Santiago Brito-Garcia

Titanium–manganese alloys have emerged as a promising option of β-phase titanium alloys, which have recently gained popularity thanks to their exceptional cold strength, deformability, and high specific strength. In this study, the vacuum arc melting process was used to obtain a Ti3Mn alloy, and its behavior in three physiological conditions was analyzed: at room temperature, simulated fever conditions (at 40 °C), and simulated severe infection conditions (pH = 1.2). Optical and scanning electron microscopy were employed to study the effect of Mn addition on the Ti-base alloy microstructure. It was observed the formation of fine precipitates of Mn2Ti, localized at the grain boundaries, allow for the increase in microhardness and blocked their growth. The beta phase of titanium was obtained as fine lamellae with a low level of porosity. The microhardness values were higher than those reported for cp-Ti. The electrochemical tests have shown a high resistance to corrosion in the three analyzed conditions. On the sample’s surface, there is a passive bilayer film, composed of a porous one being in contact with the physiological liquid and a compact one in contact with the bulk alloy. The results obtained suggest that Ti3Mn alloy can be a promising low-cost biomaterial for biomedical applications.

High-entropy alloys (HEAs) are a family of materials that, because of their particular characteristics and possible uses in a variety of industries, have garnered a lot of interest recently. One such promising HEA is the MoNbTaTiZr high-entropy alloy, which displays excellent corrosion resistance and biocompatibility alongside good mechanical properties. Another promising HEA that has attracted researchers for its potential applications in various fields is FeMoTaTiZr. Exchanging one of the elements may result in important variation of properties of a material. This work studies two different samples of high-entropy alloys, MoNbTaTiZr (named NbHEA) and FeMoTaTiZr (named FeHEA), both generated in a laboratory context using electric-arc remelting technology, keeping similar atomic percentage of the elements in both alloys. Optical microscopy and scanning electron microscopy techniques were used to characterize the microstructure of the alloys. Replacing Nb for Fe affects the distribution proportion of the other four elements, since Fe has a higher tendency than Nb to form part of the inter-dendrite region. An evaluation of the properties related to the corrosion process was accomplished using the polarization method along with electrochemical impedance spectroscopy (EIS), performed under a simulated biological environment. As a result, FeHEA showed a higher corrosion rate in simulated body fluid than NbHEA.

In response to concerns of potential cytotoxicity and adverse tissue reactions caused by vanadium and aluminum in the currently used biomaterial Ti-6Al-4V, the Ti–20Zr alloy was evaluated in this study because it has been suggested as a candidate for human body implant material. The Ti-20Zr alloy was obtained by vacuum-melting, followed by heat treatment at 1000 °C for 1 h, and then air-cooled. Optical and scanning electron microscopy revealed that the sample had an α and β lamellar microstructure. Analysis showed that the mechanical properties, in terms of hardness measurements performed at low loads, were significantly different between the two phases. Thus, it was found out that the α phase is softer by about 30% compared to the β phase. The Electrochemical Impedance Spectroscopy technique (EIS) was employed to study the electrochemical behavior in simulated body fluid (SBF). The electrochemical behavior demonstrated that Ti-20Zr alloy exhibits excellent corrosion resistance due to the stable oxide layer formed on its surface. SEM and EDS investigations showed that the surface topography, after electrochemical studies, is characterized by a porous film with increased oxygen content, which might be suitable for the osteoinductive growth of bone.

Dental alloys based on Co or Ni are commonly used in dentistry to fabricate dental prostheses, including crowns, bridges, and partial dentures, but even though both alloys are highly biocompatible, some patients may experience allergic reactions to nickel. This comparative study investigated the behavior of two dental alloys in the oral cavity, analyzing their microstructure, corrosion behavior, elastic modulus, hardness, and tensile strength for ingot and cast crowns. The microstructures of commercial Ni-Cr and Co-Cr samples were analyzed using optical microscopy, scanning electron microscopy (SEM), and X-Ray Diffraction (XRD); elastic modulus and corrosion behavior were determined after immersing the samples in artificial saliva. Ni-Cr alloy has a corrosion potential more negative than Co-Cr alloy; this means that the first alloy is more likely to undergo corrosion than the second alloy. Ni-Cr sample with a higher elastic modulus is generally more rigid and less flexible than Co-Cr sample with a lower elastic modulus. The analyzed Co-Cr alloy has a higher resistance to corrosion, resulting in a more esthetically pleasing and longer-lasting restoration. The Co-Cr alloy also has a lower density than the Ni-Cr alloy, which, combined with its strength-to-weight ratio, makes them ideal for partial dentures where the prosthesis needs to be lightweight. The Co-Cr alloy is more flexible than the Ni-Cr alloy, making it stronger and more durable. This makes them an ideal choice for dental prostheses that need to withstand high stresses and loads.

While Ti6Al4V is one of the most used titanium alloys in the biomaterials field, it is not without its challenges and limitations, among which very important is the modulus mismatch with the bone. This modulus mismatch can lead to stress shielding potentially leading to bone resorption and implant loosening. Researchers continue to explore alternative materials and modifications to address this challenge and improve the performance of biomaterials. Two new fabricated titanium alloys Ti-10Al and Ti-4Fe are analyzed in this paper from corrosion and elastic modulus points of view. Metallography, microhardness, open circuit potential, DC electrochemical linear polarization, and Electrochemical Impedance Spectroscopy were performed. It was found that the corrosion resistance measurement for the Ti4Fe alloy is two orders of magnitude lower than for the Ti10Al alloy as determined by the equivalent circuit simulation, which is also supported by the similar disparity in the corrosion rate values for the two alloys which was determined using the DC method. The modulus of elasticity values were fairly close, hovering about 35GPa, and were lower than those of many commercial alloys.

Due to the optimistic outcomes of the research on high-entropy alloys, new designs of these alloys are being encouraged. We studied the high-entropy CoCrFeMoNi alloy and the CoCrFeMoNi alloy doped with Zr. In order to choose the best electrical equivalent circuit for the prediction of the behavior of these high-entropy alloys at various potentials in artificial seawater, electrochemical impedance spectroscopy (EIS) measurements were conducted on samples with and without Zr-doped CoCrFeMoNi. At various potential levels, the impedance spectra were measured between −1.0 and +0.8 V vs. SCE. The study consists of a preliminary section with microstructure by metallography, open-circuit potential, and linear polarization curves by direct-current tests followed by visual analysis of the impedance spectra, and, finally, the selection of an equivalent electrical circuit model to fit the experimental data. By leveraging the advantages of EIS analysis, the information is essential for materials development, corrosion-mitigation strategies, and the successful implementation of these alloys in practical applications. It is important to note that selecting an equivalent circuit is often an iterative and subjective process, as it involves a balance between model complexity and the ability to accurately represent the system’s behavior.

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 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 aim of the paper is to study the Zr addition effect on the mechanical properties and corrosion behavior of a high-entropy alloy from the CoCrFeMoNi system. This alloy was designed to be used for components in the geothermal industry that are exposed to high temperature and corrosion. Two alloys, one Zr-free (named Sample 1) and another one doped with 0.71 wt.% Zr (named Sample 2), were obtained in a vacuum arc remelting equipment from high-purity granular raw materials. Microstructural characterization and quantitative analysis by SEM and EDS were performed. The Young modulus values for the experimental alloys were calculated on the basis of a three-point bending test. Corrosion behavior was estimated by linear polarization test and by electrochemical impedance spectroscopy. The addition of Zr resulted in a decrease in the value of the Young modulus but also in a decrease in corrosion resistance. The beneficial effect of Zr on the microstructure was the grain refinement, and this ensured a good deoxidation of the alloy.