Abstract
Functionally graded metal/ceramic coatings with thicknesses varying from 0.75mm to 2.1mm were designed and deposited onto a steel substrate by plasma spraying. The heat insulation performance of these coatings were studied. It was found that, at a given heat flux, the thicker specimens exhibited higher surface temperature (Ts), greater temperature difference (ΔT) and higher effective thermal conductivity (λeff). The thermal cycling test with a surface temperature of 1400°C (during heating) was also conducted for the study of fracture mode of the specimens. Furthermore, the fracture behavior of the coatings at high surface temperatures between 1500°C and 1700°C was investigated. The coating thickness and surface temperature were found to influence the number and the length of cracks. The results showed that thinner coatings were susceptible to local spallation at the top coat, and while, the thicker FGM coatings were susceptible to cracking at the interface close to the bond coat.
