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

Coating Procedure

SiC (Hexoloy SA)

Pretreatment*

Brush or spray powder (W or Mo)

IR processing

SiC

*Pretreatment: Ti vapor deposition W or Mo vapor deposition Anneal 72 hours (1300 or 1500ºC)

Vapor deposited Ti

Vapor deposited W or Mo

Anneal

Plasma Arc

Lamp

Specimen size: 25×15×3 (mm)IR processing: uniform irradiance or scan

Flash orscan

W or Mo powder

Effect of IR Processing on Surface Roughness

SiC without coating

SiC

W coating

IR processing

10µm

Interface

OM images

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

Melted W

Non-melted W

Melted W

Non-melted W

Melted W Melted W

Scan speed: 11.0 mm/sec

10.5 mm/sec 10.0 mm/sec 5.0 mm/sec5mm

IRHW31 IRHW32 IRHW30 IRHW27

Crack

Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

Melting point of tungsten: 3370 ºC

Effect of Scan Speed on Coating Microstructure

Melted W

Non-melted W

Scan speed: 11.0 mm/sec

5mm

IRHW31

Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

Cross sectional SEM image in middle region

SiC

W coating

Effect of Scan Speed on Coating Microstructure

Melted W

Non-melted W

Scan speed: 10.5 mm/sec

5mm

IRHW32

Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

SiC

W coating

Cross sectional SEM image in middle region

Effect of Scan Speed on Coating Microstructure

Melted W

5mm

IRHW30

Hexoloy SiC + W (no pretreatment), Lamp power: 23.5 MW/m2

Scan speed: 10 mm/sec SiC

W coating

Cross sectional SEM image in middle region

Relationship between Lamp Power and Maximum Scan Speed to Melt Coating

1300

1500

1700

1900

2100

2300

2500

3 5 7 9 11 13 15Maximum scan speed to melt (mm/sec)

Lamp power (W/cm

2)

W coatingMo coating

SEM Images of W Coating Processed at 23.5 MW/m2

Lamp power: 2350 W/cm2, 10 mm/sec scan

•No thick reaction interlayer•WC grains adjacent to interface•Strong interface

Back scattering SEM images

W coating

SiC

W+C

SEM Images of W Coating Processed at 18.28 MW/m2

Lamp power: 2350 W/cm2, 10 mm/sec scan

Back scattering electron images

W coating

SiC

W+C

W+C

•No thick reaction interlayer•WC grains adjacent to interface•Strong interface•Eutectic structure

100

150

200

250

3 5 7 9 11Scan speed (mm/sec)

Flexural strength (MPa)

Without VDWith VD

Effect of Processing Condition onFlexural Strength of W Coated SiC

W coating side

Four point flexural testSpecimen size: 50x4x3 mmSupport span: 40 mmLoading span: 20 mmCrosshead speed: 10um/sec

Substrate strength

W coating was not peeled off during flexural testStrength of substrate SiC was decreased by IR processingVapor deposition prior to powder coating prevented degradation of strength slightly

EDS Mapping of W Coating (Higher Power, Slower Scan)

SiC

Wcoating

W

C

SiBack scattering electron image

EDS mappingof W, C, Si

W+C W+Si

Hexoloy SiC + W (no pretreatment)Lamp power: 2350 W/cm2

Scan speed: 9mm/sec

10µm

Effect of Vapor Deposited W and Pre-heating

on Crack Propagation into SiC

10µm

SiC

W coating

2350W/cm2(3sec)

522W/cm2(20sec)+2350W/cm2(3sec)

VD W+2350W/cm2(3sec)

Vapor deposition of W and pre-heating significantly reduced cracks within the SiC.

SEM Images of W coating Formed by Uniform Irradiance

Back scattering (composition) electron image

With pre-heating 522W/cm2 (20sec) + 2350W/cm2 (3sec)

SiC

W coating

W+C

SiCSi+W

SiC and WxSiy grains which were not seen a coating by scanning method, were seen.

Thermal Fatigue Experiment Using IR Processing Facility

0

5

10

15

20

25

-200 0 200 400 600 800 1000Time (ms)

Heat flux (MW/m

2)

Rep rate: 10HzMax. flux: 23.5MW/m2 (10ms)Min. flux: 5.9MW/m2(90ms)Substrate temp. (bottom): 600 ºCSubstrate material: silicon carbide

Coating material: tungsten (50µm-thick)Specimen size: 50 x 4 x 3 (mm)

W coated specimen

Cooling table

Effect of Thermal Fatigue on Tungsten Coating

Before experiment

After 1000 cycles

Tungsten coating was not peeled off following 1000 cycle thermal fatigue experiments

Rep rate: 10HzMax. flux: 23.5MW/m2 (10ms)Min. flux: 5.9MW/m2(90ms)Cycle: 1000Substrate 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).