A Comparative Microstructural Investigation of Nanostructured and Conventional Al 2 O 3 Coatings Deposited by Plasma Spr
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. Zois, A. Lekatou, M. Vardavoulias, I. Panagiotopoulos, and A. Vazdirvanidis (Submitted June 12, 2008; in revised form September 19, 2008) Nanostructured and conventional Al2O3 powders have been plasma sprayed to produce coatings. The parameters for retaining a fraction of the nanostructure were investigated. Dissimilarities were observed between the two types of coating, regarding properties and phase proportions, which are related with the different percentages of semimolten particles in the coatings. The nanocoatings retained a higher percentage of semimolten particles than the conventional coatings owing to the higher porosity of the nanoparticle agglomerates. The molten part of both conventional and nanostructured coatings consisted of c-Al2O3 of columnar morphology. In order to investigate the mechanism of the melting front advance into the particle interior, the particles were sprayed directly into deionized water. The nanoparticles mainly formed hollow spheres, whereas the conventional particles mainly formed compact spheres. The internal porosity of the solidified nanoparticle agglomerates, which affected the overall coating porosity and, consequently, coating properties such as hardness, adhesion, and surface roughness, was linked to the hollow sphere phenomenon.
Keywords
APS coatings, influence of spray parameters, nanopowders, nanostructured coatings, porosity of coatings
1. Introduction Nanocrystalline bulk materials (having a grain size smaller than 100 nm) are experiencing a rapid development in recent years due to their existing and/or potential applications to a wide variety of technological areas, such as electronics, catalysis, ceramics, magnetic data storage, structural components, etc. As the grain size is reduced to the nanometer range, materials exhibit peculiar and interesting mechanical and physical properties, e.g.
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. D. Zois and M. Vardavoulias, Pyrogenesis SA, Technological Park of Lavrion, 19500 Lavrion, Greece; D. Zois, A. Lekatou, and I. Panagiotopoulos, Department of Materials Science and Engineering, University of Ioannina, 45111 Ioannina, Greece; and A. Vazdirvanidis, Hellenic Centre for Metal Research, Pireos 252, 17778 Athens, Greece. Contact e-mail: [email protected].
Journal of Thermal Spray Technology
increased mechanical strength, enhanced diffusivity, higher specific heat and electrical resistivity, in comparison with conventional coarse-grained counterparts. Nanostructured bulk materials and coatings are reported to demonstrate superior resistance to wear, erosion, cracking, and
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