75 research outputs found
Effect of nonmetallic and intermetallic inclusions on crater formation on the surface of TiNi alloys under the electron-beam impact
No full textAbstractThe regularities of surface cratering in commercial and precision TiNi alloys irradiated with a low-energy, high-current electron beam (LEHCEB) in dependence on non-metallic (TiC(O)) or intermetallic (Ti2Ni) inclusions presented in TiNi matrix are studied. The melting threshold of TiNi alloy was found to be achieved in the range of LEHCEBs energy density Es corresponding to 1.3-1.5 J/cm2. The dominant role of non-metallic inclusions [mainly, TiC(O)] in the nucleation of microcraters was found. The processes initiated by pulsed heating/melting near the inclusion/matrix interface were analyzed. It is proposed that the most important factor enabling the liquid-phase dissolution of inclusions and delivery of impurities of C and O [from TiC(O)] and O (from Ti4Ni2Ox) into TiNi melt are eutectic reactions taking place in the Ti-Ni-C and Ti-Ni-O systems near Ti50Ni50 composition
Tumors of the Optic Nerve and Its Sheath
No full textThe tumors of the optic nerve may arise from the nerve itself or from its sheath. Benign gliomas and meningiomas are the most frequent types, whereas other histological types are exceptional. Benign tumors cause slowly progressive visual loss and variable proptosis. The radiological diagnosis is rather easy for gliomas and meningiomas. The observation is justified in patients with preserved or stable vision. The surgery is often delayed because of the significant risk of visual worsening. Pediatric benign gliomas often respond to chemotherapy. Patients with optic nerve sheath meningiomas may be treated by stereotactic radiosurgery. However, the visual prognosis is more often poor. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023
Dimensional stability of coarse-grained and submicrocrystalline TiNi shape memory alloy for medical use under quasistatic and cyclic bending
No full textAbstractThe paper reports on a comparative study of inelastic strain accumulation in coarse-grained and submicrocrystalline titanium nickelide (TiNi) under quasistatic and cyclic loads. It is shown that the formation of submicrocrystalline structure in TiNi by equal channel angular pressing provides a steep increase in its strain resistance under quasistatic and cyclic loads. The contribution of dislocation and martensitic mechanisms to residual strain accumulation under different loading conditions is analyzed
Hydrogen-induced failure of TiNi based alloy with coarse-grained and ultrafine-grained structure
No full textAbstractThe objective of this work is to investigate the effect of hydrogen-induced fracture of TiNi-based alloy. In this report we performed the first studies comparing inelastic properties and fracture of the specimens of the binary alloy of TiNi wire under the action of hydrogen with coarse-grained (CG) and ultrafine-grained (UFG) microstructure. It is shown that hydrogen embrittlement (HE) occurs irrespective of the grain size in the studied specimens at approximately equal strain values. However, compared to the specimens with CG structure, those with UFG structure accumulate two to three times more hydrogen for the same hydrogenation time. It is found that hydrogen has a much smaller effect on the inelastic properties of specimens with UFG structure as compared to those with CG structure
Introduction of antibacterial function into biomedical TiNi shape memory alloy by the addition of element Ag
No full textA new kind of biomedical shape memory TiNiAg alloy with antibacterial function was successfully developed in the present study by the introduction of pure Ag precipitates into the TiNi matrix phase. The microstructure, mechanical property, corrosion resistance, ion release behavior in simulated body fluid, cytotoxicity and antibacterial properties were systematically investigated. The typical microstructural feature of TiNiAg alloy at room temperature was tiny pure Ag particles (at submicrometer or micrometer scales with irregular shape) randomly distributed in the TiNi matrix phase. The presence of Ag precipitates was found to result in a slightly higher tensile strength and larger elongation of TiNiAg alloy in comparison with that of TiNi binary alloy. Furthermore, a maximum shape recovery strain of similar to 6.4% was obtained with a total prestrain of 7% in the TiNiAg alloy. In electrochemical and immersion tests, TiNiAg alloy presented good corrosion resistance in simulated body fluid, comparable with that of CP Ti and TiNi alloy. The cytotoxicity evaluation revealed that TiNiAg alloy extract induced slight toxicity to cells, but the viability of experimental cells was similar to or higher than that of TiNi alloy extract. In vitro bacterial adhesion study indicated a significantly reduced number of bacteria (S. aureus, S. epidermidis and P. gingivalis) on the TiNiAg alloy plate surface when compared with that on TiNi alloy plate surface, and the corresponding antibacterial mechanism for the TiNiAg alloy is discussed. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000291181800045&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, BiomedicalMaterials Science, BiomaterialsSCI(E)41ARTICLE62758-2767
Fabrication of TiNi shape memory alloy microactuators by ion beam sputter deposition
No full textTiNi shape memory alloy has been recently investigated for use in microactuators because of the high power to volume ratio. Conventional sputtering methods, such as RF and DC sputtering and magnetron sputtering, have previously been used by other workers in order to deposit TiNi thin films. As-deposited films produced by these methods are amorphous, and are then crystallised typically by annealing at 500 deg C for 1 hour in order to exhibit the shape memory effect. These deposition methods have invariably used alloyed targets to grow thin films. In this thesis, an Ion Beam Sputter Deposition (IBSD) method has been used by which argon ions are used to bombard non- alloyed targets. The thin films grown by this technique demonstrate the characteristics of the shape memory effect. Films have been characterised by electrical resistivity, resistance and thermal measurements, giving physical properties in excellent agreement with those quoted in the literature. Compositional and density measurements were done by X-ray reflectometry and were consistent with equi-atomic composition and nominal density for TiNi. In addition thermal modelling was used to investigate implications of heating and cooling rates for microactuator operation. Finally, a novel fabrication process is proposed, combining ion beam milling and Focused Ion Beam (FIB) trepanning for the process of microactuator production. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN043198 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
High damping capacity in a wide temperature range of a compositionally graded TiNi alloy prepared by electroplating and diffusion annealing
No full textA compositionally graded TiNi alloy was prepared by electroplating of Ni coating on TiNi substrate and diffusion annealing. The temperature range with damping capacity of larger than 0.04 was enlarged to above 110 degrees C for the compositionally graded alloy, which was almost 5 times of that for the homogeneous alloy. (C) 2014 Elsevier B.V. All rights reserved.Nanoscience & NanotechnologyMaterials Science, MultidisciplinaryMetallurgy & Metallurgical EngineeringSCI(E)[email protected]
TiNi shape memory alloy coated with tungsten: A novel approach for biomedical applications
No full textThis study explores the use of DC magnetron sputtering tungsten thin films for surface modification of TiNi shape memory alloy (SMA) targeting for biomedical applications. SEM, AFM and automatic contact angle meter instrument were used to determine the surface characteristics of the tungsten thin films. The hardness of the TiNi SMA with and without tungsten thin films was measured by nanoindentation tests. It is demonstrated that the tungsten thin films deposited at different magnetron sputtering conditions are characterized by a columnar microstructure and exhibit different surface morphology and roughness. The hardness of the TiNi SMA was improved significantly by tungsten thin films. The ion release, hemolysis rate, cell adhesion and cell proliferation have been investigated by inductively coupled plasma atomic emission spectrometry, CCK-8 assay and alkaline phosphatase activity test. The experimental findings indicate that TiNi SMA coated with tungsten thin film shows a substantial reduction in the release of nickel. Therefore, it has a better in vitro biocompatibility, in particular, reduced hemolysis rate, enhanced cell adhesion and differentiation due to the hydrophilic properties of the tungsten films
Adaptive Damping in Shape Memory TiNi during Cavitation
No full textAbstractRecent studies by this author and others has demonstrated that cavitation-erosion of NiTi coatings or bulk NiTi is exceptional. Studies were undertaken to ascertain whether this property is a consequence of either the general intermetallic properties of NiTi or by an adaptive stress-dissipation mechanism of the cavitation-generated shock wave by A microstructural mechanism related to the shape memory effect.In cavitation, an oscillating pressure field causes the formation and implosion of air bubbles. As a surface easily nucleates bubbles, the subsequent implosion of the bubbles generates stresses approaching several MPa, which are large enough to ablate material, and are also high enough to generate stress-induced Martensite or Austenite, depending on whether the applied stress is tensile or compressive. The implication is that the stress wave may be partially accommodated by the stress-induced transformation, which can dissipate the energy as heat on retransformation to the materials unstressed phase.Calculations concerning the variation of the cavitation-induced stresses and temperature distribution with depth into the TiNi coupled with the associated problems of heat transfer will be presented. It will be shown that an adaptive mechanism is plausible.</jats:p
Radiation therapy for atypical and anaplastic meningiomas: an overview of current results and controversial issues
No full textMeningiomas are the most common intracranial tumors. Most meningiomas are WHO grade 1 tumors whereas less than one-quarter of all meningiomas are classified as atypical (WHO grade 2) and anaplastic (WHO grade 3) tumors, based on local invasiveness and cellular features of atypia. Surgical resection remains the cornerstone of meningioma therapy and represents the definitive treatment for the majority of patients; however, grade 2 and grade 3 meningiomas display more aggressive behavior and are difficult to treat. Several retrospective series have shown the efficacy and safety of postoperative adjuvant external beam radiation therapy (RT) for patients with atypical and anaplastic meningiomas. More recently, two phase II prospective trials by the Radiation Therapy Oncology Group (RTOG 0539) and the European Organisation for Research and Treatment of Cancer (EORTC 2042) have confirmed the potential benefits of fractionated RT for patients with intermediate and high-risk meningiomas; however, several issues remain a matter of debate. Controversial topics include the timing of radiation treatment in patients with totally resected atypical meningiomas, the optimal radiation technique, dose and fractionation, and treatment planning/target delineation. Ongoing randomized trials are evaluating the efficacy of early adjuvant RT over observation in patients undergoing gross total resection. © 2022, The Author(s
- …
