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| Abstract No.: |
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Scheduled at:
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Tuesday, September 27, 2011, Saal B2.2 2:00 PM
Tribological Coatings 1
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| Title: |
Sintering process occurring at suspension plasma sprayed of some oxides
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| Authors: |
Lech Pawlowski* / University of Limoges, SPCTS UMR 6638, France
Leszek Latka / University of Limoges/ SPCTS, France
Sergey Goryachev/ University Lille Nord de France, France
Stefan Kozerski/ Wroclaw University of Technology/Institute of Welding, Poland
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| Abstract: |
Suspension plasma spraying is a process which enables production of finely grained nanometric or submicrometric coatings. The suspensions were formulated with the use of fine powder of particles in water or alcohol with some additives. Subsequently, the suspension is injected into plasma jet and the liquid additives get evaporated. The remaining fine solids are either molten and get agglomerated or remain solid depending on their trajectory in the plasma jet. The coatings microstructure results from these two groups of particles arriving on a substrate or previously deposited coating. The previous experimental studies carried out for plasma sprayed titanium oxide, hydroxyapatite and zirconium oxide coatings enabled to find out finely grained microstructure. Some of the coatings, especially, those of titanium oxide and hydroxyapatite included two zones in microstructure which correspond to: (i) dense zone formed from well molten particles, and, (ii) agglomerated zone formed from fine solid particles arrived on the substrate in solid state. The present paper focuses on the theoretical analysis of the formation process of the agglomerated zone. The experiments described previously enabled to find the heat flux input to the coatings during spray experiments. The theoretical analysis of sintering during the coatings growth was carried out. The sintering concerns fine particles arriving on the substrate in the solid state. The models of volume, grain boundary and surface diffusion were analyzed and adapted to the size and chemistry of grains, temperature and time scales corresponding to the suspension plasma spraying conditions. The model of surface diffusion was found to be the most appropriate to describe the sintering during suspension plasma spraying. The formation of the necks having the relative size equal to 10 % of particle diameter was found to be possible during the thermal cycles occurring at the some coatings deposition. The microscopic observation made using transmission electron microscope of the agglomerated zone was made to confirm the sintering of some of the fine grains.
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