A coated cutting tool

Abstract

The invention relates to a coated cutting tool consisting of a substrate body and a coating, the substrate is of a cemented carbide and the coating comprises a layer of a first metal nitride comprising crystallites of NaCl structure and crystallites of a grain boundary phase between the crystallites of NaCl structure and / or the layer of a first metal nitride comprises crystallites of NaCl structure comprising different domain types, the domain types having different elemental composition from each other, and wherein 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 metal nitride, M is of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, X is one or more of C, B and O, the layer of Al1-v-y-zMvSiyXzN has wurtzite crystal structure.

Description

A coated cutting toolThe 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. The present invention also relates to a method of producing a coated cutting tool.BackgroundCutting 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.As wear resistant coatings are metal nitrides deposited by a PVD (physical vapor deposition) process commonly used. The metal nitride coating may be a monolayer or a multilayer of sublayers of different elemental composition. Examples of metal nitrides are (Ti,AI)N, (AI,Cr)N, (Ti, Al, Cr)N and (Ti, Al, Si)N. The most commonly used metal nitride being (Ti,AI)N.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.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.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 leads to increased wear of the cutting tool and reduced tool life. Badadhesion also generally limits the coating thickness possible to use. This is especially relevant for PVD coatings which normally show compressive stress in the coating as deposited. The thicker the coating the higher adhesion is needed to prevent flaking of the coating.When depositing a metal nitride layer by a PVD process the temperature during the process is usually kept at a moderate level. A metal nitride in an as-deposited state normally shows good adhesion to a cemented carbide substrate. Heat treatment of certain deposited metal nitride layers may improve the mechanical properties, in particular the toughness of the layer. A heat treatment may result in the provision of a thin grain boundary phase of hexagonal crystal structure between cubic crystallites within a cubic metal nitride layer. This may increase the toughness of the metal nitride layer. Furthermore, for some metal nitrides a heat treatment results in a separation into different phases, such as by spinodal decomposition, which may increase the toughness.Spinodal decomposition is a mechanism by which a single phase separates into two domains without nucleation. The resulting two domains are of the same crystal structure but contain different amounts of elements from each other. Spinodal decomposition may occur when a metastable phase is exposed to elevated temperatures. Many aluminium containing nitrides comprising crystallites of NaCI structure are known to undergo spinodal decomposition at heating. Such spinodal decomposition results in the formation of two domains of different elemental composition.However, during a heat treatment at a high temperature for a comparatively long period of time, such as during a heat treatment in order to improve the mechanical properties of a metal nitride layer as described above, 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.Object of the inventionIt is an object of the present invention to provide a coated cutting tool which shows a significant interdiffusion resistance of binder metal, between a cemented carbide substrate body and a coating. It is a further object of the present invention to provide a coated cutting tool having a substrate body of cemented carbide and a coating comprising a metal nitride layer which still after severe heat treatment shows good adhesion to the substrate body. The coated cutting tool preferably also shows high wear resistance in general, for example high flank wear resistance, in metal machining such as milling, turning and drilling. Finally, there is an object of the present invention to provide a method for producing a coated cutting tool.The inventionThe present invention relates to a coated cutting tool consisting of a substrate body and a coating, the substrate is of a cemented carbide and the coating comprises a from 0.2 to 25 pm thick layer of a first metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al, or one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al and Si, the layer of the first metal nitride comprises(i) crystallites of NaCI structure and crystallites of a grain boundary phase between the crystallites of NaCI structure, the crystallites of the grain boundary phase is of wurtzite crystal structure, the area fraction of the wurtzite crystal structure in the layer (7) of the first metal nitride is more than 0.5 but less than 10%, as measured in a SEM, or TEM, 2D sectional image, and / or(ii) crystallites of NaCI structure comprising different domain types, the domain types having different elemental composition from each other, the different elemental composition of the domain types results in repeating peaks in an intensity line profile analysis in a SEM, or TEM, 2D sectional image of a crystallite, there is a peak spacing between two consecutive peaks, and there is a mean peak spacing, from intensity line profile analysis of crystallites, which is from 5 to 30 nm,and wherein 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 metal nitride, wherein the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is from 0 to 500 nm, M is of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, X is one or more of C, B and O, the layer of Ali-v-y-zMvSiyXzN has wurtzite crystal structure.The present invention further relates to a method of producing a coated cutting tool comprising the steps of:- providing a substrate body of a cemented carbide- mounting the substrate body in a PVD chamber,- depositing a coating on the substrate body by a PVD method, forming a coated cutting tool, the coating comprises 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, the layer of Ali-v-y-zMvSiyXzN has wurtzite crystal structure, and a from 0.2 to 25 pm thick layer of a first metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al, or one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al and Si, the layer of Ali-v-y-zMvSiyXzN is situated below the layer of the first metal nitride, wherein the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is from 0 to 500 nm,- subjecting the coated cutting tool to a heat treatment in an atmosphere preventing oxidation, or in a vacuum, at from 700 to 1000°C for a time period of from 10 to 300 minutes.The coated cutting tool is suitably subjected to a heat treatment at from 800 to 950°C, preferably from 825 to 900°C. The temperature used in the heat treatment is adjusted to, on one hand, provide a sufficient level of increased mechanical properties, such as toughness within the first metal nitride layer and, on the other hand, minimise the diffusion of binder metal into said layer. The higher the temperature the more diffusion of binder metal.The coated cutting tool is suitably subjected to a heat treatment for a time period of from 30 to 150 minutes, preferably from 45 to 100 minutes.The atmosphere preventing oxidation is suitably a noble gas atmosphere, such as one or more of Ar, Xe or Kr.The PVD method used can be any known PVD method such as cathodic arc deposition, ion plating, reactive sputtering or HIPIMS.In one embodiment, the present invention relates to a coated cutting tool consisting of a substrate body and a coating, the substrate is of a cemented carbide and the coating comprises a from 0.2 to 25 pm thick layer of a first metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al, or one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al and Si, the layer of the first metal nitride comprises crystallites of NaCI structure and crystallites of a grain boundary phase between the crystallites of NaCI structure, the crystallites of the grain boundary phase is of wurtzite crystal structure, the area fraction of the wurtzite crystal structure in the layer (7) of the first metal nitride is more than 0.5 but less than 10%, as measured in a SEM, or TEM, 2D sectional image, and wherein there is a from 10 to 500 nm thick layer of Ah- v-y-zMvSiyXzN, 0<v<0.75, 0<y<0.20, 0<z<0.10, situated below the layer of the first metal nitride, wherein the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is from 0 to 500 nm, M is of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, X is one or more of C, B and O, the layer of Ah-v-y-zMvSiyXzN has wurtzite crystal structure.In one embodiment, the present invention relates to a coated cutting tool consisting of a substrate body and a coating, the substrate is of a cemented carbide and the coating comprises a from 0.2 to 25 pm thick layer of a first metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al, or one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al and Si, the layer of the first metal nitride comprises crystallites of NaCI structure comprising different domain types, the domain types having different elemental composition from each other, the different elemental composition of the domain types results in repeating peaks in an intensity line profile analysis in aSEM, or TEM, 2D sectional image of a crystallite, there is a peak spacing between two consecutive peaks, and there is a mean peak spacing, from intensity line profile analysis of crystallites, which is from 5 to 30 nm, and wherein 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 metal nitride, wherein the distance between the layer of Ah -v-y- zMvSiyXzN and the substrate body surface is from 0 to 500 nm, M is of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, X is one or more of C, B and O, the layer of Ali-v-y-zMvSiyXzN has wurtzite crystal structure.In one embodiment, the present invention relates to a coated cutting tool consisting of a substrate body and a coating, the substrate is of a cemented carbide and the coating comprises a from 0.2 to 25 pm thick layer of a first metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al, or one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al and Si, the layer of the first metal nitride comprises(i) crystallites of NaCI structure and crystallites of a grain boundary phase between the crystallites of NaCI structure, the crystallites of the grain boundary phase is of wurtzite crystal structure, the area fraction of the wurtzite crystal structure in the layer (7) of the first metal nitride is more than 0.5 but less than 10%, as measured in a SEM, or TEM, 2D sectional image, and(ii) crystallites of NaCI structure comprising different domain types, the domain types having different elemental composition from each other, the different elemental composition of the domain types results in repeating peaks in an intensity line profile analysis in a SEM, or TEM, 2D sectional image of a crystallite, there is a peak spacing between two consecutive peaks, and there is a mean peak spacing, from intensity line profile analysis of crystallites, which is from 5 to 30 nm, and wherein 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 metal nitride, wherein the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is from 0 to 500 nm, M is of one or more metal elements of group 4, 5 and 6 in the periodictable of elements, X is one or more of C, B and O, the layer of Ali-v-y-zMvSiyXzN has wurtzite crystal structure.There are herein disclosed two separate features relating to the microstructure of the layer of the first metal nitride. The first microstructural feature relating to the presence of a grain boundary phase of wurtzite structure between the crystallites of NaCI structure, and the second microstructural feature relating to the presence of crystallites of NaCI structure comprising different domain types, the domain types having different elemental composition from each other. Only one of the microstructural features may be present in the layer of the first metal nitride, alternatively, both microstructure features may be present in the layer of the first metal nitride. The elemental composition of the first metal nitride is decisive about this. Both microstructural features contribute in themselves to improvements in the mechanical properties of the layer of the first metal nitride, such as increased toughness.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%.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. This enables the provision of a metal nitride coated cemented carbide in which the metal nitride has a high toughness at the same time the coating adhesion to the substrate is excellent. The effect of w-Ali-v-y-zMvSiyXzN preventing binder metal diffusion is present already for very thin layers of w-Ali-v-y-zMvSiyXzN.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.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.In one embodiment the layer of Ali-v-y-zMvSiyXzN is situated directly below the layer of the first metal nitride.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 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 Ah-v-y-zMvSiyXzN is herein claimed as situated below the layer of the first 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.Thus, in one embodiment there is a layer of a cubic second metal nitride, 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. This cubic second metal nitride is suitably a 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.By a layer of 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 layer of a "cubic" metal nitride is at least 90%.Thus, for example, during a heat treatment there may be some amount of hexagonal structure (wurtzite structure) formed in some metal nitrides, mainly present as a grainboundary phase, the metal nitride layer may then for low amounts of hexagonal structure present, as herein defined, still be defined as a cubic metal nitride layer.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 metal nitride. This means that the distance between the layer of Ali-v-y-zMvSiyXzN and the substrate body surface is 0 nm.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.In the layer of Ali-v-y-zMvSiyXzN, suitably 0<y<0.15, or 0<y<0.10.In the layer of Ali-v-y-zMvSiyXzN, suitably 0<z<0.05, preferably 0<z<0.02.In one embodiment, in the layer of Ali-v-y-zMvSiyXzN, 0<v<0.70, 0<y<0.15, and 0<z<0.05.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 %.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.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.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.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.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.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 O. Suitably 0.05<b<0.70, or 0.05<b<0.65. Suitably 0<z<0.05, preferably 0<z<0.02.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.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.There are embodiments where the layer of the first metal nitride comprises crystallites of a grain boundary phase between the crystallites of NaCI structure, the grain boundary phase being of wurtzite crystal structure. The provision of a grain boundary phase between the crystallites of NaCI structure within the layer of the first metal nitride is believed to make it more difficult for cracks to proceed along the grain boundaries of the crystallites of NaCI structure. This means an improved toughness of the layer of the first metal nitride.The grain boundary phase does not need to be present in all boundaries between the crystallites of NaCI structure. The grain boundary phase is usually seen in a SEM, or TEM, 2D sectional image as separated grains, or segments, between the crystallites of NaCI structure.Suitably, the average thickness of the grain boundary phase is within a range of up to 30 nm, preferably up to 15 nm. The grain boundary phase is readily seen in a SEM, or TEM, 2D sectional image. The average thickness of the grain boundary phase can be determined by image analysis.The area fraction of the wurtzite crystal structure in the layer of the first metal nitride is suitably more than 1 but less than 8%, preferably more than 1 .5 but less than 6%, as measured in a SEM, or TEM, 2D sectional image.There are embodiments where the crystallites of NaCI structure comprise different domain types, the domain types having different elemental composition from each other, the different elemental composition of the domain types results in repeating peaks in an intensity line profile analysis in a SEM, or TEM, 2D sectional image of a crystallite, there is a peak spacing between two consecutive peaks, and there is a mean peak spacing, from intensity line profile analysis of crystallites, which is from 5 to 30 nm, preferably from 10 to 22 nm.Domains of different elemental composition will be visualised as areas of different brightness in a SEM, or TEM, 2D sectional image of a crystallite of NaCI structure. An example of this is seen in Fig. 9 which shows a 2D sectional SEM image of the first metal nitride layer in an embodiment of the present invention. One sees that there is a granulated substructure seen comprised of two different domains of different brightness which originates from different elemental composition of the domains.Within the term "layer of a first metal nitride" is herein included both an embodiment wherein the layer is a monolithic layer and another embodiment wherein the layer is a multilayer of alternating sublayers. The multilayer embodiment exists in case thereare more than one metal element present in the layer of the first metal nitride. 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.In the case of the layer of the first metal nitride being a multilayer, for the herein defined features of elemental composition of layer of the first metal nitride, the overall average elemental composition of the whole multilayer is considered.In one embodiment, the layer of the first metal nitride has a fracture toughness of from 4.5 to 7.5 MPa*m05, or from 5.0 to 7.0 MPa*m0 5, or from 5.5 to 6.5 MPa*m05.In one embodiment, the first metal nitride is suitably a metal nitride of one or more of Ti, Cr, Zr, Ta, Nb and V together with Al, or a metal nitride of one or more of Ti, Cr, Zr, Ta, Nb and V together with Al and Si.In one embodiment, the first metal nitride is suitably a metal nitride of one or more of Ti, Cr and Zr together with Al, or a metal nitride of one or more of Ti, Cr and Zr together with Al and Si.In one embodiment, the layer of the first metal nitride belongs to the group of (Ti,AI)N, (Ti,AI,Si)N, (Ti,AI,Cr)N, (Ti,AI,Cr,Si)N and (Cr,AI)N.In one embodiment, the content of Al in the first metal nitride is 20-70 at%, preferably 30-65 at%, out of the total metal elements.In one embodiment, the layer of the first metal nitride belongs to the group of (Ti,AI)N, (Ti,AI,Si)N, (Ti,AI,Cr)N and (Ti,AI,Cr,Si)N.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.In one embodiment, the layer of the first metal nitride is a (Ti,AI)N layer. In one embodiment, the layer of the first metal nitride is a Th-jAIjN layer, 0.30<j<0.75, or 0.40<j<0.70.The first metal nitride is suitably a cubic metal nitride as herein defined.The thickness of the layer of the first metal nitride layer is suitably from 0.5 to 15 pm, preferably from 1 to 10 pm, most preferably from 3 to 10 pm.The layer of the first metal nitride is suitably deposited by a PVD method.The layer of the cubic second metal nitride is suitably deposited by a PVD method. The layer of Ali-v-y-zMvSiyXzN is suitably deposited by a PVD method.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 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 layer of the first metal nitride is a (Ti,AI)N layer, the thickness of the layer of the first metal nitride is from 0.5 to 15 pm.In one embodiment, the thickness of the whole coating of the coated cutting tool is suitably from 0.5 to 26 pm, preferably from 2 to 16 pm, most preferably from 4 to 11 pm. The ideal thickness depends, e.g., on the metal cutting application.The substrate is a cemented carbide which comprises WC and a binder metal. The binder metal is suitably Co. 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.In one embodiment, the content of binder metal, preferably Co, within the layer of the first metal nitride between a distance of from 0.2 pm from an interface between the layer of Ali-v-y-zMvSiyXzN and the layer of the first metal nitride to 1 .2 pm from said interface, or, if the layer of the first metal nitride has a thickness of less than 1 .2 pm, tothe uppermost surface of the layer of the first metal nitride, is < 0.2 at%, suitably < 0.1 at%, preferably < 0.05 at%, most preferably < 0.02 at%.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.The cutting tool suitably comprises a rake face and a flank face with a cutting edge in between.MethodsElemental composition:The relation between metal elements in any nitride layer herein disclosed may be determined by using energy dispersive X-ray (EDX) analysis in combination with SEM or TEM.Area fraction wurtzite in the layer of the first metal nitride:The content of the wurtzite crystal structure within the layer of the first metal nitride is determined as an area fraction in a SEM, or TEM, 2D sectional image. For area fractions below 1 % TEM is preferred. The area of a SEM, or TEM, image is suitably from 2 to 4 (pm)2. In this disclosure images of about 2 pm x 1 .5 pm were used in the determination. An image analysis software is suitably used. In this disclosure a software “Gwyddion” was used which is a standard and open software for the analysis of scanning probe microscopy images. The wurtzite structure is seen as a darker phase in the image when using an Everhart Thornley detector. Standard image analysis is performed. This includes levelling the background in order to give a more homogeneous contrast. Then an image segmentation is made into two bins of pixels based on a grayscale threshold. One bin is the wurtzite precipitates (the darker part of the gray scale), the other bin is everything else. The pixel size in the image depends on the resolution and magnification of the input image. These acquisition parameters need to be chosen to adequately resolve the nanometer-scale precipitates. Then, the ratioof the pixel area of the precipitate bin and the overall pixel area of the image is determined which gives the wurtzite area fraction.Mean peak spacing in an intensity line profile analysis of crystallites of NaCI structure in the layer of the first metal nitride:To obtain a measure for the degree of the intragranular transformation, that is the decomposition into separate domains of diverging chemical composition, within the crystallites of NaCI structure in the layer of first nitride, the characteristic length of the resulting chemical undulations is analysed.As the basis for this analysis, plane-view sectional images of at least five different crystallites are acquired in a scanning electron microscope (SEM). Also a transmission electron microscope (TEM) may be used. The acquisition conditions, magnification and image resolution are selected to at least guarantee the resolution of any chemical undulations ranging over five or more nanometers. Before any image analysis all micrographs are cropped to exclusively include the interior of a single crystallite. For each image a virtual array of at least four parallel and equidistant lines is constructed to be overlayed with the image, the distance between adjacent lines being at least 20 nm. For each of the overlayed lines a corresponding line profile of the grayscale intensity is extracted from the image. For each intensity profile the local grayscale maxima corresponding to one of the domains, i.e. the position of all intensity peaks, are identified. The length of each line is chosen so that at least 15 peaks are included. As a measure for the characteristic chemical undulation distance, the mean spacing of adjacent peaks is calculated over all intensity profiles.After obtaining the mean peak spacing for a first line array the above procedure is repeated for N further line arrays each of which is rotated with respect to the previous line array by a fixed angular increment. The angular increment is chosen to capture a total angular range of 180° with > 30 line arrays in equiangular increments. This serves to obtain an average over all possible in-plane directions. The mean peak spacing as specified herein always refer to the average peak spacing over all directions and images.Thus, there is a mean peak spacing determined from at least 30 intensity line profiles within a crystallite in a SEM, or TEM, 2D sectional image of a crystallite, images from at least five crystallites are used in the determination.Fracture toughness:To quantify the fracture toughness of the investigated coatings, the micro-pillar splitting technique as developed by Sebastiani et al. [1 , 2 and 4] was applied. In this testing method, a sharp indenter tip is centered on the top face of a micron-scale pillar of the sample material. With the pillar subjected to the load of the indenter, the force is continuously increased until failure - i.e. splitting - of the pillar occurs. The critical stress intensity factor for cracks to emanate from the indenter contact, i.e. the splitting fracture toughness Kc can then be derived from the critical splitting force Pc via the following equation:Kc = y (E / H) Pc / R3 / 2, (1 ) where y represents a coefficient of proportionality that is dependent on the elasticplastic properties of the tested material (ratio of Young’s modulus E and Hardness H), while R denotes the radius of the pillar. The above equation is based on the analytical model of a semi-elliptical surface crack and validated by cohesive zone finite element modeling (CZ-FEM) [2],The pillars were micro-machined from the coatings of interest by means of focused ion beam (FIB) milling. A single-pass milling strategy that utilizes concentric ring patterns of continuously decreasing diameter was used to minimize taper of the pillars. Accordingly, the FIB probe currents were successively lowered from 15 nA (initial roughing) to a final polishing current of 300 pA. All of the tested pillars featured a diameter of 7 pm and an aspect ratio of ~1.3 (height-to-diameter ratio, > 1 is required by the pillar splitting technique [2]). Prior to any FIB milling the sample surfaces to bestructured were carefully polished using a colloidal silica suspension with a nominal grain size of 40 nm (Struers OPS0.04 pm). This step served 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.After this surface preparation the micro-pillars were consistently placed at a distance of ~120 pm from the cutting edges, near a “nose radius” of the carrying substrates. Loading of the pillars was performed in a Fischer Picodenter HM500 nanoindentation system (Helmut Fischer GmbH, Sindelfingen, Germany) using a three-sided, pyramidal cube corner diamond indenter (nominal surface angle of 35.26°). The experiment were performed in a load-controlled manner using a constant loading rate of 1 mN / s. For each coating and sample state a minimum of 12 tests were performed to account for the intrinsic scatter of the fracture experiments (20 tests in most cases). The accuracy of the sample stage and tip positioning was experimentally validated to be within 10% of the used pillar radius to not distort the measurement results [3], To calculate the fracture toughness according to equation (1 ) the coating specific / -coefficient was derived from data published by Ghidelli et al. in ref [4], Measurements can be performed by preparing a cross-section of an already coated tool or by carefully removing the top layers via mechanical polishing or focused ionbeam machining.

[0001] M. Sebastiani, K.E. Johanns, E.G. Herbert, F. Carassiti, G.M. Pharr, A novel Pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings,Philos. Mag. 95 (2015) 1928-1944. https: / / doi.org / 10.1080 / 14786435.2014.913110.[2] M. Sebastiani, K.E. Johanns, E.G. Herbert, G.M. Pharr, Measurement of fracture toughness by nanoindentation methods: Recent advances and future challenges, Curr. Opin. Solid State Mater. Sci. 19 (2015) 324-333. https: / / doi.Org / 10.1016 / j.cossms.2015.04.003.[3] C.M. Lauener, L. Petho, M. Chen, Y. Xiao, J. Michler, J.M. Wheeler, Fracture of Silicon: Influence of rate, positioning accuracy, FIB machining, and elevated temperatures on toughness measured by pillar indentation splitting, Mater. Des. 142 (2018) 340-349. https: / / doi.Org / 10.1016 / j.matdes.2018.01.015.[4] M. Ghidelli, M. Sebastiani, K.E. Johanns, G.M. Pharr, Effects of indenter angle on micro-scale fracture toughness measurement by pillar splitting, J. Am.Ceram. Soc. 100 (2017) 5731-5738. https: / / doi.org / 10.1111 / jace.15093.Thickness and adhesion test by calotte grinding: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.Qualitative elemental mapping and Quantitative line profiles of elements, low-kV EDX analysisIn 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).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 spatialresolution 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.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.Brief description of drawingsFigure 1 shows a schematic view of one embodiment of a cutting tool being an indexable 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 an image of a calotte grinding of a comparative coated cutting tool, Sample 12 (HT850°C) (comparative).Figure 4 shows an image of a calotte grinding of an embodiment of a coated cutting tool of the present invention, Sample 3 (HT850°C) (invention).Figure 5 shows an elemental mapping image of a comparative coated cutting tool. Sample 12 (HT850°C) (comparative).Figure 6 shows an elemental mapping image of an embodiment of a coated cutting tool of the present invention. Sample 3 (HT850°C) (invention).Figure 7 shows line profiles of elements of a comparative coated cutting tool. Sample 12 (HT850°C) (comparative).Figure 8 shows line profiles of elements of an embodiment of a coated cutting tool of the present invention. Sample 3 (HT850°C) (invention).Figure 9 shows a 2D sectional SEM image of the first metal nitride layer in an embodiment of the present invention. Sample 13 (HT950°C) (invention).Figure 10 shows a 2D sectional SEM image of a crystallite of NaCI structure within the first metal nitride layer in an embodiment of the present invention. Sample 13 (HT950°C) (invention).Figure 11 shows an intensity line profile on a SEM 2D sectional image of a crystallite of NaCI structure in the first metal nitride layer in an embodiment of the present invention. Sample 13 (HT950°C) (invention).Figure 12 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.Detailed description of embodiments in drawingsFigure 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.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) which has wurtzite structure and a layer (7) of a first metal nitride.Figure 9 shows a 2D sectional SEM image of the first metal nitride layer (7) in an embodiment of the present invention. A grain boundary phase (10) is seen.Figure 10 shows a 2D sectional SEM image of a crystallite of NaCI structure within the first metal nitride layer (7) in an embodiment of the present invention. Two domains, a first domain (11 ) and a second domain (12), of different darkness are seen within a crystallite of NaCI structure. This represents domains of different elemental composition.Figure 12 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).ExamplesExample 1: Manufacturing of "Samples 1-3 (as deposited)" and "Samples 4-5 (as deposited)"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.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.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.Prior to the deposition, the substrate bodies were pretreated by ultrasonic cleaning in a water-based medium.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).Deposition of an innermost barrier layer of (Ti,AI)N: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 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,AI)N barrier layers deposited was about 50 nm.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 concluded to be much less than 90%. For the sample with a barrier layer of Tio.33Alo.67N there was a pure cubic structure, i.e. , containing no wurtzite structure. All above relations of Ti-AI in the (Ti, Al) N barrier layers are based on target compositions used in the depositions. EDX may be used for determining the actual Ti-AI relation in a (Ti , AI)N layer, which may differ slightly from the relation in the target used.Deposition of a (Ti , Al )N layer:Then, for each of the five different samples a (Ti,AI)N layer was deposited as a herein denoted "first metal nitride layer". 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 (Ti , AI)N layer, a TiAl target "Ti50AI50 (Ti: Al = 50:50) was 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 600°C. A table rotation speed of 3 rpm was used.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.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.The deposited (Ti,AI)N layer was a cubic (Ti,AI)N layer.The samples made are denoted "Sample 1 (as deposited)", "Sample 2 (as deposited)", "Sample 3 (as deposited)", "Sample 4 (as deposited)" and "Sample 5 (as deposited)".Table 1.* relation metal elements as in target composition** relation metal elements from EDX dataExample 2: Manufacturing of "Sample 6 (as deposited)"The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used.Deposition of an innermost barrier layer of TiN: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.The thin TiN layer was of a complete cubic structure.Deposition of a (Ti , Al )N layer:The same process equipment and process parameters as in Example 1 were used for the deposition of the (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. The deposited (Ti,AI)N layer was a cubic (Ti,AI)N layer.The sample made is denoted "Sample 6 (as deposited)".Example 3: Manufacturing of "Sample 7 (as deposited)" and "Sample 8 (as deposited)"The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used.Deposition of an innermost barrier layer of (Cr,AI)N: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.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.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.Deposition of a (Ti , Al )N layer:The same process equipment and process parameters as in Example 1 were used for the deposition of the (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. The deposited (Ti,AI)N layer was a cubic (Ti,AI)N layer.The samples made are denoted "Sample 7 (as deposited)" and "Sample 8 (as deposited)".Table 2.* relation metal elements as in targetExample 4: Manufacturing of "Sample 9 (as deposited)" and "Sample 10 (as deposited)"The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used.Deposition of an innermost barrier layer of (Ti, Al, SDN: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.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 (Ti , Al )N layer:The same process equipment and process parameters as in Example 1 were used for the deposition of the (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. The deposited (Ti,AI)N layer was a cubic (Ti,AI)N layer.The samples made are denoted "Sample 9 (as deposited)" and "Sample 10 (as deposited)".Table 3.* relation metal elements as in targetExample 5: Manufacturing of "Sample 11 (as deposited)The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used.Deposition of an innermost barrier layer of (Zr,Ti,AI)N: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.31 Tio.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 tech-nology (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.It was concluded that the barrier layer of Zro.31Tio.34Alo.35N was of a complete wurtzite structure.Deposition of a (Ti , Al )N layer:The same process equipment and process parameters as in Example 1 were used for the deposition of the (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. The deposited (Ti,AI)N layer was a cubic (Ti,AI)N layer.The sample made is denoted "Sample 11 (as deposited)".Example 6: Manufacturing of "Sample 12 (as deposited)"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.The thickness of the deposited (Ti , Al) 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. The deposited (Ti , AI)N layer was a cubic (Ti , AI)N layer.The sample made is denoted "Sample 12 (as deposited)".All samples 1 -12 are seen in Table 4.Table 4.* relation metal elements as in target** relation metal elements from EDX data where availableExample 7: Manufacturing of "Sample 13 (as deposited)"The same substrate materials in combination with the same cutting tool bodies as in Example 1 were used.Deposition of an innermost barrier layer of (Ti,AI)N: An innermost thin barrier layer of Tio.25Alo.75N, using TiAI-targets "Ti20AI80" (Ti:AI = 20:80), was deposited using the same process conditions and using the same equipment as in Example 1 . The thickness of the thin (Ti,AI)N barrier layer deposited was about 50 nm.Deposition of a (Ti , Al )N layer:Then, a (Ti, AI)N layer different from the one deposited in the previous examples was deposited as a herein denoted "first metal nitride layer". In the deposition High Power Impulse Magnetron Sputtering (HIPIMS) was used. The coating equipment used was an Oerlikon Balzers Ingenia S3p coating system using disk-shaped, powder-metallurgical composite targets with a nominal diameter of 150 mm.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.For the deposition of the (Ti , AI)N layer, a TiAl target "Ti40AI60 (Ti: Al = 40:60) was used. The reactive gas for the nitride deposition was N2. The deposition was carried out at a DC bias level of -40 V and at a total pressure of 0.61 Pa (0.43 Pa Ar + 0.18 Pa N2). The temperature during the deposition was about 430°C. The further process parameters were pulse time 7.56 ms, duty cycle 15.1 %, pulse power 9 kW.A line of three targets of the same composition were vertically arranged to allow for a homogeneous deposition throughout the height of the reactor.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.The deposited (Ti , AI)N layer was a cubic (Ti , AI)N layer.The inserts deposited are denoted "Sample 13 (as deposited)".Example 10 - Heat treatmentAll coated cutting tool samples made were subjected to a heat treatment. Such a heat treatment was for samples 1 -12 carried out at 850°C for 1 hour with a coated cutting tool enclosed in a protective atmosphere being Ar at a pressure of 1 bar.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.For coated cutting tools of sample 13 heat treatments were carried out at 800°C, 850°C, 900°C, 950°C and 1000°C for 1 hour with a coated cutting tool enclosed in a protective atmosphere being Ar at a pressure of 1 bar. The temperature was at first ramped up linearly for about 45 minutes to the target temperature. 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. This provided samples which had been subjected to different heat treatments.Sample 3 was also subjected to heat treatments at the above different temperatures, in the same way regarding the other conditions as for sample 13, providing samples which had been subjected to different heat treatments.Thus, heat treated samples were made in which cutting tools of samples 1-13 (as deposited) had been subjected to a heat treatment according to Table 5:Table 5.* several samples made, each sample resulting from a heat treatment at a specific temperature as defined for the respective columnThe heat treated samples made are seen in Table 6.Table 6.* relation metal elements as in target** relation metal elements from EDX data where available Example 11 - AnalysisIn 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 determined 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.Table 7.* relation metal elements as in target composition** relation metal elements from EDX dataIt is concluded from the calotte grinding test that the heat treated samples 1 -3, 7 and 9-11 in Table 6 having different kinds of barrier layers of wurtzite crystal structure, showed good, or very good, results in blocking Co diffusion into the (Ti,AI)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 (HT850°C) (comparative) rated as Grade 6 with extensive delamination. Fig. 4 shows an image after calotte grinding of Sample 3 (HT850°C) (invention) rated as Grade 2 with very little delamination.Furthermore, a comparison between heat treated samples Sample 3 (HT850°C) (invention) and Sample 12 (HT850°C) (comparative) was made to evaluate the effect of the (Ti,AI)N barrier layer by making low-kV EDX analysis.Thus, the samples were subjected to qualitative elemental mapping in order to detect if any Co diffusion into the cubic (Ti,AI)N layer had taken place in the heat treated samples. The images showed that extensive diffusion of cobalt into the (Ti,AI)N layer had taken place for Sample 12 (HT850°C) (comparative). See Fig. 5. This is a sample without any inner barrier layer of the invention. Cobalt (9) is seen extending from the substrate (5) into the (Ti,AI)N layer (7). On the other hand, no diffusion of cobalt into the (Ti,AI)N layer could be seen for the samples being within the invention. Fig. 6 shows the elemental mapping image for Sample 3 (HT850°C) (invention).Sample 3 (HT850°C) (invention) and Sample 12 (HT850°C) (comparative) were also subjected to quantitative line profiles of elements. The profiles showed that for Sample 12 (HT850°C) (comparative) a clear signal from cobalt is detected up until about 1 pm into the cubic (Ti,AI)N layer. See Fig. 7. On the other hand, Fig. 8 shows the line profiles of elements for Sample 3 (HT850°C) (invention) and no diffusion of cobalt into the (Ti , Al) 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 (HT850°C) (invention) and Sample 12 (HT850°C) (comparative) was determined.Table 8.* within a distance of 0.2 to 1.2 pm from the substrate-to-coating interfaceThe 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.The result from analysis of fracture toughness within the layer of first metal nitride, herein exemplified as cubic (Ti, AI)N, in the samples within the invention is seen in Table 9.Table 9.Thus, both deposited cubic (Ti,AI)N layers of samples 3 and 13 show a significant increase in fracture toughness by heat treatment, at least for the higher temperatures, as compared with the (Ti,AI)N layers as deposited.Since the further samples within the invention, Sample 1 (HT850°C) (invention), Sample 2 (HT850°C) (invention), Sample 7 (HT850°C) (invention), Sample 9 (HT850°C) (invention), Sample 10 (HT850°C) (invention) and Sample 11 (HT850°C) (invention) each has the same Ti0.50AI0.50N layer as their first metal nitride layer as Sample 3 (HT850°C) (invention) the fracture toughness is considered to be the same for all those samples.For all samples the layer of cubic (Ti,AI)N comprised crystallites of NaCI structure and crystallites of a grain boundary phase between the crystallites of NaCI structure.For all samples the layer of cubic (Ti,AI)N comprised crystallites of NaCI structure comprising different domain types of different elemental composition.Table 10 shows the result from analysis relating to the grain boundary phase and the different domains in crystallites of NaCI within the layer of cubic (Ti,AI)N in the samples within the invention.Table 10.In the determination of area fraction wurtzite five SEM, or TEM for the lowest fractions, images were used in the determination. For determining the mean peak spacing five crystallites were analysed and 120 intensity line profiles per crystallite were used in the determination.Example 12 - Cutting testA cutting test was made in order to determine the performance of a sample of the invention.Explanations to terms used:The following expressions / terms are commonly used in metal cutting, but nevertheless explained in the table below: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"Sample 3 (HT850°C) (invention)" and "Sample 12 (HT850°C) (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 11 . As workpiece material steel ISO-P, 42CrMo4, was used.Cutting conditions:Table 11.The wear value (as averaged over the cutting edge) for 8000 mm cutting length is shown in Table 12.Table 12.

Claims

Claims1 . A coated cutting tool (1 ) consisting of a substrate body (5) and a coating (6), the substrate is of a cemented carbide and the coating (6) comprises a from 0.2 to 25 pm thick layer (7) of a first metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al, or one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al and Si, the layer (7) of the first metal nitride comprises(i) crystallites of NaCI structure and crystallites of a grain boundary phase between the crystallites of NaCI structure, the crystallites of the grain boundary phase is of wurtzite crystal structure, the area fraction of the wurtzite crystal structure in the layer (7) of the first metal nitride is more than 0.5 but less than 10%, as measured in a SEM, or TEM, 2D sectional image, and / or(ii) crystallites of NaCI structure comprising different domain types, the domain types having different elemental composition from each other, the different elemental composition of the domain types results in repeating peaks in an intensity line profile analysis in a SEM, or TEM, 2D sectional image of a crystallite, there is a peak spacing between two consecutive peaks, and there is a mean peak spacing, from intensity line profile analysis of crystallites, which is from 5 to 30 nm, characterised in that 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 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, M is of one or more metal elements of group 4, 5 and 6 in the periodic table of elements, 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.

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.

4. A coated cutting tool (1 ) according to any one of claims 1 -3, 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 metal nitride.

5. A coated cutting tool (1 ) according to any one of claims 1 -4, wherein in the layer (8) of Ali-v-y-zMvSiyXzN, 0<v<0.70, 0<y<0.15, and 0<z<0.05.

6. A coated cutting tool (1 ) according to any one of claims 1 -5, wherein, in the layer (8) of Ali-v-y-zMvSiyXzN, M is one or more of Ti, Zr, Hf, V, Nb, Ta and Cr.

7. A coated cutting tool (1 ) according to any one of claims 1 -6, wherein layer (7) of the first metal nitride has a fracture toughness of from of from 4.5 to 7.5 MPa*m°58. A coated cutting tool (1 ) according to any one of claims 1 -7, wherein the layer (7) of the first metal nitride is a metal nitride of one or more of Ti, Cr, Zr, Ta, Nb and V together with Al, or a metal nitride of one or more of Ti, Cr, Zr, Ta, Nb and V together with Al and Si.

9. A coated cutting tool (1 ) according to any one of claims 1 -8, wherein the substrate is a cemented carbide which comprises WC and a binder metal, the content of binder metal within the layer (7) of the first metal nitride between a distance of from 0.2 pm from an interface between the layer (8) of Ali-v-y-zMvSiyXzN and the layer (7) of the first metal nitride to 1 .2 pm from said interface, or, if the layer (7) of the first metal nitride has a thickness of less than 1 .2 pm, to the uppermost surface of the layer (7) of the first metal nitride, is < 0.2 at%.

10. A coated cutting tool (1 ) according to any one of claims 1 -9, wherein the substrate body (5) is a WC-Co based cemented carbide comprising from 5 to 15 wt% Co.

11. A coated cutting tool (1 ) according to any one of claims 1 -10, wherein the cutting tool (1 ) is a cutting insert for milling, a cutting insert for turning, a cutting insert for drilling, a drill or an endmill.

12. A method of producing a coated cutting tool (1 ) comprising the steps of:- providing a substrate body (5) of a cemented carbide- mounting the substrate body (5) in a PVD chamber,- depositing a coating (6) on the substrate body (5) by a PVD method, forming a coated cutting tool (1 ), the coating (6) comprises 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, the layer of Ali-v-y-zMvSiyXzN has wurtzite crystal structure and a from 0.2 to 25 pm thick layer (7) of a first metal nitride of one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al, or one or more metal elements of group 4, 5 and 6 in the periodic table of elements together with Al and Si, the layer (8) of Ali-v-y-zMvSiyXzN is situated below the layer (7) of the first metal nitride, wherein the distance between the layer (8) of Ah-v-y-zMvSiyXzN and the substrate body (5) surface is from 0 to 500 nm,- subjecting the coated cutting tool (1 ) to a heat treatment in an atmosphere preventing oxidation, or in a vacuum, at from 700 to 1000°C for a time period of from 10 to 300 minutes.

13. A method of producing a coated cutting tool (1 ) according to claim 12, wherein the coated cutting tool (1 ) is subjected to a heat treatment at from 800 to 950°C.

14. A method of producing a coated cutting tool (1 ) according to any one of claims 12-13, wherein the coated cutting tool (1 ) is subjected to a heat treatment for a time period of from 30 to 150 minutes.

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