Ternary eutectic growth and associated tensile properties of directionally solidified Al87Si11Ni2 alloy

Abstract

The directional growth mechanism and associated tensile properties of ternary Al87Si11Ni2 eutectic alloy were investigated within a wide growth velocity range from 1 to 120 μm s−1 at a constant temperature gradient of 380 K cm−1. If eutectic growth velocity was below 40 μm s−1, this alloy exhibited a ternary lamellar eutectic structure composed of Si plates, Al3Ni chips and αAl matrix. As growth velocity increased to faster regime, the microstructure evolved into a complex structure characterized by primary αAl dendrites plus ternary eutectics. Correspondingly, the preferred crystalline orientation along solidification direction transformed from 101αAl //010Al3Ni // 101Si to 001αAl // 010Al3Ni //113Si. The tensile strength initially increased with the rise of growth velocity until 40 μm s−1, primarily due to the refinement of eutectic structure, and then decreased beyond this threshold, mainly resulting from the coarsening of primary αAl phase.