Durability of Oxide/Oxide Ceramic Matrix Composites in Gas Turbine Combustors

Abstract

An integrated creep rupture strength degradation and water vapor degradation model for gas turbine oxide-based ceramic matrix composite (CMC) combustor liners was expanded with heat transfer computations to establish the maximum turbine rotor inlet temperature (TRIT) for gas turbines with 10:1 pressure ratio. Recession rates and average CMC operating temperatures were calculated for an existing baseline N720/A (N720/Al2O3) CMC combustor liner system with and without protective Al2O3 friable graded insulation (FGI) for 30,000-h liner service life. The potential for increasing TRIT by Y3Al5O12 (YAG) substitution for the fiber, matrix, and FGI constituents of the CMC system was explored, because of the known superior creep and water vapor degradation resistance of YAG compared to Al2O3. It was predicted that uncoated N720/A can be used as a combustor liner material up to a TRIT of ∼1200  °C, offering no TRIT advantage over a conventional metal + thermal barrier coating (TBC) combustor liner. A similar conclusion was previously reached for a SiC/SiC CMC liner with barium strontium aluminum silicate (BSAS)-type environmental barrier coating (EBC). The existing N720/A + Al2O3 FGI combustor liner system can be used at a maximum TRIT of ∼1350  °C, a TRIT increase over metal + TBC, and uncoated N720/A of ∼150  °C. Replacing the Al2O3 with YAG is predicted to increase the maximum allowable TRIT. Substitution of the fiber or matrix in N720/A increases TRIT by ∼100  °C. A YAG FGI improves the TRIT of the N720/A + Al2O3 FGI by ∼50  °C, enabling a TRIT of ∼1400 °C, similar to that predicted for SiC/SiC CMCs with protective rare earth monosilicate EBCs.