Exposure of Equal-Channel Angular Extruded Tungsten to Deuterium Plasma**supported by the National Magnetic Confinement Fusion Science Program of China (Nos. 2013GB105001, 2013GB105002, 2015GB109001), National Natural Science Foundation of China (Nos. 11305213, 11405201), Technological Development Grant of Hefei Science Center of CAS (No. 2014TDG-HSC003), and China National Funds for Distinguished Young Scientists (No. 51325103)

Abstract

Surface morphology and deuterium retention in ultrafine-grained tungsten fabricated by equal-channel angular pressing (ECAP) have been examined after exposure to a low energy, high-flux deuterium (D) plasma at fluences of 3×1024 D/m2 and 1×1025 D/m2 in a temperature range of 100°C-150°C. The methods used were scanning electron microscopy (SEM) and thermal desorption spectroscopy (TDS). Sparse and small blisters (∼0.1 μm) were observed by SEM after D plasma irradiation on every irradiated surface; yet they did not exhibit significant structure or plasma fluence dependence. Larger blisters or protrusions appeared after subsequent TDS heating up to 1000°C. The TDS results showed a single D desorption peak at ∼220°C for all samples and the D retention increased with increasing numbers of extrusion passes, i.e., the decrease of grain sizes. The increased D retention in this low temperature range should be attributed to the faster diffusion of D along the larger volume fraction of grain boundaries introduced by ECAP.