Hans Peter Karnthaler
University of Vienna
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Featured researches published by Hans Peter Karnthaler.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing | 2001
Bernhard Mingler; Hans Peter Karnthaler; M. Zehetbauer; Ruslan Z. Valiev
Abstract Polycrystalline samples of Cu 99.95% were deformed by equal channel angular (ECA) pressing by rotating the sample after each pass and by subsequent compression or combined compression torsion. The resulting microstructure was analysed by TEM methods. In case of pure ECA deformation the grain sizes remain unchanged with the number of passes; the misorientation of the grains increases and the distribution of grain sizes gets narrower. When applying additional deformations subsequent to ECA pressing both grain sizes and the number of adjacent grains with large misorientations increase. The changes in distribution of grain sizes depend on the mode of deformation following the ECA deformation.
Journal of The Electrochemical Society | 2010
Lidija D. Rafailović; Dragica M. Minić; Hans Peter Karnthaler; J. Wosik; T. Trišović; Gerhard E. Nauer
Ni–Co alloy deposits and their parent metals were formed on Cu substrates by electrolysis under different current densities applied in the galvanostatic regime. A quantitative scanning electron microscopy technique was employed to study the morphology and surface roughness of the obtained deposits. The structure of the deposits is governed by the nature of depositing ions and quantity of evolved hydrogen. The cauliflower morphology and the highest mean surface roughness values are the results of electrodeposition from the Ni containing bath. The structure of the Co deposits formed under the same conditions and determined by the formation of the hexagonal close-packed phase results in a more uniform grain size distribution and formation of smoother platelet deposits. The mean surface values of the parent metals are independent of the current density. The dendritic growth is a special case of a structure formed only in the Ni–Co alloy deposition at selected, high current densities of 220 and 400 mA cm �2 . The dendrites obtained at a higher current density of 400 mA cm �2 have shown more developed structures with smaller dendrites that
Materials Science Forum | 2006
E. Schafler; Anna Dubravina; Bernhard Mingler; Hans Peter Karnthaler; M. Zehetbauer
The evolution of strength characteristics and the microstructure of copper subjected to high pressure torsion (HPT) are studied under variation of strain and hydrostatic pressure. Measurements of Multiple X-ray Bragg Profile Analysis (MXPA) yield microstructural parameters like dislocation density and arrangement, as well as crystallite (domain) size and distribution, and long-range internal stresses. TEM investigations are carried out to analyse the structural elements and to compare them with the results of MXPA. The strength behaviour is studied by microhardness measurements. The investigations are performed within wide ranges of resolved shear strains = 1 to 400 and of applied pressures p = 0.8 to 8 GPa. The onset of the deformation stages IV and V is strongly affected by the hydrostatic pressure i.e. shifted to higher values of stress and strain with increasing pressure. The experimental results indicate the occurrence of recovery effects, which seem to be of static as well as of dynamic nature, and to be responsible for extended ductility in SPD materials.
Materials Science Forum | 2008
C. Rentenberger; Clemens Mangler; Stephan Scheriau; Reinhard Pippan; Hans Peter Karnthaler
Long-range ordered intermetallic alloys with L12 (Ni3Al, Cu3Au) and B2 (FeAl) structures were deformed by high-pressure torsion at room temperature up to high grades of deformation. Transmission electron microscopy shows that disordering caused by the deformation occurs on a very local scale within coarse grains along glide planes (Cu3Au, Ni3Al) and in the form of well defined local regions (Ni3Al, FeAl). The latter leads to a duplex structure consisting of an ordered coarse-grained structure and a disordered nanocrystalline structure. The different mechanisms that can lead to disordering during severe plastic deformation are discussed on the basis of the different ordering energies and on the basis of antiphase boundaries associated with gliding dislocations. The results indicate that in intermetallic alloys the formation of a nanocrystalline structure by severe plastic deformation is facilitated by the loss of order.
Materials Science Forum | 2006
Bernhard Mingler; V.V. Stolyarov; M. Zehetbauer; Wolfgang Lacom; Hans Peter Karnthaler
Conventional coarse grained (CG) commercial pure (CP) Ti Grade 2 was studied after cold rolling (CR) at room temperature, and after equal channel angular pressing (ECAP) at 450° C followed by CR, by transmission electron microscopy (TEM) methods. CR of the CG material leads to a microstructure showing initially twins with (0112) type and later subgrains separated by lowangle grain boundaries. CR carried out after ECAP yields the fragmentation of fine grains (300 – 800 nm) mostly bounded by high-angle boundaries into elongated subgrains (~ 100 nm). It was shown with in-situ annealing experiments in the TEM that this microstructure is thermally stable up to a temperature of 450° C. Tensile tests showed that the combination of ECAP with CR has the potential to produce at the same time high strength (941 MPa) and high ductility (16.7%).
Advanced Materials | 2015
Lidija D. Rafailović; C. Gammer; C. Rentenberger; T. Trišović; Christoph Kleber; Hans Peter Karnthaler
A novel synthesis strategy is presented for depositing metallic Ag at the anode during simultaneous electrochemical oxidation of Al. This unexpected result is achieved based on galvanic coupling. Metallic dendritic nanostructures well-anchored in a high surface area supporting matrix are envisioned to open up a new avenue of applications.
RSC Advances | 2016
Lidija D. Rafailović; C. Gammer; J. Srajer; T. Trišović; J. Rahel; Hans Peter Karnthaler
We present the application of newly developed Ag nanodendrites (Ag-ND) grown together with anodic aluminium oxide for surface-enhanced Raman scattering (SERS). The Ag-ND yield very pronounced SERS using a self-assembled monolayer (SAM). This is confirmed by simulations showing hot spots in the electromagnetic field at the surfaces of the Ag-ND. SERS measurements reusing Ag-ND demonstrate its long-term stability even after one year.
Materials Science Forum | 2008
D. Geist; C. Rentenberger; Hans Peter Karnthaler
The L12-structured intermetallic compound Zr3Al can be rendered amorphous easily by several techniques. In the present study the structural evolution during high pressure torsion (HPT) was investigated systematically by transmission electron microscopy (TEM) methods. Zr3Al samples were deformed at room temperature to different grades of deformation up to shear strains of 140 000%. TEM investigations revealed that the tendency to grain fragmentation, disordering and the formation of a nanocrystalline structure is weak compared to other L12 ordered alloys like Ni3Al. In addition, an amorphous phase has not been encountered. The present results differ strongly from previous ones obtained from ball-milled materials. Possible reasons for the different behavior are discussed on the basis of the temperature dependent dissociation scheme of the superlattice dislocations gliding in Zr3Al.
Acta Materialia | 2004
T. Waitz; Hans Peter Karnthaler
Materials Chemistry and Physics | 2010
Lidija D. Rafailović; Hans Peter Karnthaler; T. Trišović; Dragica M. Minić