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- ItemShort range order and topology of binary Ge-S glasses(Lausanne : Elsevier, 2022) Pethes, I.; JĆ³vĆ”ri, P.; Michalik, S.; Wagner, T.; Prokop, V.; Kaban, I.; SzĆ”raz, D.; Hannon, A.; Krbal, M.Short range order and topology of GexS100-x glasses over a broad composition range (20 ā¤ x ā¤ 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.
- ItemEffect of scanning strategy on microstructure and mechanical properties of a biocompatible Tiā35Nbā7Zrā5Ta alloy processed by laser-powder bed fusion(Berlin : Springer, 2022) Batalha, Weverson Capute; Batalha, Rodolfo Lisboa; Kosiba, Konrad; Kiminami, Claudio Shyinti; Gargarella, PiterThe influence of scanning strategy (SS) on microstructure and mechanical properties of a Tiā35Nbā7Zrā5Ta alloy processed by laser-powder bed fusion (L-PBF) is investigated for the first time. Three SSs are considered: unidirectional-Y; bi-directional with 79Ā° rotation (R79); and chessboard (CHB). The SSs affect the type and distribution of pores. The highest relative densities and more homogeneous distribution of pores are obtained with R79 and CHB scanning strategies, whereas aligned pores are formed in the unidirectional-Y. The SSs show direct influence on the crystallographic texture with unidirectional-Y strategy showing fiber texture. The R79 strategy results in a weak texture and the CHB scanning strategy forms a randomly oriented heterogeneous grain structure. The lowest Young modulus is obtained with the unidirectional-Y strategy, whereas the R79 strategy results in the highest yield strength. It is shown that the SSs may be used for tuning the microstructure of a beta-Ti alloy in L-PBF.
- ItemInfluence of isothermal omega precipitation aging on deformation mechanisms and mechanical properties of a Ī²-type Ti-Nb alloy(Lausanne : Elsevier, 2022) Pilz, S.; Hariharan, A.; GĆ¼nther, F.; Zimmermann, M.; Gebert, A.In this study, the influence of Ļiso precipitates on the active deformation mechanisms and the mechanical properties of the biomedical Ī²-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 Ļiso phase was determined by means of synchrotron XRD and the fraction and the crystallite size of Ļiso increased progressively with increasing aging time. Due to the high intrinsic Young's modulus of the Ļiso 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 Ī²-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 Ļiso, 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.
- ItemEffect of minor gallium addition on corrosion, passivity, and antibacterial behaviour of novel Ī²-type TiāNb alloys(Sao Paulo : ABM, 2023) Akman, Adnan; Alberta, Ludovico Andrea; Giraldo-Osorno, Paula Milena; Turner, Adam Benedict; Hantusch, Martin; Palmquist, Anders; Trobos, Margarita; Calin, Mariana; Gebert, AnnettMetastable TiāNb alloys are promising bone-implant materials due to improved mechanical biofunctionality and biocompatibility. To overcome increasing bacterial infection risk, alloying with antibacterial elements is a promising strategy. This study investigates the effect of minor gallium (Ga) additions (4, 8 wt% Ga) to as-cast and solution-treated Ī²-type Tiā45Nb-based alloy (96(Tiā45Nb)-4Ga, 92(Tiā45Nb)-8Ga (wt.%)) on corrosion and passive film properties, as well as cytocompatibility and antibacterial activity. The electrochemical properties were evaluated by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and Mott-Schottky analyses in phosphate-buffered saline (PBS). X-ray photoelectron spectroscopy (XPS) was performed to analyze the chemical composition of passive films. Early adhesion and viability of macrophages and Staphylococcus aureus were assessed by nucleocounting and colony-forming unit counting, respectively. The results showed that high corrosion resistance and passive film properties of Tiā45Nb are retained and even slightly improved with Ga. EIS results revealed that Ga addition improves the passive film resistance. XPS measurements of 92(Tiā45Nb)-8Ga show that the passive film contains Ti-, Nb- and Ga-based oxides, implying the formation of mixed (TiāNb-Ga) oxides. In addition, marginal Ga ion release rate was detected under free corrosion conditions. Therefore, it can be assumed that Ga species may contribute to passive film formation on Ga-containing alloys. The 92(Tiā45Nb)-8Ga elicited an antibacterial effect against S. aureus compared to cp-Ti at 4 h. Moreover, Ga-containing alloys showed good cytocompatibility with THP-1 macrophages at 24 h. In conclusion, it was demonstrated that Ga additions to Tiā45Nb are beneficial to corrosion resistance and showed promising initial host and bacterial interactions.
- ItemDurability of TiAl based surface acoustic wave devices for sensing at intermediate high temperatures(Rio de Janeiro : Elsevier, 2023) Seifert, Marietta; Leszczynska, Barbara; Weser, Robert; Menzel, Siegfried; Gemming, Thomas; Schmidt, HagenTiAl based surface acoustic wave (SAW) devices, which offer a promising cheap and easy to handle wireless sensor solution for intermediate high temperatures up to 600 Ā°C, were prepared and investigated with respect to their durability. To obtain the devices, Ti/Al multilayers were deposited on high-temperature stable piezoelectric catangasite (CTGS) substrates and structured as electrodes via the lift-off technique. AlNO cover layers and barrier layers at the substrate site served as an oxidation protection. The devices were characterized regarding their electrical behavior by ex-situ measurements of their frequency characteristics after heat treatments up to 600 Ā°C in air. In addition, long-term in situ measurements up to 570 Ā°C were performed to analyze a possible drift of the resonant frequency in dependence on the temperature and time. Scanning electron microscopy of the surfaces of the devices and scanning transmission electron microscopy of cross sections of TiAl interdigital transducer electrode fingers and the contact pads were conducted to check the morphology of the electrode metallization and to reveal if degradation or oxidation processes occurred during the heat treatments. The results demonstrated a sufficient high-temperature stability of the TiAl based devices after a first conditioning of system. A linear dependence of the resonant frequency on the temperature of about ā37 ppm/K was observed. In summary, the suitability of TiAl based SAW sensors for long-term application at intermediate temperatures was proven.
- ItemDissipation losses limiting first-order phase transition materials in cryogenic caloric cooling: A case study on all-d-metal Ni(-Co)-Mn-Ti Heusler alloys(Amsterdam [u.a.] : Elsevier Science, 2023) Beckmann, Benedikt; Koch, David; Pfeuffer, Lukas; Gottschall, Tino; Taubel, Andreas; Adabifiroozjaei, Esmaeil; Miroshkina, Olga N.; Riegg, Stefan; Niehoff, Timo; Kani, Nagaarjhuna A.; Gruner, Markus E.; Molina-Luna, Leopoldo; Skokov, Konstantin P.; Gutfleisch, OliverNi-Mn-based Heusler alloys, in particular all-d-metal Ni(-Co)-Mn-Ti, are highly promising materials for energy-efficient solid-state refrigeration as large multicaloric effects can be achieved across their magnetostructural martensitic transformation. However, no comprehensive study on the crucially important transition entropy change Īst exists so far for Ni(-Co)-Mn-Ti. Here, we present a systematic study analyzing the composition and temperature dependence of Īst. Our results reveal a substantial structural entropy change contribution of approximately 65 J(kgK)-1, which is compensated at lower temperatures by an increasingly negative entropy change associated with the magnetic subsystem. This leads to compensation temperatures Tcomp of 75 K and 300 K in Ni35Co15Mn50-yTiy and Ni33Co17Mn50-yTiy, respectively, below which the martensitic transformations are arrested. In addition, we simultaneously measured the responses of the magnetic, structural and electronic subsystems to the temperature- and field-induced martensitic transformation near Tcomp, showing an abnormal increase of hysteresis and consequently dissipation energy at cryogenic temperatures. Simultaneous measurements of magnetization and adiabatic temperature change ĪTad in pulsed magnetic fields reveal a change in sign of ĪTad and a substantial positive and irreversible ĪTad up to 15 K at 15 K as a consequence of increased dissipation losses and decreased heat capacity. Most importantly, this phenomenon is universal, it applies to any first-order material with non-negligible hysteresis and any stimulus, effectively limiting the utilization of their caloric effects for gas liquefaction at cryogenic temperatures.
- ItemAnelastic-like nature of the rejuvenation of metallic glasses by cryogenic thermal cycling(Amsterdam [u.a.] : Elsevier Science, 2022) Costa, Miguel B.; LondoƱo, Juan J.; Blatter, Andreas; Hariharan, Avinash; Gebert, Annett; Carpenter, Michael A.; Greer, A. LindsayCryogenic thermal cycling (CTC) is an effective treatment for improving the room-temperature plasticity and toughness in metallic glasses. Despite considerable attention to characterizing the effects of CTC, they remain poorly understood. A prominent example is that, contrary to expectation, the stored energy in a metallic glass first rises, and then decreases, as CTC progresses. In this work, CTC is applied to bulk metallic glasses based on Pd, Pt, Ti, or Zr. The effects on calorimetric and mechanical properties are evaluated. Critically, CTC-induced effects, at whatever stage, are found to decay over about one week at room temperature after CTC, returning the properties to those of the as-cast glass. A model is proposed for CTC-induced effects, treating them as analogous to the accumulation of anelastic strain. The implications for analysis of existing data, and for future research on CTC effects, are highlighted.