. Twinning system selection in a metastable β-titanium alloy by Schmid factor analysis. Scripta Materialia, Elsevier, 2011, 64 (12) AbstractElectron backscattering diffraction and Schmid factor analysis were used to study the twinning variant selection in a Ti-25Ta-24Nb (mass%) metastable β-titanium alloy. The two twinning systems {1 1 2} 1 1 1 and {3 3 2} 1 1 3 were observed. For each system the Schmid factor was shown to be a relevant parameter to determine the activated variant.Moreover, selection between the two twinning systems depends on the crystallographic orientation of the grain with respect to the tensile direction.Keywords: Titanium alloy; Electron backscattering diffraction; Twinning; Schmid factor Metastable β-titanium alloys can be elaborated with fully biocompatible β-stabilizer elements such as Ta, Nb, Mo, etc. Their interesting mechanical properties make them good candidates for biomedical applications [1] and [2]. Theses alloys possess a non-ordered bcc structure and are subject to numerous deformation mechanisms: a stress induced martensitic transformation which can lead to a superelastic effect, slip and twinning [3] and [4].Twinning is a common deformation mechanism in materials exhibiting a low stacking fault energy in hcp, fcc or bcc structures. In bcc structures {1 1 2} 1 1 1 is a well-known twinning system, but other twinning systems such as {3 3 2} 1 1 3 have been observed in some metastable alloys subject to a martensitic transformation, like Fe-Ni-C or Fe-Be [5]. In metastable β-titanium alloys both twinning systems {1 1 2} 1 1 1 and {3 3 2} 1 1 3 have been observed, depending on the alloy composition [6] and [7]. Each twinning system can be activated in 12 different ways, termed variants in this paper.The Schmid law is commonly used to predict the activated slip system depending on the tensile direction compared with the crystallographic orientation of the crystal. Selection of the twinning variant can also be predicted by the Schmid law for materials exhibiting hcp or fcc structures, as reported in the literature [8] and [9]. Although it is well known that both slip and twinning occur in bcc titanium alloys, the objective of this paper was to confirm that twinning variant selection in each observed system obeys the Schmid law for a metastable β-titanium alloy (bcc). As several twinning systems can be observed in this kind of alloy a selection parameter between these twinning systems will also be established.The metastable β-alloy composition chosen for this study is Ti-25Ta-24Nb (mass%). The ingot was elaborated by cold crucible levitation melting (CCLM). It underwent homogenization annealing at 950 °C for 20 h, followed by a water quench. Each ingot was then cold rolled (CR = 90%), after which a recrystallization annealing was applied at 850 °C for 0.5 h, followed by a water quench in order to retain the β-phase microstructure at room temperature in its metastable state.Before the recrystallization annealing flat tensile test specimens with a section of 3 × 0.7 mm and a gage len...

To cite this version:A. Ramarolahy, Philippe Castany, F. Prima, P. Laheurte, Isabelle Péron, et al.. Microstructure and mechanical behavior of superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N biomedical alloys.Journal AbstractIn this study, the microstructure and the mechanical properties of two new biocompatible superelastic alloys, Ti-24Nb-0.5O and Ti-24Nb-0.5N (at.%), were investigated. Special attention was focused on the role of O and N addition on α ″ formation, supereleastic recovery and mechanical strength by comparison with the Ti-24Nb and Ti-26Nb (at.%) alloy compositions taken as references. Microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy before and after deformation. The mechanical properties and the superelastic behavior were evaluated by conventional and cyclic tensile tests. High tensile strength, low Young's modulus, rather high superelastic recovery and excellent ductility were observed for both superelastic Ti-24Nb-0.5O and Ti24Nb-0.5N alloys. Deformation twinning was shown to accommodate the plastic deformation in these alloys and only the {332} 113 twinning system was observed to be activated by electron backscattered diffraction analyses.

Abstract:The primary objective of this study is the development of transparent thin film materials in the IR enabling strong infrared absorption of organic compounds in the vicinity of metal nanoparticles by the surface plasmon effect. For developing these optical micro-sensors, heterostructures combining gold nanoparticles and chalcogenide planar waveguides are fabricated and adequately characterized. Single As 2 S 3 and Ge 25 Sb 10 Se 65 amorphous chalcogenide thin films are prepared by radiofrequency magnetron sputtering. For the fabrication of gold nanoparticles on a chalcogenide planar waveguide, direct current sputtering is employed. Fabricated single layers or hetero-structures are characterized using various techniques to investigate the influence of deposition parameters. The nanoparticles of gold are functionalized by a self-assembled monolayer of 4-nitrothiophenol. Finally, the surface enhanced infrared absorption spectra of 4-nitrothiophenol self-assembled on fabricated Au/Ge-Sb-Se thin films hetero-structures are measured and analyzed. This optical component presents a ~24 enhancement factor for the detection of NO 2 symmetric stretching vibration band of 4-nitrothiophenol at 1336 cm −1 . 232-239 (1999). 19. L. Tichý, H. Ticha, P. Nagels, R. Callaerts, R. Mertens, and M. Vlcek, "Optical properties of amorphous As-Se and Ge-As-Se thin films," Mater. Lett. 39(2), 122-128 (1999). 20. J. Charrier, M. L. Anne, H. Lhermite, V. Nazabal, J. P. Guin, F. Charpentier, T. Jouan, F. Henrio, D. Bosc, and J. L. Adam, "Sulphide GaxGe25-xSb10S65(x=0,5) sputtered films: Fabrication and optical characterizations of planar and rib optical waveguides," J. Appl.

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