[nanoPost] India Ni-P based electroless robust nanocoating for corrosion resistance application

The major component of the Electroless technique is the ‘bath’. The bath consists of an aqueous solution of metal ion, catalyst, reducing agent(s), complexing agent(s), bath stabilizer(s) etc. operating at a required metal ion concentration, temperature and pH range. Unlike in conventional electro plating, no electrical current is required for deposition. Additionally, the properties of the coatings can be tailored by subsequent heat treatment.

Electroless nickel and boron are engineering coatings, normally used because of its excellent physical and mechanical properties. The composite coatings i.e. Ni-P-X (where X is second phase particles) can be tailored to obtain desired properties. Electroless nickel base coatings have many applications including the petroleum industry, chemical, plastics, optics, printing, mining, aerospace, nuclear, automotive, electronics, computers, textile, paper, etc. The coatings can be achieved on diverse components made of steel, stainless steel, aluminum, copper, brass, magnesium and a number of non-conductive materials. The pioneered electroless Ni-P-ZrO2–Al2O3 nanocomposite coatings (patented) is a co-precipitation of alumina-zirconia followed by co-deposition along with Ni-P to form in situ nanocomposite coating has improved hardness, wear and corrosion resistance properties of the coated surface.

Some of the major engineering advantages of Electroless Coatings are:

·     Uniformity: (in micro and nano-scale thickness) with amorphous/micro-crystalline deposit. The electroless deposit covers all contours of the substrate exactly, without building up at the edges and corners. A sharp edge receives the same thickness of deposit as a blind hole;

·     Excellent corrosion resistance;

·     Good solderability;

·     High hardness;

·     Lower coefficient of friction;

·     Preplate for precious metal coating;

·     Excellent adhesion deposits, consisting of  metal/metal plus metalloid/non-metallic materials;

·     No electricity needed for coating.

The author has one patent and more than 16 publications in the area of coatings.

Coating Technique

The major component of the Electroless technique is the ‘bath’. The bath consists of an aqueous solution of metal ion, catalyst, reducing agent(s), complexing agent(s), bath stabilizer(s) etc. operating at a required metal ion concentration, temperature and pH range. Unlike in conventional electro plating, no electrical current is required for deposition.

In EL coating process, the coating thickness and the coating rate are same on every section of the part exposed to coating solution and the thickness of coating can be controlled to suit the application. The coated surfaces if need be, for example to improve the strength, hardness etc. are subjected to the desired heat treatments in controlled atmosphere. The amorphous Ni-P coatings (metallic glass) are crystallized at 400oC when heat treated for 1 hour under argon atmosphere.

The ability to co-deposit fine particulate substance(s) within an electroless metal deposit has led to a new generation of coatings called composite coatings. Electroless dispersion alloy coating use the conventional electroless reduction reaction processes with a suspension of particles to produce a deposit with unique micro/ macro properties. These particles are of two types namely, soft that are used as lubricants and hard mainly used for load bearing applications. The soft particles can be of polytetrafluoroethylene (PTFE), fluorocarbon, graphite, fluoride etc., whereas hard particles are of oxides, carbides, ceramics, diamond etc

Successful co-deposition depends on the catalytic or inert nature of particle charged, electroless bath composition, compatibility of the particles with metallic matrix, coating rate, particle size distribution etc. By composite coatings one can tailor the properties by varying the type morphology and amount of second phase particles that are to be reinforced in the matrix of the coats.

Applications for Electroless Nickel

The hardness and corrosion resistance of electroless nickel are key factors in many successful applications.

Significant efforts by various investigators have been devoted to identify the wide range of metals/alloys that can be deposited by the electroless (autocatalytic) deposition route. Among them, particularly useful metals that have been demonstrated to be of practical importance are nickel, cobalt, palladium, copper, platinum, gold, silver etc. and alloys involving at least one of the above metals. Electroless nickel and boron are engineering coatings, normally used because of its excellent physical and mechanical properties. The composite coatings i.e. Ni-P-X (where X are second phase particles) can be tailored to obtain desired properties. Electroless nickel base coatings have found many applications including those in  the industries of petroleum, chemical, plastics, optics, printing, mining, aerospace, nuclear, automotive, electronics, computers, textile, paper  etc. The pioneered electroless  Ni-P-ZrO2–Al2O3 nanocomposite coatings (patented), a co-precipitation of alumina- zirconia followed by co-deposition along with  Ni-P to form in situ nanocomposite coating has been developed and is found to  improve  hardness, wear and corrosion resistance of the coated surface.

Ni-P EL coatings are used for a variety of applications including electrical connectors, microwave housings, valves and pump bodies, printer shafts; hard drive computer components and more. These unique coatings are applied to impart corrosion protection, wear resistance, to provide solderability, to provide a non-porous barrier layer, or otherwise enhance the performance or useful life of a particular component. Electroless nickel is used to coat components made of steel, stainless steel, aluminum, copper, brass, magnesium and a number of non-conductive materials. They are used in such diverse industries such as the automotive industry, chemical process industry, the oil and gas industry, the aerospace industry and the electronics industry.

Mechanical Deposit Properties

Coating Hardness

The hardness of electroless nickel is a key factor in many successful applications.

Coating Hardness after Heat Treatment

The hardness of electroless nickel coatings can be enhanced by heat treatment and is dependent on phosphorus content and heat treatment time and temperature.

Deposit Ductility

Electroless nickel deposits are not considered to be "ductile" due to their high hardness. However, there is a relationship between ductility and phosphorus content.

Corrosion Resistance

The surface condition of the substrate can have a significant effect on the ability of the electroless nickel coating to serve as a barrier to corrosion. Generally, thicker deposits are suggested for rougher substrates, such as castings, to insure low porosity and optimum corrosion resistance.

The different classes of electroless nickel coatings, either low, medium or high phosphorus, may not all perform in the same manner in a corrosive environment. For example, the low phosphorus electroless nickel coatings will tend to corrode less in strongly alkaline environments than any other electroless nickel coating. Similarly, the high phosphorus electroless nickel coatings tend to be more amorphous or "glass like" in structure and tend to perform superior to other electroless nickel coatings in strongly acid environments.

Work carried of in the proposed field

Nanocoatings 

Non- crystalline solids like amorphous metallic alloys have emerged as an important class of novel industrial materials which has received considerable attention of scientific community in the recent years. Among the various techniques used to prepare amorphous solids, electroless deposition is an important method using the catalytic surface by the reduction reaction. Synthesis and characterization of Ni-P based composite coatings by in situ co-precipitation of nano structured Al2O3 and ZrO2 followed by their co-deposition along with Al3Zr on various substrates. The tribological behavior of electroless Ni-P-X and Ni-P coatings on steel and aluminium substrates in different conditions i.e., as-coated, heat treated at various temperatures at different extents of time with different normal loads, have been studied in terms of dry sliding friction and wear against counter face of case hardened steel. Investigators have a patent based on the above studies.