Fabrication of Ni–Co–P Alloy Coatings Using Jet Electrodeposition with Varying Reciprocating Sweep Speeds and Jet Gaps to Improve Wear and Seawater Corrosion Resistance

Abstract

Type 45 steel substrate surfaces were coated with Ni–Co–P alloy coatings using jet electrodeposition in varying reciprocating sweep speed and jet gap to improve the wear and seawater polarization resistance of the substrate surface. The properties of the deposited coatings were analyzed and characterized. The results showed that the morphologies of the cross-section, thickness, and chemical composition of coatings were affected by reciprocating sweep speed and jet gap variation. At a reciprocating sweep speed of 175 mm·s−1 coupled with a jet gap of 2.0 mm, the content of Co element in the deposit attained the highest value of 47.66 wt.%. Reciprocating sweep speed and jet gap variation exhibited no significant influence on either the phase structure or the peak intensities of deposited Ni–Co–P coatings, but an obvious preferred orientation was evident in the (111) plane. Further increase in reciprocating sweep speed and jet gap caused an initial increase in the microhardness of Ni–Co–P alloy coatings followed by a decrease, where the highest value attained was 635 HV0.1. At a jet gap of 2.0 mm and a reciprocating sweep speed of 175 mm·s−1, Ni–Co–P alloy coatings reached a minimum wear scar width value of 460 µm. Electrochemical tests showed that the seawater corrosion resistance of coatings exhibited an observable change with increased reciprocating sweep speed and jet gap. The Ni–Co–P alloy coatings exhibited the highest polarization resistance (Rp) of 28.32 kΩ·cm−2 when the reciprocating sweep speed was 175 mm·s−1 and the jet gap was 2.0 mm, which indicated that the coatings had better seawater corrosion resistance.