Crater formation on the surface of metals and alloys bombarded with high-power ion beams: the effect of a preliminary treatment of the surface

Auger electron spectroscopy, scanning electron microscopy and optical microscopy in a polarized light were used to study the physico-chemical state of the surface of refractory titanium alloys (VT25U, VT8M, VT9 and VT33) and steels (EP866sh and EP718ID) subjected to various mechanical and chemical treatments, a continuous and pulsed implantation followed by exposure to a 300 keV nanosecond beam of carbon ions (70%) and protons (30%) at two ion current densities 60-80 and 120-140 A/cm² in a pulse. It is shown that pretreatment of materials can drastically change the number, size and surface distribution of radiation-induced craters. The possible mechanisms for crater formation are discussed. The most likely explanation for the craters caused by a high-power ion beam irradiation is screening of some surface regions at the initial stage of the pulse action as a result of the formation of a heterogeneous vapor-plasma cloud of volatile substances (primarily hydrocarbons) adsorbed at the surface.