Effect of temperature on the neutron irradiation-induced cavities in tungsten

To study the effect of temperature on the evolution of irradiation-induced cavities in tungsten, ITER Grade Product tungsten was characterised using transmission electron microscopy (TEM) after neutron irradiation to ∼1 dpa at 600°C, 800°C, and 1000°C. The results showcase irradiation temperature-dependent cavity formation and growth, which is majorly governed by the spatial distribution of transmutation elements in the matrix. Suppression of thermal neutrons fluence by applying stainless steel capsules resulted in a lower density of secondary phases as well as cavities than those reported in the literature for similar irradiation conditions. To further assess temperature effects on the cavity evolution and their stability, dedicated in situ TEM post-irradiation annealing (PIA) experiments were carried out. PIA of 600°C irradiated samples at 600°C for about 1 h revealed no noticeable change on the cavities size distribution. However, upon increasing annealing temperature and time, cavities became coarsened. Vacancy migration and absorption is found to be the dominant mechanism that governs cavity annealing kinetics in the present thin-foil PIA investigations. Furthermore, the cavity coarsening is dictated by the simultaneous evolution of the irradiation-induced dislocation loops, thin-foil free surfaces image forces, and the presence of the transmuted elements and their clusters in the matrix.