Microstructure and high-temperature sintering properties of APS coatings prepared from spherical thin-walled hollow-shell powders

Abstract

High-performance thermal barrier coatings (TBCs) made of 4 mol.% Y2O3–stabilized ZrO2 (4YSZ) powder with a spherical thin-walled hollow-shell (STHS) structure exhibited a special microstructure different from the conventional lamellar structure of air plasma-sprayed (APS) coatings. The as-sprayed STHS APS coatings had a completely tetragonal prime (t′) structure and non-lamellated closed-cell structure with high porosity, which resulted in relatively low thermal conductivity (∼1.0 W m−1 K−1) and high Vicker's hardness (∼6 GPa). The influences of high-temperature aging on the microstructure stability, phase stability, and sintering capability were investigated after long-time heat treatment at different temperatures. The characterization results indicated that the pore content was basically constant, and it was less than 0.5% for sintered linear shrinkage of the STHS coatings after heat treatment at 1500 °C for 100 h. Furthermore, no spalling appeared in the STHS APS coating with the t′ phase structure after 101 thermal cycles of the water-quenching method at 1050 °C, and no monoclinic ZrO2 (m-ZrO2) phase was present in all of the STHS coatings after aging at 1200 °C for 1–1100 h. The excellent anti-sintering properties and phase stability of the STHS coatings are attributed to the closed-pore microstructure and the highly pure t′ phase composition with uniform distribution of ions, respectively. The results suggested that the non-lamellated closed-cell microstructure is beneficial for improving the coating properties, and the results also provide guidelines for microstructure design of TBCs using a feedstock powder.