1. Glenn Research Center Materials Division Protective SiO 2 scales react in hot gas environment, form volatile Si(OH) 4, give paralinear (recession) kinetics. k l  gas transport model, Opila, et al: Self-Healing EBC Scales on SiC James L. Smialek, QuynhGiao N. Nguyen, R. Craig Robinson

2. Glenn Research Center Materials Division Linear Weight Loss of SiC in HPBR 6 atm, 20 m/s

3. Glenn Research Center Materials Division Normalized Recession Rate 5-15 atm, 10-30 m/s

4. Glenn Research Center Materials Division Present Solution: Plasma sprayed EBC oxides 4. BSAS topcoat (barium strontium alumino-silicate) ----------------------------------------------------------------------------- 3. Mullite + BSAS intermediate layer (furnace sprayed) ----------------------------------------------------------------------------- 2. Si bondcoat ----------------------------------------------------------------------------- 1. Molten salt etched, washed, and dried CMC surface Alternate approach: EBC scales formed on additives TiC (Ti x Si y,TiAl, TiCrAl)  TiO 2, Al 2 O 3 Hot pressed SiC-%TiX composites Furnace (air, 50% H 2 O), HPBR Characterization, optimization, kinetic models

5. Glenn Research Center Materials Division SiO 2 SiC Ti-X precursors: TiC, Ti x Si y, TiAl Idealized EBC Scale Schematic critical k p  2  m 2 /hr for healing (100hr @ 10v/o, 10  m radius) Self-healing scales TiO 2 (Al 2 O 3 ) k p = 10 5 (10 2 ) SiO 2 k p

6. Glenn Research Center Materials Division Pertinent Oxidation Background (non-oxide, multiphase ceramics) Si 3 N 4 –TiN, TiC,…Gogotsi, Lavrenko, Yaroshenko… Bellosi, Vincenzini, Tampieri… Buljan, Zilberstein… ZrC, HfC (-TiC), Shimada,.... –At 25 wt.% TiN, continuous TiO 2 surface scale forms. –TiO 2 nodules are only over individual particle at lower loadings. –HfTiO 4 inner scales develop under TiO 2 surface scale. –Carbon found in scale at carbide interface (titanium oxycarbide?).

7. Glenn Research Center Materials Division Short Subjects 50-50 SiC-TiC furnace data vs T 50-50 SiC-TiC, 1330 o C HPBR oxidation, scale microstructure 50-50, 90-10, 1000 o C HPBR weight change 50-50 SiC-TiC, 1000 o C HPBR microstructure TiSi 2 furnace oxidation

8. Glenn Research Center Materials Division Self-Healed TiO 2 Scale Formed on SiC-50TiC As-polished SiC-TiCAfter 500 hr oxidation at 1000 o C 25x

9. Glenn Research Center Materials Division

11. 170 kJ/mole o K 200 kJ/mole o K oxidation of Ti 195 kJ/mole o K oxidation of TiN 220 kJ/mole o K oxygen diffusion in Ti 189 kJ/mole o K oxygen diffusion in TiO 2 455 kJ/mole o K oxidation of Si 3 N 4 -Al 2 O 3 -TiN

12. Glenn Research Center Materials Division C Si Ti C SiC Dark phase TiC Light phase Unaffected core SiC-50TiC, HPBR,1330 o C, 7.5 hr (dispersed porosity)

13. Glenn Research Center Materials Division 6kV SiC spectra C Si C C C

14. Glenn Research Center Materials Division 1 3 C Ti O 6kV TiC spectrum

15. Glenn Research Center Materials Division C Ti, O 100  m TiO 2 External Scale Formed in HPBR SiC-50TiC, 1330 o C, 7.5 hr Surface facets Cross section 20  m

16. Glenn Research Center Materials Division C Ti O C Ti, O Si Ti, k  6kV TiO 2 spectra 15kV

17. Glenn Research Center Materials Division 1 2 10  m C Ti, O O 1) TiO 2 Si 2) SiO 2 immediate subscale

18. Glenn Research Center Materials Division

19. SiC-50TiC, HPBR, 1000 o C, 60 hr 10  m SiO 2 in TiO 2 SiC in SiO 2 10  m 100  m

20. Glenn Research Center Materials Division

21. Preliminary Status Report Hot pressed SiC-TiC; oxidized at 1000-1300 o C. At 25 and 50%, distinct, oversealing TiO 2 scales formed. Oxidation rates greatly exceeded target; porosity. HPBR tests indicate even higher growth rates. Faceted, continuous TiO 2 surface, mixed TiO 2 +SiO 2 subscale (not effective), then ‘intact’ SiC+TiO 2 (No guarantee of moisture resistance)