Comparison of the Helium Porosity Parameters in Vanadium Alloy TEM Samples Prepared by Various Techniques

Abstract

The microstructures and the porosity parameters in vanadium alloys irradiated by helium ions are compared after preparing thin films from them for transmission electron microscopy (TEM) by two different techniques. V–1% Ti, V–1% Ta, V–2% Ta, and V–1% Ta–1% W alloy samples are subjected to annealing at 1000°C for 2 h and then to 40-keV helium ion irradiation to a fluence of 5 × 1020 m–2 at a temperature of 650°C. TEM samples are prepared by one-sided electrolytic thinning (ET) on the unirradiated side and by focused ion beam (FIB) cutting normal to the irradiated surface. The microstructures of the foil samples prepared by ET and FIB are shown to be significantly different, which leads to a discrepancy between the calculated porosity parameters and the irradiation-induced swelling. When samples are prepared by ET, the picture substantially depends on the material layer to be fixed, and the layer thickness and position are not controlled. Therefore, the use of ET samples leads increases the error of measuring the porosity parameters, and reproducibility of the results can hardly be reached in this case, which should be taken into account in investigations. Using FIB technique, one can measure the foil thickness in a scanning electron microscope during sample preparation, study the total swelling of the entire irradiated layer, and analyze the distribution of objects over the depth of an irradiated target along ion trajectories.