Study of effect of temperature on structure and phase composition of yb2si2o7 coatings applied by atmospheric plasma spraying on kh20n80 alloy and sitall substrates

The phase composition and structure of Yb2Si2O7 coatings deposited by atmospheric plasma spraying on substrates of Kh20N80 alloy and sitall ST-32-11 have been studied, using high-temperature X-ray diffraction at 200-1000 °C. It was found that in the temperature range of 200-900 °C, coatings of identical phase composition are formed on both substrates, represented by amorphous and crystalline phases of Yb2Si2O7, with a monoclinic lattice, and the proportion of the amorphous phase is 53% for the coating on Kh20N80 and 69% for the coating on sitall. In the same temperature range, the coefficient of linear thermal expansion (CLTE) in different directions of the Yb2Si2O7 crystal lattice significantly exceeds the CLTE of the bulk material, which is due to tensile stresses from substrates with higher CLTE values. In the temperature range of 900-1000 °C, complete crystallization of the amorphous phase and the formation of a single-phase coating structure were noted. When heated to 1000 °C, the coating separated from the Kh20N80 alloy substrate, which was accompanied by a sharp decrease in all three lattice periods of the monoclinic phase to values characteristic of purely thermal expansion of Yb2Si2O7, which made it possible to determine the CLTE values of the coating: αa = 4.5∙10-6, αb = 2.5∙10-6 and αс = 2.6∙10-6 K-1.