The effect of pre-irradiation on deuterium retention and desorption behavior in tungsten and tungsten alloys

BackgroundTungsten (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.PurposeThis study aims to investigate the influence of pre-irradiation defects on deuterium retention and desorption behavior in W and tungsten-nickel-iron (W-Ni-Fe) alloys.MethodsFirstly, pure W and 97W-2Ni-1Fe alloy samples were irradiated with Fe¹³⁺ ions at doses of 5×10¹⁴ Fe·cm⁻² and 3×10¹⁵ Fe·cm⁻² using the heavy ion accelerator at Lanzhou University, and SRIM simulations were conducted to model the defect and Fe ion distribution in the samples. Subsequently, D plasma irradiation was performed at Hefei University of Technology for 1 h at a constant plasma flow of 4×10¹⁶ D·cm⁻² with 50 eV. Finally, 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.ResultsObservational findings show that Fe¹³⁺ ion irradiation induces significant vacancy-type defects in both materials, with higher defect concentrations in pure W compared to the alloy. D retention is observed to be higher in pure W, with desorption occurring at approximately 250 °C and 700 °C. In contrast, the 97W-2Ni-1Fe alloy shows reduced D retention, with desorption peaks at 200 °C and 700 °C. The TDS results reveal that pure W retained 2~3 times more D than the alloy. Pre-irradiation with Fe¹³⁺ ions further enhances D retention, especially in pure W. TEM analysis results confirm the formation of D bubbles in the defect regions, especially under high-dose irradiation. Compared to pure tungsten, the deuterium retention of the 97W-2Ni-1Fe alloy decreases by 65.0% and 55.8% under low and high dose pre-irradiation conditions, respectively.ConclusionsThe 97W-2Ni-1Fe alloy demonstrates superior performance in minimizing D retention, with significantly lower D desorption and reduced bubble formation compared to pure W, hence 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.