HARD CUBIC AL-RICH ALTIN COATING LAYERS PRODUCED BY PVD FROM CERAMIC TARGETS

Abstract

A PVD coating process, preferably an arc evaporation PVD coating process for producing an aluminum-rich Al.sub.xTi.sub.1-xN-based thin film having an aluminium content of >70 at-% based on the total amount of aluminium and titanium in the thin film, a cubic crystal structure and an at least partially non-columnar microstructure with a non-columnar content of >1 vol-% based on the volume of the total microstructure, wherein ceramic targets are used as material source for the aluminium-rich Al.sub.xTi.sub.1-xN-based thin film.

Claims

1. A PVD coating process for producing an aluminum-rich Al.sub.XTi.sub.1-XN-based thin film having an aluminium content of >70 at-% based on the total amount of aluminium and titanium in the thin film, a cubic crystal structure and an at least partially non-columnar microstructure with a non-columnar content of >1 vol-% based on the volume of the total microstructure, wherein ceramic targets are used as material source for the aluminium-rich Al.sub.XTi.sub.1-XN-based thin film.

2. Coating process according to claim 1, wherein an arc evaporation PVD coating process is used as PVD coating process.

3. Coating process according to claim 1, wherein the aluminum-rich Al.sub.XTi.sub.1-XN-based thin film having a mixed columnar and non-columnar microstructure with a content of >1 vol-% of the non-columnar microstructure.

4. Coating process according to claim 1, wherein the aluminum-rich Al.sub.XTi.sub.1-XN-based thin film having a non-columnar microstructure.

5. Coating process according to claim 1, wherein brittle and insulating ceramic targets are used.

6. Coating process according to claim 2, wherein arc currents >80 Ampere are used, wherein in particular arc currents between and 200 Ampere are used.

7. Coating process according to claim 1, wherein at least one target is equipped with an additional insulator in the middle, and the arc steering is manipulated in a way for the ceramic target not to crack during arc discharge.

8. Coating process according to claim 1, wherein Al.sub.XTi.sub.1-XN is used as target material, wherein X is 75.

9. Coating process according to claim 1, wherein at least one ceramic target is 99% dense and crack free even during the processing.

10. Coating process according to claim 1, wherein Al.sub.XTi.sub.1-XN is used as target material, wherein the AlN-content is >70 Vol-%, of the target material.

11. Coating process according to claim 1, wherein nitrogen is introduced as reactive gas.

12. Coating process according to claim 1, wherein a negative bias voltage (U.sub.b) is applied to the substrate to be coated.

13. Coating process according to claim 1, wherein the deposition temperature during the coating process is lower than 360 C.

14. Coating process according to claim 1, wherein a plurality of aluminum-rich Al.sub.XTi.sub.1-XN-based thin films are deposited one above the other to produce a multilayer film, wherein the content of the Al.sub.XTi.sub.1-XN showing a non-columnar microstructure in spite of cubic structure variates with respect to adjacent layers.

15. Aluminium-rich Al.sub.XTi.sub.1-XN-based thin film having an aluminium content of >70 at-% based on the total amount of aluminium and titanium in the thin film, a cubic crystal structure and at least partially non-columnar microstructure with a non-columnar content of >1 vol-% based on the total microstructure, producible by a process according to claim 1.

16. Aluminium-rich Al.sub.XTi.sub.1-XN-based thin film according to claim 15, wherein the aluminum-rich Al.sub.XTi.sub.1-XN-based thin film having a mixed columnar and non-columnar microstructure with a content of >1 vol-% of the non-columnar microstructure.

17. Aluminium-rich Al.sub.XTi.sub.1-XN-based thin film according to claim 15, wherein the thin film comprises Al, Ti and N as main components and has a chemical elements composition in atomic percentage regarding these elements according to formula (Al.sub.aTi.sub.b).sub.xN.sub.y, wherein a and b are respectively the concentration of aluminium and titanium in atomic ratio considering only Al and Ti for the calculation of the element composition in the layer, whereby a+b=1 and 0a0.7 and 0b0.2, or 0a0.8 and 0b0.2, and wherein x is the sum of the concentration of Al and the concentration of Ti, and y is the concentration of nitrogen in atomic ratio considering only Al, Ti and N for the calculation of the element composition in the layer, whereby x+y=1 and 0.45x0.55

18. Aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15, wherein the thin film shows a hardness (H) of 30 GPa measured using instrumented indentation in conformance with ISO 14577-1.

19. Aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15, wherein the thin film shows a reduced Young's modulus (Er) in a range between 350 GPa and 480 GPa measured using instrumented indentation in conformance with ISO 14577-1.

20. Aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15, wherein the thin film shows a compressive stress of more than 2.5 GPa measured using instrumented indentation in conformance with ISO 14577-1.

21. Aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15, wherein the thin film shows a high adhesion of HF 1 even at 5 m coating thickness, wherein this high adhesion in particular resulting from the deposition of the thin film by the combination of using ceramic targets and arc discharge.

22. Aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15, wherein the aluminum-rich Al.sub.XTi.sub.1-XN-based thin film is formed as a multilayer film, comprising a plurality of aluminum-rich Al.sub.XTi.sub.1-XN-based thin films deposited one above the other.

23. Aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15, wherein the thin film has an aluminium content of X75.

24. Aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15, wherein the layer thickness is >500 nm.

25. Use of an aluminium-rich Al.sub.xTi.sub.1-xN-based thin film according to claim 15 for manufacturing a coated tool or a coated component, especially a coated cutting tool or a coated forming tool or a coated turbine component or a coated component to be used in wear resistant applications.

Description

FIGURES

[0071] FIG. 1: SEM fracture cross-section image of the hard cubic Al-rich AlTiN coating film deposited according to the inventive Example 1

[0072] FIG. 2: SEM fracture cross-section image of the hard cubic Al-rich AlTiN coating film deposited according to the inventive Example 1

[0073] FIG. 3: X-ray patters of as-deposited hard cubic Al-rich AlTiN coating film deposited according to the inventive Example 1 and Example 2.

[0074] FIG. 4: SEM fracture cross-section image of the Al-rich AlTiN coating film deposited according to the comparative Example 3.

[0075] FIG. 5: SEM fracture cross-section image of the Al-rich AlTiN coating film deposited according to the comparative Example 4

[0076] FIG. 6: SEM fracture cross-section image of the Al-rich AlTiN coating film deposited according to the comparative Example 5

[0077] FIG. 7: X-ray patters of as-deposited Al-rich AlTiN coating film deposited according to the comparative Example 3.4, and 5.

[0078] FIG. 8: Ceramic target adapted for reliable operation as cathode in a cathodic arc deposition source.

[0079] FIG. 9: X-SEM (a), and coating resistance to flaking under HRC indention(b) of inventive coating coatings (#2620, and #3007), and comparative (#2301) coating.

[0080]

TABLE-US-00001 TABLE 1.1 Coating process parameters used by inventive examples Ceramic target Arc current N.sub.2 Deposition Inventive composition Temperature at target pressure Bias time Examples [at %] [ C.] [A] [Pa] voltage [min] 1 Al.sub.0.385Ti.sub.0.115N.sub.0.5 300 80 0.15 120 V 300 2 Al.sub.0.385Ti.sub.0.115N.sub.0.5 300 200 0.20 120 V 180

TABLE-US-00002 TABLE 1.2 Coating properties of hard cubic Al-rich AlTiN layers produced by inventive examples Structure Reduced growth/ Hard- Young's Inventive Al Ti N crystalline ness modulus Examples [at %] [at %] [at %] phase [GPa] [GPa] 1 36.44 11.76 51.8 Mainly 41 3 410 15 columnar/ fcc 2 36.81 11.56 51.63 non- 37 2 377 15 columnar/ fcc

TABLE-US-00003 TABLE 2.1 Coating process parameters used by comparative examples Metallic target Arc current N.sub.2 Deposition Comparative composition Temperature at target pressure Bias time Examples [at %] [ C.] [A] [Pa] voltage [min] 3 Al.sub.75Ti.sub.25 200 200 1.50 120 V 140 4 Al.sub.75Ti.sub.25 200 200 2.00 120 V 140 5 Al.sub.75Ti.sub.25 200 200 2.50 120 V 140

TABLE-US-00004 TABLE 2.2 Coating properties of hard cubic Al-rich AlTiN layers produced by comparative examples Structure Reduced Compar- Al Ti N growth/ Young's ative [at [at [at crystalline Hardness modulus Examples %] %] %] phase [GPa] [GPa] 3 37 12.5 51 non- 32.2 2 295 8 columnar/ mix of cubic and hexagonal 4 36.6 13.5 50 non- 34.9 2 290 9 columnar/ mix of cubic and hexagonal 5 36.6 13.4 50 Columnar .sup.40 2 383 9 and cubic

[0081] The film structural analyses were conducted by X-ray diffraction (XRD) using a PANalytical X'Pert Pro MPD diffractometer equipped with a CuKa radiation source. The diffraction patterns were collected in Bragg-Brentano geometry. Micrographs of the film fracture cross-sections were obtained with a FEGSEM Quanta F 200 Scanning Electron Microscope (SEM).

[0082] The hardness and indentation modulus of the as-deposited samples were determined using an Ultra-Micro-Indentation System equipped with a Berkovich diamond tip. The testing procedure included normal load of 10 mN. The hardness values were evaluated according to the Oliver and Pharr method. Thereby, we assured an indentation depth of less than 10% of the coating thickness to minimize substrate interference.

[0083] As shown in Table 1.2 shows a mainly columnar microstructure, but with at least 1 wt-% non-columnar microstructure, already allowing a facilitated coating.

FIGURES

[0084] FIG. 1: SEM fracture cross-section image of the hard cubic Al-rich AlTiN coating film deposited according to the inventive Example 1

[0085] FIG. 2: SEM fracture cross-section image of the hard cubic Al-rich AlTiN coating film deposited according to the inventive Example 1

[0086] FIG. 3: X-ray patters of as-deposited hard cubic Al-rich AlTiN coating film deposited according to the inventive Example 1 and Example 2.

[0087] FIG. 4: SEM fracture cross-section image of the Al-rich AlTiN coating film deposited according to the comparative Example 3.

[0088] FIG. 5: SEM fracture cross-section image of the Al-rich AlTiN coating film deposited according to the comparative Example 4

[0089] FIG. 6: SEM fracture cross-section image of the Al-rich AlTiN coating film deposited according to the comparative Example 5

[0090] FIG. 7: X-ray patters of as-deposited Al-rich AlTiN coating film deposited according to the comparative Example 3.4, and 5.

[0091] FIG. 8: Ceramic target adapted for reliable operation as cathode in a cathodic arc deposition source.

[0092] FIG. 9: X-SEM (a), and coating resistance to flaking under HRC indention(b) of inventive coating coatings (#2620, and #3007), and comparative (#2301) coating.

[0093] To produce inventive Al-rich AlTiN-based film and a tunable microstructure, the inventors used an arc deposition process on an insulating ceramic targets with minimum of 70 at % of Al in relation to the Ti content, in which the inventive combination of the deposition parameters were selected based on the following understanding: [0094] a) at target: Arc discharge current, distribution and strength of the magnetic field are chosen to form the desired plasma state of film forming species, consisting of single and multiple charges ions of Al, Ti, and N, wherein the Arc current is varied between 80 A and 200 A to switch the microstructure between columnar and noncolumnar structure. [0095] b) at substrate: Bias voltage is high enough to increase the kinetic energy, thereby increasing the quench rate of incident ions at the thin film growth front. Simultaneously, substrate temperature is low enough to freeze the ad-atom mobility on the growth front. [0096] c) general: Nitrogen gas pressure is manipulated within the desired window, that is low enough to reduce the population of nitrogen ions, there by supressing the nucleation of hexagonal phase enabled by gas ion induced remixing effects on the growth surface, and the nitrogen gas pressure is sufficiently high enough to form stoichiometric AlTiN thin film.

[0097] By optimizing the abovementioned process levers of the arc deposition, nucleation of thermodynamically favoured hexagonal phase is supressed at the growth surface, and there by the metastable solubility of Al in the c-AlTiN has been raised to higher concentration with more than 75 at. % (e.g. 80 at. %). Furthermore, surprisingly, the microstructure could be tuned between columnar and non-columnar while retaining single phase cubic solid solution.

Particular Advantages of the Present Invention

[0098] The present invention provides a method which allows: [0099] Synthesis of stochiometric and cubic Al-rich AlTiN thin films by Arc evaporation of ceramic targets with composition of Al.sub.77Ti.sub.23N or even comprising a higher content of Al in relation to Ti, e.g. till a composition of Al.sub.90Ti.sub.10N. [0100] Selecting parameters for stable arc discharge of ceramic targets with more than 70% vol fraction of semiconducting AlN by using a nitrogen gas pressure less than 0.2 PaGenerally, under such low gas pressure, is difficult to maintain a smooth arc movement, but ceramic targets used according to the present invention facilitate low pressure operation. [0101] Synthesis of both columnar, and non-columnar cubic phase solid solution with a composition of Al.sub.77Ti.sub.23N or even comprising a higher content of Al in relation to Ti, e.g. till a composition of Al.sub.90Ti.sub.10N. [0102] Synthesis of Al-rich AlTiN films processed via ceramic targets, which show a superior resistance to HRC indentation induced flaking compared to thin films processed via metallic targets. [0103] Arc discharge of insulating ceramic targets for producing coatings with composition of AlTiN comprising a content of AlN>75 mol %, wherein the deposition is possible by using a wide range of Arc currents between 80 A and 200 A and maintain a stable Arc discharge at low gas pressure of less than 0.2 Pa. [0104] Synthesis of AlTiN with cubic structure and content of AlN>75 mol %, in both columnar and non-columnar microstructures, and even as a modulated layer of columnar and non-columnar structures. [0105] Synthesis of AlTiN with cubic structure and content of AlN>75 mol % in both columnar and non-columnar microstructures, deposited by Arc evaporation from insulating ceramic targets, the deposited coating exhibiting very good adhesion to the substrate (HF 1) in spite a high compressive stress of even 5 GPa, and high thickness of even 5 m.