Evolution of the Microstructure of Plasma-Sprayed Deposits During Heating
Gabrielle G. Long, Andrew J. Allen, J Ilavsky
The evolution of the void microstructure of yttria-stabilized zirconia [YSZ] plasma-sprayed deposits [PSD] was studied as a function of heating in air from room temperature to 1400 C, and during a constant temperature hold at 1100 C for 19 hours. The samples were studied using the terminal slope [Porod scattering] of small-angle neutron scattering [SANS], modified for the analysis of anisotropic structures. The experiment was done in-situ using a special furnace built for use on the small-angle scattering instrument. SANS Porod scattering can distinguish between the two major void systems - interlamellar poses and intralamellar cracks - that are present in the PSD microstructure. Thus, changes in the void surfaces of the cracks and the pores could be followed separately as a function of temperature. The surface area attributable to the interlamellar cracks significantly decreased at temperatures below 1000 C, whereas the surface area of the interlamellar pores only began to decrease at temperatures above 1000 C. This suggests that there are significant differences in the sintering of these two void systems, probably associated with differences in their sizes and shapes. The first noticeable changes in the void surfaces were observed at temperatures just above 600 C, which is a very low temperature for YSZ. During annealing at 1100 C for 19 hours, there was a decrease in the interlamellar surfaces of about 10%.