Limitations of W and W-1%La2O3 for use as structural materials

Recent divertor designs for future fusion demonstration reactors include dispersion strengthened tungsten as structural material. Their operation temperature window - currently estimated to be between 800 deg C and 1200 deg C - is restricted by embrittlement on the lower limit. Therefore, standard impact tests have been performed with specimens fabricated from commercial tungsten and W-1%La2O3 rods. Due to the anisotropic microstructure, specimens were oriented parallel to rod axis for optimum Charpy properties. Nevertheless, ductile-to-brittle transition temperatures of just 800 plus/minus 50 deg C for tungsten and approximately 950 plus/minus 50 deg C for W-1%La2O3 have been determined. But for use as structural material under fusion-specific neutron irradiation, an according alloy should exhibit transition temperatures of 200-400 deg C, at least. Therefore, the impact of these results on the use of dispersion strengthened tungsten for divertor structures are discussed in detail.