On the passive and semiconducting behavior of severely deformed pure titanium in Ringer's physiological solution at 37°C: A trial of the point defect model

Enhanced Corrosion Resistance and Biological Properties of Ultrafine-Grained Ti15Zr5Cu Alloy

Titanium alloys are widely used in the biomedical field. To ensure their strength meets requirements in clinics, medical titanium alloys are generally alloyed with toxic Al and/or V elements, hence ensuring their long-term biological safety after implantation is a challenge. In our previous research, we developed an ultrafine-grained Ti15Zr5Cu alloy without toxic elements while its mechanical properties were at the same level with the most widely used Ti6Al4V alloy. In order to promote the clinical application of the ultrafine-grained Ti15Zr5Cu alloy, herein we have systematically studied the hot deformation behaviors of the material as well as evaluated its corrosion resistance and biological properties. Results showed that when the as-quenched Ti15Zr5Cu alloy deformed at 0.05 ≤ ε˙ ≤ 1, 730 °C ≤ T ≤ 750 °C, it not only possessed good workability but also can be converted into an equiaxed ultrafine-grained microstructure. Moreover, the material also exhibited better corrosion resistance, antibacterial properties and biocompatibility than the Ti15Zr alloy and the commercial pure Ti. The results of the present study help lay a foundation for the development of a new generation of medical titanium alloys.

Electronic properties and surface potential evaluations at the protein nano-biofilm/oxide interface: Impact on corrosion and biodegradation

The formation of a protein nano-biofilm, which exhibits a special electronic behavior, on the surface of metals or oxide biomaterials considerably influences the crucial subsequent interactions, particularly the corrosion and biodegradation processes. This study discusses the impact of electrical surface potential (ESP) of a single or nano-biofilm of albumin protein on the electrochemical interactions and electronic property evolutions (e.g., charge carriers, space charge capacitance (SCC), and band bending) occurring on the surface oxide of CoCrMo implants. Scanning Kelvin probe force microscopy (SKPFM) results indicated that ESP or surface charge distribution on a single or nano-biofilm of the albumin protein is lower than that of a CoCrMo complex oxide layer, which hinders the charge transfer at the protein/electrolyte interface. Using a complementary approach, which involved performing Mott-Schottky analysis at the electrolyte/protein/oxide interface, it was revealed that the albumin protein significantly increases the SCC magnitude and number of n-type charge carrier owing to increased band bending at the SCC/protein interface; this facilitated the acceleration of metal ion release and metal-protein complex formation. The nanoscale SKPFM and electrochemical analyses performed in this study provide a better understanding of the role of protein molecules in corrosion/biodegradation of metallic biomaterials at the protein nano-biofilm/oxide interface.

In Situ Electrochemical Study of the Growth Kinetics of Passive Film on TC11 Alloy in Sulfate Solution at 300 °C/10 MPa

TC11 alloy is a promising structural material, and has a wide range of applications in many corrosive and high temperature hydrothermal systems. The passive film has an important influence on its electrochemical behavior. In this study, in-situ electrochemical methods (that is, open circuit potential (OCP), linear polarization (LP) and electrochemical impedance spectroscopy (EIS)) were used to monitor the long period electrochemical behavior of TC11 alloy in 0.01 M Na₂SO₄ solution at 300 °C/10 MPa. The growth kinetics of the passive film was mainly studied. The correlation between the evolution of the electrochemical behavior and the growth of the oxide film was discussed. The results showed that although the OCP gradually stabilized after twenty thousand seconds, henceforth the polarization resistance (R_p) was still increasing due to the thickening of the passive film. An equivalent circuit was proposed to fit the EIS experimental data, leading to determination of film capacitance and film resistance. Besides, the electrochemical data was interpreted in terms of the point defect model (PDM). The EIS results are consistent with the R_p results.