Corrosion and erosion-corrosion of electrodeposited Ni–P/B 4 C composites

Abstract

The present paper reports on electrodeposition, characterisation, corrosion, and erosion–corrosion of Ni–P and Ni–P/B₄ C layers on a brass substrate. Alloys with 5%P and 8 vol.-% micrometric B₄ C were prepared from a lactate bath at pH 4 containing H₃ PO₃. The following deposit properties were measured and related to corrosion behaviour: composition (EDS, XPS), crystalline structure (XRD), morphology (inplane and cross-sectional SEM), and mechanical properties. The immersion and anodic behaviour of pure matrix and composite samples was studied in slightly acidic, aerated chloride solutions. The presence of B₄ C particles is correlated with higher crystallinity of the matrix at a given P content. Anodic linear sweep voltammograms show more noble breakdown potentials and lower plateau current densities for the composites. The pit-arresting effect of particle addition was assessed. More noble corrosion potentials and much lower mass losses, pitting, and crevice formation were observed under erosion–corrosion conditions with normal impact of a sand containing slurry.