Compressive Deformation Characteristics of Nb<sub>2</sub>Co<sub>7</sub> as Crystalline Mille-Feuille Structured Material

Abstract

The uniaxial compressive deformation characteristics of single-phase Nb2Co7 were investigated by an electron backscatter diffraction analysis focused on microstructural evolution and kink formation in order to determine whether this monoclinic intermetallic phase is a novel crystalline “mille-feuille” structured (MFS) material. During uniaxial compressive deformation, Nb2Co7 does not behave brittle but shows high plasticity. In some microstructure regions, kink-like structures are observed, showing no delamination. In kink-free regions, the frequency of boundaries with rotation angles of 60°, 120°, and 180°, which correspond to changes in the monoclinic stacking vector of Nb2Co7 layers between adjacent close-packed (CP) layers, increases significantly after the compression test. The interfaces in the kink-like structures are low-angle boundaries with rotation axes within basal (001) planes. The rotation angles and axes of interfaces in the kink-like structures take various values, suggesting that the origin of the kink-like structures is not twinning, but in fact, these structures are a result of deformation kinking. Deformation of single-phase Nb2Co7 is considered to occur due to dislocation glide on basal (001) planes and kink formation, which is regarded as playing an indispensable role in the plasticity of Nb2Co7 during compression. It can therefore be concluded that Nb2Co7 is a novel crystalline MFS material.