Development of rapidly quenched brazing foils to join tungsten alloys with ferritic steel

Results on rapidly solidified filler metals for tungsten brazing are presented. A rapidly quenched foil-type filler metal based on Nibal–15Cr–4Mo–4Fe–(0.5–1.0)V–7.5Si–1.5B was developed to braze tungsten to ferritic/martensitic Crl3Mo2NbVB steel (FS) for helium gas cooled divertors and plasma facing components. Polycrystalline W–2CeO2 and monocrystalline pure tungsten were brazed to the steel under vacuum at 1150 °C, using a 0.5 mm thick foil spacer made of a 50Fe–50Ni alloy. As a result of thermocycling tests (100 cycles between 700 °C/20 min and air–water cooling/3–5 min) on brazed joints, tungsten powder metallurgically processed W–2CeO2 failed due to residual stresses, whereas the brazed joint with zone-melted monocrystalline tungsten withstood the thermocycling tests.