The fracture toughness of Fe-Al intermetallic compound (IMC), FeAl and Fe2Al5, that forms as a thin layer on steel substrate was investigated. A model to evaluate the fracture toughness of a brittle thin layer on the elasto-plastic substrate was applied, and the fracture toughness was evaluated by the thickness of the IMC layer and crack interval in the IMC layer after uniaxial tensile testing. The phase and microstructure of the IMC layer were varied to investigate their effects on the fracture toughness of the IMC. Relation between layer thickness and crack interval was in good agreement with the theoretical model and the fracture toughness can be evaluated by the model. It was clarified that FeAl has higher fracture toughness than Fe2Al5, and that fine-grained Fe2Al5 has higher fracture toughness than coarse-grained Fe2Al5.
