Thermally oxidized electron beam melted γ-TiAl: In vitro wear, corrosion, and biocompatibility properties

In this investigation, an electron beam melting-processed gamma-TiAl alloy (Ti-48Al-2Cr-2Nb, at.%) was oxidized in air to improve its in vitro tribological, electrochemical, and biocompatibility properties. The gamma-TiAl alloy samples were oxidized at 400, 600, and 800 degrees C for 1 and 4 h. The oxidized layer thickness, composition, and surface morphology found to change with oxidation temperature. The oxidation thickness varied between 1.29 +/- 0.2 and 2.18 +/- 0.2 mu m. The primary oxides on the surface were Al2O3 and TiO2 with minor concentrations of Cr2O3, Nb2O5, and nitrides of Ti. The surface hardness of the alloy increased by 1.7-fold with increasing temperature from 400 to 800 degrees C with 1 h soaking, and at 4 h, the maximum hardness was 12.26 GPa. The high hardness of the oxidized gamma-TiAl alloy resulted in two orders of magnitude lower wear rate than the bare gamma-TiAl alloy. Oxidation at 800 degrees C for 4 h resulted in significant reduction in corrosion current and no passivity breakdown was observed. In vitro cell culture experiments, using mouse preosteoblast cells, revealed high cell density on the oxidized gamma-TiAl alloy, suggesting its enhanced cell proliferation compared to the bare gamma-TiAl alloy and CP-Ti.