Inter-diffusion and stability studies in W/Cr and W/Fe films using ion beam analysis

Plasma facing components in fusion reactors are exposed to intense plasma and the accompanying thermal loads and undergo surface modification due to sputtering and thermal diffusion. In order to get insight into the thermal diffusion in reduced-activation ferritic/martensitic (RAFM) steel, a prominent W containing plasma facing material, the compositional, structural and morphological changes occurring in W/Cr and W/Fe bi-layered films on vacuum annealing in 373–873 K temperature range were investigated. Compositional analysis by ion beam techniques established the out-diffusion of Cr and Fe through the W layer to the top surface. The diffusion coefficients of Cr and Fe in W were determined to be 8.0 × 10-19 (at 873 K) and 9.75 × 10-18 m2/s (at 773 K) respectively. The out-diffusion of Cr and Fe was substantiated by diffraction studies; however, no inter-metallic phases were formed. Annealing, besides promoting grain growth also introduced roughness in films.