Improved Corrosion Resistance of Metastable Beta Ti-X (X = 6Mn, 8Cr, and 36Nb) Binary Alloys As a Function of 10.Wt% Mo Equivalence

Tuesday, 30 May 2017
Grand Ballroom (Hilton New Orleans Riverside)
S. Kim and K. Lee (Chonnam National University)
Beta type titanium alloys are developed as metallic biomaterials due to their low elastic modulus compared to well-known Ti-6Al-4V alloy. Since Mo is known to be an efficient beta phase stabilizer, Ti-Mo binary alloy have been extensively studied on their microstructural characteristics, mechanical properties and corrosion resistance. The stability of the beta phase can be expressed using the “molybdenum equivalent” which has minimum critical value of 10-11 .wt%. Niobium is well known to be very good to resist against corrosion in simulated body fluid and presents an excellent biocompatibility. Mn was selected as an alloying element due to its beta stabilizing effect, low cytotoxicity, high availability and lower cost when compared to other popular alloying elements. Cr-induced passive layer has been proven to be strong and solid. Ti-Cr based alloys also have been widely used for dental applications. In this study, the amount of alloying additions were calculated as a function of 10 .wt% Mo equivalence in order to evaluate the corrosion performance of each alloy. Potentiodynamic polarization test and time-based electrochemical impedance spectroscopy (EIS) were used to evaluate the corrosion behavior in Ringer’s solution. It was found that the corrosion parameters obtained from potentiodynamic polarization test were not significantly different to those of Ti-10Mo alloy. Substituting Mo to the other studied elements simply shifts the corrosion potential into less-noble zone. However, the overall corrosion current density were lower compared to those of Ti-10Mo alloy. The lowest corrosion current density observed in Ti-6Mn alloy with the value of 7.742 nA/cm2, which 8 times lower than those of Ti-10Mo with the value of 48.81 nA/cm2. Impedance responses increase with increasing immersion time. There is little difference in the profiles in the high- and medium-frequency regions, but at lower frequencies the difference becomes substantial. The solution-film resistance element remains low for different immersion times at lower potentials, while film-substrate resistance increases with time. At higher potentials, both resistance have comparable values, pointing to the increased protectiveness, or less defective structure, of the outer porous layer at higher potentials. This result agrees with XPS evaluation on the passive film which formed on their most stable formation within the working potential range. At OCP, the capacitance values increase with the time. While at higher potentials, the capacitance values remain constant with time.