Abstract
Ti (Titanium), TiN (Titanium Nitride) and Ti/TiN bilayers were deposited on stainless steel (AISI 316L) using unbalanced magnetron sputtering process. Multilayered coatings were prepared with different numbers of Ti/TiN bilayer (1, 2, 4, 8, and 16). The structural, mechanical and corrosion resistance properties of TiN and Ti/TiN multilayer coatings were systematically analyzed by a variety of characterization techniques. The phases, thickness, and hardness of these coatings were determined by XRD, SEM and nanoindentation tester respectively. Surface morphology and roughness of the coatings were analyzed by AFM. The corrosion resistance properties of these coatings were evaluated by potentiodynamic polarization tests in a 3.5wt% NaCl and Hank's solution. The results showed that the Ti/TiN multilayer coatings became smoother and denser with increasing number of bilayers as compared to the coating having only TiN. XRD results revealed TiN growth in (111) plane for all the multilayer coatings having different numbers of Ti/TiN bilayers. The hardness measured by nanoindentation showed almost the same hardness i.e. 9–10GPa for the multilayer coatings while the monolithic TiN layer showed 13GPa. The corrosion resistance of the multilayer coatings improved in comparison to the monolithic TiN layer when studied in 3.5wt% NaCl and Hank's solution. Also, amongst the coatings, 16 bilayers exhibited the best corrosion resistance behavior both in 3.5wt% NaCl and Hank's solution. This is attributed to the smooth surface as well as the presence of higher number of interfaces, as the number of Ti layer increases. The pitting corrosion resistance properties improved with increase in total coating thickness.
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