Influence of Microstructure on Thermal Conductivity of Plasma-Sprayed YSZ Coating

Abstract

Thermal conductivity of plasma-sprayed YSZ thermal barrier coatings depends on microstructure and significantly influences the effectiveness of the thermal barrier. In this study, YSZ coatings are deposited by plasma spraying using fused and crushed Y2O3-ZrO2 powder. Coating microstructure was modified by substrate temperature, which was varied from room temperature to 880 °C during deposition. The coating microstructure was examined from the fractured cross-section of the deposits to reveal changes in interlamellar bonding due to substrate temperature. The thermal conductivities of the YSZ coating were tested by laser flashing from room temperature to 1300 °C. The results showed that the coating deposited at room temperature exhibited a typical lamellar structure and a thermal conductivity of 1.26 W·m-1·K-1 measured at room temperature. With the increase of substrate temperature, the thermal conductivity was increased. The coating deposited at a substrate temperature of 840-880 °C consisted of trans-lamellae long columnar grains and exhibited a value of 1.95 W·m-1·K-1 at room temperature. The influence of substrate temperature on thermal conductivity is discussed based on the changes in microstructure observed.

Formation of the Cast Iron Coatings Plasma-Sprayed at Different Substrate Temperatures

“…The horizontal cracks were mainly resulted from the nonbonded interfaces within the coatings. According to our previous works [6,12,13], high substrate temperature redounded to the formation of a strong interlamella bonding with chemical effect in ceramic coatings. Consequently, the number of the horizontal cracks decreased with the increase of the substrate temperature from 50 o C to 240 o C. Generally, it is suggested that the pores in the coatings are mainly derived from gas trapping during deposition of melting particles.…”