三元Fe₇₃B₂₂Nb₅合金的快速凝固组织控制与物理性能研究

The microstructure evolution of ternary Fe₇₃B₂₂Nb₅ alloy during rapid solidification was studied under free fall conditions. The effects of alloy microstructure on its micromechanical and magnetic properties were examined systematically. The liquidus and solidus temperatures were measured as 1525 and 1410 K, respectively. Under a near-equilibrium solidification condition, the primary Fe₂B phase forms preferentially, and then the remnant alloy melt solidified into a ternary (FeNbB+αFe+Fe₂B) eutectic structure. The diameter of the alloy droplets used in containerless processing by drop tube ranged from 90 to 1030 μm. Theoretical calculations showed that liquid undercooling and cooling rates increased exponentially with the decrease in droplet diameter. The maximum undercooling and cooling rate reached 352 K (0.23T_L) and 7.25 × 10⁴ K s⁻¹. The growth of the primary Fe₂B phase was reduced when alloy undercooling was sufficiently high, and ternary eutectic microstructures took over as the dominating microstructures. The eutectic FeNbB phase revealed a significant strengthening effect on the micromechanical property of this alloy, and its hardness and Young’s modulus attained 15.1 and 170.7 GPa. The solute trapping effect resulted in a uniform distribution of Nb elements and a higher volume fraction of the FeNbB phase. As a result, the alloy hardness achieved a maximum of up to 1197 HV. Additionally, grain refinement enhanced the soft magnetic property, while alloy coercivity significantly reduced the alloy coercivity from 79 to 54 Oe.