Patent Application
20200123647
The present invention relates to a method for producing a coated cutting tool having a coating comprising a metal nitride and an aluminum containing oxide. The present invention also relates to a coated cutting tool.
There is a continuous desire to improve cutting tools for metal machining so that they last longer, withstand higher cutting speeds and/or other increasingly demanding cutting operations. Commonly, a cutting tool for metal machining comprises a hard substrate material such as cemented carbide which has a thin hard coating usually deposited by either chemical vapour deposition (CVD) or physical vapour deposition (PVD).
The coating frequently comprises a combination of two or more individual layers of different chemical composition. Apart from the importance of the adhesion between an innermost layer of the coating to the substrate material, one further important factor influencing the tool life is the adhesion between the individual layers within the coating.
Layer combinations of a metal nitride, for example (Ti,Al)N, and an oxide layer, such as aluminum oxide are known and generally give good cutting performance in various operations.
High toughness of the whole carbide tool is important. Depositing at higher temperatures results in reduced toughness of the carbide substrate. This results in higher risk of breakage. In order to keep the toughness of the substrate and the metal nitride layer sufficiently high one may want to deposit the oxide layer at comparatively low temperature. However, adhesion problems may then occur between the metal nitride layer and the oxide layer leading to shorter tool life.
The object of the present invention is therefore to overcome the above mentioned adhesion problems between a metal nitride layer and an aluminum-containing oxide layer and present a cutting tool with improved tool life.
It has now been provided a method for producing a coated cutting tool which provides a solution to the above-mentioned objective.
The method comprises depositing a 0.5-10 μm nitride layer which is a nitride of one or more of Ti, Zr, Hf, V, Ta, Nb, Cr, Si and Al, onto a substrate followed by depositing Al or Al+Me, further followed by depositing a 0.1-5 μm oxide layer being an (AlaMe1-a)2O3 layer, 0.055≤a≤1, Me is one or more of Ti, Mg, Ag, Zr, Si, V, Fe, Hf, B and Cr, said layers are deposited by magnetron sputtering.
Suitably, in the deposited Al or Al+Me, the atomic ratio Al/(Al+Me) is from 0.05 to 1, or from 0.1 to 1, or from 0.25 to 1, or from 0.5 to 1, or from 0.75 to 1.
The deposited Al or Al+Me may form a continuous layer or islands. By “islands” is herein meant separate areas of deposited Al or Al+Me, so that the underlying nitride layer is exposed. See
The deposited Al or Al+Me may also in some areas of the nitride layer form a continuous layer and in some areas of the nitride layer form islands as defined above.
In one embodiment, Al or Al+Me is deposited forming islands covering at least 25% of the nitride layer area, or at least 50% of the nitride layer area, or at least 75% of the nitride layer area.
The width of the islands may be up to about 300 nm, in their longest extension in a direction parallel to the surface plane. The average width of the islands, in their longest extension in a direction parallel to the surface plane, may be from 2 to 200 nm, or from 5 to 100 nm, or from 5 to 80 nm, or from 10 to 60 nm, suitably measured over an area of at least 1 (μm)2.
The thickness of the islands may be from 2 to 200 nm, or from 5 to 150 nm, or from 10 to 100 nm.
The aspect ratio width to thickness of the islands is suitably from 1 to 50, or from 5 to 25.
For a continuous layer of Al or Al+Me deposited, the thickness of the Al or Al+Me layer may be from 2 to 200 nm, or from 5 to 150 nm, or from 10 to 100 nm.
In one embodiment the substrate temperature during the magnetron sputtering is from 350 to 600° C., or from 400 to 500° C.
In one embodiment, Al or Al+Me is deposited forming islands covering at least 25% of the nitride layer area, or at least 50% of the nitride layer area, or at least 75% of the nitride layer area.
For a continuous layer of Al or Al+Me deposited, the thickness of the Al or Al+Me layer may be from 2 to 200 nm, or from 5 to 150 nm, or from 10 to 100 nm.
In one embodiment the substrate temperature during the magnetron sputtering is from 350 to 600° C., or from 400 to 500° C.
In one embodiment the magnetron sputtering is High Power Impulse Magnetron Sputtering (HIPIMS).
For the deposition of the nitride layer with HIPIMS the DC bias voltage is suitably 20-100 V, or 30-75 V.
The maximum local peak power density during a pulse used in the HIPIMS process in the deposition of the nitride layer is suitably more than 100 W·cm−2, or more than 500 W·cm−2, or more than 900 W·cm−2.
The maximum local peak current density during a pulse used in the HIPIMS process in the deposition of the nitride layer is suitably more than 0.4 A·cm−2, or more than 0.8 A·cm−2, or more than 1.2 A·cm−2.
For the deposition of the nitride layer with HIPIMS the average power density is suitably 20-100 W·cm−2, or 30-75 W·cm−2.
For the deposition of the Al or Al+Me layer with HIPIMS the unipolar bias voltage is suitably 20-200 V, or 50-175 V, or 75-150 V.
For the deposition of the Al or Al+Me layer with HIPIMS the average power density is suitably 2-25 W·cm−2, or 5-15 W·cm−2.
For the deposition of the oxide layer with HIPIMS the unipolar bias voltage is suitably 20-400 V, or 50-200 V, or 75-150 V.
The maximum local peak power density during a pulse used in the HIPIMS process in the deposition of the oxide layer is suitably more than 50 W·cm−2, or more than 100 W·cm−2, or more than 200 W·cm−2.
For the deposition of the oxide layer with HIPIMS the average power density is suitably 5-150 W·cm−2, or 10-60 W·cm−2.
The maximum local peak current density during a pulse used in the HIPIMS process in the deposition of the oxide layer is suitably more than 0.2 A·cm−2, or more than 0.4 A·cm−2, or more than 0.6 A·cm−2.
The pulse length used in the HIPIMS process in both the deposition of the nitride layer and the deposition of the oxide layer is suitably from 2 μs to 200 ms, or from 10 μs to 100 ms.
The nitride layer can be represented by the general formula TibZrcHfdVeTafNbgCrhSiiAljN, wherein 0≤b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤f≤1, 0≤g≤1, 0≤h≤1, 0≤i≤1, 0≤j≤1, b+c+d+e+f+g+h+i+j=1.
In one embodiment the nitride layer is a nitride of Al and one or more of Zr, Hf, V, Ta, Nb, Si and Cr, preferably a nitride of Al and one or more of Ti and Cr.
In one embodiment the nitride layer is a (Ti,Al)N layer of the general formula TibAl1-bN, wherein 0<b<1, or 0.1<b<0.9, or 0.2<b<0.7, or 0.3<b<0.6.
In one embodiment the nitride layer is a (Ti,Al,Cr)N layer of the general formula TibCrhAl1-b-hN, wherein 0<b<1, 0<h<1, 0<b+h<1. In one embodiment 0.1<b<0.9 and 0.05<h<0.8, or 0.2<b<0.8 and 0.05<h<0.5.
In one embodiment the nitride layer is an (Al,Cr)N layer of the general formula CrhAl1-hN, wherein 0<h<1. In one embodiment 0.2<h<0.8, or 0.25<h<0.75, or 0.25<h<0.35.
Suitably, in the (AlaMe1-a)2O3 layer 0.1≤a≤1, or 0.25≤a≤1, or 0.5≤a≤1, or 0.75≤a≤1, or 0.25≤a≤0.9, or 0.25≤a≤0.7.
In one embodiment the (AlaMe1-a)2O3 layer is an (AlaCr1-a)2O3 layer.
In one embodiment the (AlaMe1-a)2O3 layer is an Al2O3 layer.
The Al2O3 layer is suitably of a gamma crystal structure.
The (AlaMe1-a)2O3 layer is suitably of a gamma crystal structure.
It has now also been provided a coated cutting tool comprising a substrate with a coating comprising a nitride layer which is a layer of a nitride of Al and additionally one or more of Ti, Zr, Hf, V, Ta, Nb, Cr and Si, and an oxide layer (A) being an (AlaMe1-a)2O3 layer, 0.05<a≤1, situated above the nitride layer, wherein Me is one or more of Ti, Mg, Ag, Zr, Si, V, Fe, Hf, B and Cr, the coating has
In the inclusions of (Al,Me,O), as well as in layer (B), the atomic ratio Al/(Al+Me) is suitably from 0.05 to 1, or from 0.1 to 1, or from 0.25 to 1, or from 0.5 to 1, or from 0.75 to 1.
In one embodiment, the coating has in the interface region next to the nitride layer inclusions of (Al,Me,O) starting from the interface between the nitride layer and the oxide layer (A). The inclusions of (Al,Me,O) originates from deposited metallic Al or Al+Me islands which have been partly or fully oxidized during a deposition process of the oxide layer (A).
Thus, in one embodiment the inclusions of (Al,Me,O) has an average atomic ratio (Al+Me)/O of more than 2/3, i.e., a higher relative Al+Me content than in the remaining oxide layer.
In another embodiment the inclusions of (Al,Me,O) are fully oxidized. Thus, the inclusions of (Al,Me,O), has an average atomic ratio (Al+Me)/O of 2/3 and which are of another crystal structure than the remaining oxide layer (A). One example is that the remaining oxide layer (A) being of gamma crystal structure and the inclusions of (Al,Me,O) being of an alpha or kappa crystal structure.
The average width of the inclusions may be from 2 to 200 nm, or from 5 to 100 nm, or from 5 to 50 nm, or from 10 to 30 nm, as determined from a cross-sectional cut, perpendicular to the surface plane of the coating, suitably measured over a length of at least 1 μm.
The inclusions may extend 5 to 150 nm, or 10 to 100 nm, in a direction towards the upper surface of the oxide layer (A), as determined from a cross-sectional cut, perpendicular to the surface plane, of the coating.
In one embodiment the Al+Me content in the inclusions of (Al,Me,O) is in average from 40 to 100 at. %, or from 45 to 95 at. %, or from 50 to 75 at. %.
In one embodiment, the coating has a layer (B) of (Al,Me,O) situated inbetween the nitride layer and the oxide layer (A). The (Al,Me,O) layer (B) originates from a deposited metallic Al or Al+Me layer which has been partly oxidized during a deposition process of the oxide layer (A).
Thus, in one embodiment there exist a layer (B) of (Al,Me,O) which has an average atomic ratio (Al+Me)/O more than 2/3, i.e., a higher relative Al+Me content than in the above situated oxide layer (A).
The thickness of the layer (B) of (Al,Me,O) may be from 2 to 200 nm, or from 5 to 150 nm, or from 10 to 100 nm.
In one embodiment the Al+Me content in the layer (B) of (Al,Me,O) is in average >40 at. % and ≤100 at. %, or ≥45 at. % and ≤95 at. %, or ≥50 at. % and ≤75 at. %.
In one embodiment the coated cutting tool has in an 100 nm interface region next to the nitride layer in the direction towards the surface of the coating an average atomic ratio metal to oxygen, (Al+Me)/O of more than 2/3.
The interface region is herein defined to be the 100 nm part of the coating directly above the nitride layer.
In the interface region the average atomic ratio metal to oxygen (Al+Me)/O, is suitably more than 0.70, or more than 0.75.
The upper limit of the average atomic ratio metal to oxygen, (Al+Me)/O, in the interface region is suitably 0.85, or 0.80, or 0.75.
The thickness of the nitride layer is suitably 0.5-5 μm, or 1-4 μm.
The thickness of the oxide layer (A) is suitably 0.1-5 μm, or 0.3-3 μm, or 0.5-1 μm.
The nitride layer can be represented by the general formula TibZrcHfdVeTafNbgCrhSiiAljN, wherein 0b≤1, 0≤c≤1, 0≤d≤1, 0≤e≤1, 0≤f≤1, 0≤g≤1, 0≤h≤1, 0≤i≤1, 0≤j≤1, b+c+d+e+f+g+h+i+j=1.
In one embodiment the nitride layer is a nitride of Al and one or more of Zr, Hf, V, Ta, Nb, Si and Cr, preferably a nitride of Al and one or more of Ti and Cr.
In one embodiment the nitride layer is a (Ti,Al)N layer of the general formula TibAl1-bN, wherein 0<b<1, or 0.1<b<0.9, or 0.2<b<0.7, or 0.3<b<0.6.
In one embodiment the nitride layer is a (Ti,Al,Cr)N layer of the general formula TibCrhAl1-b-hN, wherein 0<b<1, 0<h<1, 0<b+h<1. In one embodiment 0.1<b<0.9 and 0.05<h<0.8, or 0.2<b<0.8 and 0.05<h<0.5.
In one embodiment the nitride layer is an (Al,Cr)N layer of the general formula CrhAl1-bN, wherein 0<h<1. In one embodiment 0.2<h<0.8, or 0.25<h<0.75, or 0.25<h<0.35.
Suitably, in the (AlaMe1-a)2O3 layer 0.1≤a≤1, or 0.25≤a≤1, or 0.5≤a≤1, or 0.75≤a≤1, or 0.25≤a≤0.9, or 0.25≤a≤0.7.
In one embodiment the (AlaMe1-a)2O3 layer is an (AlaCr1-a)2O3 layer.
In one embodiment the (AlaMe1-a)2O3 layer is an Al2O3 layer.
The Al2O3 layer is suitably of a gamma crystal structure.
The (AlaMe1-a)2O3 layer is suitably of a gamma crystal structure.
In one embodiment the oxide layer (A) is the uppermost layer of the coating.
In one embodiment the coating has a further layer on top of the oxide layer (A) for wear protection-, decorative- or wear recognition purposes. This uppermost layer has suitably a thickness of 0.1-10 μm and can for example be of nitrides such as TiN, (Ti,Al)N, CrN, HfN, carbides such as TiC, borides such as TiB2 or oxides (AlMe)2O3, ZrO2, TiO2, V2O5 (including metallic interlayers) or multilayers of the forementioned.
The coating is suitably substantially free from droplets of target material on its surface.
The oxide layer (A) of the coating is preferably a PVD oxide layer, i.e., it has been deposited by a PVD process, preferably magnetron sputtering, most preferably HIPIMS.
The nitride layer of the coating is preferably a PVD nitride layer, i.e., it has been deposited by a PVD process, preferably magnetron sputtering, most preferably HIPIMS.
The substrate of the coated cutting tool can be of any kind common in the field of cutting tools for metal machining. Substrates include cemented carbide, cermet, cBN, ceramics, PCD and HSS.
In one embodiment, the substrate is cemented carbide having a composition of 6-12 wt % Co, optionally up to 10 wt % carbides or carbonitrides of one or more metals from groups 4, 5 and 6 in the periodic table of elements, and balance WC.
The metals from groups 4, 5 and 6 in the periodic table of elements are suitably belonging to the group of Ti, Ta, Nb, V, Zr, Cr, W and Mo.
The grain size of the WC, d, in the cemented carbide body is suitably 0.2-5 μm, or 0.5-2 μm. The grain size of the WC, d, is determined from the value of magnetic coercivity. The relationship between coercivity and grain size of WC is described, e.g., in Roebuck et al., Measurement Good Practice No. 20, National Physical Laboratory, ISSN 1368-6550, November 1999, Revised February 2009, Section 3.4.3, pages 19-20.
The coated cutting tool can be a coated cutting insert, such as a coated cutting insert for turning or a coated cutting insert for milling, or a coated cutting insert for drilling, or a coated cutting insert for threading, or a coated cutting insert for parting and grooving. The coated cutting tool can also be a coated solid drill, an endmill, or a tap.
In a preferred embodiment the coated cutting tool is a coated solid drill or coated endmill.
Cemented carbide solid endmill blanks were provided having a composition of 10 wt % Co, 0.4 wt % Cr and balance WC.
The grain size of the WC, determined from coercivity, was about 0.5 μm.
Sample 1:
A (Ti,Al)N layer was deposited by HIPIMS using sequential power pulses provided according to the description in US 2014/0339917A1. The following process parameters/conditions were used:
Total pressure: 0.60 Pa
Ar-pressure: 0.43 Pa
N2-pressure: 0.17 Pa
Substrate temperature: 430° C.
Bias voltage: −40 V DC
Bias current: −4.1 A
Power: 27.8 kW on 3×Ti40Al60-targets
Target diameter: 160 mm
Average power density: 46.1 W·cm−2
On-time of pulse: 7.56 ms
Pulse frequency: 20 Hz
Deposition time: 180 minutes
The layer thickness was measured to 2.8 μm. The hardness of the deposited (Ti,Al,)N layer was measured to 3300HV0.015. The reduced E-modulus was measured to 450 GPa.
Further, metallic (Al,Cr) (minor amounts Cr due to a Cr-containing fringe on the Al-target used) was deposited by HIPIMS using sequential power pulses. The following process parameters/conditions were used:
Ar-pressure: 0.6 Pa (=total pressure)
Substrate temperature: 430° C.
Bias voltage: 100 V unipolar pulsed
Bias current: −0.2 A, +0.3 A
Bias on-time: 10 μs
Bias off-time: 10 μs
Power: 5 kW on 3× Al-targets (with Al50Cr50 fringe)
Target diameter: 160 mm
Average power density: 8.3 W·cm−2
On-time of pulse: 50 ms
Pulse frequency: 6.67 Hz
Deposition time: 13 s
The (Al,Cr) was present in the form of islands of thickness between about 2 and 20 nm on the (Ti,Al)N surface.
Further an (Al,Cr)2O3 layer (slight content of Cr) was deposited by HIPIMS using sequential power pulses provided according to the description in WO2013083238A1. The following process parameters/conditions were used:
Total pressure: 0.72 Pa
Ar-pressure: 0.6 Pa
O2-pressure: 0.12 Pa
Substrate temperature: 430° C.
Bias voltage: 100 V unipolar pulsed
Bias current: −1.2 A, +1.3 A
Bias on-time: 10 μs
Bias off-time: 10 μs
Power: 10 kW on 3× Al-targets (with Al50Cr50 fringe)
Target diameter: 160 mm
Average power density: 16.6 W·cm−2
On-time of pulse: 50 ms
Pulse frequency: 6.67 Hz
Deposition time: 140 min
The deposited (Al,Cr)2O3 layer was determined by XRD to be a gamma-Al2O3 layer. The layer thickness was measured to 0.65 μm. The hardness of the deposited (Al,Cr)2O3 layer was measured to 2800HV0.015. The reduced E-modulus was measured to 370 GPa.
Sample 2:
(Ti,Al)N/(Al,Cr)/(Al,Cr)2O3 were deposited using the same procedure as for Sample 1 but using half the power, 2.5 kW when depositing the (Al,Cr) layer. This achieved a smaller amount of (Al,Cr) deposited.
Sample 3:
(Ti,Al)N/(Al,Cr)/(Al,Cr)2O3 were deposited using the same procedure as for Sample 1 but using a longer deposition time (about 27 seconds) when depositing the (Al,Cr) layer. This achieved a greater amount of (Al,Cr) deposited.
Sample 4:
A comparative sample without any deposited metallic (Al,Cr) between the nitride and the oxide layer was made by using the same procedure for the deposition of the (Ti,Al)N layer and (Al,Cr)2O3 layer as for Sample 1.
The coated endmills were then tested in a milling operation in steel.
Work piece material: 1.2311 steel
Vc=140 m/min (cutting speed in meters per minute)
f2=0.04 mm/tooth (feed rate in millimeter per tooth)
Liquid cooling
ap=4.0 mm
ae=10.0 mm
The tool geometry for the solid round endmill was Walter Prototyp Protomax ST, diameter 10 mm, 4 flute, corner chamfer 0.1 mm. All tools used in this test were from the same production order.
The cut-off criteria for tool life is 75 μm wear on at least one of the main cutting edge and chamfer.
Table 1 shows the results:
It is concluded that the coating that had been made without any deposition of any metallic (Al,Cr) between the nitride and the oxide layer (Sample 4) reached the cut-off criteria already after 30 m total milling length.
All samples with a coating that had been made including deposition of a metallic (Al,Cr) between the nitride and the oxide layer outperformed comparative Sample 4.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17172773.8 | May 2017 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2018/063296 | 5/22/2018 | WO | 00 |
