Coated cutting tool

Abstract

A coated cutting tool includes a substrate of cemented carbide and a coating. The cemented carbide is made of WC and a binder phase of one or more of Co, Fe and Ni. The carbon content in the cemented carbide is a substoichiometric carbon content SCC, wherein −0.13 wt %≤SCC<0 wt %, or −0.30 wt %≤SCC≤−0.16 wt %. The coating includes one or more layers being a metal carbide, metal nitride or metal carbonitride, the metal being at least one of Zr and Hf, and wherein Ti is present in an amount of at most 10 at-% of the amount metal. The one or more layers is situated between the substrate and the aluminum oxide layer.

Claims

1. A coated cutting tool comprising: a substrate of cemented carbide; and a coating, the cemented carbide comprising WC and a binder phase comprising one or more of Co, Fe and Ni, a carbon content in the cemented carbide being a substoichiometric carbon content SCC, wherein −0.30 wt %≤SCC≤−0.16 wt %, wherein the cemented carbide comprises an eta phase, a distribution of the eta phase being the same throughout an entirety of the cemented carbide substrate, and wherein the coating includes one or more layers of a metal carbide, metal nitride or metal carbonitride, the metal being at least one of Zr and Hf, and an aluminum oxide layer, the one or more layers being situated between the substrate and the aluminum oxide layer.

2. The coated cutting tool according to claim 1, wherein the one or more layers is at least one of ZrC, ZrN, Zr(C,N), HfC, HfN, and Hf(C,N).

3. The coated cutting tool according to claim 1, wherein the one or more layers is a Zr(C,N) or Hf(C,N) layer.

4. The coated cutting tool according to claim 1, wherein the one or more layers has a coefficient of thermal expansion CTE of between 6 and 8 10.sup.−6/K.

5. The coated cutting tool according to claim 1, wherein a total thickness of the one or more layers is from 2 to 15 μm.

6. The coated cutting tool according to claim 1, wherein a total thickness of the aluminum oxide layer is from 1 to 5 μm.

7. The coated cutting tool according to claim 1, wherein a ratio of thickness of the one or more layers and a thickness of the aluminum oxide layer is more than or equal to 1.

8. The coated cutting tool according to claim 1, further comprising, adjacent the surface of the substrate, a layer of Ti(C.sub.xN.sub.yO.sub.z) or Zr(C.sub.xN.sub.yO.sub.z), or Hf(C.sub.xN.sub.yO.sub.z), x+y+z=1, 0≤x≤1, 0≤y≤1, 0≤z<1, being from 0.05 to 1.5 μm.

9. The coated cutting tool according to claim 1, wherein a bonding layer having a thickness of 0.05 to 2 μm is present between an uppermost layer of the one or more layers and the aluminum oxide layer, the bonding layer being Ti(C.sub.xN.sub.yO.sub.z) or Zr(C.sub.xN.sub.yO.sub.z), or Hf(C.sub.xN.sub.yO.sub.z), x+y+z=1, 0<x<1, 0≤y<1, 0<z<1.

10. The coated cutting tool according to claim 9, wherein the bonding layer is Ti(C.sub.xN.sub.yO.sub.z), x+y+z=1, 0<x<1, 0≤y<1, 0<z<1.

11. The coated cutting tool according to claim 1, wherein the substoichiometric carbon content SCC in the cemented carbide is −0.28 wt %≤SCC≤−0.17 wt %.

12. The coated cutting tool according to claim 1, wherein the substoichiometric carbon content SCC in the cemented carbide is −0.28 wt %≤SCC≤−0.17 wt % and the cemented carbide comprises an eta phase in a volume fraction of between 2 and 10 vol %.

13. The coated cutting tool according to claim 12, wherein an average grain size of the eta phase is between 0.1 to 10 μm.

14. The coated cutting tool according to claim 1, wherein the cutting tool is a milling insert.

15. The coated cutting tool according to claim 1, wherein the one or more layers is a titanium metal carbide, titanium metal nitride or titanium metal carbonitride, wherein the titanium amount in the carbide, nitride or carbonitride is at most 10 at % of an amount of the total metal.

Description

EXAMPLES

Example 1

(1) Three different cemented carbide bodies of geometry R365-1505ZNE-KM were provided made from raw material powders according to Table 1.

(2) TABLE-US-00001 TABLE 1 WC grain W C Substoichiometric Cemented Co WC size (μm) addition addition carbon content in carbide (wt %) (wt %) (FSSS) (wt %) (wt %) powder (wt %) No. 1 6.0 balance 1.3 — 0.07 +0.08 No. 2 6.0 balance 1.4 — 0.01 0.00 No. 3 7.4 balance 1.4 1.88 0.02 −0.13

(3) The samples No. 1, No. 2 and No. 3 were made milling together the powders in a ball mill for 8 hours, together with a milling liquid (water/ethanol with a ratio of 9/91) and an organic binder, 2 wt % PEG (the amount of PEG is not included in the dry powder weight). Then the slurry was pan dried. The agglomerates were then pressed into a green body which then was sintered at 1410° C.

(4) The sintered pieces of samples No. 1 and No. 2 were found not to contain any eta phase. Sample No. 3 was found to contain eta phase but then in a well-dispersed form without clusters. The amount of eta phase was determined by image analysis using the software Image J using the setup “Automatic”. The images used for the analysis was LOM images with a magnification of 1000× and 2000×. Two measurements were made at each magnification and the value in Table 2 for sample No. 3 is an average value of all these.

(5) The stoichiometric carbon content in the sintered materials was further calculated by first measuring the total carbon content by using a LECO WC-600 instrument, for this analysis, the sample was crushed prior to the analysis. The accuracy of the values is ±0.01 wt %. The Co content is measured with XRF (X-ray fluorescence) using a Panalytical Axios Max Advanced instrument. By subtracting the cobalt and carbon amounts from the total weight of the sample, the W content is achieved which is used to calculate the stoichiometric carbon content, assuming the WC has a 1:1 ratio.

(6) By subtracting the stoichiometric carbon content from the total carbon content as measured by the LECO WC-600 instrument, the substoichiometric carbon content is achieved. As can be seen in Table 2, the substoichiometric carbon content in the sintered materials differs from that in the respective powder. This is due to that some part of the carbon reacts with oxygen, which is an impurity in the raw materials, which outgas as CO or CO.sub.2 during sintering, and reduces the total final C content of the alloy.

(7) TABLE-US-00002 TABLE 2 Substoichiometric carbon Cemented carbide content in sintered body (wt %) Vol % eta phase No. 1 −0.09 0 No. 2 −0.13 0 No. 3 −0.20 4.8

Example 2

(8) Cemented carbide inserts No. 1 with geometry R365-1505ZNE-KM made in Example 1 were then coated with a 3 μm Ti(C,N) layer followed by a 3 μm alpha-Al.sub.2O.sub.3 layer.

(9) A thin (0.5 μm) bonding layer of TiN between the substrate and the Ti(C,N) layer was first provided. The TiN bonding layer was deposited by using a reaction gas mixture comprising N.sub.2, TiCl.sub.4 and H.sub.2.

(10) The deposition of the Ti(C,N) layer was made in a CVD reactor based on general procedures well known in the art using a reaction gas mixture comprising H2, N2, HCl, TiCl.sub.4 and CH.sub.3CN at a deposition temperature of 885° C. and at a pressure of 55 mbar. Furthermore, a thin (0.5 μm) bonding layer of Ti(C,O) between the Ti(C,N) layer and the alpha-Al.sub.2O.sub.3 layer was provided. The TiCO bonding layer was deposited by using a reaction gas mixture comprising H.sub.2, TiCl.sub.4 and CO. After deposition, the Ti(C,O) layer was slightly oxidized in a gas mixture comprising CO and CO.sub.2 before depositing the alpha-Al.sub.2O.sub.3 layer.

(11) Further, cemented carbide inserts No. 1, No. 2 and No. 3 with geometry R365-1505ZNE-KM made in Example 1 were coated with a 3 μm Zr(C,N) layer followed by a 3 μm alpha-Al.sub.2O.sub.3 layer.

(12) The deposition of the Zr(C,N) layer was made according to general procedures (MT-CVD) in a Bernex™ 325 reactor using a reaction gas mixture comprising 64.9 vol % H.sub.2, 33.2 vol % N.sub.2, 1.3 vol % ZrCl.sub.4 and 0.6 vol % CH.sub.3CN at a deposition temperature of 930° C. and at a pressure of 55 mbar. The total gas flow was 2880 I/h.

(13) Before depositing the Zr(C,N) layer a thin (0.5 μm) bonding layer of TiN was deposited between the substrate and the Zr(C,N) layer.

(14) Before depositing the alpha-Al.sub.2O.sub.3 layer a thin (1 μm) bonding layer comprising of a sequence of HT-CVD Ti(C,N) and Ti(C,N,O) between the Zr(C,N) layer and the alpha-Al.sub.2O.sub.3 layer was provided. The deposition of the HT-CVD Ti(C,N) layer was made based on general procedures well known in the art using a reaction gas mixture comprising H.sub.2, N.sub.2, HCl, TiCl.sub.4 and CH.sub.4 at a deposition temperature of 1000° C. The deposition of the Ti(C,N,O) layer was also made based on known procedures using a reaction gas mixture comprising H.sub.2, N.sub.2, HCl, TiCl.sub.4, CH.sub.3CN and CO at a deposition temperature of 1000° C. After deposition, the Ti(C,N,O) layer was slightly oxidized in a gas mixture comprising CO and CO.sub.2 before depositing the alpha-Al.sub.2O.sub.3 layer.

(15) The deposition of the alpha-Al.sub.2O.sub.3 layer was then made based on general procedures well known in the art using a reaction gas mixture in a nucleation step comprising H2, HCl, CO.sub.2 and AlCl.sub.3 and further using a reaction gas mixture in a growth step comprising H.sub.2, HCl, CO.sub.2, AlCl.sub.3 and H.sub.2S, at a deposition temperature of about 1000° C. and a pressure of 55 mbar.

(16) The samples of coated cemented carbides are summarized in Table 3.

(17) TABLE-US-00003 TABLE 3 Sample No. Cemented carbide Coating 1 No. 1 Ti(C,N)/alpha-Al.sub.2O.sub.3 2 No. 1 Zr(C,N)/alpha-Al.sub.2O.sub.3 3 No. 2 Zr(C,N)/alpha-Al.sub.2O.sub.3 4 No. 3 Zr(C,N)/alpha-Al.sub.2O.sub.3

Example 3

(18) Samples 1 to 4 of coated cemented carbides according to Example 2 were tested in a face milling operation (roughing operation) of a motor block of grey cast iron SS0125 under dry conditions with the following cutting parameters:

(19) Vc: 362 m/min

(20) Fz: 0.29 mm/rev

(21) ap: 5 mm

(22) ae: 20 mm

(23) Cutter: R365-100Q32W15H

(24) Number of teeth: 14 (13 milling inserts +1 wiper insert)

(25) Machine: Horizontal multi-operational (GROB)

(26) Taper: HSK100

(27) The number of inserts of each sample tested in a tool body was 6, 7 or 13. The same milling cutter was used when testing the different inserts and the cutter was always mounted with in total 14 inserts also when 6 or 7 sample inserts were mounted. Each insert of samples 1 to 4 was thus subjected to the same conditions in the tests.

(28) For each test 100 components were made (corresponding to about 70 min milling time). The number of comb cracks larger than 0.2 mm per insert was then counted and an average for all sample inserts used in the same milling cutter was calculated.

(29) TABLE-US-00004 TABLE 4 Substoichio- Number Average metric carbon of sample number of Sam- Combination content in sub- inserts per comb cracks ple substrate-coating strate (wt %) cutter (>0.2 mm) 1 No. 1 - Ti(C,N)/Al.sub.2O.sub.3 −0.09 13 9.0 2 No. 1 - ZrCN/Al.sub.2O.sub.3 −0.09 13 6.4 3 No. 2- Zr(C,N)/Al.sub.2O.sub.3 −0.13 6 4.7 4 No. 3 - Zr(C,N)/Al.sub.2O.sub.3 −0.20 7 4.7