Patent Application
20210388483
The present invention relates to a method for producing a coated cutting tool having a coating comprising aluminum oxide with a significant amount of alpha phase content. 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).
Aluminium oxide (Al2O3) coatings are being used in coatings for cutting tools. The deposition of hard Al2O3 coatings in the industrial-scale PVD coaters is state of the art, but then only for gamma (γ)-Al2O3. The drawback of metastable Al2O3 phases like gamma (γ) or kappa (κ) IS phase transformation into the thermodynamically stable alpha (α)-Al2O3 (corundum, R-3c) phase in a typical temperature range between 900° C. and 1100° C. This limits the usage of metastable Al2O3 coatings in metal cutting applications to maximum temperatures below 900° C. At higher temperatures, the phase transformation takes place and the hardness, stress and volume of the metastable Al2O3 coatings change rapidly due to the heat evolved during metal cutting, resulting in cracks and flaking, and these coatings can't therefore be used in metal cutting applications. On the other hand, the usage of α-Al2O3 coatings in an as-deposited state, which is state of the art in CVD, is beneficial in high temperature cutting applications like e.g. turning.
The deposition of α-Al2O3 by PVD shows several advantages over CVD deposition methods. The α-Al2O3 deposition by CVD requires high temperatures in the range between 900° C. to 1100° C. and the coatings are having a tensile stress profile while lower temperatures are used in PVD processes. Furthermore, as-deposited PVD coatings typically have a residual stress being compressive, which is beneficial for providing high toughness which is necessary for milling applications, while CVD coatings typically have a residual stress being tensile.
A cutting tool with an Al2O3 coating of α-phase, or at least having a high content of α-phase, can thus be used at high temperature cutting applications, such as turning, while there is less beneficial to use Al2O3 coatings of α- or κ-phase.
In order to produce a sufficient amount of coated cutting tools to be offered on the commercial market one has to be able to charge a PVD reactor with many uncoated blanks or substrates. Furthermore, in the case of commercial cutting tool inserts having rake and flank faces they should generally be coated on the whole insert, i.e., the coating should be deposited as evenly as possible on all sides of an insert.
The use of rotating carousels where uncoated blanks are mounted on for example pins provides for the production of a large number of coated inserts with an evenly distribution of a coating around the inserts. One mode of deposition is two-fold (2f) rotation where there is a first axis of rotation in the center of the whole carousel (table) and then a second axis of rotation by a number of rotating spindles which in its turn have (non-rotating) pins on which inserts are mounted. Another mode of deposition is three-fold (3f) rotation where there is a first axis of rotation in the center of the whole carousel (table) and then a second axis of rotation by a number of rotating spindles which in its turn have rotating pins on which inserts are mounted forming a third axis of rotation.
One consequence of deposition in a commercial 2f- or 3f-rotating mode is that the deposition of a coating will be repeatedly interrupted due to the rotation of the inserts. The rotation leads to that an area of an insert is either facing the plasma, or not facing the plasma, or being in some position partly facing the plasma. Furthermore, the distance to a target is varying during deposition as a result of the 2f- or 3f rotation. The above mentioned issues have prevented a commercial production of cutting tools with PVD alpha-aluminium oxide coatings.
Yamada-Takamura et al, Surface and Coatings Technology, 142-144 (2001) 260-264, discloses deposition of films containing α-Al2O3 by filtered arc deposition. However, the film starts with amorphous Al2O3 and nanocrystalline γ-Al2O3 followed by nucleation and subsequent growth of α-Al2O3. Furthermore, the arc-deposited film will contain a lot of droplets.
EP151707A1 discloses the formation of an α-Al2O3 coating where the temperature has to be raised to at least 800° C.
US2009/0214894A1 discloses formation of a coating comprising α-Al2O3 by first forming an oxide layer of corundum structure by oxidising a TiAlN, TiN or TiCN layer at a temperature of about 650-800° C. and then depositing a layer comprising α-Al2O3, also at 650-800° C., by reactive sputtering.
However, when depositing a coating onto a cemented carbide substrate at high temperatures, such as 650° C., or higher, the substrate loses toughness which is a draw-back when designing a coated cutting tool. Furthermore, the use of template layers like chromium oxide or titanium oxide as templates for growing α-Al2O3 has substantial drawbacks since such template layers are mechanically weak and deteriorate the overall wear resistance of the whole coating during metal cutting.
U.S. Pat. No. 8,540,786 B2 discloses a coating comprising α-Al2O3 oxide deposited by HIPIMS (High Power Impulse Magnetron Sputtering). In this disclosure, the substrate is constantly facing the magnetron sputtering glow discharge. Thus, no 2f- or 3f-rotation is used. No disclosure of any α-Al2O3 on both a rake and a flank face is disclosed.
It would therefore be beneficial in many metal cutting applications to use a cutting tool having a PVD α-Al2O3 containing coating and therefore further desired to provide a method for the efficient deposition of α-Al2O3 containing coatings by industrial-scale PVD at low substrate temperatures, with a high deposition rate, the α-Al2O3 containing coatings having high hardness, high Young's modulus, high crystallinity, residual stress being compressive, having high phase fractions of α-Al2O3, and being substantially droplet-free.
The object of the present invention is therefore to provide a method of producing, in industrial scale, a cutting tool having a coating comprising a PVD α-Al2O3.
It has now been provided a method for producing a coated cutting tool which satisfies the above-mentioned objective. The method comprises HIPIMS deposition of α-phase containing Al2O3 coatings on two-fold (2f) and three-fold (3f) rotated substrates in industrial-scale PVD coaters for metal cutting industry with a high deposition rate and substrate temperatures in the range of from 350° C. but below 600° C.
Thus, it is hereby provided a method for producing a coated cutting tool having at least one rake face and at least one flank face, the cutting tool comprising a substrate of cemented carbide, cermet, cBN, or ceramic and a coating, the method comprises depositing on every flank face and every rake face of the cutting tool an Al2O3 layer by a HIPIMS process, in the process the peak pulse cathode power is ≥500 kW, the value of negative peak pulse voltage is ≥1200 V, the specific target peak pulse power density is ≥350 W/cm2, the specific average target power density is ≥6 W/cm2, the pulse time is 20-150 μs, the pulse frequency is ≥100 Hz, the peak pulse current is ≥400 A, the peak bias current is ≥100 A and 800 A, the specific bias current density is 5-80 mA/cm2, the oxygen partial pressure is ≥1×10−4 mbar, the total pressure is from 0.25 to 3 Pa, the method comprising the following steps:
The substrate temperature during the deposition in the HIPIMS process is suitably ≥400° C. but 580° C., preferably ≥450° C. but 560° C.
In the HIPIMS process the pulse time is suitably from 30 to 100 μs, preferably from 40 to 70 μs.
In the HIPIMS process the peak pulse cathode power is suitably ≥1 MW.
In the HIPIMS process the peak pulse current is preferably ≥600 A.
In the HIPIMS process the value of negative peak pulse voltage is suitably 1800 V.
In the HIPIMS process the pulse frequency is suitably ≥300 Hz, preferably 500 Hz.
In the HIPIMS process the oxygen partial pressure is suitably ≥3×10−4 mbar.
In the HIPIMS process the total pressure is suitably from 0.5 to 1.5 Pa. The PVD reactor chamber gas comprises a noble gas element such as Ar which during operation of the HIPIMS process is ionised. If the total pressure is too low the noble gas element is more difficult to ionise and no plasma forms. If the total pressure is too high the noble gas element ions may be so many in the plasma that the average free path is too small hindering the transport of metal ions from the target to the substrate.
In the HIPIMS process the target size is suitably from 1000 to 2000 cm2.
In the HIPIMS process the average cathode power is suitably ≥10 kW, preferably ≥15 kW.
In the HIPIMS process there is either a pulsed bias, or DC bias, voltage applied of suitably from 175 to 275 V, negative bias.
In the HIPIMS process the specific average target power density is suitably ≥8 W/cm2, preferably ≥10 W/cm2.
In the HIPIMS process the specific target peak pulse current density is suitably 0.25 A/cm2, preferably ≥0.35 A/cm2.
In the HIPIMS process the specific target peak pulse power density is suitably 650 W/cm2.
In the HIPIMS process the peak bias current is suitably ≥200 A and 400 A.
In the HIPIMS process the specific bias current density is suitably 10-40 mA/cm2.
In one embodiment, two-fold (2f) rotated substrates is used in the HIPIMS process.
In one embodiment, three-fold (3f) rotated substrates is used in the HIPIMS process.
The substrate holder can be a rotatable table (i) which comprises rotatable spindles (ii) which in its turn each comprises a number or rotatable pins (iii). In two-fold (2f) rotation (i) and (ii) rotates while in three-fold (3f) rotation all of (i), (ii) and (iii) rotate.
The PVD reaction chamber suitably has a chamber volume of ≥800 l, preferably ≥1000 l.
In one embodiment the deposited aluminium oxide layer is an α-Al2O3 layer.
Two-fold (2f) and three-fold (3f) rotation of substrates lead to an interrupted deposition process due to the rotation of the substrates in the flow of elements in the plasma. Thus, the plasma density subjected to the substrates will vary to a great extent, from high levels down to very low levels. Despite this, significant amounts of α-phase of Al2O3 is deposited.
As a result of the method described herein an Al2O3 layer is provided in which an α-phase fraction on both a flank and rake face of 2f-, or even 3f-, rotated substrates is detected. It is especially noticeable that the production-like 3f-rotated substrates showed clear α-Al2O3 phase containing XRD signals on their flank and rake faces.
The method herein disclosed provides the following benefits: no usage of nucleation layer is needed, a low deposition temperature can be used so that the deterioration of substrate toughness is minimised, a full scale production equipment can be used, droplet-free coatings are provided, the deposition process provides a constant or increased α-Al2O3 phase fraction in the coating over time, hard α-Al2O3 containing coatings are provided with hardness ≥2000 HV.
In one embodiment the Al2O3 layer is deposited directly onto the substrate. This means that in this embodiment no other previously deposited layer is present between the Al2O3 layer and the substrate.
In a 2theta XRD analysis of the deposited Al2O3 layer the diffractogram shows at least clear peaks of α-Al2O3 (113) and α-Al2O3 (024). These peaks are, according to PDF no. 42-1468 of the ICDD database, positioned at 43.36 and 52.56 degrees 2theta respectively. When identifying diffraction peaks from an actual layer the peak positions in a diffractogram are often seen slightly shifted from PDF data due to, for example, internal stresses within the layer and equipment effects.
Thus, from XRD analysis one clearly sees that the deposited Al2O3 layer shows peaks from at least α-Al2O3 (113) and α-Al2O3 (024) in XRD analysis.
The thickness of the deposited Al2O3 layer is suitably from 0.1 to 20 μm, preferably from 0.5 to 10 μm.
In one embodiment the deposited Al2O3 layer contains a mixture of α-Al2O3 and γ-Al2O3.
In one embodiment a minimum of two or more reflections of α-Al2O3 are detectable in XRD analysis.
The deposited Al2O3 layer suitably shows a relation between α-Al2O3 and γ-Al2O3 as follows:
In GIXRD (gracing incidence x-ray diffraction) analysis at 0.5° incidence angle the ratio I(α-Al2O3 (113)) to (γ-Al2O3 (400)) is suitably ≥0.5, preferably ≥1, most preferably ≥2, on at least one of the rake face or flank face of the cutting tool.
In GIXRD (gracing incidence x-ray diffraction) analysis at 0.5° incidence angle the ratio I(α-Al2O3 (024)) to (γ-Al2O3 (400)) is suitably ≥0.2, preferably ≥0.5, most preferably ≥1, on at least one of the rake face or flank face of the cutting tool.
In GIXRD (gracing incidence x-ray diffraction) analysis at 0.5° incidence angle the ratio I(α-Al2O3 (116)) to (γ-Al2O3 (400)) is suitably ≥0.1, preferably ≥0.2, most preferably ≥0.5, on at least one of the rake face or flank face of the cutting tool.
The deposited Al2O3 layer is suitably substantially droplet-free.
The deposited Al2O3 layer suitably has a Vickers hardness of ≥2000 HV, preferably from 2200 to 3000 HV, most preferably from 2600 to 3000 HV.
The deposited Al2O3 layer suitably has a reduced Young's modulus of ≥320 GPa, preferably from 330 to 420 GPa.
The coated cutting tool is a cutting tool for metal machining.
The coated cutting tool is suitably in the form of an insert, a drill or an end mill.
The α-Al2O3 is suitably present in the deposited Al2O3 layer on every rake face and every flank face of the cutting tool.
The present invention further relates to a coated cutting tool having at least one rake face and at least one flank face, comprising a substrate of cemented carbide, cermet, cBN, or ceramic and ceramic, and a coating comprising an Al2O3 layer deposited according to the method as herein disclosed.
The α-Al2O3 is suitably present in the deposited Al2O3 layer on every rake face and flank face of the cutting tool.
The thickness of the Al2O3 layer is suitably from 0.1 to 20 μm, preferably from 0.5 to 10 μm.
In one embodiment the deposited Al2O3 layer contains a mixture of α-Al2O3 and γ-Al2O3.
The Al2O3 layer suitably shows a relation between alpha-aluminium oxide and gamma-aluminium oxide as follows:
In GIXRD (gracing incidence x-ray diffraction) analysis at 0.5° incidence angle the ratio I(α-Al2O3 (113)) to (γ-Al2O3 (400)) in an XRD 2theta diffractogram is suitably 0.5, preferably ≥1, most preferably ≥2, on at least one of the rake face or flank face of the cutting tool.
In GIXRD (gracing incidence x-ray diffraction) analysis at 0.5° incidence angle the ratio I(α-Al2O3 (024)) to (γ-Al2O3 (400)) in an XRD 2theta diffractogram is suitably 0.2, preferably ≥0.5, most preferably ≥1, on at least one of the rake face or flank face of the cutting tool.
In GIXRD (gracing incidence x-ray diffraction) analysis at 0.5° incidence angle the ratio I(α-Al2O3 (116)) to (γ-Al2O3 (400)) in an XRD 2theta diffractogram is suitably 0.1, preferably ≥0.2, most preferably ≥0.5, on at least one of the rake face or flank face of the cutting tool.
The Al2O3 layer suitably has a Vickers hardness of ≥2000 HV, preferably from 2200 to 3000 HV, most preferably from 2600 to 3000 HV.
The Al2O3 layer suitably has a reduced Young's modulus of ≥320 GPa, preferably from 330 to 420 GPa.
The coated cutting tool is a cutting tool for metal machining.
The coated cutting tool is suitably in the form of an insert, a drill or an end mill.
XRD-Phase Analysis:
The X-ray diffraction patterns concerning the phase analysis were acquired by Grazing incidence mode (GIXRD) on a diffractometer from Panalytical (Empyrean). CuKalpha-radiation with line focus was used for the analysis (high tension 40 kV, current 40 mA). The incident beam was defined by a 2 mm mask and a ⅛° divergence slit in addition with a X-ray mirror producing a parallel X-ray beam. The sideways divergence was controlled by a Soller slit (0.04°). For the diffracted beam path a 0.18° parallel plate collimator in conjunction with a proportional counter (OD-detector) was used. The measurement was done in grazing incidence mode (Omega=1°). The 2Theta range was about 28-45° with a step size of 0.03° and a counting time of 10 s. For the XRD-line-profile analysis a reference measurement (with LaB6-powder) was done with the same parameters as listed above to correct for the instrumental broadening.
Vickers Hardness:
The Vickers hardness was measured by means of nano indentation (load-depth graph) using a Picodentor HM500 of Helmut Fischer GmbH, Sindelfingen, Germany. For the measurement and calculation the Oliver and Pharr evaluation algorithm was applied, wherein a diamond test body according to Vickers was pressed into the layer and the force-path curve was recorded during the measurement. The maximum load used was 15 mN (HV 0.0015), the time period for load increase and load decrease was 20 seconds each and the holding time (creep time) was 10 seconds. From this curve hardness was calculated. Hardness values and values for the reduced Young's modulus, indicated in the examples were each measured on the flank face of the coated tool.
Reduced Younq's Modulus
The reduced Young's modulus (reduced modulus of elasticity) was determined by means of nano-indentation (load-depth graph) as described for determining the Vickers hardness.
Thickness:
The thickness of the coating layers was determined by calotte grinding. Thereby a steel ball was used having a diameter of 30 mm for grinding the dome shaped recess and further the ring diameters were measured, and the layer thicknesses were calculated therefrom. Measurements of the layer thickness on the rake face (RF) of the cutting tool were carried out at a distance of 2000 μm from the corner, and measurements on the flank face (FF) were carried out in the middle of the flank face.
On a WC—Co based cemented carbide substrate, having a Co content of 8 wt % and balance WC, an aluminium oxide coating was deposited in a Hauzer HTC1000 equipment under the following process conditions:
In 2f rotating mode an aluminium oxide coating having a thickness of 0.75 μm on the rake face and in 3f rotating mode an aluminium oxide coating having a thickness of 0.81 μm on the flank face was made.
The hardness was 2887 HV and the red. Young's modulus was 384 GPa.
Further Examples 2-7, using the same equipment as in Example 1, providing aluminium oxide coatings according to the invention were made where the process conditions had been varied according to Tables 1-4. Both 2f rotating and 3f rotating samples were produced.
Aluminium oxide coatings with thicknesses, hardnesses and red. Young's modulus according to Table 5 resulted from the depositions.
Grazing Incidence XRD (GIXRD) Measurements:
GIXRD measurements in the 2theta range 35 to 60° of inventive examples no. 1-7 were made under an angle of 0.5° of a 3f rotated flank. The XRD diffractograms all show clearly α-Al2O3 (113), (024) and (116) peaks (43.363°, 52.559° and 57.504°, respectively, in PDF no. 42-1468 of the ICDD database). All diffractograms were found to show peaks of α-Al2O3 (113), (024) and (116).
Inventive example No. 1 was investigated further.
A GIXRD measurement in the 2theta range 20 to 60°, and a fine scan GIXRD measurement in the 2theta range 49 to 61°, were made on inventive example no. 1 with an incident angle of 1° of a 2f rotated rake face are shown in
A GIXRD measurement in the 2theta range 20 to 70° of inventive example no. 1 was made under an angle of 0.2° of a 2f rotated rake face and is shown in
The conclusion of GIXRD of a 2f-rotated rake face of inventive example no. 1 from
A GIXRD measurement in the 2theta range 35 to 62° of inventive example no. 1 was made under an angle of 0.5° of a 3f rotated flank and is shown in
The conclusion of GIXRD of a 3f-rotated flank face of inventive example no. 1 from
From
On a WC—Co based cemented carbide substrate, having a Co content of 8 wt % and balance WC, an aluminium oxide coating was deposited in a Hauzer HTC1000 equipment using dual magnetron sputtering (DMS) 20 kW. The further process conditions were:
In 2f and 3f rotating mode an aluminium oxide coating having a thickness of approx. 1.2 μm was made. The hardness was 2792 HV and the red. Young's modulus was 340 GPa.
Only γ-Al2O3 peaks in XRD analysis were seen.
| Number | Date | Country | Kind |
|---|---|---|---|
| 18205208.4 | Nov 2018 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2019/080399 | 11/6/2019 | WO | 00 |
