Dr. Valentin Dalbauer

Wissenschaftlicher Mitarbeiter


Zeitschriftenartikel
  • C. Koller
  • Valentin Dalbauer
  • S. Kolozsvári
  • J. Ramm
  • P. Mayrhofer
Microstructure and phase evolution of gradually-structured arc evaporated Al0.25Cr0.75-based oxide coatings, vol. 155, pg. 645-649.

In: Vacuum

  • 2018

DOI: 10.1016/j.vacuum.2018.07.003

The structural evolution from the (inter)metallic to the oxide-stoichiometric regime within oxygen-gradient Al0.25Cr0.75-based coatings was investigated by transmission electron microscopy (TEM). Grain refinement of the (inter)metallic Cr(Al) structure — induced by the addition of oxygen to the growth process — is less significant than for the higher Al-containing Al0.50Cr0.50-based coatings. Our detailed TEM studies clearly show that between 110 and 120 sccm O2 per active Al0.25Cr0.75-source (corresponding to 0.7–0.9 Pa), the coating structure changes from partially oxidised — where (inter)metallic Cr(Al) particles are encapsulated by amorphous-like Al-rich oxides — to a columnar, corundum-type sesquioxide structure. Contrary to the higher Al-containing Al0.50Cr0.50-based coatings, this transformation takes place without the formation of metastable cubic (Al1-xCrx)2O3 structures.
  • TC Hutthurm
  • NACHHALTIG
Zeitschriftenartikel
  • Valentin Dalbauer
  • J. Ramm
  • S. Kolozsvári
  • V. Paneta
  • C. Koller
  • P. Mayrhofer
On the phase formation of cathodic arc evaporated Al1−xCrx-based intermetallic coatings and substoichiometric oxides, vol. 352, pg. 392-398.

In: Surface & Coatings Technology

  • 2018

DOI: 10.1016/j.surfcoat.2018.08.038

The phase evolution of Al1−xCrx-based intermetallic coatings and corresponding substoichiometric oxides grown by cathodic arc evaporation was investigated in order to obtain a better understanding of the relation between oxygen flow rate, Al and Cr content, and structural evolution of the coatings deposited. When using 20 sccm Ar, or 50 sccm O2, or 100 sccm O2 per active source (p.a.s.) the cathode reaction zone consists of various intermetallic Al-Cr-compounds, which are in good agreement with the binary Al-Cr phase diagram. This is generally also reflected in the phase composition of the metallic and substoichiometric oxide coatings. The Al-rich compositions, Al0.75Cr0.25 and Al0.70Cr0.30, show a strong tendency for the formation of γ1-Al8Cr5 phases. Mostly, the coating compositions of the metallic constituents of the synthesised intermetallic and substoichiometric oxide coatings deviate from the elemental compositions of the cathode, show enrichment in Cr. This deviation is more pronounced for Cr-rich cathodes using low O2 flow rates during deposition. The dense columnar structure of the intermetallic coatings (hardness values between 2.5 and 10.2 GPa) turns into a nano-composite-like morphology for depositions with 50 and 100 sccm O2 p.a.s., which in turn leads to a significant hardness increase up to ~24 GPa. Among all coatings investigated, the Cr-rich compositions have higher hardness and denser morphology than the Al-rich layers.
  • TC Hutthurm
  • NACHHALTIG
Zeitschriftenartikel
  • C. Koller
  • Valentin Dalbauer
  • A. Schmelz
  • R. Raab
  • P. Polcik
  • J. Ramm
  • P. Mayrhofer
Structure, mechanical properties, and thermal stability of arc evaporated (Al1-xCrx)2O3 coatings, vol. 342, pg. 37-47.

In: Surface & Coatings Technology

  • 2018

DOI: 10.1016/j.surfcoat.2018.02.077

Cathodic arc evaporated (Al1-xCrx)2O3 coatings, prepared from powder-metallurgically produced Al0.75Cr0.25, Al0.70Cr0.30, Al0.50Cr0.50, and Al0.25Cr0.75 cathodes using an industrial-type batch facility were investigated with respect to their microstructure, mechanical properties, and structural evolution upon annealing in vacuum and oxidising atmosphere. Both Al-rich coatings crystallise in a mixed microstructure consisting of a corundum-type solid solution and fine-crystalline metastable cubic phase fractions. The latter irreversibly phase transform into α-(Al1-xCrx)2O3 between 800 and 1050 °C, which either proceeds via a γ- or θ-structured intermediate stage depending on the annealing environment (i.e., vacuum or flowing O2). Both Cr-rich coatings initially crystallise in a corundum-type solid solution, and are therefore not affected from any phase transition upon annealing to at least 1500 °C. Hardness and indentation moduli of our coatings are, next to the phase composition, strongly related to the microstructure but also the substrate material used, showing a relatively large spread from 11 to 23 GPa for H and 190 to 375 GPa for E, respectively.
  • TC Hutthurm
  • NACHHALTIG
Zeitschriftenartikel
  • C. Koller
  • Valentin Dalbauer
  • A. Kirnbauer
  • M. Sauer
  • S. Kolozsvári
  • J. Ramm
  • P. Mayrhofer
Impact of Si and B on the phase stability of cathodic arc evaporated Al0.70Cr0.30-based oxides, vol. 152, pg. 107-111.

In: Scripta Materialia

  • 2018

DOI: 10.1016/j.scriptamat.2018.04.018

Al0.70Cr0.30-, Al0.665Cr0.285B0.05-, and Al0.665Cr0.285Si0.05-based cathodic arc evaporated oxides were investigated with respect to their structural evolution during vacuum annealing. Unalloyed (Al0.69Cr0.31)2O3 crystallises with a mixed phase microstructure composed of corundum (α) and metastable cubic and γ-/θ-type phases. Alloying 5 at.% of B or Si to the cathodes results in significant grain refinement of the coatings and the suppression of the α-phase in as-deposited state. In addition, the thermally-induced phase transition from metastable into singe-phased α-structured coatings is effectively shifted from ~900 °C to 950 °C or 1150 °C, respectively.
  • TC Hutthurm
  • NACHHALTIG