Exposure of Equal-Channel Angular Extruded Tungsten to Deuterium Plasma

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/m ² and 1×10 ²⁵ D/m ² 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.