The Role of Substrate Surface Chemistry on Splat Formation During Plasma Spray Deposition by Experiments and Simulations
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A.T.T. Tran and M.M. Hyland (Submitted April 25, 2009; in revised form August 16, 2009) NiCr single splats were plasma-sprayed on aluminum and stainless steel substrates, which were modified by immersion in boiling water, to grow specific types of oxide/oxyhydroxide on the surface. It was observed that there was no splat formation on aluminum substrate. In contrast, a significant number of splats were formed on stainless steel substrate. The differences in splat formation on aluminum and stainless steel surfaces corresponded to the variations of thickness and proportions of the oxide/ oxyhydroxide layer on the surfaces. A three-dimensional numerical model was developed to simulate the impact of a droplet onto the substrate. The simulation illustrated good agreement with experimental observations. The effect of the oxide layer on the splat morphology was also examined. It was suggested that the splat morphology was more strongly influenced by water release from the dehydration of oxyhydroxide to oxide rather than by simple presence of the oxide layer on the substrate surface.
Keywords
FEM, numerical modeling, oxyhydroxide, surface chemistry, water desorption
above a given temperature, (defined as the transition temperature by Fukumoto (Ref 12) gave rise to favorable, disk-shaped splats. In contrast, splats on substrates held Nomenclature
1. Introduction Plasma spray technology has been widely employed for deposition of engineering coatings. Coatings produced with customized surface properties are used for a variety of industrial applications. Fundamentally, the coatings are formed as the molten particles impact and spread out to form overlapping splats. Thus, the performance of the coatings is closely linked with the way the individual splats are formed. The layered microstructure and splatsubstrate bonding are profoundly affected by the spraying conditions, substrate surface, and the particle conditions (Ref 1, 2). During the last decade, many papers have demonstrated that splat morphology and behavior in plasma spray strongly depend on substrate temperature (Ref 1-11). Such works showed that substrates heated This article is an invited paper selected from presentations at the 2009 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Expanding Thermal Spray Performance to New Markets and Applications: Proceedings of the 2009 International Thermal Spray Conference, Las Vegas, Nevada, USA, May 4-7, 2009, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2009. A.T.T. Tran and M.M. Hyland, Chemical & Materials Engineering Department, The University of Auckland, Private Bag 92019, Auckland, New Zealand. Contact e-mail: atra021@aucklanduni. ac.nz.
Journal of Thermal Spray Technology
B Cp f F k L n Rc T T0 Tm p t u a q l r j d l m ox s sub a b
body force specific heat capacity mass fraction volume of fraction of the droplet thermal conductivity la
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