Session BB9.4

4:15 PM BB9.4
MICROSTRUCTURAL CHANGES IN PLASMA-SPRAYED DEPOSITS DURING ANNEALING. Jan Ilavsky*, Andrew J. Allen, Gabrielle G. Long, National Institute of Standards and Technology, Materials Science and Engineering Laboratory, Gaitherburg, MD, * Current address: Institute of Plasma Physics, Prague, CZECH REPUBLIC; Christopher C. Berndt, Herbert Herman, SUNY at Stony Brook, Dept. Materials Science and Engineering, Stony Brook, NY.

The anisotropic microstructure of plasma-sprayed yttria-stabilized-zirconia deposits was investigated as a function of temperature by means of small-angle neutron scattering (SANS). SANS Porod scattering measurements, as applied to anisotropic structures, can be used to determine the surface characteristics of the void systems. The experiments were performed in-situ in a ceramic furnace built for use on the SANS instrument. The evolution of the microstructure was followed (1) with the temperature increasing from 600$^{\circ}$C to 1400$^{\circ}$C at a heating rate of 50$^{\circ}$C per hour, and (2) at 1100$^{\circ}$C over the course of 23 hours. The microstructure of plasma-sprayed coatings is sufficiently anisotropic for the interlamellar pores and the intralamellar cracks to be characterized independently. During the furnace experiments, the specific surface areas of the interlamellar pores decreased at higher temperatures. The anisotropy of the microstructure increased below 1000$^{\circ}$C due to decreasing specific surface area of the intralamellar cracks. At 1100$^{\circ}$C the anisotropy decreased roughly exponentially with time. These results suggest that significant microstructural changes in ceramic deposits may occur at operating temperatures and that these are a complex function of temperature and time.