Damage and structural defects in the surface lager of pure molybdenum induced by high-current pulsed electron beam

High-current pulsed electron beam (HCPEB) technique was applied to induce the surface irradiation of pure molybdenum. Microstructures and damaging effect of the irradiated surface were investigated in detail by X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After 1 pulse of HCPEB irradiation, a high level of residual stress is amassed in the irradiated surface layer, while after several pulses of irradiation, a large number of adiabatic shear bands are formed on the unmelted regions of the surface, and local cracking occurs in these regions. Microstructure observations show that scattered dislocations and large amounts of vacancy clusters are formed on the irradiated surface. The adiabatic shear bands are composed of fine recrystallized grains with an average size about 1 mu m. The partial softening of the irradiated surface induced by adiabatic shear bands, and the segregation of interstitial atoms in grain boundaries are primarily responsible for the surface cracking of the material. Further, nanocrystallines (20 nm) are also formed in some melted regions of the surface.