# Presentation: 085827

## Self-Healing EBC Scales on SiC

**k****l**** ******** gas transport model, Opila, et al:**

**Self-Healing EBC Scales on SiC**
**James L. Smialek, QuynhGiao N. Nguyen, R. Craig Robinson**

## Linear Weight Loss of SiC in HPBR

**Linear Weight Loss of SiC in HPBR**
- 6 atm, 20 m/s

## Normalized Recession Rate

**Normalized Recession Rate**
**5-15 atm, 10-30 m/s**

## 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 (TixSiy,TiAl, TiCrAl)  TiO2, Al2O3
- Hot pressed SiC-%TiX composites
- Furnace (air, 50% H2O), HPBR
- Characterization, optimization, kinetic models

## Idealized EBC Scale Schematic

**SiO****2**

**SiC**

**Ti-X precursors:**
**TiC, Ti****x****Si****y****, TiAl**

**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**

## Pertinent Oxidation Background(non-oxide, multiphase ceramics)

- Si3N4–TiN, TiC,...**	****Gogotsi**, Lavrenko, Yaroshenko...
- 				**Bellosi**, Vincenzini, Tampieri...
- 				**Buljan**, Zilberstein...
- ZrC, HfC (-TiC), 	**Shimada**,....
- At 25 wt.% TiN, continuous TiO2 surface scale forms.
- TiO2 nodules are only over individual particle at lower loadings.
- HfTiO4 inner scales develop under TiO2 surface scale.
- Carbon found in scale at carbide interface (titanium oxycarbide?).

## Short Subjects

- 50-50 SiC-TiC furnace data vs T
- 50-50 SiC-TiC, 1330oC HPBR oxidation, scale microstructure
- 50-50, 90-10, 1000oC HPBR weight change
- 50-50 SiC-TiC, 1000oC HPBR microstructure
- TiSi2 furnace oxidation

## Self-Healed TiO2 Scale Formed on SiC-50TiC

## Slide 9

## Slide 10

## 170 kJ/moleoK 

**170 kJ/mole****o****K **

- 200 kJ/moleoK  oxidation of Ti
- 195 kJ/moleoK  oxidation of TiN
- 220 kJ/moleoK  oxygen diffusion in Ti
- 189 kJ/moleoK oxygen diffusion in TiO2
- 455 kJ/moleoK oxidation of Si3N4-Al2O3-TiN

## Unaffected core

**C**

**Si**

**Ti**

**C**

**SiC**
**Dark phase**

**TiC**
**Light phase**

- SiC-50TiC, HPBR,1330oC, 7.5 hr

**(dispersed  porosity)**

## 6kV SiC spectra

**6kV SiC spectra**

**C**

**Si**

**C**

**Si**

**C**

**Si**

**C**

**Si**

## 6kV TiC spectrum

- 1

- 3

**C**

**Ti**

**O**

**6kV TiC spectrum**

## TiO2 External Scale Formed in HPBR SiC-50TiC, 1330oC, 7.5 hr

**TiO****2 ****External Scale Formed in HPBR**** ****SiC-50TiC, 1330****o****C, 7.5 hr**

**Surface facets**

**Cross section**

**20 ********m**

## 6kV TiO2 spectra

**6kV TiO****2 ****spectra**

**15kV**

## C

- 1

- 2

**10 ********m**

**C**

**Ti, O**

**O**

**1) TiO****2**

**Si**

**2) SiO****2**

**immediate **
**subscale**

## Slide 18

## SiC-50TiC, HPBR, 1000oC, 60 hr

**SiC-50TiC, HPBR, 1000****o****C, 60 hr**

**SiO****2****in TiO****2**

**SiC in SiO****2**

## Slide 20

## Preliminary Status Report

- Hot pressed SiC-TiC; oxidized at 1000-1300oC.
- At 25 and 50%, distinct, oversealing TiO2 scales formed.
- Oxidation rates greatly exceeded target; porosity.
- HPBR tests indicate even higher growth rates.
- Faceted, continuous TiO2 surface, mixed TiO2+SiO2 subscale (not effective), then ‘intact’ SiC+TiO2
- (No guarantee of moisture resistance)