Formation of low angle boundaries and stray grains in welds of single-crystal Mo-3Nb alloys

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.