Accelerated oxidation during 1350°C cycling of ytterbium silicate environmental barrier coatings

Abstract

public-access-plan).

Steam oxidation and microstructural evolution of rare earth silicate environmental barrier coatings

“…Furnace cyclic testing (FCT) was performed in a vertical automated cyclic rig with a thoroughly aged alumina reaction tube 16 , 21 at 1350°C, with each cycle consisting of a 1‐h exposure at temperature, followed by air cooling for 10 min. A 90 vol.% H 2 O (g)/10 vol.% air environment was achieved through preheating liquid H 2 O at 400°C.…”

“…8,12 Yet, it is well known that EBCs are still subjected to chemical degradation despite being a protective layer for the CMC. 13 A significant concern for EBC systems is oxidation of the intermediate Si-bond coating, [14][15][16] where the formation of SiO 2 at the bond coating-EBC interface results in debonding and spallation of the coating.…”

“…This work compares the microstructure evolution and the steam oxidation kinetics of the Si-bond coating beneath two unique EBCs, (Y 1.2 Yb 0.8 ) 2 Si 2 O 7 , termed (Y/Yb)DS throughout this work, and Yb 2 Si 2 O 7 , termed YbDS/YbMS, to determine the impact of EBC composition on steam oxidation kinetics. Furnace cyclic testing (FCT) was performed in a vertical automated cyclic rig with a thoroughly aged alumina reaction tube 16,21 at 1350 • C, with each cycle consisting of a 1-h exposure at temperature, followed by air cooling for 10 min. A 90 vol.% H 2 O (g)/10 vol.% air environment was achieved through preheating liquid H 2 O at 400 • C. An airflow rate of 130 cm 3 /min and liquid H 2 O pump rate of 54 ml/h resulted in a calculated flow rate of 1.5 cm/s.…”

Holistic comparison of environmental barrier coating material candidates through design of a figure of merit

“…Coated EBC-CMC systems are often compared against each other through cyclic furnace testing and direct measurement of thermally grown oxide formation at the EBC-Si or EBC-SiC interfaces. [40][41][42] In addition, high water vapor pressure in industrial gas turbines implies that oxidant transport to the interface may also be governed by water vapor. Wada et al 43 have shown that oxidant transport through phase pure Yb 2 Si 2 O 7 is increased in a water vapor environment compared with a dry oxygen environment.…”

“…No reliable published data are known for oxygen transport rates through APS‐deposited EBCs. Coated EBC‐CMC systems are often compared against each other through cyclic furnace testing and direct measurement of thermally grown oxide formation at the EBC–Si or EBC–SiC interfaces 40–42 . In addition, high water vapor pressure in industrial gas turbines implies that oxidant transport to the interface may also be governed by water vapor.…”