Fracture Toughness Evaluation of Thin Fe-Al Intermetallic Compound Layer at Reactive Interface between Dissimilar Metals

The fracture toughness of Fe-Al intermetallic compounds (IMCs), FeAl and Fe2Al5, that form as a thin layer on steel substrate was investigated. A model for evaluating the fracture toughness of a brittle thin layer on an elastoplastic substrate was applied, and the fracture toughness was evaluated from the thickness of the IMC layer and the 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. The relationship between layer thickness and crack interval was in a good agreement with the theoretical model, and the fracture toughness was evaluated adequately using 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.