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 Ni-bal-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-2CeO(2) and monocrystalline pure tungsten were brazed to the steel under vacuum at 1150 degreesC, using a 0.5 mm thick foil spacer made of a 50Fe-50Ni alloy. As a result of thermocycling tests (100 cycles between 700 degreesC/20 min and air water cooling/ 3-5 min) on brazed joints, tungsten powder metallurgically processed W-2CeO(2) failed due to residual stresses, whereas the brazed joint with zone-melted monocrystalline tungsten withstood the thermocycling tests. (C) 2004 Elsevier B.V. All rights reserved.