COATED CUTTING TOOL

Abstract

A coated cutting tool is CVD coated and includes a substrate of a cemented carbide, wherein the metallic binder in the cemented carbide Includes Ni. The CVD coating includes an inner layer of TiN and a subsequent layer of TiCN.

Claims

1. A method of making a coated cutting tool, the method comprising chemical vapor deposition of a coating including an inner layer of TiN and a subsequent layer of TiCN on a substrate, wherein the substrate is made of cemented carbide composed of hard constituents in a metallic binder and wherein the metallic binder comprises 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 is performed in a gas comprising 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 preferably comprises 0.5-1.5 vol % HC1, and the TiN-2 deposition is performed in a gas comprising 2-3 vol % TiCl.sub.4 and H.sub.2 and N.sub.2, wherein the volume ratio H.sub.2/N2 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 comprising 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 comprising 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 metallic binder includes 10-20 wt % Fe.

4. The method of claim 1, wherein the metallic binder includes 65-88 wt % Ni.

5. The method of claim 1, wherein the metallic binder includes 3-8 wt % Co.

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

7. 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 includes 60 to 90 wt % Ni, and wherein the coating comprises includes an inner TiN layer and a TiCN layer, 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.

8. The coated cutting tool of claim 7, wherein the metallic binder includes 10-20 wt % Fe.

9. The coated cutting tool of claim 7, wherein the metallic binder includes 65-88 wt % Ni, preferably 70-87 wt % Ni, more preferably 75-85 w t%.

10. The coated cutting tool of claim 7, wherein the metallic binder includes 3-8 wt % Co.

11. The coated cutting tool of claim 7, wherein the metallic binder content in the cemented carbide is 3-20 wt.

12. The coated cutting tool of claim 7, wherein the thickness of the TiN layer is 0.3-1 μm, preferably and wherein the TiN layer is deposited directly on the cemented carbide substrate.

13. The coated cutting tool of claim 7, wherein the TiCN layer exhibits a texture coefficient TC(hkl), as measured by X-ray diffraction using CuKαradiation and θ-2θscan, defined according to Harris formula $\mathrm{TC}\left(\mathrm{hk}l\right)={\frac{I\left(\mathrm{hk}l\right)}{I_0\left(hkl\right)}\left[\frac{1}{n}\underset{n=1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hk}l\right)}{I_0\left(hkl\right)}\right]}^{-1}$ where I(hkl) is the measured intensity (integrated area) of the (hkl) reflection, Io(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.

14. The coated cutting tool of claim 7, wherein the thickness of the TiCN layer is 6-12 μm.

15. The coated cutting tool of claim 7, 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 including α-Al.sub.2O.sub.3 and/or κ-Al.sub.2O.sub.3.

16. The coated cutting tool of claim 7, wherein a total thickness of the CVD coating is 2-20 μm.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0037] Embodiments of the invention will be described with reference to the accompanying drawings, wherein:

[0038] 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),

[0039] 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, the grain size in the TiCN can be measured in this view,

[0040] FIG. 3 is a cross-sectional SEM micrograph showing the TiN layer and the TiCN layer of a reference coated cutting tool (Reference 1B),

[0041] 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, the grain size in the TiCN can be measured in this view,

[0042] 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,

[0043] 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,

EXAMPLES

[0044] 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.

SUBSTRATES

[0045] Cemented carbide substrates of ISO-type CNMG120408 for turning and of ISO-type SNMA120408 were manufactured.

[0046] 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 orginated 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.

[0047] 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.

CVD Deposition

[0048] 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 Substrate TiN total TiCN Sample binder TiN- 1 TiN-2 [μm] [μm] Invention 1  NiFeCo Yes Yes 0.4 8.9 Reference 1A Co Yes Yes 0.4 9.5 Reference 1B NiFeCo No Yes 0.4 9.5 Reference 1C Co No Yes 0.4 10.2 

[0049] Before starting the coating deposition, the CVD chamber was heated up to reach 885° C.

[0050] This pre-heating step was performed at 200mbar 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.

[0051] 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.

[0052] 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 Pressure H.sub.2 N.sub.2 HCl TiCl.sub.4 CH.sub.3CN (885° C.): [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

COATING ANALYSIS

[0053] XRD was used to analyse the TC values of 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 1000x 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 3.

TABLE-US-00003 TABLE 3 XRD results Sample Substrate binder TC (4 2 2) of TiCN Invention 1  NiFeCo 3.88 Reference 1A Co 4.19 Reference 1B NiFeCo 3.40 Reference 1C Co 4.52

[0054] 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 4.

[0055] 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 (9μm) and fine polishing (1 μm) using a diamond slurry solution. 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.

[0056] The SEM used for the grain size study a Carl Zeiss AG-Supra 40 type operated at 3kV acceleration voltage using a 60 μm aperture. The SEM images were acquired at 40.000x 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 4.

[0057] The Ni content in TiCN grains was studied with an 80mm.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.

[0058] 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.

[0059] Ni profile EDS linescans are shown in FIGS. 5 and 6.

TABLE-US-00004 TABLE 4 TiCN grain size Average TiCN grain size Sample [μm] Invention 1  0.21 Reference 1B 0.37

[0060] 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.