The mechanical properties and electrochemical behavior of two new titanium alloys, Ti20Mo7Zr and Ti20Mo7Zr0.5Si, are investigated in this paper. The alloys have been manufactured by vacuum arc remelting (VAR) technique and studied to determine their microstructure, corrosion behavior, and mechanical properties. Metallographic observations and quantitative microanalysis by optical microscopy, scanning electron microscopy SEM, and energy dispersive X-rays spectroscopy EDX were performed. Data about the three-point bending test and microhardness are presented. For electrochemical properties, three different environments were used: Ringer solution at 25 °C, Ringer solution at 40 °C simulating fever condition, and 3.5% NaCl solution. Metallographic investigation revealed the biphasic and dendritic structure of both samples when the procedures were performed. Electrochemical testing in body simulation fluid, fever conditions, and saline medium showed that the lower the proportion of silicon in the samples, the higher the corrosion resistance. The formation of a titanium oxide layer on the surface of both samples was noticed using quantitative EDX analysis. The three-point bending test for the two samples revealed that the presence of silicon decreases the modulus of elasticity; the surface of the samples displayed soft and hard phases in the microhardness test. Electrochemical impedance spectroscopy (EIS) measurements were carried out at different potentials, and the obtained spectra exhibit a two-time constant system, attesting double-layer passive film on the samples.

The design principle of high-entropy alloys is to mix many chemical elements in equal or nearly equal proportions to create new alloys with unique and special properties such as high strength, ductility and corrosion resistance. Some properties of high-entropy alloys can be adjusted via introducing new doping elements, which are selected according to working conditions. The high-entropy alloy CoCrFeMoNi was examined to determine the impact of Ti doping on its micro-structure, microhardness and elastic modulus. Microstructure analysis revealed a core structure consisting of both face-centered cubic (FCC) and body-centered cubic (BCC) phases, along with the formation of a Laves phase. The addition of Ti made the alloy grains finer and reduced the Mo concentration difference between the interdendritic and dendritic regions. As a result of Ti doping, the microhardness of the alloy increased from 369 HV 0.2 to 451 HV 0.2. Ti doping produced a doubling of the breaking strength value, although no significant changes were observed in the elastic modulus of the CoCrFeMoNi alloy.

The promising results obtained in the research of high-entropy alloys are increasingly encouraging new configurations of these alloys. Our research was conducted on the high-entropy CoCrFeMoNi alloy and the Ti-doped CoCrFeMoNi alloy. Electrochemical impedance spectroscopy (EIS) measurements were performed on samples with and without Ti-doped CoCrFeMoNi high-entropy alloys in order to evaluate the influence of voltage on their behavior in a simulated aggressive environment. The impedance spectra were measured between −1.0 and +0.8 V vs. SCE at various potential levels. Using an electrical equivalent circuit to match the experimental data, the impedance spectra were analyzed. The corresponding circuit that successfully fits the spectra has two time constants: the first one is for the attributes of the compact passive layer and the second one is for the features of the porous passive layer. The results show that doping CoCrFeMoNi alloy with 0.36 at.% Ti reduces the alloy’s ability to resist corrosion, as the alloy can react more quickly to the surrounding environment and cause a decrease in the corrosion resistance of the alloy.

The main purpose of this research is to evaluate the mechanical characteristics and biocompatibility of two novel titanium alloys, Ti15Mo7ZrxSi (x = 0, 0.5, 0.75, 1). These samples had already undergone grinding, polishing, cutting, and chipping. Electrochemical, metallographic, three-point bending, and microhardness studies were conducted on the studied materials to determine their corrosion behavior, microstructure, Young’s modulus, and hardness. The first investigations revealed that both samples had biphasic and dendritic structures, elastic moduli that were between the highest and minimum values achieved by around 20 GPa, and favorable behavior when in contact with physiological fluids at ambient temperature. Ti15Mo7Zr0.5Si and Ti15Mo7Zr0.75Si, the research samples, had greater corrosion potentials, reduced corrosion rates, and therefore higher corrosion resistance, as well as modulus of elasticity values that were comparable to and closer to those of human bone. The results of this investigation indicate that both alloys exhibit favorable corrosion behavior, great biocompatibility, Young’s modulus results lower than those of conventional alloys used in biomedical implants, and hardness values higher than commercially pure titanium.