Nano-YSZ(7.5 wt%) and nano-Al2O3 powders(Jiangsu Lida Hi-Tech Special Material Co. Ltd, China) measuring<50 nm were used as raw materials. The Al2O3-doped YSZ coatings were fabricated using an A-2000 atmospheric plasma spraying (APS) system equipped with an F4-MB plasma gun(Sulzer Metco AG, Switzerland) using six different sets of parameters, as listed in Table 1. To ensure high flow ability in the APS system, Al2O3 and YSZ powders were mixed and reconstituted into spherical particles measuring 5-45 um by spray drying. The mass mixing ratios of Al2O3 into YSZ powders were 5 wt%,10 wt%,15 wt%, and 25wt%, and the corresponding granulated powders were labeled 5AlYSZ,10AlYSZ,15AIYSZ, and 25AlYSZ powders, whereas the corresponding coatings were labeled A5,B5,C5..... coating(capital letters represent APS process parameters, and numbers represent Al2O3addition).Aluminum plates(124 mm × 85 mm × 2 mm) were used as substrates.
Table 1 Operating parameters used for APS.
The spray-dried Al2O3-YSZ powders are composed of tetragonal YSZphase(t-YSZ),a-Al2O3 phase, and a small amount of monoclinic Y2O3 phase, as shown in Fig.1. The SEM images in Fig.2 reveal that the powders are spherical and that Al2O3 particles are dispersed in the YSZ particles.
Fig.1.XRD patterns of spray-dried Al2O3-YSZ powders.
Fig.2. SEM images and EDS profiles of spray-dried AlzO3-YSZ powders:(a,e,i) 5AlYSZ;(b,f,j)10AlYSZ;(c,g,k)15AlYSZ;(d,h,I)25AlYSZ;(e-h) surface morphologies of single spherical particles in a-d, respectively.
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