Abstract:The microstructure and fracture behavior of B₂-ordered iron aluminides with and without Mn (1.5%, mole fraction) were investigated by tensile tests (TT) and scanning electron microscope (SEM). The results show that the addition of Mn into the alloy can improve tensile properties and plasticity of the alloy and change the fracture behavior of the alloy from transgranular cleavage into intergranular mixed with transgranular cleavage. The theoretical calculation, by computer, indicates that the B₂-ordered Fe-28Al alloy cleaves on {100} planes because of weak bond strength. Addition of Mn into the alloy, whose atoms likely occupy sites I in the unit cell, can increase the cleavage strength of the alloy on {100}, leading to higher fracture strength and plasticity of the alloy after Mn addition.

Key words:  fracture; cleavage strength; iron aluminide