A coated cutting tool

Abstract

The present invention relates to a coated cutting tool for metal machining comprising a cBN composite material substrate body and a from 0.5 to 10 μm thick coating thereon, the cBN composite material comprises cBN grains and a ceramic binder, or cBN grains and a combination of a ceramic binder and a metallic binder, the coating comprises a from 0.5 to 10 μm thick TiN layer situated on the cBN composite material substrate body surface. Within an innermost part of the TiN layer, in an elemental content analysis line profile, the content of N decreases to a point of a minimum content of N, the minimum content of N is from 5 to 25% lower than an average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N, the point of the minimum content of N is located at a distance of from 0 to 3 nm from the surface of the cBN grain.

Description

[0001] A coated cutting tool

[0002] The present invention relates to a coated cutting tool for metal machining wherein there is a cubic boron nitride (cBN) composite substrate with a coating comprising a TiN layer.

[0003] Introduction

[0004] In metal machining operations cutting tools, such as inserts, are used. A cutting tool generally has at least one rake face and at least one flank face. A cutting edge is present where a rake face and flank face meet. Metal machining operations include, for example, turning, milling, and drilling. As examples of cutting tools are cutting inserts, endmills and drills.

[0005] Since it was first introduced as a cutting tool material in the 1980s, the use of cBN composites have evolved to become a common machining solution. The application areas include hardened steels (ISO-H). This workpiece material is generally recognised as being difficult to machine. A cutting tool of a cBN material can withstand high cutting temperatures and forces and still retain its cutting edge. This is why cBN delivers long, consistent tool life and produces components with excellent surface finish.

[0006] When used in cutting tools the cBN composite may only constitute a part of the cutting tool, e.g., a cutting insert, more specifically a part engaged in the cutting operation such as a tip portion. In such a case a tip of cBN composite is attached to a supporting body of, usually, cemented carbide. The tip of cBN composite is usually attached to the supporting body by brazing.

[0007] In order to provide a long tool life, a cutting tool should have high resistance against different types of wear. A coating of TiN deposited in a physical vapour deposition process on a cBN composite substrate of a cutting tool is commonly used. The influence of the properties of the interface between a cBN composite substrate and a TiN layer to metal cutting performance is complex. One aspect can be referred to as the adhesion between the TiN layer and the cBN composite substrate. In order to provide high performance of the cutting tool the adhesion must be sufficiently high avoiding that the coating flakes off during use of the cutting tool.

[0008] Cutting tools for metal machining are subjected to different types of wear during use. One type of wear which is of high importance in turning operations is flank wear which takes place on a flank face of the cutting edge, mainly from an abrasive wear mechanism. The flank face is subjected to workpiece movement and too much flank wear will lead to poor surface quality of the workpiece, inaccuracy in the cutting process and increased friction in the cutting process.

[0009] The properties of an interface between a cBN composite substrate and a coating thereon may influence not only flaking behaviour as discussed above but also other types of wear, such as flank wear.

[0010] There is a continuing demand for wear resistant coated cutting tools with improved tool life.

[0011] Object of the invention

[0012] There is an object of the present invention to provide a coated cutting tool for metal machining having a cBN composite substrate which has a long tool life in metal cutting operations.

[0013] The invention

[0014] It has now been provided a coated cutting tool for metal machining which, at least, shows high flaking resistance and high flank wear resistance in metal cutting operations in ISO-H workpiece materials.

[0015] The present invention relates to a coated cutting tool for metal machining comprising a rake face and a flank face and a cutting edge inbetween. The coated cutting tool further comprises a cBN composite material substrate body and a from 0.5 to 10 pm thick coating thereon, the cBN composite material comprises cBN grains and a ceramic binder, or cBN grains and a combination of a ceramic binder and a metallic binder. The coating comprises a from 0.5 to 10 pm thick TiN layer situated on the cBN composite material substrate body surface. Within an innermost part of the TiN layer, in an elemental content analysis line profile made from within the TiN layer into a cBN grain perpendicular to the surface plane of the cBN grain, the content of N decreases to a point of a minimum content of N, the minimum content of N is from 5 to 25% lower than an average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N. In the elemental content analysis line profile, the point of the minimum content of N is located at a distance of from 0 to 3 nm from the surface of the cBN grain, the location of the surface of the cBN grain in the elemental content analysis line profile is herein defined as the location of a half value point where the B content has its half value of an average B content as measured in the cBN grain between 2 and 8 nm from said half value point.

[0016] The coated cutting tool herein disclosed shows at least high flaking resistance as well as high resistance to flank wear, in a finishing turning operation of an ISO H workpiece material.

[0017] In the elemental content analysis line profile made from within the TiN layer into a cBN grain perpendicular to the surface plane of the cBN grain, the content of N decreases to a point of a minimum content of N, the minimum content of N is suitably from 8 to 20% lower than an average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N.

[0018] In the elemental content analysis line profile, the point of the minimum content of N is located at a distance of suitably from 0.5 to 2 nm from the surface of the cBN grain

[0019] In one embodiment, the decrease in content of N to the point of a minimum content of N is followed by an increase in content of N, forming a negative peak of N content. The negative peak of N content has suitably a full width at its half minimum, as determined from the average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N, of from 0.5 to 3 nm, suitably from 1 to 2 nm.

[0020] The TiN layer is suitably from 1 to 8 pm thick, preferably from 2 to 6 pm thick. By varying the components and the relative amounts of the components, cBN composite materials can be designed for optimum performance in different applications, e.g. continuous or interrupted cutting, and in machining of different metals. Known methods for manufacturing a cBN composite material for metal machining are based on conventional powder metallurgical techniques, which include mixing and milling the raw materials to a powder mixture, forming the powder mixture to a green body and subjecting the green body to a sintering operation at high pressure and high temperature (HPHT sintering) to form a sintered body of a cBN composite material. The sintered body of a cBN composite material can either be formed on a support material of, for example, cemented carbide, or be formed without a support material. If a support material is intended to be used the sintered body of a cBN composite material is suitably cut into a tip which is then be brazed to the support material.

[0021] The cBN composite suitably comprises from 25 to 95 wt% cBN, or 35 to 75 wt% cBN, the specific amount is selected to provide optimum performance in a specific cutting application.

[0022] The cBN composite material comprises a ceramic binder which may comprise, for example, a nitride, carbide or carbonitride of a Group 4, 5 or 6 transition metal or mixtures thereof. The transition metal may, for example, be titanium.

[0023] The cBN composite material may additionally comprise a metallic binder. An example of a suitable metallic binder is aluminium.

[0024] The average cBN grain size is suitably from 0.2 to 4 pm, or from 0.5 to 3 pm. A suitable grain size is selected to provide optimum performance in a specific cutting application.

[0025] The coated cutting tool can be a cutting tool insert, a drill, or a solid endmill, for metal machining. In the case of the cutting tool being an insert it is suitably a milling, drilling or turning insert.

[0026] In one embodiment, the coated cutting tool is a cutting tool insert and comprises a supporting body of cemented carbide comprising WC in a metallic binder and the cBN composite material substrate body is a cutting edge tip. The metallic binder is suitably Co. In an elemental content analysis the location of a line profile assigned to an element in the analysis may be seen as if a very low level of the element is present, forming a baseline level, even when the element is actually not present at all. This is a result from the background extrapolation for the signal extraction in the data handling procedure. Thus, in the elemental content analysis line profile of W within the TiN layer, which does not contain W, the baseline content of W may be displayed in the analysis as if a level of up to 1 -2 at% is present.

[0027] When the coated cutting tool comprises a supporting body of cemented carbide comprising WC in a metallic binder there is an embodiment wherein, in an elemental content analysis line profile made from within the TiN layer into a cBN grain perpendicular to the surface plane of the cBN grain, there is a peak of W content in the lowermost part of the TiN layer. The peak of W content is believed to result from re-sputtering from the WC in the cemented carbide carrier body. The peak of W content has its point of maximum content of W suitably located at a distance of from 0 to 3 nm, suitably at a distance of from 0 to 2 nm from the surface of the cBN grain.

[0028] The peak of W content has a maximum content of W of suitably from 0.5 to 2.5 at% , or from 1 .0 to 1 .75 at%, higher than the baseline content of W of the line profile of W within the TiN layer, as measured in the TiN layer between 8 and 14 nm from said point of the maximum content of W.

[0029] In one embodiment, the peak of W content has a full width at its half maximum, as determined from the baseline content of W in the TiN layer, of from 0.5 to 3 nm, suitably from 1 to 2 nm.

[0030] The TiN layer is a PVD layer, i.e. , the TiN layer is deposited by using a PVD process. Any type of PVD process may be used such as reactive sputtering, HIPIMS, ion plating or cathodic arc evaporation. Preferably, a cathodic arc evaporation process is used. Thus, the TiN layer is preferably a cathodic arc-deposited PVD layer

[0031] The cBN composite material substrate body is pre-treated prior to deposition of the coating. The pre-treatment includes a first treatment step comprising etching in an Ar atmosphere at about -200 V substrate bias voltage and a second treatment step comprising Ti ion etching in an Ar atmosphere at a substrate bias voltage of about -200 V. See further the examples section for details about manufacture of the coated cutting tool.

[0032] Methods:

[0033] Preparation of TEM lamellas for analysis:

[0034] Scanning electron and focused ion beam microscopy (SEM / FIB) (Helios NanoLab 650, FEI) was used for fabrication of site specific thin lamellas for transmission electron microscopy (TEM). A standard lift out technique was used with two low kV steps, 5kV and 2kV. The TEM lamella thickness was aimed at to be thinner than 100 nm. The TEM lamellas were obtained by cutting a section including the uppermost part of the cBN composite substrate body and the lowermost part of the coating in a direction perpendicular to the surface of the substrate body.

[0035] The TEM lamellas should be cut at a position on a flank face at a position of about 30 to 300 pm distance from the surface plane of a rake face. Also, there should be a distance of at least 0.5 mm away from any other flank face.

[0036] The turning inserts used in the examples herein were of a geometry having a negative land. The TEM lamellas were cut at a position on a flank face at a position of about 40 pm distance from the negative land. Also, there was a distance of at about 0.8 mm away from any other flank face. The TEM lamellas contained the full coating thickness of the samples and at least 2 pm of the uppermost part of the substrate.

[0037] TEM analysis:

[0038] TEM data, including scanning TEM (STEM) images, EDS and electron energy loss spectroscopy (EELS) images, were collected on a Titan G2 aberration-corrected (image and probe) TEM operated at 300 kV. EDX data were collected on a SuperX detector and EELS data on a Gatan Quantum ERS system. STEM images were collected at a camera length of 29.5 mm on Gatan ADF, Gatan HAADF and FEI HAADF detectors. The beam convergence angle was 21 .3 mrad. The beam current for image acquisition was ~100 pA and for spectrum imaging 350-600 pA.

[0039] STEM image and spectrum image analysis were done in GMS version 3.53. EDX quantification was done in Broker Esprit version 1 .9.4 on data extracted from spectrum images.

[0040] Elemental content analysis line profiles of elements, such as N, B and W, were provided from EELS data.

[0041] EELS characterisation details:

[0042] EELS spectrum images were acquired on a Csimage and probe corrected Titan G2 60-300 High Base TEM operated in STEM mode with spot size 9 at 300kV using a Gatan GIF Quantum ERS spectrometer with a nominal camera length of 29.5mm and a C2 50pm aperture corresponding to a 21.3 mrad convergence semi-angle and using a current of approximately 0.35nA to 0.4nA. A Gatan Digital Micrograph 64-bit software version 2.32.888.0 was used for the acquisition of dual-EELS spectrum images, i.e. low-loss and high-loss EELS data. Simultaneously image data was acquired using an FEI High Angle Annular dark field (HAADF) detector, a Gatan Annular darkfield (ADF) detector and a Gatan HAADF detector in addition to EDX-data acquired with a Super-X EDX detector using all four detectors. For the acquisition and quantification the convergence semi angle of 21 .3 mrad and a collection semi angle of 37.8mrad (5mm GIF entrance aperture) were used. Energy dispersion of 1 eV per channel was used for Dual EELS acquisition. Areas with sharpest interfaces between substrate and coating were localised and characterised.

[0043] For EELS quantification a Gatan GMS 3 Digital Micrograph software version 3.53.4031.2 was used. Spectrum Images and Gatan ADF STEM images were used for the calculation of EELS curves and extraction of intensity profiles, respectively. Settings used in the software: In the "Global Info" and "Global Tags" under "Prefs" in "Quantification", "Pre-edge buffer" was set to 7.0eV, Under "SI" "Bkgd average nearest neighbours" was set to 2, "disable model Electron energy-loss near edge structure (ELNES)" was set to FALSE, "Do bkgd average" was set to TRUE, "exclude ELNES" was set to TRUE, "Include ELNES integral" was set to FALSE, "Model ELNES" was set to TRUE, "Splice model ELNES smoothly" was set to TRUE, "post edge delay" was set to 50eV and "Support model ELNES" was set to TRUE. "ELNES width" was set to 40eV and "N ELNES iterations" was set to 50.

[0044] In "Elemental Quantification window for maps", "disable Model ELNES’ for 2D SI maps" was unchecked.

[0045] It is important to correct for plural scattering using low-loss data including the zero-loss peak acquired at the same time as the core-loss data including the edges. For the quantification, care was taken to select the chemical shifts and ELNES and signal windows such that the modelled ELNES and cross-section curve followed the measured spectrum intensities as good as possible. This was checked for all elements and spectrum images for each sample and adjusted if needed.

[0046] The thickness of the TEM specimen in the analysed region was approximately between 0.7 and 1.3 t / lambda.

[0047] Description of drawings

[0048] 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 a turning insert.

[0049] Figure 2 shows a schematic view of one embodiment of a cutting tool 1 being a turning insert having a supporting body 5 and cBN cutting edge tips 6. The insert is of geometry CNGA 120408-S01030A.

[0050] Figure 3 shows a schematic view of a cross section of an embodiment of the coated cutting tool of the present invention having a substrate 7 of a composite cBN material and a coating 8.

[0051] Figure 4 shows a STEM image of a cross section of Sample 3 (invention) showing an interface region between a cBN grain and the coating.

[0052] Figure 5 shows EELS data of Sample 3 (invention) which are elemental content line profiles when going (left to right) from within a TiN layer into a cBN grain. Figure 6 shows EELS data of Sample 2 (comparative) which are elemental content line profiles when going (left to right) from within a cBN grain into a TiN layer.

[0053] Figure 7 shows a SEM image of the edge portion of Sample 1 (invention) after a cutting test.

[0054] Figure 8 shows a SEM image of the edge portion of Sample 3 (invention) after a cutting test.

[0055] Figure 9 shows a SEM image of the edge portion of Sample 2 (comparative) after a cutting test.

[0056] Examples

[0057] Example 1 :

[0058] Cutting tool insert blanks of the geometry CNGA 120408-S01030A (turning insert) were provided and placed in a PVD chamber.

[0059] The inserts had a cutting edge tip of a cBN composite attached to a supporting body of cemented carbide based on WC-Co.

[0060] The composition of the cBN composite was 48 wt% cBN, 47 wt% Ti(C,N), 5 wt% Al, based on used amounts of raw material powders. The cutting edge tips of cBN composites had been made by milling raw material powders, pressing the powder mixture into the desired tip geometry followed by sintering. During milling of the powders and the subsequental sintering of the pressed cutting edge tips there may be small amounts, up to a couple of wt%, of additional components unavoidably included into the cBN composite, such as WC from milling bodies and oxygen. The cBN had a bimodal grain size distribution made from combining two different grain distributions, one with a mean grain size of about 1 pm and one of about 2.5 pm.

[0061] The cutting tool insert were coated by cathodic arc evaporation in a PVD vacuum chamber comprising three arc flanges, each flange comprising two cathode evaporators.

[0062] Targets of Ti were mounted in the evaporators in two of the flanges. The targets were circular and planar with a diameter of 100 mm available on the open market. Suitable arc sources to be used within this invention are the ones called Super Fine Cathode (SFC) from Kobelco (Kobe Steel Ltd.), which was herein used in the substrate treatments and deposition of TiN. SFC cathodes are discussed in Yamamoto et al., "Cutting Performance of Low Stress Thick TiAIN PVD Coatings during Machining of Compacted Graphite Cast Iron (CGI)", Coatings 2018, 8, 38; doi:10.3390 / coatings8010038.

[0063] The PVD chamber comprises a circular rotatable substrate table and the uncoated cutting tool insert blanks, which each has a hole like the inserts in the schematic figures 1 and 2, were mounted on pins located at the circumference of the substrate table. The table diameter was 0.32 m. The distance between the circumference of the substrate table and the targets was about 27 cm.

[0064] The mounting of the inserts was such that the flank faces of the inserts would substantially face the cathode evaporators during rotation in the PVD chamber during the sample preparation processes.

[0065] The cutting tool insert blanks underwent a three-fold rotation in the PVD chamber during treatments before deposition of the coating as well as during deposition of the coating. The chamber was pumped down to high vacuum (less than 10’2Pa) and heated to about 300°C by heaters located inside the chamber.

[0066] The cutting tool insert blanks were subjected to treatments as follows:

[0067] At first, the insert blanks were subjected to an Ar ion etching step. The purpose of the Ar etching is to remove any loose fragments that may be present on the substrate surface and also to remove any binder phase present on the uppermost cBN grains facing the surface which may remain after earlier substrate preparation steps. In this etching step the substrates are cleaned thourogly from such defects. In the following sample preparation a substrate bias level of -200V and about 1 .2 Pa of Ar-pressure was used resulting in an average bias current of about 3-5 A for the used substrate table. The table rotation speed was 1 .4 rpm. During the etching the temperature in the chamber was about 250-300°C. The etching time was 72 minutes.

[0068] Then, a Ti ion treatment step was performed. In this step an arc current of 150 A was applied to the Ti targets in the PVD chamber, and a DC bias voltage of -200 V was used and an Ar pressure of 1 Pa resulting in an average bias current of about 15-16 A for the used substrate table. The table rotation speed was 3 rpm. The duration of the Ti ion treatment was 2 minutes.

[0069] A part of the inserts, intended to be comparative inserts, were not subjected to any Ti ion treatment step.

[0070] Then, a layer of TiN was deposited on the inserts.

[0071] The TiN layer was deposited by cathodic arc evaporation in a gas containing N2 using the mounted targets of Ti. N2was injected into the chamber replacing Ar and the total pressure (N2) was 3 Pa. The substrate bias voltage was -70 V DC (relative to the chamber walls) and the arc current for the cathodes was 150 A. The temperature was maintained at about 300°C. The table rotation speed was 1 .4 rpm.

[0072] A TiN layer having a thickness of about 4 pm was deposited on the inserts, as measured on the flank face about 200 pm from the edge line by using light optical microscopy.

[0073] The samples made were "Sample 1 (invention)" which were TiN coated inserts where a Ti ion treatment step before deposition of TiN as described above was made and "Sample 2 (comparative)" which were TiN coated inserts where no Ti ion treatment step before deposition of TiN as described above was made. A further sample within the invention was made, "Sample 3 (invention)", which was made in exactly the same way as "Sample 1 (invention)" but with the difference that the TiN layer was deposited at a total pressure (N2) of 5 Pa. For "Sample 3 (invention)" the thickness of the deposited TiN layer was about 2.5 pm.

[0074] Example 2 (TEM analysis):

[0075] TEM analysis was performed on "Sample 2 (comparative)" and "Sample 3 (invention)". The procedure as described herein under section "Methods" was followed.

[0076] TEM lamellas were cut at a position on a flank face at a position of about 40 pm distance from the negative land. Also, there was a distance of at about 0.8 mm away from the other flank face. STEM images were obtained as described herein and the interface region between the cBN composite substrate body and the coating was studied.

[0077] The contents of elements within an investigated area going from the cBN composite substrate substrate into the coating were obtained by EELS. The procedure as described herein under section "Methods" herein was followed.

[0078] Figure 4 shows a STEM image of a cross section of Sample 3 (invention) showing an interface region between a cBN grain and the coating which is TiN. In the STEM image there is a lowermost part of the TiN coating appearing as a brighter zone which is due to a relatively higher presence of heavier elements.

[0079] Fig. 5 shows the result from an elemental content analysis as line profiles (EELS data) for "Sample 3 (invention)" extending (left to right in the figure) from within the TiN layer the cBN grain.

[0080] It was concluded from EELS data of "Sample 3 (invention)" that in close proximity to the cBN substrate surface the content of N in the TiN layer decreases to a point of a minimum content of N being about 46 at%. The average content of N in the TiN layer is about 52 at% as measured in the TiN layer between 8 and 14 nm from the point of the minimum content of N. Thus, the minimum content of N is 11 .5% lower than the average content of N in the TiN layer.

[0081] It was further concluded from EELS data of "Sample 3 (invention)" that the minimum content of N is located at a distance of about 1 .0 nm from the surface of the cBN grain. The location of the surface of the cBN grain in the elemental content analysis line profile is herein defined as the location of a half value point where the B content has its half value of an average B content as measured in the cBN grain between 2 and 8 nm from said half value point. The location of the half value point of B in the elemental content analysis profile can be easily obtained by only very few iteration steps. At first an approximate first value of the half value point of B content is assigned. This can be made by approximating the B content in the content profile as present well within the cBN grain. This gives an approximate first location of the half value point of B content. Then, it is determined an average value of B content between 5 and 10 nm from this first location of the half value point of B content from which a second location of a half value point of B is obtained. Already now a sufficient accurate location of the half value point of B content should have been provided. If necessary repeat the iteration a couple of times until there is no significant difference obtained by a further iteration step.

[0082] It is further seen in the EELS data of "Sample 3 (invention)" that the decrease in content of N to the point of a minimum content of N is followed by an increase in content of N, forming a negative peak of N content. The negative peak of N content has a full width at its half minimum, as determined from the average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N, is about 1 .5 nm.

[0083] It is further seen in the EELS data of "Sample 3 (invention)" that there is a peak of W content present in the coating closest to the surface of the cBN grain. The peak of W content has a maximum content of W of from about 1 .2 at% higher than the baseline content of W of the line profile of W within the TiN layer, the baseline content of W is determined in the TiN layer between 8 and 14 nm from said point of the maximum content of W. The peak of W content has a full width at its half maximum, as determined from the baseline content of W in the TiN layer, of about 1 .3 nm.

[0084] Fig. 6 shows the result from an elemental content analysis as line profiles (EELS data) for "Sample 2 (comparative)" extending (left to right in the figure) from within the cBN grain into the TiN layer.

[0085] It was concluded from EELS data of "Sample 2 (comparative)" that in close proximity to the cBN substrate surface there was no decrease in content of N seen.

[0086] It was further concluded from EELS data of "Sample 2 (comparative)" that there was no peak of W content present in the coating closest to the surface of the cBN grain.

[0087] Example 3:

[0088] Cutting tests were made in order to determine the performance of samples.

[0089] Explanations to terms used: The following expressions / terms are commonly used in metal cutting, but nevertheless explained in the table below:

[0090] Vc (m / min): cutting speed in meters per minute fn (mm / rev) feed rate per revolution (in turning) z: (number) number of teeth in the cutter ap (mm): axial depth of cut in millimeter

[0091] Flaking resistance:

[0092] Tests were made using a test method of continuous face turning of a case-hardened steel, at fixed cutting conditions up to a fixed time. The method generates a combination of flank and crater wear. Any significant difference in flaking tendencies would be resolved by the test. In this test, two edges per sample was run to six passes. One edge was run to 24 passes. The inserts were kept in the tool holder for the full test time. A qualitative wear evaluation in SEM was done after the test end where flaking area is seen as irregular flank wear, with exposed substrate covered by workpiece material (appearing as white areas).

[0093] Operation: Facing (turning)

[0094] Work piece material: Disc of case hardened steel 16NiCrS4, L=16 mm, D=102 mm, ~62 HRC

[0095] Insert type: CNGA 120408-S01030A

[0096] Depth of cut ap = 0.1 mm

[0097] Cutting speed Vc = 180 m / min

[0098] Feed rate fz = 0.1 mm / rev

[0099] Cooling: no, dry cutting

[0100] It was concluded from the SEM analysis of wear after 24 passes that "Sample 1 (invention)" and "Sample 3 (invention)" showed only minor flaking (see figures 7 and 8) while "Sample 2 (comparative)" showed substantial flaking (see figure 9). It was also concluded that the amount of flank wear for "Sample 3 (invention)" was very small.

Claims

Claims1 . A coated cutting tool (1 ) for metal machining comprising a rake face (2) and a flank face (3) and a cutting edge (4) inbetween, the coated cutting tool (1 ) further comprises a cBN composite material substrate body (7) and a from 0.5 to 10 pm thick coating (8) thereon, the cBN composite material comprises cBN grains and a ceramic binder, or cBN grains and a combination of a ceramic binder and a metallic binder, the coating (8) comprises a from 0.5 to 10 pm thick TiN layer situated on the cBN composite material substrate body (7) surface,- within an innermost part of the TiN layer, in an elemental content analysis line profile made from within the TiN layer into a cBN grain perpendicular to the surface plane of the cBN grain, the content of N decreases to a point of a minimum content of N, the minimum content of N is from 5 to 25% lower than an average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N,- in the elemental content analysis line profile, the point of the minimum content of N is located at a distance of from 0 to 3 nm from the surface of the cBN grain,- the location of the surface of the cBN grain in the elemental content analysis line profile is defined as the location of a half value point where the B content has its half value of an average B content as measured in the cBN grain between 2 and 8 nm from said half value point.

2. A coated cutting tool (1 ) according to claim 1 , wherein in the elemental content analysis line profile made from within the TiN layer into a cBN grain perpendicular to the surface plane of the cBN grain, the content of N decreases to a point of a minimum content of N, the minimum content of N is from 8 to 20% lower than an average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N.

3. A coated cutting tool (1 ) according to any one of claims 1 -2, wherein in the elemental content analysis line profile, the point of the minimum content of N is located at a distance of from 0.5 to 2 nm from the surface of the cBN grain.

4. A coated cutting tool (1 ) according to any one of claims 1 -3, wherein the decrease in content of N to the point of a minimum content of N is followed by an increase in content of N, forming a negative peak of N content.

5. A coated cutting tool (1 ) according to claim 4, wherein the negative peak of N content has a full width at its half minimum, as determined from the average content of N as measured in the TiN layer between 8 and 14 nm from said point of the minimum content of N, of from 0.5 to 3 nm.

6. A coated cutting tool (1 ) according to any one of claims 1 -5, wherein the TiN layer is from 1 to 8 pm thick.

7. A coated cutting tool (1 ) according to any one of claims 1 -6, wherein the cBN composite comprises from 25 to 95 wt% cBN.

8. A coated cutting tool (1 ) according to any one of claims 1 -7, wherein the coated cutting tool (1) is a cutting tool insert, a drill, or a solid end-mill, for metal machining.

9. A coated cutting tool (1 ) according to any one of claims 1 -8, wherein the coated cutting tool (1) is a cutting tool insert and comprises a supporting body (5) of cemented carbide comprising WC in a metallic binder and the cBN composite material substrate body (7) is a cutting edge tip (6).

10. A coated cutting tool (1 ) according to claim 9, wherein within an innermost part of the TiN layer, in an elemental content analysis line profile made from within the TiN layer into a cBN grain perpendicular to the surface plane of the cBN grain, there is a peak of W content in the lowermost part of the TiN layer.

11. A coated cutting tool (1 ) according to claim 10, wherein the peak of W content has a maximum content of W of from 0.5 to 2.5 at% higher than thebaseline content of W of the line profile of W within the TiN layer, the baseline content of W is determined in the TiN layer between 8 and 14 nm from said point of the maximum content of W.

12. A coated cutting tool (1 ) according to any one of claims 10-11 , wherein the peak of W content has a full width at its half maximum, as determined from the baseline content of W in the TiN layer, of from 0.5 to 3 nm.

13. A coated cutting tool (1 ) according to any one of claims 1 -12, wherein the TiN layer is a cathodic arc-deposited PVD layer.

Images