COATED CUTTING TOOL

Abstract

A coated cutting tool for metal machining has a base body of cemented carbide, cermet, ceramics, steel or high-speed steel, and a wear resistant coating deposited thereon. The coating includes a layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z with 0.40≤x≤0.95, 0≤y≤0.10 and 0.85≤z≤1.15, and a portion of MeC.sub.aN.sub.b, 0≤a≤1, 0≤b≤1, a+b=1, present on the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z. The portion of MeC.sub.aN.sub.b covers from 5 to 28% of the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z. A process for the production of the coated cutting tool and the use of the coated cutting tool in machining of stainless steel is also provided.

Claims

1. A coated cutting tool comprising: a rake face, a flank face and a cutting edge between the rake face and the flank face; a base body of cemented carbide, cermet, ceramics, steel or high-speed steel; and a coating having a total thickness of from 2 to 20 μm, wherein said coating comprises a layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z with 0.40≤x≤0.95, 0≤y≤0.10 and 0.85≤z≤1.15, having a thickness of from 1 to 18 μm, wherein the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z includes crystallites with grain boundaries and being of a columnar structure, the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z having a ≥85 vol-% face-centered cubic (fcc) crystal structure, and, on the rake face, a portion of MeC.sub.aN.sub.b, 0≤a≤1, 0≤b≤1, a+b=1, present on the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, wherein the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z together with the portion of MeC.sub.aN.sub.b forms an outermost part of the coating, Me is Ti and/or Zr, wherein a portion of MeC.sub.aN.sub.b in an area on the rake face at a distance of from 200 to 400 μm from the cutting edge covers from 5 to 28% of the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, the portion of MeC.sub.aN.sub.b being distributed over said area.

2. The coated cutting tool according to claim 1, wherein the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z includes precipitations of Ti.sub.1-oAl.sub.oC.sub.pN.sub.q at grain boundaries of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites, the precipitations of Ti.sub.1-oAl.sub.oC.sub.pN.sub.q have a higher Al content than inside the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites, wherein 0.95≤o≤1.00, 0≤p≤0.10, 0.85≤q≤1.15 and (o-x)≥0.05.

3. The coated cutting tool according to claim 2, wherein the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z includes precipitations of Ti.sub.1-oAl.sub.oC.sub.pN.sub.q at grain boundaries of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites in a 0.3 μm uppermost part of the layer.

4. The coated cutting tool according to claim 2, wherein the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z includes precipitations of Ti.sub.1-oAl.sub.oC.sub.pN.sub.q at grain boundaries of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites throughout an entirety of the layer.

5. The coated cutting tool according to claim 2, wherein the precipitations of Ti.sub.1-oAl.sub.oC.sub.pN.sub.q at grain boundaries of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites have AlN with a hexagonal wurtzite crystal structure (w-AlN).

6. The coated cutting tool according to claim 1, wherein the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z has a ≥90 vol-% face-centered cubic (fcc) crystal structure.

7. The coated cutting tool according to claim 1, wherein the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z has stoichiometric coefficients of 0.60≤x≤0.90, y=0 and 0.85≤z≤1.15.

8. The coated cutting tool according to claim 1, wherein the portion of MeC.sub.aN.sub.b in an area on the rake face at a distance of from 200 to 400 μm from the cutting edge covers from 7 to 24% of the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, the portion of MeC.sub.aN.sub.b being distributed over said area.

9. The coated cutting tool according to claim 1, wherein the MeC.sub.aN.sub.b is TiN or Ti(C,N).

10. The coated cutting tool according to claim 1, wherein a surface roughness, Ra, of the coating on the rake face is from 20 to 60 nm, at a distance of from 200 to 400 μm from the cutting edge.

11. A process for the production of a coated cutting tool having a rake face, a flank face and a cutting edge between the rake face and the flank face, the cutting tool including a base body of cemented carbide, cermet, ceramics, steel or high-speed steel, and a from 2 to 20 μm thick coating including a from 1 to 18 μm thick layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z with 0.40≤x≤0.95, 0≤y≤0.10 and 0.85≤z≤1.15, the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z having crystallites with grain boundaries and being of a columnar structure, the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z having a ≥85 vol-% face-centered cubic (fcc) crystal structure, wherein the process comprises the following steps: providing the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z by a CVD process; providing a layer of MeC.sub.aN.sub.b, 0≤a≤1, 0≤b≤1, a+b=1, by a CVD process directly above the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, wherein Me is Ti and/or Zr; blasting a surface of the coating until there is a portion of MeC.sub.aN.sub.b remaining in an area on the rake face at a distance of from 200 to 400 μm from the cutting edge covering from 5 to 28% of the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, the portion of MeC.sub.aN.sub.b being distributed over said area.

12. The process according to claim 11, wherein, before the step of blasting the surface of the coating, the deposited layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z is subjected to an annealing at a temperature within the range of from 700 to 950° C. for a duration of from 0.5 to 12 hours under exclusion of air or oxygen, wherein the conditions are selected in a way that at grain boundaries of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites precipitations of Ti.sub.1-oAl.sub.oC.sub.pN.sub.q are generated, the precipitations of Ti.sub.1-oAl.sub.oC.sub.pN.sub.q having a higher Al content than inside the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites, wherein 0.95≤o≤1.00, 0≤p≤0.10, 0.85≤q≤1.15 and (o-x)≥0.05.

13. The process according to claim 12, wherein the annealing of the deposited layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z takes place both before, during, and after the deposition of the layer of MeC.sub.aN.sub.b.

14. The process according to claim 11, wherein the CVD process for the deposition of the layer of Ti.sub.1-xAl.sub.xC.sub.yN.sub.z is a LP-CVD process and wherein the CVD process is carried out at a process pressure in the CVD reactor of from 0.05 to 8 kPa.

15. The process according to claim 11, wherein the blasting of the surface of the coating is made by wet blasting using a slurry of aluminium oxide particles which the slurry exits a blasting gun nozzle, the wet blasting is performed using a blasting pressure at the exit of the nozzle of from 1.8 to 3.5 bar, a concentration of aluminium oxide particles in the slurry being from 10 to 25 vol-%, wherein the aluminium oxide particles belong to one or more of the FEPA designations F120 to F240, wherein the distance between the blasting gun nozzle and the surface of the coated cutting tool is from 75 to 200 mm, and wherein the wet blasting is performed in a blasting direction having an angle to the surface of the coated cutting tool from 40 to 90°, the blasting time being from 1 to 75 minutes.

16. A use of a coated cutting tool according to claim 1 in machining of stainless steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0086] FIG. 1 shows one embodiment of a coated cutting tool which is a milling insert.

[0087] FIG. 2 shows a schematic representation of a cross-section of one embodiment of a coated cutting tool of the present invention.

[0088] FIG. 3 shows a SEM image which is a cross-section of a coating of TiAlN with an upper layer of TiN.

[0089] FIG. 4 shows a SEM image which is a cross-section of a coating of one embodiment of the invention.

[0090] FIG. 5 shows a top view SEM image of a coated cutting tool of one embodiment of the present invention showing portions of TiN on the surface.

[0091] FIG. 6 shows a top view SEM image, which has been subjected to image processing, of a coated cutting tool of one embodiment of the present invention showing portions of TiN on the surface.

[0092] FIG. 7 shows the same image-processed SEM image as in FIG. 6 with a grid of about 2.5 μm×2.5 μm squares put over the image in order to determine the distribution of the portion of TiN on the surface.

DETAILED DESCRIPTION OF THE DRAWINGS

[0093] FIG. 1 shows a schematic view of one embodiment of a cutting tool (1) having a rake face (2) and flank faces (3) and a cutting edge (4). The cutting tool (1) is in this embodiment a milling insert.

[0094] FIG. 2 shows schematically a cross section of a coated cutting tool (1) of an embodiment of the invention having a base body (5) and a coating (6). The coating (6) consists of a layer of TiN (7) closest to the base body (5) followed by a layer of TiAlN (8). Portions of TiN (9) remain on the layer of TiAlN (8) after post treatment.

[0095] FIG. 3 shows a SEM image which is a cross-section of a coating of TiAlN (8) with an upper layer of TiN (9) deposited. No post treatment of the coating has been made.

[0096] FIG. 4 shows a SEM image which is a cross-section of a coating of one embodiment of the invention. A layer of TiN (7) is present on a cemented carbide base body (5) followed by a layer of TiAlN (8). The surface of the coating has been post treated so there has been a substantial smoothening and in particular the top facets of the TiAlN crystallites have been worn down. Portions of TiN (9) are present to a certain extent, in particular over grain boundaries of TiAlN crystallites.

[0097] FIG. 5 shows a SEM image in 5000× magnification of an embodiment of the invention showing an area of about 18 μm×25 μm. Portions of TiN (9) is seen on the layer of TiAlN (8). The portions of TiN (9) are brighter on the image than the exposed TiAlN (8).

[0098] FIG. 6 shows a SEM image in 5000× magnification of an embodiment of the invention showing an area of about 18 μm×25 μm. The SEM image has been subjected to image processing in order to be able to separate areas of TiN from areas of TiAlN in image analysis. Portions of TiN (8) is seen in white on the layer of TiAlN (8) in black. The coverage of TiN on the TiAlN is about 9%.

[0099] FIG. 7 shows the same image-processed SEM image as in FIG. 6 with a grid of about 2.5 μm×2.5 μm squares put over the image in order to determine the distribution of the portions of TiN (9). The total number of squares is 60.

EXAMPLES

Example 1

[0100] As base bodies in these examples cemented carbide cutting inserts (milling inserts) of the geometry R390-11 M-MM having a composition of 90.5 wt-% WC, 8 wt-% Co and 1.5 wt-% (NbC+TaC) were used.

[0101] FIG. 1 shows an embodiment of the coated cutting tool (1) being a milling insert. The cutting tool (1) has a rake face (2), a flank face (3) and a cutting edge (4) in between.

[0102] For the coating of the cemented carbide indexable cutting inserts a CVD coating reactor of the type Bernex BPX325S with a reactor height of 1250 mm, a reactor diameter of 325 mm and a volume of the charge arrangement of 40 liters was used. The gas flow was radially with respect to the longitudinal axis of the reactor.

[0103] For the adhesion of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer, immediately on the cemented carbide base body there was first deposited an about 0.3 μm thick TiN layer by CVD under the deposition conditions indicated in table 1:

TABLE-US-00001 TABLE 1 Reaction gas mixture Temp. Pressure Time [vol-%] [° C.] [kPA] [min] TiCl.sub.4 N.sub.2 H.sub.2 850 15 120 1.0 44.0 55.0

[0104] For the preparation of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer a first precursor gas mixture (VG1) containing the starting compounds TiCl.sub.4 and AlCl.sub.3 and a second precursor gas mixture (VG2) containing the starting component NH.sub.3 as reactive nitrogen component were introduced into the reactor separately so that a blending of the two gas streams took place not earlier than at the entry into the reaction zone. The volume gas streams of the precursor gas mixtures (VG1) and (VG2) were set in a manner that a mean retention time of the reaction gases in the reactor and a total volume stream under normal conditions was achieved. The parameters for the preparation of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer are indicated in table 2. The thickness of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer was about 8 μm.

TABLE-US-00002 TABLE 2 Precursor Precursor Total gas mixture gas mixture volume Retention (VG1) (VG2) Temp. Pressure Time stream time [vol-%] [vol-%] [° C.] [kPa] [min] [I.sub.N/min] [sec] TiCl.sub.4 AlCl.sub.3 H.sub.2 H.sub.2 NH.sub.3 725 0.80 75 145.8 0.13 0.02 0.17 52.2 47.2 0.41

[0105] After this, the prepared cutting inserts were subjected to a period of heat treatment under the conditions indicated in table 3.

TABLE-US-00003 TABLE 3 Time [h] Temperature [° C.] Atmosphere 3 h 15 min 850° C. vacuum

[0106] During the heat treatment period a 0.3 μm top layer of TiN was deposited. The process parameters for the preparation of this TiN layer is indicated in table 4. Thus, out of the 3 h 15 min heat treatment there was a period of 45 minutes TiN deposition.

TABLE-US-00004 TABLE 4 Reaction gas mixture Temp. Pressure Time [vol-%] [° C.] [kPA] [min] TiCl.sub.4 N.sub.2 H.sub.2 NH.sub.3 850 0.7 45 0.11 44.15 55.19 0.55

[0107] For the characterization of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer there were applied X-ray diffraction (XRD), electron diffraction, especially EBSD, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM).

[0108] In the deposited Ti.sub.1-xAl.sub.xC.sub.yN.sub.z, x=0.80, y=0 and z=1.

[0109] The average grain size of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z was determined to be 0.4 μm. The grain size was determined by drawing a line in the middle of the layer, measuring the width of each Ti.sub.1-xAl.sub.xC.sub.yN.sub.z columnar crystallite, and calculate an average value. A cross-sectional SEM image in magnification 5000× was taken and an average value of the individual width of about 20 crystallites was calculated.

[0110] Sample 1 was not post treated at all while samples 2-8 were post treated by different blasting procedures of different severity.

[0111] The wet blastings were performed with aluminium oxide grits (sand) the size in “mesh” stated in the table. The distance between the blasting gun nozzle and the coating surface was 120 mm for top blasting, otherwise 135 mm. When using shot peening in sample 2, ZrO.sub.2-based beads were used in dry form, the beads being of a size between 70-120 μm. The blasting angle is the angle between the coating surface plane and the blasting direction. The blasting pressure is the pressure when the slurry exits the blasting gun nozzle.

[0112] The different treatments were:

[0113] 1. No treatment

[0114] 2. Shot peening (90°, 5.3 bar)+fine wet blasting (11-15°, 2.6 bar, FEPA 240 mesh grit size, 3 minutes)

[0115] 3. TB3 (top wet blasting 90°, 2.1 bar, FEPA 230 mesh grit size, 27 minutes)

[0116] 4. ERB (angled wet blasting 55°, 2.8 bar, FEPA 280 mesh grit size, 3 minutes)

[0117] 5. TB1 (top wet blasting 90°, 2.0 bar, FEPA 230 mesh grit size, 54 minutes)

[0118] 6. ERB (angled wet blasting 55°, 2.8 bar, 150 mesh grit size, 1.8 minutes)

[0119] 7. ERB (angled wet blasting 55°, 2.1 bar, 150 mesh grit size, 3 minutes)

[0120] 8. ERB (angled wet blasting 55°, 3.2 bar, 150 mesh grit size, 4.5 minutes)

[0121] The amount of TiN remaining on the outer surface was for each samples determined by image analysis of a SEM image in 5000× magnification. An about 18 μm×25 μm area about 250 μm from the cutting edge on the rake face was analysed. The software used for image analysis was “ImageJ”.

[0122] The surface roughness, Ra, of the coating after the post treatment was measured for some samples. It was measured on the rake face at a distance of about 250 μm from the cutting edge.

[0123] The results are seen in table 5.

TABLE-US-00005 TABLE 5 TiN Surface coverage roughness, Sample (%) Ra, (nm) 1 100 62 2 62 — 3 25 53 4 23 — 5 20 42 6 9 — 7 6 — 8 2 —

[0124] The portion of TiN was distributed over the area on the rake face at a distance of 250 μm from the cutting edge in a way that when a grid of 2.5 μm×2.5 μm squares was put over a top view Scanning Electron Microscope (SEM) image with a magnification of 5000×, then the following results were provided:

TABLE-US-00006 TABLE 6 TiN coverage Distribution Sample (%) (2.5 × 2.5 μm)* 1 100 — 2 62 — 3 25 100% (60/60) 4 23 100% (60/60) 5 20 100% (60/60) 6 9 95% (57/60) 7 6 95% (57/60) 8 2 — *proportion of 2.5 μm × 2.5 μm squares (out of 60 squares) showing both TiN and Ti.sub.1−xAl.sub.xC.sub.yN.sub.z

[0125] FIG. 6 shows a SEM image in 5000× magnification of sample 6 showing an area of about 18 μm×25 μm. The image has been subjected to image processing. Portions of TiN are seen in white and the TiAlN is seen in black.

[0126] FIG. 7 shows the same image-processed SEM image as in FIG. 6 with a grid of about 2.5 μm×2.5 μm squares put over the image in order to determine the distribution of the portion of TiN on the surface.

[0127] Analysis by using transmission electron microscopy (TEM) has confirmed that the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer comprises Ti.sub.1-oAl.sub.oC.sub.pN.sub.q precipitations at the grain boundaries of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites. Furthermore, there is a presence of face-centered cubic (fcc) phase, >95 vol. %, in the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallite, an epitaxial relationship to the crystalline domains in the Ti.sub.1-oAl.sub.oC.sub.pN.sub.q precipitation at an adjacent grain boundary, and a presence of w-AlN phase in the Ti.sub.1-oAl.sub.oC.sub.pN.sub.q precipitation. The average distance between Ti.sub.1-xAl.sub.xC.sub.yN.sub.z crystallites having Ti.sub.1-oAl.sub.oC.sub.pN.sub.q precipitations, having w-AlN structure, at their grain boundaries is about 25 nm.

[0128] Furthermore, a lamellar structure of the Ti.sub.1-xAl.sub.xC.sub.yN.sub.z layer is present. There are alternating lamellae of higher Ti proportions (lower Al proportions) and lower Ti proportions (higher Al proportions). The regions of higher Ti proportions are in general significantly thinner than the Al-rich regions of the lamellar structure.

[0129] Furthermore, the total structure consists of face-centered cubic (fcc) phase. The entire lamellar structure consists of face-centered cubic (fcc) phase, whereby within one crystallite the same orientation is present.

Example 2: Cutting Tests

[0130] Samples 1-8 were tested in a milling operation (wet comb crack and flaking test) under the following cutting conditions:

[0131] Work piece material: Stainless steel: SS2343-28PR

[0132] Procedure: up milling, wet coolant

[0133] Feed per tooth: f.sub.z=0.2 mm

[0134] Depth of cut: a.sub.p=3 mm

[0135] Cutting speed: v.sub.c=150 m/min

[0136] Milling width: a.sub.e=15 mm

[0137] Pass length: 200 mm

[0138] The cut-off criteria, VBmax is chipping >0.3 mm

[0139] The results are seen in table 7.

TABLE-US-00007 TABLE 7 Relative amount TiN Tool life flak- Tool life of tested edges coverage ing (average) (average) having early Sample (%) (No. passes)* (No. passes)** flaking (%) 1 100 1.0 10.0 100 2 62 3.75 15.5 50 3 25 12.0 18.8 25 4 23 18.8 32.0 25 5 20 20.9 28.2 0 6 9 20.0 30.5 0 7 6 11.5 28.3 25 8 2 1.25 16.5 100 *passes until first flaking, i.e., the slightest visible flaking **passes until cut-off criteria VBmax