Crater formation on the surface of titanium irradiated by a high-intensity pulsed ion beam

Surface morphology and roughness of pure Ti irradiated by a high-intensity pulsed ion beam (HIPIB) have been investigated by using scanning electronic microscopy and profilometry in order to explore the interaction mechanism between HIPIB and metallic materials. Two groups of Ti samples of different initial surface roughness (Ra) were prepared to determine the effect of original surface states on the crater formation as a result of HIPIB irradiation. Particularly, the cratering behavior under various irradiation intensities was clarified by examining large Ti samples of high initial roughness with Ra of 0.18 μm. It is noted that no obvious cratering took place on Ti of low initial roughness. For high-roughness Ti, the Ra significantly increased from an initial value of 0.18 μm to the maximal 0.43 μm at 250 A/cm2 with 1 shot, and then decreased continuously to a final 0.06 μm with 30 shots presenting a planar ablated surface. The similar trend for Ra was also found for the low-roughness Ti, but the maximal value was limited to 0.18 μm from the initial 0.07 μm. The micro non-uniformity of the original surfaces resulted in the cratering on pure Ti by inducing a selective ablation and disturbance of the molten surfaces under HIPIB irradiation. A more uniform ablated Ti surface without crater formation was obtained by multi-shot irradiation due to the gradually decreased non-uniformity at the repetitive ablation.