Mo–3Nb single crystal is an important material used for processing the emitter of space thermionic reactor. The present research focuses on the microstructures of precipitated phases in the Mo–3Nb matrix and the joint welded by the vacuum electron beam, to reveal the microstructural transformation during the welding process. Characterization of the precipitates was conducted by transmission electron microscopy (TEM) with energy dispersive spectrum (EDS). The results show that the precipitated phases in the Mo single crystal matrix and the welds were all NbC of a crystalline cubic with space group: Fm-3m (225). After the welding, the morphology of NbC changed significantly, from a polygonal shape with a diameter of 100–200 nm to a thin rod with a length of 10–50 nm. High-temperature solution-quenching treatment on single crystal rods is suggested to further improve performance.

Mo–3Nb单晶是用于处理空间热电子反应器发射极的重要材料。本研究集中于Mo-3Nb基体和真空电子束焊接接头的析出相的微观结构，以揭示焊接过程中的显微组织转变。通过具有能量色散谱（EDS）的透射电子显微镜（TEM）对沉淀物进行表征。结果表明，Mo单晶基体和焊缝中的析出相均为NbC立方晶，空间群为Fm-3m（225）。焊接后，NbC的形态发生了显着变化，从直径为100–200 nm的多边形到长度为10–50 nm的细棒。