Search

The main goal of this study was to achieve poreless titanium alloys with nanocrystalline structure. To this end, the influence of Ta, Mg and Zn content on the properties of Ti alloys was investigated. At first, nanocrystalline powders of TixTayMg and TixTayZn, where x = (30 and 40 wt.%) and y = (3 and 5 wt.%), were prepared using the mechanical alloying process at room temperature. Then, hot-pressing at 750 °C under vacuum was applied for 10 s to consolidate powders. The structure, microstructure, chemical composition, mechanical properties, corrosion resistance, wettability and MTT assay have been investigated. Alloys with Mg were allowed to undergo a shorter mechanical alloying process, achieve greater grain refinement after consolidation and improve mechanical properties. In all cases with increasing amounts of additives in titanium, more Ti-β phase was available. Furthermore, with increasing elements content, hot-pressed alloys consisting of Mg tended to have a more hydrophobic surface. According to the MTT test, all new alloys show non-toxic properties. Among all alloys tested in this study, Ti40Ta5Mg had the most interesting properties for biomedical applications, the highest content of Ti-β phase (81.3%), lowest porosity (0.07%), lowest Young modulus (102.1 GPa) and the lowest surface free energy (38.45 mN/m). [ABSTRACT FROM AUTHOR]

With the continuously rapid development of materials science, better properties are equably required in the area of material surface engineering, especially the surface friction and high-temperature oxidation resistance of titanium alloy. It is a great approach to select a scientific way for surface treatment to improve the surface performance so as to obtain surface films/coatings/layers. It can provide a vital latent remedy to the insufficient high-temperature oxidation resistance and wear resistance of titanium alloys. Pack cementation is a reliable means at present by virtue of its distinct composition, covering pollution-free and the firm metallurgical bonding between the alloying coating and the matrix. In the last few years, with the growing demands for the surface performance of materials in multifarious harsh environments, the coating obtained by pack cementation is developing toward controlling coating composition accurately and applying it to complex parts. This review opens with an abbreviated introduction of pack cementation technology. The recent developments of pack cementation technology for enhancing diverse surface properties are scientifically reviewed in the aspects of background, previous research results and the future development directions. [ABSTRACT FROM AUTHOR]

The aircraft industry is always looking for improved efficiency through higher in-service engine temperatures and lighter structures. Titanium-based alloys are good candidates for such applications because of their high specific strength. However, when exposed to high-temperature oxidizing environments, a large amount of dissolved oxygen can be found in such alloys beneath the growing oxide scale, possibly leading to embrittlement. Consequently, evaluating the oxidation resistance of these alloys is essential. With this aim, long-term oxidation tests were carried out on Ti6242S alloy between 500 and 650 °C to study the effect of temperature, surface preparation and microstructure on oxide scale and oxygen dissolution. While increasing the temperature from 560 to 625 °C led to accelerated oxidation kinetics, surface preparation had no noticeable effect on mass variations and oxygen diffusion profiles. Regarding microstructure, when comparing Ti6242S samples having similar α-phase fraction but very different microstructures (fineness and morphology), there wasn't any significant effect found on mass change and oxygen diffusion after 1 kh at 650 °C. [ABSTRACT FROM AUTHOR]

Nowadays, one of the main challenges in metal implants for bone substitution is the achievement of an elastic modulus close to that of human cortical bone as well as to provide an adequate interaction with the surrounding tissue avoiding in vivo foreign body reaction. From this perspective, a new Ti-based alloy has been developed with Nb and Hf as alloying elements which are known as non-toxic and with good corrosion properties. The microstructure, mechanical behaviour and the physicochemical properties of this novel titanium alloy have been studied. Relationship of surface chemistry and surface electric charge with protein adsorption and cell adhesion has been evaluated due to its role for understanding the mechanism of biological interactions with tissues. The Ti25Nb21Hf alloy presented a lower elastic modulus than commercial alloys with a superior ultimate strength and yield strength than CP-Ti and very close to Ti6Al4V. It also exhibited good corrosion resistance. Furthermore, the results revealed that it had no cytotoxic effect on rat mesenchymal stem cells and allowed protein adsorption and cell adhesion. The experimental results make this alloy a promising material for bone substitution or for biomedical devices. [ABSTRACT FROM AUTHOR]

Abstract: The effects of three electrode materials – stainless steel (SS), pure titanium (PT), and titanium-based alloy (TA) – on the PEF-induced degradation, spectral characteristics, visual colour, and antioxidant capacity of cyanidin-3-glucoside (Cy-3-glc) and cyanidin-3-sophoroside (Cy-3-soph) were studied. Cy-3-glc and Cy-3-soph were degraded by PEF; SS retained Cy-3-glc and Cy-3-soph the most, while PT and TA led to greater degradation. Cy-3-glc was more susceptible to PEF than Cy-3-soph. The intensity of UV–Vis spectra absorbance at 520nm decreased, but it increased at 280 and 325nm after PEF when using the three electrodes. Their lightness (L ∗) exhibited no changes with SS, but showed a significant reduction with PA and TA. Redness (a ∗) significantly decreased with all three electrodes; the yellowness (b ∗) of Cy-3-glc with PA and TA, and of Cy-3-soph with SS, were also significantly reduced. The antioxidant capacity of Cy-3-glc and Cy-3-soph with SS, in contrast to PT and TA, was enhanced after PEF. [Copyright &y& Elsevier]

The most commonly used titanium (Ti)-based alloy for biological applications is Ti-6Al-4V, but some studies associate the vanadium (V) with the cytotoxic effects and adverse reactions in tissues, while aluminum (Al) has been associated with neurological disorders. Ti-Nb alloys belong to a new class of Ti-based alloys with no presence of Al and V and with elasticity modulus values that are very attractive for use as a biomaterial. It is well known that the presence of interstitial elements (such as oxygen, for example) changes the mechanical properties of alloys significantly, particularly the elastic properties, the same way that heat treatments can change the microstructure of these alloys. This article presents the effect of heat treatment and oxygen doping in some mechanical properties and the biocompatibility of three alloys of the Ti-Nb system, characterized by density measurements, X-ray diffraction, optical microscopy, Vickers microhardness, in vitro cytotoxicity, and mechanical spectroscopy. [ABSTRACT FROM AUTHOR]

A friction- and wear-resistant Al–Cu–Fe–Cr quasicrystalline coating was fabricated on substrate of titanium alloy by low-pressure plasma-spraying (LPPS) method. The LPPS Al–Cu–Fe–Cr quasicrystalline coating has a rapidly solidified lamellar microstructure consisting of mainly decagonal phase and small amount of cubic phase peaks. The results showed that Al–Cu–Fe–Cr quasicrystalline coating improved the friction and wear resistance of titanium-based alloys under dry sliding wear test conditions. The excellent wear resistance may be attributed to the high hardness of Al–Cu–Fe–Cr quasicrystal. [Copyright &y& Elsevier]

The high-temperature oxidation behavior of titanium-based alloys coated with Al–Cu–Fe–Cr quasicrystal using the low-pressure plasma spraying (LPPS) method was studied. The results showed that Al–Cu–Fe–Cr quasicrystal line coating improved the oxidation resistance of titanium-based alloys. The weight gains at 750 and 800 °C for Al–Cu–Fe–Cr quasicrystalline coating are very low and the oxidation kinetics follows a parabolic law. During the oxidation period there is no evident spallation of the coating from the substrate. Oxide formed on the surface of Al–Cu–Fe–Cr quasicrystalline coating after oxidation consisted of Al2O3. [Copyright &y& Elsevier]

Ti-based alloys are widely used in medical applications. When implant devices are used to reconstruct disordered bone, prevent bone resorption and enhance good bone remodeling, the Young's modulus of implants should be close to that of the bone. To satisfy this requirement, many titanium alloys with different biocompatible elements (Zr, Ta, Mo, Si etc.) interact well with adjacent bone tissues, promoting an adequate osseointegration. Four new different alloys were obtained and investigated regarding their microstructure, mechanical, chemical and biological behavior (in vitro and in vivo evaluation), as follows: Ti20Mo7Zr15Ta, Ti20Mo7Zr15Ta0.5Si, Ti20Mo7Zr15Ta0.75Si and Ti20Mo7Zr15TaSi. 60 days after implantation, both in control and experimental rabbits, at the level of implantation gap and into the periimplant area were found the mesenchymal stem cells which differentiate into osteoblasts, then osteocytes and osteoclasts which are involved in the new bone synthesis and remodeling, the periimplant fibrous capsule being continued by newly spongy bone tissue, showing a good osseointegration of alloys. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay confirmed the in vitro cytocompatibility of the prepared alloys. [ABSTRACT FROM AUTHOR]

When used at high temperature in air, titanium-based alloys form an oxide scale at their surface but also dissolve large amount of oxygen in their metallic matrix and this is a cause of embrittlement. Nitrogen is a secondary oxidant, which also dissolves in and embrittles the alloy. Oxidation experiments of Ti-6Al-2Sn-4Zr-2Mo-0.1Si titanium-based alloy, for 1000 h at 650 °C in synthetic air (N 2 -20%O 2) and in a mixture of Ar-20%O 2 , showed that nitrogen decreases both oxide scale growth and oxygen dissolution. Atom probe tomography was used to investigate the alloy/oxide interface. The results revealed that the nitrogen effect is due to the formation of interfacial layers of oxynitrides and nitride (Ti 2 N), but also to the formation of a nitrogen rich α-titanium-based solid solution, which all act as diffusion barriers for oxygen, because of their low oxygen solubility. A comparison between the experimental results and thermodynamic calculations is also reported. [ABSTRACT FROM AUTHOR]