Blistering and deuterium retention in Nb-doped W exposed to low-energy deuterium plasma

•The hardness and Young's modulus as well as lattice parameter of tungsten are obviously improved due to niobium doping, the possible causes are discussed.•The effects of niobium alloying on surface morphology and deuterium retention in tungsten exposed to deuterium plasma are investigated and deep research is done on searching mechanism.•The samples are exposed to low energy deuterium plasma with a constant plasma density at different temperatures and fluences. Tungsten and tungsten-niobium alloy with niobium concentration of 5 wt% were exposed to deuterium plasma at ~470 – 506 K, with flux of ~1.8 × 1021 D/m2/s, an ion energy of 100 eV and fluence of 1.3 × 1025 D/m2 – 5.2 × 1025 D/m2. Before exposure, the hardness and Young's modulus as well as lattice parameter of W are improved due to Nb doping. After exposure, the TDS spectra can be deconvoluted into two major Gaussian peaks located at ~700–800 K and ~900–1000 K for all samples. At low fluence (1.3 × 1025 D/m2) and low temperature (470 K), only sparse and small blisters are formed on the pure W surface, while the strip-like surface structures are observed on the W-5Nb surface. The total D retention is significantly reduced due to the Nb doping, where the D retention in W-5Nb is 1.34 times lower than that of in pure W. With increasing fluence up to 2.6 × 1025 D/m2, both the blister size of pure W and W-5Nb alloy continue to increase. The blister size of W-5Nb alloy is slightly bigger than that of pure W, but the opposite trend is observed in blister density. The total D retention in W-5Nb alloy is also observed to be 1.38 times higher than that of pure W. Further increase of irradiation fluence (5.2 × 1025 D/m2) and temperature (506 K) at the same time lead to the significant increase of blister size and D retention for the pure W. However, whether the blister size or D retention are greatly suppressed in W-5Nb alloy. Moreover, the deuterium retention in W-5Nb is about 3 times less than that in pure W, implying that niobium alloying suppress the surface blistering and reduce the deuterium retention in tungsten exposed to D plasma with a fluence of 5.2 × 1025 D/m2 at 506 K.