Phase and microstructure evolution in plasma sprayed Yb2Si2O7 coatings

TLDR: Yb2Si2O7 coatings were deposited on Si/SiC substrates by atmospheric plasma spray (APS) as discussed by the authors, and different power and plasma chemistries used in this work produced mainly amorphous crack-free coatings with compositions shifted to lower SiO2 content with higher power and H2 flow.

Abstract: Yb2Si2O7 coatings were deposited on Si/SiC substrates by atmospheric plasma spray (APS). The different power and plasma chemistries used in this work produced mainly amorphous crack-free coatings with compositions shifted to lower SiO2 content with higher power and H2 flow. Differences in microstructure and thermomechanical properties (crystallization behavior, thermal expansion coefficient and thermal conductivity) of as-deposited and thermally treated coatings were directly related to the evolution from amorphous to crystalline phases. A Yb2SiO5 metastable phase was identified after thermal treatments at temperatures ∼ 1000 °C that transformed to its stable isomorph at 1220 °C. This transformation, followed by the growth of the crystal cell volume, promoted the coating expansion and the “healing” of microcracks present in the amorphous as-sprayed coating.