Microstructural evolution in the vicinity of Mo–W interfaces after long-term high-temperature exposure

Molybdenum–tungsten single-crystal system is a key component in thermionic energy converters which transform heat directly into electrical energy. In this paper, the thermal stability of the molybdenum–tungsten single-crystal system was studied after exposure at 1873 K for 5000 h. The microstructure was investigated by the coupling of scanning X-ray Laue diffraction and electron microscopy techniques. After thermal exposure, the interface between the tungsten layer and molybdenum substrate was transformed into a wavy morphology. Moreover, recrystallization phenomenon was only observed in the tungsten layer. The large difference in diffusivity between tungsten and molybdenum caused the formation of wavy interface. The recrystallization processing in the tungsten layer was related to the internal stress generated during the high-temperature exposure. This study is instructive for the lifetime prediction and developing next-generation tungsten emitters for the thermionic energy converter application.