Thermochemical Interaction of Thermal Barrier Coatings with Molten CaO–MgO–Al2O3–SiO2 (CMAS) Deposits

Thermal barrier coatings (TBCs) are increasingly susceptible to degradation by molten calcium–magnesium alumino silicate (CMAS) deposits in advanced engines that operate at higher temperatures and in environments laden with siliceous debris. This paper investigates the thermochemical aspects of the degradation phenomena using a model CMAS composition and ZrO2–7.6%YO1.5 (7YSZ) grown by vapor deposition on alumina substrates. The changes in microstructure and chemistry are characterized after isothermal treatments of 4 h at 1200°–1400°C. It is found that CMAS rapidly penetrates the open structure of the coating as soon as melting occurs, whereupon the original 7YSZ dissolves in the CMAS and reprecipitates with a different morphology and composition that depends on the local melt chemistry. The attack is minimal in the bulk of the coating but severe near the surface and the interface with the substrate, which is also partially dissolved by the melt. The phase evolution is discussed in terms of available thermodynamic information.

[1]  N. Fleck,et al.  Scaling laws governing the erosion and impact resistance of thermal barrier coatings , 2006 .

[2]  D. Clarke,et al.  High temperature aging of YSZ coatings and subsequent transformation at low temperature , 2005 .

[3]  A. Evans,et al.  A delamination mechanism for thermal barrier coatings subject to calcium-magnesium-alumino-silicate (CMAS) infiltration , 2005 .

[4]  U. Schulz.  Phase Transformation in EB-PVD Yttria Partially Stabilized Zirconia Thermal Barrier Coatings During Annealing , 2004 .

[5]  N. Fleck,et al.  Mechanisms governing the high temperature erosion of thermal barrier coatings , 2004 .

[6]  Robert E. Schafrik,et al.  Saga of gas turbine materials. Part IV , 2004 .

[7]  C. Levi.  Emerging materials and processes for thermal barrier systems , 2004 .

[8]  M. Heb,et al.  Mechanisms governing the high temperature erosion of thermal barrier coatings , 2004 .

[9]  H. P. Yang,et al.  Novel soft solution synthesis and characterization of submicromic LiCoVO4 , 2003 .

[10]  A. Evans,et al.  Foreign object damage in a thermal barrier system: Mechanisms and simulations , 2003 .

[11]  S. G. Terry.  Evolution of microstructure during the growth of thermal barrier coatings by electron-beam physical vapor deposition , 2001 .

[12]  J. Nicholls,et al.  A Mechanism for the Erosion of EB PVD TBCS , 2001 .

[13]  Anthony G. Evans,et al.  Mechanisms controlling the durability of thermal barrier coatings , 2001 .

[14]  J. Nicholls,et al.  A comparison between the erosion behaviour of thermal spray and electron beam physical vapour deposition thermal barrier coatings , 1999 .

[15]  P Wright,et al.  Mechanisms governing the performance of thermal barrier coatings , 1999 .

[16]  A. Clare,et al.  An estimation of the surface tension for silicate glass melts at 1400°C using statistical analysis , 1999 .

[17]  G. H. Geiger,et al.  Transport Phenomena in Materials Processing , 1998 .

[18]  D. Clarke,et al.  A thermodynamic approach to the wetting and dewetting of grain boundaries , 1997 .

[19]  L. Peluso,et al.  Role of environment deposits and operating surface temperature in spallation of air plasma sprayed thermal barrier coatings , 1996 .

[20]  J. Smialek,et al.  Turbine airfoil degradation in the persian gulf war , 1994 .

[21]  F. Stott,et al.  Degradation of Thermal-Barrier Coatings at Very High Temperatures , 1994 .

[22]  F. Stott,et al.  Corrosion mechanisms of ZrO2-Y2O3 thermal barrier coatings in the presence of molten middle-east sand , 1993 .

[23]  Michael G. Dunn,et al.  Deposition of Volcanic Materials in the Hot Sections of Two Gas Turbine Engines , 1992 .

[24]  F. Stott,et al.  The effects of molten silicate deposits on the stability of thermal barrier coatings for turbine applications at very high temperatures , 1992 .

[25]  James L. Smialek,et al.  The chemistry of Saudi Arabian sand: A deposition problem on helicopter turbine airfoils , 1992 .

[26]  A. Heuer,et al.  PHASE TRANSFORMATIONS IN ZrO//2-CONTAINING CERAMICS: II, THE MARTENSITIC REACTION IN t-ZrO//2. , 1984 .

[27]  E. T. Turkdogan.  Physical chemistry of high temperature technology , 1980 .

[28]  M. Lewis,et al.  The microstructures of silicon nitride ceramics during hot-pressing transformations , 1974 .