, Volume 5, Issue 4, pp 431-438

Influence of dopant on the thermal properties of two plasma-sprayed zirconia coatings Part I: Relationship between powder characteristics and coating properties

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Abstract

Plasma- sprayed coatings produced with two zirconia powders (− 90 + 10 µm, spray dried and partially sintered) that were stabilized (9 wt %) with dysprosia (DSZ) and ytterbia (YbSZ) were compared to coat-ings sprayed with a yttria (7 wt %) stabilized zirconia (YSZ) powder (45 + 22 µm, fused and crushed). The YSZ particles in the coating were almost fully molten (less than 0.2 % monoclinic m- phase), with excellent contact between the layered splats (adhesion of 54 MPa). The DSZ particles were only partially melted (3.1 % m- phase), with coating adhesion greater than 34 MPa; the YbSZ particles were less melted (6.1 % m- phase), with coating adhesion of 27 MPa. The thermal properties (diffusivity, a; specific heat, cp; and thermal conductivity, κ) of the coatings were about the same. Under thermal cycling (1 h heating at 1100 °C in a furnace followed by fast cooling for approximately 3 min by air jets) of the coatings sprayed on FeCrAl alloy manufactured by powder metallurgy, the behavior of the DSZ coating was simi-lar to that of the YSZ, whereas the YbSZ coating was partially detached. However, in all cases the percent-age of the monoclinic phase decreased and the ratio of the hexagonal structure increased to 1.013 of the nontransformable tetragonal phase t′.