Magnetic and compressive properties of ternary Ni–Fe–Ti eutectic alloy processed by electromagnetic levitation technique

The magnetic and compressive properties of the ternary Ni_40.6Fe_36.4Ti₂₃ eutectic alloys solidified under electromagnetic levitation condition were investigated. An undercooling range from 32 to 141 K was achieved, and a ternary eutectic consisting of a fibrous Fe₂Ti phase and lamellar γ-Fe(Ni) + Ni₃Ti phases formed. In the ternary eutectic, the γ-Fe(Ni) and Ni₃Ti phases kept cooperative growth, while the Fe₂Ti phase grew either cooperatively with these two phases or sometimes independently. Theoretical calculations showed that there existed a vertical flow field and temperature gradient in the center of the levitated alloy droplet, contributing to the directional growth behavior of eutectic grain. The growth velocity of primary Ni₃Ti dendrite increased by 2.4 times, while that of ternary eutectic increased by 77% as undercooling rose, and consequently, the microstructures were significantly refined. The temperature stability of coercivity and residual magnetization below ambient temperature was improved once alloy undercooling reached 128 K, ascribed to the enhancement of the exchange coupling effect between the magnetic domains inside refined grains. The fracture strain of the ternary eutectic alloy increased with undercooling because microcrack propagation was further hindered and the plastic deformation was more homogeneous. Meanwhile, the fracture was dominated by transgranular (TG) mode at an undercooling of 132 K because the bonding force of grain boundaries became stronger.