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| Abstract No.: |
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Scheduled at:
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Tuesday, June 03, 2008, Auditorium 2 3:00 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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| Title: |
A numerical assessment of the failure of plasma sprayed thermal barrier coatings
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| Authors: |
Saeed Asghari / Department of Mechanical Engineering, Isfahan University of Technology, Iran
Mahmood Salimi / Department of Mechanical Engineering, Isfahan University of Technology, Iran
Mahdi Salehi*/ Department of Materials Engineering, Isfahan University of Technology, Iran
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| Abstract: |
Failure of thermal barrier coatings (TBC) under thermomechanical loading is a very complicated phenomenon because it is influenced by many factors such as thermal mismatch between different layers, thermal gradient in top coat layer, oxidation of bond coat layer, interface roughness between top and bond coat layers, creep and plastic deformation of bond coat layer, sintering of top coat layer and phase transformation in some types of bond coats. In this research, a fracture mechanics approach was developed, by means of which cracks are modeled in the critical areas of the TBC system and assessed. The results of the parametric unit cell FEM analyses revealed a strong dependency of the local stresses responsible for crack growth on the local morphology of the interface roughness between top and bond coat layers, the sintering of the top coat layer, creep of bond coat layer, the thickness of the thermally grown oxide (TGO) layer and the strains and the stresses associated with the growth of TGO layer at high temperatures. Also in this paper, Interactions between cracks induced in thermal barrier coatings (TBCs) upon thermal cycling have been calculated. The results indicate that the energy release rate G cycles as the temperature changes, with the largest value arising at ambient temperature. It increases on a cycle-by-cycle basis. Improvements in the durability upon increasing the high temperature strength of the bond coat and upon decreasing the growth stress in the TGO are established as well as the influence of the geometric imperfections in the bond coat. At last, the effect of considering of top coat sintering and thermal gradients across coating on stress magnitudes, energy release rates of the cracks and durability of the system are explored.
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