The ductile versus brittle response of L12 intermetallic bicrystals

A micromechanical model for understanding the brittleness of L12 intermetallic alloys is proposed. Based on the Rice-Thomson concept that the brittle versus ductile response of a crack tip is controlled by the competition between dislocation blunting of the tip and cleavage decohesion, the model shows that when glissile CSF-coupled dissociation of superdislocations occurs, an L12 intermetallic alloy may be intrinsically ductile, while APB-coupled dissociation leads to an intrinsically brittle behavior. Converting the DO22 structure to the L12 structure does not guarantee a ductile fracture behavior. In order to develop a ductile L12 alloy, the alloying element must be able to change the atomic bonding nature so that the CSF-coupled dislocation dissociation is promoted.