Numerical Investigation into the Effect of Splats and Pores on the Thermal Fracture of Air Plasma-Sprayed Thermal Barrie
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Numerical Investigation into the Effect of Splats and Pores on the Thermal Fracture of Air Plasma-Sprayed Thermal Barrier Coatings Jayaprakash Krishnasamy1 • Sathiskumar A. Ponnusami2 • Sergio Turteltaub1 Sybrand van der Zwaag1
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Submitted: 1 July 2019 / in revised form: 24 October 2019 Ó The Author(s) 2019
Abstract The effect of splat interfaces on the fracture behavior of air plasma-sprayed thermal barrier coatings (APS-TBC) is analyzed using finite element modeling involving cohesive elements. A multiscale approach is adopted in which the explicitly resolved top coat microstructural features are embedded in a larger domain. Within the computational cell, splat interfaces are modeled as being located on a sinusoidal interface in combination with a random distribution of pores. Parametric studies are conducted for different splat interface waviness, spacing, pore volume fraction and fracture properties of the splat interface. The results are quantified in terms of crack nucleation temperature and total microcrack length. It is found that the amount of cracking in TBCs actually decreases with increased porosity up to a critical volume fraction. In contrast, the presence of splats is always detrimental to the TBC performance. This detrimental effect is reduced for the splat interfaces with high waviness and spacing compared to those with low waviness and spacing. The crack initiation temperature was found to be
& Jayaprakash Krishnasamy [email protected] Sathiskumar A. Ponnusami [email protected] Sergio Turteltaub [email protected] Sybrand van der Zwaag [email protected] 1
Faculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS Delft, The Netherlands
2
Department of Mechanical Engineering and Aeronautics, City, University of London, Northampton Square, London EC1V 0HB, UK
linearly dependent on the normal fracture properties of the splat interface. Insights derived from the numerical results aid in engineering the microstructure of practical TBC systems for improved resistance against thermal fracture. Keywords cohesive elements fracture porosity splats thermal barrier coatings
Introduction Thermal barrier coatings (TBC) are heat insulation layers applied on the high-temperature regions of aircraft jet engines in order to protect the crucial structural components against overheating and consequently to extend the lifetime of these components. They also improve the combustion efficiency of the engine by allowing higher operational temperature. The most common TBC system is a multilayered system. It consists of two layers; an outer ceramic layer that protects the substrate from high-temperature gases and an intermediate metallic layer which provides adhesion between the substrate and the ceramic layer. The metallic layer also protects the substrate from high-temperature oxidation and corrosion. The outer ceramic layer is called top coat (TC) and is often made of yttria stabilized zirconia (YSZ). The metallic layer is
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