Dose dependence of helium bubble formation in nano-engineered SiC at 700 °C

Abstract

Knowledge of radiation-induced helium bubble nucleation and growth in SiC is essential for applications in fusion and fission environments. Here we report the evolution of microstructure in nanoengineered (NE) 3C SiC, pre-implanted with helium, under heavy ion irradiation at 700 °C up to doses of 30 displacements per atom (dpa). Elastic recoil detection analysis confirms that the as-implanted helium depth profile does not change under irradiation to 30 dpa at 700 °C. While the helium bubble size distribution becomes narrower with increasing dose, the average size of bubbles remains unchanged and the density of bubbles increases somewhat with dose. These results are consistent with a long helium bubble incubation process under continued irradiation at 700 °C up to 30 dpa, similar to that reported under dual and triple beam irradiation at much higher temperatures. The formation of bubbles at this low temperature is enhanced by the nano-layered stacking fault structure in the NE SiC, which enhances point defect mobility parallel to the stacking faults. This stacking fault structure is stable at 700 °C up to 30 dpa and suppresses the formation of dislocation loops normally observed under these irradiation conditions.

Atomistic simulations of a helium bubble in silicon carbide

“…It is especially the case for high dose rates of incoming helium atoms combined with a restricted vacancy supply. In silicon carbide, several studies reported observations of helium-filled bubbles and platelets [4][5][6][7][8][9][10][11][12]. Such highly pressurized defects can significantly degrade the structural integrity of the host, a particularly annoying feature for a structural or confining material.…”

Investigation of Microstructure and Nanoindentation Hardness of C+ & He+ Irradiated Nanocrystal SiC Coatings during Annealing and Corrosion

“…Under the bombardment of high-energy neutrons, a lot of He atoms are produced by transmutation in the fuels and claddings. The implantation of He always causes irradiation swelling and has an effect on the mechanical properties of materials [43,44]. According to the computational simulation, He tends to be trapped in small voids, which explains the observation of He bubbles at vacancy defects in SiC [45].…”

Low-temperature investigations of ion-induced amorphisation in silicon carbide nanowhiskers under helium irradiation

“…Since SRIM estimates the damage in a planar target, an algorithm using MATLAB known as Ion Damage and RAnge in the Geometry Of Nanowires (IDRAGON) [30] was designed to account for the circular cross-sectional shape of a nanowire. The IDRAGON calculations were performed for 3000 He ions at an energy of 6 keV, with a displacement energy of 35 eV for Si and 21 eV for C [31], and the target density to 3.21 g/cm 3 [32]. The 6 keV He energy ensures that the peak damage is placed close to the centre of a 60 nm diameter NW (average NW size used in this work) and in a 60 nm thick foil as shown in figure 1.…”

“…It is therefore necessary to carefully select structural materials capable of withstanding extreme conditions (high radiation damage levels, temperatures, thermo-mechanical stresses etc.). Silicon carbide (SiC) has been proposed for use as a first-wall material in fusion reactors, as an accident tolerant cladding material for currently light water reactors (LWRs), TRIstructure-ISOtropic (TRISO) fuel particle coatings for gas-cooled Generation IV fission reactors and as an inert matrix for the transmutation of plutonium [1], [2], [3], [4], [5], [6]. This is due to the fact that it possesses a high melting temperature (3000 K), high thermal conductivity (490 Wm -1 K -1 at 1273 K), low activation under neutron irradiation, chemical inertness and small neutron-capture cross-sections which collectively make it promising for applications in advanced nuclear systems [6] - [9].…”

“…Silicon carbide materials in fusion environments will be exposed to high radiation doses (up to 200 dpa) due to the large momentum transferred to the primary knock-on atoms by fast-moving neutrons at high temperatures (>1273 K) [3], [9]. This can initiate a cascade of subsequent atomic displacements resulting in the formation of point defect clusters that can grow to form extended defects such as dislocation loops.…”