Abstract
Superalloy substrates coated with plasma-sprayed CoNiCrAlY bond coats and yttria-stabilized zirconia top coats (TCs) have been subjected to a high heat flux under a controlled atmosphere. The sintering exhibited by the TC under these conditions has been studied and compared with the behavior observed during isothermal heating. Sintering has been characterized by (a) microstructural examinations, (b) dilatometry, in both the in-plane and through-thickness directions, and (c) stiffness measurements, using both cantilever bending and nanoindentation. A numerical model has been used to explore the stress state under isothermal and thermal gradient conditions. Dilatometry data indicate significant linear contractions during holding at elevated temperatures, particularly in the through-thickness direction. This is largely attributed to microstructural changes associated with sintering, with any volume changes due to phase transformations making relatively small contributions. Sintering proceeds faster at higher temperatures but is retarded by the presence of tensile stresses (from differential thermal expansion between the coating and substrate) within the TC. Thus, it occurs preferentially near the free surface of the TC under gradient conditions, not only due to the higher temperature, but also because the in-plane stress is more compressive in that region.
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M.P. Taylor, P. Niranatlumpong, H.E. Evans, and C.B. Ponton: “Observations of the Spallation Modes in an Overlay Coating and the Corresponding Thermal Barrier Coating System,” Mater. High Temp., 2000, 17, pp. 219–24.
J. Rosler, M. Baker, and M. Volgmann: “Stress State and Failure Mechanisms of Thermal Barrier Coatings: Role of Creep in Thermally Grown Oxide,” Acta Mater., 2001, 49, pp. 3659–70.
A.G. Evans, D.R. Mumm, J.W. Hutchinson, G.H. Meier, and F.S. Pettit: “Mechanisms Controlling the Durability of Thermal Barrier Coatings,” Prog. Mater. Sci., 2001, 46, pp. 505–53.
R.A. Handoko, J.L. Beuth, G.H. Meier, F.S. Pettit, and M.J. Stiger: “Mechanisms for Interfacial Toughness Loss in Thermal Barrier Coating Systems,” Key Eng. Mater., 2001, 197, pp. 165–83.
T. Vogt, B.A. Hunter, and J. Thornton: “Structural Evolution of Thermal-Sprayed Yttria-Stabilized ZrO2 Thermal Barrier Coatings With Annealing: A Neutron Diffraction Study,” J. Am. Ceram. Soc., 2001, 84, pp. 678–80.
R. Vassen, G. Kerkhof, and D. Stover: “Development of a Micromechanical Life Prediction Model for Plasma Sprayed Thermal Barrier Coatings,” Mater. Sci. Eng. A Struct., 2001, 303, pp. 100–09.
J.W. Hutchinson and A.G. Evans: “On the Delamination of Thermal Barrier Coatings in a Thermal Gradient,” Surf. Coat. Technol., 2002, 149, pp. 179–84.
P.A. Langjahr, R. Oberacker, and M.J. Hoffmann: “Long-Term Behaviour and Application Limits of Plasma-Sprayed Zirconia Thermal Barrier Coatings,” J. Am. Ceram. Soc., 2001, 84, pp. 1301–08.
D.M. Zhu and R.A. Miller: “Thermal Conductivity and Elastic Modulus Evolution of Thermal Barrier Coatings under High Heat Flux Conditions,” J. Thermal Spray Technol., 2000, 9, pp. 175–80.
R. Dutton, R. Wheeler, K.S. Ravichandran, and K. An: “Effect of Heat Treatment on the Thermal Conductivity of Plasma-Sprayed Thermal Barrier Coatings,” J. Thermal Spray Technol., 2000, 9, pp. 204–09.
D. Basu, C. Funke, and R.W. Steinbrech: “Effect of Heat Treatment on Elastic Properties of Separated Thermal Barrier Coatings,” J. Mater. Res., 1999, 14, pp. 4643–50.
J.A. Thompson and T.W. Clyne: “The Effect of Heat Treatment on the Stiffness of Zirconia Top Coats in Plasma-Sprayed TBCs,” Acta Mater., 2001, 49, pp. 1565–75.
J. Brandon and R. Taylor: “Phase Stability of Zirconia-Based Thermal Barrier Coatings: Part I. Zirconia-Yttria Alloys,” Surf. Coat. Technol., 1991, 46, pp. 75–90.
R.W. Trice, Y.J. Su, J.R. Mawdsley, K.T. Faber, A.R. De Arellano-Lopez, H. Wang, and W.D. Porter: “Effect of Heat Treatment on Phase Stability, Microstructure, and Thermal Conductivity of Plasma-Sprayed YSZ,” J. Mater. Sci., 2002, 37, pp. 2359–65.
J. Moon, H. Choi, H. Kim, and C. Lee: “The Effects of Heat Treatment on the Phase Transformation Behavior of Plasma-Sprayed Stabilized ZrO2 Coatings,” Surf. Coat. Technol., 2002, 155, pp. 1–10.
R.A. Miller, J.L. Smialek, and R.G. Garlick: “Phase Stability in Plasma-Sprayed, Partially Stabilized Zirconia-Yttria” in Proceedings of First International Conference on the Science and Technology of Zirconia, A.H. Heuer and L.W. Hobbs, ed., American Ceramic Society, Westerville, OH, 1980, pp. 241–53.
H.G. Scott: “Phase Relationships in the ZrO2-Y2O3 System,” J. Mater. Sci., 1975, 10, pp. 1527–35.
H.E. Eaton and R.C. Novak: “Sintering Studies of Plasma Sprayed Zirconia,” Surf. Coat. Technol., 1987, 32, pp. 227–36.
D.M. Zhu and R.A. Miller: “Sintering and Creep Behaviour of Plasma-Sprayed Zirconia- and Hafnia-Based Thermal Barrier Coatings,” Surf. Coat. Technol., 1998, 109, pp. 114–20.
I.R. Gibson, G.P. Dransfield, and J.T.S. Irvine: “Sinterability of Commercial 8 mol% Yttria-Stabilized Zirconia Powders and the Effect of Sintered Density on the Ionic Conductivity,” J. Mater. Sci., 1998, 33, pp. 4297–4305.
R. Vassen, N. Czech, W. Mallener, W. Stamm, and D. Stoever: “Influence of Impurity Content and Porosity of Plasma-Sprayed Yttria-Stabilized Zirconia Layers on the Sintering Behaviour,” Surf. Coat. Technol., 2001, 141, pp. 135–40.
J.A. Thompson and T.W. Clyne: “The Stiffness of Plasma Sprayed Zirconia Top Coats in TBCs,” in Proceedings of United Thermal Spray Conference, E. Lugscheider and P.A. Kammer, ed., DVS, Dusseldorf, Germany, 1999, pp. 835–40.
R.J. Damani and P. Makroczy: “Heat Treatment Induced Phase and Microstructural Development in Bulk Plasma Sprayed Alumina,” J. Eur. Ceram. Soc., 2000, 20, pp. 867–88.
F. Cardarelli: Materials Handbook: A Concise Desktop Reference, Springer-Verlag, London, UK, 2000.
J. Malzbender and R.W. Steinbrech: “Mechanical Methods to Determine Layer Compliances Within Multilayered Composites,” J. Mater. Res., 2003, 18, pp. 1374–82.
S.C. Gill and T.W. Clyne: “Stress Distributions and Material Response in Thermal Spraying of Metallic and Ceramic Deposits,” Met. Trans., 1990, 21B, pp. 377–85.
T.W. Clyne and S.C. Gill: “Heat Flow and Thermal Contraction During Plasma Spray Deposition” in Heat Transfer in Manufacturing and Processing of New Materials, I. Tanasawa, ed., Hemisphere, New York, NY, 1991, pp. 33–48.
T.W. Clyne and S.C. Gill: “Residual Stresses in Thermally Sprayed Coatings and Their Effect on Interfacial Adhesion: A Review of Recent Work,” J. Thermal Spray Technol., 1996, 5, pp. 1–18.
Y.C. Tsui, J.A. Thompson, and T.W. Clyne: “The Effect of Bond Coat Creep on Residual Stresses and Debonding in Plasma Sprayed Thermal Barrier Systems” in Proceedings of Thermal Spray: Meeting the Challenges of the 21st Century. Proceedings of the 15th International Thermal Spray Conference, C. Coddet, ed., ASM International, Materials Park, OH, 1998, pp. 1565–70.
J.A. Thompson, J. Matejicek, and T.W. Clyne: “Modelling and Neutron Diffraction Measurement of Stresses in Sprayed TBCs” in Proceedings of Superalloys 2000, T.M. Pollock, R.D. Kissinger, R.R. Bowman, K.A. Green, M. McLean, S.L. Olsen, and J.J. Schirra, ed., TMS, Warrendale, PA, 2000, pp. 639–47.
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Tsipas, S.A., Golosnoy, I.O., Clyne, T.W. et al. The effect of a high thermal gradient on sintering and stiffening in the top coat of a thermal barrier coating system. J Therm Spray Tech 13, 370–376 (2004). https://doi.org/10.1361/10599630420380
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DOI: https://doi.org/10.1361/10599630420380