Alloying Effects and Grain-Boundary Fracture in L12 Ordered Intermetallics

This article involves a number of studies on the alloying effects on intergranular fracture of L1₂ ordered intermetallics, and demonstrates that their ductility strongly depends upon atomistic composition and associated crystal and electronical structures at grain boundaries. Component atoms with large size, which occupy anti-structure site and disordered sites, and their preferential sites as third (or quaternary atoms), are shown to influence the grain boundary strength and fracture behavior in moderate levels of additions. Addition of interstitial atoms such as boron, carbon and beryllium with small size is extremely effective to enhance or to reduce the grain boundary cohesive strength in trace amount of levels in matrix but in highly enriched levels at grain boundaries. Also, gaseous hydrogen atoms with small size, which is mobile and penetrated from environment at room temperature, are shown to dynamically reduce the grain boundary strength, resulting in the environmental embrittlement. It is suggested that the grain boundary strength and therefore ductility of L1₂ ordered intermetallics can be controlled by compositions of components and interstitials, state of ordering and prohibition of penetration of hydrogen.