Preliminary study of HDA coating on CLAM steel followed by high temperature oxidation

Abstract A hot-dip aluminizing process is expected to produce aluminide coatings on structural materials to resist tritium permeation, corrosion, and magnetohydrodynamic (MHD) effects in the fusion reactor blanket. China Low Activation Martensitic (CLAM) steel, which is the candidate structural material for the LiPb blanket system in China, was coated with pure aluminum and with an Al–Si alloy. Factors affecting the thickness and morphology of the aluminide coatings were studied. After the hot-dipping treatment, FeAl 3 and Fe 2 Al 5 were observed at the Al/steel interface. The existence of silicon in the molten aluminum suppressed the growth of Fe 2 Al 5 , built up the thickness of FeAl 3 slightly, and contributed to reducing the thickness of the intermetallic layer. The brittle phase of Fe 2 Al 5 had completely transformed to ductile phases of FeAl 2 , FeAl and α-Fe(Al) after high temperature heat-treatment in air. Kirkendall voids were found in the diffusion layer, due to the rapid interdiffusion of iron and aluminum during oxidation. Cracks and pores were observed on the coating surface and at the interlayer. Grazing incidence X-ray diffraction indicates the presence of α-Al 2 O 3 in the oxide layer.