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

Abstract

Suspension plasma spraying (SPS) is a new, innovative plasma spray technique using a feedstock consisting of fine powder particles suspended in a liquid. Using SPS, ceramic coatings with columnar microstructures have been produced which are used as topcoats in thermal barrier coatings. The microstructure contains a wide pore size range consisting of inter-columnar spacings, micro-pores and nano-pores. Hence, determination of total porosity and pore size distribution is a challenge. Here, x-ray microscopy (XRM) has been applied for describing the complex pore space of the coatings because of its capability to image the (local) porosity within the coating in 3D at a resolution down to 50 nm. The possibility to quantitatively segment the analyzed volume allows analysis of both open and closed porosity. For an yttria-stabilized zirconia coating with feathery microstructure, both open and closed porosity were determined and it could be revealed that 11% of the pore volumes (1.4% of the total volume) are closed pores. The analyzed volume was reconstructed to illustrate the distribution of open and closed pores in 3D. Moreover, pore widths and pore volumes were determined. The results on the complex pore space obtained by XRM are discussed in connection with other porosimetry techniques.

A study of suspension plasma-sprayed insulated pistons evaluated in a heavy-duty diesel engine

“…It was estimated that 60% of the TBC volume is a porous ceramic, and it was further assumed that 89% of all pores in the ceramic are surface-connected. The latter value is taken from Klement et al, 29 who have measured the fraction of connected pores in an SPS coating.…”

The Influence of Heat Treatments on the Porosity of Suspension Plasma-Sprayed Yttria-Stabilized Zirconia Coatings

“…Along with higher porosity, pores in SPS topcoats are found to be distributed over a wider size range (starting form nano-sized pores) and encompass smaller pore sizes compared to conventional, atmospheric plasma-sprayed (APS) coatings (Ref 10,15,21). The small pore sizes in SPS TBCs can favor the reduction of thermal conductivity due to the enhanced phonon scattering interfaces (Ref 22,23).…”

Computational image analysis of Suspension Plasma Sprayed YSZ coatings

“…In general, many characterization techniques may be used for porosity analysis. The basic ones are [1,[9][10][11][12][13][14][15][16] The manner of porosity evaluation is classified differently by the literature [1,[17][18][19][20]. Two main approaches can be distinguished: (i) shape-based [1,[16][17][18], and (ii) size-related [1,16,17,20].…”