Surface modification and deuterium retention of tungsten and tungsten-rhenium alloys exposed to deuterium plasma

Abstract

• Pure W and W-Re alloys with Re concentration of 1, 3, 5 and 10 wt% were exposed to D plasma to various D fluences. • The fluence dependence of surface modifications was observed. • Blistering behaviour of W-Re alloys was analysed by EBSD and FIB&SEM. • The D retention in both types of materials was examined by TDS. Surface modification and deuterium (D) retention in pure tungsten (W) and tungsten-rhenium (W-Re) alloys with Re concentration of 1, 3, 5 and 10 wt.% were investigated after exposure to D plasma with an incident energy of 38 eV/D at about 400 K and various fluences ranging from 7.2 × 10 23 to 2.6 × 10 25 D/m 2 . It is found that blistering depends strongly on the exposure fluence for both W and W-Re alloy samples. When the D fluence is higher than 2.8 × 10 24 D/m 2 , the surface of W is covered by two types of blisters. One type is small blisters (<2 μm), which appeared in groups only on grains with surface orientation close to (1 1 1). The other type is large-sized (>8 μm) and extents over several grains. In the cases of W-Re alloys, only small blisters can be observed on their surface. The blisters on the surface of W-Re alloys preferentially appeared on grains with surface orientation close to (1 1 1). Cross-section views of blisters show that the blisters on W-Re alloys always originate from intra-granular cavities. The small and large blisters on W originate from intra- and inter-granular cavities, respectively. The surface blistering fluence threshold for W-Re alloys is lower than for W. For both types of materials, rupture of blisters occurs if the underlying crack reaches the surface at the edge of a blister. The number of ruptured blisters increases with increasing D fluence. TDS results show that there is an additional high-temperature peak at ∼ 800 K in W-Re alloys. The amount of D released from W and W-Re alloys increases with increasing D fluence. In addition, the accumulation of D in W-Re alloys is not noticeably influenced by the amount of Re doping at the exposure temperature of ∼ 400 K.