Advanced Microscopic Study of Suspension Plasma-Sprayed Zirconia Coatings with Different Microstructures

Abstract

The present paper is focused on the characterization of the differences between two microstructures that can be obtained using SPS technology, namely (i) columnar and (ii) two-zone microstructure including lamellas and fine unmelted particulates. The optimization of spray parameters was made, and the advanced microstructural studies of obtained coatings were performed. The work was focused on zirconia stabilized by yttria (YSZ, ZrO 2 + 14 wt.% Y 2 O 3 ) and both by yttria and ceria (YCSZ, ZrO 2 + 24 wt.% CeO 2 + 2.5 wt.% Y 2 O 3 ) which are frequently used as thermal barrier coatings. Two types of microstructure were achieved using two different plasma torches, namely SG-100 of Praxair and Triplex of Oerlikon Metco. The microstructure of prepared coatings was analyzed using scanning electron microscopy with secondary electrons detector and backscattered electrons. Energy dispersive spectroscopy was performed to analyze the chemical composition of sprayed coatings. By electron backscatter diffraction grain shape, size, and crystal orientation were determined. The analysis enabled the discussion of the coatings growth mechanism. Finally, the Shape From Shading technique was applied to recreate and to analyze 3D views of coatingsÕ topographies, and using laser confocal microscopy, the surface roughness was examined.

Effects of Processing Parameters on the Deposition of Yttria Partially Stabilized Zirconia Coating During Suspension Plasma Spray

“…10, especially at troughs of the undulated substrate surface with a higher drag force generated by a higher gas flow. Results in this study as well as previous studies 18,19,26,32,33,43 confirm that both columnar and DVC YSZ coatings developed in SPS are results from the successive deposition of much finer splats. 10.…”

“…It is confirmed that the undulated substrate surface originated from the hemispherical surface of alloy particles which were not fully melted during HVOF processing. As reported, 19,32,33,39 the finer the in-flight ceramic droplets are, the easier for them to follow the plasma gas flow with increased lateral velocity along the substrate surface. Figure 9(c) displays a similar case in C2 with 6.5 mm torch nozzle.…”

“…Results indicated that the suspension concentration had a strong influence on the SPS YSZ coating's microstructure, i.e., a lower suspension concentration was also beneficial for columnar structure formation. 32,33 Guignard et al showed that the DVC YSZ coating prepared by SPS with a crack density of 6.5 cracks/mm exhibited a poorer thermal cycling lifetime compared to the conventional APS YSZ coating due to the presences of unmelted or spherical particles in the SPS coating leading to poorer adhesive strength. 16 Julia et al's 26 study demonstrated that the SPS YSZ splat could even be produced by the deposition of a single starting YSZ powder particle with the average size of 0.7 AE 0.4 lm, and almost no reagglomeration happened to such fine powder particles during the SPS process.…”

Computational image analysis of Suspension Plasma Sprayed YSZ coatings

“…The views were created automatically by assembling four SEM micrographs, taken by symmetrically located BSD detectors (Phenom G2 pro, Phenom-World B.V., Eindhoven, the Netherlands). More details on SFS are provided in work [25].…”

3D Analysis of Porosity in a Ceramic Coating Using X-ray Microscopy

“…The particles of the liquid suspension used in SPS can be of submicron size, i.e., \1 lm (Ref 1), whereas 10-100 times larger particle are used in APS ( Ref 2). The smaller particles are more influenced by the plasma jet flow as it interacts with the substrate (Ref 3) and the difference in droplet flight path leads to formation of a columnar structure (Ref 4,5). Hence, the coating build-up occurs in a different manner as compared to conventional APS spraying.…”