Effect of He-appm/DPA ratio on the damage microstructure of tungsten

Abstract

In-situ ion irradiation and transmission electron microscopy has been used to examine the effects of the He appm to DPA ratio, temperature and dose on the damage structure of tungsten (W). Irradiations were performed with 15 or 60 keV He + ions, achieving He-appm/displacements per atom (DPA) ratios of ~40,000 and ~2000, respectively, at temperatures between 500 and 1000°C to a dose of ~3 DPA. A high number of small dislocation loops with sizes around 5-20 nm and a He bubble lattice were observed for both He-appm/DPA ratios at 500°C with a bubble size ~1.5 nm. Using the g.b=0 criterion the loops were characterised as b = ±1/2<111> type. At 750°C bubbles do not form an ordered array and are larger in size compared to the irradiations at 500°C, with a diameter of ~3 nm. Fewer dislocation loops were observed at this temperature and were also characterised to be b = ±1/2<111> type. At 1000°C, no dislocation loops were observed and bubbles grew as a function of fluence attributed to vacancy mobility being higher and vacancy clusters becoming mobile.

A study of the effect of helium concentration and displacement damage on the microstructure of helium ion irradiated tungsten

“…Dislocation loops was observed at irradiation temperatures below 1000°C and were characterised as b = ±½<111> type with no <100> type observed at the lowest He-appm/DPA ratio of 500. This continues the observation made in our preliminary work [12] where no <100> type loops were observed in samples irradiated to He-appm/DPA ratios of 40,000 and 2,000. However, it is still in contrast to previous work on self-ion irradiation reported in the literature [29] where a mixtures of b = ±½<111> and <100> loops are observed .…”

“…The Stopping Range of Ions in Matter (SRIM-2013) Monte Carlo code [16] was used to calculate DPA and helium concentration from implantation, using the method of DPA calculation proposed by Stoller et al [17]. Further details of sample preparation and SRIM calculations can be found in our previous work [12]. In situ ion irradiation was performed at the Microscopes and Ion Accelerators for Materials Investigation facility (using the MIAMI-1 system) described elsewhere [18].…”

“…projectile, irradiation temperature, starting material and fluence/dose). The current work builds on our previous preliminary results [12] whereby we perform experiments at different temperatures, He ion beam energy (to achieve different He-appm/DPA ratios) and by observing in situ as the He fluence (and thus damage dose) increases. Simply by increasing the energy of the He ions, the amount of implanted helium is reduced as an increased percentage of the ions are transmitted through the TEM foil at higher energies.…”

“…Also observed were small dislocation loops with equal populations of vacancy and interstitial types mainly with b = ±1/2<111> but a minority with b = <100>. Harrison et al [12] irradiated W with 15 and 60 keV He + ions (He-appm/DPA ratios of 40,000 and 2,000 respectively) to doses of 3.0 DPA at temperature of 500, 750 and 1000°C. The authors noted the presence of dislocation loops with b = ±1/2<111> and none with b = <100> which was attributed to the presence of He inhibiting ±1/2<111> loop mobility as it is theorised that the <100> loop arises from interaction of b = ±1/2<111> in bodycentred-cubic (BCC) materials.…”

Effect of He implantation on the microstructure of zircaloy-4 studied using in situ TEM

“…One area of particular interest has been the implantation of inert gases such He, Xe and Ar into metals [15] and much work has been done for many different systems including iron and its alloys [16], tungsten [17][18][19], copper [20], nickel [21], molybdenum [22,23] and carbon [24] which are important for both fission and fusion reactors.…”