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Mg-0.7 at%Zn-1.4 at%Y alloys annealed at low temperatures after quenching in water from 520 C were studied by high-resolution transmission electron microscopy (HRTEM) and high-angle annular detector dark-field scanning transmission electron microscopy (HAADF-STEM). Stacking faults, thin bands of a 14H-type long period stacking (LPS) phase and relatively thick bands of LPS were precipitated in -Mg crystalline grains by annealing at 300 C, 400 C and 500 C, respectively. The precipitation of stacking faults, LPS phase and a supersaturated solid solution without any precipitates were reversibly transformed by annealing at low temperatures. It can be concluded that the stacking faults and LPS phase are stabilized by the segregation of Zn and Y from a supersaturated solid solution.

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This study investigated the fabrication of Nb tubes via the caliber-rolling process at various rolling speeds from 1.4 m/min to 9.9 m/min at ambient temperature, and the effect of the caliber-rolling speed on the microstructural and microtextural evolution of the Nb tubes. The caliber-rolling process affected the grain refinement when the Nb tube had a higher fraction of low angle grain boundaries. However, the grain size was identical regardless of the rolling speed. The dislocation density of the Nb tubes increased with the caliber-rolling speed according to the Orowan equation. The reduction of intensity for the <111> fiber texture and the development of the <112> fiber texture with the increase of the strain rate are considered to have decreased the internal energy by increasing the fraction of the low-energy Σ3 boundaries.

No abstract