Effect of initial exposure temperature on the deuterium retention and surface blistering in tungsten

Abstract

• Exposure temperature in the initial stage strongly affects the subsequent deuterium behavior in tungsten. • Initial exposure at 420 K significantly inhibits the formation of intergranular blisters and leads to a reduction in the size of intragranular blisters. • Initial exposure at a relatively high temperature of 600 K leads to a reduction in the size of intergranular blisters and reduces deuterium retention by ∼ 34 %. • The gradient distribution of deuterium over a larger depth leads to the intergranular cracks more prone to propagate along sloping grain boundaries. Temperature is one of the critical factors that strongly affect the behavior of hydrogen isotopes in tungsten (W). This work investigates the effect of initial exposure temperature on the deuterium (D) retention and surface blistering in recrystallized W. D plasma exposure is started at 420 K and 600 K, respectively, and then changed to the same temperature of 520 K. For each temperature, the irradiation fluence is ∼ 1 × 10 26 D m −2 , and therefore the total fluence is ∼ 2 × 10 26 D m −2 for each sample. A reference W sample was also exposed at 520 K with the same total fluence. Compared with the reference sample, it is found that the initial temperature of 420 K significantly inhibits the formation of intergranular blisters and leads to a reduction of intragranular blisters in size. Although the initial temperature of 600 K facilitates the formation of intergranular blisters, the intergranular blister size is reduced. This is possibly related to the relatively higher concentration of trapped D over a large depth range as revealed by the TMAP simulation results, leading to the fact that intergranular cracks are more prone to propagate along sloping grain boundaries. Thermal desorption spectra results show that the initial exposure temperature of 420 K and 600 K reduce D retention by a factor of ∼ 56 % and ∼ 34 %, respectively. It is considered to be connected with the blistering-induced defects and D transport in W, which are strongly affected by the initial exposure temperature. This work demonstrates that the initial exposure temperature plays a crucial role in D behavior in W, improving the understanding of the temperature effects of hydrogen isotopes behavior in W.