Grain boundary character distribution of ductile L1₂-type Ni₃Al intermetallic alloys

Grain boundary structures of Ni₃Al intermetallic alloys different in ductility are examined by electron back scattering pattern (EBSP) method. Special boundaries like Σ3 and Σ1 were observed frequently in these alloys, suggesting a correlation between the frequencies of these special boundaries and mechanical ductility. The frequency of these special boundaries become higher in the order as Ni₇₅Al₂₅ with boron, Ni₇₆Al₂₄ with boron, Ni₇₅Al₂₃Pd₂, normal purity Ni_76.5Al_23.5 and high purity Ni_76.5Al_23.5. This order is independent of the order of ductility. The mechanism of ductilization in Ni₃Al is discussed based on a chemical bonding effect in grain boundary vicinity applicable for boron-doped alloy and a grain boundary geometry effect for Pd doped and purified Ni₃Al alloys.