Electrochemical Characterization of Titanium Alloys Subjected to an Atmospheric Pressure Plasma Treatment

Test coupons of three different titanium alloys, i.e., Ti-6 Al-4 V, Ti-6 Al-4 V-0.01 B and Ti-6 Al-4 V - 1.09 B (all in mass%), were polished to a mirror-like finish using standard metallographic procedures.  These alloy coupons were exposed to an atmospheric pressure plasma containing a mixture of helium and oxygen for 5 seconds. Contact angles of water with respect to the pre- and post-treated samples were measured.  The contact angles decreased significantly for all of the alloy coupons when the measurements were conducted immediately after the cold plasma treatment and slowly increased when measured after 2 h from the time of treatment. Electrochemical characterization of the pre- and post-plasma treated alloys were carried out in deaerated 3.5 mass% sodium chloride solution. The electrochemical tests included three distinct stages: (i) a 1 h open circuit exposure during which voltage  Vs time data (OCV) were obtained (ii) a linear polarization scan from -30 mV to +30 mV relative to the OCV to obtain the linear polarization resistance (LPR) and (iii) a Tafel plot from -400 mV to + 400 mV relative to the OCV. Results thus far indicate that the corrosion potentials increased after plasma treatment, i.e., the alloys indicated more nobility after the exposure.