Corrosion and tribocorrosion of hafnium in simulated body fluids

A Review: Design from Beta Titanium Alloys to Medium-Entropy Alloys for Biomedical Applications

β-Ti alloys have long been investigated and applied in the biomedical field due to their exceptional mechanical properties, ductility, and corrosion resistance. Metastable β-Ti alloys have garnered interest in the realm of biomaterials owing to their notably low elastic modulus. Nevertheless, the inherent correlation between a low elastic modulus and relatively reduced strength persists, even in the case of metastable β-Ti alloys. Enhancing the strength of alloys contributes to improving their fatigue resistance, thereby preventing an implant material from failure in clinical usage. Recently, a series of biomedical high-entropy and medium-entropy alloys, composed of biocompatible elements such as Ti, Zr, Nb, Ta, and Mo, have been developed. Leveraging the contributions of the four core effects of high-entropy alloys, both biomedical high-entropy and medium-entropy alloys exhibit excellent mechanical strength, corrosion resistance, and biocompatibility, albeit accompanied by an elevated elastic modulus. To satisfy the demands of biomedical implants, researchers have sought to synthesize the strengths of high-entropy alloys and metastable β-Ti alloys, culminating in the development of metastable high-entropy/medium-entropy alloys that manifest both high strength and a low elastic modulus. Consequently, the design principles for new-generation biomedical medium-entropy alloys and conventional metastable β-Ti alloys can be converged. This review focuses on the design from β-Ti alloys to the novel metastable medium-entropy alloys for biomedical applications.

Characterization of Structural, Optical, Corrosion, and Mechanical Properties of HfO2 Thin Films Deposited Using Pulsed DC Magnetron Sputtering

Various properties of HfO₂, such as hardness, corrosion, or electrical resistance, depend on the method and the conditions of deposition. In this work, a thorough comparison of scarcely investigated mechanical properties of HfO₂ thin films deposited with different conditions of reactive magnetron sputtering process is presented. Four thin films were sputtered in processes that varied in plasma ignition method (continuous or sequential) and target-substrate distance. The structural characteristics of the HfO₂ thin films were examined using Raman spectroscopy and X-ray diffraction measurements. Furthermore, the optoelectronic properties were determined based on transmittance and current-voltage characteristics. The mechanical properties of the HfO₂ thin films were determined using nanoindentation and scratch test. In turn, the corrosion properties were determined by analyzing the voltametric curves. The transparent HfO₂ thin films deposited in the continuous process are characterized by better corrosion resistance than the same layer formed in the sequential process, regardless of the target-substrate distance (8 cm or 12 cm). Furthermore, these samples are also characterized by the highest value of Young's modulus and scratch resistance. The combination of good corrosion and scratch resistance could contribute to the new application of HfO₂ as a corrosion protective material.

Influence of Hafnium Addition on the Microstructure, Microhardness and Corrosion Resistance of Ti20Ta20Nb20(ZrMo)20-xHfx (where x = 0, 5, 10, 15 and 20 at.%) High Entropy Alloys

The presented work aimed to investigate the influence of the hafnium/(zirconium and molybdenum) ratio on the microstructure, microhardness and corrosion resistance of Ti₂₀Ta₂₀Nb₂₀(ZrMo)_20-xHf_x (where x = 0, 5, 10, 15 and 20 at.%) high entropy alloys in an as-cast state produced from elemental powder and obtained via the vacuum arc melting technique. All studied alloys contained only biocompatible elements and were chosen based on the thermodynamical calculations of phase formation predictions after solidification. Thermodynamical calculations predicted the presence of multi-phase, body-centered cubic phases, which were confirmed using X-ray diffraction and scanning electron microscopy. Segregation of alloying elements was recorded using elemental distribution maps. A decrease in microhardness with an increase in hafnium content in the studied alloys was revealed (512-482 HV1). The electrochemical measurements showed that the studied alloys exhibited a high corrosion resistance in a simulated body fluid environment (breakdown potential 4.60-5.50 V vs. SCE).

Influence of Molybdenum on the Microstructure, Mechanical Properties and Corrosion Resistance of Ti20Ta20Nb20(ZrHf)20-xMox (Where: x = 0, 5, 10, 15, 20) High Entropy Alloys

The presented work was focused on investigating the influence of the (hafnium and zirconium)/molybdenum ratio on the microstructure and properties of Ti20Ta20Nb20(ZrHf)20-xMox (where: x = 0, 5, 10, 15, 20 at.%) high entropy alloys in an as-cast state. The designed chemical composition was chosen due to possible future biomedical applications. Materials were obtained from elemental powders by vacuum arc melting technique. Phase analysis revealed the presence of dual body-centered cubic phases. X-ray diffraction showed the decrease of lattice parameters of both phases with increasing molybdenum concentration up to 10% of molybdenum and further increase of lattice parameters. The presence of two-phase matrix microstructure and hafnium and zirconium precipitates was proved by scanning and transmission electron microscopy observation. Mechanical property measurements revealed decreased micro- and nanohardness and reduced Young's modulus up to 10% of Mo content, and further increased up to 20% of molybdenum addition. Additionally, corrosion resistance measurements in Ringers' solution confirmed the high biomedical ability of studied alloys due to the presence of stable oxide layers.

Corrosion Behavior and In Vitro Cytotoxicity of Ni-Ti and Stainless Steel Arch Wires Exposed to Lysozyme, Ovalbumin, and Bovine Serum Albumin

In this study, the tendency and mechanisms by which protein and mechanical loads contribute to corrosion were determined by exposing Ni-Ti and stainless steel arch wires under varying mechanical loads to artificial saliva containing different types of protein (lysozyme, ovalbumin, and bovine serum albumin). The corrosion behavior and in vitro cytotoxicity results show that exposure to both protein and mechanical stress significantly decreased the corrosion resistance of stainless steel and increased the release of toxic corrosion products. Adding protein inhibited the corrosion of Ni-Ti, but the mechanical loads counteracted this effect. Even proteins containing the same types of amino acids had different effects on the corrosion resistance of the same alloy. The effect of protein or stress, or their combination, should be considered in the application of metal medical materials.

Effect of Protein and Mechanical Strain on the Corrosion Resistance and Cytotoxicity of the Orthodontic Composite Arch Wire

In this study, the effects of the exposure to different types of salivary proteins (fibrinogen, IgG, and mucin) and application of an in vitro bending strain on the laser welding orthodontic composite arch wire (CAW) were investigated, and the resultant corrosion behavior and cytotoxicity were studied in vitro. The purpose was to determine the mechanisms by which protein exposure and bending loads contribute to the corrosion of the CAW either alone or in combination by mimicking the clinical application. The results showed that the application of a mechanical strain significantly decreased the corrosion resistance of the CAW and increased the release of toxic corrosion products. The addition of the proteins inhibited the corrosion of the CAW, but the mechanical loads counteracted this effect. Mucin enhanced the corrosion resistance of the CAW. The effects of the proteins or strain, either alone or in combination, should be considered in the application of medical materials of heterogenetic alloys.

Tribocorrosion behaviour of pure titanium in bovine serum albumin solution: A multiscale study

Tribocorrosion behaviour of pure titanium in phosphate buffer saline (PBS) solution has been investigated systematically as a function of surface chemistry and bovine serum albumin (BSA) content in the solution. A ball-on-disk tribometer coupled with an electrochemical cell was used to study the effect of electrochemical conditions (i.e. anodic and cathodic applied potentials, as well as at open circuit potential) on the tribocorrosion response of titanium. It was found that the main material loss is due to mechanical wear caused by plastic deformation. The mechanical wear was higher under anodic conditions than under cathodic, partially due to an increased presence of debris particles at the sliding interface that act as third bodies. The effect of BSA on the interaction between alumina and titanium, as well as the behaviour of third bodies during the mechanical wear, were investigated in the nanoscale level using atomic force microscopy based force spectroscopy. It was found that the presence of BSA affects tribocorrosion in various ways. Firstly, it increases the repassivation rate of the oxide film by inhibiting the cathodic reactions and accelerating the anodic reactions. Secondly, it increases the mechanical wear by increasing the adhesion of debris onto the sliding interface, while at anodic conditions it increases the rolling efficiency of the debris particles that further enhances the mechanical wear.

TiZrNbTaMo high-entropy alloy designed for orthopedic implants: As-cast microstructure and mechanical properties

Combining the high-entropy alloy (HEA) concept with property requirement for orthopedic implants, we designed a Ti₂₀Zr₂₀Nb₂₀Ta₂₀Mo₂₀ equiatomic HEA. The arc-melted microstructures, compressive properties and potentiodynamic polarization behavior in phosphate buffer solution (PBS) were studied in detail. It was revealed that the as-cast TiZrNbTaMo HEA consisted of dual phases with bcc structure, major bcc1 and minor bcc2 phases with the lattice parameters of 0.3310nm and 0.3379nm, respectively. As confirmed by nanoindentation tests, the bcc1 phase is somewhat harder and stiffer than the bcc2 phase. The TiZrNbTaMo HEA exhibited Young's modulus of 153GPa, Vickers microhardness of 4.9GPa, compressive yield strength of σ_y=1390MPa and apparent plastic strain of ε_p≈6% prior to failure. Moreover, the TiZrNbTaMo HEA manifested excellent corrosion resistance in PBS, comparable to the Ti6Al4V alloy, and pitting resistance remarkably superior to the 316L SS and CoCrMo alloys. These preliminary advantages of the TiZrNbTaMo HEA over the current orthopedic implant metals in mechanical properties and corrosion resistance offer an opportunity to explore new orthopedic-implant alloys based on the TiZrNbTaMo concentrated composition.

Standards of external fixation in prolonged applications to allow safe conversion to definitive extremity surgery: the Aachen algorithm for acute ex fix conversion

External fixation has become an important tool in orthopedic surgery. Technology has improved the design and material as well as the construct of the fixator. As most patients are converted from external fixation to definite stabilization during later clinical course, prevention of complications such as infection is of high importance. Based on the current literature, principles of temporary external fixation were summarized. We focused on minimizing the risk of infection and introduce a standardized algorithm how to proceed when converting from external to internal fixation, which also was examined for effectiveness.