Study on joining of single crystals of refratory metal by using brazing material with high melting-point

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1.Brazing of single-crystalline molybdenum by using Mo-40%Ru alloyPreparation of sheets of Mo-40%Ru or Mo-40%Ru-B alloys by powder metallurgy was not successful. Then brazing of single-crystalline molybdenum was performed by using mixture of powders and organic solvent. The joint strength gradually increased by adding boron as small as 2%, and was as high as that of the bulk Mo crystal. Additonally the joint was "full-bended" until a bend angle of 100ﾟand was not failed at room temperature. This result reggests the toughness of Mo-40%Ru alloy was substantially improved by a small addition of boron.2. Brazing between single-crystalline molybdenum and carbon-ceramicsBy using palladium, platinum or zirconium, the brazed joint between single-crystalline molybdenum and carbon-ceramics demonstrated a strength as high as 100MPa. Investigation by EPMA suggested the joint strength depends on both composition and pores particularly near the surface.3. Degradation of the joint strength in a simulated atmosphereThe brazed joints mentioned above should be used in a relatively high-temperature circumstance for a prolonged period. Thereby the specimen was kept in a vacuum at high temperature and the change of structure, composition and strength of the brazed joint was examined. The brazed joints by using Mo-40%Ru-1%B alloy demonstrated a ductility, though small, and a higher strength than that by using Mo-40%Ru alloy. The brazed joint between single-crystalline molybdenum and carbon-ceramics by using palladium or platinum demonstrated approximately a half of the original strength after heat treatment.