Ion beam irradiation-induced effects on microstructure and mechanical properties of molybdenum

Molybdenum is used as a plasma-facing component (PFC) in tokamaks, where it is exposed to high-energy neutrons and plasma particles (He and H ions). It is also proposed as a nuclear fuel cladding material for future nuclear reactors. This study examines the effects of copper ion beam with varying doses (0.108, 1.08, and 10.8 dpa) on the microstructure, surface morphology and mechanical properties of molybdenum samples, to emulate the impact of high-energy particle cascade damage. Following exposure to high-energy copper ion beams, changes in microstructure, crystal size, lattice constant, microstrain (%), and surface morphology were observed. Lower ion dose (0.108 dpa) resulted in severe cracking as shown in SEM images, attributed to a high dislocation density because of increased microstrain (%) and decreased crystal size. Features like dents, melt craters, and a rough surface were observed at high ion doses of 1.08 and 10.8 dpa. Initially, crystal size decreased (fragmentation) at low ion doses of 0.108 and slightly increased at ion dose of 1.08 dpa. However, at higher ion doses of 10.8 dpa decrease in crystal size (refinement) and the microstrain (%) was observed. A decrease in lattice constant seems linear with the ion dose, as clear from XRD results, indicating the progressive radiation damage. The change in hardness with increasing dose was nonlinear. Hardness was observed to increase first at lower ion dose (0.108 and 1.08 dpa); however, at higher ion doses of 10.8 dpa, a decrease in hardness is observed due to radiation induced structure recovery/recrystallization effects.