Interphase boundary fracture and grain boundary precipitation of Ni_3Al(gamma') phase in beta-NiAl bicrystals

摘要

The effect of the crystallography of film-like Ni_3Al(gamma') precipitates along grain boundaries of NiAl(beta) on the fracture stress at room temperature was examined using beta bicrystals with controlled orientations. The selected variant of gamma'-film satisfied the Kurdjumov-Sachs (K-S) relation with a neighbouring beta crystal, and deviated from the relation with an adjacent beta crystal. In the course of tensile deformation at ambient temperature, fracture occurred preferentially at the (beta/gamma') interphase boundary deviating from the K-S relation, which showed no plastic flow, and the fracture stress decreased with increasing deviation angle. In contrast, slip transfer from gamma'-film to beta crystal across coherent (beta/gamma') interface was observed, when the variant of gamma'-film satisfied the K-S relation with both neighbouring beta crystals. To clarify the relation between the interphase boundary fracture and the deviation angle from the K-S relation, the boundary structure of incoherent (beta/gamma') interfaces was discussed using O-lattice theory and transmission electron microscopic observations.