Shock-induced α" martensitic transformation in Nb single crystals

The structural and mechanical response of pure body-centered cubic (BCC) Nb under shock loading were systematically studied. Shock-induced orthorhombic (α") martensitic transformations were observed in single crystals Nb with different orientations, in which dense lenticular α" martensite variants distribute uniformly along different directions by forming a hierarchical structure. Neighbouring martensite variants share a {111}<110>α" twinning relationship between each other, and high-density dislocations are found distributing along the α"/BCC(β) interface. The formation of α" martensite was dominated by a mechanism of collinear shuffling of alternating {110}β planes along with <1 1¯ 0>β direction by a displacement δ. The collision between martensite variants along different direction induce abundant microcracks, with BCC-to-ω and BCC-to-FCC phase transformations occurring at the crack tips. These findings not only provide the experimental evidence of shock-induced α" martensitic transformation in pure BCC metals, but also link the microstructure interaction of materials to their macroscopic shock failure directly, which may have a broad impact on the study of shock deformation in different materials.