超声场中 Ni_77.6Si_22.4 合金的凝固组织演变与应用性能提升

The dynamic solidification mechanism of binary Ni_77.6Si_22.4 hypereutectic alloy within ultrasonic field under different ultrasound amplitudes was studied by three-dimensional ultrasonic solidification method. The results show that, under static condition, the solidified microstructure is featured coarse primary β(Ni₃Si) dendrites and regular lamellar α(Ni)+β(Ni₃Si) eutectic in interdendritic regions. As the ultrasonic amplitude increasing, the primary β(Ni₃Si) phase dendrites transform into fine equiaxed grains, with the grain size decreasing from 1950 μm to 35 μm. The α(Ni) + β(Ni₃Si) eutectic structures undergo the morphological evolution process of “lamellar eutectic→irregular eutectic→divorced eutectic”. The transient cavitation generates the local high undercooling in the alloy melt, which increases the nucleation rate of primary phase, serving as the dominant factor in grain refinement. During subsequent eutectic transformation, the transient cavitation effect increases the difference in nucleation rates between the eutectic β(Ni₃Si) and α(Ni) phases, finally resulting in a divorced eutectic structure. The ultrasonically solidified microstructures exhibit a maximum compressive strength of 2.65 GPa and a strain rate of 20.4%, which are 1.4 and 1.7 times higher than those under the static condition, respectively. Furthermore, the self-corrosion current density of solidified alloy decreases from 2.0×10^-6 A/cm² under the static solidification to 7.8×10^-7 A/cm² under the ultrasonic condition.