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This work presents a systematic investigation of the corrosion behavior of two materials, 316 stainless steel (316), and Ti6Al4V alloy (Ti6Al4V), in simulated seawater (3.5wt.% NaCl solution). This includes electrochemical tests, immersion experiments, scanning electron microscopy (SEM), energy disperse spectroscopy (EDS) analyses. The polarization curves demonstrate that passivation occurs in both alloys. The lower self-corrosion and passivation current densities of Ti6Al4V indicate that its corrosion resistance is superior to that of 316. However, the impedance spectrum of the 316 shows a larger capacitive arc radius, which is indicative of the presence of a more robust passivation film on its surface. The results of the immersion experiments demonstrate that 316 exhibits a high-corrosion rate under static conditions, which can be attributed to the instability of the passivation film and environmental factors. However, under dynamic conditions, the corrosion rate is lower due to the effect of scouring. In contrast, Ti6Al4V demonstrated superior corrosion resistance in a variety of environmental conditions. In the context of simulated seawater, both 316 and Ti6Al4V exhibited varying degrees of corrosion behavior. Consequently, when selecting corrosion-resistant materials, it is imperative to select suitable materials according to the specific use environment and requirements.

Titanium is a highly operational alloy for use in dental implants. Surface inertness of the titanium alloy surfaces reduces osseointegrate, raising concerns about implant loosening. Hydroxyapatite (HA)-rich porous titanium surfaces with moderated surface roughness have better osteoconductivity. This study focused on the surface alteration of Ti6Al4V via hydroxyapatite mixed electric discharge-assisted centerless turning (HA-mixed-EDCLT) to find the optimum surface. The experiments were planned based on a four-factor, three-level Box-Behnken design. HA-powder concentration (Cp), revolutions per minute (RPM), duty factor and impulse current (IP) were the input parameters. The Ra value of machined surfaces ranged from 1.12$\mu$m to 1.63$\mu$m, which is in the bone growth supportive implants range. The average hardness reached 415.8–962.7HV, where untreated surfaces’ hardness was $340\pm 6$HV. Porous, hydrophilic coating with a high Ca, P, and O content deposited on the implant surfaces supports the biocompatibility of implants. Analysis of the elements and compounds shows that the machined surface layer is rich with Ca₃(PO${}_4{)}_2$ and TiO${}_{2,}$which improves the bioactivity of the alloy.

The effects of heat treatment on the microstructure, mechanical properties and wear resistance of Selective Laser Melting Ti6Al4V alloy were systematically studied. The results show that the as-built part has an acicular ${\alpha }^{\prime }$ martensite structure. The increase in heat treatment temperature causes the decomposition of acicular ${\alpha }^{\prime }$ martensite, which leads to the decrease of the hardness of Ti6Al4V alloy. When the heat treatment temperature is 800^∘C, the alloy forms an ${\alpha }^{\prime }$/$\alpha$ structure, which increases the tensile strength and elongation of the alloy by 12% and 23%, respectively. When the heat treatment reaches above 900^∘C, the mechanical properties of the alloy decrease sharply due to the disappearance of the ${\alpha }^{\prime }$/$\alpha$ structure, the coarse grains of the $\alpha$ phase, and the increase of the content of the $\beta$ phase. The tensile strength decreased from 935MPa to 815MPa, and the elongation decreased from 8.7% to 3.1%. With the increase of heat treatment temperature, the friction coefficient and wear rate increase linearly, which is opposite to the changing trend of hardness, and the wear mechanism is changed from single abrasive wear to abrasive wear and oxidative wear. This is attributed to the increase in the grain size of the alloy and the increase in the content of the $\beta$ phase, resulting in a decrease in the overall hardness of the alloy.

The wear resistances of AZ91D magnesium alloy with and without microarc oxidation (MAO) coating and Ti6Al4V alloy in artificial saliva were investigated at room temperature. The wear resistance of AZ91D magnesium alloy in artificial saliva was significantly improved after microarc oxidation treatment. The volume loss of untreated AZ91D magnesium alloy sample was 20.95 times of that of AZ91D magnesium alloy with MAO coating, and that of Ti6Al4V was 5.42 times of that of MAO. Furthermore, the wear resistance of AZ91D magnesium alloy was lower than that of Ti6Al4V alloy in artificial saliva. The wear mechanisms of AZ91D magnesium and Ti6Al4V were discussed. It was found that the wear mechanism of the MAO was associated with abrasion and microfracture. There were two dominative wear mechanisms for AZ91D alloy and Ti6Al4V alloy under the loading conditions used in the experiment, namely, micro-machining wear and deformation-induced wear.

Biocompatibility is crucial for implants. In recent years, numerous researches were conducted aiming to modify titanium alloys, which are the most extensively used materials in orthopedic fields. The application of zirconia in the biomedical field has recently been explored. In this study, the biological ZrO₂ coating was synthesized on titaniumalloy (Ti6Al4V) substrates by a duplex-treatment technique combining magnetron sputtering with micro-arc oxidation (MAO) in order to further improve the corrosion resistance and biocompatibility of Ti6Al4V alloys. The microstructures and phase constituents of the coatings were characterized by scanning electron microscope (SEM) equipped with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), the surface wettability was evaluated by contact angle measurements. The results show that ZrO₂ coatings are porous with pore sizes less than 2$\mu$m and consist predominantly of the tetragonal ZrO₂ (t-ZrO${}_2)$ and cubic ZrO₂(c-ZrO${}_2)$ phase. Electrochemical tests indicate that the corrosion rate of Ti6Al4V substrates is appreciably reduced after surface treatment in the phosphate buffer saline (PBS). In addition, significantly improved cell adhesion and growth were observed from the ZrO₂/Zr surface. Therefore, the hybrid approach of magnetron sputtering and MAO provides a surface modification for Ti6Al4V to achieve acceptable corrosion resistance and biocompatibility.