Thermal desorption spectroscopy of high fluence irradiated ultrafine and nanocrystalline tungsten: helium trapping and desorption correlated with morphology

Abstract

Microstructural changes due to displacement damage and helium desorption are two phenomena that occur in tungsten plasma facing materials in fusion reactors. Nanocrystalline metals are being investigated as radiation tolerant materials that can mitigate these microstructural changes and better trap helium along their grain boundaries. Here, we investigate the performance of three tungsten grades (nanocrystalline, ultrafine and ITER grade tungsten), exposed to a high fluence of 4 keV helium at both RT and 773 K, during a thermal desorption spectroscopy (TDS) experiment. An investigation of the microstructure in pre-and post-TDS sample sets was performed. The amount of desorbed helium was shown to be highest in the ITER grade tungsten and lowest in the nanocrystalline tungsten. Correlating the desorption spectra and the microstructure (grain boundaries decorated with nanopores and crack formation) and comparing with previous literature on coarse grained tungsten samples at similar irradiation and TDS conditions, revealed the importance of grain boundaries in trapping helium and limiting helium desorption up to a high temperature of 1350 K in agreement with transmission electron microscopy studies on helium irradiated tungsten which showed preferential and large facetted bubble formation along the grain boundaries in the nanocrystalline tungsten grade.

Comparison of deuterium retention in tungsten exposed to deuterium plasma and gas

“…The retention of hydrogen isotopes in W is mainly affected by trap sites, such as dislocations, grain boundaries, vacancies and microvoids in the matrix material [7][8][9][10] .…”

Quantitative investigation of surface structure and interatomic potential with impact-collision ion scattering spectroscopy

“…These interactions are affected by helium ion channeling, which occurs preferentially for certain crystalline orientations [1][2][3]. The channeling of helium ions influences the precise depths and locations where the helium ions and their associated energy are deposited [4][5][6]. For magnetic confinement fusion, the implantation of helium into the near surface of tungsten has been shown to lead to the development of a surface nanostructure called tungsten 'fuzz' [7][8][9][10][11][12].…”

“…The nanostructure growth, which is affected by the location and depth of the implanted helium [4,8] and sputtering by higher energy helium ions [13], has been found to vary with the local grain orientation [4,14,15]. One factor driving this variation is helium ion channeling [4,14], which influences both the implantation of and sputtering by helium.…”

Manufacturing of tungsten and tungsten composites for fusion application via different routes

“…To eliminate or alleviate the brittle behaviors and satisfy the fusion engineering application, an advanced W material is required and developed. Many researchers claimed that grain boundaries can act as traps to annihilate point defects (interstitial atoms or vacancies) from irradiation [12,[17][18][19][20]. Klimenkov et al [12] and Fukuda et al [17] performed a neutron irradiation test on W materials and found that the neutron Tungsten www.springer.com/42864 irradiation-induced defects were likely to gather or be annihilated at grain boundaries.…”

“…Klimenkov et al [12] and Fukuda et al [17] performed a neutron irradiation test on W materials and found that the neutron Tungsten www.springer.com/42864 irradiation-induced defects were likely to gather or be annihilated at grain boundaries. EI-Atwani et al [18][19][20] reported the effects of grain sizes on the irradiation resistance of pure W materials that the grain refinement could enhance its irradiation resistance. Tan et al [21] performed an ELM-like thermal shock test on the second-phase-doped W materials with a report that the addition of the second phase would improve the resistance by strengthening grain boundaries.…”