Microstructural characterization of unidirectional solidified eutectic Al–Si–Ni alloy

Al–11.1wt.%Si–4.2wt.%Ni eutectic alloy was directionally solidified upward at a constant temperature gradient (G = 5.82 K/mm) in a wide range of growth rates (V = 4.60–243.33 μm/s) and a constant growth rate (V = 11.63 μm/s) with different temperature gradients (G = 2.11–5.82 K/mm) by using a Bridgman type directional solidification furnace. The microstructure of directionally solidified Al–11.1wt.%Si–4.2wt.%Ni alloy was observed to be irregular plates of Al3Ni and Si within an α–Al matrix from quenched samples. The values of eutectic spacings (λSi and λAl3Ni) were measured from transverse sections of the samples. The dependency of λSi and λAl3Ni on the values of V and G was found to be λSi = 12.58V− 0.50, λAl3Ni = 7.94V− 0.47, λSi = 5.57G− 0.42 and λAl3Ni = 4.31G− 0.45, respectively by using linear regression analysis. The values of bulk growth were also determined to be λSi2V= 170.52 and λAl3Ni2V= 82.01 μm3/s by using the measured values of λSi, λAl3Ni and V. The values of λSi and λAl3Ni obtained in present work were compared with the values of λSi and λAl3Ni obtained in previous works for Al–Si and Al–Ni eutectic alloys. From the comparison, it can be seen that the values of λSi and λAl3Ni for A1–Si–Ni eutectic alloy are smaller than the values of λSi and λAl3Ni for A1–Si and A–Ni eutectic alloys under similar growth conditions.