Abstract(s) :

(Anglais) Electroless nickel-boron coatings usually contain a non-negligible amount of a third element due to the co-deposition of heavy metals whose salts are used as stabilizer during the plating process. It is possible to deposit purely binary electroless nickel-boron coatings by strongly modifying the plating conditions, i.e. increasing the alkalinity of the plating bath and the amount of chelating agent. The coatings obtained by this method differ significantly from typical electroless nickel-boron coatings: they present smooth featureless surface and high boron content (up to 8 wt.%). Their as-plated hardness is also significantly lower than that of standard electroless nickel-boron-(lead) coatings. For this reason, it’s interesting to optimize heat treatment of the purely binary coatings. It has been shown that, while the hardness of as-plated coatings is strongly influenced by the presence of a third element (originating from the stabilizer), the hardness of the heat-treated coatings depends more on the presence of hard phases such as Ni3B nickel borides.