An assessment of the corrosion resistance of powder sprayed titanium coatings

Abstract

Aluminium and stainless steels are susceptible to pitting corrosion in sea water. Mild steel is susceptible to corrosion in general. Titanium however, has good corrosion resistance in chloride solutions and thus is not susceptible to pitting in sea water. The following is an assessment of the corrosion resistance of Titanium powder coatings. Potentiostatic electrochemical experiments were carried out on three substrates (stainless steel, mild steel and Aluminium) coated using two spray methods (plasma and HVOF). A discussion of the results was given with reference to the polarisation curves that were created, SEM images, XRD results, estimates of porosity, and Pourbaix diagrams. It was concluded that the plasma coating provides the best corrosion resistance due to the fact that it had less porosity than HVOF and that it is made up of Titanium oxides. Also, the corrosion mechanism for the coatings is pitting of the substrates at the end of pores. The extent of this is far greater for the HVOF than the plasma coating. It was found that features found in the polarisation curves for the substrates are present in the curves for coatings. This is more evident in the HVOF polarisation curves. Mild steel benefited the most from the Titanium coatings compared to the substrate (more so for the plasma coating). Finally, the plasma coating improves the substrate based on corrosion rate and thermodynamics, except for Aluminium which remains the same thermodynamically.