(西北工业大学 应用物理系，西安 710072)
摘 要: 采用落管无容器处理技术实现Fe-8%Mo和Fe-26%Mo合金的深过冷快速凝固。结果表明：大尺寸Fe-8%Mo合金液滴的凝固组织由α-Fe枝晶晶粒组成，溶质Mo主要富集于晶界处。随着合金粒子直径的减小，α-Fe相组织形态由粗大枝晶向等轴晶转变并显著细化，同时α-Fe相的微观偏析逐渐减弱。当粒子直径减小到约100 μm时，发生显著的溶质截留效应，过冷度和冷却速率的增大抑制了溶质Mo的扩散。大尺寸Fe-26%Mo合金液滴的快速凝固组织由残余α-Fe相和层片共析组织(μ+α-Fe)组成，且随着粒子直径的减小，凝固组织由层片状逐渐转变为颗粒状。理论计算表明，随着过冷度的增大，α-Fe枝晶发生由溶质扩散控制生长向热扩散控制生长的转变。发生该转变所需的临界过冷度随合金中Mo含量的增大而增大。
关键字: 深过冷；快速凝固；溶质截留；枝晶生长；落管
（Department of Applied Physics, Northwestern Polytechnical University, Xi’ an 710072, China）
Abstract:Rapid solidification of Fe-8%Mo and Fe-26%Mo alloys was investigated by drop tube technique. The results show that for Fe-8%Mo alloy, the rapid solidification product is α-Fe dendrite in large droplet, a mount of solute Mo distributes at the grain boundaries. The grain refinement effect occurs and it displays a morphological transition of “coarse dendrite−equiaxed grain” with the decrease of droplet diameters, meanwhile, the microsegregation inside the α-Fe dendrite is suppressed. The solute trapping effect occurs when the droplet diameter reduces to approximately 100 μm. For Fe-26%Mo alloy, the solidification microstructure is composed of residual α-Fe dendrite and lamellar eutectoid structure (μ+α-Fe) in large droplet. When the droplet diameter decreases to a certain degree, the microstructure changes into the granular eutectoid structure (μ+α-Fe). Theoretical analysis indicates that the rapid dendritic growth of α-Fe transforms from “solute diffusion controlled” into “thermal diffusion controlled” growth with the enhancement of undercooling. The critical undercooling for this transition increases with the rise of Mo content in the alloy.
Key words: undercooling; rapid solidification; solute trapping; dendrite growth; drop tube
