(西北工業(yè)大學(xué) 應(yīng)用物理系，西安 710072)
摘 要: 采用落管無容器處理技術(shù)實(shí)現(xiàn)Fe-8%Mo和Fe-26%Mo合金的深過冷快速凝固。結(jié)果表明：大尺寸Fe-8%Mo合金液滴的凝固組織由α-Fe枝晶晶粒組成，溶質(zhì)Mo主要富集于晶界處。隨著合金粒子直徑的減小，α-Fe相組織形態(tài)由粗大枝晶向等軸晶轉(zhuǎn)變并顯著細(xì)化，同時(shí)α-Fe相的微觀偏析逐漸減弱。當(dāng)粒子直徑減小到約100 μm時(shí)，發(fā)生顯著的溶質(zhì)截留效應(yīng)，過冷度和冷卻速率的增大抑制了溶質(zhì)Mo的擴(kuò)散。大尺寸Fe-26%Mo合金液滴的快速凝固組織由殘余α-Fe相和層片共析組織(μ+α-Fe)組成，且隨著粒子直徑的減小，凝固組織由層片狀逐漸轉(zhuǎn)變?yōu)轭w粒狀。理論計(jì)算表明，隨著過冷度的增大，α-Fe枝晶發(fā)生由溶質(zhì)擴(kuò)散控制生長向熱擴(kuò)散控制生長的轉(zhuǎn)變。發(fā)生該轉(zhuǎn)變所需的臨界過冷度隨合金中Mo含量的增大而增大。
關(guān)鍵字: 深過冷；快速凝固；溶質(zhì)截留；枝晶生長；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
