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 mu m/s) and a constant growth rate (V = 11.63 mu m/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 alpha-Al matrix from quenched samples. The values of eutectic spacings (lambda(si) and lambda(Al3Ni)) were measured from transverse sections of the samples. The dependency of lambda(si) and lambda(Al3Ni) on the values of V and G was found to be lambda(si) = 12.58V(-0.50), lambda(Al3Ni) = 7.94V(-0.47), lambda(Si) = 5.57G(-0.42) and lambda(Al3Ni) = 4.31G(-0.45), respectively by using linear regression analysis. The values of bulk growth were also determined to be lambda V-2(Si) = 170.52 and lambda V-2(Al3Ni) = 82.01 mu m(3)/S by using the measured values of lambda(si), lambda(Al3Ni) and V. The values of lambda(Si) and lambda(Al3Ni) obtained in present work were compared with the values of lambda(Si) and lambda(Al3Ni) obtained in previous works for Al-Si and Al-Ni eutectic alloys. From the comparison, it can be seen that the values of lambda(Si) and lambda(Al3Ni) for Al-Si-Ni eutectic alloy are smaller than the values of lambda(Si) and lambda(Al3Ni) for Al-Si and A-Ni eutectic alloys under similar growth conditions. (c) 2011 Elsevier Inc. All rights reserved.