New insights into microstructure of neutron-irradiated tungsten

The development of appropriate materials for fusion reactors that can sustain high neutron fluence at elevated temperatures remains a great challenge. Tungsten is one of the promising candidate materials for plasma-facing components of future fusion reactors, due to several favorable properties as for example a high melting point, a high sputtering resistivity, and a low coefficient of thermal expansion. The microstructural details of a tungsten sample with a 1.25 dpa (displacements per atom) damage dose after neutron irradiation at 800 degrees C were examined by transmission electron microscopy. Three types of radiation-induced defects were observed, analyzed and characterized: (1) voids with sizes ranging from 10 to 65 nm, (2) dislocation loops with a size of up to 10 nm and (3) W-Re-Os containing sigma- and chi -type precipitates. The distribution of voids as well as the nature of the occurring dislocation loops were studied in detail. In addition, nano-chemical analyses revealed that the sigma- and chi -type precipitates, which are sometimes attached to voids, are surrounded by a solid solution cloud enriched with Re. For the first time the crystallographic orientation relationship of the sigma- and chi -phases to the W-matrix was specified. Furthermore, electron energy-loss spectroscopy could not unambiguously verify the presence of He within individual voids.

Automated summary

The development of appropriate materials for fusion reactors that can sustain high neutron fluence at elevated temperatures remains a challenge. Tungsten, with its favorable properties such as high melting point and sputtering resistivity, is a promising candidate material for plasma-facing components. After neutron irradiation, tungsten samples showed various radiation-induced defects including voids, dislocation loops, and W-Re-Os containing precipitates. The study also revealed the crystallographic orientation relationship of the precipitates to the W-matrix.