Oxidation and wear protection of pultruded C/C composites using atmospheric plasma-sprayed environmental barrier coatings

C/C composites exhibit a unique property profile, including high specific strength, flexural strength, excellent thermal shock resistance and low density. These properties make C/C an attractive material with great potential for high-temperature applications such as furnace technology. However, the low oxidation resistance of the material at high temperatures as well as its low wear resistance are critical factors that restrict its in-service lifetime and can lead to premature material failure.

This study investigates to what extent oxidation and wear resistance can be increased by the deposition of atmospheric plasma-sprayed coatings. Therefore, different coating systems are investigated, which consist of Mo or Si as intermediate coating and Al₂O₃, Al₂O₃-8%Cr₂O₃, Al₂O₃-40%TiO₂, an experimental (Al,Cr,Ti)₂O₃ solid solution or Yb₂Si₂O₇ as top coat. The wear resistance is determined by means of a ball-on-disc test, while the oxidation protection and damage mechanisms of the coating systems are evaluated by thermocyclic tests up to 1000 °C and rapid cooling in air. The microstructure of the coatings is analyzed using a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD).

The results show that atmospheric plasma-sprayed coatings, despite their typical microstructure, which is characterized by pores and microcracks, can significantly improve the oxidation resistance of the C/C composite by reducing the rate of degradation in an oxidative environment. In addition, the oxide ceramic coatings provide considerably higher wear resistance than the C/C composite.