The main aim of the present study has been to investigate the electrochemical behavior of, and oxide film formation on, the bulk amorphous Zr55Cu30Ni5Al10 alloy and the crystalline counterpart in simulated body fluid. Different analytical methods, e.g., polarization and electrochemical impedance measurements, were used to compare the results of the samples when exposed to, phosphate buffered saline (PBS), with or without the addition of protein (albumin). Moreover, the influence of pH on the corrosion behavior of the materials was also investigated. Pitting corrosion was observed to exist on both amorphous and crystalline samples after exposure to the PBS solution, but the passivity region was much smaller for the crystalline material. The addition of protein to the PBS solution improved passive behavior and led to higher pitting potential in the case of the crystalline samples, while the pitting corrosion potential decreased slightly in the case of the amorphous samples. Furthermore, a decrease in the pH level accelerates the dissolution rate of both materials when exposed to the PBS environment, however, in the presence of albumin the pitting corrosion potential increased in the case of both materials.
Electrochemical behavior of, and metal ion release from the bulk amorphous (glassy) Zr55Cu30Ni5Al10 alloy (Zr‐MG) was evaluated in simulated body fluid (phosphate buffer saline [PBS]), with and without additions of protein (albumin Fraction V) at pH 7.4 and 5.2 and at body temperature 310 K (37 °C). The passivation behavior and susceptibility to pitting of the Zr‐MG was compared with conventional load bearing implant materials, that is, the medical grade ASTM F75 cast CoCrMo alloy (CoCrMo) and AISI 316 LVM low carbon vacuum re‐melted stainless steel alloy (SS). Furthermore, the metal ion release from the main constituent elements of each alloy was measured and compared. All materials showed passive behavior in the PBS solution with and without presence of albumin, though the passive region was smaller for the Zr‐MG compared to the CoCrMo and SS. Moreover, all materials experienced pitting corrosion in the PBS solution while the Zr‐MG was the most susceptible and the CoCrMo was the least one. Protein additions to the CoCrMo and SS prevented the formation of stable pits at pH 7.4 and 5.2. A decrease in passive region and pitting potential was seen in the case of albumin additions for the Zr‐MG at pH 7.4, while the opposite was seen at pH 5.2. Furthermore, the total metal ion release from the Zr‐MG was less than for the CoCrMo.
In the present study, the CALPHAD (CALculation of PHAse Diagrams) methodology and thermodynamic data were used to calculate the equilibrium phase diagram of the Zr-Fe-Al system. Furthermore, the information for the enthalpy of mixing (ΔHmix) and the atomic radius of the constituent elements, in terms of the generalized topological instability factor (λ), were combined with the ternary phase diagram to predict compositions with high Glass Forming Ability (GFA). Compositions with a Zr content ranging from 67 to 73 at. % were proposed and later produced by rapid cooling using suction casting. The obtained results revealed that 12 out of the initial 14 compositions were successfully made into glassy structures with a critical diameter ranging from 0.5 to 2.5 mm. The achieved results show good agreement between the predictions made and the experimental results, and the corresponding λ value obtained for the highest GFA was used to identify the optimum area of interest for producing Zr-Fe-Al metallic glasses. It is believed that the proposed computational approach can be used as a guideline to predict glass forming areas/compositions in even other systems.
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