Influence of zinc sulfate concentration in baths on the structure, morphology and tribocorrosion properties of Fe-Zn alloy coating

Abstract

To address the glazing issue of impregnated diamond bit in drilling hard and compact rock formations, Fe-Zn alloys were electrodeposited from acid sulfate baths and the surface morphology , phase composition, microhardness and tribocorrosion property of the deposits were studied. As the ZnSO 4 concentration increased from 0 g/L to 20 g/L, the morphology of deposits changed from fine-grained clusters to triangular based pyramids, and finally to granular grains. α phase, η phase and a mixture of α phase and η phase were identified in Fe-Zn coatings. And the microhardness of the deposits is influenced by the Zn content and grain size of Fe-Zn alloy. Furthermore, tribocorrosion behaviors of the deposits were investigated in NaCl solutions by electrochemical measures (potentiodynamic polarization, electrochemical current noise) with an abrasion-corrosion rig. Results of tribocorrosion tests showed that the primary form of the material loss was pure mechanical wear , except the deposit obtained at 20 g/L ZnSO 4 , whose mass loss due to corrosion-induced abrasion contributed most to its total material loss. The degradation mechanism of Fe-Zn deposits was also detailed in this paper. • Fe-Zn alloy was electrodeposited from an acid bath with improved stability. • The morphology of Fe-Zn deposits changed with the variation of phase structure. • Fe-Zn coating with 20% Zn provided the best combination of hardness and mass loss. • The wear mechanism of Fe-Zn deposits in silica slurry with NaCl was discussed.