M. Zehetbauer

University of Vienna, Wien, Vienna, Austria

Are you M. Zehetbauer?

Claim your profile

Publications (196)304.55 Total impact

  • Michael Zehetbauer · Florian Spieckermann

    No preview · Article · Nov 2015 · Polymer International
  • Peyman Rafiee · Golta Khatibi · Michael Zehetbauer

    No preview · Article · Oct 2015 · Microelectronics International
  • Peyman Rafiee · Golta Khatibi · Martin Lederer · Michael Zehetbauer · Rainer Pelzer

    No preview · Conference Paper · Oct 2015
  • F Failamani · A Grytsiv · G Giester · G Polt · P Heinrich · H Michor · E Bauer · M Zehetbauer · P Rogl
    [Show abstract] [Hide abstract]
    ABSTRACT: The novel compounds Ba5{V,Nb}12Sb19+x, initially found in diffusion zone experiments between Ba-filled skutterudite Ba0.3Co4Sb12 and group V transition metals (V,Nb,Ta), were synthesized via solid state reaction and were characterized by means of X-ray (single crystal and powder) diffraction, electron probe microanalysis (EPMA), and physical (transport and mechanical) properties measurements. Ba5V12Sb19.41 (a = 1.21230(1) nm, space group P4[combining overline]3m; RF(2) = 0.0189) and Ba5Nb12Sb19.14 (a = 1.24979(2) nm, space group P4[combining overline]3m; RF(2) = 0.0219) are the first representatives of the Ba5Ti12Sb19+x-type, however, in contrast to the aristotype, the structure of Ba5V12Sb19.41 shows additional atom disorder. Temperature dependent ADPs and specific heat of Ba5V12Sb19.41 confirmed the rattling behaviour of Ba1,2 and Sb7 atoms within the framework built by V and Sb atoms. Electrical resistivity of both compounds show an upturn at low temperature, and a change from p- to n-type conductivity above 300 K in Ba4.9Nb12Sb19.4. As expected from the complex crystal structure and the presence of defects and disorder, the thermal conductivity is suppressed and lattice thermal conductivity of ∼0.43 W m(-1) K(-1) is near values typical for amorphous systems. Vicker's hardness of (3.8 ± 0.1) GPa (vanadium compound) and (3.5 ± 0.2) GPa (niobium compound) are comparable to Sb-based filled skutterudites. However, the Young's moduli measured by nanoindentation for these compounds EI(Ba4.9V12Sb19.0) = (85 ± 2) GPa and EI(Ba4.9Nb12Sb19.4) = (79 ± 5) GPa are significantly smaller than those of skutterudites, which range from about 130 to 145 GPa.
    No preview · Article · Sep 2015 · Physical Chemistry Chemical Physics
  • [Show abstract] [Hide abstract]
    ABSTRACT: In-situ X-ray diffraction was applied to isotactic polypropylene with a high volume fraction of !-phase (!-iPP) while it has been compressed at temperatures below and above its glass transition temperature Tg. The diffraction patterns were evaluated by the Multi-reflection X-ray Profile Analysis (MXPA) method, revealing microstructural parameters such as the density of dislocations and the size of coherently scattering domains (CSD-size). A significant difference in the development of the dislocation density was found compared to compression at temperatures above Tg, pointing at a differ- ent plastic deformation mechanism at these temperatures. Based on the individual evolutions of the dislocation density and CSD-size observed as a function of compressive strain, suggestions for the deformation mechanisms occurring below and above Tg are made.
    No preview · Article · Aug 2015 · eXPRESS Polymer Letters
  • Source
    R.Z. Valiev · Y. Estrin · Z. Horita · T.G. Langdon · M.J. Zehetbauer · Y.T. Zhu
    [Show abstract] [Hide abstract]
    ABSTRACT: Bulk nanoSPD materials are materials with nanostructural features, such as nanograins, nanoclusters, or nanotwins, produced by severe plastic deformation (SPD) techniques. Such nanostructured materials are fully dense and contamination free and in many cases they have superior mechanical and functional properties. Here, we provide a critical overview of such materials, with a focus on the fundamentals for the observed extraordinary properties. We discuss the unique nanostructures that lead to the superior properties, the underlying deformation mechanisms, the critical issues that remain to be investigated, future research directions, and the application potential of such materials.
    Full-text · Article · Jul 2015 · Materials Research Letters
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this study nanoindentation creep experiments on polyethylene were carried out in order to investigate dislocation based plastic deformation mechanisms. Similarly to a recent paper published by Li and Ngan (Li J. Ngan A.H.W. Scr. Mater. 62(7) 488–91 (2010).), discrete deformation processes occur during nanoindentation creep tests which again seem to arise from the break-off of dislocation avalanches. That interpretation is supported from systematic studies of variations of the loading rate and of the applied load on the number and the height of bursts.
    No preview · Article · Jul 2015 · Polymer International
  • Source
    Andreas Grill · Jelena Horky · Ajit Panigrahi · Gerhard Krexner · Michael Zehetbauer

    Full-text · Dataset · Jun 2015
  • Source
    Andreas Grill · Jelena Horky · Ajit Panigrahi · Gerhard Krexner · Michael Zehetbauer

    Full-text · Dataset · Jun 2015
  • Source
    Andreas Grill · Jelena Horky · Ajit Panigrahi · Gerhard Krexner · Michael Zehetbauer

    Full-text · Dataset · Jun 2015
  • Source
    Andreas Grill · Jelena Horky · Ajit Panigrahi · Gerhard Krexner · Michael Zehetbauer

    Full-text · Dataset · Jun 2015
  • Source
    Andreas Grill · Jelena Horky · Ajit Panigrahi · Gerhard Krexner · Michael Zehetbauer

    Full-text · Dataset · Jun 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: In ultrafine and/or nanograined materials, precipitation phenomena are significantly affected by the high surface area of grain boundaries. Therefore, this work tried to evaluate the influence of grain boundaries on precipitation processes in detail. Samples of 7475 aluminium alloy were solution annealed, water quenched and processed at RT by hydrostatic extrusion (HE) and high pressure torsion (HPT). While both processing procedures yield significant reductions in grain size there are differences in the resulting grain shape (fibre-like for HE, pancake-like for HPT) and in the grain boundary type. Extensive grain boundary precipitation occurs in both samples, albeit more pronounced and faster in HPT ones, which can be attributed to the different characters of grain boundaries involved. Inside the grains, precipitates are significantly smaller than in micrograined materials, which has been discussed in terms of HE / HPT induced vacancy concentrations in micro- and nanostructured samples.
    No preview · Conference Paper · Jun 2015
  • Source
    G. Rogl · A. Grytsiv · P. Heinrich · E. Bauer · P. Kumar · N. Peranio · O. Eibl · J. Horky · M. Zehetbauer · P. Rogl
    [Show abstract] [Hide abstract]
    ABSTRACT: The best p-type skutterudites so far are didymium filled, Fe/Co substituted, Sb-based skutterudites. Substitution at the Sb-sites influences the electronic structure, deforms the Sb-4-rings, enhances the scattering of phonons on electrons and impurities and in this way reduces the lattice thermal conductivity. In this paper we study structural and transport properties of p-type skutterudites with the nominal composition DD0.7Fe2.7Co1.3Sb11.7{Ge/Sn}(0.3), which were prepared by a rather fast reaction annealing melting technique. The Ge-doped sample showed impurities, which did not anneal out completely and even with ZT > 1 the result was not satisfying. However, the single-phase Sn-doped sample, DD0.7Fe2.3Co1.3Sb11.8Sn0.2, showed a lower thermal and lattice thermal conductivity than the undoped skutterudite leading to a higher ZT = 1.3, hitherto the highest ZT for a p-type skutterudite. Annealing at 570 K for 3 days proved the stability of the microstructure. After severe plastic deformation (SPD), due to additionally introduced defects, an enhancement of the electrical resistivity was compensated by a significantly lower thermal conductivity and the net effect led to a record high figure of merit: ZT = 1.45 at 850 K for DD0.7Fe2.7CO1.3Sb11.8Sn0.2.
    Full-text · Article · Jun 2015 · Acta Materialia
  • Source
    A. Panigrahi · M. Bönisch · T. Waitz · M. Calin · W. Skrotzki · J. Eckert · M.J. Zehetbauer
    [Show abstract] [Hide abstract]
    ABSTRACT: Biocompatible Ti–Nb-based alloys are potential materials for orthopedic implants. In particular, implants made of Ti–Nb alloys with a cubic β- or orthorhombic α”-phase show a low Young´s modulus that can prevent adverse stress shielding effects on bone. In the present work, phase transformations of a Ti–16.1 wt.% Nb alloy induced by high pressure torsion (HPT) and subsequent annealing were systematically studied by X-ray diffraction using synchrotron radiation. Upon HPT, the parent α” martensite transforms into a bulk nanocrystalline ω-phase. The formation of the ω-phase is triggered by pressure and strain. In-situ heating synchrotron experiments show a decomposition of the ω-phase into the hexagonal α and the cubic β equilibrium phases that starts at a temperature of about 300°C. Upon heating, the phase fraction of β increases in agreement with the phase diagram. However, most of the ω-phase is consumed by α-phase. Before the ω-phase vanishes at a temperature of about 460ºC, a strong increase of the phase fraction of α with temperature is observed till, at a temperature of about 500°C, it starts to decrease as expected from the phase diagram. An ultrafine grained structure is observed even upon heating to a temperature of 500°C. Therefore, HPT followed by annealing provides a new processing route via an intermediated nanocrystalline ω-phase for the production of bulk Ti-Nb alloys with an ultrafine grained and equiaxed α+β phase structure.
    Full-text · Conference Paper · Jun 2015
  • Andreas Grill · Jelena Horky · Ajit Panigrahi · Gerhard Krexner · Michael Zehetbauer
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract This paper reports long-term hydrogen storage experiments on MgH2 and on the Mg alloy ZK60 following prior Severe Plastic Deformation (SPD). Although SPD processing leads to significant enhancements of hydrogen absorption and desorption rates in both materials, these are not necessarily stable with respect to repeated loading/unloading cycles. Cold rolled (CR) MgH2 shows a reduction of capacity by 30% after 100 cycles. In contrast, in ZK60 (Mg-5Zn-0.8Zr) processed by High Pressure Torsion (HPT), both kinetics and storage capacity are stable for at least 200 absorption/desorption cycles. Analysis by means of Johnson-Mehl-Avrami theory clearly suggests that in the case of CR MgH2 nucleation is followed by growth of extended MgH2 domains leading to a gradual deterioration of hydrogen diffusion and storage/release characteristics. In the case of HPT ZK60, however, no further growth occurs subsequent to nucleation thus allowing for permanently enhanced hydrogen diffusion and stable storage/release properties. These results can be understood in terms of the different density and stability of SPD-induced lattice defects acting as nucleation sites in both materials studied.
    No preview · Article · Jun 2015 · International Journal of Hydrogen Energy
  • C Tränkner · R Chulist · W Skrotzki · T Lippmann · J Horky · M Zehetbauer
    [Show abstract] [Hide abstract]
    ABSTRACT: NiAl is an intermetallic compound with a brittle-to-ductile transition temperature of about 300°C at ambient pressure. At standard conditions, it is very difficult to deform, but fracture stress and fracture strain are increased under hydrostatic pressure (HP). On account of this, deformation at low temperatures is only possible at high HP, as for instance used in high pressure torsion (HPT). In order to study the influence of HP on texture evolution, small discs of polycrystalline NiAl were deformed by HPT at different temperatures ranging from room temperature to 500°C and different HPs. The influence of HP is presented for deformation at room temperature and 500°C. It is found that HP affects the formability of the samples as well as texture and microstructure.
    No preview · Article · Apr 2015 · IOP Conference Series Materials Science and Engineering
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Abstract A coarse grained biocompatible Ti–16.1Nb (wt.%) alloy was used to study the impact of severe plastic deformation on microstructural changes, phase transformations, and mechanical properties. The starting material, showing a rather low value of Young’s modulus (66 GPa), contained orthorhombic α” martensite. Hydrostatic pressure of 4 GPa solely yields a partial transformation to the ω-phase; increasing the pressure to 8 GPa increases the volume fraction of the ω-phase and causes a concomitant increase of Young’s modulus. By processing samples through high pressure torsion at room temperature, i.e. applying both hydrostatic pressure and shear deformation, a nanocrystalline structure was obtained. The samples almost exclusively contained the ω-phase and showed rather high values of Young’s modulus (up to 130 GPa) and hardness (up to 4.0 GPa). The ω-phase formed during high pressure torsion revealed stability upon unloading. However, upon heating to about 500°C the ω-phase decomposes into a phase mixture of hexagonal α and body centred cubic β phases which is still ultra-fine. Cold rolling and folding achieves a microstructure consisting of ω, α/α’ and α” phases. Concomitant decrease of grain size and increase of defect density yield a hardness (3.3 GPa) which is smaller than that of high pressure torsion but a Young’s modulus of about 100 GPa being closer to that of the initial material.
    Full-text · Article · Apr 2015 · Journal of Alloys and Compounds
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bulk nanostructured Cu was prepared by in-situ consolidation through room temperature ball milling. The consolidated parts consist of hollow spheres having a diameter which increases with increasing the milling time. Microhardness maps reveal that the distribution of the hardness is relatively homogeneous after 2 h of milling. After 34 h the hardness is higher at the outer edge and decreases toward the inner edge and, finally, after 70 h the distribution is uniform again. Electron microscopic results show that the microstructure after 70 h of milling consists of two types of grains: elongated ultrafine grains with high density of defects and equiaxed nanosized grains produced by dynamic recrystallization. Continuous dynamic recrystallization is the dominant mechanism for the formation of the nanosized grains. Evidence for the occurrence of discontinuous dynamic recrystallization through twinning was also found in a few regions of the in-situ consolidated samples.
    No preview · Article · Jan 2015 · Materials and Design
  • Peyman Rafiee · Golta Khatibi · Michael Zehetbauer

    No preview · Article · Jan 2015 · Microelectronics International

Publication Stats

3k Citations
304.55 Total Impact Points

Institutions

  • 1980-2015
    • University of Vienna
      • • Fakultät für Physik
      • • Physics of Nanostructured Materials Group
      • • Institut für Physikalische Chemie
      Wien, Vienna, Austria
  • 1994
    • Masaryk University
      Brünn, South Moravian, Czech Republic
  • 1991
    • Technische Universität Braunschweig
      • Institut für Werkstoffe
      Braunschweig, Lower Saxony, Germany