Effect of TiC addition and high-temperature annealing on the microstructure and electrical conductivity of shrouded-plasma-sprayed FeAl/TiC composites for SOFC support

FeAl and FeAl/TiC coatings are deposited by shrouded plasma spraying. The microstructure of the as-sprayed and annealed coatings is characterized by scanning electron microscopy. The electrical conductivity of the coatings along the direction parallel to the coating surface is measured. Results show that the as-sprayed coatings exhibit lower electrical conductivity than that of the corresponding bulks, which is due to their inherent lamellar microstructure. The thin interlamellar gaps become more spherical pores and the metallurgical bonding regions are increased by high-temperature annealing due to solid-state diffusion between flattened splats. The electrical conductivity of the coatings increases with the increase of the annealing time. The room temperature electrical conductivity of the coatings annealed at 1100 °C for over 10 h reaches to about 90% of that of the corresponding bulks. Besides, it is found that the electrical conductivity of the FeAl/TiC coatings increases with the increase of the TiC content. When 45 vol.% TiC is added into the FeAl matrix, the electrical conductivity of the FeAl/TiC coating annealed at 1100 °C reaches 5.35 × 10³ S cm^-1 at 1000 °C, which is much higher than that of the commonly used Ni/YSZ support material in solid oxide fuel cells.