Surface chemical and nanomechanical aspects of air PIII-treated Ti and Ti-alloy

Abstract

Plasma immersion ion implantation (PIII) of Ti and Ti6Al4V alloy in dry air plasma has been performed with 25 kV negative pulses up to 1.9×10 18 cm −2 doses. For comparison, prolonged (50–100 h), high-temperature (600–650 °C) heat treatment of a similar Ti-alloy in air (TO treatment) was also performed. The changes in chemical composition, structure and hardness of the modified surfaces were studied by XPS, X-ray diffraction (XRD) analysis and nanoindentation measurements. According to XPS, surface oxidation and strong surface enrichment of Al occurred on the Ti-alloys after both the “non-equilibrium” PIII treatment and the “equilibrium” TO treatment. After the air PIII treatment Ti and Al were present in fully oxidized (TiO 2 and Al 2O 3) states, and neither nitrogen nor vanadium could be detected in the topmost layer. XRD showed the formation of rutile and substoichiometric TiO 2− x phases on the PIII-treated Ti and TO-treated Ti-alloy, but no crystalline oxide phase was found on the PIII-treated Ti-alloy. The surface hardness and the scratch resistance of the samples increased significantly after PIII treatment. The surface hardening and the improved scratch resistance of the oxidized Ti-alloy samples can be explained mainly by the surface segregation of Al and the formation of a layer containing oxidized Ti and Al.