Study of electroless nickel coatings on EN-GJS-500-7 spheroidal graphite cast iron

Abstract

EN-GJS-500-7 spheroidal graphite (SG) cast iron was coated with chemical Ni-P. The kinetic study reveals that the limiting step corresponds to a classical surface process, but the morphological study shows, at short times, an imperfect Ni-P coating on the graphite spheroids. The initial Ni-P growth appears to be blocked. This problem has been solved by the application of a cathodic polarization for a few minutes as a pretreatment of the surface. It was observed after this first step that both chemical and electrochemical reduction of nickel cation and hypophosphite on the SG cast iron took place at the same time, leading to the growth of a homogeneous Ni-P scale, in particular on graphite spheroids.