Influence of phase composition and microstructure on corrosion behavior of laser based Ti–Co–Ni ternary coatings on Ti–6Al–4V alloy

Although Ti–6Al–4V alloy has wide applications in marine and chemical industries, its application is highly limited in corrosive environment such as sulphuric acid. This is due to the dissolution of the passive titanium hydride (TiH₂) film formed on the surface which accelerates the corrosion of titanium alloy in concentrated sulphuric acid. In this work, laser surface modification technique was used to develop high performance anti–corrosive coatings for aggressive sulphuric environment. The effects of parameter variations and volume fraction of Ti–Co–Ni clad layer on Ti–6Al–4V were investigated. The corrosion behaviors of Ti-6A-l4V, TiCo–10Ni and CoNi–10Ti coatings were studied in 0.5 M sulphuric acid using potentiodynamic polarization technique. Thereafter, the morphologies of the coatings before and after corrosion were analyzed using scanning electron microscope (SEM) equipped with energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD) analysis to examine phase compositions and changes. The corrosion result shows that the clad compositions have significant influence on the potential by shifting the potential to more noble values and reduced the corrosion rate when compared with as-received Ti–6Al–4V. In addition, the corrosion resistance performance of CoNi–10Ti deposited at 1.2 m/min is best among all the ternary coated samples. The increase in corrosion resistance of alloys with cobalt and nickel on titanium is due to formation of dense passive CoO, TiO, TiAl, Ni₂TiO₃, V₂O₅ and Al₂O₃ oxides on the samples surfaces. With this result, the use of laser cladding technique could be established in improving the corrosion resistance of Ti–6Al–4V with Ti–Co–Ni alloy coatings.