Growth of inter-metallic compound layers on CLAM steel by HDA and preparation of permeation barrier by oxidation

Abstract

Hot-dip aluminizing (HDA) on China Low Activation Martensitic (CLAM) steel and followed by oxidation to obtain an Al2O3/FexAly layer covering was considered to be a promising method to resist the harsh environments in fusion reactors. In the present study, CLAM steel was coated in molten pure Al and Al-0.3Ce (wt.%) melt. The growth behavior of the inter-metallic compound (IMC) layers after different immersion time and temperature was investigated and described. The IMC layer mainly consists of Fe2Al5 and FeAl3 after hot-dipping. And the addition of Ce in the molten pure Al could promote the growth of IMC layers, which provided the idea of obtaining a certain thickness of the IMC layer at a lower temperature. After two independent oxidation processes (normalized heat-treatment and 760°C for 15h) in air, the Fe2Al5 and FeAl3 of IMC layers had been transformed into ductile phases (FeAl2 and FeAl), and Al2O3 layers were detected on the coating surface. The oxidation of 760°C for 15h was considered to form a denser Al2O3 film. However, cracks and pores were observed in the IMC layer after oxidation due to the heat-treatment and cooling methods