Microstructural and columnar growth characteristics of 7YSZ thermal barrier coatings fabricated by plasma spray physical vapor deposition

Thermal barrier coating (TBC) applications of 7 wt% yttria stabilized zirconia (7YSZ) must meet low thermal conductivity and excellent high temperature stability. However, the resulting morphology of 7YSZ TBCs fabricated by PS-PVD currently remains poorly studied. The present study addresses this issue by evaluating the microstructure, phase composition, grain distribution, and columnar crystal orientations of 7YSZ coatings fabricated by PS-PVD. The results demonstrate that the growth of YSZ columnar crystals exhibits an obvious preferred orientation [101] that is consistent throughout the entire coating cross-sectional area. The contents of tetragonal phase in the coating is 65.8 %, and the phase has a strongly preferred growth tendency toward 001 . The nano-indentation test shows that the microhardness of the coating increases gradually from bottom to top. In addition, the observed characteristics of 7YSZ particle are evaluated based on the results of numerical simulations of the temperature, velocity, and pressure fields in the plasma jet.