A possible thermodynamic mechanism of craters formation on metal surfaces caused by intense pulsed ion beams

It was found that some craters appeared on the irradiated surfaces that have been melted under intense pulsed ion beam (IPIB) irradiation. These craters with various sizes and morphologies limit the utilization of IPIB as a novel means of surface processing in some cases. In this work we examined surfaces of 45^# steel and Ni₃Al samples irradiated with IPIB at different beam parameters with scanning electronic microscopy (SEM) and energy dispersive spectrometry (EDS), and found that the craters basically can be sorted into two groups. The first kind of craters directly relates to droplet from the ion source, and the other kind of craters is due to the non-equilibrium process of ultra fast quenching. According to the dynamic theory of interaction between ions and materials and the thermodynamic theory about defects, a possible forming mechanisms for the second kind of craters is proposed in this paper. The vacancy densities produced in IPIB irradiation at various pulse parameters are calculated. Moreover, the process of cratering is analyzed in detail, and the variety of the crater morphologies is discussed.