1. Plasma Arc Lamp Operation

2. Properties of the Plasma Radiant Source
Maximum lamp power: 35 MW/m2
Non-contact heating
Rapid heating and cooling
Concentration of heating on surface
Environment: argon, vacuum, air
Three separate plasma heads: 10, 20 and 35 cm arcs
Power delivery: flash mode or scan mode as wide as 35 cm, presently
Lamp power: form 2% to 100% of available radiant output
Change of power levels: less than 20 ms
Wavelength of radiant output: µm
Wavelength: constant and independent of power level and anode/cathode wear

3. Brush or spray powder (W or Mo)
Coating Procedure
SiC (Hexoloy SA)
Plasma Arc Lamp
Flash or scan
Pretreatment*
Brush or spray powder (W or Mo)
W or Mo powder
IR processing
Vapor deposited W or Mo
Anneal
*Pretreatment:
Ti vapor deposition W or Mo vapor deposition
Anneal 72 hours (1300 or 1500ºC)
Vapor deposited Ti
SiC
Specimen size: 25×15×3 (mm)
IR processing: uniform irradiance or scan

4. Effect of IR Processing on Surface Roughness
SiC without coating
IR processing
OM images
W coating
Interface
SiC
10µm
SiC was removed by sublimation of the surface of the SiC prior to ordering the W powder melt. Rough interface was formed.

5. Effect of Scan Speed on Coating Surface
IRHW31
IRHW32
IRHW30
IRHW27
Melted W
Melted W
Melted W
Melted W
Crack
Non-melted W
Non-melted W
Scan speed: mm/sec
10.5 mm/sec
10.0 mm/sec
5.0 mm/sec
5mm
Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2
Melting point of tungsten: 3370 ºC

6. Effect of Scan Speed on Coating Microstructure
IRHW31
Melted W
W coating
Non-melted W
5mm
Scan speed: mm/sec
SiC
Cross sectional SEM image in middle region
Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

7. Effect of Scan Speed on Coating Microstructure
IRHW32
Melted W
W coating
Non-melted W
5mm
Scan speed: mm/sec
SiC
Cross sectional SEM image in middle region
Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

8. Effect of Scan Speed on Coating Microstructure
IRHW30
W coating
Melted W
5mm
Scan speed: 10 mm/sec
SiC
Cross sectional SEM image in middle region
Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

9. Relationship between Lamp Power and Maximum Scan Speed to Melt Coating

10. SEM Images of W Coating Processed at 23.5 MW/m2
No thick reaction interlayer
WC grains adjacent to interface
Strong interface
SiC
Lamp power: 2350 W/cm2, 10 mm/sec scan
Back scattering SEM images

11. SEM Images of W Coating Processed at 18.28 MW/m2
SiC
Lamp power: 2350 W/cm2, 10 mm/sec scan
No thick reaction interlayer
WC grains adjacent to interface
Strong interface
Eutectic structure
W+C
Back scattering electron images

12. Effect of Processing Condition on Flexural Strength of W Coated SiC
Substrate strength
W coating side
Four point flexural test
Specimen size: 50x4x3 mm
Support span: 40 mm
Loading span: 20 mm
Crosshead speed: 10um/sec
W coating was not peeled off during flexural test
Strength of substrate SiC was decreased by IR processing
Vapor deposition prior to powder coating prevented degradation of strength slightly

13. EDS Mapping of W Coating (Higher Power, Slower Scan)
SiC
W+Si
Back scattering electron image
10µm Si
Hexoloy SiC + W (no pretreatment)
Lamp power: 2350 W/cm2
Scan speed: 9mm/sec
EDS mapping of W, C, Si

14. Effect of Vapor Deposited W and Pre-heating on Crack Propagation into SiC
W coating
SiC
2350W/cm2(3sec)
VD W+2350W/cm2(3sec)
522W/cm2(20sec)+2350W/cm2(3sec)
10µm
Vapor deposition of W and pre-heating significantly reduced cracks within the SiC.

15. SEM Images of W coating Formed by Uniform Irradiance
With pre-heating 522W/cm2 (20sec) W/cm2 (3sec)
Si+W
SiC
W coating
W+C
SiC
Back scattering (composition) electron image
SiC and WxSiy grains which were not seen a coating by scanning method, were seen.

16. Thermal Fatigue Experiment Using IR Processing Facility
W coated specimen
Cooling table
Rep rate: 10Hz
Max. flux: 23.5MW/m2 (10ms)
Min. flux: 5.9MW/m2(90ms)
Substrate temp. (bottom): 600 ºC
Substrate material: silicon carbide
Coating material: tungsten (50µm-thick)
Specimen size: 50 x 4 x 3 (mm)

17. Effect of Thermal Fatigue on Tungsten Coating
Before experiment
Tungsten coating was not peeled off following 1000 cycle thermal fatigue experiments
After 1000 cycles
Rep rate: 10Hz
Max. flux: 23.5MW/m2 (10ms)
Min. flux: 5.9MW/m2(90ms)
Cycle: 1000
Substrate temp. (bottom): 600 ºC

18. Summary of IR processing
Silicon carbide was removed by sublimation of the surface of the SiC prior to ordering the W powder melt. Rough interface was formed.
It was found that less reaction time made W coating porous and too much reaction time break SiC. The scan speed and processing time were optimized for each lamp power.
The WxCy grains were formed near interface within W coating in all specimens. Many round WxCy grains and eutectic structure were found in the coating formed at lower power and slower scan speed, while those were not found in the coating formed at higher power and faster scan speed.
In uniform irradiance, SiC was broken easily by IR processing. It was found that vapor deposition of W and pre-heating significantly reduced cracks within the SiC. The scanning processing also reduced the cracks within SiC, since it includes pre-heating.
Not only W grains adjacent to interface SiC and WxSiy grains were observed within W coating.

19. Summary of Thermal Fatigue Experiment
Thermal fatigue experiments were carried out successfully using IR processing facility. Preliminary results showed tungsten coating was stable following the heat load (10Hz, 23.5MW/m2 (10ms), 1000cycles).