Influence of Surface State on the Crater Formation of Metallic Material Surface Irradiated by High Current Pulsed Electron Beam

In order to investigate the influence of crystallographic properties of materials on the formation mechanism of surface craters, high current pulsed electron beam (HCPEB) was used to irradiate a 304 austenitic stainless steel with and without shot peening treatment. The morphologies of surface crater induced by HCPEB were characterized in detail. The experimental results indicate that a large number of volcano-like craters are inevitably formed on the surface sample after HCPEB irradiation. The number density and dimension of craters decrease with the increase in electron beam energy. It is found that inclusions on the surface layer easily become the new nucleation sites of craters; however, they are gradually removed during the period of eruption in the formation of the crater, and showing a surface purification effect. Additionally, it is established that the number density of craters on shot peening samples is significantly increased than untreated ones. The number densities of craters on the samples with and without shot peening treatment follow the similar law. The present results indicate that the crystallographic properties of materials have a great importance to the formation of surface craters, and the structure defects, such as grain boundaries and dislocations are the preferred sites of the nucleation of craters.