Dynamic tribochemical behavior of TiN/TiCN coated Ti6Al4V in artificial seawater

Abstract

TiN/TiCN double coatings were deposited on Ti6Al4V alloy by arc ion plating to improve wear resistance of the titanium alloy in seawater. The TiN interface layer was incorporated between the top TiCN coating and Ti6Al4V substrate. The TiN/TiCN coatings have a typical columnar crystal of the inner TiN coating with a thickness of 1 μm and top TiCN coating with a thickness of 1 μm. The TiN/TiCN coatings have a hardness of about 30 GPa and a low friction coefficient of 0.15, which is far lower than 0.35 of untreated Ti6Al4V alloy. The Ti6Al4V with TiN/TiCN coatings have a minimum wear rate of 2.42 × 10⁻⁵ mm³ N⁻¹ m⁻¹, which is far lower than 23.3 × 10⁻⁵ mm³ N⁻¹ m⁻¹ for uncoated Ti6Al4V alloy. During a friction process in seawater, these coatings have a small fluctuation in the potential and show more stability. However, the untreated Ti6Al4V substrate shows notable fluctuation in potential and it is more affected by the interactions of corrosion and wear. Compared with the TiN coating and Ti6Al4V alloy, TiN/TiCN coatings have a small amount of the removable surface layer and little chemical transfer film due to a lower friction coefficient, excellent chemical stability, and high hardness. Seawater medium accelerates the initiation of cracks and induces formation of delamination failure of the coatings.