The corrosion-wear response of Cr-Ti coatings

Titanium alloys display problematic behaviour in environments where wear and corrosion take place either simultaneously or sequentially. While various surface treatments have been proposed for the alleviation of corrosion and wear of Ti-6Al-4V, there is still scope for new and novel approaches. In the work reported here, three coating compositions: Cr-13 at.%Ti, Cr-33 at.%Ti and Cr-48 at.%Ti, were synthesised by unbalanced magnetron sputter deposition and applied to Ti-6Al-4V substrates. In the as deposited state the coatings were single phased, while subsequent vacuum heat treatment at 800 °C resulted in the formation of the Laves phase (α-TiCr2). Coated Ti-6Al-4V test pieces were subjected to reciprocation sliding corrosion-wear tests in 0.9% NaCl solution at 37 °C. All the coated variants tested showed a reduction in corrosion-wear compared to uncoated Ti-6Al-4V. The most effective coatings were those that contained the Laves phase (α-TiCr2). It is proposed that the passive film formed on the Laves phase had greater mechanical integrity than any others formed during corrosion-wear testing and this phenomenon was a key factor in providing the observed enhanced surface durability.