The Effect of Pre-irradiation on Deuterium Retention and Desorption Behavior in Tungsten and Tungsten Alloys

[Background] Tungsten (W) and tungsten alloys, such as 97W-2Ni-1Fe, are critical materials for nuclear fusion reactors due to their excellent thermal conductivity and high melting point. However, the performance of these materials can be significantly affected by irradiation-induced defects and deuterium (D) retention, which is crucial for maintaining material integrity and minimizing fuel retention in fusion environments. [Purpose] This study aims to investigate the influence of pre-irradiation defects on deuterium retention and desorption behavior in tungsten (W) and tungsten-nickel-iron (W-Ni-Fe) alloys. [Methods] Pure W and 97W-2Ni-1Fe alloy samples were irradiated with Fe13+ ions at doses of 5 × 10¹⁴ Fe/cm² and 3 × 10¹⁵ Fe/cm² using the heavy ion accelerator at Lanzhou University. Subsequently, D plasma irradiation was performed at Hefei University of Technology for 1 hour at a constant plasma flow of 4 × 10¹⁶ D/cm² with 50 eV. The D retention and desorption behaviors were studied using Thermal desorption Spectroscopy (TDS), Doppler-broadening Spectroscopy (DBS) of Positron Annihilation, Transmission Electron Microscopy (TEM), and Scanning Electron Microscopy (SEM). SRIM simulations were also conducted to model the defect and D atom distributions in the materials. [Results] Fe13+ ion irradiation induced significant vacancy-type defects in both materials, with higher defect concentrations in pure W compared to the alloy. D retention was observed to be higher in pure W, with desorption occurring at approximately 250°C and 700°C. In contrast, the 97W-2Ni-1Fe alloy showed reduced D retention, with desorption peaks at 200°C and 700°C. The TDS results revealed that pure W retained 2-3 times more D than the alloy. Pre-irradiation with Fe13+ ions further enhanced D retention, especially in pure W, where more D bubbles formed. TEM analysis confirmed the formation of D bubbles in the defect regions, especially under high-dose irradiation. [Conclusions] The 97W-2Ni-1Fe alloy demonstrates superior performance in minimizing D retention, with significantly lower D desorption and reduced bubble formation compared to pure W. The TDS results show that pure W retains 2-3 times more D than the 97W-2Ni-1Fe alloy, indicating that the alloy's defect structure and composition contribute to its lower D retention. TEM analysis further confirms that the alloy exhibits fewer D bubbles and less damage, particularly in the form of less D bubble formation during irradiation and plasma exposure. These findings suggest that the 97W-2Ni-1Fe alloy is a more favorable material for applications where minimizing D retention and associated damage is critical, such as in fusion reactors. The results highlight the importance of material composition and defect structure in controlling D behavior under irradiation and plasma conditions, offering valuable insights into the design of next-generation plasma-facing materials.