COATED CUTTING TOOL

Abstract

A coated cutting tool is provided. The cutting tool is CVD coated and has a substrate of cemented carbide, wherein a metallic binder in the cemented carbide includes Ni. The CVD coating has an inner layer of TiN and a subsequent layer of TiCN and a layer of Al.sub.2O.sub.3 located between the TiCN layer and an outermost surface of the coated cutting tool.

Claims

1. A method of making a coated cutting tool, the method comprising chemical vapor deposition of a coating on a substrate, wherein said coating includes an inner layer of TiN, a subsequent layer of TiCN and a Al.sub.2O.sub.3 layer located between the TiCN layer and an outermost surface of the coated cutting tool, wherein the substrate is made of cemented carbide composed of hard constituents in a metallic binder and wherein the metallic binder includes 60 to 90 wt % Ni, wherein the TiN layer is deposited on the cemented carbide substrate in two subsequent steps at a temperature of about 850-900° C. and a pressure of about 300-600 mbar: a first TiN deposition of TiN-1, followed by a second TiN deposition of TiN-2, the TiN-1 deposition being performed in a gas having 1-1.5 vol % TiCl.sub.4 and H.sub.2 and N.sub.2, wherein the volume ratio H.sub.2/N.sub.2 is 0.05-0.18, and wherein the gas includes 0.5-1.5 vol % HCl, and the TiN-2 deposition is performed in a gas having 2-3 vol % TiCl.sub.4 and H.sub.2 and N.sub.2, wherein the volume ratio H.sub.2/N.sub.2 is 0.8-2.5.

2. The method of claim 1, wherein the layer of TiCN is deposited in two subsequent steps at a temperature of about 875-895° C. and a pressure of about 50-70 mbar: a first deposition of TiCN, followed by a second deposition of TiCN, the first TiCN deposition is performed in gas having 55-65 vol % H.sub.2, 35-40 vol % N.sub.2, 2.8-3.1 vol % TiCl.sub.4 and 0.4-0.5 vol % CH.sub.3CN, and the second TiCN deposition is performed in a gas having 75-85 vol % H.sub.2, 6-9 vol % N.sub.2, 2.3-2.5 vol % TiCl.sub.4, 0.6-0.7 vol % CH.sub.3CN and 7-9 vol % HCl.

3. The method of claim 1, wherein the method further comprises deposition of a layer of Al.sub.2O.sub.3 between the TiCN layer and the outermost surface of the coated cutting tool, said deposition of Al.sub.2O.sub.3 being performed in at least two steps, both steps at a temperature of 980-1020° C. and a pressure of 50-60 mbar, wherein a first step is performed in a gas composition of 1.1-1.3 vol % AlCl.sub.3, 4.5-5 vol % CO.sub.2, 1.6-2.0 vol % HCl and the rest H.sub.2, and wherein a subsequent second step is performed in a gas composition of 1.1-1.3 vol % AlCl.sub.3, 4.5-5 vol % CO.sub.2, 2.8-3.0 vol % HC1, 0.55-0.6 vol % H.sub.2S and the rest H.sub.2.

4. The method of claim 1, wherein the metallic binder includes 10-20 wt % Fe, and/or 65-88 wt % Ni, and/or 3-8 wt % Co.

5. The method of claim 1, wherein the metallic binder content in the cemented carbide is 3-20 wt %.

6. A coated cutting tool comprising: a substrate; and a coating, wherein the substrate is made of cemented carbide composed of hard constituents in a metallic binder and wherein said metallic binder comprises 60 to 90 wt % Ni, and wherein the coating includes an inner TiN layer, a TiCN layer and a A1203 layer located between the TiCN layer and an outermost surface of the coated cutting tool and, wherein the TiCN is composed of crystal grains and wherein the grain size of the TiCN layer as measured along a line in a direction parallel to the surface of the substrate at a position of 1 μm from the TiN layer is about 0.10-0.30 μm.

7. The coated cutting tool of claim 6, wherein the metallic binder includes 10-20 wt % Fe, and/or 65-88 wt % Ni, and/or 3-8 wt % Co.

8. The coated cutting tool of claim 6, wherein the metallic binder content in the cemented carbide is 3-20 wt %.

9. The coated cutting tool of claim 6, wherein the thickness of the TiN layer is 0.3-1 μm deposited directly on the cemented carbide substrate.

10. The coated cutting tool of claim 6, wherein the TiCN layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKα radiation and θ-2θ scan, defined according to Harris formula $TC\left(hkl\right)={\frac{I\left(\mathrm{hk}l\right)}{I_0\left(hkl\right)}\left[\frac{1}{n}\underset{n=1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hk}l\right)}{I_0\left(hkl\right)}\right]}^{-1}$ where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I.sub.0(hkl) is the standard intensity according to ICDD's PDF-card No 42-1489, n is the number of reflections, reflections used in the calculation are (1 1 1), (2 0 0), (2 2 0), (3 1 1), (3 3 1), (4 2 0), (4 2 2) and (5 1 1), wherein TC(4 2 2) is ≥3.5.

11. The coated cutting tool of claim 6, wherein the thickness of the TiCN layer is 6-12 μm.

12. The coated cutting tool of claim 6, wherein the CVD coating further includes one or more layers selected from TiN, TiCN, AlTiN, ZrCN, TiB.sub.2, Al.sub.2O.sub.3, or multilayers comprising of α-Al.sub.2O.sub.3 and/or κ-Al.sub.2O.sub.3.

13. The coated cutting tool of claim 6, wherein the total thickness of the CVD coating is 2-20 μm.

14. The coated cutting tool of claim 6, wherein the Al.sub.2O.sub.3 layer between the TiCN layer and an outermost surface of the coated cutting tool is an α-Al.sub.2O.sub.3 layer.

15. The coated cutting tool of claim 14, wherein said α-Al.sub.2O.sub.3 layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using Cukα radiation and θ-274 scan, defined according to Harris formula where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, I.sub.0(hkl) is the standard intensity according to ICDD's PDF-card No. 00-010-0173, n is the number of reflections used in the calculation, and where the (hkl) reflections used are (1 0 4), (1 10), (1 1 3), (024), (1 1 6), (2 14), (3 0 0) and (0 0 12) wherein TC(0 0 12)≥6.

16. The coated cutting tool of claim 14, wherein the α-Al.sub.2O.sub.3 layer exhibits an intensity ratio I(0 0 12)/I(0 1 14) of ≥0.8.

17. The coated cutting tool of claim 6, wherein the thickness of the Al.sub.2O.sub.3 layer located between the TiCN layer and an outermost surface of the coated cutting tool is 4-8 μm.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0045] Embodiments of the invention will be described with reference to the accompanying drawings, wherein:

[0046] FIG. 1 is a cross-sectional SEM micrograph showing the TiN layer and the TiCN layer of a coated cutting tool according to one embodiment of the invention (Invention 1), the grain size in the TiCN can be measured in this view,

[0047] FIG. 2 is a close-up of the TiN layer and the lower part of the TiCN layer of the coated cutting tool shown in FIG. 1,

[0048] FIG. 3 is a cross-sectional SEM micrograph showing the TiN layer and the TiCN layer of a reference coated cutting tool (Reference 1B), the grain size in the TiCN can be measured in this view,

[0049] FIG. 4 is a close-up of the TiN layer and the lower part of the TiCN layer of the coated cutting tool shown in FIG. 2, pores are visible as dark spots inside the coating and at the substrate-coating interface,

[0050] FIG. 5 shows a SEM micrograph and an EDS scan of the Ni content in the cemented carbide-coating interface of the sample Invention 1,

[0051] FIG. 6 shows a SEM micrograph and an EDS scan of the Ni content in the cemented carbide-coating interface of the sample Reference 1B,

[0052] FIG. 7 is a cross-sectional SEM micrograph showing the TiN layer, the TiCN layer, the bonding layer and the α-Al.sub.2O.sub.3 layer of a coated cutting tool according to one embodiment of the invention (Invention 3),

[0053] FIG. 8 is a cross-sectional SEM micrograph showing the TiN layer, the TiCN layer, the bonding layer and the α-Al.sub.2O.sub.3 layer of a reference coated cutting tool (Reference 2B),

[0054] FIG. 9 is a cross-sectional SEM micrograph showing the TiN layer and the lower part of the TiCN layer of a coated cutting tool according to one embodiment of the invention (Invention 2) where the Ni containing grain boundaries are visible as white lines, and

[0055] FIG. 10 is a cross-sectional SEM micrograph showing the TiN layer and the lower part of the TiCN layer of a reference coated cutting tool (Reference 2B) where the Ni containing grain boundaries are visible as white lines.

EXAMPLES

[0056] Exemplifying embodiments of the present invention will now be disclosed in more detail and compared to reference embodiments. Coated cutting tools (inserts) were manufactured and analysed.

[0057] Substrates

[0058] Cemented carbide substrates of ISO-type CNMG120408 for turning and of ISO-type SNMA120408 were manufactured.

[0059] Cemented carbide substrates with an alternative binder were manufactured with a binder comprising about 80.7 wt % Ni, 13.7 wt % Fe and 5.6 wt % Co. The binder content in the cemented carbide was about 7 wt %. The cemented carbide substrates with the alternative binder were manufactured from a powder mixture with a composition of about 6.09 wt % Ni, 1.02 wt % Fe, 0.039 wt % Co, 1.80 wt % Ti, 2.69 wt % Ta, 0.41 wt % Nb, 0.09 wt % N and balance WC. The powder mixture was milled, dried, pressed and sintered at 1450° C. The sintered cemented carbide substrates comprised a binder enriched surface zone from the substrate surface and to a depth of about 30 μm into the body being essentially free from cubic carbides as measured in a light optical microscope. The amount carbon in the powder was about 6.07 wt %, while the amount carbon as measured in chemical analysis of the sintered cemented carbide was about 5.87 wt %. The sintered cemented carbide comprised about 0.4 wt % Co, 1.0 wt % Fe and 5.9 wt % Ni. The Co originated mainly from the milling bodies that were worn during the milling step. No free graphite or eta phase was visible in a SEM micrograph of a cross section of the cemented carbide substrates.

[0060] As a reference, Co-containing cemented carbide substrates were manufactured from a powder mixture with a composition of about 7.20 wt % Co, 1.80 wt % Ti, 2.69 wt % Ta, 0.41 wt % Nb, 0.09 wt % N and balance WC. The powder mixture was milled, dried, pressed and sintered at 1450° C. The sintered cemented carbide substrates comprised a Co enriched surface zone from the substrate surface and to a depth of about 23 μm into the body being essentially free from cubic carbides as measured in a light optical microscope. The sintered cemented carbide substrates comprised about 7.2 wt % Co. No free graphite or eta phase was visible in a SEM micrograph of a cross section of the cemented carbide substrates.

[0061] CVD Deposition

[0062] CVD coatings were deposited on the two cemented carbide compositions and a summary of the samples is given in Table 1. Prior to the coating deposition every substrate was cleaned in a gentle blasting step to remove the outermost metal from the surfaces.

TABLE-US-00001 TABLE 1 Summary of samples bonding Substrate TiN total TiCN layer α-Al.sub.2O.sub.3 Sample binder TiN-1 TiN-2 [μm] [μm] [μm] [μm] Invention 1 NiFeCo Yes Yes 0.4 8.9 — — (CNMG) Reference 1A Co Yes Yes 0.4 9.5 — — (CNMG) Reference 1B NiFeCo No Yes 0.4 9.5 — — (CNMG) Reference 1C Co No Yes 0.4 10.2 — — (CNMG) Invention 2 NiFeCo Yes Yes 0.3 7.1 0.8 5.5 (CNMG) Reference 2A Co Yes Yes 0.5 7.5 0.7 5.2 (SNMA) Reference 2B NiFeCo No Yes 0.8 8 1.1 5.2 (CNMG) Reference 2C Co No Yes 0.3 8.4 0.9 5.4 (SNMA) Invention 3 NiFeCo Yes Yes 0.4 8.2 0.8* 4.6 (CNMG) Reference 3A Co No Yes 0.4 8.4 0.9* 5.4 (SNMA) *bonding layer deposition with increased N.sub.2 partial pressure

[0063] Before starting the CVD deposition the CVD chamber was heated up to reach 885° C. For samples Invention 1 and References 1A, 1B, 1C this pre-heating step was performed at 200 mbar and in 100 vol % N.sub.2 from room temperature up to 600° C., and from 600° C. up to 885° C. in 100 vol % H.sub.2. For the samples Inventions 2, 3 and References 2A, 2B, 2C, 3A the pre-heating step was performed at 1000 mbar and in 100 vol % H.sub.2.

[0064] The substrates were first coated with an about 0.4 μm thick TiN-layer at 885° C. Two alternative depositions of TiN were performed, with or without an initial step of TiN-1. The aim of the TiN-1 step is to prevent intermetallic phases such as Ni.sub.3Ti from forming in the CVD coating and at the substrate-coating interface. During the TiN-1 deposition the N.sub.2 partial pressure was high and the H.sub.2 partial pressure was low, and HCl was added, as compared to the TiN-2 deposition step which was performed without HCl and with a 50/50 relation for the H.sub.2/N.sub.2 gasses. When the TiN-1 was deposited, the subsequent TiN-2 deposition time was adapted to reach a total TiN layer thickness of 0.4 μm. The TiN-1 deposition was run for 150 minutes.

[0065] Thereafter an approximately 8 μm TiCN layer was deposited by employing the well-known MTCVD technique using TiCl.sub.4, CH.sub.3CN, N.sub.2, HCl and H.sub.2 at 885° C. The volume ratio of TiCl.sub.4/CH.sub.3CN in an initial part of the MTCVD deposition of the TiCN layer was 6.6, followed by a period using a ratio of TiCl.sub.4/CH.sub.3CN of 3.7. The details of the TiN and the TiCN deposition are shown in Table 2.

TABLE-US-00002 TABLE 2 MTCVD of TiN and TiCN MT CVD of TiN and TiCN (885° C.): Pressure H.sub.2 N.sub.2 HCl TiCl.sub.4 CH.sub.3CN [mbar] [vol %] [vol %] [vol %] [vol %] [vol %] TiN-1 400 10.5 87.4 0.88 1.25 — TiN-2 400 48.8 48.8 — 2.44 — TiCN inner 55 59.0 37.6 — 2.95 0.45 TiCN outer 55 81.5 7.8 7.8 2.38 0.65

[0066] After the deposition of the TiCN outer layer the temperature was increased from 885° C. to 1000° C. in an atmosphere of 75 vol % H.sub.2 and 25 vol % N.sub.2. In two of the samples, samples Invention 3 and Reference 3A, the gas flow during this temperature increase was 100% nitrogen.

[0067] A 1-2 μm thick bonding layer was deposited at 1000° C. on top of the MTCVD TiCN layer by a process consisting of four separate reaction steps. First a HTCVD TiCN step using TiCl.sub.4, CH.sub.4, N.sub.2, HCl and H.sub.2 at 400 mbar, then a second step (TiCNO-1) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar, then a third step (TiCNO-2) using TiCl.sub.4, CH.sub.3CN, CO, N.sub.2 and H.sub.2 at 70 mbar and finally a fourth step (TiN-3) using TiCl.sub.4, N.sub.2 and H.sub.2 at 70 mbar. During the third deposition step some of the gases were continuously changed as indicated by a first start level and a second stop level presented in Table 2. Prior to the start of the subsequent Al.sub.2O.sub.3 nucleation, the bonding layer was oxidized for 4 minutes in a mixture of CO.sub.2, CO, N.sub.2 and H.sub.2.

[0068] The details of the bonding layer deposition are shown in Table 3.

TABLE-US-00003 TABLE 3 Bonding layer deposition Bonding Pressure H.sub.2 N.sub.2 CH.sub.4 HCl CO TiCl.sub.4 CH.sub.3CN CO.sub.2 layer [mbar] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] Temp. 75 25 increase HTCVD 400 67.9 25.5 3.4 1.7 — 1.55 — — TiCN TiCNO-1 70 83.7 12.0 — 1.2 1.2 1.5  0.40 — TiCNO-2 70 63.1-61.1 31.5-30.6 — — 1.6-4.6 3.15-3.06 0.65-0.63 — TiN-3 70 64.5 32.3 — — — 3.23 — — Oxidation 55 53.8 30 — — 12.5  — — 3.7

[0069] For samples Invention 3 and Reference 3A, an increased N.sub.2 partial pressure was applied during the deposition of the bonding layer, see Table 4.

TABLE-US-00004 TABLE 4 Bonding layer deposition of samples Invention 3 and Reference 3A Bonding Pressure H.sub.2 N.sub.2 CH.sub.4 HCl CO TiCl.sub.4 CH.sub.3CN CO.sub.2 layer [mbar] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] [vol %] Temp. 100 increase HTCVD 400 56.43 38.21 2.82 1.25 — 1.29 — — TiCN TiCNO-1 70 73.17 23.09 — 1.2 1.05 1.3  0.35 — TiCNO-2 70 52.98-51.61 42.5-41.41 — — 1.32-3.87 2.65-2.58 0.54-0.53 — TiN-3 70 49.92 47.59 — — — 2.50 — — Oxidation 55 53.8 30 — — 12.5  — — 3.7

[0070] On top of the bonding layer an α-Al.sub.2O.sub.3 layer was deposited. All the α-Al.sub.2O.sub.3 layers were deposited at 1000° C. and 55 mbar in two steps. The first step using 1.2 vol-% A101.sub.3, 4.7 vol-% CO.sub.2, 1.8 vol-% HCl and balance H.sub.2 giving about 0.1 μm α-Al.sub.2O.sub.3 and a second step as disclosed below giving a total α-Al.sub.2O.sub.3 layer thickness of about 5 μm. The second step of the α-Al.sub.2O.sub.3 layer was deposited using 1.16% AlCl.sub.3, 4.65% CO.sub.2, 2.91% HCl, 0.58% H.sub.2S and balance H.sub.2.

[0071] Coating Analysis

[0072] XRD was used to analyse the TC values of the α-Al.sub.2O.sub.3 and the TiCN in accordance with the method as disclosed above. The layer thicknesses were analysed in a light optical microscope by studying a cross section of each coating at 1000× magnification and both the bonding layer and the initial TiN layer are included in the TiCN layer thickness, see Table 1. The results from the XRD are presented in Table 5.

TABLE-US-00005 TABLE 5 XRD results Substrate TC(0 0 12) I(0 0 12)/I(0 1 14) TC(4 2 2) Sample binder of α-Al.sub.2O.sub.3 of α-Al.sub.2O.sub.3 of TiCN Invention 1 NiFeCo — — 3.88 (CNMG) Reference 1A Co — — 4.19 (CNMG) Reference 1B NiFeCo — — 3.40 (CNMG) Reference 1C Co — — 4.52 (CNMG) Invention 2 NiFeCo 6.62 1.11 4.19 (CNMG) Reference 2A Co 7.53 1.63 4.17 (SNMA) Reference 2B NiFeCo 5.63 0.63 2.11 (CNMG) Reference 2C Co 7.62 2.53 4.63 (SNMA) Invention 3 NiFeCo 7.20 1.24 4.34 (CNMG) Reference 3A Co 7.71 2.80 4.75 (SNMA)

[0073] The coatings were also analysed using SEM and in EDS to study the grain sizes of the TiCN and to study any Ni presence in the TiN and TiCN layers. The results are present in Table 6.

[0074] Before SEM/EDS analysis, the as coated inserts were mounted in a black conductive phenolic resin from AKASEL which were afterwards ground down 1 mm and then polished in two steps: rough polishing (9 μm) and fine polishing (1 μm) using a diamond slurry solution. The SEM cross section from FIG. 9 and FIG. 10 are viewed in the SEM after this sample preparation procedure. To observe layers microstructure the samples were further polished using a colloidal silica suspension named “MasterPolish 2”. The polishing was performed until a scratch free cross section was acquired. The samples were afterwards cleaned with deionized water and detergent to remove residual polishing suspension and dried with clean air spray.

[0075] The SEM used for the grain size study a Carl Zeiss AG- Supra 40 type operated at 3 kV acceleration voltage using a 60 μm aperture. The SEM images were acquired at 40.000× magnification and 10 mm working distance. A 9.3 μm long horizontal line was drawn parallel to the substrate and at distance of 1 μm from TiN layer. The grain boundaries crossing the horizontal line were counted and their average size value was calculated and given in the table 6.

[0076] The Ni content in TiCN grains was studied with an 80 mm.sup.2 X-Max EDX detector mounted in the SEM used for grain size study. The used EDS detector operated using Oxford Instruments “AZtec” software version 3.3 SP1 data acquisition. The measurements were performed by applying the electron beam with 10 kV acceleration voltage and 60 μm aperture on the sample placed at a working distance of 8.2 mm and sequentially acquiring 5 completed framed EDS maps. The EDS map was sized to a of width of 9.5 μm and a height of 7.1 μm a process time 5.

[0077] After EDS mapping, linescan measurements were applied in the EDS map data to extract the Ni profile in the TiN/TiCN coating in the first 1.5 to 2.5 μm from the TiN layer/substrate interface. The linescan was to sized to 6.3 μm long and about 1 μm wide. A bining factor was set to 2 to reduce the noise profile.

[0078] Ni profile EDS linescans are shown in FIGS. 5 and 6.

TABLE-US-00006 TABLE 6 Results related to grain size and Ni content Average TiCN Sample grain size [μm] Invention 1 0.21 (CNMG) Reference 1B 0.37 (CNMG) Invention 2 0.24 (CNMG) Reference 2B 0.40 (CNMG) Invention 3 0.22 (CNMG)

[0079] While the invention has been described in connection with various exemplary embodiments, it is to be understood that the invention is not to be limited to the disclosed exemplary embodiments; on the contrary, it is intended to cover various modifications and equivalent arrangements within the appended claims.