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

1.用Mo-40%Ru合金钎焊单晶钼用粉末冶金法制备Mo-40%Ru或Mo-40%Ru-B合金板材是不成功的。然后用粉末和有机溶剂的混合物对单晶钼进行了钎焊。加入2%的硼后，接头强度逐渐提高，达到了块体钼的强度水平。此外，关节被“完全弯曲”，直到弯曲角度为100ﾟ，并且在室温下没有失效。这一结果表明，添加少量的硼可以显著提高Mo-40%Ru合金的韧性。单晶钼与碳陶瓷之间的钎焊用钯、铂或锆，单晶钼与碳陶瓷之间的钎焊接头的强度高达100 Mpa。EPMA研究表明，接头强度取决于成分和气孔，尤其是表面附近的气孔。焊接接头强度在模拟环境中的退化上述钎焊接头应在较高温度的环境中长期使用。将试件置于真空高温保存，观察焊点的组织、成分和强度的变化。使用Mo-40%Ru-1%B合金的焊接接头虽然塑性较小，但比使用Mo-40%Ru合金的接头具有更高的强度。单晶钼与碳瓷的钯或铂钎焊接头经热处理后强度约为原始强度的一半。

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.