The reactivity between rare-earth (RE-) oxide stabilized ZrO 2 or HfO 2 thermal barrier coatings (TBCs) and a calcium-magnesium-aluminum-silicate (CMAS) melt was studied at 1310°C. These reactions are representative of the ingestion of siliceous materials by the intake air of gas turbines (e.g., in aircraft engines) at high temperatures (>1200°C). These materials can melt and react with coated components in the hot section, resulting in premature failure. The goal of this work was to probe the effect of various RE (RE = Y, Yb, Dy, Gd, Nd, and Sm) oxides in the melt phase equilibrium and stability of the top-coating system. Thermodynamic calculations of the phase assemblage of the (1Àx) ZrO 2 -xY 2 O 3 coating materials and CMAS melt are compared with the experimental findings.CMAS was found to penetrate the samples at the grain boundaries and dissolve the coating materials to form silicate phases containing the RE elements. Furthermore, apatite and garnet crystalline phases formed in the samples with total REoxide content higher than 16 mol% in the reaction zone for the ZrO 2 system. In general, samples with nominal compositions ZrO 2 -9Dy 2 O 3 , HfO 2 -7Dy 2 O 3 , ZrO 2 -8Y 2 O 3 , HfO 2 -6Er 2 O 3 , ZrO 2 -9.5Y 2 O 3 -2.25Gd 2 O 3 -2.25Yb 2 O 3 , and ZrO 2 -30Y 2 O 3 exhibited lower reactivity, or more resistance, to CMAS than the other coating compositions. K E Y W O R D S coatings, degradation, rare earths, thermal barrier coatings

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An experimental investigation of the combustion dynamic characteristics of a research multi-element lean direct injection (LDI) combustor under simulated gas turbine conditions was conducted. The objective was to gain a better understanding of the physical phenomena inside a pressurized flametube combustion chamber under acoustically isolated conditions. A nine-point swirl venturi lean direct injection (SV-LDI) geometry was evaluated at inlet pressures up to 2,413 kPa and non-vitiated air temperatures up to 867 K. The equivalence ratio was varied to obtain adiabatic flame temperatures between 1388 K and 1905 K. Dynamic pressure measurements were taken upstream of the SV-LDI, in the combustion zone and downstream of the exit nozzle. The measurements showed that combustion dynamics were fairly small when the fuel was distributed uniformly and mostly due to fluid dynamics effects. Dynamic pressure fluctuations larger than 40 kPa at low frequencies were measured at 653 K inlet temperature and 1117 kPa inlet pressure when fuel was shifted and the pilot fuel injector equivalence ratio was increased to 0.72.