Evaluation of helium effect on ion-irradiation hardening in pure tungsten by nano-indentation method

Abstract

a b s t r a c tAs-received and recrystallized pure tungsten (W) were irradiated with 6.4 MeV Fe 3 + up to 2 dpa with or without He + at 300 °C, 500 °C, 700 °C and 1000 °C respectively. Irradiation hardening was measured by the nano-indentation method. An equation to evaluate the bulk equivalent hardness was derived on the assumption that the geometrically necessary dislocation (GND) densities at an indentation depth were the same before and after irradiation. Ion-irradiation always induces hardening in both as-received and recrystallized W at all the experiment temperatures. In the case of single-beam irradiation, the recrystallized W exhibited higher hardening than as-received one. The effect of helium on the irradiation hardening is dependent on the material condition: as-received W showed an additional hardening by helium at all the irradiation temperatures, while in recrystallized W the hardening was not affected by helium below 700 °C.

Evaluation of Ion-Irradiation Hardening of Tungsten Single Crystals by Nanoindentation Technique Considering Material Pile-Up Effect

“…Figure 6 summarizes the ion-irradiation hardening results, based on the eq. (10) of this work in comparison with the previously obtained ion-irradiation results by our group 5) as well as with the neutron-irradiation hardening results by Vickers hardness tests of other researchers 34,35) . The damage levels that are referred to in this gure are averaged damage levels over the projected ion range up to 2000 nm and represent the dpa at a depth of about 600 nm.…”

“…Zhang et al 5) proposed a method to evaluate bulk equivalent hardness of Fe 3+ irradiated (2 dpa at 573 K, 773 K, 973 K and 1273 K) pure recrystallized and as received W. The method is based on the assumption that the geometrically necessary dislocation density at an indentation depth is unchanged by ion-irradiation. Their results of ion-irradiation hardening for different irradiation temperatures between 573 K and 973 K are shown in Fig.…”

“…To simulate fusion environment for W, ion-irradiation is extensively in use [5][6][7][8][9][10] . A realistic estimation of the actual irradiation hardening behaviour by ion-irradiation experiments in W is essential in order to apply it as a plasma facing component in fusion power reactors.…”

Probing nanoscale damage gradients in ion-irradiated metals using spherical nanoindentation

“…A possible explanation could be that the ion-irradiation introduces a large density of defects (such as dislocation loops 54 , or He bubbles, etc.) into the material structure that can help set up highly potent dislocation sources, as reported by numerous indentation studies on ion-irradiated materials 15 , 55 – 57 . Another obvious consequence of these new defects introduced by irradiation is that the Y ind values in the irradiated samples are higher than the corresponding values in the annealed samples.…”

“…These methods are cost-effective in extracting huge amounts of reliable and consistently reproducible information from very small nanometer sample volumes. Compared to standard hardness measurements using sharper pyramidal indenters, which provide a variation of hardness and modulus with respect to indentation depth 16 , 55 , 56 , 63 , 72 , 73 , the indentation stress-strain analysis technique can provide us with the local loading and unloading elastic moduli, the local indentation yield strengths, and the post-yield strain hardening behavior and quantify these changes before and after radiation induced damage. Additionally, by simply varying the indenter size, this technique can be used to provide remarkable new insights into the mechanical response of the irradiated layers in these samples, and correlate those effects with the local material structure obtained from EBSD and/or TEM.…”