ABSTRACT Mo-3Nb single-crystal alloy is an ideal material for emitters of thermionic fuel elements. In this experiment, heat-affected zone of electron beam welding of Mo-3Nb single-crystal tubes was investigated, and it was discovered that heat-affected zone basically inherited the orientation of parent metal while there were still plenty of low angle boundaries and a few stray grains (SGs). Those low angle boundaries (LABs) stemmed from the fusion line and converged toward the centreline. Besides, the distribution of LABs was asymmetrical about the centreline of welding pool, and Laue diffraction pattern showed that the side with more LABs had higher dislocation density than the other. Furthermore, SGs existed merely at the bottom of welding pool and were discontinuously distributed along the circumferential direction of single-crystal tube.

中文翻译：

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单晶Mo-3Nb合金焊缝中小角晶界和杂散晶粒的形成

摘要 Mo-3Nb 单晶合金是一种理想的热离子燃料元件发射体材料。本实验对Mo-3Nb单晶管电子束焊接热影响区进行了研究，发现热影响区基本继承了母材的取向，但仍有大量的低角边界和很少有杂散颗粒 (SG)。这些低角度边界 (LAB) 源于融合线并会聚到中心线。此外，LABs的分布关于熔池中心线是不对称的，劳厄衍射图表明LABs较多的一侧的位错密度高于另一侧。此外，SGs仅存在于熔池底部，沿单晶管圆周方向不连续分布。