冷卻速率對急冷Fe-Al-Nb三元合金凝固組織形成的影響冷卻速率對急冷Fe-Al-Nb三元合金凝固組織形成的影響INFLUENCE OF COOLING RATE ON MICROSTRUCTURAL FORMATION OF MELT-SPUN Fe-Al-Nb TERNARY ALLOY 采用單輥急冷技術研究了Fe67.5Al22.8Nb9.7三元合金的快速凝固和組織形成規(guī)律.當輥速從10 m?s-1增大到40 m?s-1時，合金條帶厚度減少一個數量級，冷速增加了7倍,輥速為40 m?s-1時樣品形狀除規(guī)則條帶外還出現了魚骨狀條帶和球狀液滴.合金樣品由Nb(Fe,Al)2和(αFe)兩相組成，隨著輥速增大凝固組織發(fā)生特征變化并且顯著細化.隨著輥速的增大，合金條帶近輥面凝固組織始終由不規(guī)則共晶組成，近自由面凝固組織則由初生(αFe)相和層片共晶向碎斷層片共晶轉變.輥速達到40 m?s-1時，規(guī)則條帶完全由不規(guī)則共晶組成；合金液滴由于獲得的冷速相對較低，其凝固組織主要由初生(αFe)相和層片共晶組成，且隨著直徑的減小初生相由樹枝晶向等軸晶轉變. Rapid solidification and microstructure formation of Fe67.5Al22.8Nb9.7 ternary alloy were investigated by melt spinning technique. As the wheel speed increased from 10 to 40 m?s-1, the thickness of alloy ribbon decreased by one order of magnitude, the cooling rate increased by seven times, and the alloy shape transformed from regular ribbon to regular ribbon, fishbone-like ribbon and droplets. The alloy consisted of Nb(Fe,Al)2 and (αFe) phases. The enhancement of wheel speed leaded to the microstructural transition and refinement. When the wheel speed increased, the ribbon microstructure of near roller surface region was always anomalous eutectic, however that of near free surface region changed from primary (αFe) phase plus lamellar eutectic to fragmented lamellar eutectic. Once the wheel speed was up to 40 m?s-1, anomalous eutectic is the only microstructure of the fishbone-like ribbon. Meanwhile, owing to the relative low cooling rate, the microstructures of alloy droplets were comprised of primary (αFe) phase and lamellar eutectic, and the dendrite to equiaxed grain transition of primary (αFe) phase occurred with the decrease of droplet size.
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