.53N 2 μm 0.94 2.4 μm 0 0.91 0.04 0.05 19.91 I5 Ti.sub.0.47Al.sub.0.53N 2 μm 0.88 0.8 μm 0 0.53 0.39 0.08 0.71 I6 Ti.sub.0.47Al.sub.0.53N 2 μm 0.87 0.8 μm 10 0.44 0.46 0.10 0.51 I7 Ti.sub.0.47Al.sub.0.53N 2 μm 0.87 0.8 μm 25 0.44 0.50 0.06 0.46 I8 Ti.sub.0.47Al.sub.0.53N 2 μm 0.86 0.8 μm 50 0.46 0.49 0.05 0.43 I9 Ti.sub.0.47Al.sub.0.53N 2 μm 0.88 0.8 μm 100 0.56 0.37 0.07 0.28 I10 Ti.sub.0.47Al.sub.0.53N 2 μm 0.88 0.8 μm 150 0.63 0.30 0.07 0.13 I11 Ti.sub.0.38Al.sub.0.62N/Ti.sub.0.93Si.sub.0.07/N* 2.5 μm 0.86 0.3 μm 0 0.90 0.01 0.09 0.54 I12 Ti.sub.0.93Si.sub.0.07N 2.5 μm 0.97 0.3 μm 0 0.92 0.02 0.06 0.12 I13 TiN 2.5 μm 0.30 0.3 μm 0 0.90 0.01 0.09 1.36 I14 Cr.sub.0.31Al.sub.0.69N 2.5 μm —** 0.3 μm 0 —** —** —** —** I15 (Cr.sub.0.30Al.sub.0.70).sub.2O.sub.3 2.5 μm —*** 0.3 μm 0 0.94 0.02 0.04 —*** Comparative Composition Thickness RA Hardness C1 Ti.sub.0.47Al.sub.0.53N 2 μm 0.87 31 GPa C2 Ti.sub.0.38Al.sub.0.62N/Ti.sub.0.93Si.sub.0.07N* 2.5 μm 0.86 29 GPa C3 Ti.sub.0.93Si.sub.0.07N 2.5 μm 0.97 30 GPa C4 TiN 2.5 μm 0.30 28 GPa C5 Cr.sub.0.31Al.sub.0.69N 2.5 μm —** 30 GPa C6 (Cr.sub.0.30Al.sub.0.70).sub.2O.sub.3 2.5 μm —*** 25 GPa *Nanolaminate with sublayer thickness about 10 nm. **Could not be evaluated due to peak overlaps ***Not evaluated since coating is not in NaCl structure

(11) The hardness of coating C1, corresponding to the first layer of coatings I1-I10, was evaluated from nanoindentation experiments, after mechanical polishing of the surface, using a UMIS 2000 nanoindentation system with a Berkovich diamond tip and a maximum tip load of 25 mN. The hardness was evaluated from the load-displacement curves using the method of Oliver and Pharr [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)]. An average of about 30 indents was made and a fused silica reference sample was used to check calibration. The hardness of coatings C2-C6, corresponding to the first layers of coatings I11-I15, was also evaluated from nanoindentation experiments, after mechanical polishing of the surface, using a Berkovich diamond tip and a maximum tip load of 4 mN. The hardness was evaluated from the load-displacement curves using the method of Oliver and Pharr [W. C. Oliver and G. M. Pharr, J. Mater. Res. 7, 1564 (1992)]. An average of about 20 indents was made and a fused silica reference sample was used to check calibration. The thus evaluated hardnesses of coatings C1-C6 are shown in Table 1. The standard error was estimated to ±2 GPa.

Example 2

(12) WC—Co inserts (ISO geometry TPUN160308) with about 6 wt % Co and coated with inventive coatings I2-I4 and comparative coating C1 from Example 1 were tested in turning of 316L. The test was made with repeated 5 mm cutting lengths, using the following data:

(13) Cutting speed: 80 m/min

(14) Feed: 0.2 mm/rev

(15) Depth of cut: 2 mm

(16) Performance criterion: Flank wear

(17) Table 2 shows a lower flank wear for the inventive coatings relative to the reference comparative coating.

(18) TABLE-US-00002 TABLE 2 Relative flank wear. Coating Flank wear I2 73 I3 77 I4 71 C1 100

Example 3

(19) WC—Co inserts (ISO geometry TPUN160308) with about 13 wt % Co and coated with coatings I1 and C1 from Example 1 were tested in turning of 316L with the following data:

(20) Cutting speed: 150 m/min

(21) Feed: 0.2 mm/rev

(22) Depth of cut: 3 mm

(23) Performance criterion: Flank wear

(24) The resulting flank wear of the inventive coating I1 was about 80% of the flank wear of the reference comparative coating.

Example 4

(25) WC—Co inserts (ISO geometry XOMX120408TR-ME08) with about 13 wt % Co and coated with coatings I1 and C1 from Example 1 were tested in milling of 316L with the following data:

(26) Milling cutter: R417.69-2525.3-12-3A

(27) Cutting speed: 120 m/min

(28) Feed: 0.19 mm/tooth

(29) Depth of cut: 5 mm

(30) a.sub.e: 3 mm (12%)

(31) Performance criterion: Flank wear

(32) The resulting flank wear of the inventive coating I1 was about 65% of the flank wear of the reference comparative coating.

Example 5

(33) WC—Co inserts (ISO geometry TPUN160308) with about 6 wt % Co and coated with inventive coatings I2-I10 and comparative coating C1 from Example 1 were tested in turning of 316L. The test was made with repeated 20 mm cutting lengths using the following data:

(34) Cutting speed: 80 m/min

(35) Depth of cut: 2 mm

(36) Performance criterion: Flank wear

(37) Table 3 shows a lower flank wear for the inventive coatings relative to the reference comparative coating.

(38) TABLE-US-00003 TABLE 3 Relative flank wear. Coating Flank wear I2 91 I3 71 I4 82 I5 89 I6 86 I7 69 I8 78 I9 85 I10 70 C1 100

Example 6

(39) WC—Co inserts (ISO geometry SNUN120308) with about 6 wt % Co and coated with inventive coatings I1 and I11-I15 and comparative coatings C1-C6 from Example 1 were tested in sliding tests which were performed using a commercially available scratch tester (CSM Instruments Revetest®). In the test, a stainless steel (AISI 316L) pin with a diameter of 10 mm and a polished (R.sub.a=25 nm) hemispherical shaped end surface (radius 5 mm) was loaded against the PVD coated cemented carbide inserts. Sliding tests were performed under dry conditions in ambient air (21-22° C., 25-26% RH) using a normal load of 20 N and a relative sliding speed of 10 mm/min. The sliding distance was 10 mm and each test was repeated three times. During testing friction coefficient and acoustic emission were continuously recorded.

(40) The reduction in measured friction coefficient for each inventive coating compared to the corresponding comparative coating is shown in Table 4. It is clear that the inventive coatings show a significant decrease in friction coefficient compared to their corresponding comparative coating.

(41) TABLE-US-00004 Inventive coating Comparative coating Friction reduction I1 C1 40% I11 C2 18% I12 C3 16% I13 C4 19% I14 C5 22% I15 C6 17%