25,000-hour hybrid oxide CMC field test summary

A Hybrid Oxide CMC Liner was evaluated in field testing of a Solar Turbines Incorporated Centaur® 50S engine for 25,404 hours and 109 starts between 2003 and 2006. The Hybrid Oxide CMC configuration consisted of a Nextel 720 aluminosilicate fiber/alumina matrix CMC and overlaying Friable Graded Insulation (FGI). The liner remained functional throughout the engine test. Borescoping during the first half of the field testing revealed little visual damage to the CMC liner, but erosion, affecting about 1-2 mm of the initial ̃ 5mm FGI thickness was noticed upon inspection of the liner after the midpoint of the field test. The erosion correlated with the hottest areas of the liner surface. Field testing was continued after minor liner repair. Damage to one area of the liner surface was observed in borescoping during the second half of the field test. Visual inspection after completion of the engine test indicated large areas of considerable CMC porosity/delamination within a few plies from the OD surface. Residual thickness measurements following the engine field testing indicated that of the original thickness, 2.0 - 2.6 mm of FGI had been lost. The surface recession is in the range expected based on a degradation model for alumina-based CMCs.