Plasma Arc Lamp Operation

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: 0.2-1.4 µm Wavelength: constant and independent of power level and anode/cathode wear

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

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.

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: 11.0 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

Effect of Scan Speed on Coating Microstructure IRHW31 Melted W W coating Non-melted W 5mm Scan speed: 11.0 mm/sec SiC Cross sectional SEM image in middle region Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

Effect of Scan Speed on Coating Microstructure IRHW32 Melted W W coating Non-melted W 5mm Scan speed: 10.5 mm/sec SiC Cross sectional SEM image in middle region Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

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

Relationship between Lamp Power and Maximum Scan Speed to Melt Coating

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

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

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

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

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.

SEM Images of W coating Formed by Uniform Irradiance With pre-heating 522W/cm2 (20sec) + 2350W/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.

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)

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

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.

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).