Electrochemical comparative study on corrosion behavior of conventional and powder metallurgy titanium alloys in physiological conditions

This article focuses on the electrochemical study of two titanium alloys employed in the manufacture of orthopedic implants - Ti-6Al-4V and Ti-6Al-7Nb - both of them obtained through powder metallurgy (PM). For comparative purposes, Ti-6Al-4V fabricated conventionally has also been investigated. Samples were immersed in a simulated body fluid (SBF) and incubated at 37 °C for different immersion time. Under these experimental conditions, we compared the influence of the processing method of alloys (PM or conventional) and their composition in the corrosion resistance. The corrosion resistance of these alloys in contact with SBF was evaluated with electrochemical impedance spectroscopy (EIS). The resulting impedance plots of all of them showed good reproducibility. For the lowest frequency tested (10 mHz) all of the samples showed high impedance modulus value approximately on the order of 106 Ω. This behavior is usually ascribed to a high corrosion protection performance. Although no significant differences in the evolution of the corrosion behavior for different immersion times has been found; the Ti-6Al-7Nb alloy processed by PM delivers a steady growth of corrosion resistance from day one until twelve weeks immersion. This sample showed the best performance between the two studied compositions. The resulting impedance plots show how powder metallurgy allows obtaining materials with similar or superior corrosion resistance in physiological conditions, than alloys obtained conventionally. Alloys characterization by scanning electron microscopy revealed no evidence of pitting corrosion phenomenon.