Alloys For Biomedical Applications Research Articles

Corrosion Behavior of SLMed Ti6Al4V-Equine Bone Nanocomposites

Ti6Al4V is one of the most widely used Ti alloys in biomedical applications, such as orthopedic and dental implants, due to its excellent mechanical properties, biocompatibility, and high corrosion resistance. Metal implants require high bonding strength between the implant and bone for long-term use in the human body; Hydroxyapatite (HAp) has generally been used as it can be expected to provide high osseointegration. However, in this study, Equine Bone (EB), which is a biowaste with a similar chemical composition to HAp and is environmentally friendly, was used instead. Ti6Al4V and EB were mixed through ball milling and then fabricated into Ti6Al4V-0.05EB composites using Selective Laser Melting (SLM). During the SLM process, localized high thermal gradients and rapid cooling rates leads to high strength and low ductility, making it challenging to use as a biomaterial. To overcome these issues, heat treatment was performed at temperatures corresponding to the <i>β</i> phase transformation. Subsequently, to evaluate the corrosion behavior after implantation in the body, the corrosion resistance of the Ti6Al4V-0.05EB nanocomposites was assessed through potentiodynamic polarization tests in a 0.9% NaCl solution, which simulates the physiological environment of the human body. Additionally, the effects of EB addition and heat treatment temperature on the corrosion behavior were also observed.

Role of Mo and Zr Additions in Enhancing the Behavior of New Ti–Mo Alloys for Implant Materials

AbstractThe utilization of Ti–Mo alloys in biomedical applications has gained attention for use in biomedical applications owing to their non-toxicity, reasonable cost, and favorable properties. In the present study, Ti–12Mo–6Zr and Ti–15Mo–6Zr alloys were prepared using elemental blend and mechanical alloying techniques. The effect of alloying elements Mo and Zr of Ti–Mo alloy, as well as the effect of fabrication techniques of Ti–Mo–Zr trinary alloys, were investigated. Thermodynamic calculations supported by CALPHAD analysis revealed that the addition of Zr increases lattice distortion, which contributes to enhancing the strength. Conversely, adding Mo decreases the enthalpy, facilitating improved mixing and solid solution formation. The as-sintered samples were characterized by X-ray diffraction, optical microscope, and scanning electron microscopy, and their microhardness, compressive, and corrosion behavior were investigated. Among all the investigated alloys, Ti–15Mo–6Zr alloy prepared by the mechanical alloying technique, milled for six hours at 300 rpm, compacted at 600 MPa, and sintered at 1250 ℃, shows good comprehensive mechanical properties with a preferable compressive strength (− 1710 MPa) and hardness (396 HV5), as well as the lowest wear rate (0.69%) and corrosion rate (0.557 × 10–3 mm/year). This can be related to the solid solution strengthening and relative density, together with dispersion and precipitation strengthening of the α phase. Remarkably, the combination of high mechanical and corrosion properties can be achieved by tailoring the content of the α phase, controlling the density, and providing new fabricating techniques for β Ti alloys. Graphical Abstract

Achieving biomimetic porosity and strength of bone in magnesium scaffolds through binder jet additive manufacturing

Magnesium (Mg) alloys are a promising candidate for synthetic bone tissue substitutes. In bone tissue engineering, achieving a balance between pore characteristics that facilitate biological functions and the essential stiffness required for load-bearing functions is extremely challenging. This study employs binder jet additive manufacturing to fabricate an interconnected porous structure in Mg alloys that mimics the microporosity and mechanical properties of human cortical bone types. Using scanning electron microscopy, micro-computed tomography, and mercury intrusion porosimetry, we found that the binder jet printed and sintered (BJPS) MgZnZr alloys possess an interconnected porous structure, featuring an overall porosity of 13.3 %, a median pore size of 12.7 μm, and pore interconnectivity exceeding 95 %. The BJPS MgZnZr alloy demonstrated a tensile strength of ~130 MPa, a yield strength of ~100 MPa, an elastic modulus of ~21.5 GPa, and an ultimate compressive strength of ~349 MPa. These values align with the ranges observed in human bone types and outperform those of porous Mg alloys produced using the other conventional and additive manufacturing methods. Moreover, the BJPS MgZnZr alloy showed level 0 cytotoxicity with a greater MC3T3-E1 cell viability, attachment, and proliferation when compared to a cast MgZnZr counterpart, since the highly interconnected 3D porous structure provides cells with an additional dimension for infiltration. Finally, we provide evidence for the concept of using binder jet additive manufacturing for fabricating Mg implants tailored for applications in hard tissue engineering, including craniomaxillofacial procedures, bone fixation, and substitutes for bone grafts. The results of this study provide a solid foundation for future advancements in digital manufacturing of Mg alloys for biomedical applications.

Preparation, Mechanical Properties, and Degradation Behavior of Zn-1Fe-xSr Alloys for Biomedical Applications.

As biodegradable materials, zinc (Zn) and zinc-based alloys have attracted wide attention owing to their great potential in biomedical applications. However, the poor strength of pure Zn and binary Zn alloys limits their wide application. In this work, a stir casting method was used to prepare the Zn-1Fe-xSr (x = 0.5, 1, 1.5, 2 wt.%) ternary alloys, and the phase composition, microstructure, tensile properties, hardness, and degradation behavior were studied. The results indicated that the SrZn13 phase was generated in the Zn matrix when the Sr element was added, and the grain size of Zn-1Fe-xSr alloy decreased with the increase in Sr content. The ultimate tensile strength (UTS) and Brinell hardness increased with the increase in Sr content. The UTS and hardness of Zn-1Fe-2Sr alloy were 141.65 MPa and 87.69 HBW, which were 55.7% and 58.4% higher than those of Zn-1Fe alloy, respectively. As the Sr content increased, the corrosion current density of Zn-1Fe-xSr alloy increased, and the charge transfer resistance decreased significantly. Zn-1Fe-2Sr alloy had a degradation rate of 0.157 mg·cm-2·d-1, which was 118.1% higher than the degradation rate of Zn-1Fe alloy. Moreover, the degradation rate of Zn-1Fe-xSr alloy decreased significantly with the increase in immersion time.

Engineering Triphasic Nanocomposite Coatings on Pretreated Mg Substrates for Biomedical Applications.

Biodegradable polymer-based nanocomposite coatings provide multiple advantages to modulate the corrosion resistance and cytocompatibility of magnesium (Mg) alloys for biomedical applications. Biodegradable poly(glycerol sebacate) (PGS) is a promising candidate used for medical implant applications. In this study, we synthesized a new PGS nanocomposite system consisting of hydroxyapatite (HA) and magnesium oxide (MgO) nanoparticles and developed a spray coating process to produce the PGS nanocomposite layer on pretreated Mg substrates, which improved the coating adhesion at the interface and their cytocompatibility with bone marrow derived mesenchymal stem cells (BMSCs). Prior to the spray coating process of polymer-based nanocomposites, the Mg substrates were pretreated in alkaline solutions to enhance the interfacial adhesion strength of the polymer-based nanocomposite coatings. The addition of HA and MgO nanoparticles (nHA and nMgO) to the PGS matrix, as well as the alkaline pretreatment of the Mg substrates, significantly enhanced the interfacial adhesion strength when compared with the PGS coating on the nontreated Mg control. The average BMSC adhesion densities were higher on the PGS/nHA/nMgO coated Mg than the noncoated Mg controls under direct contact conditions. Moreover, the addition of nHA and nMgO to the PGS matrix and coating the nanocomposite onto Mg substrates increased the average BMSC adhesion density when compared with the PGS/nHA/nMgO coated titanium (Ti) and PGS coated Mg controls under direct contact. Therefore, the spray coating process of PGS/nHA/nMgO nanocomposites on Mg substrates or other biodegradable metal substrates could provide a promising surface treatment strategy for biodegradable implant applications.

Biocompatibility and mechanical performance of magnesium alloys for biomedical application- a state of the art review

This review addresses the problems associated with various types of implants, providing a brief background on their challenges and surgical implications. Preclinical and clinical studies are discussed to understand the causes of implant failures. The review specifically examines the potential of magnesium-based alloys in biomedical applications, focus on existing research to offer a comprehensive overview of their advantages and disadvantages in biodegradable implants. It explores how alloying elements can enhance mechanical properties and corrosion behavior in Mg alloys. This review indicates how specific percentages of different alloying elements, combined with suitable manufacturing and post-processing techniques, can yield optimized results. Additionally, the review assesses the impact of magnesium alloy degradation on the healing process and suggests strategies to mitigate adverse effects. By thoroughly analyzing the literature, this paper offers valuable insights into fabricating magnesium-based implants to achieve ideal mechanical and corrosion properties, enhancing their effectiveness in biomedical applications.

Microstructure and Mechanical Properties of As-Built Ti-6Al-4V and Ti-6Al-7Nb Alloys Produced by Selective Laser Melting Technology.

Additive manufacturing from metal powders using selective laser melting technology is gaining increasing interest in various industries. The purpose of this study was to determine the effect of changes in process parameter values on the relative density, microstructure and mechanical properties of Ti-6Al-4V and Ti-6Al-7Nb alloy samples. The experiment was conducted in response to a noticeable gap in the research on the manufacturability of the Ti-6Al-7Nb alloy in SLM technology. This topic is significant given the growing interest in this alloy for biomedical applications. The results of this study indicate that by properly selecting the volumetric energy density (VED), the relative density of the material produced and the surface roughness of the components can be effectively influenced. Microstructural analyses revealed similar patterns in both alloys manufactured under similar conditions, characterized by columnar β phase grains with needle-like α' phases. Increasing the VED increased the tensile strength of the fabricated Ti-6Al-4V alloy components, while the opposite effect was observed for components fabricated from Ti-6Al-7Nb alloy. At the same time, Ti-6Al-7Nb alloy parts featured higher elongation values, which is desirable from the perspective of biomedical applications.

Development of new β Ti-10-Mo-Mn alloys for biomedical applications

Metallic biomaterials play a crucial role in various biomedical applications, particularly in developing implants and prostheses. Hence, this study aimed to produce and analyze the structure, microstructure, hardness, and preliminary cytotoxicity of Ti-10Mo-xMn system alloys (with x ranging from 0 to 8 wt%) intended for biomedical applications as biomaterials. The alloys underwent thorough characterization, including chemical composition analysis through EDS measurements, mapping, and density assessments. Structural and microstructural analyses were conducted using x-ray diffraction (XRD), Rietveld refinement, optical (OM), and scanning electron microscopy (SEM), while Vickers microhardness testing provided insights into mechanical properties. Rapid cytotoxicity tests via MTT were also performed to assess biocompatibility. Results indicated that the produced alloys exhibited good quality and homogeneity regarding chemical composition. Adding Mn to the Ti-10Mo alloy facilitated the formation of the β phase, transforming it from a biphasic (α" + β) to a single-phase alloy.Moreover, Mn-induced reductions in lattice parameters and average crystallite size of the β phase were observed due to the smaller atomic radius of substituting Mn than Ti. Despite a decrease in hardness attributed to β phase formation, all alloys demonstrated non-cytotoxic behavior in cell adhesion and viability assays, with values exceeding 70 %. Overall, these findings highlight the potential of Ti-10Mo-xMn alloys as viable biomaterials, warranting further exploration and development in biomedical engineering.

Investigation of the structural properties of Si4+-doped HAP coatings on Ti-6Al-4V substrate as a corrosion barrier in biomedical media

The coatings of co-substituted bioactives play an important role in stimulating biological and physical properties for biomedical applications. Hydroxyapatite (HAP), a mineral compound possessing a hexagonal structure, exhibits high thermodynamic stability under typical physiological conditions. In this experimental study, Si4+-doped HAP coatings with varying concentrations (2.5 %, 5 %, and 10 % wt) were prepared on a Ti-6Al-4V substrate using the spin-coating technique and extreme centrifugal force (2500 rpm). The coated samples were characterized by XRD, FTIR, AFM, FESEM, and EDS techniques. The presence of cracks and voids in the HAP coatings detrimentally affected the performance of the implants. Tetraethyl orthosilicate (TEOS) was used in the coatings to mitigate the cracks and voids. Polarization and EIS studies in the simulated body fluid (SBF) were used to assess the corrosion resistance of the coatings. The decrease in current density and the improved resistance to corrosion observed in the coated samples, as compared to the uncoated Ti-6Al-4V, demonstrate the corrosion-inhibiting effects of anodizing. The integration of Si4+ ions in the structure of HAP caused the size of nanoparticles to decrease from 16.23 nm to 11.67 nm, and the surface roughness of the produced coatings exhibited a decrease from 29.18 to 5.65 nm. In the Nyquist plots, the 5 % Si4+-doped HAP coating displayed the highest Rct value of 17.99 MΩ.cm2 compared to the bare Ti-6Al-4V with a resistance of 0.13 MΩ.cm2. The 5 % Si4+-doped HAP coating was chosen as the optimal sample based on the study results. The results of this work show that surface modification with Si4+-doped HAP coatings is a promising approach for improving the functionality of the Ti-6Al-4 V alloy for biomedical applications.

Synergistic effects of laser powder bed fusion and annealing on the texture-selective recrystallization of magnetostrictive Fe-Ga-NbC alloys for biomedical applications

IntroductionMagnetostrictive Fe-Ga alloys have garnered extensive attention owing to their excellent magnetic properties and acceptable biocompatibility. Nevertheless, the polycrystalline Fe-Ga alloys currently available tend to display random texture orientations, which constrain their magnetostrictive performance. ObjectivesTo regulate the texture orientation of Fe-Ga-NbC alloys and thereby enhancing magnetostriction. MethodsIn this study, a processing route comprising laser powder bed fusion (LPBF) followed by secondary recrystallization annealing (800, 1000, and 1200 °C, respectively) was developed to prepare Fe-Ga-NbC alloys. ResultsThe results showed that the LPBF-ed (Fe81Ga19)99(NbC)1 alloys exhibited a high content of high energy grain boundaries (HEGBs) due to the repeated melting and solidification. In subsequent annealing process, the migration of HEGBs induced the rearrangement and recrystallization of grains, during which NbC was found to locate at the grain boundaries and influence the migration path of HEGBs via selective pinning, thereby resulting in a strong Goss texture. With the rise in annealing temperature, the content of Goss texture gradually increased from the initial 3.9 % to 71.3 % at 1200 °C, leading to enhanced magnetostriction, lower saturation magnetization and coercivity. Furthermore, in alternating magnetic fields, the alloys annealed at 1200 °C also exhibited higher magnetostriction than the LPBF-ed alloys. And a noteworthy grain coarsening was also observed after annealing, accompanied by a discernible inclination of magnetic domains towards strip domains. Additional, cell tests demonstrated that the prepared alloys had satisfactory biocompatibility and the ability to promote osteogenic differentiation. ConclusionThese findings indicated that the LPBF-ed and annealed Fe-Ga-NbC alloys might be a promising alternative as magnetostrictive-driven materials for biomedical applications.

Effect of Heat Treatment on Microstructure, Mechanical and Corrosion Behavior of Ti-7Mo-8Nb Alloy for Biomedical Applications

Effect of Heat Treatment on Microstructure, Mechanical and Corrosion Behavior of Ti-7Mo-8Nb Alloy for Biomedical Applications

Nanopowder-mixed EDM on biodegradable Mg alloy AZ31B for improved surface characteristics and biocompatibility

Powder-mixed electrical discharge machining (PM-EDM) was conducted on biodegradable magnesium (Mg) alloys for biomedical applications. The Mg alloy AZ31B has shown outstanding mechanical properties, similar to human bone, and is lightweight. Efforts were made to enhance the EDM capabilities by a PM-EDM process using nanopowder mixed in the dielectric medium and copper tool electrode amid the machining of Mg alloy AZ31B, followed by investigating surface modification by minimum machining time, morphology, chemistry, topography and wettability of the surfaces. The surface produced by nano PM-EDM operation exhibits minimal cracks and craters, an acceptable range of recast layer thickness (2.4 − 2.7μm), satisfactory corrosion resistance and surface roughness (Ra = 2.87μm) as well as suitable hydrophobic behaviour (CA122q) and bioactivity with Ringer’s solution, suggesting an improvement in the degradation rate. Thus, PM-EDM-induced surface modification suggests the suitability of Mg alloy AZ31B as a biodegradable implant in adults and children.

Tribological properties of MAO ceramic coatings with annulus array texture on disposable surgical gloves.

Introduction: In recent research, the expansion in the use of Mg alloys for biomedical applications has been approached by modifying their surfaces in conjunction with micro-arc oxidation (MAO) techniques which enhance their abrasion and corrosion resistance. Methods: In this study, combining laser texturing and MAO techniques to produce the dense ceramic coatings with microstructures. On the surface of the AZ31 Mg alloy, a micro-raised annulus array texture has been designed in order to increase the surface friction under liquid lubrication and to improve the operator's grip when holding the tool. For this work, the micro-morphology of the coatings was characterised, and the friction properties of the commonly used scalpel shank material 316L, the untextured surface and the textured surface were comparatively analysed against disposable surgical gloves. Results and discussion: The results show that the Laser-MAO ceramic coating grows homogenous, the porosity decreases from 14.3% to 7.8%, and the morphology after friction indicates that the coating has good wear resistance. More specifically, the average coefficient of friction (COF) of the three types of gloves coated with Laser-MAO ceramic was higher than that of the 316L and MAO ceramic coatings under the action of the annulus-integrated texture under the lubrication conditions of physiological saline and defatted sheep blood, which achieved the goal of increasing friction for the purpose of helping to prevent the problem of tool slippage from the hand.

Inhibiting stress corrosion cracking of a prefabricated surface‐defective magnesium alloy thanks to biological organic components

AbstractBiomedical magnesium (Mg) alloys remain a challenge for their mainstream application, because the combination of bio‐mechanical stress and corrosive physiological environment leading to stress corrosion cracking (SCC). It is crucial to avoid the sudden brittle fracture of Mg alloys in vivo for predicting their service duration. However, the key factors, such as surface or physiological environment features, determining the origination or propagation of SCC behavior are still unclear. In the present study, a prefabricated surface defects coating was prepared by the phytic acid (PA, C6H18O24P6) conversion treatment. Four mimicking physiological media were used, ranging from simple to equivalent (Dulbecco's Modified Eagle Medium and Protein [DMEM+Pro]). The results showed that the PA film with numerous micro‐cracks provided limited protective ability in synthetic biological media. A striking finding was determined that although initial high corrosion rate of samples in DMEM+Pro led to an increased SCC nucleation, significant ductile fracture with elongation to failure (14.86%) was observed. Combined with the fracture features, the adsorption or deposition of biological composition into the tunnel of SCC cracks significantly inhibited the hydrogen embrittlement (HE) behavior. These results indicate that preventing the propagation of SCC crack by biological composition, rather than nucleation, plays a key role in avoiding the sudden fracture of Mg alloys. It provides a novel perspective to determine the non‐brittle fracture of Mg alloys for biomedical applications.

Multifunctional Coatings on Mg‐Based Metallic Biomaterials and Implants

Multifunctional materials are propitious materials with numerous functionalities that make them an ideal option for implants and biomedical applications that should simultaneously fulfill various requirements, including satisfactory mechanical strength, biocompatibility, antibacterial property, hydrophilicity, etc. Magnesium, as a metallic biomaterial, fulfills the required mechanical properties, but unfortunately, in some ways alone, it cannot provide the required biological properties. For instance, magnesium alloys suffer from poor corrosion resistance and high biodegradability, which should be carefully controlled. On the other hand, multifunctional materials alone are not able to provide the required properties in biomedical applications because the vast majority of them do not have the necessary strength and stability. Therefore, the use of magnesium together with multifunctional or composite coatings will be a very advantageous choice for meeting the needs of implants and biomedical materials. The current study focuses on the introduction and utilization of various multifunctional coatings and composites on Mg‐based alloys for biomedical applications. Numerous organic and inorganic materials could be utilized as composites or multifunctional materials. In this regard, numerous types of coating and composite materials, their production technologies, mechanisms, resultant properties, and the involved parameters are thoroughly discussed to provide a comprehensive guide for those interested in this field.

Experimental Investigation of the Impact of Niobium Additions on the Structural Characteristics and Properties of Ti-5Cr-xNb Alloys for Biomedical Applications.

In this study, a series of Ti-5Cr-xNb alloys with varying Nb content (ranging from 1 to 40 wt.%) were investigated to assess their suitability as implant materials. Comprehensive analyses were conducted, including phase analysis, microscopy examination, mechanical testing, and corrosion resistance evaluation. The results revealed significant structural alterations attributed to Nb addition, notably suppressing the formation of the ω phase and transitioning from α' + β + ω to single β phase structures. Moreover, the incorporation of Nb markedly improved the alloys' plastic deformation ability and reduced their elastic modulus. In particular, the Ti-5Cr-25Nb alloy demonstrated high values in corrosion potential and polarization resistance, signifying exceptional corrosion resistance. This alloy also displayed high bending strength (approximately 1500 MPa), a low elastic modulus (approximately 80 GPa), and outstanding elastic recovery and plastic deformation capabilities. These aggregate outcomes indicate the promising potential of the β-phase Ti-5Cr-25Nb alloy for applications in orthopedic and dental implants.

Laser texturing and oxidation of TiZrTa thin films to improve the biocompatible performance of titanium alloys

Titanium (Ti) and Ti alloys possess extensive applications in the medical field due to their non-toxic, biocompatible, and antibacterial properties. This study investigates the biocompatibility enhancement of a Ti-based alloy, Ti-6Al-4V, through a multi-step process involving cathodic arc ion plating of a TiZrTa thin film and subsequent laser-textured oxidation (LTO). LTO treatment produced a structured microtopography with regular groove patterns, including straight lines (L-s), circles (L-c), and checkboards (L-ch), resulting in surface oxidation and the formation of various oxides on the TiZrTa coating. Microstructure analyses revealed substantial alterations in surface topography induced by laser texturing. Antibacterial assessments against Staphylococcus aureus (S. aureus) showed that the films with LTO treatment did not exhibit significant advantages after 12 or 24 h of coculture because the laser-textured portions consisted of a combination of the film and the substrate, and the antibacterial effect was not obvious. Coatings with LTO treatment significantly improved L-929 mouse fibroblasts cell viability at 48 h, particularly for samples with a 50 μm spacing of straight and circular patterns (L-s and L-c). After two weeks of MG-63 human osteosarcoma cell culture, the viability of all samples reached similar levels. It suggested that the TiZrTa-coated Ti-6Al-4V exhibited good biocompatibility with both cells. This study contributed to the understanding of surface modification techniques for enhancing the biocompatibility of Ti-based alloys in biomedical applications.

Heat treatment protocol for additively manufactured nitinol shape memory alloys in biomedical applications

Additive manufacturing (AM) is getting significant attention in realizing customizable nitinol (NiTi) devices for biomedical applications. However, due to the change in composition and constituent phases occurring during printing and the microstructural inhomogeneity in the printed parts, obtaining a desired set of phase transformation behaviors and superelastic properties is a major challenge. In this work, laser powder bed fusion (LPBF) was used to fabricate NiTi at a very low laser energy density (35 J/mm3) on a titanium base plate while keeping these behaviors and properties within desirable ranges without any structural defects such as crack and delamination. Our measurements showed that the as-printed NiTi exhibited distinct one-step phase transformation with the austenite finish (Af) temperature of 2.1 °C. To increase the Af temperature to 30.2 °C (within the recommended range of Af temperature for biomedical applications), a heat treatment protocol was developed, which includes a solution cycle (at 900 °C for 1 h) followed by an aging cycle (at 450 °C for 30 min). The heat treatment protocol enabled us to attain the homogenized microstructure while creating ultrafine metastable Ni-rich precipitate, Ni4Ti3, which facilitated the desirable phase transformation behavior with the increased Af temperature. The heat-treated sample showed narrower and sharper two-step martensitic phase transformation with the formation of intermediate R-phase. The presence of both Ni4Ti3 and the R-phase was confirmed by the transmission electron microscopic (TEM) analysis. In the superelasticity test at the body temperature, these samples, starting from the 2nd cycle, demonstrated a recovery ratio of more than 90% and a recoverable strain of more than 6.5%. After 10th cycles, the stable recoverable strain was 6.52% with a recovery ratio of 96%, which is the highest superelasticity reported for the LPBF processed NiTi to the best of our knowledge. After the initial deformation process, we expect these NiTi samples to attain near full superelasticity during service. The micro-hardness study also showed that the hardness of the heat-treated samples is less affected by the cyclic loading. Therefore, this paper presents a viable heat treatment protocol, which provides an important processing roadmap in making NiTi implants by AM while maintaining excellent functional properties of NiTi for biomedical applications.

Development of an equiatomic octonary TiNbTaZrMoHfWCr super-high-entropy alloy for biomedical applications

A super-high-entropy alloy (SHEA) with ΔSmix ≥ 2.0R (where R is the gas constant) was designed to produce metallic materials with superior mechanical properties to conventional alloys. As an alternative to conventional quinary high-entropy alloys (HEAs), herein, octonary SHEAs for biomedical applications (BioSHEAs) are proposed for the first time, and the TiNbTaZrMoHfWCr BioSHEA was fabricated. Arc-melted BioSHEA exhibited an extremely high yield strength of 1953 ± 84 MPa, which was approximately 550 MPa higher than that of the quinary TiNbTaZrMo BioHEA. This yield strength is considerably higher than that estimated by the rule of mixtures for pure metals, confirming the achievement of significant solid-solution strengthening induced by a supermulticomponent solid solution composed of elements with different atomic radii. Its biocompatibility was comparable to that of pure Ti and the quinary BioHEA, and superior to that of SUS316L. This study demonstrates the validity of a novel entropy-based guideline for increasing the mixing entropy to achieve metallic materials with ultrahigh strength.

Improved Corrosion Properties of Mg-Gd-Zn-Zr Alloy by Micro-Arc Oxidation

In order to improve the corrosion resistance of Mg-3Gd-1Zn-0.4Zr (GZ31K) alloys for biomedical application, the alloy was micro-arc oxidation (MAO)-treated using silicate electrolyte system under various voltages (400 V, 425 V, 450 V, 475 V). The effects of voltage on the microstructure and corrosion properties of MAO coating were investigated via X-ray diffraction (XRD) and a scanning electron microscope (SEM) combined with an energy-dispersive spectrometer (EDS), X-ray photoelectron spectroscope (XPS), and electrochemical experiments. The results showed that, with the increase in voltage, the MAO coatings became thicker and the micropores on the MAO coating increased in diameter. The main phase compositions of the MAO coatings were MgO and Mg2SiO4. Potentiodynamic polarization curve results showed that MAO coatings could enhance corrosion resistances, where the corrosion current density decreased by six orders of magnitude and the corrosion potential of the specimens increased by 300 mV for the voltage of 450 V in the MAO treatment; nevertheless, the corrosion resistance rapidly deteriorated due to the creation of large micropores in the MAO coating, which provide a pathway for corrosive media when the voltage is 475 V. The electrochemical impedance spectroscopy results showed that MAO treatments could increase low-frequency modulus resistance and increase the corrosion resistance of Mg alloys. In addition, MAO-treated GZ31K alloys still exhibited uniform corrosion, which is desirable for biomedical applications.