TiAlCN layers with lamellar structure

Abstract

A tool has a main part of hard metal, cermet, ceramic, steel, high-speed steel, and a single or multilayer wear protection coating applied onto the main part by CVD and which has a thickness from 3 m to 25 m. The wear protection coating has at least one Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer with stoichiometric coefficients 0.70x<1.0y<0.25 and 0.75z<1.15 and a thickness from 1.5 m to 17 m. The T.sub.1xAl.sub.xC.sub.yN.sub.z layer has a lamellar structure with lamellae with thickness of no more than 150 nm, preferably no more than 100 nm, particularly preferably no more than 50 nm. Lamellae are made of periodically alternating regions of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer with alternatingly different stoichiometric proportions of Ti and Al, having the same crystal structure (crystallographic phase), and the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has at least 90% vol. % of face centered cubic (fcc) crystal structure.

Claims

1. A tool comprising a base body of carbide, cermet, ceramic, steel or high speed steel, and a single-layer or multi-layer wear-protection coating applied thereto in a CVD process and of a thickness in the range of 3 m to 25 m, wherein the wear-protection coating has at least one Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer having stoichiometry coefficients 0.70<x<1, 0<y<0.25 and 0.75<z<1.15, and with a thickness in the range of 1.5 m to 17 m, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has a lamellar structure with lamellae of a thickness of not more than 150 nm, wherein the lamellae are formed from periodically alternating regions of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer with alternately different stoichiometric proportions of Ti and Al, having the same crystal structure (crystallographic phase), and wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has at least 90 vol-% of face-centred cubic (fcc) crystal structure.

2. A tool according to claim 1, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has at least 95 vol-% of face-centred cubic (fcc) crystal structure.

3. A tool according to claim 1, wherein in the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer with lamellae comprising periodically alternating regions with alternately different stoichiometric proportions of Ti and Al regions with other Ti and Al proportions which respectively adjoin below and above a region of the lamellae in the layer growth direction have the same crystallographic orientation.

4. A tool according to claim 1, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has a columnar microstructure, wherein the columnar crystallites have a mean length which is at least 0.35 times the thickness of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer, and/or wherein the columnar crystallites have a ratio of the mean length to the mean width, measured at 50% of the thickness of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer, of at least 2.5.

5. A tool according to claim 4, wherein the mean length of the columnar crystallites is at least 0.5 times the thickness of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer.

6. A tool according to claim 4, wherein the ratio of the mean length to the mean width of the columnar crystallites, measured at 50% of the thickness of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer, is at least 5.

7. A tool according to claim 1, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has a preferential orientation of crystal growth with respect to a crystallographic {hkl} plane, characterised by a texture coefficient TC (hkl)>1.5, wherein the texture coefficient TC (hkl) is defined as follows: $\mathrm{TC}\left(\mathrm{hkl}\right)={\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\left[\frac{1}{n}\underset{n=1}{\overset{n}{.Math.}}\frac{I\left(\mathrm{hkl}\right)}{I_0\left(\mathrm{hkl}\right)}\right]}^{-1},$ wherein l(hkl) are the intensities of the diffraction reflexes, measured by X-ray diffraction, lo(hkl) are the standard intensities of the diffraction reflexes in accordance with PDF chart 00-046-1200, n is the number of reflexes used for the calculation, and the reflexes (111), (200), (220) and (311) are used for the calculation of TC(hkl), and wherein the preferential orientation of the crystal growth of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer is present with respect to the crystallographic {111}-, {200}-, {220}- or {311}-plane.

8. A tool according to claim 1, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has stoichiometry coefficients 0.70x<1,y=0 and 0.95z<1.15.

9. A tool according to claim 7, wherein the preferential orientation of the crystal growth of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer is present with respect to the crystallographic {111}-plane.

10. A tool according to claim 1, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has a preferential orientation of crystal growth with respect to a crystallographic {hkl}-plane, which is characterised in that the maximum of the X-ray diffraction peak of the crystallographic {hkl}-plane, measured by X-ray diffraction diffractometry (XRD) and/or by electron backscatter diffraction (EBSD), is measured within an angle a =20degrees relative to the perpendicular to the surface of the base body, wherein the preferential orientation of the crystal growth of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer is present with respect to the crystallographic {111}-, {200}-, {220}- or {311}-plane.

11. A tool according to claim 10, wherein the maximum of the X-ray diffraction peak of the crystallographic {hkl}-plane, measured by X-ray diffraction diffractometry (XRD) and/or by electron backscatter diffraction (EBSD), is measured within an angle =+10 degrees relative to the perpendicular to the surface of the base body.

12. A tool according to claim 10, wherein the preferential orientation of the crystal growth of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer is present with respect to the crystallographic {111}-plane.

13. A tool according to claim 1, wherein the full width at half maximum (FWHM) of at least one of the X-ray diffraction peaks of the crystallographic {111}-, {200}-, {220}- and {311}-planes is <1 2.

14. A tool according to claim 13, wherein the full width at half maximum (FWHM) of at least one of the X-ray diffraction peaks of the crystallographic {111}-, {200}-, {220}- and {311}-planes is <0.6 2.

15. A tool according to claim 13, wherein the full width at half maximum (FWHM) of the X-ray diffraction peaks of the crystallographic {111}-plane is <1 2.

16. A tool according to claim 1, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has a preferential orientation of crystal growth with respect to the crystallographic {111}-plane, which is characterised by a ratio of the intensities of the X-ray diffraction peaks of the crystallographic {111}-plane and the {200}-plane, l{111} and l{200}, in which l{111}/l{200} >1+h(In h).sup.2, wherein h is the thickness of Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer in m.

17. A tool according to claim 16, wherein l{111}/l{200} >1+(h+3)(ln h).sup.2.

18. A tool according to claim 7, wherein the texture coefficient TC (hkl) is greater than 2.

19. A tool according to claim 1, wherein the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer has a Vickers hardness (HV)>2300 HV.

20. A tool according to claim 1, further comprising, arranged between the base body and the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer, at least one further carbide layer of a thickness of 0.05 m to 7 m, selected from a TiN layer, a TiCN layer deposited by means of high temperature CVD (CVD) or medium temperature CVD (MT-CVD), an A1.sub.2O.sub.3 layer and combinations thereof and/or arranged over the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer is at least one further carbide layer.

21. A process for the production of a tool according to claim 1, wherein, for producing the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer with a lamellar structure, the process comprises: a) placing the body to be coated in a substantially cylindrical CVD reactor designed for an afflux flow of the bodies to be coated with the process gases in a direction substantially radially relative to the longitudinal axis of the reactor, b) providing two precursor gas mixtures (VG1) and (VG2), wherein the first precursor gas mixture (VG1) contains 0.005% to 0.2 vol-% TiCl.sub.4, 0.025% to 0.5vol-% AlCl.sub.3 and as a carrier gas hydrogen (H.sub.2) or a mixture of hydrogen and nitrogen (H.sub.2/N.sub.2) and the second precursor gas mixture (VG2) contains 0.1 to 3.0vol-% of at least one N-donor selected from ammonia (NH.sub.3) and hydrazine (N.sub.2H.sub.4) and as a carrier gas hydrogen (H.sub.2) or a mixture of hydrogen and nitrogen (H.sub.2/N.sub.2) and the first precursor gas mixture (VG1) and/or the second precursor gas mixture (VG2) optionally contains a C-donor selected from acetonitrile (CH.sub.3CN), ethane (C.sub.2H.sub.6), ethene (C.sub.2H.sub.4) and ethyne (C.sub.2H.sub.2) and mixtures thereof, wherein the total vol-% proportion of N-donor and C-donor in the precursor gas mixtures (VG1VG2) is in the range of 0.1 to 3.0vol-%, c) maintaining the two precursor gas mixtures (VG1, VG2) separate before passing into the reaction zone and introducing the two precursor gas mixtures (VG1, VG2) substantially radially relative to the longitudinal axis of the reactor at a process temperature in the CVD reactor in the range of 600 C. to 850 C. and a process pressure in the CVD reactor in the range of 0.05 to 18kPa, wherein the volume gas flows ({dot over (V)}) of the precursor gas mixtures (VG1, VG2) are so selected that the mean residence time (T) in the CVD reactor is less than 1 second.

22. A process according to claim 21, wherein the volume gas flows ({dot over (V)}) of the precursor gas mixtures (VG1, VG2) are so selected that the mean residence time (T) in the CVD reactor is less than 0.5 second.

23. A process according to claim 21, wherein at least one of the process temperature in the CVD reactor is in the range of 625 C. to 800 C. and the process pressure in the CVD reactor is in the range of 0.05 to 8kPa.

24. A process according to claim 21, wherein the ratio of the volume gas flows ({dot over (V)}) of the precursor gas mixtures (VG1, VG2) ({dot over (V)}(VG1)/{dot over (V)}(VG2)) is less than 1.5.

25. A tool according to claim 1, further comprising, arranged between the base body and the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer, at least one further carbide layer of a thickness of 0.05 m to 7 m, selected from a TiN layer, a TiCN layer deposited by means of high temperature CVD (CVD) or medium temperature CVD (MT-CVD), an Al.sub.2O.sub.3 layer and combinations thereof and/or arranged over the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer is at least one Al.sub.2O.sub.3 layer of the modification -Al.sub.2O.sub.3, -Al.sub.2O.sub.3 or -Al.sub.2O.sub.3.

26. A tool according to claim 1, further comprising, arranged between the base body and the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer, at least one further carbide layer of a thickness of 0.05 m to 7 m, selected from a TiN layer, a TiCN layer deposited by means of high temperature CVD (CVD) or medium temperature CVD (MT-CVD), an Al.sub.2O.sub.3 layer and combinations thereof and/or arranged over the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer is an -Al.sub.2O.sub.3 layer, wherein the Al.sub.2O.sub.3 layer is deposited by means of high temperature CVD (CVD) or medium temperature CVD (MT-CVD).

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 shows a scanning electron microscope image (SEM) of a layer according to the invention,

(2) FIG. 2 shows a further scanning electron microscope image (SEM) of the layer according to the invention as shown in FIG. 1 at higher magnification. It is possible to see in the image with an InLEns-SE detector that the lamellae structure extends substantially over the entire layer,

(3) FIG. 3 shows STEM images of the layer according to the invention as shown in FIGS. 1 and 2. FIG. 3A: bright field image; FIG. 3B: HAADF (high angle annular dark field) image. The contrast inversion when changing between the two detector signals is a sign of differences in the chemical composition between the light and dark regions of the lamellae.

(4) FIG. 4 shows a high-resolution HRTEM image of the lamellar structure of the layer according to the invention as shown in FIGS. 1 and 2, and

(5) FIG. 5 shows Fourier transforms of the overall image of FIG. 4 (FIG. 5(A)) and portions from FIG. 4 (FIGS. 5(B), 5(C) and 5(D)).

DEFINITIONS AND METHODS

(6) Mean Residence Time

(7) The mean residence time in the reaction zone of the CVD reactor in accordance with the present invention is defined as the quotient of the reactor volume V.sub.R and the issuing volume gas flow {dot over (V)} at the process pressure p measured at the reactor outlet:

(8) $=\frac{V_R}{\stackrel{.}{V}}=\frac{V_{R}p}{{\stackrel{.}{V}}_N{p}_N}$
wherein {dot over (V)}.sub.N denotes the volume gas glow under normal conditions and p.sub.N is the normal pressure=101.325 Pa. For calculating the mean residence time according to the present application, instead of the total reactor volume, only the volume of the batch constitution in the reactor is used as the volume V.sub.R.
X-ray Diffractometry (XRD)

(9) X-ray diffraction measurements were implemented on a diffractometer of type GE Sensing & Inspection Technologies PTS3003 using CuK radiation. For -2 residual stress and pole figure measurements a parallel beam optical system was used, which at the primary side comprised a polycapillary means and a 2 mm pinhole as a collimator. At the secondary side a parallel plate collimator with 0.4 divergence and a nickel K.sub. filter was used.

(10) Peak intensities and full width at half maximums were determined on the basis of -2 measurements. After deduction of the background pseudo-Voigt functions were fitted to the measurement data, wherein the K.sub.2 deduction was effected by means of K.sub.1/K.sub.2 doublet matching. The values in respect of intensities and full-width half-maximums set out in Table 4 relate to the K.sub.1 interferences fitted in that way. The lattice constants are calculated in accordance with Vegard's law on the assumption of the lattice constants of TiN and AlN from PDF charts 38-1420 and 00-46-1200 respectively.

(11) Characterisation of Lamellar Structures in Ti.sub.1xAl.sub.xC.sub.yN.sub.z Layers

(12) Detection and characterisation of the existence of lamellar structures in the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layers according to the invention by means X-ray diffraction (XRD) and conventional and high-resolution transmission electron microscopy (TEM and HR-TEM) was effected as described in J Keckes et al Self-organized periodic soft-hard nanolamellae in polycrystalline TiAlN thin films, Thin Solid Films 545 (2013), pages 29-32. A transmission electron microscope FEI Titan 80-300 with a field emission cathode with an acceleration voltage of 300 kV was used. Scanning transmission electron microscope images were recorded with bright field (BF) and high angle annular dark field (HAADF) detectors. For sample preparation for transmission electron microscopy a combined FIB/SEM system was used (FIB=focused ion beam) which was equipped with a liquid gallium ion source and a field emission cathode as the electron source as well as a system for ion- and electron-supported deposition of Pt. By means of that system polished cross-sections were prepared as lamellae by in-situ lift-out out of the layer and diluted to adequate electron transparency.

(13) Pole Figures

(14) Pole figures of the {111} reflex were implemented at 2=38.0 over an angle range of 0<<75 (increment 5) and 0<<360 (increment 5) with a circular arrangement of the measurement points. The intensity distribution of all measured and back-calculated pole figures was approximately rotationally symmetrical, that is to say the layers investigated exhibited fibre textures. For checking the preferential orientation pole figures were measured in addition to the {111} pole figure at the {200} and {220} reflexes. The orientation density distribution function (ODF) was calculated with the software LaboTex3.0 from LaboSoft, Poland, and the preferential orientation represented as an inverse pole figure. With the layers according to the invention the intensity maximum was in the crystallographic direction <hkl> corresponding to the set preferential orientation or at 20 angle deviation from <hkl>, wherein <hkl> was equal to <111>, <200>, <220> or <311>, preferably <111>.

(15) EDX Measurements (Energy-dispersive X-ray Spectroscopy)

(16) EDX measurements were carried out on a scanning electron microscope Supra 40 VP from Carl Zeiss with 15 kV acceleration voltage with an EDX spectrometer type INCA x-act from Oxford Instruments, UK.

(17) Microhardness Determination

(18) Measurement of microhardness was effected in accordance with DIN EN ISO 14577-1 and -4 with a universal hardness tester of type Fischerscope H100 from Helmut Fischer GmbH, Sindelfingen, Germany, on a polished section of the coated bodies.

EXAMPLES

Example 1

Production of Coated Carbide Indexable Cutting Bits

(19) In these examples the substrate bodies used are carbide indexable cutting bits of the geometry SEHW1204AFN with a composition of 90.5 wt-% WC, 8 wt-% Co and 1.5 wt-% (NbC+TaC) and with a mixed-carbide-free edge zone.

(20) For coating the carbide indexable cutting bits a CVD coating installation of the type Bernex BPX325S with a reactor height of 1250 mm, a reactor diameter of 325 mm and a volume of the charge constitution of 40 liters was used. The gas flow was radially relative to the longitudinal axis of the reactor.

(21) For bonding the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layers according to the invention and the comparative layers a TiN layer approximately 0.3 m in thickness was firstly directly applied to the carbide substrate by means of CVD under the deposit conditions set out in Table 1.

(22) TABLE-US-00001 TABLE 1 Reaction conditions in the production of the bonding layer Reactive gas mixture Bonding Temp. Pressure Time vol [%] layer [ C. ] [kPA] [min] TiCl.sub.4 N.sub.2 H.sub.2 TiN 850 15 90 1.0 44.00 55.0

(23) To produce the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layers according to the invention a first precursor gas mixture (VG1) with the starting compounds TiCl.sub.4 and AlCl.sub.3 and a second precursor gas mixture (VG2) with the starting compound NH.sub.3 as the reactive nitrogen compound were introduced into the reactor separately from each other so that mixing of the two gas flows took place only upon passing into the reaction zone. The volume gas flows of the precursor gas mixtures (VG1) and (VG2) were so set that a mean residence time of the reaction gas in the reactor and an overall volume flow under normal conditions {dot over (V)}.sub.N was achieved. The parameters in the production of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z coating 1) according to the invention and the comparative coating 2) are reproduced in Table 2.

(24) TABLE-US-00002 TABLE 2 Reaction conditions in the production of Ti.sub.1xAl.sub.xC.sub.yN.sub.z coatings Total Precursor gas Precursor volume mixture gas mixture Temp. Pressure Time flow {dot over (V)}.sub.N (VG1) (VG2) # layer [ C. ] [kPA] [min] [l.sub.N/min] [sec] TiCl.sub.4 AlCl.sub.3 H.sub.2 H.sub.2 NH.sub.3 1) TiAIN 670 1.2 260 107 0.27 0.03 0.23 52.5 46.9 0.35 (inv. ) 2) TiAIN 670 1.2 260 25 1.14 0.03 0.23 52.5 46.9 0.35 (comp. )

(25) X-ray diffraction (XRD), electron diffraction, in particular EBSD, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) as well as microhardness measurement were used to characterise the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layers according to the invention.

(26) The layer thickness of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer 1) according to the invention was 4.5 m and the layer thickness of the comparative layer 2) was 6.25 m. The microhardness of the layer 1) according to the invention was 3070 HV.sub.0.05 while the microhardness of the comparative coating 2) was measured at 2300 HV.sub.0.05.

(27) The XRD analysis showed that the layer 1) according to the invention substantially comprised pure face-centred cubic (fcc) phase and had a strong {111} preferential orientation of crystal growth. The full width at half maximums of the {111} reflex was 0.64 2 and the composition of the layer could be determined as about Ti.sub.0.195Al.sub.0.805N.sub.1.05.

(28) The comparative coating 2) showed in the XRD analysis wide signals in the range of 30240 which were fitted by the software used as two peaks (2=36.98, FWHM=1.28 and 2=37.83, FWHM=0.94). The large peak width points to a fine-crystalline structure. The composition of the layer was around Ti.sub.0.3Al.sub.0.17N.sub.1.0. It was not possible to uniquely determine on the basis of the diffractogram the components to which the XRD signal was to be attributed to the {101} interference of hexagonal AlN and to the {111} reflex of cubic Ti.sub.1xAl.sub.xN.sub.z. It is however to be assumed that significant proportions of hexagonal AlN are present in the layer. As the layer interferences with the highest intensity occur in the angle range 30240 it is possible to conclude that there is a {111} preferential orientation of the cubic component of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer.

(29) The {101}- and {202}-interferences of hexagonal AlN and the {111}- and {222}-reflections of cubic Ti.sub.1xAl.sub.xC.sub.yN.sub.z can be more or less greatly superimposed depending on the respective chemical composition. Only the interference of the {200}-plane of the cubic Ti.sub.1xAl.sub.xC.sub.yN.sub.z is superimposed by no further interferences, like for example due to the substrate body or layers arranged thereover or therebeneath, and has the highest intensity for random orientation.

(30) Therefore measurements (-2 scans) were carried out at two different tilt angles (=0 and =54.74) to assess the volume proportion of hexagonal AlN in the measurement volume and to avoid misinterpretations in respect of the {111}- and {200} intensities of the cubic Ti.sub.1xAl.sub.xC.sub.yN.sub.z. As the angle between the plane normals of {111} and {200} is about 54.74 then with a strong {111} fibre texture there is an intensity maximum of the {200} reflex at the tilt angle =54.74 while the intensity of the {111} reflex tends towards zero. Conversely with the tilt angle =4.74 a strong intensity maximum of the {111-reflex is obtained with a strong {200} fibre texture while the intensity of the {200} reflex tends towards zero.

(31) In that way, for the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layers produced, a check was made to ascertain whether the measured intensity at 238.1 is predominantly to be associated with the face-centred cubic Ti.sub.1xAl.sub.xC.sub.yN.sub.z phase or whether greater proportions of hexagonal AlN are contained in the layer. Both X-ray diffraction measurements and also EBSD measurements conformingly revealed only very small proportions of hexagonal AlN phase in the layers according to the invention. The chemical composition of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer 1) according to the invention was around Ti.sub.0.19Al.sub.0.81N, which on the basis of the position of the {111} peak in accordance with Vegard's law and using the corresponding {111} peak positions for pure fcc TiN in accordance with PDF chart 38-1420 and pure fcc AlN in accordance with PDF chart 46-1200 was calculated as reference values.

(32) Cross-sections of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layers according to the invention were investigated by means of scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM). The layer 1) according to the invention consisted of columnar crystallites of a typical length near the layer thickness of about 3-4 m and a mean width, measured at 50% of the thickness of the Ti.sub.1xAl.sub.xC.sub.yN.sub.z layer, of about 200 nm. The length-to-width ratio was thus about 17.5. Scanning electron microscope images (SEM) of a polished cross-section of the comparative layer 2) revealed a fine structure in which it was not possible to see any discrete crystallites. No lamellae structure could be found in the layer.

(33) FIGS. 1 and 2 show scanning electron microscope images (SEM) of the layer 1) according to the invention.

(34) FIG. 3 shows STEM images of the layer 1) according to the invention in the bright field mode (BF) (FIG. 3A) and in the high angle annular dark field (HAADF) dark field mode (FIG. 3B). The lamellar structure according to the invention is to be clearly seen in all crystallites, wherein the sharpness of the contrast depends on the orientation of the crystallites relative to the electron beam. The thickness of the lamellae is about 30 nm. The images in FIG. 3 were taken approximately at the centre of the layer but the columnar crystallites with a lamellar structure were observed in the entire layer. The direction of layer growth is from left to right in the images in FIG. 3. In the crystallites which exhibit the highest contrast regions of differing thicknesses are to be seen within the lamellae structure. It was possible to show by EDS analysis that the narrower regions of the lamellae which appear dark in the BF and bright in the HAADF have higher Ti proportions and lower Al proportions than the wider regions. The nitrogen proportion however was of equal magnitude within the measurement accuracy in the various regions. The overall composition determined by means of EDS is the same as the overall composition determined by XRD.

(35) FIG. 4 shows a high-resolution HRTEM image of the lamellar structure of the layer 1) according to the invention. It is possible to see two lamellae regions, wherein the narrower regions with a higher Ti content are to be seen as dark bands in the upper and lower regions in FIG. 4. Fourier transform operations were conducted in respect of the three regions (B, C, D) of the image shown in FIG. 4, that are marked by square outlines in FIG. 4. They are reproduced in FIG. 5 as FIGS. 5(B), 5(C) and 5(D). The squares B and D in FIG. 4 (corresponding to FIGS. 5(B) and 5(D)) cover the narrower regions which have a higher Ti content, whereas the square C in FIG. 4 (corresponding to FIG. 5(C)) covers a wider region which has a higher Al content. FIG. 5(A) shows the Fourier transform of the whole of FIG. 4.

(36) The Fourier transforms of FIG. 5 show that the entire structure comprises face-centred cubic (fcc) phase. Within the accuracy of the method the lattice constant determined on the basis of the patterns of Fourier transforms of 4.04 is in conformity with the lattice constant determined by XRD of 4.08 . In addition FIGS. 5(B), 5(C) and 5(D) show that the same crystal structure (fcc) and the same orientation prevail in the three different regions, covered by those Figures, of the lamellar structure.

Example 2

Cutting Trials

(37) The carbide indexable cutting bits produced in accordance with Example 1 with the TiAlN layer 1) according to the invention and the comparative layer 2) respectively as well as a carbide indexable cutting bit of a commercially available kind from a competitor were used for milling cast materials. The competitor tool had a multi-layer coating involving the layer sequence TiN (0.5 m)-TiCN (2 m)-TiAlN (3 m), wherein the TiAlN layer in accordance with XRD analysis solely consisted of a phase mixture of hexagonal AlN and cubic Ti.sub.1xAl.sub.xN.sub.z. A two-phase structure with partial formation of lamellae could be seen in SEM images, similarly to the structure described in WO 2013/134796.

(38) Milling operations were carried out under the following cutting conditions with the cutting inserts:

(39) Workpiece material: grey cast iron GGG70

(40) Co-directional, dry machining

(41) Tooth feed: f.sub.z=0.2 mm

(42) Cutting depth: a.sub.p=3 mm

(43) Cutting speed: v.sub.c=283 m/min

(44) Setting angle: =45

(45) Working engagement: a.sub.e=98 mm

(46) Projection: u.sub.e=5 mm.

(47) Then the maximum wear mark width v.sub.B,max at the main cutting edge was determined after 4000 m of milling travel:

(48) TABLE-US-00003 Wear mark width Number of Tool v.sub.B, max [mm] comb cracks 1) (invention) 0.20 1 2) (comparative example) 0.39 6 Comparative tool 0.35 4 (competition)