Effects of Transmutation Elements on Neutron Irradiation Hardening of Tungsten

Abstract

Tungsten (W) is a candidate material for Plasma facing materials of fusion reactors. During fusion reactor operation, not only irradiation damages but also transmutation elements such as rhenium (Re) and osmium (Os) are produced by neutron irradiation. As a result, the original pure tungsten changes to W-Re or W-Re-Os alloys. Thus, the mechanical and physical properties are expected to change. The aim of this study is to investigate the effects of transmutation elements on neutron irradiation hardening and microstructure changes of tungsten.To simulate the effects of transmutation elements, tungsten base model alloys were used in this study. The examined compositions of the alloys were selected from the calculated changes in solid solution area of W-Re-Os alloy. Neutron irradiation was performed in fast test reactor JOYO in JAEA. The irradiation damages and temperature ranges were 0.17-1.54 dpa and 400-750 C respectively. After the irradiation, Vickers hardness test and TEM observation were performed.There were clear differences between Re and Os in effects on irradiation hardening. In the case of W-Re alloys, when damages were less than 0.40 dpa, the irradiation hardenings were nearly equal to those of pure tungsten independent of Re addition. But when the damage was 1.54 dpa, the irradiation hardenings increased lineally with Re content. Microstructural observations showed that precipitations mainly formed in W-Re alloys. In the case of W-Os alloys, the irradiation hardenings (ÁHv) of W-3Os alloys were larger than those of pure tungsten. And the differences were about 400 independent of dpa and irradiation temperature. Effects of Re and Os on irradiation hardening based on the microstructural observations were discussed.

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.…”

“…6. By converting this temperature tendency to our results, it appears that the pile-up corrected ion irradiation hardening results based on the EMC method are consistent with the available neutron-irradiation hardening results 34,35) obtained by Vickers hardness tests for higher temperatures, although the displacement rate effect should be considered.…”

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

“…Tanno et al [3], [4] report the formation of a void lattice in fast neutron irradiated W in the JOYO reactor at 750°C at 1.54 DPA (He-appm/DPA ~0.6). The authors report the formation of small voids of around 5 nm in samples irradiated at 400 and 750°C.…”

Effects of Re Content and Fabrication Process on Microstructural Changes and Hardening in Neutron Irradiated Tungsten

“…5) Although the solute Re improves the mechanical properties of W, 1416) the irradiation-induced precipitates cause severe irradiation hardening and embrittlement. 9,10,13) The mechanical properties of W also change depending on the fabrication process, including the subsequent heat treatment. Different fabrication processes and heat treatments change the grain structure, such as grain size and shape, as well as other aspects of the microstructure, such as dislocation and defect density.…”