International. A new method of deposition of nickel alloy coatings on high-performance materials in engineering applications may replace environmentally toxic chromium coatings.
The coatings obtained are also highly resistant to corrosion and useful for the plastics industry.
With an increasing demand for high-performance materials in engineering applications, nanocrystalline coatings can meet the need to replace environmentally hazardous chromium coatings.
Chromium coatings have been used in the plastic bottling industry to improve the service life of die casting components.
However, chrome plating is a toxic process and the strict standard permissible exposure limit (PEL) for toxic hexavalent chromium and all its compounds must be met in all industrial chrome plating workplaces.
Scientists at the Centre for Engineering Coatings at the International Centre for Advanced Research in Powder and New Materials Metallurgy (ARCI), an autonomous Research and Development Centre of the Department of Science and Technology (DST) of the Government of India, has developed a laboratory-scale process for depositing novel nanostructured nickel alloy coatings.
The process uses pulsed current electroplating, which is environmentally benign with a high production capacity.
Unlike conventional direct current used for chrome plating, the research group led by Dr. Nitin P. Wasekar at ARCI has used electric current in the form of pulses lasting a few milliseconds for electroplating purposes.
The process consists of environmentally friendly electrolytes consisting of nickel and tungsten ions that are the strengthening source of elemental tungsten (W) and nickel (Ni).
The pulsed current is applied between the components to be coated, acting as a cathode and non-consumable anode.
The pulsed current effect was used for nanocrystalline coatings in which a high instantaneous current density for a very small duration resulted in a high nucleation rate.
Unlike conventional direct current coating, the coatings were virtually free of porosity, cracks and minimal hydrogen absorption.
The use of pulsed current resulted in the nanocrystallization of nickel tungsten alloy coatings with high hardness (700-1200 HV) and wear resistance.
The coatings were extremely resistant to corrosion and could withstand up to 700 hours of salt spray.
Coatings developed in ARCI can withstand temperatures up to 500°C without thermal softening and can improve the service life of matrix components at least twice as long as conventional chrome plating.
They were successfully applied to die casting components used in the plastic bottling industry, where temperatures at the die interface can exceed 280°C.
With numerous automotive, defense and aerospace applications for these coatings, process knowledge is ready to be transferred as a replacement for conventional chrome plating.
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