Electroless nickel-boron coatings

Chemical nickel-boron coatings are closely related to chemical nickel-phosphorus coatings and electrolytic nickel coatings. They result from the aqueous-phase reduction of nickel salts but, unlike electrolytic deposits, do not require the use of an external power source. As their name suggests, they contain a significant boron content, which gives them a number of interesting properties. In addition to the usual properties of electroless coatings, i.e. dimensional conformity and thickness homogeneity, coating of complex parts and blind holes, coating of non-conductive substrates, nickel-boron deposits feature a high hardness that can exceed that of hard chromium coatings after heat treatment, excellent resistance to abrasive and sliding wear, and acceptable corrosion resistance. They are also good electrical conductors and possess catalytic properties due to the presence of boron.

All these properties open up a wide range of applications for nickel-boron chemical coatings in a variety of industrial fields.

This article presents the theory of electroless nickel deposition on the one hand, and the means of synthesizing it on the other, including the parameters for regulating the deposition baths. The various properties of the coatings obtained are also discussed and related to the properties of nickel-phosphorus coatings, which are more widely known. Recent and future developments are also discussed.

At the end of the article, readers will find a glossary and a table of symbols used.