Search Results

Now showing 1 - 3 of 3
  • Item
    On the process of co-deformation and phase dissolution in a hard-soft immiscible CuCo alloy system during high-pressure torsion deformation
    (Amsterdam : Elsevier, 2016) Bachmaier, Andrea; Schmauch, Jörg; Aboulfadl, Hisham; Verch, Andreas; Motz, Christian
    In this study, dual phase Cusingle bondCo composites with a total immiscibility in the solid state and a very different initial phase strength are deformed by severe plastic deformation. Nanocrystalline supersaturated solid solutions are reached in all Cusingle bondCo composites independent of the initial composition. The deformation and mechanical mixing process is studied thoroughly by combining scanning electron microscopy, transmission electron microscopy, three-dimensional atom probe tomography and nanoindentation. The indentation hardness of the Cu and Co phase and its evolution as a function of the applied strain is linked to deformation and mechanical mixing process to gain a better understanding how the phase strength mismatch of the Cu and Co phase effects the amount of co-deformation and deformation-induced mixing. Our results show that co-deformation is not a necessary requirement to achieve mechanical mixing.
  • Item
    Continuous wet chemical synthesis of Mo(C,N,O)x as anode materials for Li-ion batteries
    (London [u.a.] : RSC, 2023) Abdirahman Mohamed, Mana; Arnold, Stefanie; Janka, Oliver; Quade, Antje; Schmauch, Jörg; Presser, Volker; Kickelbick, Guido
    Molybdenum carbides, oxides, and mixed anionic carbide–nitride–oxides Mo(C,N,O)x are potential anode materials for lithium-ion batteries. Here we present the preparation of hybrid inorganic–organic precursors by a precipitation reaction of ammonium heptamolybdate ((NH4)6Mo7O24) with para-phenylenediamine in a continuous wet chemical process known as a microjet reactor. The mixing ratio of the two components has a crucial influence on the chemical composition of the obtained material. Pyrolysis of the precipitated precursor compounds preserved the size and morphology of the micro- to nanometer-sized starting materials. Changes in pyrolysis conditions such as temperature and time resulted in variations of the final compositions of the products, which consisted of mixtures of Mo(C,N,O)x, MoO2, Mo2C, Mo2N, and Mo. We optimized the reaction conditions to obtain carbide-rich phases. When evaluated as an anode material for application in lithium-ion battery half-cells, one of the optimized materials shows a remarkably high capacity of 933 mA h g−1 after 500 cycles. The maximum capacity is reached after an activation process caused by various conversion reactions with lithium.
  • Item
    High strength nanocrystalline Cu–Co alloys with high tensile ductility
    (Cambridge : Cambridge University Press, 2018) Bachmaier, Andrea; Rathmayr, Georg Benedikt; Schmauch, Jörg; Schell, Norbert; Stark, Andreas; de Jonge, Niels; Pippan, Reinhard
    A supersaturated single-phase Cu–26 at.% Co alloy was produced by high-pressure torsion deformation, leading to a nanocrystalline microstructure with a grain size smaller than 100 nm. The nonequilibrium solid solution decomposed during subsequent isothermal annealing. In situ high-energy X-ray diffraction was used to map changes linked to the separating phases, and the development of a nanoscale Cu–Co composite structure was observed. To gain further information about the relationship of the microstructure and the mechanical properties after phase separation, uniaxial tensile tests were conducted on as-deformed and isothermally annealed samples. Based on the in situ diffraction data, different isothermal annealing temperatures were chosen. Miniaturized tensile specimens with a round cross section were tested, and an image-based data evaluation method enabled the evaluation of true stress–strain curves and strain hardening behavior. The main results are as follows: all microstructural states showed high strength and ductility, which was achieved by a combination of strain-hardening and strain-rate hardening.