Corrosion Characteristics of High-Temperature Oxidized TC21 Alloy in Simulated Body Fluid Containing Proline Coated with Nb/Ag

The effect of various thermal oxidation parameters on the shape, oxide layer thickness, and oxidation kinetics of TC21 alloy was investigated in a 50-h dry air experiment at temperatures of 650, 750, and 850 °C. The oxidation rate at these temperatures was determined using a parabolic equation based on weight gain. The parabolic rate constants at 650, 750, and 850 °C were 2.0*10⁻⁹, 8.0*10⁻⁸, and 1.0*10⁻⁶ g²/(cm⁴ h), respectively, with an activation energy of 268.6 kJ/mol. SEM and EDX analyzed scale morphology, while XRD determined phase composition. The study assessed surface shape, phase composition, and oxidation kinetics. The corrosion behavior at room temperature of oxidized TC21 alloy at 850 °C for 50 h in dry air coated with Nb or Ag in simulated body fluid (SBF) with proline was tested using immersion and potentiodynamic polarization (PDP) methods. Ag-coated TC21 showed the lowest corrosion rate values (12.9 mm/y by weight loss and 0.11 mm/y electrochemically) after 3 months, indicating its potential for medical applications. Elemental analysis and surface appearance of corroded TC21 were also evaluated.