PSI - Issue 13

Elena Fedorova et al. / Procedia Structural Integrity 13 (2018) 741–745 E.Fedorova et al./ Structural Integrity Procedia 00 (2018) 000 – 000

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It is clear from the graphs on the Fig. 5, the TGO shape has a significant impact on the stress state in both TGO/TC and TGO/BC interfaces. In the case of “ defect ” shape, the compressive stresses reach the value of -2741 MPa at the peak of TC/TGO interface, which is almost three times higher (in absolute value) than the stresses developed at the same location in the TBC system with the regular TGO layer. A similar effect, although less pronounced (-2108 vs - 1382 MPa), is observed in the peak region of the TGO/BC interface. The level of compressive stresses implies a higher possibility of TBC failure at the TGO/TC interface than at the boundary between TGO and BC layers. Besides of the difference in stresses magnitude, the TGO defect causes a drastic change in stress profile (especially at the TGO/TC interface) along the y-axis direction.

a b Fig. 5.  3 stress profile the TGO layer after cooling to room temperature with the rate of 30 °C/min at: (a) the TGO/TC interface, (b) at the TGO/BC interface. Calculations carried out to check whether such significant difference between the stress states is due to the increased thickness of TGO layer revealed its insignificant influence (up to 3% varying the thickness in the range from 7 to 30 μm ). Interestingly, the shear stresses, being relatively high, are not significantly influenced by the shape of TGO as the difference of the maximum values for the regular and defective shape does not exceed 10 %. In the latter case, the shear stresses value reaches 638 MPa at the TGO/BC interface. Conclusions The numerical analysis of stress development in Ni-based superalloys protected with the TBC system is presented. It has been established that the geometry of the TGO layer significantly influences the magnitude and distribution of minimum principal stresses. In comparison, the effect of the cooling rate is much less pronounced. The results of calculations performed for the considered TBC system using finite-element model allow localizing the region of possible TBC failure and are in good agreement with the results of experimental studies using the SEM-EDS analysis. References Evans, A.G., Mumm, D.R., Hutchinson, J.W., Meier, G.H., Pettit, F.S., 2001. Mechanisms controlling the durability of thermal barrier coatings. Progress in Materials Science 46, 505 – 553. Pindera, M.-J., Aboudi, J., Arnold, SM., 2005. Analysis of the spallation mechanism suppression in plasma-sprayed TBCs through the use of heterogeneous bond coat architectures. International Journal of Plasticity 21, 1061-1096. Hille, T.S., Turteltaub, S., Suiker, A.S.J., 2011. Oxide growth and damage evolution in thermal barrier coatings. Engineering Fracture Mechanics 78, 2139 – 2152. Eliseev, J.S., Poklad, V.A., Ospennikova, O.G., Larionov, V.N., Logunov, A.V., Razumovskij, I. M., 2008. Composition of heat-resistant nickel alloy (versions), Russian Patent № 2 353 691, April 2008. Baker, M., Seiler, Ph., 2017. A Guide to Finite Element Simulations of Thermal Barrier Coatings. Journal of Thermal Spray Technology 26, 1146 – 1160. ANSYS Academic Research: Release 14.5, Help System. 2013. Munro, R. G., 1997. Evaluated Material Properties for a Sintered-Alumina. Journal of the American Ceramic Society 80, 1919 – 1928 Haynes, J. A., Pint, B.A., Porter, W.D., Wright, I.G., 2004. Comparison of thermal expansion and oxidation behavior of various high-temperature coating materials and superalloys. Materials at High Temperatures 21, 87 – 94.