Mechanical properties and bio-tribological behaviors of novel beta-Zr-type Zr-Al-Fe-Nb alloys for biomedical applications

Effect of Mo Content on the Structural, Mechanical, and Tribological Properties of New Zr-Nb-Mo Alloys Obtained by Combining Powder Metallurgy and Vacuum Arc Melting Methods

Considering the high demand for innovative solutions in medicine, a major increase in interest in biomaterials research has been noticed, with the most significant advancements in metals and their alloys. Titanium-based alloys are one of the most recognised in the scientific community but do not represent the only way to achieve optimal results. Zirconium alloys for medical applications are a novelty with significant research potential based on their outstanding properties, which may be of value for medicine. The aim of the present study was to obtain new biomedical Zr-Nb-Mo alloys with varying ratios of their respective elements-Zr and Mo-using combined powder metallurgy (PM) and arc melting (VAM) methods. The obtained samples underwent microstructure analysis using an optical microscope (OM) and a scanning electron microscope (SEM). The study of element distribution was conducted with energy dispersive spectroscopy (EDS), whereas the phase composition was determined using X-ray diffraction (XRD). Mechanical properties were examined with a Micro Combi Tester MCT3, whereas tribological properties were assessed with a TRN Tribometer, and Ringer's solution was used as a lubricant. Additionally, the wear tracks of the studied samples were observed using the SEM. The research results indicated that increased Mo content conduced to microstructure refinement and homogeneity. Furthermore, the higher content of this element contributed to the growth of the HVIT, HIT, and EIT parameters, together with the improvement in the tribological performance of the alloys. XRD analysis revealed that the obtained samples were multiphase, and raising the Mo addition promoted the formation of new phases, including a ternary phase-Zr0.9Nb0.66Mo1.44 (Fd3¯m). The chemical composition study showed uneven distribution of niobium and areas of uneven mutual distribution of zirconium and molybdenum.

Evaluation of biocompatibility and osseointegration of Nb-xTi-Zr alloys for use as dental implant materials

The aim of this study was to evaluate the biocompatibility and osteogenic potential of 50%Nb-xTi-Zr (NTZ, x=20%, 30%, 40% by weight) alloys as compared with dental commercial pure titanium (cpTi). Cell cytotoxity assay, fluorescence microscopy and electron microscopy were used to measure the in vitro biocompatibility of NTZ. The expression of alkaline phosphatase (ALP), integrin β1, osteocalcin (OC), Ki67 and collagen-I (Col-I) at the mRNA level was measured by real-time reverse transcription-polymerase chain reaction (RT-PCR). Osseointegration ability was determined using X-ray evaluation and histological analysis in vivo. Compared with the MG63 cells grown on cpTi on day 3, the viability, adherence and proliferation rates of cells cultured on NTZ alloys were significantly improved (p < 0.05). Furthermore, similar expression levels of Ki67, Col-Ⅰ, OC and ALP were found in the MG63 cells grown on NTZ alloys and those grown on cpTi. The Cbf α1 level was significantly higher for the 50%Nb-30%Ti-Zr (NTZ3) than for the cpTi group on day 6 (p < 0.01), indicating that NTZ alloys can induce osteogenesis. A considerable amount of new bone formation and osseointegration was observed around NTZ3 implants compared with cpTi implants in vivo. Collectively, NTZ3 showed superior biocompatibility and osteogenic activity; therefore, NTZ3 may be an excellent replacement for dental Ti implants.

New Zr-25Ti-xMo alloys for dental implant application: Properties characterization and surface analysis

A series of Zr-25Ti-xMo (x = 0, 2.5, 5, 7.5, 10 and 12.5 wt %) as-cast alloys were designed to advance a new-brand Zr-based alloy with low Young's elastic, moderate compression strength, superior corrosion resistance and good wear behavior for the application of dental implant materials. In the present study, the microstructures of the alloys were evaluated by X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy. The microhardness and uniaxial compression measurement were performed to evaluate the mechanical properties of the alloys. The electrochemical behaviors of the alloys was investigated in artificial saliva solution. The friction and wear performances of the Zr-25Ti-xMo alloys were examined by pin-on-disk under the load of 15 N. The results shows that the crystalline structure transforms from hexagonal close-pack (α phase, x = 0 wt %) to body-centered cubic structure (β phase, 5 ≤ x ≤ 12.5 wt %) through a α + β dual-phase region (x = 2.5 wt %). They exhibits excellent mechanical properties with low elastic modulus (from 17.7 to 24.4 GPa) and moderate compression strength (from 1154.4 to 1310.8 MPa). The Zr-25Ti-xMo alloys possess good corrosion resistance due to the formation of a protective passive film consisting mainly of ZrO₂, TiO₂ and minor MoO₃. Especially, the polarization curves demonstrates that the Zr-25Ti-7.5Mo alloy has a wider passive region than the other five alloys and it possesses the lower corrosion current density and corrosion rate. Furthermore, this alloy exhibits good abrasion resistance with the lowest coefficients of friction and volume wear loss. Thus, the Zr-25Ti-7.5Mo alloy has a combination of excellent mechanical properties such as low elastic modulus, moderate yield strength and the compression strength, good electrochemical stability and well wear resistance, it is considered a promising candidate for orthopedic materials as dental implant.

Fretting corrosion behaviour of Ti-6Al-4V reinforced with zirconia in foetal bovine serum

Fretting corrosion is a critical challenge in the design of hip prosthesis used in total hip arthroplasty (THA) surgeries. Currently, the design of hip implants includes a tapered junction which introduces additional interfaces that connect different parts of the hip implant such as the femoral neck and head or stem and neck interface. Micro motions that occur under the influence of load, together with chemical changes in the host environment, make these interfaces susceptible to tribocorrosion processes, particularly fretting corrosion. Commonly used metallic biomaterials are based on stainless steels, cobalt chrome-based alloys as well as titanium and titanium alloys. Each of these materials possess some degree of limitations, particularly where tribocorrosion events are concerned. Titanium alloy Ti-6Al-4V is widely used in biomedical applications for non-bearing components of total joint arthroplasty (TJA) surgeries. Its poor wear resistance continues to remain a challenge in load-bearing joints where parts articulate against one another as in the case of modular junctions. Some of the attempts made to improve the wear properties of Ti-6Al-4V is through the incorporation of second phase particles like ceramics in its matrix to produce metal matrix composites of Ti-6Al-4V. The aim of this work is to investigate the effect of zirconia reinforcement on spark plasma sintered Ti-6Al-4V composites (zirconium oxide particles incorporated into Ti-6Al-4V matrix) on the fretting corrosion properties of Ti-6Al-4V. Fretting corrosion tests were carried out on as-sintered Ti-6Al-4V and Ti-6Al-4V with 5 and 10 wt.% ZrO₂. The tests were carried out in foetal bovine serum under applied normal loads of 85 and 115 N using the cylinder-on-flat contact configuration. The evolution of OCP, dissipated energy and friction coefficient were recorded throughout the test. Microstructural analysis of the samples before fretting corrosion tests showed the presence of globular agglomerates throughout the Ti-6Al-4V matrix due to zirconia additions; the volume of the agglomerates was higher in the composites having 10 wt.% ZrO₂. Ti-6Al-4V composites having zirconia additions produced a nobler OCP during fretting in foetal bovine serum, compared to pure Ti-6Al-4V. Furthermore, the fretting corrosion results showed a significant improvement in the tribocorrosion resistance of Ti-6Al-4V with 10 wt.% ZrO₂ at all loads. This composition also produced the least amount of degradation. and metal ion release. Mechanical data showed that increasing the applied normal load promoted a transition from gross slip to partial slip conditions for all compositions. Partial slip was found to be prevalent at a higher normal load (drastic decrease of the dissipated energy and consequently the friction coefficient). This mechanical condition prevents a large amount of degradation.

On the Corrosion Behaviour of Low Modulus Titanium Alloys for Medical Implant Applications: A Review

The corrosion behaviour of new generation titanium alloys (β-type with low modulus) for medical implant applications is of paramount importance due to their possible detrimental effects in the human body such as release of toxic metal ions and corrosion products. In spite of remarkable advances in improving the mechanical properties and reducing the elastic modulus, limited studies have been done on the electrochemical corrosion behaviour of various types of low modulus titanium alloys including the effect of different beta-stabilizer alloying elements. This development should aim for a good balance between mechanical properties, design features, metallurgical aspects and, importantly, corrosion resistance. In this article, we review several significant factors that can influence the corrosion resistance of new-generation titanium alloys such as fabrication process, body electrolyte properties, mechanical treatments, alloying composition, surface passive layer, and constituent phases. The essential factors and their critical features are discussed. The impact of various amounts of α and β phases in the microstructure, their interactions, and their dissolution rates on the surface passive layer and bulk corrosion behaviour are reviewed and discussed in detail. In addition, the importance of different corrosion types for various medical implant applications is addressed in order to specify the significance of every corrosion phenomenon in medical implants.