Growth of carbon layers on Ti-6Al-4V alloy by very high dose carbon implantation

Ion implantation is a useful technique to tailor the surface properties of Ti-6Al-4V alloys. In particular, very high dose C⁺ implantation (in the range of 10¹⁸ ions cm^-2) offers the possibility of forming carbon layers without a sharp interface with the substrate material. In this study, ion implantation treatments have been performed on Ti-6Al-4V with C⁺ doses up to 4 × 10¹⁸ ions cm^-2. XPS analyses have been carried out to evaluate the chemical states after ion implantation. A change in C 1s binding energies has been observed depending on the carbon concentration in the implanted layer. At relatively low or medium concentrations (about 41 at.% C) mainly carbidic bonds were present, but when the concentration increased up to 88 at.%, the binding peak shifted to values that correspond to C-C bonds. Dynamic microindentation techniques, used to evaluate the hardness of the implanted material, have shown a significant change in relative hardness as a function of C⁺ dose, owing to the formation of a carbon layer in the titanium alloy surface. A two-fold increase in the hardness ratio and elastic recovery values is observed for the highest implanted dose.