Texture evolution and temperature-dependent deformation modes in ambient- and cryogenic-rolled nanolayered Zr-2.5Nb

Abstract

Interface-dominate properties can be strengthened when the interface spacing is further reduced to nanoscale dimensions. To analyze the dominant deformation modes in α-Zr sandwiched by α/β interfaces, a nanolayered Zr-2.5Nb alloy was rolled to various reductions at room temperature (RT) and near-liquid-nitrogen temperature (LNT). The α/β lamellar structures are refined significantly when rolling reduction exceeds 25% at both RT and LNT rolling. We show that the alloy is remarkably formable at both RT and LNT, as indicated by homogeneous deformation with no shear banding detected. Based on a combination of microstructural analysis, texture measurements and multi-scale polycrystal model simulations, two types of tensile {11¯02}<1¯101> and {1¯1¯21}<112¯6> twins were found to form at LNT rolling and expand until they reoriented all α-Zr lamellae in the same colony to the twin orientation. In addition, the high density of α/β interfaces substantially enhances the activity of pyramidal <c+a> dislocations in α-Zr during both RT and LNT rolling, eventually tilting the <c> axis of α-Zr nearly parallel to the normal direction of the as-rolled sample. The higher fraction slip activity of <c+a> dislocations and deformation twins accommodate deformation along <c> direction in α-Zr, increasing the formability of this ultra-strong nanolayered Zr-2.5Nb alloy.