Coated cutting tool

Abstract

A coated cutting tool includes a body and a hard and wear resistant coating on the body. The coating has at least one NbN layer with a thickness between 0.2 m and 15 m, wherein the NbN layer includes a phase mixture of a cubic phase, c-NbN, and a hexagonal phase, h-NbN.

Claims

1. A coated cutting tool comprising: a body; and a hard and wear resistant PVD coating on the body, the coating having at least one NbN layer with a thickness between 0.2 m and 15 m and a (Ti.sub.1-xAl.sub.x)N.sub.y layer arranged between the body and the NbN layer, the (Ti1-xAlx)Ny layer being a cubic c-(Ti1-xAlx)Ny layer where 0.4<x<0.7 and 0.7<y<1.1, and wherein the NbN layer is a phase mixture of a cubic phase, c-NbN, and a hexagonal phase, h-NbN, with a X-ray diffraction peak area ratio of 0.64<R.sub.0<1, where R.sub.0=I.sub.c-NbN(200)/(I.sub.c-NbN(200)+I.sub.h-NbN(100)), and I.sub.c-NbN(200) and I.sub.h-NbN(100) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK.sub.-radiation for the c-NbN (200) and h-NbN (100) diffraction peaks, respectively.

2. The coated cutting tool according to claim 1, wherein the cubic phase c-NbN has a crystallographic orientation of 0.2<R.sub.21, where R.sub.2=I.sub.c-NbN(200)/(I.sub.c-NbN(200)+I.sub.c-NbN(111)), and I.sub.c-NbN(200) and I.sub.c-NbN(111) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK.sub.-radiation for the c-NbN (200) and c-NbN (111) diffraction peaks, respectively.

3. The coated cutting tool according to claim 2, wherein the peak area ratio R.sub.2 is 0.4<R.sub.21.

4. The coated cutting tool according to claim 2, wherein the peak area ratio R.sub.2 is 0.6<R.sub.21.

5. The coated cutting tool according to claim 1, wherein the NbN layer has a crystallographic orientation relation of 0.5<R.sub.11, where R.sub.1=I.sub.c-NbN(200)/(I.sub.c-NbN(200)+I.sub.h-NbN(101)), and where I.sub.c-NbN(200) and I.sub.h-NbN(101) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK.sub.-radiation for the c-NbN (200) and h-NbN (101) diffraction peaks, respectively.

6. The coated cutting tool according to claim 5, wherein the peak area ratio R.sub.1 is 0.7<R.sub.11.0.

7. The coated cutting tool according to claim 1, wherein the c-(Ti.sub.1-xAl.sub.x)N.sub.y layer and the NbN layer has a thickness ratio d.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y:d.sub.NbN of 2:3<d.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y:d.sub.NbN<6:1, preferably 1:1<d.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y:d.sub.NbN<5:1.

8. The coated cutting tool according to claim 1, wherein the cubic c-(Ti.sub.1-xAl.sub.x)N.sub.y layer contains less than 5 at % of cubic c-TiN, cubic c-AlN and hexagonal h-AlN phases.

9. The coated cutting tool according to claim 1, wherein the c-(Ti.sub.1-xAl.sub.x)N.sub.y layer has a crystallographic orientation relation of 0.5<R.sub.71, where R.sub.7=I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(200)/(I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(200)+I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(111)), and I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(200) and I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(111)) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK.sub.-radiation for the c-(Ti.sub.1-xAl.sub.x)N.sub.y (200) and c-(Ti.sub.1-xAl.sub.x)N.sub.y (111) diffraction peaks, respectively.

10. The coated cutting tool according to claim 9, wherein the peak area ratio R.sub.7 is 0.6<R.sub.71.

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

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a fractured cross-sectional view SEM micrograph of a c-(Ti.sub.0.45Al.sub.0.55)N/NbN coating according to one embodiment of the invention where the c-(Ti.sub.1-xAl.sub.x)N.sub.y layer, I, is arranged between the body, S, and the NbN layer, II.

(2) FIG. 2 shows X-Ray -2 diffractograms of A: c-(Ti.sub.0.34Al.sub.0.66)N/NbN and B: c-(Ti.sub.0.45Al.sub.0.55)N/NbN coatings according to one embodiments of the invention.

(3) FIG. 3 shows grazing incidence, =1.5, X-Ray detector 2 diffractograms of A: c-(Ti.sub.0.34Al.sub.0.66)N/NbN and B: c-(Ti.sub.0.45Al.sub.0.55)N/NbN coatings according to one embodiments of the invention.

(4) FIG. 4 shows an X-ray -2 diffractogram of the as-deposited c-(Ti.sub.0.45Al.sub.0.55)N/NbN coating according to one embodiment of the invention including pseudo-Voigt profile fitted diffraction peaks. Each peak position (2) used in the fit are listed in the table.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(5) According to one embodiment of the invention, there is provided a coated cutting tool comprising a body and a hard and wear resistant coating on the body, the coating comprises at least one NbN layer comprising a phase mixture of a cubic phase, c-NbN, and a hexagonal phase, h-NbN, with a X-ray diffraction peak area intensity ratio of 0.4<R.sub.0<1.0, where R.sub.0=I.sub.c-NbN(200)/(I.sub.c-NbN(200)+I.sub.h-NbN(100)), and where I.sub.c-NbN(200) and I.sub.h-NbN(100) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK.sub.-radiation for the c-NbN (200) and h-NbN (100) diffraction peaks, respectively. The NbN-layer has a thickness between 0.2 m and 15 m as measured on the thinnest part of the coating thickness over the cutting edge, the flank face or the rake face of the coated cutting tool.

(6) According to one embodiment of the invention, the NbN layer has a crystallographic orientation relation of 0.5<R.sub.11, preferably 0.6<R.sub.11.0, most preferably 0.7<R.sub.11.0, where R.sub.1=I.sub.c-NbN(200)/(I.sub.c-NbN(200)+I.sub.h-NbN(101)), and where I.sub.c-NbN(200) and I.sub.h-NbN(101) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK.sub.-radiation for the c-NbN (200) and h-NbN (101) diffraction peaks, respectively.

(7) According to one embodiment of the invention the cubic phase c-NbN has a crystallographic orientation relation of 0.2<R.sub.21, preferably 0.4<R.sub.21, most preferably 0.6<R.sub.21, where R.sub.2=I.sub.c-NbN(200)/(I.sub.c-NbN(200)+I.sub.c-NbN(111), and where I.sub.c-NbN(200) and I.sub.c-NbN(111) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK.sub.-radiation for the c-NbN (200) and c-NbN (111) diffraction peaks, respectively.

(8) According to one embodiment of the present invention said coating comprising a cubic c-(Ti.sub.1-xAl.sub.x)N.sub.y layer where 0<x<0.7 and 0.7<y<1.1, preferably 0.4<x<0.7, arranged between the body and the NbN layer.

(9) According to one embodiment the coating comprises a c-(Ti.sub.1-xAl.sub.x)N.sub.y layer with a thickness between 0.2 m and 15 m, preferably between 0.2 m and 10 m, more preferably between 0.5 m and 5 m and a NbN layer with a thickness between 0.1 m and 10 m, preferably between 0.1 m and 5 m, most preferably between 0.2 m and 3 m as measured on the thinnest part of the coating thickness over the cutting edge, the flank face or the rake face of the coated cutting tool.

(10) According to one embodiment of the present invention the c-(Ti.sub.1-xAl.sub.x)N.sub.y layer has a crystallographic orientation relation of 0.5<R.sub.71, preferably 0.6<R.sub.71, where R.sub.7=I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(200)/(I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(200)+I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(111)) and where I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(200) and I.sub.c-(Ti.sub.1-x.sub.Al.sub.x.sub.)N.sub.y.sub.(111) are the X-ray diffraction peak areas as extracted from the pseudo-Voigt peak profile fitting results of -2 scans obtained with CuK-radiation for the c-(Ti.sub.1-xAl.sub.x)N.sub.y (200) and c-(Ti.sub.1-xAl.sub.x)N.sub.y (111) diffraction peaks, respectively.

(11) 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. 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.

(12) The deposition method for the coating is based on PVD techniques, preferably cathodic arc deposition, using one or more pure, composite or alloyed cathodes in a reactive gas atmosphere containing N.sub.2 and optionally mixed with Ar at total gas pressure between 1.0 Pa and 7.0 Pa, preferably between 2.5 Pa and 5 Pa. Both gas mixture and cathode composition are selected such to reach the targeted composition for the deposited NbN and (Ti.sub.1-xAl.sub.x)N.sub.y, 0.4<x<0.7 and 0.7<y<1.1 layers. Depositions is made with an evaporation arc current between 50 A and 200 A, a negative substrate bias between 20 V and 300 V, preferably between 20 V and 150 V, most preferably between 20 V and 60 V, and a deposition temperature between 200 C. and 800 C., preferably between 300 C. and 600 C. A higher evaporation current is needed for larger cathodes in order to achieve comparable deposition conditions.

(13) The coating has a columnar microstructure with an average column width of <1 m, preferably <0.9 m, more preferably <0.8 m as estimated from scanning electron microscopy micrographs, obtained by a LEO Ultra 55 scanning electron microscope operated at 20 kV, from a middle region of the layer, i.e. within a region of 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.

(14) FIG. 1 shows a fractured cross-sectional view SEM micrograph of a c-(Ti.sub.0.45Al.sub.0.55)N/NbN coating consisting of a c-(Ti.sub.0.45Al.sub.0.55)N layer (I) arranged between the body (S) and the NbN layer (II) according to a embodiment of the invention.

(15) Coating phase detection was performed by X-ray diffractometry (XRD) using a Bruker AXS D8-advance x-ray diffractometer and Cu K radiation in both Bragg-Brentano and grazing incident angle configurations. Typically, the detection limit for each phase in a polycrystalline mixed phase materials is less than 5 vol %.

(16) FIG. 2 shows -2 X-ray diffractograms for 33263 of A: c-(Ti.sub.0.34Al.sub.0.66)N/NbN and B: c-(Ti.sub.0.45Al.sub.0.55)N/NbN coatings, respectively, according to two embodiments of the invention. Both the A and B diffractograms displays diffraction peaks originating from the WCCo substrate, S, and coating phases of cubic c-NbN, hexagonal h-NbN and cubic c-TiAlN. The coating phases were indexed with respect to the JCPDS cards 38-1155 (c-NbN), 25-1361 (h-NbN) and 38-1420 (c-TiAlN). For the cubic c-NbN and c-TiAlN phases, the (111) and (200) diffraction peak positions are marked in the diffractograms. For the c-NbN phase also the position for the c-NbN (220) peak is marked. Both the c-NbN and c-TiAlN phases reveal a 200 preferred orientation with stronger diffracted intensities for their respective (200) diffraction peaks. For the h-NbN phase, the positions for the (100), (101), (103) and (110) diffraction peaks are also marked in the diffractograms. 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 neglected.

(17) Grazing incidence XRD was conducted to reveal the details of the different coating phases, i.e., avoiding the overlap of the diffracted intensities from the WCCo substrate. FIG. 3 shows grazing incident, =1.5, X-ray detector 2 diffractograms for 33263 of A: c-(Ti.sub.0.34Al.sub.0.66)N/NbN and B: c-(Ti.sub.0.45Al.sub.0.55)N/NbN coatings, respectively, according to two other embodiments of the invention. The A and B diffractograms displays diffraction peaks originating from cubic phase c-NbN, hexagonal phase h-NbN and cubic phase c-TiAlN phases. For the cubic c-NbN and c-TiAlN phases their respective (111) and (200) diffraction peak positions are marked in the diffractograms. In addition, for the c-NbN also the c-NbN (220) peak is marked. For the h-NbN phase, the positions for the (100), (101), (103) and (110) diffraction peaks are marked in the diffractograms. Small amounts, below the detection limit, of the substrate material as well as of cubic phase c-TiN, cubic phase c-AlN and hexagonal phase h-AlN cannot be neglected.

(18) The position and area (integral intensity) of the crystalline peaks in the XRD diffractograms are fitted using a pseudo-voigt function for each crystalline peak and initial peak positions according to Table 1. 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.

(19) TABLE-US-00001 TABLE 1 Peak Position # (2) 1 34.4 2 35.0 3 35.7 4 37.0 5 38.7 6 41.0 7 43.3 8 44.0 9 46.2 10 48.3 11 51.2 12 58.9 13 61.0 14 61.7

(20) FIG. 4 shows an X-ray -2 diffractogram of the as-deposited c-(Ti.sub.0.45Al.sub.0.55)N/NbN coating according to coating B in FIG. 3.

(21) The pseudo-Voigt fitting results for the A: c-(Ti.sub.0.34Al.sub.0.66)N/NbN and B: c-(Ti.sub.0.45Al.sub.0.55)N/NbN coatings according to embodiments of the invention are shown in Table 2.

(22) TABLE-US-00002 TABLE 2 Diffraction Peaks Peak Position h-NbN c-NbN c-Ti.sub.1xAl.sub.xN Peak Area # (2) Substrate (25-1361) (38-1155) (38-1420) A coating B coating 1 34.4 (100) 758.1 457.7 2 35.0 (111) 225.9 474.7 3 35.7 S 2364.9 2283.1 4 37.0 (111) 690.4 194.9 5 38.7 (101) 142.6 177.3 6 41.0 (200) 358.2 1166.7 7 43.3 (200) 1322.3 538.0 8 44.0 S 195.2 41.5 9 46.2 S 124.5 103.4 10 48.3 S (102) 2550.2 2385.3 11 51.2 S 35.9 73.3 12 58.9 (220) 145.6 61.6 13 61.0 (103) 138.4 51.4 14 61.7 (110) 410.1 195.3 15 63.0 (220) 74.1 10.5

(23) The correlation of the different XRD diffraction peak(s) with its respective fitted peak area intensities and various peak area intensities ratios for the A: c-(Ti.sub.0.34Al.sub.0.66)N/NbN and B: c-(Ti.sub.0.45Al.sub.0.55)N/NbN coatings are shown in Table 3 and Table 4, respectively.

(24) TABLE-US-00003 TABLE 3 Peak Area Peak A coating B coating I.sub.h0 = I(h-NbN(100)) 758.1 457.7 I.sub.h1 = I(h-NbN(101)) 142.6 177.3 I.sub.h2 = I(h-NbN(103)) + I(hNbN(110)) 548.5 246.7 I.sub.c1 = I(c-NbN(200)) 358.2 1166.7 I.sub.c2 = I(c-NbN(111)) 225.9 474.7 I.sub.c3 = I(c-NbN(220)) 145.6 61.6 I.sub.c4 = I(c-TiAlN(200)) 1322.3 538.0

(25) TABLE-US-00004 TABLE 4 Peak Area Ratio A coating B coating R.sub.0 = I.sub.c1/(I.sub.c1 + I.sub.h0) 0.3 0.7 R.sub.1 = I.sub.c1/(I.sub.c1 + I.sub.h1) 0.7 0.9 R.sub.2 = I.sub.c1/(I.sub.c1 + I.sub.c2) 0.6 0.7 R.sub.3 = I.sub.h1/(I.sub.h1 + I.sub.c1) 0.3 0.1 R.sub.4 = I.sub.c1/(I.sub.c1 + I.sub.h2) 0.4 0.8 R.sub.5 = I.sub.h1/(I.sub.h1 + I.sub.h2) 0.2 0.4 R.sub.6 = I.sub.h2/I.sub.c3 3.8 4.0 R.sub.7 = I.sub.c4/(I.sub.c4 + I.sub.c5) 0.7 0.7

(26) According to one embodiment of the invention, the body is a cutting tool comprising, e.g., indexable cutting inserts for milling, turning and drilling applications and solid drills or end mills, for machining by chip removal comprising a body of a hard alloy of cemented carbide, cermet, ceramics, cubic boron nitride (CBN) based material or high speed steel.

(27) According to one embodiment the body consists of cemented carbide comprising WC/Co 95 wt %/5 wt %.

(28) According to one embodiment the body consists of cemented carbide comprising WC/Co 94 wt %/6 wt %.

(29) According to one embodiment the body consists of cemented carbide comprising WC/Co 90 wt %/10 wt %.

(30) According to one embodiment the body consists of cemented carbide comprising WC/Co 87 wt %/13 wt %.

(31) According to one embodiment the coated cutting tool is a drill for machining in ISO S materials, such as titanium and titanium alloys, is used at cutting speeds of 10-100 m/min, preferably 35-80 m/min, with an average feed rate, of 0.05-0.50 mm/revolution, preferably 0.1-0.4 mm/revolution.

(32) According to one embodiment the coated cutting tool is an insert for milling and turning 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

(33) Cemented carbide (WCCo) cutting tools with a range of compositions comprising 4 to 15 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 with different geomentris, e.g., indexable inserts and solid drills or endmills were used as a body for the layer depositions by using a Oerlikon-Balzers Domino Large cathodic arc deposition system.

(34) 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 2.010.sup.3 Pa, after which the tools were sputter cleaned with Ar ions. (Ti.sub.1-xAl.sub.x)N.sub.y, 0<x<0.7, 0.7<y<1.1 and NbN layers were grown at 450 C. using Ti.sub.1-zAl.sub.z, 0z0.75 and pure Nb cathodes in a reactive N.sub.2 gas atmosphere at a total gas pressure between 2.5 Pa and 5 Pa selected such to reach the targeted composition for the deposited (Ti.sub.1-xAl.sub.x)N.sub.y and NbN layers. In addition, the depositions were made with an evaporation arc current between 50 A and 200 A, a negative substrate bias between 20 V and 100 V.

(35) Table 5 show the different layer depositions made on solid drills (WCCo with 10% Co) with a drill diameter of 8 mm (SD216A-8.0-120-8R1).

(36) TABLE-US-00005 TABLE 5 1st Layer (Ti.sub.1-xAl.sub.x)N 2nd Layer NbN Sample x d (m) d (m) A 0.66 2.2 1.2 B 0.55 2.1 1.3 C 0.50 2.2 1.3 D 0.25 2.0 1.3 Comparative Comp1 0.66 3.2 Comp2 0.55 3.1 Comp3 0 3.0 Comp4 3.2

Example 2

(37) Example 1 was repeated using WCCo inserts (ISO geometry XOEX120408R-M07) with about 13 wt % Co as a body for the different layer depositions as shown in Table 6.

(38) TABLE-US-00006 TABLE 6 1st Layer (Ti.sub.1-xAl.sub.x)N 2nd Layer NbN Sample x d (m) d (m) E 0.66 2.0 1.0 F 0.50 2.0 1.0 Comparative Comp5 uncoated Comp6 0.66 2.0 Comp7 1.0

Example 3

(39) Cutting tests were performed using the coatings from Table 5 (Example 1) in a drilling operation with the following data:

(40) Drill dia: SD216A-8.0-120-8R1

(41) Application: Drilling

(42) Work piece material: TA6V

(43) Cutting speed: 38 m/min

(44) Feed: 0.08 mm/rev

(45) Drill depth: 18 mm

(46) Performance criterion: Build up edge

(47) Table 7 shows the relative cutting behavior with a vast relative improvement for the inventive coating relative to reference comparative coatings 1 and 2.

(48) TABLE-US-00007 TABLE 7 Relative Sample performance B 170 Comp 1 100 Comp 2 105

Example 4

(49) For a cutting test using the coatings from Table 6 (Example 2) in a milling operation with the following data:

(50) Geometry: XOEX120408R-M07

(51) Application: Milling

(52) Work piece material: Ti6-4

(53) Cutting speed: 50 m/min

(54) Feed: 0.165 mm/rev.

(55) Axial depth of cut, a.sub.p: 15 mm

(56) Radial depth of cut, a.sub.e: 3 mm

(57) Performance criterion: Tool life

(58) Table 8 show the cutting results with improved life time for sample B having a coating according to an embodiment of the present invention relative to reference coatings in samples 5, 6 and 7.

(59) TABLE-US-00008 TABLE 8 Sample Life time (min) B 26 Comp 5 13 Comp 6 22.5 Comp 7 13