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- ItemInfluence of isothermal omega precipitation aging on deformation mechanisms and mechanical properties of a β-type Ti-Nb alloy(Lausanne : Elsevier, 2022) Pilz, S.; Hariharan, A.; Günther, F.; Zimmermann, M.; Gebert, A.In this study, the influence of ωiso precipitates on the active deformation mechanisms and the mechanical properties of the biomedical β-type Ti-40Nb alloy are revealed. Low temperature heat treatments (aging) at 573 K for durations up to 108.0 ks were carried out for a cold-rolled and recrystallized sample state. After an aging time of 3.6 ks the ωiso phase was determined by means of synchrotron XRD and the fraction and the crystallite size of ωiso increased progressively with increasing aging time. Due to the high intrinsic Young's modulus of the ωiso phase, the Young's modulus increased gradually with the aging time from 63 GPa, for the recrystallized reference condition, to values of 70 GPa (3.6 ks), 73 GPa (14.4 ks), 81 GPa (28.8 ks) and 96 GPa (108.0 ks). Depending on the aging time, also a change of the active deformation mechanisms occurred, resulting in significantly altered mechanical properties. For the single β-phase reference microstructure, stress-induced martensite (SIM) formation, {332} <113> twinning and dislocation slip were observed under tensile loading, resulting in a low 0.2% proof stress of around 315 MPa but a high elongation at fracture of 26.2%. With increasing aging time, SIM formation and mechanical twinning are progressively hindered under tensile loading. SIM formation could not be detected for samples aged longer than 3.6 ks. The amount and thickness of deformation twins is clearly reduced with increasing aging time and for samples aged longer than 14.4 ks deformation twinning is completely suppressed. As a result of the changed deformation mechanisms and the increase of the critical stress for slip caused by ωiso, the 0.2% proof stress of the aged samples increased gradually from 410 MPa (3.6 ks) to around 910 MPa (108.0 ks). With regard to application as new bone implant material, a balanced ratio of a low Young's modulus of E = 73 GPa and higher 0.2% proof stress of 640 MPa was achieved after an aging time of 14.4 ks.
- ItemShort range order and topology of binary Ge-S glasses(Lausanne : Elsevier, 2022) Pethes, I.; Jóvári, P.; Michalik, S.; Wagner, T.; Prokop, V.; Kaban, I.; Száraz, D.; Hannon, A.; Krbal, M.Short range order and topology of GexS100-x glasses over a broad composition range (20 ≤ x ≤ 42 in at%) was investigated by neutron diffraction, X-ray diffraction, and Ge K-edge extended X-ray absorption fine structure (EXAFS) measurements. The experimental data sets were fitted simultaneously in the framework of the reverse Monte Carlo simulation method. It was found that both constituents (Ge and S) satisfy the Mott-rule in all investigated glasses: Ge and S atoms have 4 and 2 neighbours, respectively. The structure of these glasses can be described with the chemically ordered network model: Ge-S bonds are preferred; S-S bonds are present only in S-rich glasses. Dedicated simulations showed that Ge-Ge bonds are necessary in Ge-rich glasses. Connections between Ge atoms (such as edge-sharing GeS4/2 tetrahedra) in stoichiometric and S-rich glasses were analysed. The frequency of primitive rings was also calculated.