Technical field

The present invention relates to a coated cutting tool having a coating comprising a (Ti,AI)N layer with 111 crystallographic texture.

Background

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 wear resistant coating.

When depositing a wear resistant coating the general methods used are chemical vapour deposition (CVD) or physical vapour deposition (PVD). There are limitations on which coatings characteristics that are possible to provide by either method. Even when coatings of the same chemical composition are deposited with either method their properties will vary in terms of, for example, internal residual stress, density, crystallinity and crystal size. Their characteristics and performance in an end- use metal cutting application will therefore be different.

The wear resistant coating usually comprises a layer of, or combination of layers of, a metal nitride, a metal carbonitride or a metal oxide. The origin of a metal element in a coating deposited by a PVD method is a so called "target" in the PVD reactor. Various PVD methods exist, of which the main categories are cathodic arc evaporation and magnetron sputtering. Within the general term "magnetron sputtering" there furthermore exist different methods which differ from each other, such as dual magnetron sputtering (DMS) and High Power Impulse Magnetron Sputtering (HIPIMS).

Titanium aluminium nitride (Ti,AI)N coatings deposited by a PVD method are well-known, as well as their use as wear resistant coatings in cutting tools. One type of (Ti,AI)N coating is a single-layer where the (Ti,AI)N composition is essentially the same throughout the layer. A single-layer coating is provided when the one or more targets used in the deposition process have the same Ti:AI ratio. Another type of (Ti,AI)N coating is a multilayer where there are (Ti,AI)N sublayers of different composition present in the layer. Such a multilayer can be provided when at least two of the targets used in the deposition process have different Ti:AI ratios so that when the substrate is rotated in the chamber sublayers of different composition are deposited in alternation. A special type of multilayer is a nano-multilayer where the individual layer thicknesses may be as low as only a few nanometers.

The crystal structure of (Ti,AI)N in PVD coatings can be cubic or hexagonal. In prior art studies generally a lower Al content, such as < 60 at% of Al+Ti, in (Ti,AI)N gives a single phase cubic structure while a substantial amount of hexagonal structure is seen at an Al content > 67 at%, and particularly at an Al content >70 at% of Al+Ti, in (Ti,AI)N. A specific limit of the level of Al content for giving either a single phase cubic structure or a mixed structure comprising both cubic and hexagonal structure have been reported and vary to some extent depending on, for example, the deposition conditions.

(Ti,AI)N of cubic phase is known to possess good properties in terms of hardness and elastic modulus. These properties are beneficial to have for a coating of a cutting tool. (Ti,AI)N of hexagonal phase, on the other hand, has worse mechanical properties negatively influencing the wear resistance of the coating in metal cutting.

Object of the invention

The object of the present invention is to provide a coated cutting tool showing excellent wear resistance, especially excellent flank wear resistance in milling operations.

The invention

It has now been provided a coated cutting tool which satisfies the above- mentioned objectives. The coated cutting tool having at least one rake face and at least one flank face and a cutting edge inbetween, the coated cutting tool comprising a substrate and a coating, the coating comprises a (Ti,AI)N layer, the (Ti,AI)N layer is either a single monolithic layer or a multilayer of two or more alternating (Ti,AI)N sub layer types different in their composition, the (Ti,AI)N layer having an overall atomic ratio AI/(Ti+AI) of >0.67 but £ 0.85, wherein the (Ti,AI)N layer shows a distribution of 111 misorientation angles, a 111 misorientation angle being the angle between a normal vector to the surface of the (Ti,AI)N layer and the <111 > direction that is closest to the normal vector to the surface of the (Ti,AI)N layer, a cumulative frequency distribution of the 111 misorientation angles is such that ³ 60% of the 111 misorientation angles are less than 10 degrees.

If one excludes anti-parallel directions/planes (e.g., -1-1-1 is anti-parallel to 111), there are 4 unique {111}-type sets of planes in the cubic crystal structure ((111), (1-1-1), (-11-1), and (-1-11)). They stand in 70.5° angles to each other. If one of these planes is in parallel to the (Ti,AI)N surface, i.e. , an ideal 111 orientation, the 111 misorientation angle would be 0° but there would be other {111}-type planes still having a larger angle to the normal vector of the surface than the 0° misorientation angle. The 111 misorientation angle as herein meant is the smallest angle, i.e., the angle between a normal vector to the (Ti,AI)N layer and the <111 > direction that is closest to the normal vector to the (Ti,AI)N layer.

The distribution of 111 misorientation angles can be determined in an electron backscatter analysis (EBSD). However, the columnar grain width is generally increasing by increasing thickness of the (Ti,AI)N layer, especially for the first micrometers of the (Ti,AI)N layer and EBSD analysis may not be suitable if the grain width is too small. Therefore, in the case of having a (Ti,AI)N layer of a thickness of 2 pm or less the distribution of 111 misorientation angles is preferably determined in an transmission electron microscope (TEM) analysis, if the grain size is regarded to be too small for EBSD analysis. The EBSD or TEM analysis is made within a distance of 0.7 mm from the cutting edge.

The cumulative frequency distribution of the 111 misorientation angles is such that suitably ³ 75%, preferably ³ 90%, of the 111 misorientation angles are less than 10 degrees.

The cumulative frequency distribution of the 111 misorientation angles is such that suitably from 75 to 97%, preferably from 90 to 95%, of the 111 misorientation angles are less than 10 degrees.

In one embodiment, the cumulative frequency distribution of the 111 misorientation angles is such that ³ 20%, preferably ³ 35%, of the 111 misorientation angles are less than 5 degrees.

In one embodiment, the cumulative frequency distribution of the 111 misorientation angles is such that from 20 to 90%, preferably from 30 to 75%, most preferably from 35 to 65%, of the 111 misorientation angles are less than 5 degrees.

In one embodiment the (Ti,AI)N layer has a thickness of 0.1-15 pm, preferably 0.5-12 pm, most preferably 1-8 pm. In one embodiment, the (Ti,AI)N layer has a Vickers hardness of ³ 3000 HV (15 mN load), preferably 3500-4200 HV (15 mN load).

In one embodiment the (Ti,AI)N layer has a plain strain modulus of ³ 450 GPa, preferably ³ 475 GPa. The (Ti,AI)N layer has preferably a plain strain modulus of 450- 540 GPa, more preferably 475-530 GPa.

The (Ti,AI)N layer suitably has an overall atomic ratio AI/(Ti+AI) of 0.70-0.85, preferably 0.70-0.80, most preferably 0.72-0.76.

In one embodiment the (Ti,AI)N layer is a single monolithic layer.

In one embodiment the (Ti,AI)N layer is a multilayer of two or more alternating (Ti,AI)N sub-layer types different in their composition of which at least one (Ti,AI)N sub layer type has atomic ratio AI/(Ti+AI) of 0.50-0.67, preferably 0.55-0.67, most preferably 0.60-0.67, and at least one (Ti,AI)N sub-layer type has an atomic ratio AI/(Ti+AI) of 0.70-0.90, preferably 0.75-0.90, most preferably 0.75-0.85.

In one embodiment the (Ti,AI)N layer is a multilayer of one or two (Ti,AI)N sub layer type/types having an atomic ratio AI/(Ti+AI) of 0.50-0.67, preferably 0.55-0.67, most preferably 0.60-0.67 alternating with one or two (Ti,AI)N sub-layer type/types having an atomic ratio AI/(Ti+AI) of 0.70-0.90, preferably 0.75-0.90, most preferably 0.75-0.85.

In a preferred embodiment the (Ti,AI)N layer is a multilayer of one (Ti,AI)N sub layer type having an atomic ratio AI/(Ti+AI) of 0.50-0.67, preferably 0.55-0.67, most preferably 0.60-0.67 alternating with one (Ti,AI)N sub-layer type having an atomic ratio AI/(Ti+AI) of 0.70-0.90, preferably 0.75-0.90, most preferably 0.75-0.85.

A (Ti,AI)N sub-layer type in a multilayer suitably has an average thickness of 1- 100 nm, preferably 1.5-50 nm, most preferably 2-20 nm.

In one embodiment, the ratio between the average thicknesses of the different (Ti,AI)N sublayer types is from 0.5 to 2, preferably from 0.75 to 1.5.

The (Ti,AI)N layer comprises a cubic crystal structure.

In one embodiment the (Ti,AI)N layer is of a single phase cubic B1 crystal structure, at least over a distance of 0.5 mm, preferably at least over a distance of 1 mm, from a point at the cutting edge along a direction perpendicular to a cutting edge on the rake face and/or the flank face.

The determination of crystal structure or structures present in the (Ti,AI)N layer is suitably made by X-ray diffraction analysis, alternatively TEM analysis.

In one embodiment, the (Ti,AI)N layer, within 0.5 mm, preferably within 1 mm, from the cutting edge, shows in X-ray diffraction analysis, or in TEM analysis, only cubic (Ti,AI)N reflections. The determination of crystal structure or structures present in the (Ti,AI)N layer is suitably made by X-ray diffraction analysis, alternatively TEM analysis.

In X-ray diffraction analysis, or TEM analysis, suitably only cubic (Ti,AI)N reflections are seen, at least when measured within 1 mm from the cutting edge.

In one embodiment, the (Ti,AI)N layer has an average columnar grain width, measured at a distance of up to 2 pm from the lower interface of the (Ti,AI)N layer, of less than 175 nm, preferably less than 150 nm.

In one embodiment, the (Ti,AI)N layer has an average columnar grain width, measured at a distance of up to 2 pm from the lower interface of the (Ti,AI)N layer, of 80-175 nm, preferably 100-150 nm.

In one embodiment, below the (Ti,AI)N layer, there is an innermost layer of the coating, directly on the substrate, of a nitride of one or more elements belonging to group 4, 5 or 6 of the periodic table of elements, or a nitride of Al together with one or more elements belonging to group 4, 5 or 6 of the periodic table of elements. This innermost layer may at least partly act as a bonding layer to the substrate increasing the adhesion of the overall coating to the substrate. Such a bonding layer are commonly used in the art and a skilled person would choose a suitable one. Preferred alternatives for this innermost layer are TiN and (Th- _X AI _X )N, x being suitably > 0 but £ 0.67. The thickness of this innermost layer is suitably less than 3 pm. The thickness of this innermost layer is in one embodiment 0.1-3 pm, preferably 0.2-1 pm.

In one embodiment, there is one or more other layers commonly used in coatings for cutting tools combined with the (Ti,AI)N layer of the present invention. For example, nitrides of one or more elements belonging to group 4, 5 or 6 of the periodic table of elements, or nitrides of Al together with one or more elements belonging to group 4, 5 or 6 of the periodic table of elements. For example, a layer of (Tii. _y Al _y )N, y being suitably > 0 but £ 0.67.

In one embodiment, the coating comprises an inner layer of (Th- _y Al _y )N, 0.25£y£0.67, of a thickness 0.5-3 pm, followed by a (Ti,AI)N layer of the present invention of a thickness of 0.5-5 pm.

The (Ti,AI)N layer according to the invention is deposited by PVD, i.e. , the (Ti,AI)N layer is a PVD layer. Suitably, the (Ti,AI)N layer is a PVD layer deposited by a sputtering process, preferably a High-Power Impulse Magnetron Sputtering (HIPIMS) - deposited layer. The substrate of the coated cutting tool can be of any kind common in the field of cutting tools for metal machining. The substrate is suitably selected from cemented carbide, cermet, cubic boron nitride (cBN), ceramics, polycrystalline diamond (PCD) and high speed steel (HSS).

In one preferred embodiment, the substrate is cemented carbide.

The coated cutting tool is suitably in the form of an insert, a drill or an end mill.

Brief descriptions of the drawings

Figure 1 shows a schematic view of one embodiment of a cutting tool being a milling insert.

Figure 2 shows a schematic view of a cross section of an embodiment of the coated cutting tool of the present invention showing a substrate and a coating.

Figure 3 shows a frequency distribution curve of 111 misorientation angles from electron backscatter diffraction (EBSD) analysis of an embodiment of the invention "Sample 2a (invention)".

Figure 4 shows a frequency distribution curve of 111 misorientation angles from electron backscatter diffraction (EBSD) analysis of an embodiment of the invention "Sample 5 (invention)".

Figure 5 shows a frequency distribution curve of 111 misorientation angles from electron backscatter diffraction (EBSD) analysis of "Sample 6 (comparative)".

Figure 6 shows a transmission electron microscope (TEM) electron diffraction pattern for the (Ti,AI)N layer of an embodiment of the invention "Sample 2a (invention)".

Detailed description of embodiments in drawings

Figure 1 shows a schematic view of one embodiment of a cutting tool (1) having a rake face (2), a flank face (3) and a cutting edge (4). The cutting tool (1) is in this embodiment a milling insert. Figure 2 shows a schematic view of a cross section of an embodiment of the coated cutting tool of the present invention having a substrate body (5) and a (Ti,AI)N coating (6). Methods

Electron back scattering diffraction (EBSD):

The EBSD measurements were performed on the flank face of the cutting tool samples at a distance of 50 pm from the cutting edge.

Prior to the EBSD scans the respective sample surfaces were carefully polished using a colloidal silica suspension with a nominal grain size of 40 nm (Struers OPS 0.04 pm). This step serves to remove any roughness present on the as deposited coating surface. No more than 100 nm of the top coating is removed by this procedure. If the (Ti,AI)N layer would not have been the uppermost layer of the coating, a suitable method, such as polishing, is used for removing the layer(s) situated above the (Ti,AI)N layer, in order to eventually provide a polished (Ti,AI)N surface for the EBSD scans.

The electron diffraction patterns were acquired in a Zeiss CrossBeam 540 FIB- SEM (Carl Zeiss AG, Oberkochen, Germany) in conjunction with an EDAX DigiView 5 EBSD camera (EDAX Inc., Mahwah NJ, USA) at a standard sample tilt of 70° and a working distance of 5 mm. An e-beam acceleration voltage of 10 to 13 kV was used for the acquisition. The step size for the mappings was 20 nm. The mapping area was 15.00 x 11.25 pm. Indexed via the EDAX TEAM software, the determined crystal orientation data was further evaluated using the EDAX OIM Analysis software.

A cumulative frequency distribution of 111 misorientation angles was calculated as follows: For each spot measurement of the total EBSD scan (representing an incremental surface area of the overall analyzed surface region) the crystallographic direction perpendicular to the surface plane of the (Ti,AI)N layer, is derived from the absolute crystallographic orientation measured (i.e. the orientation data in Euler angles).

Subsequently, the vector angle between this crystallographic direction and the closest <111 >-type direction is calculated. Where “closest” refers to the <111 >-type direction (among all four crystallographically equivalent possibilities) that includes the smallest possible angle with the surface normal. This angle is defined as the 111 misorientation angle. As each measurement point constitutes an equal fraction of the analyzed area the relative frequency distribution of these angular misorientation values characterizes the overall degree of the 111 surface texture. Electron diffraction in transmission electron microscopy (TEM):

In the electron diffraction analysis made herein these are TEM measurements which were carried out using a Transmission Electron Microscope: JEOL ARM 200F microscope, 200 kV. Only the coating should contribute to the diffraction pattern by using a selected area aperture. The TEM was operated with parallell illumination for the diffraction in a selected area electron diffraction (SAED) procedure.

The samples were analysed in cross-section, i.e. , the incident electron beam was parallell to the film plane. To rule out an amorphisation during sample preparation different methods can be used, i) classical preparation including mechanical cutting, gluing, grinding and ion polishing and ii) using a FIB to cut the sample and make a lift out to make the final polishing. The position of the analysis was near the substrate, about 200 nm from the substrate. The position of the analysis was further at a distance within 1 mm from the cutting edge.

SAED data were obtained for the samples. From the SAED data a diffraction intensity profile was provided along the 111 ring that is centered around the angular position that corresponds to the coating normal. Then normalized integrations were made both at the 111 diffraction spot and the -1-1-1 diffraction spot, respectively, going to 45 degrees misorientation angle. The two integrations were combined into one intensity distribution curve. The intensity distribution data from both the 111 diffraction spot and the -1-1-1 diffraction spot were used in order to increase the number of data points thereby reducing the signal to noise ratio as much as possible.

The intensity at a certain misorientation angle is directly proportional to the sample volume that exhibits this misorientation. Thus, the intensity distribution curve is equivalent to the distribution of 111 misorientation angles. Then, correspondingly, a cumulative intensity curve obtained from the intensity distribution curve is equivalent to a cumulative frequency distribution of 111 misorientation angles.

X-Ray Diffraction:

The X-ray diffraction patterns were acquired by Grazing incidence mode (GID) on a diffractometer from Seifert / GE (PTS 3003). Cu-Ka-radiation with a polycapillary lens (for producing a parallel beam) was applied for the analysis (high tension 40 kV, current 40 mA). The incident beam was defined by a 0,5 mm pinhole. For the diffracted beam path an energy dispersive detector (Meteor 0D) was used. The measurement was done in grazing incidence mode (Omega = 4°). The 2theta range was about 20- 80° with a step size of 0.03° and a counting time of 6 s. The XRD measurements were performed on the flank face of the cutting tool samples at a distance within 1 mm from the cutting edge.

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. From this curve hardness was calculated.

Plane strain modulus:

The elastic properties of the coating samples were characterized by the so- called plane strain modulus E _ps as derived by nanoindentation via the Oliver and Pharr method. The nano-indentation data was obtained from indentation as described for Vickers hardness above.

Grain width:

The average (Ti,AI)N grain width was determined through the evaluation of SEM cross-sections by the stereological line intersection method: A line grid is overlaid to a SEM micrograph and the intersections of the lines with the grain boundary network are marked. The statistics of the distances between adjacent intersections reflect the size of the three-dimensional grains (see, e.g., B. Ilschner, R.F. Singer, Werkstoffwissenschaften und Fertigungstechnik, Springer Berlin Heidelberg, 2016, ISBN: 978-3-642-53891-9). The SEM micrographs were taken at a distance of about 0.7 pm from the cutting edge, on the flank face.

Examples:

Example 1:

A layer of (Ti,AI)N was deposited onto WC-Co based substrates using a target set-up of one target with the composition Tio _.33 Alo _.67 and one target with the composition Tio _.20 Alo _.80 . The WC-Co based substrates were inserts of flat geometry for easier analysis of the coating. The substrates had a composition of 8 wt% Co and balance WC.

HIPIMS mode was used in a Hauzer Flexicoat 1000 equipment. In three separate runs of depositions the total pressure was varied while keeping all other conditions the same. Three different total pressures were tested, 0.505 Pa, 0.219 Pa and 0.167 Pa.

The following process parameters were used:

Temperature: 300°C

Average power: 40 kW (20 kW per target)

Pulse duration: 80 ps

Set peak current: Target 1 : 800 A, target 2: 800 A

DC pulse voltage: 1800 V Ar-Flow: 500 see I 180 seem 130 seem

Total pressure (I h+Ar): 0.505 Pa I 0.219 Pa 0.167 Pa

(-167 seem N2) I (-115 seem N2) (-108 seem N2)

Bias Potential: -100 V (Ti,AI)N layers with a thickness of about 1.75 pm were deposited. From the substrate rotation speed an average thickness of a (Ti,AI)N sublayer was calculated to be about 3 nm.

The coated cutting tools provided are called "Sample 1 (comparative)", "Sample 2 (invention)" and "Sample 3 (invention)".

A further sample corresponding to "Sample 2 (invention)" was made with a higher thickness (7.3 pm). The process parameters were:

Temperature: 300°C Average power: 40 kW (20 kW per target)

Pulse duration: 80 ps

Set peak current: Target 1 : 800 A, target 2: 800 A

DC pulse voltage: 1800 V Ar-Flow: 180 seem Total pressure (I h+Ar): 0.22 Pa (-115 seem N2) Bias Potential: -110 V

The coated cutting tool provided is called "Sample 2a (invention)". An even further sample according to the invention was made intended for testing in metal cutting. A first layer of 1.3 pm conventional Tio.4oAl ₀ .6oN deposited by cathodic arc evaporation was provided onto a WC-Co based substrate followed by a 1.25 pm (Ti,AI)N layer very similar to the (Ti,AI)N layer of "Sample 2 (invention)". The WC-Co based substrate was of two different milling insert geometries, SPMW12 and ADMT160608R-F56. The substrate had a composition of 8 wt% Co and balance WC.

The main purpose of the arc-evaporation deposited innermost layer is to improve adhesion to the substrate so that tool life is not limited by flaking. The two layers were made as follows: Innermost layer of Tin Mn _f snN:

A 1.3 pm layer of Ti _0.4 oAl _0.6 oN was deposited onto a WC-Co based substrate using a target with the composition Ti _0.4 oAl _0.6 o·

Arc mode was used in a Hauzer Flexicoat 1000 equipment. The deposition was run at total pressure 5 Pa, DC bias -40 V and temperature 580°C.

Laver of (Ti.AhN:

A 1.25 pm layer of (Ti,AI)N was deposited onto the arc-deposited Tio _.4 oAlo _.6 oN layer using a target set-up of one target with the composition Tio _.33 Alo _.67 and one target with the composition Tio _.20 Alo _.80 . HIPIMS mode was used in a Hauzer Flexicoat 1000 equipment.

The following process parameters were used:

Temperature: 300°C Average power: 40 kW (20 kW per target)

Pulse duration: 80 ps

Set peak current: Target 1 : 800 A, target 2: 800 A

DC pulse voltage: 1800 V Ar-Flow: 180 seem Total pressure (N ₂ +Ar): 0.22 Pa (-115 seem N ₂ ) Bias Potential: -100 V

From the substrate rotation speed an average thickness of a (Ti,AI)N sublayer was calculated to be about 3 nm.

The resulting coated cutting tool is called "Sample 4 (invention)".

Example 2: A layer of (Ti,AI)N, single monolithic layer, was deposited onto WC-Co based substrates using a target set-up of one target with the composition Ti _0.2 oAl _0.8 o· The WC- Co based substrates were inserts of flat geometry for easier analysis of the coating. The substrates had a composition of 8 wt% Co and balance WC.

HIPIMS mode was used in a Hauzer Flexicoat 1000 equipment.

The following process parameters were used:

Temperature: 200°C

Average power: 20 kW

Pulse duration: 80 ps

Set peak current: 800 A

DC pulse voltage: 1800 V

Ar-Flow: 150 seem

Total pressure (I h+Ar): 0.190 Pa

(~88 seem N2)

Bias Potential: -150 V

A (Ti,AI)N layer with a thickness of about 1.7 pm was deposited on the inserts. The coated cutting tools provided are called "Sample 5 (invention)".

Example 3 (comparative):

A Tio _. 40Alo _. 60N layer was deposited onto WC-Co based substrates being cutting tools of a milling insert types SPMW12 and ADMT160608R-F56 and as well flat inserts (for easier analysis of the coating) using HI PI MS mode in an Oerlikon Balzers equipment using S3p technology. This HIPIMS-deposited coating was known to give very good results in machining of steel (ISO-P) materials.

The substrates had a composition of 8 wt% Co and balance WC.

The deposition process was run in HIPIMS mode using the following process parameters

Target material: Tio.4oAlo.60

Target size: 6x circular, diameter 15 cm

Average power per target: 9 kW Peak pulse power: 55 kW

Pulse on time: 4 ms Temperature: 430°C

Total pressure: 0.61 Pa

Argon pressure: 0.43 Pa Bias potential: -40 V

A layer thickness of about 7.2 pm was deposited.

The coated cutting tool provided is called "Sample 6 (comparative)

Example 4 (comparative):

A Tio _.i oAlo _. 9oN mono-layer was deposited onto WC-Co based substrates being flat cutting inserts for easy analysis of the coating. Two targets of Ti _0.i oAl _0. 9o were used facing each other. The deposition was made using HIPIMS mode with the following process parameters:

Target material: (2x) Tio.ioAlo.9o Temperature: 300°C Average power: 40 kW (20 kW per target)

Pulse duration: 80 ps

Set peak current: Target 1 : 800 A, target 2: 800 A

DC pulse voltage: 1800 V Ar-Flow: 150 seem Total pressure (N2+Ar): 0.19 Pa (-125 seem N2) Bias Potential: -110 V

A layer thickness of about 1.4 p was deposited.

The coated cutting tool provided is called "Sample 7 (comparative)"

Example 5 (analysis):

XRD:

XRD analysis was made on "Sample 1 (comparative)", "Sample 2 (invention)", "Sample 3 (invention)", and "Sample 5 (invention").

All four samples show peaks from the cubic (111), (200) and (220) planes. However, "Sample 1 (comparative)" in addition shows significant peaks at about 57 and 70 degrees 2theta, the peaks being the hexagonal (110) (hex AIN 57.29°), and one or both of (112) (hex AIN 68.85°) and (201) (hex AIN 69.98°).

XRD analysis was also made on "Sample 7 (comparative)".

Significant hexagonal peaks were seen.

EBSD:

Electron backscatter diffraction (EBSD) analysis was made on "Sample 2a (invention)", "Sample 5 (invention)" and "Sample 6 (comparative)". The grain size was sufficiently large for being able to do an EBSD analysis on "Sample 5 (invention)" even though its layer thickness was only 1.7 pm. A cumulative frequency distribution of 111 misorientation angles was calculated, as described in the "Methods" section. Figure 3 shows a frequency distribution curve of 111 misorientation angles from EBSD analysis of "Sample 2a (invention)". Figure 4 shows a frequency distribution curve of 111 misorientation angles from EBSD analysis of "Sample 5 (invention)". Figure 5 shows a frequency distribution curve of 111 misorientation angles from EBSD analysis of "Sample 6 (comparative)".

For "Sample 2a (invention)" the (Ti,AI)N layer shows a cumulative frequency distribution of the 111 misorientation angles such that about 94% of the 111 misorientation angles are less than 10 degrees, and about 55% of the 111 misorientation angles are less than 5 degrees.

For "Sample 5 (invention)" the (Ti,AI)N layer shows a cumulative frequency distribution of the 111 misorientation angles such that about 77% of the 111 misorientation angles are less than 10 degrees, and about 37% of the 111 misorientation angles are less than 5 degrees.

For "Sample 6 (comparative)", the Tio.4oAlo.6oN layer shows a cumulative frequency distribution of the 1 1 1 misorientation angles such that about 14% of the 1 1 1 misorientation angles are less than 10 degrees, and about 4% of the 111 misorientation angles are less than 5 degrees.

TEM:

Transmission electron microscope (TEM) analysis was made on "Sample 2a (invention)". Figure 6 shows a TEM electron diffraction pattern for the (Ti,AI)N layer of "Sample 2a (invention)".

The diffraction pattern from "Sample 2a (invention)" shows distinct spots which means high crystallographic texture. The diffraction pattern shows a 111 textured layer.

TEM analysis on "Sample 2a (invention)" also showed that the average thickness of each of the (Ti,AI)N sublayer types was about the same being about 3 nm.

EDX:

The average composition of the (Ti,AI)N layer of "Sample 2a (invention)" was proven to correspond to the expected values from target composition by Energy Dispersive X-Ray Spectroscopy (EDX) analysis. The average composition was Tio _. 27Alo _. 73N, i.e. , the (Ti,AI)N layer had an overall atomic ratio AI/(Ti+AI) of 0.73.

Mechanical properties:

Hardness measurements (load 15 mN) were carried out on the flank face of the coated cutting tools listed in Table 1 to determine Vickers hardness and plain strain mo modulus (E _pS ).

Table 1.

Samples 1, 2 and 5 within the invention all show high hardness and high plane strain modulus values.

It is concluded that if a too high total pressure is used as in "Sample 1 (comparative)" the hardness becomes low and also the plain strain modulus becomes low. this implies insufficient amount of cubic crystal structure in the coating. XRD results also shows the presence of hexagonal peaks besides cubic peaks.

"Sample 6 (comparative)" is a fully cubic Tio _.4 oAlo _.6 oN sample having an Al content well below the limit for possible formation of hexagonal phase. The good mechanical properties are therefore as expected.

It is further concluded that if there is a too high Al content in the (Ti,AI)N layer as in "Sample 7 (comparative)" the hardness becomes low and also the plain strain modulus becomes low. This implies insufficient amount of cubic crystal structure in the coating. XRD analysis also shows a significant presence of hexagonal peaks besides quite weak cubic peaks.

Grain width:

The grain width was determined for "Sample 2a (invention)". The grain width was determined at distances from the lower interface to the substrate of 2, 4 and 6 pm. The average grain width values were 127, 165 and 247 nm, respectively.

Example 5:

Cutting test, ISO-P milling: "Sample 4 (inventien)" was further tested in an ISO-P milling test, and the flank wear was measured. In this test "Sample 4 (inventien)" was cempared with a cutting insert almcst identical tc "Sample 6 (ccmparative)" kncwn tc be gccd in ISO-P milling.

The ccmparative samples were cnes frcm ccmmercial prcducticn. In additicn tc what is present in "Sample 6 (ccmparative)" they further had an upper thin ZrN layer of 0.2 pm deposited for the purpose of colour and easier wear detection. However, this additional layer does not influence the wear resistance in any substantial way.

The comparative coated tool was made by providing milling insert cemented carbide substrates of geometry SPMW12, having a composition of 8 wt% Co and balance WC, and depositing a coating according to the conditions below:

Innermost layer:

Target material: Tio.4oAlo.60 Target size: 6 x circular, diameter 15 cm

Average power per target: 9 kW Peak pulse power: 55 kW

Pulse on time: 4 ms Temperature: 430°C Total pressure: 0.61 Pa

Argon pressure: 0.43 Pa

Bias potential: -40 V

A layer of 2.1 pm was deposited.

Outermost ZrN layer:

Target material: Zr

Target size: 3 x circular, diameter 15 cm

Average power per target: 9 kW Peak pulse power: 27 kW

Pulse on time: 26 ms Temperature: 430°C

Total pressure: 0.55 Pa

Argon pressure: 0.43 Pa

Bias potential: -40 V

A layer of 0.2 pm was deposited. The test conditions and test data are summarized below. As workpiece material steel (ISO-P) was used. Test conditions:

A milling test was performed at a cutting speed of 240 m/min. The other testing conditions are as follows: Tool geometry: Insert geometry: SPMW12 Tool diameter D _c : 125 mm Setting angle K: 45° Cutting data:

Contact width a _e : 100 mm Cutting depth a _p : 3 mm Cutting speed: 240 m/min Feed per tooth: 0.2 mm

Workpiece:

Material ISO-P steel, 42CrMoV4 type

Tensile strength 785 MPa Cutting fluid: none, i.e. dry

In this test the wear maximum was observed at the cutting edge on the flank side. Three cutting edges were tested of each sample and the averaged value for each cutting length is shown in Table 2.

Table 2. The comparative sample has a coating known to give very good results in milling of ISO-P steel. Nevertheless, it is concluded that "Sample 4 (invention)" performs much better than the comparative sample.

The comparative sample is essentially "Sample 6 (comparative)" and "Sample 4 (invention)" can be seen as having the upper half of the coating of "Sample 6

(comparative)" exchanged into the inventive (Ti,AI)N layer of "Sample 2 (invention)".

"Sample 6 (comparative)" and "Sample 2 (invention)" have similar mechanical properties (hardness and plain strain modulus) as seen in Table 1. Nevertheless "Sample 6 (comparative)" performs much worse than the inventive sample in this cutting test.

Example 6:

Cutting test, ISO-M milling: Sample 4 (inventien) was further tested in an ISO-M milling test, and the flank wear was measured. In this test "Sample 4 (inventien)" was cempared with a cutting insert having an arc-depcsited ccating kncwn tc be gccd in ISO-M milling.

The ccmparative ccated tccl was made by providing milling insert cemented carbide substrates having a ccmpcsiticn cf 8 wt% Cc and balance WC and depcsiting a ccating acccrding tc the ccnditicns belcw:

Innermcst multilayer Tin snAIn snN/ Tin R7N layer: Target material: 1x Tio.50Alo.50 /1x Tio.33Alo.e7 Temperature: 550°C

Tctal pressure: 10 Pa

Bias pctential: -60 V

A layer cf 1.3 pm was deposited. Outermost multilayer Tip snAln snN/ Tip 33AI0 B7N layer:

Target material: 1x Tio.50Alo.50 /2x Tio.33Alo.e7

Temperature: 550°C

Total pressure: 10 Pa

Bias potential: -50 V A layer of 1.2 pm was deposited. The test conditions and test data are summarized below. As workpiece material stainless steel (ISO-M) was used.

Test conditions: Tool geometry:

Insert geometry: ADMT160608R-F56

Tool diameter D _c : 63 mm

Setting angle K: 90°

Number of teeth/ inserts mounted: 3

Cutting data:

Contact width a _e : 50 mm

Cutting depth a _p : 3 mm

Cutting speed: 240 m/min Feed per tooth: 0.15 mm

Workpiece:

Material 1.4571/V4A-stainless steel

Tensile strength 720 MPa

Cutting fluid: none, i.e. dry

In this test the wear maximum was observed at the cutting edge on the flank side. Three cutting edges were tested of each coating and the averaged value for each cutting length is shown in Table 3.

Table 3. The comparative sample has a coating known to give very good results in milling of stainless steel (ISO-M). Nevertheless, it is concluded that "Sample 4 (invention)" performs much better than the comparative sample.