WO2022084519A1

WO2022084519A1 - Tunable multifunctional carbon-based coatings

Info

Publication number: WO2022084519A1
Application number: PCT/EP2021/079373
Authority: WO
Inventors: Stéphane Lucas; Emile HAYE; Jean-Jacques Pireaux
Original assignee: Université De Namur
Priority date: 2020-10-23
Filing date: 2021-10-22
Publication date: 2022-04-28

Abstract

The present invention concerns a coating comprising based on the total amount of atoms in said coating: from 0.5 at. % to 50.0 at. % of at least one metal element which is homogeneously dispersed in at least one hydrogenated amorphous carbon matrix. Said coating is amorphous and has no phase separation between said at least one metal element and said matrix as determined by transmission electron microscopy (TEM) with a resolution of 0.5 nm.

Description

Tunable multifunctional carbon-based coatings

Field of the invention

The present invention relates to carbon-based coating and more specifically to carbon-based coatings comprising a homogeneously dispersed metal, displaying improved mechanical, tribological, corrosion and/or electrical properties, while retaining these properties upon mechanical deformation and displaying isotropic elongation.

Background of the invention

Metal corrosion is the process by which a metal is oxidized by the action of a corrosive media such as an acid. In many fields of technology, it is often necessary to use anticorrosion coatings in order to protect a particular article from corrosion.

For example in fuel cells and particularly for bipolar plates, a corrosionresistant coating is usually necessary in order to avoid degradation of the bipolar plates and maintain the efficiency of the fuel cell.

In addition to anti-corrosion properties, it is often necessary that the coating displays good mechanical and tribological properties.

Carbon-based coatings have attracted much attention due to their interesting mechanical, tribological, and anti-corrosion properties.

CN102560396A discloses a metal substrate that is coated with a first layer of metal chromium. The metal chromium is also coated with a first layer which contains carbon and 96% - 99% of chromium. The first layer is coated with a second layer containing carbon and 80%-90% of chromium. While the document discloses corrosion-resistant properties, it remains silent regarding other properties and their retention after isotropic elongation.

Despite the efforts made towards the development of new materials to improve the properties of carbon-based coatings, several challenges remain.

First of all, it remains a challenge to provide a coating in which antagonist properties, i.e. high corrosion resistance/reasonable price, high decorative standards/coating on complex shape substrate, low friction/flexibility are combined. Moreover, it is also challenging to provide a coating displaying isotropic elongation.

In view of the above, there is still a need for improved materials wherein said materials combine excellent mechanical, tribological, corrosion, and/or electrical properties while retaining these properties upon elongation and displaying isotropic elongation.

Summary of the invention

The inventors have now found that it is possible to provide coatings and coated articles fulfilling the above-mentioned needs.

Thus, there is now provided a coating comprising based on the total amount of atoms in said coating: from 0.5 at. % to 50.0 at. % of at least one metal element which is homogenously dispersed in at least one hydrogenated amorphous carbon matrix [hereinafter, matrix (P)]; wherein said coating is amorphous and has no phase separation between said at least one metal element and said matrix (P) as determined by transmission electron microscopy (TEM) with a resolution of 0.5 nm and wherein the matrix (P) comprises at least 20 at. % and at most 80 at.% of sp2 hybridized carbons and at least 20 at.% and at most 80 at.% of sp3 hybridized carbons based on the total amount of carbons in said coating as measured by XPS..

The present invention also concerns an article comprising a substrate having at least one surface, said surface being in direct contact with the coating according to the present invention.

The present invention also relates to a method of providing said coated article. Detailed description

Thus, the coating according to the present invention comprises based on the amount of atoms in said coating: from 0.5 at. % to 50 at. % of at least one metal element which is dispersed in at least one hydrogenated amorphous carbon matrix [hereinafter, matrix (P)]. Preferably said at least one metal element is homogeneously dispersed in said at least one matrix (P).

As used herein and in the claims, the terms “comprising” and “including” are inclusive and open-ended and do not exclude additional unrecited elements and compositional elements. Accordingly, the terms “comprising” and “including” encompass the more restrictive terms “consisting essentially of” and “consisting of”.

The coating according to the present invention is amorphous.

Within the context of the present invention, the term “amorphous” is intended to denote that the coating according to the present invention does not show any diffraction pattern with diffraction peaks in X-ray diffraction or electron diffraction spectroscopy.

According to the invention, there is no phase separation between said at least one metal element and said matrix (P) as determined by transmission electron microscopy (TEM) with a resolution of 0.5 nm.

In particular, no phase separation is observed because the at least one metal element is finely, more particularly atomically and homogeneously dispersed in the matrix (P). In other words, the at least one metal element cannot be distinguished from the matrix (P) when using TEM with a resolution of 0.5 nm.

Within the context of the present invention, the term “homogenously dispersed” is intended to denote that the at least one metal element is dispersed in the matrix (P) so that when the coating is observed using TEM with a resolution of 0.5 nm, one single phase is observed. For example, this means that when observing the coating using said TEM, phases having different concentrations in metal elements cannot be observed if they are smaller than 0.5nm. This does not exclude the presence of different layers in said coating. For example, the coating according to the present invention may comprise different layers, each layer having a matrix (P) wherein said metal element is homogenously dispersed but wherein the concentration of said metal element may be different than in other layers and wherein each layer may be distinguished using TEM with a resolution of 0.5 nm, for example by observing the cross-section of said coating.

The inventors have surprisingly found that the coating according to the present invention has isotropic elongation properties. This property is related to the amounts of sp2 and sp3 hybridized carbons. Indeed, a too high sp3 hybridized carbon amount leads to the diamond-like behavior namely, a highly isotropic coating, extremely hard but brittle, with poor electrical conductivity. On the opposite, a too high sp2 hybridized carbon amount leads to the formation of graphite-like behavior, namely, really soft with high electrical conductivity but anisotropic behavior (pure graphite is composed of graphene plans, where the conductivity is excellent in the plane direction, but almost null in the out of plane direction). Here, the coatings according to the present invention contain both sp2 and sp3 hybridized carbons in proportions which enables the coating to have good elongation properties in all directions.

In the context of the present invention, a coating displays isotropic elongation if it can withstand high elastic or plastic deformation in x, y, or z direction without delamination, and it keeps its properties (black color, low interfacial contact resistance, corrosion resistance ...) after deformation.

In addition, the coating according to the present invention displays excellent mechanical properties.

Advantageously, the coating has a Young modulus of at least 10 GPa, preferably at least 20 GPa, more preferably at least 30 GPa. If desired, the coating has a Young modulus of at most 300 GPa, or at most 275 GPa, or at most 250 GPa, or at most 200 GPa. Advantageously, the coating has a Young modulus comprised between 10 GPa and 300 GPa, preferably between 20 GPa and 275 GPa, more preferably between 30 GPa and 250 GPa, even more preferably between 30 GPa and 200 GPa. The Young modulus may be measured by any method known by the skilled in the art, for example, the above values were measured by nano-indentation tests based on norm ISO 14577. Moreover, the coating according to the present invention also has good hardness.

Advantageously, the coating has a hardness of at least 100 HV, preferably at least 150 HV, more preferably at least 200 HV. If desired, the coating has a hardness of at most 2500 HV, or at most 2000 HV, or at most 1900 HV.

In a particular embodiment, the coating has a hardness comprised between 100 HV and 2500 HV, preferably between 150 HV and 2000 HV, more preferably between 200 HV and 2000 HV, even more preferably between 200 HV and 1900 HV. The hardness may be measured by any method known by the skilled in the art, for example, the above values were measured according to the nano-indentation test based on norm ISO 14577.

The coating according to the present invention also displays excellent tribological properties.

Advantageously, the coating according to the present invention has a friction coefficient p_cof at most 0.25, preferably at most 0.20, more preferably at most 0.15. If desired, the coating has a friction coefficient p_c of at least 0.10, or at least 0.12.

Advantageously, the coating according to the present invention has a friction coefficient p_c comprised between 0.10 and 0.25, preferably between 0.10 and 0.20, more preferably between 0.12 and 0.20, even more preferably between 0.12 and 0.15. The friction coefficient p_c may be measured by any method known by the skilled in the art, for example, the above values were measured according to a reciprocating ball on disk test taking place for a plastic deformation contact. For an elastic deformation contact, the p_c is as low as 0.02. The coating according to the present invention also displays excellent electrical properties.

Advantageously, the coating according to the present invention has an interfacial contact resistance (ICR) of at most 15 mQ.cm², preferably at most 12 mQ.cm², more preferably at most 10 mQ.cm². If desired, the coating has an interfacial contact resistance (ICR) of at least 1 mQ.cm² or at least 3 mQ.cm² or at least 5 mQ.cm².

Advantageously, the coating according to the present invention has interfacial contact resistance (ICR) comprised between 1 and 15 mQ.cm², preferably between 1 and 12 mQ.cm², more preferably between 1 and 10 mQ.cm², even more preferably between 3 and 10 mQ.cm², even more preferably between 5 and 10 mQ.cm². The ICR may be measured by any method known by the skilled in the art, for example, the above values were measured according to the methodology described in Wang, et al. (Stainless steel as bipolar plate material for polymer electrolyte membrane fuel cells, Heli Wang, Mary Ann, Sweikart, John A Turner, Journal of Power Sources, Volume 1 15, Issue 2, 10 April 2003, Pages 243-251 ) and used by US Department of Energy as a standard test.

The coating according to the present invention also displays excellent resistance to corrosion.

Advantageously, the coating according to the present invention has a corrosion current (l_COrr) comprised of at most 0.2 pA/cm², preferably at most 0.15 pA/cm², more preferably at most 0.1 pA/cm². If desired, the coating has a corrosion current (l_COrr) of at least 0.02 pA/cm² or at least 0.05 pA/cm².

Advantageously, the coating according to the present invention has a corrosion current (l_COrr) comprised between 0.02 and 0.2 pA/cm², preferably between 0.05 and 0.15 pA/cm², more preferably between 0.05 and 0.1 pA/cm². The korr may be measured by any method known by the skilled in the art, for example, the above values were measured by corrosion test in three electrodes cell, in H2SO4 0.6 M at 60°C, with potential vs saturated calomel electrode of 0.48V during 16h.

It was also found by the inventor that the color of the coating has a color ranging from grey to black.

In general, the darkness of a colour can be quantified by using the CIE Lab standard value L* value, as notably defined by the CIE (Commission Internationale de I'Eclairage) in 1976.

CIE L*a*b* (CIELAB) is a colour space specified by the International Commission on Illumination. The L*a*b* colour space includes all perceivable colours, and one of the most important attributes of the L*a*b* colour space is the device independency, meaning that the colours are independent of their nature of creation. The three coordinates of CIELAB represent the lightness of the colour (L* = 0 yields black and L* = 100 indicates diffuse white (specular white might be higher)), its position between red/magenta and green (a*, negative values indicate green, while positive values indicate magenta) and its position between yellow and blue (b*, negative values indicate blue and positive values indicate yellow).

In particular, the coating has an L* value lower than 60, preferably lower than 55, more preferably lower than 50, even more preferably lower than 47.

In particular, the coating has an L* value higher than 20 and lower than 60, preferably higher than 25 and lower than 55, more preferably higher than 30 and lower than 50, even more preferably higher than 30 and lower than 35.

In particular, the coating has an A* value higher than -10 and lower than 10, preferably higher than -7 and lower than 7, more preferably higher than -5 and lower than 4.

In particular, the coating has a B* value higher than -5 and lower than 3, preferably higher than -3 and lower than 2, more preferably higher than -1 , and lower than 0.3. ln a preferred embodiment, the coating has an L* value comprised between 37 and 47 and an A* value comprised between -5 and 4, and a B* value comprised between -1 and 0.3.

Finally, another advantage of the coating according to the present invention is that its properties make it very versatile in its use. Indeed, the coating can be used for applications in storage battery or fuel cell (e.g. deformable conductive coating for electrode, deformable electrodes for proton exchange membranes fuel cells), mechanical field involving sliding contacts (low friction coating), decorative field (colored coating), solar absorber (Infra- Red transparency), water repellent (hydrophobic coating), antimicrobial field (destruction of bacteria).

Metal

Thus, according to the present invention, the coating comprises, based on the total amount of atoms in said coating, from 0.5 at. % to 50.0 at. % of at least one metal element which is dispersed in the at least one matrix (P).

Particularly, the at least one metal element is finely dispersed in said at least one matrix (P), more particularly, the at least one metal element is atomically dispersed in said at least one matrix (P).

In general, the at least one metal element may be in metallic form or in the form of a metal carbide, metal oxide, metal nitride or a combination thereof (e.g. metal oxynitride).

The term “metallic form” is intended to denote a metal having an oxidation state of zero.

In particular, the at least one metal element is selected from the group consisting of Be, Mg, Sr, Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Nd, Mn, Re, Fe, Co, Rh, Ir, Eu, Ni, Pd, Pt, Gd, Cu, Ag, Au, Zn, Cb, B, Al, Ga, In, Ge, Sn, Pb, Te, and Yb and combinations thereof.

In a preferred embodiment of the present invention, the at least one metal element is selected from the group consisting of Be, Mg, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, B, Al, and Ge and combinations thereof.

In a more preferred embodiment of the present invention, the at least one metal element is selected from the group consisting of Ti, Zr, Nb, Cr, Mo, W, Mn, Co, Ag, Au, Zn, B, and and combination thereof.

In a more preferred embodiment of the present invention, the at least one metal element is selected from Cr, W, Ti, and combinations thereof.

Preferably, the coating comprises at least 1 at. %, more preferably at least 1 .3 at. %, even more preferably at least 1 .5 at. %, even more preferably at least 2 at. % of the at least one metal element based on the total amount of atoms in said coating.

It is understood that the coating may preferably comprise at most 40 at. %, more preferably at most 30 at. %, even more preferably at most 20 at. %, even more preferably at most 15 at. % of the at least one metal element based on the total amount of atoms in said coating.

In a preferred embodiment, the coating may comprise at least 1 at. % and at most 40 at.%, preferably at least 1 .3 at.% and at most 30 at.%, more preferably at least 1 .5 at.% and at most 20 at.%, even more preferably at least 2 at.% and at most 15 at.% of the at least one metal element based on the total amount of atoms in said coating.

Matrix (P)

As used herein, the term “Hydrogenated amorphous carbon” is intended to refer to its meaning known in the art, in particular it is known by the skilled in the art as being a special type of diamond-like carbon. More particularly, hydrogenated amorphous carbon matrices comprise aliphatic carbon chains which are at least partially crosslinked and are sometimes described as polymer-like chains.

This being said, the matrix (P) comprises carbon and hydrogen and possibly oxygen and/or nitrogen. Preferably, the matrix (P) comprises hydrogen in a content of at least 5 at. %, preferably of at least 10 at. %, more preferably of at least 20 at. %, based on the total amount of atoms in said coating.

Preferably, the matrix (P) comprises hydrogen in a content of at most 90 at.%, more preferably at most 80 at.%, even more preferably at most 70 at.%, even more preferably at most 60 at.%, even more preferably at most 50 at.%, even more preferably at most 40 at. %, preferably of at most 35 at. %, more preferably of at most 30 at. %, based on the total amount of atoms in said coating.

According to a preferred embodiment of the present invention, the matrix (P) comprises hydrogen in a content of at least 5 at.% and at most 90 at.%, preferably at least 5 at.% and at most 80 at.%, more preferably at least 5 at.% and at most 70 at.%, even more preferably at least 10 at.% and at most 60 at.%, even more preferably at least 10 at.% and at most 50 at.%, even more preferably at least 10 at.% and at most 40 at.%, preferably at least 10 at.% and at most 35 at.%, more preferably at least 20 at.% and at most 30 at.% based on the total amount of atoms in said coating.

Preferably, the matrix (P) comprises carbon in a content of at least 10 at. %, preferably of at least 30 at. %, more preferably of at least 50 at. %, even more preferably at least 60 at. %, based on the total amount of atoms in said coating.

Preferably, the matrix (P) comprises carbon in a content of at most 98 at. %, preferably of at most 80 at. %, more preferably of at most 70 at. %, based on the total amount of atoms in said coating.

It is further understood that the matrix (P) may comprise a carbon content of at most 98 at. %, preferably of at most 80 at. %, more preferably of at most 70 at. %, based on the total amount of atoms in said coating.

If desired, the matrix (P) may comprise carbon in a content of at least 10 at. %, preferably at least 30 at.%, more preferably at least 50 at.%, even more preferably at least 60 at.% based on the total amount of atoms in said coating. According to a preferred embodiment of the present invention, the matrix (P) comprises carbon in a content of at least 10 at. % and at most 98 at.%, preferably at least 30 at.% and at most 80 at.%, more preferably at least 50 at.% and at most 80 at.%, even more preferably at least 60 at.% and at most 70 at.%, based on the total amount of atoms in said coating.

The carbon present in the matrix (P) can be sp1 , sp2 or sp3 hybridized.

Preferably, the matrix (P) comprises at least 20 at.%, more preferably at least 30 at.%, even more preferably at least 35 at.%, even more preferably at least 40 at.%, even more preferably at least 50 at.%, even more preferably at least 60 at. %, preferably of at least 70 at. %, more preferably of at least 80 at. %, more preferably at least 85 at. % of sp2 hybridized carbons based on the total amount of carbons in said coating.

Is it further understood that the matrix (P) may comprise at most 95 at. %, preferably of at most 93 at. %, more preferably of at most 90 at. % of sp2, even more preferably at most 85 at.%, even more preferably at most 80 at.% hybridized carbons based on the total amount of carbons in said coating.

According to a preferred embodiment of the present invention, matrix (P) comprises between 20 at.% and 80 at.%, preferably between 30 at. % and 80 at.%, preferably between 35 at;% and 80 at.%, more preferably between 40 at.% and 80 at.%, even more preferably between 50 at.% and 80 at.%, even more preferably between 65 at. % and 80 at. %, preferably between 70 at. % and 80 at. %, of sp2 hybridized carbon based on the total amount of carbons in said coating.

Preferably, the matrix (P) comprises at most 80 at.%, more preferably at most 70 at.%, even more preferably at most 60 at.%, even more preferably at most 50 at.%, even more preferably at most 35 at. %, more preferably of at most 30 at. %, even more preferably of at most 25 at. % of sp3 hybridized carbons based on the total amount of carbons in said coating.

Preferably, the matrix (P) comprises at least 5 at. %, more preferably of at least 10 at. %, even more preferably of at least 15 at. %, even more preferably at least 20 at.%, even more preferably at least 25 at.%, even more preferably at least 30 at.%, even more preferably at least 35 at.% of sp3 hybridized carbons based on the total amount of carbons in said coating.

According to a preferred embodiment of the present invention, the matrix (P) comprises between 5 at.% and 35 at.%, preferably between 10 at.% and 30 at.%, more preferably between 15 at.% and 30 at.% of sp3 hybridized carbons based on the total amount of carbons in said coating.

According to a preferred embodiment of the present invention, the matrix (P) comprises between 20 at.% and 80 at.%, preferably between 30 at.% and 70 at.%, of sp3 hybridized carbons based on the total amount of carbons in said coating.

If desired, the matrix (P) comprises oxygen in a content of at least 1 at. %, preferably of at least 3 at. %, more preferably of at least 5 at. %, based on the total amount of atoms in said coating.

Is it further understood that the matrix (P) comprises oxygen in a content of at most 25 at. %, preferably of at most 15 at. %, more preferably of at most 10 at. %, based on the total amount of atoms in said coating.

According to a particular embodiment of the present invention, the matrix (P) comprises oxygen in a content of at least 1 at.% and at most 25 at.%, preferably at least 3 at.% and at most 15 at.%, more preferably at least 5 at.% and at most 10 at.% based on the total amount of atoms in said coating.

If desired, the matrix (P) comprises nitrogen in a content of at least 0.1 at. %, preferably of at least 0.5 at. %, more preferably of at least 1 at. %, based on the total amount of atoms in said coating.

Is it further understood that the matrix (P) comprises nitrogen in a content of at most 30 at. %, preferably of at most 20 at. %, more preferably of at most 10 at. %, based on the total amount of atoms in said coating.

According to a preferred embodiment of the present invention, the matrix (P) comprises nitrogen in a content of at least 0.1 at.% and at most 30 at.%, preferably at least 0.5 at.% and at most 20 at.%, more preferably at least 1 at.% and at most 10 at.% based on the total amount of atoms in said coating.

Measurement of the atomic percentages of metal, carbon, oxygen, and nitrogen by XPS

It is understood that within the context of the present invention the atomic percentages of said at least one metal, the atomic percentages carbon, the atomic percentages oxygen, and the atomic percentages nitrogen as mentioned above and in the claims are measured by X-ray photoelectron spectroscopy (XPS). Preferably, the coatings according to the present invention are profiled using a monoatomic Ar⁺ beam working at 2 keV and 10 pA, on a K-Alpha Thermo Scientific spectrometer (Al Ka radiation 1486.68 eV) with a spot size of 250x250 pm, and raster size of 1.25x1 ,25mm. To generate the profile, ten snapshots of Cr 2p, N 1 s, O 1 s, C 1 s, and Si 2p levels have been recorded after every etch step (8 s, approximately 2 nm), at a pass energy of 150 eV. Then, the concentration of each species is derived from the spectrum area of the scan, after subtraction of a Shirley background.

Measurement of the atomic percentages of sp2 and sp3 hybridized carbons by XPS

It is understood that within the context of the present invention, the atomic percentages of sp3 and sp2 hybridized carbons based on the total amount of carbons in said coating are determined by XPS, preferably by XPS with the method as described in “Controlled modification of mono- and bilayer graphene in O2, H₂ and CF4 plasmas, Felten et aL, Nanotechnology 24, 35, 355705, 2013 (doi 10.1088/0957-4484/24/35/355705”. More precisely, the C-C contribution of C 1 s signal is fitted using two subcontributions, at 284.6eV corresponding to sp2 carbon and 285.1 eV corresponding to sp3 contribution. The concentration is derived from the area of each peak, considering a Shirley background. Measurement of the atomic percentages of hydrogen by ERDA and RBS

It is understood that within the context of the present invention, the atomic percentages of hydrogen are measured by ion beam analysis, namely by the combination of elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS), using He+ beam at high energy. The full description of hydrogen atomic percentages determination is available in the document “Production and preliminary characterization of DC plasma polymerized allylamine film (PPAA) by NRA, ERD, and XPS, S. Lucas a Nuclear Instruments and Methods in Physics Research B 266 (2008) 2494-2497” which is included by reference. A ³He⁺ ion beam of 2.385 MeV produced by a particle accelerator is sent toward the sample surface at an angle of 25°. Produced forward recoils of hydrogen are detected in an ERD detector placed at 30°. The incident ions also make some usable nuclear reactions on carbon (^ ³C(³He,p/)^N with i = 0-4), nitrogen

14|\|(³He, a o ³N) and eventually on oxygen

^{1 6}O(³He, a o) ¹⁵0).

The protons (pi) and alpha particles (or o) were detected by the NRA detector placed at 90°. A 15.2 pm Mylar foil is placed in front of the ERD and NRA detectors to stop the scattered primary ³He⁺. A RBS detector, placed at 165_ is used to monitor the number of incident particles. The simultaneously obtained spectra are analyzed to derive the concentration of the elements in layers analyzed.

Article

As mentioned above, the present invention also concerns an article comprising a substrate having at least one surface, said surface being in direct contact with the coating according to the present invention. All the preferences, definitions, and embodiments regarding the coating according to the present invention also applies to the coating comprised in the article according to the present invention.

Said substrate may be made of any material that is generally used by the skilled in art. Non-limiting examples of such materials include metals, ceramics, polymers, wood, textiles, or a mixture thereof.

Said at least one surface of said substrate may be of any shape, such for example round shapes, flat-shapes, wire-shapes, or complex 3D shapes with or without cavities or a combination thereof.

Preferably, said coating has a thickness of at least 1 nm, more preferably at least 5 nm, even more preferably of at least 10 nm.

It is understood that said coating may have a thickness of at most 20000 nm, preferably at most 15000 nm, more preferably at most 10000 nm, even more preferably at most 5000 nm, even more preferably at most 1000 nm.

In a preferred embodiment, said coating has a thickness of at least 1 nm and at most 20000 nm, preferably at least 5 nm and at most 15000 nm, more preferably at least 10 nm and at most 10000 nm.

The coating of the present invention being in direct contact with the at least one surface of the substrate of the article may be manufactured by applying said coating onto the at least one surface in one layer or in more than one layer. When applied in more than one layer, the coating is a multilayer coating. In general, said multilayer coating comprises at most 1000 layers, or at most 500 layers, or at most 400 layers, or at most 300 layers, or at most 200 layers or at most 100 layers.

The article according to the present invention may further comprise additional layers such as an adhesion layer.

In a preferred embodiment, the article according to the present invention further comprises an adhesion layer between said coating according to the invention and said substrate.

The adhesion layer improves the adhesion of the coating to the substrate. Said adhesion layer can be made of any metal known by the skilled in the art that is usually used as an adhesion layer.

Particularly, said adhesion layer may be made of at least one metal nitride, preferably at least two metal nitrides.

Preferably said at least one metal nitride or said at least two metal nitrides are selected from the group consisting of chromium nitride, titanium nitride, and mixtures thereof.

Preferably, said adhesion layer comprises at least 70 wt. %, more preferably at least 75 wt. %, even more preferably at least 80 wt. % of at least one metal nitride based on the total weight of said adhesion layer.

It is understood that the adhesion layer may comprise up to 100 wt. % of at least on metal nitride.

Coating Method

Non-limiting examples of coating methods are notably CVD (Chemical Vapor deposition), PVD (Physical vapor deposition) or PECVD (Plasma- enhanced chemical vapor deposition).

Preferably, the coating is applied on said at least one surface of said substrate by using PVD, more particularly pulsed magnetron sputtering

According to a preferred embodiment of the present invention, the coating is applied on said substrate by using pulsed magnetron sputtering with at least one metal target and in presence of Ar/CsHsor Ar/CFk atmosphere.

The carbonaceous gas is used as a reactive gas, and its flowrate is adapted over time: the amount of C2H2 (or CPU) injected is controlled using a feedback monitoring system, based on the optical emission of the plasma (preferably) or target voltage variation or target current variation.

Preferably, the gases (Ar, C2H2 (or CH₄)) are provided at a total pressure ranging from 0.25 Pa to 6.6 Pa, more preferably from 0.6 Pa to 2 Pa.

The flow rate of the argon gas may vary from 80 to 500 seem (Standard Cubic Centimeters per Minute), preferably from 100 to 200 seem. The flow rate of the C2H2 or CH₄ gas may vary from 20 to 500 seem, preferably from 50 to 200 seem.

Preferably, graphite targets are not used.

Preferably, the metal used for the targets is independently selected from the group consisting of Be, Mg, Sr, Sc, Y, La, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Nd, Mn, Re, Fe, Co, Rh, Ir, Eu, Ni, Pd, Pt, Gd, Cu, Ag, Au, Zn, Cb, B, Al, Ga, In, Ge, Sn, Pb, Te, Yb, and combinations thereof.

In a preferred embodiment of the present invention, the metal used for the targets is independently selected from the group consisting of Be, Mg ,Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, B, Al, and Ge and combinations thereof.

In a more preferred embodiment of the present invention, the metal used for the targets is independently selected from the group consisting of Ti, Zr, Nb, Cr, Mo, W, Mn, Co, Ag, Au, Zn, B, and combinations thereof.

In a more preferred embodiment of the present invention, the metal used for the targets is independently selected from Cr, W or Ti and combinations thereof.

Possibly, a voltage can be applied on the substrate either in DC or pulsed mode. When in pulsed mode, it may be synchronized with pulses of the waveform applied on the target(s).

The voltage applied on the substrate, may range from -20 V to -200 V, preferably from -100V to -200V. The corresponding current ranges from 0.1 A to 1 .5 A.

The current applied on the target is related to the target’s dimension, but can be anything between 1 to 2000 A per negative or positive pulse. The peak voltage varies according to the formula peak-current*peak-voltage.

When in pulsed mode, the applied frequency may for example range from 50 Hz to 3000 Hz. Alternatively, the applied frequency can range from 50 Hz to 500 Hz or from 1250 Hz to 2500 Hz. Duty cycles may for example range from 1% to 80%. Alternatively, the duty cycle may range from 1 % to 20% or from 50 % to 75 %.

The power pulse may range from 0.2 to 3.0 kWcm^-2.

The coating method comprises applying said coating onto the at least one surface of said substrate in one layer or in more than one layer. When applied in more than one layer, the obtained coating is a multilayer coating. In general, at most 1000 layers, or at most 500 layers, or at most 400 layers, or at most 300 layers, or at most 200 layers may be applied onto the at least one surface of said substrate.

Example 1

The inventions will be now described in more details with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

On a flat and rectangular substrate made of stainless steel, a coating according to the invention was applied using pulsed magnetron sputtering The sputtering parameters are summarized in Table 1 .

Table 1

The obtained article was thus made of a coating coated on a substrate. An adhesion layer between the substrate and the coating was applied by pulse sputtering of chromium.

The color of the coating was grey-black with a L value of 37:47, an A value of - 5:4 and a B value of -1 :0.3. The characteristics of the coating are summarized in table 2.

Table 2

The young modulus and hardness values were measured by nano-indentation test based on norm ISO 14577.

The friction coefficient p_c was measured according to reciprocating ball on disk test taking place for a plastic deformation contact.

The ICR was measured according to the methodology described in Wang, et al (Stainless steel as bipolar plate material for polymer electrolyte membrane fuel cells, Heli Wang, Mary Ann, Sweikart, John A Turner, Journal of Power Sources, Volume 115, Issue 2, 10 April 2003, Pages 243-251 ).

The korr was measured by corrosion test in three electrodes cell, in H2SO4 0.6 M at 60°C, with potential vs saturated calomel electrode of 0.48V during 16h.

The coating also displayed good conductivity and kept its properties after elongation. Moreover, the coating displayed isotropic elongation. The coating comprised a hydrogenated amorphous carbon matrix in which a metal (Cr) was homogeneously dispersed. The coating was also amorphous as no diffraction pattern with diffraction peaks in electron diffraction spectroscopy could be observed. Figure 1 shows diffuse circular rings, without a clear spot or circle, demonstrating an amorphous structure.

As shown in Figure 1 , when the coating was observed using TEM, only one phase is observed and it was not possible to distinguish the metal from the matrix (P) by using TEM with a resolution of 0.5 nm. The TEM observation is carried out on a JEOL 7500 transmission electron microscope, in secondary electron mode, at 15kV and a working distance of 5mm.

Regarding the sample preparation for the above TEM measurements, thin cross-section TEM samples were prepared in a dual-beam FIB (focused ion beam)/SEM (scanning electron microscope) FEI Helios Nanolab 650 equipped with Omniprobe micromanipulator. To protect the surface layers from the ion beam damage two Pt-layers were deposited -using an electron beam and the thicker one with an ion beam. TEM lamella cut was performed with an ion beam energy of 30 kV. Final thinning of the specimen was done at an ion beam of 2 kV/0.2 nA to achieve the thickness around 50 nm and to minimize irradiation damage generated during high-voltage FIB thinning.

Regarding the TEM measurements themselves, analysis of microstructure and chemical composition of the sample was conducted in a FEI Tecnai Osiris (Scanning) transmission electron microscope equipped with X- FEG high brightness electron source and four windowless Super-X SDD EDX detectors. The microscope was operated at 200 kV acceleration voltage. A selected area (SAED) was employed for structural analysis.

Figure 2 is an observation of free-standing film by scanning electron microscopy (SEM) and shows a piece of the coating (for sake of presentation, the coating is presented without substrate), with the carbon-based coating and the adhesion layer. Element 1 represents the coating layer according to the invention and element 2 represents the adhesion layer. Figure 3 illustrates an XPS depth profile of the coating obtained in example 1 , and shows the evolution of the elemental composition as a function of the depth.

The coating has been profiled using a monoatomic Ar⁺ beam working at 2 keV and 10 pA, on a K-Alpha Thermo Scientific spectrometer (Al Ka radiation 1486.68 eV) with a spot size of 250x250 pm, and raster size of 1.25x1.25mm. To generate the profile, ten snapshots of Cr 2p, N 1 s, O 1 s, C 1 s and Si 2p levels have been recorded after every etch step (8 s, approximately 2 nm), at a pass energy of 150 eV. Then, the concentration of each species is derived from the spectrum area of the scan, after subtraction of a Shirley background.

In the present example, the coating according to the present invention comprises one layer of -125 nm and there was an adhesion layer of -35 nm. The adhesion layer is comprised of pure chromium, while the coating according to the present invention comprised of -44 at.% of carbon and -56 at.% of chromium, as measured by XPS depth profile in Figure 3. The hydrogen content cannot be directly measured by XPS. Thus the content of Cr measured by XPS is overestimated because hydrogen atoms are not taken into account. When hydrogen atoms are taken into account, the coating comprises from 2 to 15 at.% of Cr, based on the total amount of atoms in the coating.

The matrix (P) is made of hydrogenated amorphous carbon.

The matrix (P) comprised, based on the total amount of atoms in the coating : 60-70 at.% of C, 20-30 at.% of H, 0-10 at.% of O and at most 10 at.% of N.

Hydrogen content was measured by ion beam analysis, namely by the combination of elastic recoil detection analysis (ERDA) and Rutherford backscattering spectroscopy (RBS), using He+ beam at high energy. The full description of hydrogen atomic percentages determination is available in the document “Production and preliminary characterization of DC plasma polymerized allylamine film (PPAA) by NRA, ERD and XPS, S. Lucas a Nuclear Instruments and Methods in Physics Research B 266 (2008) 2494-2497” which is included by reference. A ³He⁺ ion beam of 2.385 MeV produced by a particle accelerator is send toward the sample surface at an angle of 25°. Produced forward recoils of hydrogen are detected in a ERD detector placed at 30°. The incident ions also make some usable nuclear reactions on carbon (12c(3|-ie,p/)14N with i = 0-4), nitrogen

14|\|(³He, cropl and eventually on oxygen

i = 0-2 and ^{1 6}0(³He,cro) ^{1 5}0).

The protons (pi) and alpha particles (cro) were detected by the NRA detector placed at 90°. A 15.2 pm Mylar foil is placed in front of the ERD and NRA detectors to stop the scattered primary ³He⁺. A RBS detector, placed at 165_ is used to monitor the number of incident particles. The simultaneously obtained spectra are analyzed to derive the concentration of the elements in analyzed layers.

In the matrix (P) 48 % of the C was hybridized sp3 and 52 % of the C was hybridized sp2, based on the total amount of C in the coating. To determine this sp2 and sp3 concentration, XPS analysis is used. More precisely, the C 1 s signal is recorded at a pass energy of 20 eV, with 20 scans. The measurement is done on K-Alpha Thermo Scientific spectrometer (Al Ka radiation 1486.68 eV) with a spot size of 250x250 pm, and a raster size of 1 .25x1 ,25mm, and a flood gun is used for charge neutralization (preventing shift effect). Then, the C-C contribution of C1 s signal is fitted with two Lorentz/Gaussian functions, with L/G ratio of 30%, centered at 284.6eV for sp2 hybridized carbons and 285.1 eV and sp2 hybridized carbons. The concentration of each species is derived from area of each peak, considering a Shirley background.

The obtained coating was subjected to a biaxial deformation of 20% in the x- direction and 5% in the y-direction, no change in structure, composition, or properties was observed and no delamination occured, confirming isotropic elongation. Figures 4a and 4b show XRD measurement before and after deformation respectively. No diffraction peaks are observed for the coating, confirming that it remained amorphous after deformation. The XRD measurement were measure is performed on X’pert Pro Panalytical diffractometer, using Cu Ka radiation 1 .54059A, working at 45kV and 30mA, in 0/20 mode.

Figures 5a and 5b show XPS depth profiling before and after deformation. To obtain the composition of the film along with the thickness, the coating has been profiled using a monoatomic Ar⁺ beam working at 2 keV and 10 pA, on a K- Alpha Thermo Scientific spectrometer (Al Ka radiation 1486.68 eV) with a spot size of 250x250 pm, and raster size of 1 .25x1 ,25mm. The Cr 2p, N 1 s, O 1 s, C

1 s and Si 2p levels have been recorded after every etch step (8 s, approximately

2 nm), at a pass energy of 150 eV, with 10 snaps. Then, the concentration of each species is derived from the spectrum area of the scan, after subtraction of a Shirley background.

Example 2

A coating according to the present invention was deposited on an elastomeric isobutylene-isoprene copolymer support. The process used to deposit the coating is the same as in example 1 , with the exception of the targets which are tungsten (W) targets and with the exception of the C2H2 Flow rate which was of 150sccm.

The coating comprises from 11 .3 at.% of W, based on the total amount of atoms in the coating, homogeneously dispersed in a matrix (P). The matrix (P) comprised, based on the total amount of atoms in the coating : 58.1 at.% of C, 25 at.% of H, 5.3 at.% of O and 0.4 at.% of N.

In the matrix (P) 20 % of the C was hybridized sp3 and 80 % of the C was hybridized sp2, based on the total amount of C in the coating. The atomic percentages of W, C, O, N and H were measured according to the same methods as in Example 1 . The atomic percentages of sp2 hybridized C and sp3 hybridized C were measured as described in example 1 . The coating was amorphous as no diffraction pattern with diffraction peaks in electron diffraction spectroscopy could be observed. When the coating was observed using TEM, only one phase is observed and it was not possible to distinguish the metal from the matrix (P) by using TEM with a resolution of 0.5 nm. The electron diffraction spectroscopy and TEM analysis were carried out as in Example 1 .

The coating was subjected to a tensile test and showed no delamination after 300% elastic deformation and kept its properties after deformation, thus showing isotropic elongation.

Example 3

A coating according to the present invention was deposited on a 0.1 mm stainless steel sheet. The process used to deposit the coating is the same as in example 1 , with the exception of the C2H2 Flow rate which was of 55sccm.

The coating comprises from 26.4 at.% of Cr, based on the total amount of atoms in the coating, homogeneously dispersed in a matrix (P).

The matrix (P) comprised, based on the total amount of atoms in the coating: 51 .6 at.% of C, 20 at.% of H, 1 .6 at.% of O, and 0.4 at.% of N.

In the matrix (P) 46 % of the C was hybridized sp3 and 54 % of the C was hybridized sp2, based on the total amount of C in the coating.

The atomic percentages of W, C, O, N and H were measured according to the same methods as in Example 1 . The atomic percentages of sp2 hybridized C and sp3 hybridized C were measured as described in example 1 .

The coating was amorphous as no diffraction pattern with diffraction peaks in electron diffraction spectroscopy could be observed. When the coating was observed using TEM, only one phase is observed and it was not possible to distinguish the metal from the matrix (P) by using TEM with a resolution of 0.5 nm. The electron diffraction spectroscopy and TEM analysis were carried out as in Example 1 .

Then, the obtained coating was subjected to a biaxial deformation of 20% in the x-direction and 5% in the y-direction. The corrosion current and the interfacial contact resistance were measured before and after deformation, the results are shown in table 3.

Table 3

The corrosion current and the interfacial contact resistance do not change significantly after deformation, which shows that the obtained coating displays isotropic elongation. The corrosion current and the interfacial contact resistance were measured as in Example 1 .

In another experiment, the obtained coating was subjected to a biaxial deformation of 6% in the x-direction and 4% in the y-direction and was then observed by SEM microscopy. Figure 6 shows a SEM image of a portion of the obtained coating after elongation. No delamination was observed as shown in Figure 6.

Claims

-26- CLAIMS

1 . A coating comprising based on the total amount of atoms in said coating: from 0.5 at. % to 50.0 at. % of at least one metal element which is homogenously dispersed in at least one hydrogenated amorphous carbon matrix [hereinafter, matrix (P)]; wherein said coating is amorphous and has no phase separation between said at least one metal element and said matrix (P) as determined by transmission electron microscopy (TEM) with a resolution of 0.5 nm and wherein the matrix (P) comprises at least 20 at. % and at most 80 at.% of sp2 hybridized carbons and at least 20 at.% and at most 80 at.% of sp3 hybridized carbons based on the total amount of carbons in said coating as measured by XPS.

2. A coating according to claim 1 , wherein the at least one metal element is in metallic form or in the form of a metal carbide, metal oxide, metal nitride or a combination thereof.

3. A coating according to any one of the preceding claims, wherein the at least one metal element is selected from the group consisting of Be, Mg, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, B,AI, and Ge and combinations thereof.

4. A coating according to any one of the preceding claims, wherein the at least one metal element is selected from the group consisting of Ti, Zr, Nb, Cr, Mo, W, Mn, Co, Ag, Au, Zn, B, and combinations thereof.

5. A coating according to any one of the preceding claims, wherein the coating comprises at most 40 at. %, preferably at most 30 at.%, more preferably at most 20 at.%, even more preferably at most 15 at.%, of the at least one metal element based on the total amount of atoms in said coating, as measured by XPS.

6. A coating according to any one of the preceding claims, wherein the matrix (P) comprises hydrogen in a content of at least 5 at. %, preferably at least 10 at.%, more preferably at least 20 at.% based on the total amount of atoms in said coating, as measured by ERDA and RBS.

7. A coating according to any one of the preceding claims, wherein the matrix (P) comprises hydrogen in a content of at most 90 at.%, more preferably at most 80 at.%, even more preferably at most 70 at.%, even more preferably at most 60 at.%, even more preferably at most 50 at.%, even more preferably of at most 40 at. %, preferably at most 35 at.%, more preferably at most 30 at.%, based on the total amount of atoms in said coating, as measured by ERDA and RBS.

8. A coating according to any one of the preceding claims, wherein the matrix (P) comprises carbon in a content of at least 10 at. %, preferably at least 30 at.%, more preferably at least 50 at.%, even more preferably at least 60 at.% based on the total amount of atoms in said coating as measured by XPS.

9. A coating according to any one of the preceding claims, wherein the matrix (P) comprises carbon in a content of at most 80 at. %, preferably at most 70 at.%, based on the total amount of atoms in said coating as measured by XPS.

10. A coating according to any one of the preceding claims, wherein the matrix (P) comprises at least 30 at.%, even more preferably at least 35 at.%, even more preferably at least 40 at.%, even more preferably at least 50 at.%, even more preferably at least 60 at. %, preferably of at least 70 at. %, more preferably of at least 80 at. %, more preferably at least 85 at. % of of sp2 hybridized carbons based on the total amount of carbons in said coating, as measured by XPS.

1 1. A coating according to any one of the preceding claims, wherein the matrix (P) comprises at most 70 at.%, more preferably at most 60 at.%, even more preferably at most 50 at.%, even more preferably at most 35 at. %, preferably at most 30 at.%, more preferably at most 25 at.% of sp3 hybridized carbons based on the total amount of carbons in said coating as measured by XPS.

12. An article comprising a substrate having at least one surface, said surface being in direct contact with a coating according to any one of the preceding claims.

13. An article according to claim 12, wherein said coating has a thickness of at least 1 nm, preferably at least 5 nm, more preferably at least 10 nm, and preferably at most 20000 nm, more preferably at most 15000 nm, even more preferably at most 10000 nm.

14. An article according to claim 12 or claim 13, further comprising an adhesion layer between said coating according to the invention and said substrate.