Divize progresívních kovových materiálů

Browse

Recent Submissions

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Ab initio study of properties of Co- and Cu- doped Ni-Mn-Ga alloys
    (Elsevier Ltd., 2015-11-06) Zelený, Martin; Sozinov, Alexei; Björkman, Torbjörn; Straka, Ladislav; Nieminen, Risto M.
    The influence of Co and Cu doping on Ni-Mn-Ga alloy is investigated using the first-principles exact muffin-tin orbital method in combination with the coherent-potential approximation. The energy difference between the austenite (A) and the nonmodulated (NM) martensite E_A-NM depends linearly on the Cu concentration and distribution, with a minimum for all Cu at Mn sites and a maximum for all Cu at Ga sites. For alloys simultaneously doped by Co in Ni sublattice and Cu in Mn or Ga sublattice, the effects of the individual dopants on E_A-NM and (c/a)_NM and are almost independent. The alloy with composition Ni46Co4Mn24Ga22Cu4 exhibits decreased equilibrium (c/a)_NM and increased E_A-NM in comparison with Ni50Mn25Ga25, which is in agreement with the previous experimental results.
  • Thumbnail Image
    Item
    Ab initio study of Ni2MnGa under shear deformation
    (EDP Sciences, 2015-12-07) Zelený, Martin; Straka, Ladislav; Sozinov, Alexei
    The effect of shear deformation on Ni2MnGa magnetic shape memory alloy has been investigated using ab initio electronic structure calculations. We used the projector-augmented wave method for the calculations of total energies and stresses as functions of applied affine shear deformation. The studied nonmodulated martensite (NM) phase exhibits a tetragonally distorted L21 structure with c/a > 1. A large strain corresponding to simple shears in <100>{001}, <001>{100} and <010>{100} systems was applied to describe a full path between two equivalent NM lattices. We also studied <10-1>{101} shear which is related to twining of NM phase. Twin reorientation in this system is possible, because applied positive shear results in path with significantly smaller energetic barrier than for negative shear and for shears in other studied systems. When the full relaxation of lattice parameters is allowed, the barriers further strongly decrease and the structures along the twinning path can be considered as orthorhombic.
  • Thumbnail Image
    Item
    Preparation and Characterization of Zinc Materials Prepared by Powder Metallurgy
    (MDPI, 2017-09-27) Krystýnová, Michaela; Doležal, Pavel; Fintová, Stanislava; Březina, Matěj; Zapletal, Josef; Wasserbauer, Jaromír
    The use of zinc-based materials as biodegradable materials for medical purposes is offered as a possible alternative to corrosion-less resistant magnesium-based materials. Zinc powders with two different particle sizes (7.5 µm and 150 µm) were processed by the methods of powder metallurgy: cold pressing, cold pressing followed by sintering and hot pressing. The microstructure of prepared materials was evaluated in terms of light optical microscopy, and the mechanical properties were analyzed with Vickers microhardness testing and three-point bend testing. Fractographic analysis of broken samples was performed with scanning electron microscopy. Particle size was shown to have a significant effect on compacts mechanical properties. The deformability of 7.5 µm particle size powder was improved by increased temperature during the processing, while in the case of larger powder, no significant influence of temperature was observed. Bending properties of prepared materials were positively influenced by elevated temperature during processing and correspond to the increasing compacting pressures. Better properties were achieved for pure zinc prepared from 150-µm particle size powder compared to materials prepared from 7.5 µm particle size powder.