Speaker
Description
Thermal oxidation is a method of surface treatment to improve the wear characteristics of titanium alloys, a material group frequently exposed to wear, e.g. in orthopedic implants or engine valves. Different process designs of thermal oxidation have been shown in the past. Single-step oxidation at elevated temperature in an oxidizing environment, such as air, leads to a protective TiO2 layer with only poor adherence. Such a TiO2 layer can be removed in a subsequent second heat treatment step in vacuum, during which oxygen from the TiO2 layer diffuses into the substrate. This leads to a surface near oxygen diffusion zone with an increased hardness compared to the substrate. By adding a third step of thermal oxidation, e.g. in air, a surface consisting of a protective oxide layer on a pronounced oxygen diffusion hardened zone is obtained.
These three processes designs have been implemented and applied to Ti6Al4V at our institute. The resulting surface morphologies and elemental constitutions are described using scanning electron microscopy and a combination of qualitative energy-dispersive X-ray spectroscopy and X-ray diffraction analysis. Microhardness-depth profiles and oxygen concentration-depth profiles, derived from glow discharge optical emission spectroscopy, are determined to investigate the extend of oxygen diffusion resulting from different thermal oxidation process designs.
In a next step, an attempt is made to transfer the process experience gained during thermal oxidation of Ti6Al4V to a new material system – the high entropy alloy TiZrNbHfTa. Since this high entropy alloy contains the elements Ti, Zr, and Hf, all showing distinctive oxygen solubility, it is an ideal candidate for thermal oxidation treatment.
| Speaker Country | Germany |
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