Speaker
Description
To improve the performance and efficiency of combustion engines, higher operating temperatures are required. Commonly used high temperature structural materials (e.g. Ni-base) reach their limitations beyond 1100 °C.
Refractory metals are promising substitutes due to their high melting point and their good mechanical properties at high temperatures. One major drawback of most of these metals is their low oxidation resistance, so further processing, such as coating or alloying, is necessary for their use as high-temperature materials. Among the class of refractory metals, Cr has an outstanding resistance in oxidizing and hot corrosion environments while Mo-Si-based or Nb-Si-based alloys exhibit outstanding mechanical properties.
Using in situ chemical vapor deposition (CVD), Cr-coatings with layer thicknesses below 10 m were successfully applied on the refractory bulk materials Mo, Nb, Ta and W. In addition, such coatings were manufactured on recently developed Mo-Si-Ti alloys (eutectic and eutectoid) [1]. Thermogravimetric analysis (TGA) was used during exposure for 100 h in synthetic air at three different temperatures (700 °C, 900 °C, 1300 °C) to record the oxidation kinetics. The applied layers, the formed intermetallic phases and the formed oxide scales were analyzed before and after exposure to the oxidizing atmospheres using optical microscopy, XRD, SEM, EDX and EPMA. The coated materials show an improved oxidation behavior due to the formation of a protective Cr2O3-scale. This results in a substantially decreased oxide growth rate in comparison to uncoated substrates.
[1] Schliephake, Daniel, et al. "Constitution, oxidation and creep of eutectic and eutectoid Mo-Si-Ti alloys." Intermetallics 104 (2019): 133-142.
| Speaker Country | Germany |
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