Toward Highly Sintering-Resistant Nanostructured ZrO 2 -7wt.%Y 2 O 3 Coatings for TBC Applications by Employing Differen
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JTTEE5 17:846–852 DOI: 10.1007/s11666-008-9217-x 1059-9630/$19.00 Ó ASM International
Toward Highly Sintering-Resistant Nanostructured ZrO2-7wt.%Y2O3 Coatings for TBC Applications by Employing Differential Sintering R.S. Lima and B.R. Marple (Submitted May 1, 2008; in revised form July 16, 2008) There are still concerns in the scientific community about the stability of nanostructured YSZ coatings at high temperatures. Questions have been raised about the possibility of accelerated sintering of these ultrafine materials and the associated changes in properties that could accompany this sintering. In this work, nanostructured YSZ coatings were engineered to counteract sintering effects by tailoring the coatings to exhibit a bimodal microstructure formed by (i) a matrix of dense YSZ zones (produced from molten YSZ particles) and (ii) large porous nanostructured YSZ zones (produced from semimolten nanostructured YSZ particles) that were embedded in the coating microstructure during thermal spraying. These coatings were subjected to heat treatment in air at 1400 °C for 1, 5, and 20 h. The superior driving force for sintering exhibited by the porous nanozones, when compared to that of the dense zones, caused the nanozones to shrink at much faster rates than those exhibited by the denser matrix zones (i.e., differential sintering), thereby creating a significant network of voids in the coating microstructure. Due to these effects, after 20 h exposure at 1400 °C, the thermal conductivity and elastic modulus values of the conventional coatings were approximately two times higher than those of the nanostructured ones.
Keywords
differential sintering, elastic modulus, nanostructured ZrO2-7wt.%Y2O3 (YSZ), thermal barrier coatings (TBCs), thermal conductivity
1. Introduction 1.1 Nanostructured YSZ Coatings There is an ongoing need to develop materials and strategies to enhance the performance of thermal barrier coatings (TBCs). Different approaches have been employed to achieve this goal. One of the possible approaches is based on the thermal spraying of porous nanostructured agglomerated ZrO2-7-8wt.%Y2O3 (YSZ) powders, in which individual nanostructured YSZ This article is an invited paper selected from presentations at the 2008 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Thermal Spray Crossing Borders, Proceedings of the 2008 International Thermal Spray Conference, Maastricht, The Netherlands, June 2-4, 2008, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2008. R.S. Lima and B.R. Marple, National Research Council of Canada, 75 de Mortagne Blvd., Boucherville J4B 6Y4, QC, Canada. Contact e-mail: [email protected].
846—Volume 17(5-6) Mid-December 2008
particles are agglomerated via spray-drying into microscopic clusters. By using this type of feedstock, it is possible to engineer coatings that exhibit a bimodal microstructure, wh
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