Microstructural modifications in tungsten induced by high flux plasma exposure: TEM examination

Abstract

We have performed microstructural characterization using transmission electron microscopy (TEM) techniques to reveal nanometric features in the sub-surface region of tungsten samples exposed to high flux, low energy deuterium plasma. TEM examination revealed formation of a dense dislocation network and dislocation tangles, overall resulting in a strong increase in the dislocation density by at least one order of magnitude as compared to the initial one. Plasmainduced dislocation microstructure vanishes beyond a depth of about 10 μm from the top of the exposed surface where the dislocation density and its morphology becomes comparable to the reference microstructure. Interstitial edge dislocation loops with Burgers vector a 0 /2〈111〉 and a 0 〈100〉 were regularly observed within 6 μm of the sub-surface region of the exposed samples, but absent in the reference material. The presence of these loops points to a co-existence of nanometric D bubbles, growing by loop punching mechanism, and sub-micron deuterium flakes, resulting in the formation of surface blisters, also observed here by scanning electron microscopy.S Online supplementary data available from stacks.iop.org/PSTOP/T167/014030/mmedia

Neutron irradiation effects on mechanical properties of ITER specification tungsten

“…Overall, the irradiation doses varied from 0.1 up to 1 dpa, and the irradiation temperature varied from 600 up to 1200 °C, depending on particular type of the sample. In the case of hardness, 3 PB and tensile tests, we provide a comparison of data with Plansee ITER specification W (IGP) [3,[10][11][12][13][14][15][16][17]. The microstructural analysis by transmission electron microscopy is now in progress, and therefore, the discussion of the results accounts for the currently established knowledge about the microstructure obtained in other neutron irradiation campaigns, most of which executed in HFIR and Joyo reactors [46,47].…”

“…Based on the review of the available open literature data, one can single out three providers of tungsten products that have been fabricated according to the ITER specification, with dimensions suitable for the application in ITER. These providers include: (i) Plansee (Austria), see, e.g., [3,[10][11][12][13][14][15][16][17]; (ii) Advanced Technology and Materials AT&M (China), see, e.g., [18][19][20][21][22][23][24][25], and A.L.M.T. (Japan), see, e.g., [13,[26][27][28][29][30][31].…”

On the onset of void swelling in pure tungsten under neutron irradiation: An object kinetic Monte Carlo approach

“…This treatment should result in a substantial reduction of the dislocation density, and improve the uniformity of grains. According to available studies [8], the dislocation density is expected to be ρ d ≈ 10 12 m −2 (typical core radii should be r d = 2.25a 0 ), while the grain size should be within a range of 5 − 50µm. Considering the above equations, one can appreciate that 1-D migrating SIA defects, if not recombined with vacancy defects in the simulation box, are very likely to be sunk at the grain boundary preferably to the dislocation network.…”

“…In any case, operation below DBTT induces a risk of cracking for plasma-facing components, because they cannot dissipate thermal stresses by plastic deformation [7]. If plasma damage is associated to a rather narrow penetration depth (around a few tens of micrometers as revealed by direct TEM investigations [8,9]), neutron irradiation, in contrast, affects the whole components resulting in a nearly homogeneous damage rate; the consequent microstructure pattern should, nevertheless, be strongly heterogeneous be-Email address: nicolas.m.b.castin@gmail.com (N. Castin) cause of the temperature gradient from the plasma-facing surface towards heat sinks [10]. Undoubtedly, the present lack of consistent data on the performance of tungsten with respect to heat loads and transients under neutron irradiation remains to be filled in.…”

Effect of high flux plasma exposure on the micro-structural and -mechanical properties of ITER specification tungsten

“…However, it is expected that the high flux DPE at temperatures of 600K and below primarily results in top-and sub-surface retention, because the diffusion of deuterium is limited by the material's microstructure (dislocations and grain boundary) [11,12]. TEM investigation of the surface microstructure of a heavily deformed tungsten was recently performed in [13]. The pre-deformed tungsten was exposed to high flux plasma at 620K.…”