Electrospark deposition of wear and corrosion resistant Ta(Zr)C-(Fe,Mo,Ni) coatings to protect stainless steel from tribocorrosion in seawater

The offshore and coastal infrastructure needs additional protection from wear, corrosion, and tribocorrosion. Herein, electrospark deposition (ESD) was employed to deposit composite TaC-(Fe,Mo,Ni) and (Ta,Zr)C-(Fe,Mo,Ni) coatings with a metallic matrix (similar in elemental composition to that of stainless steel) reinforced with carbide nanoparticles. The coatings were produced using TaC–Mo–Ni and TaC–ZrC–Mo–Ni electrodes under different energy regimes by varying frequency, voltage, and pulse duration to obtain different carbide contents. The obtained coatings have a bilayer composite structure: core-shell TaC–ZrC crystallites embedded in an Fe-based metal matrix with a (Ta,Zr)C network (zone 1) and approximately 5 nm Fe-based nanocrystallites surrounded by amorphous interlayers (zone 2). The tribological properties of TaC-(Fe,Mo,Ni) and (Ta,Zr)C-(Fe,Mo,Ni) coatings were superior to those of uncoated AISI 304 stainless steel, both in the 3.5% NaCl solution and in 3.5% NaCl + SiC suspension. The electrochemical characteristics of the best coatings were comparable to those of the stainless steel. Tribocorrosion tests indicated that when load is applied, the open-circuit potential values of steel reduce more significantly than those of the coatings. • Composite Ta(Zr)C-(Fe,Mo,Ni) coatings obtained by electrospark deposition in vacuum. • Carbide grains with core-shell structure: Zr-rich core, Ta-rich shell. • Coatings with enhanced tribological properties in 3.5% NaCl and SiC suspension. • In stationary corrosion Ta(Zr)C carbides protect Fe-based matrix. • At polarization, corrosion is determined by dissolution of more active matrix phase.