FIELD OF INVENTION
The present invention describes the electroless Ni-C-P composite coating and process thereof for application on the surface of ball bearing and galvanising sink roll to improve performance efficiency and life.
The composite coating obtained by electroless process shows lower surface roughness, co-efficient of friction. This coating also provides excellent resistance capability against caustic and chloride attack.
BACKGROUND OF THE INVENTION
Electroless metal deposition solutions ("electroless plating solutions") deposit metal over a catalytically active surface by chemical reduction in the absence of an external electric circuit. Those solutions containing nickel are used in a wide range of industrial applications. Nickel-boron and nickel-phosphorus coatings are recognized in the art for their corrosion resistance, hardness and associated wear-resistance. See, for example, U.S. Pat. Nos. 2,726,170; 3,045,334; 3,378,400; 3,738,849; 3,674,447; 3,432,338; 3,918,137; 4,395,442; 4,567,066; 4,706616; 4,724,819; 5,019,163 5,148,780; and 6,178,306.

Typical electroless nickel plating solutions generally comprise a water-soluble nickel salt, a water-soluble alloying salt (if an alloy is present), a reducing agent, and a chelating or completing agent. Additives may also be added in relatively low concentrations to enhance various characteristics of the solution of plated article. One continuing need with respect to electroless nickel plating solutions has been the need to increase the stability of the solution. It has been found, however, that in certain instances the addition of stabilizers to meet this need interferes with the formation of the nickel coating, in that during the formation of the nickel coating the accelerator co-deposits in the nickel. Some stabilizers are also known to cause discoloration of the deposit. In the present invention a Ni-C-P composite coating was obtained on the steel surface by electroless process. OBJECTS OF THE INVENTION
An object of the present invention is to obtain Ni-P-C composite coating for steel substrate.
Another object of the present invention is to prepare a coating which can provide caustic and chloride resistance property.

Still another object of this invention is to develop a coating that provides a
uniform coating on steel surface, when applied by electroless process.
Further, object of this invention is to provide the coating lower co-efficient of
friction and high hardness to wear resistance performance and coating can be
deposited on the single on in bunch.
Another object of the invention is to provide a steel sheet coated with this
coating is not reactive to molten zinc.
Summary of the Invention
The invention discloses a Nickel-carbon-phosphorus (Ni-C-P) composite coating
for application on the surface of ball bearing and sink roll by electroless process.
The coating formulation comprises the following elements:

The composite coated material showed significant improvement in corrosion resistance against chloride/molten zinc environments compared to bare steel.

The phosphorous gets reduced during the electro less deposition process and a coating of the following composition gets deposited on the substrate:

DETAILED DESCRIPTION OF THE INVENTION
The Ni-C-P coating as per the current invention contains the following ingredients

The above proportion of the coating can be achieved by taking the base material as per the following table 2 and PH 7 and Temperature in the range of 80-90 °C


Ni is being used as metallic component in the composite coating. Ni is nobler metal compare to iron and hence expected to provide very good barrier protection. Ni is good in electrical and thermal conduction. The materials used in the present invention are ball bearing or sink roll. Further, Phosphorous is very good in corrosion resistance and the purpose of lubrication. Phosphorous reduces co-efficient of friction. Fine graphene powder is used to incorporate C in the coating. Graphene is used in the coating for many inherent good properties like lighter, lubricator, good electrical and thermal conductor and excellent resistivity against corrosion. The stabilizer used in the formulation is selected from the following class of compounds:
(i) compounds of group VI elements: S, Se, Te,
(ii) Compounds containing oxygen: AsO-2, IO-3/ MoO-24.,
(iii) heavy metal cations: Sn+2, Pb+2, Hg+, Sb+3 and
(iv) Unsaturated organic acids: Maleic, itaconic.

The stabilizers concentration varies in the range of 0.05 to 10 mg/l and preferably 0.5 to 1.5 ppm of thiourea is used. Though nickel sulphate is used preferably as nickel salt however a soluble nickel salt selected from the group consisting of nickel chloride, nickel sulfate, nickel formate, and nickel acetate and nickel hypophosphite can be used in the formulation to achieve the desired results. The coating formulation of the current invention also comprises a reducing agent selected from the group consisting of hypophosphorous acid, hypophosphites, borohydrides, dimethylamine borane, trimethylamine borane, hydrazine, thiosulfates, ascorbates and combinations thereof, preferably sodium hypophosphide and hydrazine. The reducing agent concentration varies in the range of 0.88 to 88 g/l
The coating may comprises a complexing agent and complexing agent is selected from the group consisting of ammonia and organic complex-forming agents containing functional groups such as primary amino, secondary amino, tertiary amino, imino, carboxy and hydroxy. In an embodiment of the invention, the complexing agent is selected from the group consisting of ethylenediamine,

diethylene triamine, triethylene tetramine, triethylenetriamine, sodium citrate, sodium pyrophosphate, organic acids, water soluble salts of organic acids, and amino acids. The complexing agent concentration varies in the range of 1 to 150 g/l. The Nickel-Carbon-phosphorus based electroless composite coating further comprises an organic acid selected from the group consisting of malic acid, succinic acid, lactic acid, oxalic acid, citric acid, tartaric acid, and ethylene diamine tetra acetic acid.
The formulation is deposited on the substrate at a temperature range temperature varying from 70 to 95° C and pH of formulation varies in the range of 3 to about 11, preferably 7. Pickling solutions
In the present work, we first optimize the process parameters to remove high temperature oxide scale from steel surface. Pickling process parameters were as mentioned in table 3.


After pickling, rinsing is done thoroughly in tap water before dipping all the samples in an electroless coating solution prepared as per the table 1 and tabl2 specifications. Cathodic and anodic reactions happen simultaneously on the steel substrate as mentioned in equations (i & ii).


Graphene powder was co-deposited along with Ni & P. Deposition rate is very much sensitive to concentration of different metallic and non-metallic ingredients in the solution, pH and temperature of the solution. Temperature of the bath has a significant effect for optimum deposition. Optimum temperature range for required deposition is 70-95° C. Nickel gets dissolved out from the surface at a bath temperature more than 95° C.
The coating formulation includes stabilizers from the following classes: (i) compounds of group VI elements: S, Se, Te (ii) compounds containing oxygen: AsO-2/ IO-3, MoO-24 (iii) heavy metal cations: Sn+2, Pb+2, Hg+, Sb+3 and (iv) unsaturated organic acids: Maleic, itaconic. The stabilizers concentration varies in the range of 0.05 to 10 mg/l, preferably 0.5-1.5 ppm thiourea Stabilizer concentrations should be optimum. Stabilizer hastens the deposition rate up to certain ppm level above that stabilizer act as poison and even stops the deposition of metal completely. The coating thickness is directly proportional to coating time. After electroless coating all samples are rinsed in tap water and subsequently dried in open atmosphere. Surface appearance of the coated samples is bright.

The data of surface roughness, co-efficient of friction and material loss against aggressive corrosive environments are shown in Table 4. It is evident that after coating surface roughness, co-efficient of friction and material loss against aggressive corrosive environment drop down significantly.

As evident from the table above, the composite coated material showed significant improvement in corrosion resistance against chloride/molten zinc environments compared to bare steel.

WE CLAIM:
1. A Nickel-Carbon-phosphorus based electroless composite coating for ball
bearings and sink roll, the coating comprises:

2. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1 further comprising a stabilizer selected from the group consisting of compounds of group VI elements: S, Se, Te, compounds containing oxygen: AsO-2, IO-3, MoO-24., heavy metal cations: Sn+2, Pb+2, Hg+, Sb+3 and unsaturated organic acids: Maleic, itaconic.
3. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 2, wherein the stabilizers concentration varies in the range of 0.05 to 10 mg/l, preferably 0.5-1.5 ppm of thiourea.

4. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the soluble nickel salt is selected from the group consisting of nickel chloride, nickel sulfate, nickel formate, and nickel acetate and nickel hypophosphide, preferably nickel sulphate.
5. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the reducing agent is selected from the group consisting of hypophosphorous acid, hypophosphites, borohydrides, dimethylamine borane, trimethylamine borane, hydrazine, thiosulfates, ascorbates and combinations thereof, preferably sodium hypophosphite and hydrazine.

6. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the reducing agent concentration preferably varies in the range of 20 to 30 g/L.
7. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the complexing agent is selected from the group consisting of ammonia and organic complex-forming agents containing functional groups such as primary amino, secondary amino, tertiary amino, imino, carboxy and hydroxy.

8. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the complexing agent is selected from the group consisting of ethylenediamine, diethylene triamine, triethylene tetramine, triethylenetriamine, sodium citrate, sodium pyrophosphate, organic acids, Glycolic Acid, water soluble salts of organic acids, and amino acids.
9. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1 further comprising organic acids are selected from the group consisting of malic acid, succinic acid, lactic acid, oxalic acid, citric acid, tartaric acid, and ethylene diamine tetra acetic acid.
10. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the complexing agent concentration varies in the range of 1 to 150 g/l.
11. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the formulation is deposited on the substrate at a temperature range temperature varying from 70 to 95° C and pH of formulation varies in the range of 3 to about 11, preferably 7.

12. The Nickel-Carbon-phosphorus based electroless composite coating as per the claim 1, wherein the coating on the substrate comprises: