Low thermal conductivity vapor deposited zirconia microstructures

Low thermal conductivity yttria stabilized zirconia (YSZ) coatings have bee n grown using a low-vacuum (0.20 Torr) electron beam directed vapor deposit ion process. In this approach, a transsonic helium jet was used to entrain and transport an evaporated YSZ flux to a substrate. The interaction of the helium jet with the coating surface resulted in many of the evaporated spe cies making oblique angles of contact with the substrate. This resulted in the formation of a highly porous, columnar microstructure without substrate rotation. When the substrate was positioned perpendicular to the axis of t he jet, coatings with intercolumnar pores normal to the substrate surface w ere formed. The ambient temperature thermal conductivity of a coating grown in this arrangement was 1.9 Wm/K, comparable to that of conventinal, high- vacuum electron beam coatings. When the column and pore orientation was inc lined (by tilting the substrate) the thermal conductivity was observed to f all. By alternating the inclination angle as growth progressed, coatings co ntaining zig-zag columns and pores could be synthesized. Using this techniq ue, YSZ coatings with thermal conductivities as low as 0.8 W/m K were obtai ned. The observed thermal conductivity reduction arises from the longer the rmal diffusion path of the zig-zag pore micro-structures. (C) 2001 Acta Mat erialia Inc. Published by Elsevier Science Ltd. All rights reserved.