*3.2.1 Corrosion (electrochemical polarization) test*

Corrosion behavior of all coated samples are evaluated by electrochemical polarization test in simulated fluid as proposed by Kokubo and Takadama [39]. The primary reason to use Tafel polarization was to evaluate corrosion current density of all HA-CNT coatings in simulated body fluids whereas Potentiodynamic measurement were carried out to study the passive behavior of the coatings. Tafel polarization measurement were carried out starting from −250OCP mV to +250OCP mV with a scan rate of 1 mV/s, whereas Potentiodynamic polarization were carried out starting from -250OCP mV to 1600SCE mV. **Table 4** represents the polarization test results. The corrosion current in the case of SS 316 L is more as compared to that of CoCrMo and Ti6Al4V, hence it can be inferred that corrosion resistance of Co and Ti-based alloy is more than that of SS. Also, the passivation range of Ti alloy obtained from potentiodynamic curves is comparatively larger than that of SS and Co alloy, which supports the results of the Tafel polarization method. The results obtained from Potentiodynamic polarizer suggests that all as sprayed HA-CNT coatings show passive behavior in simulated body fluids which support the low current density presented by Tafel polarization method.
