Electrochemical analysis of mechanically alloyed Ti_50%-Ni_50% alloy for bone implants use

The corrosion resistance of an implant material is an essential element of its biocompatibility. This research focuses on studying the effect of grinding/milling time on the corrosion behavior of the mechanically alloyed Ti_{50 %}-Ni_{50 %} (at%) alloy, for bone implant use, at varying milling times of 2, 6, 12, and 18 h. The powder particles' size, shape, and homogeneous chemical content were examined employing scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The alloyed particles' structural characteristics were determined by X-ray diffraction (XRD). Moreover, the characterization of the electrochemical properties was performed utilizing open-circuit potential (OCP) measurement, the Potentiodynamic Polarization (PD), and the Electrochemical Impedance Spectroscopy (EIS) technique. Electrochemical tests were conducted in physiological mediums simulating the human body: Hank's solution. The results revealed that; as the grinding time increased the crystallite size reduced from 57 nm to 29 nm, whereas the lattice parameters increased slightly from 3.18 to 3.22 Å, while the microstrain increased from 0.32 % to 0.99 %. Moreover, the hardness and Young's Modulus increased by about 70 and 16 %, respectively with milling period going from 2 to 18 h. The findings of the electrochemical test demonstrated that as milling progressed, corrosion resistance increased. The evolution of OCP curves as a function of the duration of immersions indicated that OCP increased with the duration of immersion up to 2500 s; this is due to a stable passive layer that has formed on the samples' surface. The results of potentiodynamic polarization curves revealed that both corrosion current density (i_corr) and corrosion rate (CR) decreased reaching a value of 3.6945E-07 A/cm² and 0.0074722 mm/year, respectively, at longer milling time (18 h). While, corrosion potential (E_corr) increased from −0.51255 V/_SCE to −0.29997 V/_SCE with increasing grinding time. Additionally, the EIS data indicated that the resistance of the passive film increased with increasing milling times. The samples of Ti₅₀-Ni₅₀ produced at longer milling time exhibited excellent corrosion resistance due to the formation of a stable passive film which makes them useful for bone implants.