Effect of zirconia coating on Ti6Al4V at elevated substrate temperature on its wear, corrosion and hemocompatibility properties

Titanium and its alloys have been recognized as biocompatible materials since decades although these materials can at times show wear, corrosion and thrombosis leading to various health complications. Surface coating has been found to be one of the effective techniques to overcome this issue in-vitro as well as in-vivo. In this paper, thin film coating of zirconia (ZrO2) on Ti6Al4V is reported using pulsed laser deposition (PLD) technique at elevated substrate temperatures ranging from room temperature to 800 degrees C (TiZr800). The morphology, composition, wettability and average surface roughness of the samples were analyzed by scanning electron microscope, Raman spectrometer, water contact angle (WCA) and profilometer, respectively. Adhesion between film and substrate was qualified using Elcometer. The tribological studies were performed in ball-on-disc against ZrO2 counterpart, the electrochemical potential analysis was done in simulated body fluid to replicate body environment and the hemocompatibility test was evaluated on the basis of human whole blood adsorption and distribution of Red Blood Cells (RBCs) on the samples. The results revealed an increase in WCA and film adhesion with increased substrate temperature. At 800 degrees C, formation of zirconium carbide, a relatively harder material, was observed due to diffusion of substrate carbon into ZrO2 film, as confirmed by the Raman analysis. In comparison to pristine, TiZr800 sample showed a reduction in wear rate from 3.5 x 10-3 mm3/Nm to 1.1 x 10-3 mm3/Nm indicating improved resistance of the sample against abrasive wear. Further, drop in Icorr from 4.96 x 10- 7 A/cm2 to 2.75 x 10-7 A/cm2 resulted in a 44 % increase in corrosion protective efficiency of the sample coated at 800 degrees C. Additionally, a 4.5 fold increase in RBC counts was observed on TiZr800 sample. Therefore, it is inferred that while ZrO2 coating can improve overall surface properties of Ti-6Al-4V, additional benefits can be obtained by performing PLD at higher substrate temperatures, more so when the temperature is such as to promote formation of ZrC in the coating.