Mechanical properties of proton bombarded SS316L thin foils using the small punch technique

Abstract

The mechanical properties of thin foils (∼25 μm), to be used as a target’s window in a high intensity accelerator, require non-standard characterization techniques. In the current research, the innovative small punch test technique (SPT) had been used to map and determine the mechanical properties of SS 316L foil irradiated by high intensity of proton beams. The SPT results and the energy to fracture are presented and the fracture modes were determined by scanning electron microscopy (SEM) observations and electron backscatter diffraction (EBSD) analysis. The irradiated samples were exposed to 3.6 MeV proton bombardment at 250 μA and 290 μA, for 42 and 5 h, respectively. The major damage, as was reflected by significant ductility and energy to fracture losses, was associated with the irradiated zones which experienced the highest temperature and protons flux. Based on the observed evidence of deformation twins and dense dislocation bands, as well as the EBSD analysis, it was revealed that the limited deformation in the irradiated samples is related mainly to radiation damage and probably a minor effect of hydrogen embrittlement phenomenon. The limited ductility was explained by the accumulation of radiation damage that most probably hinder dislocations mobility through crystallographic glide. Nevertheless, these alternative deformation mechanisms involve nucleation and propagation of dislocation slip bands (DSBs) and intra-grain fragmentation. The DSBs intersections were proposed as the source for stress localization, which initiates crack formation which was followed by crack propagation through slip bands. This cracking mechanism was exhibited by a unique “saw tooth” fracture mode.