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

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 101_αAl //010_Al3Ni // 101_Si to 001_αAl // 010_Al3Ni //113_Si. 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.