CA2600097A1 - Physical vapour deposition process for depositing erosion resistant coatings on a substrate - Google Patents

Abstract

An improved process of coating a substrate by physical vapour deposition with a coating selected from the group consisting of MAIN and MN, wherein M is selected from the group consisting of Ti, Cr and Zr, the process comprising (i) loading the substrate in a vacuum chamber (ii) locating at least one metallic cathode selected from the group consisting of M and MAI within the vacuum chamber; (iii) providing the vacuum chamber with a nitrogen gas atmosphere; and (iv) vapourizing the cathode in the nitrogen atmosphere; the improvement comprising setting the total cathode current ratios to a desired value, and applying a negative bias voltage selected from -75V to -10V to the substrate during the vapourizing step (iii).

Description

PHYSICAL VAPOUR DEPOSITION PROCESS FOR DEPOSITING
EROSION RESISTANT COATINGS ON A SUBSTRATE
FIELD OF THE INVENTION

This invention relates to processes that improve service life and durability of machine components; to repair of components and reconstitution of their properties;
and particularly to gas turbine blades and vanes; and primarily to coatings applied to metal surfaces of aircraft engine compressor blades and vanes.

BACKGROUND OF THE INVENTION

Ingested airborne solid particles, such as sand, grit and the like, can cause severe erosion damage to machine components, particularly, aircraft engine compressor blades and other components which could lead to engine structural deterioration and failure. W.
Tabakoff, "Surface and Coating Technology", 39-40, (1989) 371 and D. Garg, P.
N. Dyer, "Wear" 162-164 (1993) 552 disclose that solid particles ingested by turbine engines hit the compressor blades at various impact angles and velocities. It is known that a high coating hardness and fracture toughness is required to resist particle erosion at over a wide range of impact angles, and that an excellent erosion performance is achieved by a good combination of high hardness and good fracture toughness.
Nitride coatings have been applied for wear protection of cutting tools and solid particle erosion protection of metal parts, such as for above turbine compressor blades and vanes. It is known, for example, from U.S. Patent No. 6,797,335, issued September 28, 2004 to Paderov et al and U.S. Patent No. 4,904,542, issued February 27, 2000 to Mroczkowski that an improvement in particle erosion resistance at high impact angles can be achieved by the deposition of alternating layers of metallic and ceramic materials. While most of the research and patents on nitride coating have been focused on multilayer wear and solid particle erosion resistance coating systems, limited efforts have been devoted to the manufacture of single layer multi-nitride coatings, although the manufacture of single layer coatings is simpler and, accordingly, more cost-effective.

I

Modern turbine compressors spin at very high angular velocities of 40,000 rpm and higher. At that high rotational speed, the ingested airborne solid particles impinge at the airfoil leading edge at very high velocities and transfer significant part of their momentum to the airfoil. Under these conditions, the geometry of the leading edge is distorted, which is termed the Leading Edge Curl Effect. This effect leads to the deterioration in engine performance, increase in fuel consumption and compressor overhaul frequency.
Modern turbine compressors also work at elevated temperatures. For example, H.A.
Jehn et al. in Thin Solid Films Vol. 153 (1987) pp. 45 report that TiAIN
coatings have a very good high temperature oxidation resistance due to the formation of protective A1203 layer on the coating's surface which suppresses oxygen diffusion. W.-D. Minz, Journal of Vacuum Science and Technology, A4 (6) (1986) pp. 2117 reports that the oxidation temperature of TiAIN coatings can reach 700-800 C. X.Z Ding et al. in Surface and Coatings Technology Vol. 200 (2005) pp. 1372 and O. Banakh et al. in Surface and Coatings Technology Vol. 163 (2003) pp. 57 report that CrAIN exibits even higher oxidation resistance than TiA1N.
United States Patent No. 4,904,528 - United Technologies Corporation, issued February 27, 1990, describes coated gas turbine engine hardware comprising a titanium alloy substrate having a coating thereon consisting essentially of titanium nitride wherein the ratio of nitrogen to titanium is greater than one. Such coatings have a residual compressive stress state which aids in minimizing the fatigue debit which would otherwise result from the use of a hard coating on a titanium substrate. Coatings are applied by the use of a vacuum arc deposition process.
United States Patent No. 4,904,542 - Midwest Research Technologies, Inc., issued February 27, 1990, describes an erosion and corrosion resistant coating formed of a plurality of alternating layers of metallic and ceramic materials. The two materials selected for the layers have complementary wear resistant characteristics, such that one is relatively ductile and the other is relatively brittle. The concentration of the two materials at the interface between adjacent layers is graded to improve the adhesion of the layers and to provide a more unified coating. Preferably radio-frequency sputtering is employed to deposit the coating.
United States Patent No. 6,033,768 - Hauzer Industries BV, issued March 7, 2000, describes ternary hard material layers to which a small proportion of yttrium is added to increase the resistance to wear at elevated temperatures, are manufactured by means of one of cathodic arc evaporation, sputtering, combination processes of sputtering/cathodic arc

2 evaporation, sputtering/low voltage electron beam evaporation, or low voltage evaporation/cathodic arc evaporation. The hard material coatings consist substantially of: a hard material layer of a binary, ternary or quaternary TiAI based multicomponent hard material layer comprising nitride or carbonitride with an Al-content of 10 to 70 at %, wherein the layer contains about 0.1 to 4 at % yttrium unevenly distributed over the entire hard material layer in a growth direction of the coating.
United States Patent No. 6,309,738 B 1- OSG Corporation, issued October 30, 2001, describes a hard multilayer coated tool including: (a) a substrate; and (b) a multilayer coating covering the substrate, the multilayer coating comprising first and second coating layers which are alternately laminated on the substrate, each of the first coating layers has an average thickness of 0.10 - 0.50 m and coatings titanium therein, each of the second coating layers has an average thickness of 0.10 - 0.50 pm and contains aluminum therein, the multilayer coating having an average thickness of 0.50 - 10.0 m.
United States Patent No. 6,797,335 B1 - Paderov, A. N. et al., issued September 28, 2004, describes a method for depositing wear-resistant coatings on metal surfaces of machine components and articles to improve service life of parts and to reshape geometrical size of parts during repair, the method comprises (i) providing an ion-plasma deposition chamber;
(ii) locating as an anode said machine components or articles being treated inside said ion-plasma deposition chamber; (iii) locating in said chamber cathodes made from the Group IVB-VIB metals and/or alloys thereof; (iv) establishing in said chamber a gas atmosphere wherein the gas is selected from the group consisting of inert or non-inert gases and mixtures thereof; (v) effecting, whenever necessary, ion cleaning of surfaces of said machine components or articles; (vi) effecting selective ion-plasma deposition of at least three layers of a coating, wherein: at least one layer (a) consists of said metals, mixtures thereof or substitution alloys, said at least one layer having a thickness of 0.02 - 5 microns, a second layer (b) consists of interstitial solid solutions of nonmetallic atoms of nitrogen, carbon, and boron in said Group IVB-VIB metals, said second layer having a thickness of 0.4 - 10 microns, and a third layer (c) consists of chemical compounds of interstitial chases of said Group IVB-Group VIB metals with nonmetals in the form of nitrides, carbides, borides and mixtures thereof, said third layer having a thickness of 0.1 - 12.5 microns, wherein said first second and third layers have thickness ratios of about 1:2:2.5 respectively;
(vii) subjecting one or more of said layers to treatments by implanting thereinto non-metallic ions

3 simultaneously with the step of effecting ion-plasma deposition, said non-metallic ions selected from the group consisting of argon, nitrogen, carbon or boron ions;
and (viii) cooling and unloading said machine components or articles from said chamber.
United States Patent No. 7,160,635 B2 - Sheffield Hallam University (GB), issued January 9, 2007, describes coatings for the protection of substrates operating at moderately elevated temperatures, and, more particularly, for the protection of titanium-alloy aircraft and stationary gas turbine components as well as engine components for automotive applications, articles having such coatings and a method for their production.
United States Patent No. 7,211,138 B2 - Kobe Steel, Ltd., issued May 1, 2007, describes a hard film formed of a material having composition indicated by a chemical formula: (TiaAlbV SidBf) (C1,Ne), in which subscripts a, b, c, d, f and e indicate atomic ratios of Ti, Al, V, Si, B and N, respectively, and meet relational expressions: 0.02 <a<0.5, 0.4<b_<0.8, 0.05<c, 0<d<0.5, 0<f<0.1, 0.01<d+f<0.5, 0.5<e_<l and a+b+c+d=1.
The hard film is harder than and more excellent in wear resistance than TiAIN films and conventional (TiAIV) (CN) films.
United States Patent No. 7,217,466 B2 - Joerg Guehring, issued May 15, 2007, describes a wear-resistant coating on rotary metal-cutting tools such as drill bits, countersinks, milling cutters, screw taps, reamers, etc. The coating consists essentially of nitrides of Cr, Ti and Al with an unusually high share of Cr atoms, namely 30 to 60% referred to the totality of metal atoms. In multilayer coatings and even more in coatings made of homogeneous mixed phases, this high Cr share results in particularly large tool life distances for the tools hardened with these coatings.
United States Patent No. 7,226,659 B2 - Mitsubishi Heavy Industries, Ltd., issued June 5, 2007, describes a high wear resistant hard film having a coating layer consisting of a metal nitride, which is formed on the outside surface of an object to be treated; a substrate layer consisting of a nitride of Ti or Cr, which is provided between the coating layer and the object to be treated; and an intermediate layer containing compositions of the coating layer in contact with the intermediate layer and the substrate layer, which is provided at an interface between the coating layer and the substrate layer. A tool is provided with the film. The hard film has excellent oxidation resistance even at 1000 C. or higher and also has very high wear resistance.

4 United States Patent No. 7,226,670 - OC Oerlikon Balzers AG, issued June 5, 2007, describes a work piece or structural component coated with a system of film layers at least one of which is composed of AlyCr, _yX , where X = N, C, B, CN, BN, CBN, NO, CO, BO, CNO, BNO or CBNO, with the composition within the film being either essentially constant or varying over the thickness of the film, continually, or in steps, as well as a process for producing it.
However, there is still a need to provide coatings protective to particle impact at different velocities and impinging angles and that offer an adequate protection, particularly, to the leading and trailing edges of an airfoil and, at the same time, possessing high temperature oxidation resistance.

SUMMARY OF THE INVENTION -It is an object of the present invention to provide a Physical Vapour Deposition process that produces metallic coated substrates having improved particle erosion resistance, particularly at relatively high impact angles of the erodent to the surface of the substrate.
It is a further object to provide apparatus for carrying out said process.
It is a further object to provide a coated substrate made by said process.
Accordingly, in one aspect the invention provides an improved process of coating a substrate by physical vapour deposition with a coating selected from the group consisting of MAIN and MN, wherein M is selected from the group consisting of Ti, Cr and Zr, said process comprising (i) loading said substrate in a vacuum chamber (ii) locating at least one metallic cathode selected from the grot7p consisting of M
and MAI within said vacuum chamber;
(iii) providing said vacuum chamber with a nitrogen gas atmosphere; and (iv) vapourizing said cathode in said nitrogen atmosphere; the improvement comprising;
(v) setting the total cathode current ratios to a desired level; and (vi) applying a negative bias voltage selected from -75V to -I OV to said substrate during said vapourizing step (iii).

5 Preferably, in one aspect the invention provides a process wherein said negative bias voltage is selected from -30V to -IOV.
Thus, the present invention provides a process that provides a single layer or a plurality of nanolayered particle erosion resistant coatings which provides a single layer or nanolayered coating that significantly improves the particle erosion resistance at relatively high angles;
provides a single layer or nanolayered particle erosion resistant coatings that resist coating chipping and flaking from the sharp edges of an airfoil;
provides a particle erosion resistant coating having a relatively high temperature oxidation resistance;
produces said coatings by Physical Vapour Deposition (PVD) on heat-treated metal parts, without affecting the substrate mechanical properties.
To achieve the above mentioned objectives a single layer of a MAIN or a nanolayered coating structure containing MN and MAIN, wherein M is selected from Ti, Cr or Zr, is deposited on a metal substrate by PVD techniques, such as Cathodic Arc, DC or AC
magnetron sputtering, Ion Beam Sputtering and the like.
The invention provides methods for producing the particle erosion coatings comprising the following steps:
= Ex-situ substrate preparation;
= Loading the substrate in a vacuum chamber containing M and/or MAI (where M
is Ti, Cr or Zr) cathodes, turntable with turning satellites and inlets for a nitrogen containing gas mixture;
= Pumping down the chamber to a required base pressure;
= In-situ surface cleaning by energetic particle bombardment;
= Vaporization of MAI or co-vaporization of M and MAI (where M is Ti, Cr or Zr) in nitrogen containing gas atmosphere to form a single or nanolayered coating structure;
= Control of the coating microstructure by applying a negative Bias Voltage to the substrate.
To control the coating microstructure that allows improved erosion resistance at high angles and good sharp edge coverage the range of the applied negative bias voltage varies from -75V to -IOV, preferably between -30V and -IOV.

6 The working nitrogen partial pressure during deposition can be between 8.Oxl0-3Torr to 2.5x10-2 Torr, preferably between 1.1x10-2 Torr and 2.0x10-2 Torr.
The coatings applied by the process according to the invention are most valuable when the substrate is selected from titanium, iron, nickel, cobalt, manganese, copper, aluminum and molybdenum. Examples of commercially available composite substrates include stainless steel special alloys, such as, AM350TM and 17-4PHTM, nickel-chromium alloys, such as, Inconel 718TM, and titanium alloys, such as, 6A1-4V.
Preferably, the invention provides a process as hereinabove defined wherein said coating comprises MAIN or MN having a thickness selected from 10-100 microns.
Further, the invention provides a process as hereinabove defined wherein said coating comprises a plurality of alternating nanolayers of MN and MAIN, wherein each of said nanolayers has a thickness selected from 3 to 50 nanometers.

BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be better understood, preferred embodiments will now be described, by way of example, only, with reference to the accompanying drawings wherein Fig. 1 is a diagrammatic cross-section of a coated substrate made by a process according to the present invention;
Fig. 2 represents an X-ray diffraction pattern of a coated substrate according to the invention;
Figs. 3, 4 and 5 are block diagrams of comparative erosion-testing results represented as the mass loss versus the mass of erodent blasted;
Fig. 6 is a diagrammatic horizontal cross-section of a Steered CA PVD
apparatus of use in the practice of the present invention;
Fig. 7 is a diagrammatic horizontal cross-section of an alternative Steered CA
PVD
apparatus of use in the practice of the invention; and wherein the same numerals denote like parts.

7 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. I shows generally as 10, a coated stainless steel (AM350) substrate 12 having a single layer of TiA1N 14 bonded to substrate 12 through a bonding layer 16 initially formed for providing better adhesion between layers 12 and 14.
Fig. 2 represents an XRD pattern of a TiA1N layer and shows it to have mainly a face-centred cubic TiN solid solution phase with grain sizes of about l Onm. XRD
also shows that wurtzite A1N is present.
It is known that a high coating hardness and fracture toughness is required to resist particle erosion at a wide range of impact angles. An excellent erosion performance is achieved by a good combination of high hardness and good fracture toughness.
The latter can be achieved by a careful selection of the coating composition and control of the coating microstructure by choosing optimal deposition parameters. In the practice of the present invention, it has been found that the layer coating structures deposited at low bias voltage exhibits increased fracture toughness and at the same time retains a high hardness value. The unique structure also acts as a crack inhibitor by retaining the crack propagation and results in a higher erosion resistance at large impact angles and an increased leading and trailing edge protection of a substrate.
Figs. 3, 4 and 5 illustrate comparative erosion-testing results with TiA1N
where the mass loss is plotted versus the mass of A1203 erodent blasted. The A12O3 powder had an average particle size of 50 m and a A12O3 particle velocity of 180-200 m/s was used. The erodent - air ambient flux was directed towards the testing substrate part at an impact angle of 20 or 60 relative to the substrate surface plane (Fig. 5). The weight lost of the tested material (TiA1N or AM350) was measured after every 250g and 50g of erodent blasted at an erodent flux angle 20 or 60 . A total of 1 Kg for 20 and 150g of erodent for 60 was blasted during each test. The erosion improvement is defined as the mass loss of the coating divided by the mass loss of the uncoated stainless steel substrate AM350 substrate at one and the same amount of erodent blasted.

Thus, Fig. 3 shows a mass loss of a TiAIN coating at an impact angle of 60 and Fig.
4 at an impact angle of 20 . Fig. 5 shows the erosion improvement over bare stainless steel AM350.

8 Example 1 Fig. 6 shows generally as 20 a Steered Cathodic Arc coating apparatus having a vacuum chamber 22 within housing 24, a high vacuum pump 26, a turntable 28 having a plurality of turning satellites 30 for holding AM350 substrate samples 32, and a trio of cathodes 34. Housing 24 has a nitrogen purge source 36. Each of cathodes 34 is formed of an alloy of 33 atomic % Ti and 67 atomic % of Al, and arranged in a plane on one of chamber 24 vertical sides 38.
The general process steps comprise the following steps.
(i) Preparation of the AM350 substrates and subsequent loading on satellites 30;
(ii) Evacuation of atmosphere in chamber 22 to desired base pressure level by pump 26;
(iii) Energetic particle bombardment of surface of substrate 32;
(iv) Passing N2 gas into chamber 22 to desired pressure;
(v) Vapourizing TiAl from cathodes 34 to form a single layer of TiA1N on substrate 32, in this embodiment, under control to provide the desired microstructure of the applied negative bias voltage, selected from -75V to -IOV, preferably between -30V and -I OV. The working nitrogen partial pressure during deposition is selected from 8.0 x 10-3 Torr to 2.5 x 10-2 Torr, and preferably between 1.0 to 2.0 x 10-2 Torr.
The aforesaid process is used preferably to deposit a single coating layer of TiAIN, and had the main process conditions listed in Table 1.
Table 1 Parameter Preferred Value Units N2 Pressure 1.1 - 2x10"Z Torr Bias Voltage 15 V
Number of TiAI 33/67 3 at% cathodes Total Cathode Current 300 Amps for TiAI cathodes Temperature 420-450 C
Coating Thickness 18-20 m Cathodes Sizes 10 lcm

9 Example 2 An alternative embodiment of the apparatus, shown generally as 50 in Fig. 7, has a vacuum chamber 52 with housing 54, high vacuum pump 26, turntable 28, turning satellites 30, AM350 substrates 32, and nitrogen inlet 36.
In this embodiment for producing a plurality of alternating nanolayers constituting the coating on substrate 32, the cathodes consist of two TiAI (33 atomic % Ti:67 atomic % Al) alloy cathodes on distinct wall surfaces 56 and 58 of housing 24, and a single Ti cathode 60 on wall 62, all cathodes were arranged in a horizontal plane.
The general process of operation is analogous to that given under Example 1 and wherein co-vaporization of Ti and TiAl is selected to control the relative nanolayer thicknesses by selecting appropriate table rotation speed, cathode current ratio and nitrogen partial pressure.

The main process parameters are given in Table II.
Table II
Parameter Preferred Value Units N2 Pressure 1.7 - 2.0 x 10"2 Torr Bias Voltage 25 V
Number of pure Ti cathodes I
Cathode Size 7 Cm Number of TiA133/67 at% 2 cathodes Cathode Current for Ti 50 A
Total Cathode Current for TiAI 200 A
Temperature 280-350 C
Coating Thickness 18-20 m As described hereinabove, the erosion tests were performed using A1203 powder as erodent with an average particle size of 50 m. The mass loss and erosion improvement for the single and nanolayered coatings deposited in Examples I and 2, respectively are presented in Table 3 and compared with the particle erosion results from an uncoated stainless steel AM350 substrate. The mass loss, measured in mg, and erosion improvement were compared for impact angles 20 and 60 . The improvement was calculated by dividing the are AM350 substrate mass loss to the coating's mass loss before the coating's breakthrough at 150g and 1000g of erodent blasted for the erosion test at 60 and 20 , respectively.

Tested Part 20 impact angle 60 impact angle Mass Loss, mg Improvement Mass Loss, mg Improvement Bare AM350 1134 1 96 1 Example 1 11.0 103.1 4.5 21.3 Example 2 12.0 94.5 4.8 20.0 Although this disclosure has described and illustrated certain preferred embodiments of the invention, it is to be understood that the invention is not restricted to those particular embodiments. Rather, the invention includes all embodiments, which are functional or mechanical equivalence of the specific embodiments and features that have been described and illustrated.

Claims (15)

Claims:

1. An improved process of coating a substrate by physical vapour deposition with a coating selected from the group consisting of MAIN and MN, wherein M is selected from the group consisting of Ti, Cr and Zr, said process comprising (i) loading said substrate in a vacuum chamber (ii) locating at least one metallic cathode selected from the group consisting of M
and MAI within said vacuum chamber;
(iii) providing said vacuum chamber with a nitrogen gas atmosphere; and (iv) vapourizing said cathode in said nitrogen atmosphere; the improvement comprising (v) setting the total cathode current ratios to a desired value, and (vi) applying a negative bias voltage selected from -75V to -10V to said substrate during said vapourizing step (iv).

2. A process as claimed in claim 1 wherein said negative bias voltage is selected from -30V to -10V.

3. A process as claimed in claim 1 or claim 2 wherein said coating comprises MAIN or MN having a thickness selected from 10-100 microns.

4. A process as claimed in claim 1 or claim 2 wherein said coating comprises a plurality of alternating nanolayers of MN and MAIN, wherein each of said nanolayers has a thickness selected from 3 to 50 nanometers.

5. A process as claimed in claim 4 wherein the thickness of said plurality of alternating nanolayers is selected from 10 microns to 100 microns.

6. A process as claimed in any one of claims 1 to 5 wherein M is titanium.

7. A process as claimed in any one of claims 1 to 5 wherein M is chromium.

8. A process as claimed in any one of claims 1 to 7 wherein said physical vapour deposition process is selected from steered cathodic arc, DC or AC magnetion sputtering, and ion beam sputtering.

9. A method as claimed in any one of claims 1 to 6 wherein said TiAl cathode has a composition ratio of Ti:Al within the range 33:67 atomic % to 50:50 atomic %.

10. A method as claimed in any one of claims 1 to 5 wherein said CrA1 cathode has a Cr:A1 composition ratio within the range 21:79 atomic % to 50:50 atomic %.

11. A process as claimed in any one of claims 1 to 10 wherein said nitrogen atmosphere is selected from the group consisting of pure nitrogen and an inert gas-nitrogen mixture wherein said inert gas is selected from helium, argon and zenon.

12. A process as claimed in any one of claims 1 to 11 wherein said substrate is selected from the group consisting of titanium, iron, nickel, cobalt, manganese, copper, aluminum, molybdenum and alloys thereof.

13. A process as claimed in any one of claims 1 to 12 wherein said cathode current ratio is the ratio selected from between (i) Ti and TiA1, (ii) Ti and CrA1, (iii) Cr and TiA1 and (iv) Cr and CrA1 total cathode currents.

14. A process as claimed in claim 13 wherein said cathode current ratio is selected from the range 0 to 0.5.

15. A coated substrate when made by a process as claimed in any one of claims 1 to 14.