Abstract
The authors developed 1400 °C (2552 °F) class ceramic matrix composite (CMC) material system, which consists of silicon carbide (SiC) fibers and SiC matrix and ytterbium silicate base matrix, aiming for higher temperature capability. Then they designed and manufactured high pressure turbine (HPT) shrouds for aircraft engines using that 1400 °C class material system, and they conducted strength tests and thermal cycle tests for turbine shroud components. After that, they conducted engine tests for the CMC turbine shrouds' demonstration in the actual engine environment jointly with the Japan Aerospace Exploration Agency (JAXA) in 2021. The engine test was conducted for over 75 h including over 35 h hot time. After that, the test teardown inspection was conducted. No spallation of environmental barrier coating (EBC), no recession, and no wear on CMC turbine shrouds were found. As the result of the microstructure observation for cut faces of CMC turbine shrouds, no oxidation in SiC fibers, no chemical reaction in matrix, and no microcrack in matrix were found, but, some oxidation in fiber interface coating and microcrack in EBC were found. Bending strength tests with specimens cut out from CMC turbine shrouds were conducted in order to survey the degradation of material. As the result of bending test, the strength of the specimens cut out from engine-tested shrouds were equivalent to the strength of the specimens cut out from unused shrouds. The CMC turbine shrouds after engine test were determined to be serviceable; therefore, the developed 1400 °C class CMC shrouds were proven to be sound in an actual engine environment.
