On the thermal stability of the nanostructured tungsten coatings

Tungsten is a candidate to be used as plasma facing materials in future fusion nuclear reactors. There, the material has to withstand large radiation fluxes and thermal loads. Nowadays, nanostructured tungsten (NW) seems to exhibit a better radiation-resistance than the coarse grained. However, the thermal stability of NW is still an open question. On these bases, the thermal stability of NW coatings is studied in the temperature range from 1000 to 1473 K. For this purpose, Samples were isothermally annealed in vacuum at temperatures from 298 to 1473 K. The morphological and microstructural properties of the samples were characterized by atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-Ray diffraction (XRD), respectively. For T < 1000 K nanostructured are preserved and only a small reduction in the internal stress of the films is observed. For T > 100 K, nanostructures start to grow in a bimodal fashion with activation energy of 0.259 eV, reaching a submicron-sized threshold at T ≈ 1473 K.