Uncovering the weakening mechanism of electron beam welded joints of La2O3 dispersion strengthened molybdenum alloy: Experiment and simulation

Electron beam welding of La2O3 dispersion strengthened molybdenum alloy is carried out in this experiment. Optical microscopy (OM) and scanning electron microscope (SEM) were used to study the microstructure of the joint. Microhardness tests and tensile tests were conducted to evaluate the mechanical properties of the joint. Results show that coarse columnar grains are generated in the weld owing to the absence of the La2O3 strengthening phase. The joint is softened with a mean hardness of 200 HV, lower than 250HV of the base metal. Micro cracks in some grain boundary regions are detected with MoO2 phase. High residual stress is accumulated in the weld region. Both the generation of the MoO2 phase and the high stress promotes the weakening of the joint. The strength of the joint is only 54 MPa.