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1243 |
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Tuesday, June 03, 2008, Auditorium 2 2:20 PM Gasturbines 3 Coatings for mobile and stationary turbines, protection against wear, high temperature corrosion and thermal stresses, clearance control coatings for a better efficiency |
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Effect of undercooling on solidification of YSZ splats |
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Hai Bo Liu* / Center for Advanced Coating Technology, Canada Markus Bussmann / Centre for Advanced Coating Technologies (CACT) ,University of Toronto, Canada Javad Mostaghimi/ Centre for Advanced Coating Technologies (CACT) ,University of Toronto, Canada |
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Plasma sprayed Yttria-Stabilized Zirconia (YSZ) coatings are widely used as thermal barrier coatings in the gas turbine industry. These coatings enable engines to operate at elevated temperatures, hence increasing thermal efficiency. The impact and solidification history of individual YSZ particles has been the subject of many experimental and theoretical studies. But in analyzing the solidification of individual splats, it is customary to assume that solidification occurs at the equilibrium temperature. Furthermore, the diffusion of yttria in the liquid phase during solidification of a splat has not been considered. In this work, we study non-equilibrium effects during the rapid solidification of a molten YSZ particle, by solving so-called hyperbolic equations for heat and mass transfer, that predict the interface undercooling (due to thermal, solutal, and interface curvature effects) and velocity as a function of time, as well as the solute (yttria) redistribution within the solid phase. Results are then compared to corresponding ones that we obtained from an equilibrium model, in order to assess the extent to which YSZ solidification is influenced by non-equilibrium effects. Results indicate that these effects are limited to the early part of the solidification process, when undercooling is most significant, the interface velocity is highest, and solute redistribution is most evident. As solidification progresses, the non-equilibrium effects wane and solidification can then be properly modeled as an equilibrium process. |