A coated cutting tool

Abstract

The invention relates to a coated cutting tool consisting of a substrate body and a coating, the substrate is a cemented carbide and the coating comprises a layer of a first cubic metal nitride and there is a from 10 to 500 nm thick layer of Al1-v-y- zMvSiyXzN, 0≤v≤0.75, 0≤y≤0.20, 0≤z≤0.10, situated below the layer of the first cubic metal nitride, wherein the distance between the layer of Al1-v-y-zMvSiyXzN and the substrate body surface is from 0 to 500 nm, wherein M is of one or more metal elements of group 3, 4, 5 and 6 in the periodic table of elements, and, wherein X is one or more of C, B and O, the layer of Al1-v-y-zMvSiyXzN has wurtzite crystal structure.

Description

[0001] A coated cutting tool

[0002] The present invention relates to a coated cutting tool comprising a substrate body of cemented carbide and a wear resistant coating deposited on the substrate body.

[0003] Background

[0004] Cutting tools for metal cutting, commonly consist of a substrate body made of cemented carbide having a wear-resistant coating deposited thereon. Cemented carbide comprises hard constituents of tungsten carbide, WC, within a metallic binder phase of, usually, cobalt.

[0005] As wear resistant coatings are metal nitrides deposited by a PVD (physical vapor deposition) process commonly used. The metal nitride coating may be a mono-layer metal nitride or a multilayer of sublayers of different elemental composition. Examples of metal nitrides are TiN, (Ti,AI)N, (AI,Cr)N, (Ti,Si)N and (Ti,AI,Si)N. The most commonly used metal nitride being (Ti,AI)N.

[0006] The general shape and specific geometry of the cutting tool depend on the intended metal cutting operation. Examples of cutting tools are milling inserts, turning inserts, drills, and endmills.

[0007] Different wear processes on the tool eventually deteriorate the performance of the tool and it has to be replaced by a new one. Thus, when preparing a coated cutting tool for metal cutting, a major goal is that the tool should perform in service as long as possible, i.e. , the tool life should be as long as possible.

[0008] Apart from that the coating itself should show wear resistant properties in a metal cutting operation, good adhesion between the substrate body and the wear resistant coating is of high importance. A main consequence of bad adhesion is flaking of the coating which then leads to increased wear of the cutting tool and reduced tool life. Bad adhesion also generally limits the coating thickness possible to use. This is especially relevant for PVD coatings that normally show compressive stress in the coating as deposited. The thicker the coating the higher adhesion is needed to prevent flaking of the coating.

[0009] When depositing a cubic metal nitride layer by a PVD (physical vapor deposition) process the temperature during the process is usually kept at a moderate level. A cubic metal nitride in an as-deposited state normally shows good adhesion to a cemented carbide substrate. However, during prolonged exposure to heat during a metal cutting operation the adhesion of the coating to the substrate may decrease leading to reduced tool life. This risk is increased during metal cutting operations generating especially high levels of heat, such as when cutting so called "difficult-to- cut" materials, which include nickel-based superalloys such as Inconel. A high cutting speed is another factor which increases the generated heat, as well as the cutting depth. The reason for the decrease in adhesion is that at prolonged subjection of the coated cutting tool to a high level of heat there is a risk of diffusion of binder metal, which is usually cobalt, from the cemented carbide substrate body into the deposited metal nitride layer. This may affect the adhesion between the substrate body and the metal nitride layer negatively and consequently lead to shorter tool life for the coated cutting tool.

[0010] There may, furthermore, be a desire to deposit PVD metal nitride coatings at higher temperatures than usual to provide different effects. Such effects may be, for example, a reduction of residual compressive stress within the coating or providing higher mobility of elements during deposition of the coating giving a denser coating. However, deposition of a metal nitride by a PVD process at higher temperature than usual may then increase the risk of diffusion of binder metal into a deposited metal nitride layer giving the adverse effects mentioned above.

[0011] Furthermore, a heat treatment may be desired in order to increase the fracture toughness of a deposited coating. For example, some metal nitride layers exhibit an in- crease in fracture toughness when subjected to a heat treatment under certain conditions. Thus, such a procedure may increase the risk of diffusion of binder metal into the deposited metal nitride layer giving the adverse effects mentioned above.

[0012] Finally, there may be a desire to deposit a layer by a CVD process on top of an already PVD deposited metal nitride layer such as deposition of an alpha-alumina layer. CVD processes are generally run at much higher temperatures than PVD processes. Thus, such a procedure may increase the risk of diffusion of binder metal into the deposited metal nitride layer giving the adverse effects mentioned above.

[0013] Object of the invention

[0014] It is an object of the present invention to provide a coated cutting tool which shows a significant interdiffusion resistance of binder metal, such as cobalt, between a cemented carbide substrate body and a coating. The coated cutting tool preferably also shows high wear resistance in general, for example high flank wear resistance and / or high crater wear resistance in metal machining such as milling, turning and drilling.

[0015] The invention

[0016] The present invention relates to a coated cutting tool consisting of a substrate body and a coating, the substrate is a cemented carbide and the coating comprises a layer of a first cubic metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, or, a layer of a first cubic metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with one or more of Al and Si. There is a from 10 to 500 nm thick layer of Ali-v-y-zMvSiyXzN, 0<v<0.75, 0<y<0.20, 0<z<0.10, situated below the layer of the first cubic metal nitride, wherein the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is from 0 to 500 nm, and wherein M is of one or more metal elements of group 3, 4, 5 and 6 in the periodic table of elements, and, wherein X is one or more of C, B and 0, the layer of Ali-v-y-zMvSiyXzN has wurtzite crystal structure.

[0017] The layer of Ali-v-y-zMvSiyXzN has wurtzite crystal structure, which is herein meant that no or very little amounts of cubic structure, or any other crystal structure, is present within the Ali-v-y-zMvSiyXzN layer. This is herein defined as that in a TEM analysis, or a combination of SEM and TEM analysis, in a 2D sectional image, the area fraction of crystallites of wurtzite structure in the Ali-v-y-zMvSiyXzN layer is at least 90%, preferably at least 95%.

[0018] By a "cubic" metal nitride is herein meant a metal nitride which is to a great extent is of cubic structure, i.e. , has no or only small amounts of hexagonal structure, or any other crystal structure, present within the metal nitride layer. This is herein defined as that in a TEM analysis, or a combination of SEM and TEM analysis, in a 2D sectional image, the area fraction of crystallites of cubic structure in a "cubic" metal nitride layer is at least 90%, preferably at least 95%.

[0019] Suitably, the layer of Ali-v-y-zMvSiyXzN has a thickness of from 20 to 300 nm, or from 30 to 150 nm, or from 40 to 75 nm.

[0020] Suitably, the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is from 0 to 200 nm, preferably from 0 to 100 nm, most preferably from 0 to 50 nm.

[0021] In one embodiment the layer of Ali-v-y-zMvSiyXzN is situated directly below the layer of the first cubic metal nitride.

[0022] The layer of Ali-v-y-zMvSiyXzN is in a preferred embodiment situated on the substrate body surface. However, the present invention will work as well if, e.g., a thin layer of a second cubic metal nitride, i.e., not being of wurtzite structure, would be placed inbetween the substrate body surface and the layer of Ali-v-y-zMvSiyXzN. Therefore, the layer of Ali-v-y-zMvSiyXzN is herein claimed as situated below the layer of the first cubic metal nitride, wherein the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is from 0 to 500 nm, suitably from 0 to 200 nm, preferably from 0 to 100 nm, most preferably from 0 to 50 nm.

[0023] Thus, in one embodiment there is a second cubic metal nitride layer, being up to 500 nm thick, or up to 200 nm thick, or up to 100 nm thick, or up to 50 nm thick, situated on the substrate body surface below the layer of Ali-v-y-zMvSiyXzN. The second cubic metal nitride layer is suitably a cubic metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, optionally in combination with Al and / or Si.

[0024] In a preferred embodiment the layer of Ali-v-y-zMvSiyXzN is situated on the substrate body surface and being situated directly below the layer of the first cubic metal nitride. This means that the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is 0 nm.

[0025] It has surprisingly been found that a thin layer of Ali-v-y-zMvSiyXzN which has wurtzite structure acts as an efficient barrier layer for binder metal diffusion from a cemented carbide substrate up into a metal nitride coating. Such a binder metal diffusion may occur under the subjection of prolonged heat to a coated cutting tool. The effect of w- Ah-v-y-zMvSiyXzN preventing binder metal diffusion is present already for very thin layers of w-Ah-v-y-zMvSiyXzN.

[0026] In the layer of Ali-v-y-zMvSiyXzN, suitably 0<v<0.70, or 0.05<v<0.70, or 0.10<v<0.70.

[0027] In the layer of Ali-v-y-zMvSiyXzN, suitably 0<y<0.15, or 0<y<0.10.

[0028] In the layer of Ali-v-y-zMvSiyXzN, suitably 0<z<0.05, preferably 0<z<0.02.

[0029] In one embodiment, in the layer of Ali-v-y-zMvSiyXzN, 0<v<0.70, 0<y<0.15, and 0<z<0.05.

[0030] In the layer of Ali-v-y-zMvSiyXzN, small amounts of noble gases, such as Ne, Ar, Kr, and Xe, may additionally be present as a consequence of their possible use in the PVD deposition process. Suitably, noble gases may be present in an amount of up to about 5 at% out of the whole of (Ali-v-y-zMvSiyXzN + noble gas), or up to about 3 at%, or up to 1 at %.

[0031] It is important in the present invention that the layer of Ali-v-y-zMvSiyXzN is of wurtzite crystal structure. The one or more metal elements M can be chosen from a range of metal elements as herein disclosed, as long as the layer of Ali-v-y-zMvSiyXzN formed has wurtzite crystal structure.

[0032] In the layer of Ali-v-y-zMvSiyXzN, M is suitably one or more metal elements of group 4, 5 and 6 in the periodic table of elements.

[0033] In the layer of Ali-v-y-zMvSiyXzN, M is suitably one or more of Ti, Zr, Hf, V, Nb, Ta, Cr, preferably one or more of Ti, Zr and Cr.

[0034] In general, a quite high Al content is needed in Ali-v-y-zMvSiyXzN in order to form a wurtzite crystal structure. However, different metals M promote the formation of wurtzite crystal structure differently. For example, Zr promotes the formation of wurtzite at a lower Al content than Ti does. The following specific embodiments within the general formula Ali-v-y-zMvSiyXzN reflect this.

[0035] In one embodiment, the layer of Ali-v-y-zMvSiyXzN is Ali-a-zTiaXzN, 0<a<0.30, 0<z<0.10, X is one or more of C, B and 0. Suitably 0.05<a<0.27, or 0.05<a<0.22. Suitably 0<z<0.05, preferably 0<z<0.02.

[0036] In one embodiment, the layer of Ali-v-y-zMvSiyXzN is Ah-b-zZrbXzN, 0<b<0.70, 0<z<0.10, X is one or more of C, B and 0. Suitably 0.05<b<0.70, or 0.05<b<0.65. Suitably 0<z<0.05, preferably 0<z<0.02.

[0037] In one embodiment, the layer of Ali-v-y-zMvSiyXzN is Ali-c-d-zTicZrdXzN, 0<c+d<0.70, 0<z<0.10, X is one or more of C, B and 0. Suitably 0.05<c+d<0.70. Suitably 0.05<c<0.45, or 0.10<c<0.40. Suitably 0.05<d<0.40, or 0.10<d<0.35. Suitably 0<z<0.05, preferably 0<z<0.02. In one embodiment, the layer of Ali-v-y-zMvSiyXzN is Ali-e-zCreXzN, 0<e<0.25, 0<z<0.10, X is one or more of C, B and 0. Suitably 0.05<e<0.20. Suitably 0<z<0.05, preferably 0<z<0.02.

[0038] In one embodiment, the layer of Ali-v-y-zMvSiyXzN is Ah-f-g-zTifSigXzN, 0<f<0.50, 0<g<0.20, 0<z<0.10, X is one or more of C, B and 0. Suitably 0.05<f<0.40. Suitably 0.05<g<0.15. Suitably 0<z<0.05, preferably 0<z<0.02.

[0039] Within the term "first cubic metal nitride layer" is herein included both an embodiment wherein the first cubic metal nitride layer is a monolithic layer and another embodiment wherein the first cubic metal nitride layer is a multilayer of alternating sublayers. The multilayer embodiment exists in case there are more than one metal element present in the first cubic metal nitride layer. The multilayer of alternating sublayers may be a multilayer of one or more sublayers of different elemental composition having individual thicknesses of from 1 to 200 nm, or from 1 to 100 nm, or from 1 to 50 nm.

[0040] In the case of the first cubic metal nitride layer being a multilayer, for the herein defined features of elemental composition of the first cubic metal nitride layer, the overall average elemental composition of the whole multilayer is considered.

[0041] The first cubic metal nitride is suitably a metal nitride of one or more of Ti, Cr and Zr or Ti, Cr and Zr together with one or more of Al and Si.

[0042] In one embodiment, the first cubic metal nitride layer belongs to the group of TiN, CrN, ZrN, TiCrN, (Ti,AI)N, (Ti,AI,Si)N, (Ti,AI,Cr)N, (Ti,AI,Cr,Si)N and (Cr,AI)N.

[0043] In one embodiment, the layer of the first metal nitride is a Th-h- IhMeiN layer, 0.30<h<0.75, or 0.40<h<0.70, and 0<i<0.10, or 0<i<0.05, wherein Me belong to the group of one or more metal elements of group 4, 5 and 6 in the periodic table of elements and Si. In one embodiment, Me is one or more of V, Cr, Zr, Ta, Nb and Si.

[0044] In one embodiment, the first cubic metal nitride layer is a (Cr,AI)N layer. In one embodiment, the first cubic metal nitride layer is a (Ti,AI)N layer.

[0045] In one embodiment, the first cubic metal nitride layer is a Th , AljN layer, 0.30<j<0.70, or 0.40<j<0.67.

[0046] The thickness of the first cubic metal nitride layer is suitably from 0.2 to 25 pm, preferably from 0.5 to 15 pm, more preferably from 1 to 10 pm, most preferably from 3 to 10 pm.

[0047] The first cubic metal nitride layer is suitably deposited by a PVD method.

[0048] The second cubic metal nitride layer is suitably deposited by a PVD method.

[0049] The layer of Ali-v-y-zMvSiyXzN is suitably deposited by a PVD method.

[0050] In one embodiment, the coated cutting tool the layer of Ali-v-y-zMvSiyXzN is situated on the substrate body surface and being situated directly below the layer of the first cubic metal nitride, the layer of Ali-v-y-zMvSiyXzN is Ali-a-zTiaXzN, X is one or more of C, B and O, 0.05<a<0.22, 0<z<0.02, the first cubic metal nitride layer is a (Ti,AI)N layer, the thickness of the first cubic metal nitride layer is from 0.5 to 15 pm.

[0051] The substrate comprises WC in a metallic binder. The substrate is suitably a WC-Co based cemented carbide comprising from 5 to 15 wt% Co. The substrate optionally comprises further cubic carbides or carbonitrides, as is generally known in the art.

[0052] The cutting tool is suitably an indexable cutting insert, such as a cutting insert for milling, a cutting insert for turning, or a cutting insert for drilling. Alternatively, the cutting tool is suitably a drill or an endmill.

[0053] The cutting tool suitably comprises a rake face and a flank face with a cutting edge in between. Methods

[0054] Thickness and adhesion test by calotte grinding:

[0055] The thickness of a layer was determined by calotte grinding using a steel ball 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 of the cutting tool were carried out at a distance of 2000 pm from the corner, and measurements on the flank face were carried out in the middle of the flank face. A spherical calotte was ground in the coating and substrate material by a rotating the 30 mm steel ball wetted with a drop of 1 pm water-based monocrystalline diamond suspension (Buehler MetaDi blue) and driven by a driving shaft at 400 rpm. The grinding process was stopped when the calotte diameter in the substrate material reached approx. 300 pm. The appearance of the coating after having being subjected to calotte grinding was also evaluated. The amount of delamination at the calotte ground was assessed. The degree of delamination is reflecting the adhesion of the coating to the substrate.

[0056] Qualitative elemental mapping and Quantitative line profiles of elements, low-kV EDX analysis

[0057] In order to Quantify interdiffusion of elements between the substrate and the coating EDX measurements were conducted on cross-sectional specimens of the samples. The sample inserts were halved edge-center to edge-center and embedded in graphite filled hot curing resin. The resulting microsections were ground and polished with diamond suspensions of progressively decreasing particle size (down to 1 pm) and finished by a chemo-mechanical polishing step using an alkaline colloidal silica suspension with an average particle size of 40 nm (Struers OPS).

[0058] The EDX measurements were conducted in a Zeiss Supra 40P FEG-SEM using an Oxford Instruments Ultirn Max 170 SDD detector. With the aim of maximizing spatial resolution and to reliably separate coating and substrate portions a low electron-beam acceleration voltage of 5 kV was used. An aperture size of 60 pm was selected. The measurements were performed with a working distance of 8 mm and a EDX process time setting of 3. The channel resolution was set up to be 5 eV.

[0059] The data was captured at a distance of 120 pm from the cutting edge line. Each analysis was set up as an EDX-mapping over a field of 7.6 pm by 5.3 pm and a scanning resolution of 1024 by 768 points. Each measurement was performed for 65 min. During the measurements a continuous drift correction by digital image correlation was applied.

[0060] Brief description of drawings

[0061] Figure 1 shows a schematic view of one embodiment of a cutting tool being an indexable insert.

[0062] 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.

[0063] Figure 3 shows an image of a calotte grinding of a comparative coated cutting tool. Figure 4 shows an image of a calotte grinding of an embodiment of a coated cutting tool of the present invention.

[0064] Figure 5 shows an elemental mapping image of a comparative coated cutting tool. Figure 6 shows an elemental mapping image of an embodiment of a coated cutting tool of the present invention.

[0065] Figure 7 shows line profiles of elements of a comparative coated cutting tool.

[0066] Figure 8 shows line profiles of elements of an embodiment of a coated cutting tool of the present invention.

[0067] Figure 9 shows a STEM image of a cross section of an embodiment of the coated cutting tool of the present invention showing a substrate and an innermost part of a coating.

[0068] 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) and flank faces (3) and a cutting edge (4). The cutting tool (1 ) is in this embodiment an indexable insert.

[0069] Figure 2 shows a schematic view of a cross section of an embodiment of the coated cutting tool (1 ) of the present invention having a substrate body (5) and a coating (6). The coating (6) comprising an innermost thin metal nitride layer (8) of wurtzite structure and a first cubic metal nitride layer (7).

[0070] Figure 9 shows a STEM image of a cross section of an embodiment of the coated cutting tool (1 ) of the present invention having a substrate body (5), an innermost thin metal nitride layer (8) of wurtzite structure and a first cubic metal nitride layer (7).

[0071] Examples

[0072] Example 1 : Manufacturing of "Samples 1-3 (as deposited) (invention)" and "Samples 4-5 (as deposited) (comparative)"

[0073] As a substrate was used cutting tool bodies (called "blanks") being inserts having a geometry SPHT120408 (milling insert), and flat inserts for analysis of coating.

[0074] The cutting tool body was for the geometry SPHT120408 made out of a cemented carbide of the composition 90.6 wt% WC, 1 .4 wt% (Ta, Nb)C and a binder phase of 8 wt% Co. The average WC grain size dWC was 0.8 pm.

[0075] The cutting tool body was for the flat inserts for analysis made out of a cemented carbide of the composition 94 wt% WC, and a binder phase of 6 wt% Co.

[0076] Prior to the deposition, the substrate bodies were pretreated by ultrasonic cleaning in a water-based medium.

[0077] The PVD reactor was evacuated to 8 x 10’5mbar, and the substrate was pre-treated at 550°C. The pre-treatment included an Ar ion etching procedure. The coating equipment used for depositing the coating according to the invention was a Hauzer HTC1000 (IHI Hauzer Techno Coating B.V., The Netherlands) with a chamber size of 1 m3

[0078] Deposition of an innermost barrier layer of (Ti,AI)N:

[0079] Samples, each having an innermost thin barrier layer of (Ti,AI)N different from each other, were made. There was deposited different barrier layers being Ti0.05AI0.95N, Ti0.10AI0.90N, Ti0.20AI0.80N, Tio.27Alo.73N and Tio.33Alo.67N the metal elemental relation based on target composition. As deposited the Al content decreased by about five at% as measured by EDX. See further Table 1. In the deposition cathodic arc evaporation was used. In the Hauzer HTC1000 equipment used a circular Arc-PVD technology (CARC+) using constant magnetic field configuration was applied during deposition. For the different samples TiAI-targets "Ti5AI95" (Ti:AI = 5:95), "Ti10AI90" (Ti:AI = 10:90), "Ti20AI80" (Ti:AI = 20:80), "Ti27AI73" (Ti:AI = 27:73) and "Ti33AI67" (Ti:AI = 33:67) were used respectively. The targets had a diameter of 100 mm. The reactive gas for the nitride deposition was N2. The depositions were carried out at an arc current at the target of about 80 A, a bias level of -35 V and at a total pressure of 10 Pa in a pure N2 atmosphere. The temperature during the depositions was about 600°C. A table rotation speed of 5 rpm was used. The thickness of each of the thin (Ti,AI)N barrier layers deposited was about 50 nm.

[0080] It was concluded that for the thin barrier layers of Ti0.05AI0.95N, Ti0.10AI0.90N and Ti0.20AI0.80N a complete wurtzite structure was present. For the sample with a barrier layer of Tio.27Alo.73N there was a mixture of both wurtzite structure and cubic structure, the area fraction of crystallites of wurtzite structure in a 2D sectional image of the layer estimated to be much less than 90%. For the sample with a barrier layer of Tio.33Alo.67N there was a cubic structure.

[0081] Deposition of a cubic (Ti,AI)N layer:

[0082] Then, for each of the five different samples a cubic (Ti,AI)N layer was deposited. In the deposition cathodic arc evaporation was used. In the Hauzer HTC1000 equipment used a circular Arc-PVD technology (CARC+) using constant magnetic field configuration was applied during deposition. For the deposition of the cubic (Ti,AI)N layer, TiAl targets "Ti50AI50 (Ti:AI = 50:50) were used. The targets had a diameter of 100 mm. The reactive gas for the nitride deposition was N2. The deposition was carried out at an arc current at the target of about 150 A, a bias level of -35 V and at a total pressure of 10 Pa in a pure N2 atmosphere. The temperature during the deposition was about 550°C. A table rotation speed of 3 rpm was used.

[0083] If reference is herein made to a target of a particular composition, this means that, due to the layout of the used PVD reactor, a line of four targets of the same composition were vertically arranged to allow for a homogeneous deposition throughout the height of the reactor.

[0084] The thickness of the deposited (Ti,AI)N layer was about 7 pm, measured at the edge (at the beginning of the edge rounding) on both the rake face and the flank face and calculating an average.

[0085] The samples made are denoted "Sample 1 (as deposited) (invention)", "Sample 2 (as deposited) (invention)", "Sample 3 (as deposited) (invention)", "Sample 4 (as deposited) (comparative)" and "Sample 5 (as deposited) (comparative)".

[0086] Table 1.

[0087] * relation metal elements as in target

[0088] ** relation metal elements from EDX data

[0089] Example 2: Manufacturing of "Sample 6 (as deposited) (comparative)

[0090] Deposition of an innermost barrier layer of TiN:

[0091] A sample, having an innermost thin layer of TiN was made. The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used. In the deposition cathodic arc evaporation was used. In the Hauzer HTC1000 equipment used a circular Arc-PVD technology (CARC+) using constant magnetic field configuration was applied during deposition. For the sample Ti-targets were used. The targets had a diameter of 100 mm. The reactive gas for the nitride deposition was N2. The deposition was carried out at an arc current at the target of about 80 A, a bias level of -35 V and at a N2 pressure of 10 Pa. The temperature during the deposition was about 600°C. A table rotation speed of 5 rpm was used. The thickness of the thin TiN layer deposited was about 50 nm.

[0092] The thin TiN layer was of a cubic structure.

[0093] Deposition of a cubic (Ti,AI)N layer:

[0094] The same process equipment and process parameters as in Example 1 were used for the deposition of the cubic (Ti,AI)N layer. The thickness of the deposited (Ti,AI)N layer was about 7 pm, measured at the edge (at the beginning of the edge rounding) on both the rake face and the flank face and calculating an average.

[0095] The sample made is denoted "Sample 6 (as deposited) (comparative)". Example 3: Manufacturing of "Sample 7 (as deposited) (invention)" and "Sample 8 (as deposited) (comparative)"

[0096] Deposition of an innermost barrier layer of (Cr,AI)N:

[0097] Samples, each having an innermost thin barrier layer of (Cr,AI)N different from each other, were made. There was deposited different barrier layers being Cr0.10AI0.90N and Cr0.30AI0.70N, the metal elemental relation based on target composition. As deposited the Al content will decrease by a couple of at%. The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used.

[0098] In the deposition cathodic arc evaporation was used. In the Hauzer HTC1000 equipment used a circular Arc-PVD technology (CARC+) using constant magnetic field configuration was applied during deposition. For the different samples CrAI-targets "Cr10AI90" (Cr:AI = 10:90) and "Cr30AI70" (Cr:AI = 30:70) were used respectively. The targets had a diameter of 100 mm. The reactive gas for the nitride deposition was N2. The depositions were carried out at an arc current at the target of about 80 A, a bias level of -35 V and at a N2 pressure of 10 Pa. The temperature during the depositions was about 600°C. A table rotation speed of 5 rpm was used. The thickness of each of the thin (Cr,AI)N barrier layers deposited was about 50 nm.

[0099] It was concluded that the thin barrier layer of Cr0.10AI0.90N was of a complete wurtzite structure. The sample with a barrier layer of Cr0.30AI0.70N was of a cubic structure and no wurtzite structure could be detected.

[0100] Deposition of a cubic (Ti,AI)N layer:

[0101] The same process equipment and process parameters as in Example 1 were used for the deposition of the cubic (Ti,AI)N layer. The thickness of the deposited (Ti,AI)N layer was about 7 pm, measured at the edge (at the beginning of the edge rounding) on both the rake face and the flank face and calculating an average.

[0102] The samples made are denoted "Sample 7 (as deposited) (invention)" and "Sample 8 (as deposited) (comparative)". Table 2.

[0103] * relation metal elements as in target

[0104] Example 4: Manufacturing of "Sample 9 (as deposited) (invention)" and "Sample 10 (as deposited) (invention)"

[0105] Deposition of an innermost barrier layer of (Ti, Al, SDN:

[0106] Samples, each having an innermost thin barrier layer of (Ti , Al, Si)N different from each other, were made. There was deposited different barrier layers being Ti0.35AI0.60Si0.05N and Ti0.35AI0.55Si0.10N, the metal elemental relation based on target composition. As deposited the Al content will decrease by a couple of at%. The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used. In the deposition cathodic arc evaporation was used. In the Hauzer HTC1000 equipment used a circular Arc-PVD technology (CARC+) using constant magnetic field configuration was applied during deposition. For the different samples TiAISi-targets "Ti35AI60Si5" (Ti:AI:Si = 35:60:5) and "Ti35AI55Si10" (Ti:AI:Si = 35:55:10) were used respectively. The targets had a diameter of 100 mm. The reactive gas for the nitride deposition was N2. The depositions were carried out at an arc current at the target of about 80 A, a bias level of -35 V and at a N2 pressure of 10 Pa. The temperature during the depositions was about 600°C. A table rotation speed of 5 rpm was used. The thickness of each of the thin (Ti, Al, Si)N barrier layers deposited was about 50 nm.

[0107] It was concluded that both the barrier layer of Ti0.35AI0.60Si0.05N and the barrier layer of Ti0.35AI0.55Si0.10N were of a complete wurtzite structure. Deposition of a cubic (Ti,AI)N layer:

[0108] The same process equipment and process parameters as in Example 1 were used for the deposition of the cubic (Ti,AI)N layer. The thickness of the deposited (Ti,AI)N layer was about 7 pm, measured at the edge (at the beginning of the edge rounding) on both the rake face and the flank face and calculating an average.

[0109] The samples made are denoted "Sample 9 (as deposited) (invention)" and "Sample 10 (as deposited) (invention)".

[0110] Table 3.

[0111] * relation metal elements as in target

[0112] Example 5: Manufacturing of "Sample 11 (as deposited) (invention)

[0113] Deposition of an innermost barrier layer of (Zr,Ti,AI)N:

[0114] Samples, each having an innermost thin barrier layer of (Zr,Ti, AI)N different from each other, were made. There was deposited a barrier layer being Zro.31Tio.34Alo.35N, the metal elemental relation as measured by EDX. As deposited the Al content out of total metal elements was about 5 at% lower in the as deposited layer than the Al content in the target used. The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used. In the deposition cathodic arc evaporation was used. In the Hauzer HTC1000 equipment used a circular Arc-PVD technology (CARC+) using constant magnetic field configuration was applied during deposition. A ZrTiAI-target "Zr40Ti20AI40" (Zr:Ti:AI = 40:20:40) was used. The target had a diameter of 100 mm. The reactive gas for the nitride deposition was N2. The deposition was carried out at an arc current at the target of about 80 A, a bias level of -35 V and at a N2 pressure of 10 Pa. The temperature during the deposition was about 600°C. A table rotation speed of 5 rpm was used. The thickness of the thin (Zr,Ti, AI)N barrier layer deposited was about 50 nm.

[0115] It was concluded that the barrier layer of Zro.31Tio.34Alo.35N was of a complete wurtzite structure.

[0116] Deposition of a cubic (Ti,AI)N layer:

[0117] The same process equipment and process parameters as in Example 1 were used for the deposition of the cubic (Ti,AI)N layer. The thickness of the deposited (Ti,AI)N layer was about 7 pm, measured at the edge (at the beginning of the edge rounding) on both the rake face and the flank face and calculating an average.

[0118] The sample made is denoted "Sample 11 (as deposited) (invention)".

[0119] Example 6: Manufacturing of "Sample 12 (as deposited) (comparative)"

[0120] The same substrate materials, cutting tool bodies and procedures were used as in Example 1 except for that no innermost thin layer of wurtzite-(Ti,AI)N, wurtzite- (Cr,AI)N, wurtzite-(Ti,AI,Si)N, or wurtzite-(Ti,Zr,AI)N was deposited.

[0121] The thickness of the deposited cubic (Ti,AI)N layer was about 7 pm, measured at the edge (at the beginning of the edge rounding) on both the rake face and the flank face and calculating an average.

[0122] The sample made is denoted "Sample 12 (as deposited) (comparative)".

[0123] All samples 1 -12 are seen in Table 4. Table 4.

[0124] * relation metal elements as in target

[0125] ** relation metal elements from EDX data where available Example 7 - Heat treatment

[0126] All coated cutting tool samples made were subjected to an isothermal heat treatment. Such a heat treatment was carried out at 850°C for 1 hour with a coated cutting tool enclosed in a protective atmosphere being Ar.

[0127] The temperature was at first ramped up linearly for about 45 minutes to 850°C. Then, the temperature was kept constant for 1 hour. Then, the oven was shut off and let cool down for about 1 to 2 hours.

[0128] The heat treatment made simulates to a certain extent an exposure to heat that a cutting tool may be subjected to, e.g., at severe cutting conditions, PVD deposition at higher temperatures than usual, if a heat treatment is made for increasing the fracture toughness of a metal nitride layer, or deposition of a further layer by CVD which usually occurs at a high temperature.

[0129] Heat treated samples were made in which cutting tools of samples 1 -12 (as deposited). The heat treated samples made are called:

[0130] "Sample 1 (HT) (invention)"

[0131] "Sample 2 (HT) (invention)"

[0132] "Sample 3 (HT) (invention)"

[0133] "Sample 4 (HT) (comparative)"

[0134] "Sample 5 (HT) (comparative)"

[0135] "Sample 6 (HT) (comparative)"

[0136] "Sample 7 (HT) (invention)"

[0137] "Sample 8 (HT) (comparative)"

[0138] "Sample 9 (HT) (invention)"

[0139] "Sample 10 (HT) (invention)"

[0140] "Sample 11 (HT) (invention)"

[0141] "Sample 12 (HT) (comparative)" Example 8 - Analysis

[0142] In order to compare samples to evaluate the effect of different (Ti,AI)N barrier layers a calotte grinding test was made. The amount of delamination of the coating was de- termined visually. A scale was used ranging from Grade 1 to Grade 6 as ratings of delamination, wherein Grade 1 reflects a perfect calotte without any delamination at all seen and Grade 6 reflects extensive delamination.

[0143] Table 5.

[0144] * relation metal elements as in target

[0145] ** relation metal elements from EDX data where available

[0146] It is concluded from the calotte grinding test that the heat treated samples 1-3, 7 and 9-11 in table 5 having different kinds of barrier layers of wurtzite crystal structure, showed good, or very good, results in blocking Co diffusion into the cubic (Ti, Al) N layer. Heat treated sample 2-3 and 9-11 showed the very best performance. Fig. 3 shows an image after calotte grinding of "Sample 12 (HT) (comparative)" rated as Grade 6 with extensive delamination. Fig. 4 shows an image after calotte grinding of "Sample 3 (HT) (invention)" rated as Grade 2 with very little delamination.

[0147] Furthermore, a comparison between heat treated samples "Sample 3 (HT) (invention)" and "Sample 12 (HT) (comparative)" was made to evaluate the effect of the (Ti, AI)N barrier layer by making low-kV EDX analysis.

[0148] Thus, the samples were subjected to qualitative elemental mapping in order to detect if any Co diffusion into the cubic (Ti , Al )N layer had taken place in the heat treated samples. The images showed that extensive diffusion of cobalt into the cubic (Ti , AI)N layer had taken place for Sample 12 (HT) (comparative). See Fig. 5. This is a sample without any wurtzite barrier layer of the invention. Cobalt (9) is seen extending from the substrate (5) into the cubic (Ti, AI)N layer (7). On the other hand, no diffusion of cobalt into the cubic (Ti, AI)N layer could be seen for the samples being within the invention. Fig. 6 shows the elemental mapping image for "Sample 3 (HT) (invention)".

[0149] "Sample 3 (HT) (invention)" and "Sample 12 (HT) (comparative)" were also subjected to quantitative line profiles of elements. The profiles showed that for "Sample 12 (HT) (comparative)" a clear signal from cobalt is detected up until about 1 pm into the cubic (Ti , Al )N layer. See Fig. 7. On the other hand, Fig. 8 shows the line profiles of elements for "Sample 3 (HT) (invention)" and no diffusion of cobalt into the cubic (Ti, AI)N layer can be seen. The average Co content within the cubic (Ti,AI)N layer within a distance of 0.2 to 1 .2 pm from the substrate-to-coating interface for "Sample 3 (HT) (invention)" and "Sample 12 (HT) (comparative)" was determined.

[0150] Table 6.

[0151] * within a distance of 0.2 to 1.2 pm from the substrate-to-coating interface

[0152] The results from the qualitative elemental mapping as well as the results from the quantitative line profiles of elements go along very well with the results from the calotte grinding test made for the same samples.

[0153] Example 9 - Cutting test

[0154] A cutting test was made in order to determine the performance of a sample of the invention.

[0155] Explanations to terms used:

[0156] The following expressions / terms are commonly used in metal cutting, but nevertheless explained in the table below:

[0157] Vc (m / min): cutting speed in meters per minute fz (mm / tooth): feed rate in millimeter per tooth (in milling) fn (mm / rev) feed rate per revolution (in turning) z: (number) number of teeth in the cutter ae(mm): radial depth of cut in millimeter ap(mm): axial depth of cut in millimeter

[0158] "Sample 3 (HT) (invention)" and "Sample 12 (HT) (comparative)", being milling inserts of type SPHT120408 were tested in a milling test, and the flank wear was measured. The cutting conditions are summarized in Table 7. As workpiece material steel ISO-P, 42CrMo4, was used.

[0159] Cutting conditions:

[0160] Table 7.

[0161] The wear value (as averaged over the cutting edge) for 8000 mm cutting length is shown in Table 8.

[0162] Table 8.

Claims

Claims1 . A coated cutting tool (1 ) consisting of a substrate body (5) and a coating (6), the substrate is a cemented carbide and the coating (6) comprises- a layer (7) of a first cubic metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, or,- a layer (7) of a first cubic metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with one or more of Al and Si, there is a from 10 to 500 nm thick layer (8) of Ali-v-y-zMvSiyXzN, 0<v<0.75, 0<y<0.20, 0<z<0.10, situated below the layer (7) of the first cubic metal nitride, wherein the distance between the layer (8) of Ali-v-y-zMvSiyXzN and the substrate body (5) surface is from 0 to 500 nm, wherein M is of one or more metal elements of group 3, 4, 5 and 6 in the periodic table of elements, and, wherein X is one or more of C, B and O, the layer (8) of Ali-v-y-zMvSiyXzN has wurtzite crystal structure.

2. A coated cutting tool (1 ) according to claim 1 , wherein the layer (8) of A -v-y- zMvSiyXzN has a thickness of from 20 to 300 nm, or from 30 to 150 nm, or from 40 to 75 nm.

3. A coated cutting tool (1 ) according to any one of claims 1 -2, wherein the distance between the layer (8) of Ali-v-y-zMvSiyXzN and the substrate body (5) surface is from 0 to 200 nm, or from 0 to 100 nm, or from 0 to 50 nm.

4. A coated cutting tool (1 ) according to any one of claims 1 -2, wherein there is a second cubic metal nitride layer (9), being up to 500 nm thick, or up to 200 nm thick, or up to 100 nm thick, or up to 50 nm thick situated on the substrate body (5) surface below the layer (8) of Ali-v-y-zMvSiyXzN, the second cubic metal nitride layer (9) is acubic metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, optionally in combination with Al and / or Si.

5. A coated cutting tool (1 ) according to any one of claims 1 -4, wherein the layer (8) of Ali-v-y-zMvSiyXzN is situated directly below the layer (7) of the first cubic metal nitride.

6. A coated cutting tool (1 ) according to any one of claims 1 -5, wherein the layer (8) of Ah-v-y-zMvSiyXzN is situated on the substrate body (5) surface and being situated directly below the layer (7) of the first cubic metal nitride.

7. A coated cutting tool (1 ) according to any one of claims 1 -6, wherein, in the layer (8) of Ali-v-y-zMvSiyXzN, 0<v<0.70, 0<y<0.15, 0<z<0.05.

8. A coated cutting tool (1 ) according to any one of claims 1 -7, wherein, in the layer (8) of Ali-v-y-zMvSiyXzN, M is one or more of Ti, Zr, Hf, V, Nb, Ta and Cr.

9. A coated cutting tool (1 ) according to any one of claims 1 -8, wherein the layer (8) of Ah-v-y-zMvSiyXzN is Ali-a-zTiaXzN, 0<a<0.30, 0<z<0.10, X is one or more of C, B and 0.

10. A coated cutting tool (1 ) according to any one of claims 1 -8, wherein the layer (8) of Ah-v-y-zMvSiyXzN is Ah-b-zZrbXzN, 0<b<0.70, 0<z<0.10, X is one or more of C, B and O.

11. A coated cutting tool (1 ) according to any one of claims 1 -8, wherein the layer (8) of Ah-v-y-zMvSiyXzN is Ali-c-d-zTicZrdXzN, 0<c+d<0.70, 0<z<0.10, X is one or more of C, B and O.

12. A coated cutting tool (1 ) according to any one of claims 1 -8, wherein the layer (8) of Ah-v-y-zMvSiyXzN is Ali-e-zCreXzN, 0<e<0.25, 0<z<0.10, X is one or more of C, B and 0.

13. A coated cutting tool (1 ) according to any one of claims 1 -8, wherein the layer (8) of Ali-v-y-zMvSiyXzN is Ah-f-g-zTifSigXzN, 0<f<0.50, 0<g<0.20, 0<z<0.10, X is one or more of C, B and 0.

14. A coated cutting tool (1 ) according to any one of claims 1 -13, wherein the first cubic metal nitride (7) is a cubic metal nitride of one or more of Ti, Cr and Zr or Ti, Cr and Zr together with one or more of Al and Si.

15. A coated cutting tool (1 ) according to any one of claims 1 -14, wherein the thickness of the first cubic metal nitride layer (7) is from 0.2 to 25 pm.

16. A coated cutting tool (1 ) according to any one of claims 1 -16, wherein the substrate body (5) is a WC-Co based cemented carbide comprising from 5 to 15 wt% Co.

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