Investigation of early stage deformation mechanisms in a metastable β titanium alloy showing combined twinning-induced plasticity and transformation-induced plasticity effects

International audienceAs expected from the alloy design procedure, combined Twinning Induced Plasticity (TWIP) and Transformation Induced Plasticity (TRIP) effects are activated in a metastable β Ti-12(wt.%)Mo alloy. In-situ Synchrotron X-ray diffraction (XRD), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) observations were carried out to investigate the deformation mechanisms and microstructure evolution sequence. In the early deformation stage, primary strain/stress induced phase transformations (β->ω and β->α'') and primary mechanical twinning ({332} and {112}) are simultaneously activated. Secondary martensitic phase transformation and secondary mechanical twinning are then triggered in the twinned β zones. The {332} twinning and the subsequence secondary mechanisms dominate the early stage deformation process. The evolution of the deformation microstructure results in a high strain hardening rate (~2GPa) bringing about high tensile strength (~1GPa) and large uniform elongation (> 0.38)

Finite element analysis of the mechanical performance of self-expanding endovascular stents made with new nickel-free superelastic β-titanium alloys

International audienceNew Ni-free superelastic β-titanium alloys from the Ti–Zr–Nb–Sn system have been designed in this study to replace the NiTi alloy currently used for self-expanding endovascular stents. The simulation results, carried out by finite element analysis (FEA) on two β-type Ti–Zr–Nb–Sn alloys using a commonly used superelastic constitutive model, were in good agreement with the experimental uniaxial tension data. An ad-hoc self-expanding coronary stent was specifically designed for the present study. To assess the mechanical performance of the endovascular stents, a FEA framework of the stent deployed in the arterial system was established, and a simply cyclic bending loading was proposed. Six comparative simulations of three superelastic materials (including NiTi for comparison) and two arterial configurations were successfully conducted. The mechanical behaviours of the stents were analysed through stress localization, the increase in artery diameter, contact results, and distributions of mean and alternating strain. The simulation results show that the Ti–22Zr–11Nb–2Sn (at. %) alloy composition for the stent produces the largest contact area (9.92 mm2) and radial contact force (49.5 mN) on the inner surface of the plaque and a higher increase in the stenotic artery diameter (70 %) after three vascular bending cycles. Furthermore, the Ti–22Zr–11Nb–2Sn stent exhibited sufficient crimping capacity and reliable mechanical performance during deployment and cyclic bending, which could make it a suitable choice for self-expanding coronary stents. In this work, the implementation of finite element analysis has thus made it possible to propose a solid basis for the mechanical evaluation of these stents fabricated in new Ni-free superelastic β-Ti alloys

Interaction between Deformation and Crack Initiation under Vickers Indentation in Na2O-TiO2-SiO2 Glasses

International audienceAn observed minimum in the critical crack initiation load at Poisson's ratio (nu) of 0.21-0.22 in Na2O-TiO2-SiO2 glasses was investigated. Vickers indentation was used to examine hardness and average cracking length, fracture toughness was measured through the single-edge pre-cracked beam method, and volumes of densification and shear flow around indents were measured using atomic force microscopy. Relations between the critical crack initiation load and hardness, average crack length, fracture toughness, and the volume fractions of densification and shear flow were studied. No correlations were observed between hardness, average crack length, or fracture toughness with the critical crack initiation load. A link between the minimum in crack initiation load and a change in deformation mechanisms (densification versus shear flow) was observed

Design of a novel superelastic Ti-23Hf-3Mo-4Sn biomedical alloy combining low modulus, high strength and large recovery strain

International audienceIn this study, a new Ti-23Hf-3Mo-4Sn superelastic alloy for biomedical applications was elaborated and characterized. Outstanding combination of high strength (~1 GPa), low Young's modulus (55 GPa) and large recovery strain of about 4% were achieved. These mechanical properties make this newly developed Ti-23Hf-3Mo-4Sn alloy very promising for biomedical applications

Titane Alloys for Marine Application : the case of an innovating winch

International audienc

Titane Alloys for Marine Application : the case of an innovating winch

International audienc