Commercial hydrothermally synthesized BaTiO3 powder with a cubic structure was annealed in a temperature range of 650–900 ℃, and the cubic-tetragonal structure transition and microstructure evolution of the powder were investigated in relation to the annealing process. The BaTiO3 powder used had a cubic structure below an annealing temperature of 800 ℃ and a tetragonal structure above 850 ℃. Particle growth occurred under a low activation energy of ~33.2 kJ/mol because of the nanocrystalline size effect, while the crystallite size slightly decreased in the powder with the cubic structure and sharply increased in that with the tetragonal structure. This was because the OH group in the powder with the cubic structure influenced the lattice extension on the particle surface. This stabilized the cubic structure and reduced the crystal ordering, which retarded the crystallite size. When the annealing temperature was increased, the crystallite growth reduced the intrinsic strain and enhanced the tetragonality in the powder with the tetragonal structure as a result of the removal of the OH group.

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Copper sheets were subjected to differential speed rolling (DSR) at roll speed ratios (RSRs) from 1 to 3. The effects of the RSR on the yield strength, uniform strain, microstructure, and texture evolution in the copper sheets were investigated. The grain refinement and uniformity were obviously enhanced, the yield strength and uniform strains increased slightly, and the shear texture components were further widely distributed when the RSR was increased up to 2. At RSR=3, the yield strength decreased, with a distinct increase in the uniform strains due to dynamic recovery and recrystallization as a result of the steep reduction in the geometrically necessary dislocation (GND) density and the grain orientation spread (GOS), thereby increasing the work hardening coefficient (n) and decreasing the work hardening rate (θ).

With an increase in the annealing temperature, the hydrothermally synthesized BaTiO3 nanopowders increased in particle sizes from 100 to 260 nm and decreased in pore volume from 7.2 to 2.82 cm3/g, while the pore size remained constant at 3.06 nm. Samples with different initial particle sizes were sintered in the temperature range of 1210–1300 ℃ and for periods of 0.5– 48 h at 1270 ℃. The kinetic grain-growth exponent of the sintered BaTiO3 samples, n, was proportional to the increaseof an initial particle size and the decrease of pore volume, and the grain growth obeyed the Arrhenius equation. Theactivation energies for the grain growth of the sintered BaTiO3 samples with initial particle size of 100, 155 and 260 nm were 737, 702 and 755 kJ/mol, respectively, indicating that the activation energy was independent of the initial particle size in the range of 100–300 nm under identical purity conditions, and pore volume was supposed to be attributed to the velocity of grain growth.

In this study, Mg+B wires were prepared by powder in tube method using Nb and Cu tubes as barrier and sheath, respectively, followed by cold drawing. Microstructural, textural, and mechanical properties of the Nb barrier at different drawing strains (εd) were investigated. The results showed that the Nb barrier demonstrated a saturation hardness of 159.4 HV. The microstructure of the Nb barrier became elongated along the drawing direction increasing εd. Sub-grains existing inside the deformed grains rotated from low-angle grain boundaries to high-angle grain boundaries and developed into new grains. The main textural components of the Nb barrier were {111}<110> γ-fiber and {hkl}<110> α-fiber. Recrystallized grains exhibited a low maximum orientation distribution function intensity, weak {100}<110> α-fibers, and strong {111}<110> γ-fibers as compared to those of the deformed grains. The relationship between the microstructure evolution and mechanical properties of the Nb barrier and the changes in the cross-sectional area fractions of the materials constituting the Mg+B composite wire are discussed. The current study provides details about the misorientation profile inside deformed grains and continuous dynamic recrystallization mechanism of the cold-drawn Nb barrier.