三元等原子比Fe_(33.3)Cu_(33.3)Sn_(33.3)合金的快速凝固机理与室温组织磁性研究

Rapid solidification mechanism and magnetic property of ternary equiatomic Fe_(33.3)Cu_(33.3)Sn_(33.3) alloy

采用自由落体和熔体急冷两种实验技术实现了三元等原子比Fe_(33.3)Cn_(33.3)Sn_(33.3)合金的快速凝固,研究了其组织形成机理和室温磁性特征.实验发现,合金熔体在不同快速凝固条件下都没有发生液相分离,其室温组织均由初生αFe相枝晶以及CU_3SU和CU_6Sn_5二个包晶相组成计算表明,落管中合金液滴的表面冷却速率和过冷度分别达1.3×10~5 K·s^(-1)和283 K(0.19 T_L)当表面冷却速率增大至3.3×10~3 K·s^(-1),初生αFe相发生由粗大枝晶向碎断枝晶的演化.急冷快速凝固过程中,初生αFe相凝固组织沿辊面向自由面方向形成细晶区和粗晶区,其中细晶区以粒状晶为特征而粗晶区存在具有二次分枝的树枝晶随着表面冷却速率由8.9×10~6增大至2.7×10~7 K·s^(-1),αFe相平均晶粒尺寸显著减小,合金条带的矫顽力增大一倍多.

Rapid solidification is a typical non-equilibrium phase transition process,and the crystallization rate of liquid metal is larger than 1 cm·s^-1.If the alloy is solidified in this case,the solute segregation is reduced or even eliminated and the solid solubility can be improved significantly.Rapid solidification technique can be used to refine the microstructures of alloys,which provides an effective method to prepare the novel metastable materials and improve their strengths,plasticities magnetic properties,etc.In this work,the rapid solidification mechanism and magnetic property of ternary equiatoniic Fe33.3Cu33.3Sn33.3 alloy are investigated by drop tube and melt spinning techniques.It is known that Fe-Cu-Sn ternary alloy forms a typical immiscible system.However,the experimental results reveal that the liquid phase separation does not take place during the rapid solidification of ternary equiatoniic Fe33.3Cu33.3Sn33.3 alloy.The solidification microstructures are all composed of primary aFe dendrites together with Cu3Sn and Cu6Sn5 phases.Under the free fall condition,as the drop tube technique provides microgravity and containerless states,the maximum surface cooling rate and maximum undercooling of alloy droplets are 1.3 × 10^5 K·s^-1 and 283 K（0.19 TL）,respectively.When the surface cooling rate reaches 1.9 × 10^3 K·s^-1,the primary aFe phase appears as coarse dendrites,and its maximum dendrite length is 41 μm.Meanwhile,the Cu_3Sn and Cu6Sn5 phases are distributed in the aFe interdendritic spacings.Once the surface cooling rate increases up to 3.3 × 10^3 K·s^-1,the morphology of the primary aFe phase transforms from coarse dendrites into broken dendrites.It is found that the cooling rate and undercooling greatly affect the solidification niicrostructure of alloy droplets.During the melt spinning experiments,since the large temperature gradient exists between the wheel surface and free surface,the solidification niicrostructure is subdivided into two crystal zones according to the different niicrostructure morphologies of aFe phase：fine grain（zone I） and coarse grain（zone Ⅱ）,where zone Ⅰ is characterized by granular grains while zone Ⅱ has some dendrites with secondary branch.Under the rapid cooling condition,the microstructures of ternary equiatoniic Fe33.3Cu33.3Sn33.3 alloy ribbons are refined significantly and show soft magnetic characteristics.As the surface cooling rate increases from 8.9 × 10^-16 to 2.7 × 10^-17 K·s^-1,the lattice constant of aFe solid solution rises rapidly and the coercivity increases from 93.7 to 255.6 Oe.Furthermore,the results indicate that the grain size of aFe phase is the main factor influencing the coercivity of alloy ribbons.