Thermally sprayed ceramic coatings have a layered structure with a limited interface bonding. Substrate surface temperature prior to droplets impact during deposition significantly influences the microstructure and properties of the coatings. Through the controlling of substrate surface temperature, the lamellar interface bonding of the deposits could be possibly improved. Al 2 O 3 coatings were deposited by atmospheric plasma spraying at the surface temperatures of 100, 275, 375, 480, 530 and 660°C. The fractured cross-section morphology was characterized by scanning electron microscopy. X-ray diffraction was used to analyse the phase contents. Micro-hardness, Young’s modulus and thermal conductivity of the deposits were measured. It was observed that the interface area with columnar grain growth across splat-splat interfaces was increased with increasing deposition temperature. Consequently, micro-hardness, Young’s modulus and thermal conductivity were increased with the increase of deposition temperature. The improvement of properties suggest that the lamellar interface bonding in the deposits was improved as the substrate surface temperature is increased.

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 Y 2 O 3 -ZrO 2 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.

In this study, yttria-stabilized zirconia (YSZ) coatings were plasma sprayed on heated substrates at temperatures ranging from room temperature to 1100 °C. Lamellar mean bonding ratio was estimated from the ionic conductivity of the coatings and mechanical properties were measured by indentation testing. The bonding ratio, elastic modulus, and fracture toughness of the YSZ coatings were found to increase with substrate surface temperature. The results show that the mechanical properties of plasma sprayed ceramic coatings are determined by interlamellar bonding and that significant improvements can be achieved by controlling coating surface temperature.

Plasma-sprayed ceramic coatings exhibit a lamellar structure with a mean bonding ratio of less than 32%, which dominates coating properties and limits the performance that can be achieved. In this study, yttria-stabilized zirconia (YSZ) coatings were plasma sprayed at different deposition (substrate surface) temperatures up to a maximum of 1100 °C. The lamellar mean bonding ratio, estimated from the ionic conductivity of the YSZ coatings, was found to increase from 32% in room temperature deposits to more than 75% in the deposits prepared at 1100 °C. Evidence of this improvement is also observed in fractured deposit cross-sections. The results show that controlling deposition temperature is an effective way to optimize lamellar interface bonding and, as a result, coating properties.

During plasma spraying, high substrate temperature contributes to increase the interface temperature between flattening droplet and substrate and subsequently promotes the through-lamella grain growth in the coating. In this study, yttria stabilized zirconia (YSZ) coatings are prepared by atmospheric plasma spray (APS) on the stainless steel substrate preheated to different temperatures from room temperature to 1100°C. The microstructure of the coatings is characterized from polished and fractured cross sections by SEM. The ionic conductivities of the coatings are measured using both DC and AC methods, and the relationship between ionic conductivity and microstructure of coatings is examined. SEM observation shows that the coatings exhibit different microstructures with different substrate temperatures. With the increase of substrate temperature, the columnar grain growth continuously across lamellar interfaces is enhanced and subsequently the intersplat bonding ratio in the coating is increased. The ionic conductivity of YSZ coatings at the direction perpendicular to coating surface is significantly increased through the microstructure development by increasing deposition temperature.

Yttria stabilized zirconia (YSZ) splats were plasma sprayed on the YSZ substrate preheated to different temperature to examine the influence of the temperature of the underlying surface on which molten droplet impacts on deposition characteristics. The splat morphology and the bonding at the splat-substrate interfaces were examined by SEM. It was found that the crack density decreases rapidly with the increase of the temperature when the splat were formed on an YSZ substrate preheated to above 800°C. The nucleation of YSZ melt on the base of YSZ substrate grains takes place during solidification leading to the formation of the bonding between the splat and substrate when the temperature is increased to over 600°C. The substantial bonding was observed at the interface between YSZ splat and YSZ substrate as the temperature is increased to over 800°C. The results revealed that the temperature of the previous splat on which a molten droplet impacts significantly influence the formation of the interface bonding. In addition, the mechanism and condition for the bonding formation of a splat on a substrate with the identical compositions were discussed.