Dose rate effects on damage accumulation and void growth in self-ion irradiated tungsten

Abstract

• Disordering rates at the damage peak in tungsten (W) irradiated to 1 dpa at 900 K is ~6 times lower at 10 −4 than 10 −3 dpa/s. • A uniform distribution of voids is observed in the self-ion irradiated W at both dose rates. • The void diameter varies from 1.5 to 3.4 nm with the number density on the order of 2 × 10 17 voids/cm 3 . • Void growth in W irradiated at 900 K is faster at 10 −4 than 10 −3 dpa/s. • Void growth is faster in monocrystalline than polycrystalline W irradiated at 900 K. • A simplified three-dimensional model is proposed to assess the dose rate effects. This study reports on dose rate effects in self-ion irradiated monocrystalline tungsten (mono-W) and polycrystalline tungsten (poly-W). Both mono-W and poly-W were irradiated at 900 K to 1 dpa at two dose rates, 10 −4 and 10 −3 dpa/s. An additional mono-W disk was irradiated at 300 K up to 44 dpa. The irradiated samples were analyzed using Rutherford backscattering spectrometry in channeling geometry (RBS/C) and transmission electron microscopy. The RBS/C data suggest that self-interstitial atoms in mono-W are extremely mobile at 300 K and higher; the disordering rate in mono-W irradiated at 900 K is ~6 times lower at 10 −4 than 10 −3 dpa/s at the depth of the damage peak. There is a uniform distribution of voids in both mono-W and poly-W irradiated at 900 K. The observed void diameters were corrected, which ranged from 1.5 to 3.4 nm. The void number density is on the order of 2 × 10 17 voids/cm 3 in mono-W irradiated at 900 K to 1 dpa at 10 −3 dpa/s. The growth rate of the voids in W irradiated at 900 K is higher at 10 −4 than 10 −3 dpa/s. At the same dose rate, voids grow faster in mono-W than poly-W. A simplified three-dimensional model is proposed to assess the dose rate effects based on the diffusion and interaction of migrating point defects from two consecutive damage cascades.