Al3Ni nanowires were fabricated via the selective etching of directionally solidified Al–Ni eutectic alloys. The effects of different growth rates from 2 to 1000 μm/s on the microstructure and morphology of eutectic alloys under a temperature gradient of 10 K/cm were investigated. The mechanism of the cross-sectional morphology transformation of Al3Ni nanofibers was investigated using the dynamic undercooling degree \(\Delta {T}_{\text{k}}\) . Then, the morphologies of the Al3Ni nanowires at different growth rates and corrosion time were studied using the constant potential corrosion method. Increasing the growth rate increased the roundness of the section and decreased the fiber phase spacing and diameter. At a growth rate of 2 μm/s, both Al and Al3Ni exhibited kinetic undercooling ( \({\Delta T}_{\text{k},{\text{Al}}_{3}\text{Ni}}\) and \({\Delta T}_{\text{k},\text{Al}}\) ), with values below the critical kinetic undercooling ( \({\Delta T}_{\text{k},{\text{Al}}_{3}\text{Ni}}^{\text{c}}\) and \({\Delta T}_{\text{k},\text{Al}}^{\text{c}}\) ). The Al3Ni fibers underwent faceted growth and developed a thin ribbon structure. At 5 μm/s, the kinetic undercooling of Al3Ni and Al exceeded \({\Delta T}_{\text{k},{\text{Al}}_{3}\text{Ni}}^{\text{c}}\) and \({\Delta T}_{\text{k},\text{Al}}^{\text{c}}\) , respectively, leading to nonfaceted growth and elliptically shaped Al3Ni fibers. With prolonged corrosion time, the length of the Al3Ni nanowires increased.
