FORM 2

THE PATENTS ACT,1970 (39 of 1970)
COMPLETE SPECIFICATION
(SEE SECTION 10)
TITLE
A method of coating steel components with diamond by chemical vapour deposition (CVD) and steel components obtained thereby
APPLICANTS
IIT Bombay, Indian Institute of Technology, Powai, Mumbai - 400076, Maharashtra, India
INVENTORS
Under Section 28(2)
Dr Devi Shanker Misra and Arun Kumar Sikder, both Indian Nationals and of Department of Physics, IIT Bombay, Powai, Mumbai 400076, Maharashtra, India

The following specification particularly describes and ascettams the nature of this ,
invetation and the mamber in winch it is to be performed : 25-3-2004
3 7 7/MUM|2OO0 GRANTED

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This invention relates to a method of coating steel components with diamond by chemical vapour deposition (CVD) and steel components obtained thereby.
Diamond when coated on steel components enhances the hardness thereof. Diamond coated steel components find applications, for instance, as cutting or grinding tools, abrasive wheels, end mills or load bearing elements such as ball- bearings or inserts.
Steel components are coated with diamond by the chemical vapour deposition technique comprising heating the components at high temperatures upto 500 - 900°C in a vacuum chamber under a flow of reactant gases at low pressures of 20 to 100 Torr within the chamber. In the case of hot filament CVD heating may be carried out through a heated filament with a power supply of 400-1000W, The reactant gases may be a mixture of methane (CH4), acetylene (C2H2), carbondioxide (C02) and hydrogen (H2) at about 40 Torr. Commonly a mixture of methane (CE,) and hydrogen (H2) in a ratio of 1 : 99 is used. Typical conditions for hot filament CVD of

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Attempts have been made to improve the quality of diamond deposition on steel components. In one instance titanium ions are implanted on steel components using ion beams before CVD of diamond. [Chemical vapour deposition of diamond onto steel: The effect of Ti implant layer, Paul S Weiser, Surface coatings Technology,? 1,(1995), 167 -174]. Diamond coating obtained by this method contains graphitic impurities and produces poorly adhered diamond coating. In another instance, steel components are first coated with a strike nickel layer by electroplating, followed by a composite nickel-diamond layer by electroplating, before CVD of diamond is carried out. This method also suffers from formation of graphitic clusters and results in poor adhesion of diamond on the steel surface due to catalytic action of nickel [Chemical vapour deposition of diamond on stainless steel: effect of Ni-diamond composite coated buffer caver, A K Sikder etal Diamond Related Mater, 7, (1998), 1010-1013].
In another instance, the components are coated with alternate coatings of nickel and discrete diamond nuclei by CVD followed by topmost continuous layer of CVD diamond. This method also sutlers from
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graphitic pliase fonnation due to the catalytic effect of nickel. [ Application of nickel plating for the synthesis of chemical vapour deposition on steels, HC Shih et al, Thin Solid Films, 236 (1993) 111-114].
In yet another instance, a chromium nitride layer is formed on steel components by nitridation of chromium coated steel, prior to CVD of diamond, The chromium present as nitride on steel cannot form carbide with CVD diamond. Therefore CVD diamond nucleates on the chromium nitride layer instead of being adhered thereon. This results in impure diamond coating by this method due to graphitic cluster formation. (Deposition of continuous and well-adhering diamond films on steel, A Fayer etal, Appl Phys Lett, 67, (1995), 2299-2301).
In yet another instance molybdenum is coated on steel components using electron beams prior to subjecting them to CVD of diamond. Due to the oxidation and subsequent evaporation of molybdenum under CVD conditions, the uniformity and compactness of the deposited diamond and adhesion/growth of diamond film on the steel components is poor. In yet another instance, molybdenum, nickel and molybdenum are

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consecutively deposited on steel components using an electron beam evaporator prior to CVD of diamond. The diamond film so deposited shows improved uniformity and compactness but contains non-diamond carbon and molybdenum carbide impurities. In yet another instance, steel components coated with TiN by reactive sputtering, are treated in a suspension of diamond dust for providing active nucleation sites followed by CVD of diamond. Diamond coating obtained by this method is impure and poorly adheres to steel due to graphitic cluster formation. In yet another instance, sihcon is coated on steel components in two different thicknesses using electron beam evaporator prior to carrying out CVD of diamond. Due to the evaporation of sihcon and/or the mutual alloying of iron with carbon at high CVD temperature, graphitic phase impurities are found to be deposited on the steel components. (Application of diamond coating to tool steels, HC Shih et al, Diamond and Related Mater, (1992) pp 605 - 611).
An object of the invention is to provide a method of coating steel components with diamond by CVD which improves the adhesion of diamond coated on the steel components.
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Another object of the invention is to provide a method of coating steel components with diamond by CVD which improves the quahty of diamond coated on the steel components.
Another object of the invention is to provide a method of coating steel components with diamond by CVD which enhances the hardness of diamond coated steel components.
Another object of the invention is to provide steel components coated with diamond by CVD, having improved adhesion of diamond on the steel components.
Another object of the invention is to provide steel components coated with diamond by CVD, having improved quahty diamond coating on the steel components.
Another object of the invention is to provide steel components coated with diamond with CVD, having enhanced hardness.
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According to the invention there is provided a method of coating steel components with diamond by chemical vapour deposition (CVD) which comprises:
a) cleaning the components in a known manner;
b) electroplating a strike nickel layer of 0.5-1.2 microns thickness on the components with a nickel chloride electrolytic bath at pH < 1.0 and at room temperature;
c) electroplating a nickel-diamond composite layer of 15-30 microns thickness on the components with a nickel sulfate-nickel chloride electrolytic bath, containing added diamond particles in concentration of 5-10 g/100 ml of the electrolyte, at pH 4-4.5 and at 50 -60°C;
d) electroplating chromium layer of 3-8 microns thickness on
the components with chromic acid electrolytic bath at pH < 1.0 and at
room temperature; and

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e) Chemical vapour deposition coating of diamond of thickness 5-15 microns on the components in a known manner.
According to the invention there is also provided steel components coated with diamond by chemical vapour deposition (CVD) having intervening precoatings of strike nickel layer of 0.5-1.2 microns thickness on the components followed by nickel-diamond composite layer of 15-30 microns thickness and chromium layer of 3 - 8 microns thickness and CVD diamond thickness of 5-15 microns.
The steel components are cleaned in known manner for instance, by washing with a detergent solution followed by deionised water. The components are further washed with an aqueous alkali solution such as NaOH followed by deionised water. The components are electrocleaned viz anodic cleaned, for example, using a sulfuric acid bath at room temperature. The purpose of anodic cleaning is to remove the oxides present on the steel components.
Preferably, the thickness of the strike nickel layer is 1 micron.
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The concentration of diamond in the nickeJ sulfate-nickel chloride electrolyte is preferably 2-6 g/100 ml and the thickness of the nickel-diamond composite layer is preferably 20 - 30 microns. The thickness of the chromium layer is preferably 5 microns. The thickness of the CVD diamond layer is, preferably, 5 to 8 microns.
According to the invention the steel components are coated with three prelayers viz nickel layer, nickel-diamond composite layer and chromium layer prior to CVD of diamond. These pre-layers are thermally stable at the high CVD temperature. The nickel layer enhances the adhesion of the nickel-diamond composite layer to the steel components because of the acidic nature of the strike nickel bath. Chromium being interactive with diamond, the composite nickel-diamond layer which is well adhering to the steel components, also adheres to the chromium layer well. Because of the structural compalibMy due to the carbidic interaction between diamond and chromium, the chemical vapour deposited diamond settles and adheres to the cliromium layer very well thereby enhancing the adhesion of the CVD of diamond on the steel components. Therefore, according to the method of the invention, adhesion of diamond on steel components is improved.
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Since diamond interacts with chromium, carbon (diamond) from the chemical vapour deposited diamond does not diffuse into steel. Besides, the three pre layers viz nickel layer, nickel-diamond composite layer and chromium layer also act as a barrier and prevent diffusion of chemical vapour deposited diamond into steel. Therefore, formation of the graphite clusters is eliminated and the diamond deposited on steel is of good quality i.e. it shows good crystaUinity and better adhesion. Besides, since chromium is known to enchance the hardness properties of diamond; diamond deposited on chromium coated steel as per the invention, enchances the hardness properties of the steel components.
The following experimental example is representative of the invention but not limitative of the scope thereof
Example 1
a) A 304 stainless steel plate component (10 mm x 10 mm x
1 mm size) was washed with detergent solution followed by deionised
water. The component was dipped in 30% NaOH at 60°C for 10 minutes
and rinsed with deionised water again. The component was electrocleaned
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in a 30% H2S04 bath at a current density of 3-4V using it as anode and a stainless steel plate as counter electrode for 60-90 sees at room temperature. The component was again rinsed with deionised water. A strike nickel layer of 1 micron thickness was electroplated on the component using nickel chloride {NiCl2.GH2O} solution (240 g/l), maintained at pH 1 by addition of HCl (100 g/1). The electroplating was carried out at a current of density 30A/ft for 3-5 mins at room temperature. The component was used as cathode and a nickel plate was used as anode. A nickel-diamond composite layer of 20 microns thickness was electroplated on the component using a solution of nickel sulphate (NiS04.7H20) (275 g/1) and nickel chloride (NiCl2. 6H20) (60 g/1) in ratio 5:1 maintained at pH 4 - 4.5 by addition of H3BO3 (40 g/1) and containing added diamond (particle sizes 8 -20 urn, 2-6 g/100 ml). The electroplating was carried out at a current of density 37 - 40 A/ft2 and at 55-60°C for 10 - 30 mins. The component was used as cathode and a nickel plate was used as anode. A chromium layer of 5 microns thickness was electroplated on the component using a solution of chromic acid (ie Cr03 + H2S04 + H20) maintained at pH < 1.0 and current of density 40 - 50 A/dm2 for 5 - 10 mins at 50-60°C. The component was used as cathode and a tin-lead plate was used as anode. Chemical vapour
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deposition (CVD) of diamond film of 5 - 8 microns thickness was carried out in a vacuum chamber for 3 hours. The component was heated at 890°C with tungsten filaments at a power supply of 400W. A reactant gas mixture of methane (0.8%) and hydrogen (99.2%) was allowed into the chamber and the gas pressure within the chamber was 40 Torr. The diamond coated steel component was allowed to cool down to room temperature and removed.
Studies on the diamond coated steel plate component of Example 1 were carried out as follows :
1) Scanning Electron Microscopy (SEMV
The following Fig 1A shows the SEM of chemical vapour deposited diamond on steel plate component coated with a strike nickel layer and a nickel - diamond composite layer, without chromium layer. The following Fig IB shows the SEM of steel plate component of Example 1.
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Fig 1A

Fig IB

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From the Figs 1A and 1B, it is clear that the diamond coated on the steel plate component of Example 1 had high crystallinity and was therefore highly pure.
2) Raman Spectroscopy:
Fig 2A of the accompanying drawings shows the Raman spectra of the steel plate component coated with nickel followed by nickel-diamond composite layer, but prior to deposition of chromium and CVD of diamond. Fig 2A shows two peaks at 1334 cm"1 and 1500 cm'1. The sharp peak at 1334 cm"1 indicates the deposition of diamond. The broad band at 1500 cm"1 indicates the graphitic cluster impurities. Fig 2B of the accompanying drawings shows the Raman spectra of the steel plate component of Example 1. A single sharp intense peak at 1334 cm'1 indicates the deposition of diamond and absence of any other impurities. This shows that good quality diamond with no graphitic impurities was deposited on the steel plate component.
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3) Microhardness tests:
Microhardness tests were carried out on bare steel plate component and after CVD of diamond on the component and the results were as under.
Hardness (HV)
Bare 304 stainless steel plate component 200-300
(10 mm x 10 mm x 1 mm size)
Coated steel plate component > 1500 and
of Example 1 showed no indentation

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We claim :
1) A method of coating steel components with diamond by chemical vapour deposition (CVD) which comprises:
a) cleaning the components in a known manner;
b) electroplating a strike nickel layer of 0.5-1.2 microns thickness on the components with a nickel chloride electrolytic bath at pH < 1.0 and at room temperature;
c) electroplating a nickel-diamond composite layer of 15-30 microns thickness on the components with a nickel sulfate-nickel chloride electrolytic bath, containing added diamond particles in concentration of 5-10 g/100 ml of the electrolyte, at pH 4 - 4.5 and at 50 -60°C;
d) electroplating chromium layer of 3-8 microns thickness on
the components with chromic acid electrolytic bath at pH < 1.0 and at
room temperature; and
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e) Chemical vapour deposition coating of diamond of thickness 5-15 microns on the components in a known manner.
2) A method as claimed in claim 1, wherein the thickness of the nickel layer is 1 micron.
3) A method as claimed in claim 1 or 2, wherein the concentration of diamond in the nickel sulfate-nickel chloride electrolyte is 2-6 g/100 ml and the thickness of the nickel-diamond composite layer is 20 microns.
4) A method as claimed in any one of claims 1 to 3, wherein the thickness of the chromium layer is 5 microns.
5) A method as claimed in any one of claims 1 to 4, wherein the thickness of the CVD diamond is 5 to 8 microns.
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6) A method of coating steel components with diamond by chemical vapour deposition (CVD) substantially as herein described particularly with reference to Example 1.
7) Steel components coated with diamond by chemical vapour deposition (CVD) as claimed in claim 1 having intervening precoatings of strike nickel layer of 0.5-1.2 microns thickness on the components followed by nickel-diamond composite layer of 15-30 microns thickness and chromium layer of 3 - 8 microns thickness and CVD diamond thickness of 5 -15 microns.
8) Steel components coated with diamond by chemical vapour deposition (CVD) as claimed in claim 7, wherein the thickness of the nickel layer is 1 micron.
9) Steel components coated with diamond by chemical vapour deposition (CVD) as claimed in claim 7 or 8, wherein the thickness of the nickel-diamond composite layer is 20 microns.
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10) Steel components coated with diamond by chemical vapour deposition (CVD) as claimed in any one of claims 7 to 9, wherein the thickness of the chromium layer is 5 microns.
11) Steel components coated with diamond by chemical vapour deposition (CVD) as claimed in any one of claims 7 to 10, wherein the thickness of CVD diamond is 5 to 8 microns.
Dated this 20th day of April 2000.

(M A Jose) of DePENNING & DePENNING Agent for the Applicants
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