Andreas Kolitsch

Copper and silver ion implantation of aluminium oxide-blasted titanium surfaces: proliferative response of osteoblasts and antibacterial effects.

Implant infection still represents a major clinical problem in orthopedic surgery. We therefore tested the in vitro biocompatibility and antibacterial effects of copper (Cu)- and silver (Ag)-ion implantation. Discs of a commonly used titanium alloy (Ti6AlV4) with an aluminium oxide-blasted surface were treated by Cu- or Ag-ion implantation with different dosage regimen (ranging from 1e15–17 ions cm−2 at energies of 2–20 keV). The samples were seeded with primary human osteoblasts and cell attachment and proliferation was analyzed by an MTT-assay. In comparison to the reference titanium alloy there was no difference in the number of attached viable cells after two days. After seven days the number of viable cells was increased for Cu with 1e17 ions cm−2 at 2 and 5 keV, and for Ag with 1e16 ions cm−2 at 5 keV while it was reduced for the highest amount of Ag deposition (1e17 ions cm−2 at 20 keV). Antibacterial effects on S.aureus and E.coli were marginal for the studied dosages of Cu but clearly present for Ag with 1e16 ions cm−2 at 2 and 5 keV and 1e17 ions cm−2 at 20 keV. These results indicate that Ag-ion implantation may be a promising methodological approach for antibacterial functionalization of titanium implants.

Stress measurement and stress relaxation during magnetron sputter deposition of cubic boron nitride thin films

Abstract Dynamic in situ analysis of stress and film thickness provide fast and more physical information on growth and stress evolution in cBN layers than integrating (ex situ) methods. Especially, features of the layered structure of boron nitride films, like the evolution of instantaneous stress and growth rates during deposition can be resolved by in situ methods. This work is concerned with dynamic in-situ stress measurement by means of cantilever bending during magnetron sputter deposition of cBN thin films. Laser deflection in combination with in situ ellipsometry is used to determine the instantaneous stress of the films. The results show in agreement with results that were obtained previously from ion beam assisted deposition (IBAD), that the hBN and cBN layers exhibit different levels of stress under constant deposition conditions. The stress increases from less than −4 GPa to very high values (−10 GPa) after the coalescence of the cBN nuclei. Therefore, it is possible to establish the point of cBN nucleation instantly. A simultaneous medium energy ion bombardment is used for stress relaxation during film deposition. A modified substrate bias voltage, combining negative high and low voltage pulses, is used to enable an ion bombardment of the growing film with energies up to 8 keV. In this way, cBN films with a stress as low as −1.7 GPa could be produced without destroying the sp 3 -bonds significantly.

Comparison of fluorination treatments to improve the high temperature oxidation resistance of TiAl alloys in SO2 containing environments

Surfaces of titanium aluminides were treated by fluorine either physically using Plasma Immersion Ion Implantation (PI³) or chemically with a F-based polymer. By controlling the fluorination parameters, both treatments improve the oxidation resistance even in the presence of sulfur dioxide (0.1 vol%). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen in the alloy was found to be reduced in the presence of SO2.

Optimization of the Fluorine Effect for Improving the Oxidation Resistance of Tial-Alloys

The oxidation resistance of TiAl-alloys can be improved drastically by treating the surface of the components with small amounts of fluorine. The oxidation mechanism is changed. Hence, the formation of a fast growing mixed oxide scale on untreated alloys is suppressed. Instead a thin protective alumina scale is formed on samples after fluorine treatment. The different methods only influence the surface region of the components so that the bulk properties are not affected. Recent results achieved with F-containing inorganic compounds showed that the fluorine effect can be improved even further. TiAl-specimens were treated only with fluorine and with F-containing compounds in several ways and their performance during high temperature oxidation tests in air was investigated. Results of isothermal and thermocyclic oxidation tests are presented. The results are discussed in terms of a later use of the fluorine effect for technical applications.

Economic Surface Treatment of Ti-Alloys to Improve their Resistance against Environmental High Temperature Attack

High temperature Ti-alloys are usually sophisticated and hence expensive. To allow the use of cheaper alloys at elevated temperatures an economic and easy to apply procedure was developed to improve their high temperature capability. The treatment consists of a combination of Al-enrichment in a shallow surface region plus additional fluorination. The Al-enrichment at elevated temperatures leads to the formation of intermetallic TiAl-phases. These phases improve the oxidation resistance of Ti-alloys but not to a sufficient extent. An additional fluorine treatment of the Al-enriched surface leads to the formation of a protective alumina scale due to the fluorine effect. In this paper results from high temperature exposure tests performed on different Ti-alloys without any treatment and with a combination of Al-treatment plus fluorination are presented. The results are discussed in the view of the use of the optimized Ti-components for several high temperature applications.

Improvement of the Resistance of Titanium Aluminides to Environmental Embrittlement

ATZ Entwicklungszentrum An der Maxhutte 1, D-92237 Sulzbach-Rosenberg 2 TU Wien, Institut fur Fertigungstechnik Karlsplatz 13/311, A1040 Wien Dechema Forschungsinstitut Theodor-Heuss-Allee 25, D-60486 Frankfurt/Main 4 Helmholtz-Zentrum Dresden-Rossendorf P.O. 510119, D-01314 Dresden 5 TU Belfort-Montbeliard, LERMPS F-90010 Belfort 6 Helmholtz-Zentrum-Geestacht Max-Planck-Strase 1, D-21502 Geesthacht 7 TU Freiberg, Institute of Materials Science Gustav-Zeuner-Str. 5, D-09599 Freiberg 8 Osterreichisches Gieserei-Institut (OGI) Parkstrasse 21, A-8700 Leoben