Microstructure and Phase Composition of Sputter-Deposited Zirconia-Yttria Films

Abstract

ABSTRACTThin ZrO2 -Y2 O3 coatings ranging in composition from 3 to 15 mole % Y2 O3 were produced by rf sputter deposition. This composition range spanned the region on the equilibrium ZrO2 -Y2O3 phase diagram corresponding to partially stabilized zirconia (a mixture of tetragonal ZrO2 and cubic solid solution). Microstructural characteristics and crystalline phase composition of as-deposited and heat treated films (1100°C and 1500°C) were determined by transmission electron microscopy (TEM) and by x-ray diffraction (XRD). Effects of substrate bias (0 ∼ 250 volts), which induced ion bombardment of the film during growth, were also studied. The as-deposited ZrO2-Y2O3 films were single phase over the composition range studied, and XRD data indicated considerable local atomic disorder in the lattice. Films produced at low bias contained intergranular voids, pronounced columnar growth, and porosity between columns. At high bias, the microstructure was denser, and films contained high compressive stress. After heat treatment, all deposits remained single phase, therefore a microstructure and precipitate distribution characteristic of toughened, partially stabilized zirconia appears to be difficult to achieve in vapor deposited zirconia coatings.