Abstract No.:
2582

 Scheduled at:
Wednesday, September 28, 2011, Saal C2.1 10:15 AM
Nanomaterial Coatings 2


 Title:
Ultra-small angle X-Ray scattering (USAXS) in-situ quantification of void network evolution during annealing of nanometer-sized YSZ plasma sprayed coatings

 Authors:
Ghislain Montavon* / LERMPS - EA3316 UTBM, France
Jan Ilavsky/ APS, Argonne national laboratory, USA
Alain Denoirjean/ SPCTS - University of Limoges, France
Pierre Fauchais/ SPCTS - University of Limoges, France
Antoine Bacciochini/ SPCTS - University of Limoges, France
Karine Wittmann-Tenèze/ CEA-DAM, LE RIPAULT, France

 Abstract:
Suspension plasma spraying (SPS) is able to process a stabilized suspension of nanometer-sized feedstock particles to form thin (from 20 to 100 µm) coatings with unique microstructures.
The void network architecture of these ceramic coatings is challenge to quantify using commonly used techniques due to small sizes involved. Nevertheless, the discrimination of these pore architectures in terms of size and shape distribution, anisotropy, specific surface area, etc., is critical for the understanding of processing, microstructure, and properties relationships. USAXS (Ultra-Small Angle X-Rays Scattering) combined with He-pycnometry appeared as a suitable combination of measurement techniques allowing discriminating the void size distribution over a large range (up to five orders of magnitude) and quantifying the open void content.
Results indicate that as-sprayed SPS coatings exhibit unusual porous architecture: 1) average void size exhibits about the same size scale as the feedstock size; i.e., nanometer sizes with multimodal void size distribution (up to 6 modes were identified); 2) about 80% of the pores exhibit characteristic dimensions smaller than 30 nm; 3) the total void content varies between 13 to 20% depending upon considered operating parameters; 4) most of the voids were found to be opened with only between one-tenth and one-third of voids volume being inaccessible by intrusion.
In-situ annealing measurements were performed as they proved to deliver more relevant results compared to ex-situ measurements: even at temperatures as low than 800°C, the microstructure transforms - while the total void content does not change significantly. Indeed, it has been demonstrated that the smallest voids (equivalent diameters smaller than 50 nm) coalescence was the predominant mechanism and that it was more sensitive to temperature than time.


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