Abstract
The densification and bonding of aluminum powder subjected to ultrasonic vibration under uniaxial pressure were characterized and their mechanisms were investigated by transmission electron microscopy (TEM). Full densification was achieved in just 1 second at a nominal consolidation temperature of 573 K and in 4 seconds at 473 K. The particle shape-change required for densification occurs by rapid plastic deformation, associated with dynamic recovery and continuous dynamic recrystallization, and repetitive formation and transfer of supercooled liquid into the particle interstices where the liquid solidifies into layers of amorphous and nanocrystalline aluminum. The liquid transfer also provides oxide-free surfaces required for metallurgical bonding at the particle junctions. The occurrence of rapid plastic deformation and formation of supercooled liquid is explained by the effects of excess vacancies generated in the deforming powder particles.
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