Wide-velocity range high-energy plasma sprayed yttria-stabilized zirconia thermal barrier coating - Part II: Structural defects and thermal-bonding properties

Traditional porous plasma-sprayed YSZ thermal barrier coatings (TBCs) present an inverse relationship between bonding strength and thermal insulation properties; achieving the synergistic improvement of both properties is a huge challenge for current plasma spraying methods. To address this challenge, in this work, we focus on regulating the structural defects of the TBCs by modifying the melting and in-flight behavior of plasma-spray particles. Dual-modal subsonic and novel multi-modal supersonic coatings were fabricated. The results suggested that the multi-modal structure of the supersonic coating with a defect content of approximately 13 % exhibited the highest tensile bonding strength (similar to 74 MPa) and the lowest thermal conductivity (0.75-0.80 W center dot m(-1)center dot K-1 from 200 degrees C to 1000 degrees C). The high bonding strength was attributed to the epitaxial growth and mechanical interlocking of submicron-/nano-grains, whereas the low thermal conductivity came from the coexistence of an overlapping distribution of submicron-sized splats, discontinuous interfaces, and high-density crystal defects. Due to the competitive sintering of finer unmelted particles and recrystallization zones, the supersonic coating exhibited superior thermal insulation. Therefore, supersonic coating is considered as good candidates for high-performance TBCs.