Evolution And Computer Simulation Of Microstructure Of Mo Single Crystal Weld

Space nuclear reactor power systems have become the preferred choice for space exploration due to their long service life,compact structure and high power and so on.The Mo-3Nb alloy single crystal is the component of fuel element of the space nuclear reactor,and the service life of the reactor is determined by its performance.Thus,the weld of Mo-3Nb alloy single crystal material has become a key scientific technology for space thermal ion reactor power system in space exploration applications,which helps to avoid the generation of grain boundaries in the weld zone and improve the service life of fuel components.In this paper,the mechanical properties test,microstructure observation and computer simulation of Mo-3Nb alloy single crystal welds are carried out.The research can be divided into three parts.First,the load-displacement curve was obtained in the electronic universal testing machine by the small punch test device and the yield strength of specimen was calculated by double tangent method.The fractures were observed by scanning electron microscopy to determine the type of fractures.The hardness of the weld and the matrix specimen was tested using the micro-hardness tester.Second,the precipitated phase in the sample was observed using a transmission electron microscope or the like,and the composition of the precipitated phase was examined by EDS,and the change of the precipitated phase of the material before and after the welding was studied.Third,computer simulation of the weld zone was achieved programming on the mat lab software platform by using the cellular automata.The test results show that the hardness of the material of Mo-3Nb single crystal material is basically unchanged before and after welding.The yield strength of the weld zone material is lower than that of the base material,which is about 85%of the yield strength of the matrix material.The fracture displacement is smaller and the brittleness of the weld material increases.By observing the Mo-3Nb alloy single crystal specimen,it is found that the material has round-shape precipitate phase.The shape of precipitated phase became a long rod after weld under TEM,and there was no significant change in the composition of the precipitated phase before and after the welding.Through the computer microstructure simulation,the mechanism of the competitive growth of the weld grain and the growth process of formation of the grain boundary are visualized,which contributes to the analysis and improvement of the welding process and improves the service life of the Mo-3Nb alloy single crystal.