The effect of Ni 1-2 wt.% addition on the microstructure and hardness of the aged A319 alloy were studied. Characterization analyses by x-ray diffraction, optical microscopy and scanning electron microscopy suggest clearly that Ni addition forms Al-Ni-Cu-Fe, Al-Cu-Ni and Al-Ni intermetallic compounds that correlates well with equilibria conditions. Analyses by transmission electron microscopy show that aging heat treatment promotes microstructural changes in morphology, size, and spatial distribution of precipitates. Vickers micro-hardness test of Ni 1 and 2 wt.% specimens have a hardness increase from that of A319 alloy of ~6-8% with mean values of 140.98 and 142.93 HV, respectively.

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Pure and Mn-doped barium titanate nanofibers were synthesized by the electrospinning method. The morphology, microstructure and crystal structure of as-spun and annealed composite nanofibers were characterized by scanning electron microscopy and transmission electron microscopy. After annealing at 850°C, we obtain nanofibers a few μm long, formed by nanoparticles of irregular shape with sizes around 100 nm. X-ray diffraction and Raman spectroscopy show that a partial phase transition from tetragonal to hexagonal takes place for BaTi 0.90 Mn 0.10 O 3 . Vibrational phonon modes were calculated for BaTiO 3 within the density functional theory (DFT) framework. Ferroelectricity has been probed on pure and Mn-doped BaTiO 3 nanofibers, by means of piezoresponse force microscopy in an atomic force microscope, confirming the polar domain switching behavior of the fibers. The measured piezoelectric coefficient d 33 were 31 and 22 pm/V for BaTiO 3 and BaTi 0.90 Mn 0.10 O 3 . Magnetic properties of the samples were probed in a superconducting quantum interference device. Diamagnetic and paramagnetic behaviors were found in pure and Mn-doped samples, respectively. K E Y W O R D S atomic force microscopy, barium titanate, electrospinning, ferroelectricity/ferroelectric materials, perovskites

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