Effects of heat treatment and cooling rate on microstructural and mechanical characteristics of aluminide coatings on MANET steel

R and D studies concerning Pb-17Li blankets for DEMO suggest the use of coatings either as tritium permeation barriers for the water cooled blanket or as electrical insulators for the self cooled blanket. The production of coatings resistant to the thermal and mechanical stresses typical of the blanket operating conditions is the target. The present work describes the results of an experimental programme aimed at evaluating the effects of heat treatment and cooling rate on the microstructural and mechanical characteristics of aluminide coatings deposited on MANET steel (DIN 1.4914) by the hot-dipping process. The temperature of the post-deposition heat treatment that allows obtaining structures like FeAl and α-Fe(Al), instead of the more brittle FexAly intermetallics, has been identified. The coatings have been characterized by optical metallography, microhardness measurements, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS) and X-ray diffraction on the surface. (orig.)