采用单辊急冷技术研究了Fe_67.5Al_22.8Nb_9.7三元合金的快速凝固和组织形成规律。

当辊速从10 m/s增大到40 m/s时,合金条带厚度减少1个数量级,冷速增加了7倍;辊速为40 m/s时样品形状除规则条带外还出现了鱼骨状条带和球状液滴。合金显微组织由Nb(Fe, Al)₂和α-Fe组成,随着辊速增大,凝固组织特征发生变化并且显著细化。随着辊速的增大,合金条带近自由面凝固组织则由初生α-Fe相和层片共晶向碎断层片共晶转变,近辊面凝固组织始终由不规则共晶组成。辊速达到40 m/s时,规则条带完全由不规则共晶组成;合金液滴由于获得的冷速相对较低,其凝固组织主要由初生α-Fe相和层片共晶组成,且随着液滴直径的减小初生相由树枝晶向等轴晶转变。

Fe-Al-Nb ternary alloys as a sort of high-temperature structure materials are paid more attention in recent years. The pseudobinary eutectic composed of Nb(Fe, Al)₂ and α-Fe phases in Fe-Al-Nb alloy transformed from lamellar shape to fiber with the increase of growth rate in directional solidification. Heat treatment techniques were applied to investigate the strengthening mechanism related to microstructural formation. However, influence of cooling rate on microstructure especially pseudobinary eutectic is not clear yet. In this work, rapid solidification and the microstructural formation of Fe_67.5Al_22.8Nb_9.7 ternary alloy were investigated by melt spinning technique to reveal the rapid solidification mechanism of the alloy. As the wheel rate increases from 10 m/s to 40 m/s, the thickness of alloy ribbon decrease by one order of magnitude, i.e. from 67.70 μm to 4.69 μm, the cooling rate increases by seven times, i.e. from 1.24×10⁶ K/s to 9.53×10⁶ K/s. Consequently, the sample shape transforms from regular ribbon to regular ribbon, fishbone-like ribbon and droplets. The microstructure consists of Nb(Fe, Al)₂ and α-Fe phases. The rise of wheel rate leaded to the microstructural transition and refinement, as well as the refinement in terms of eutectic interlamellar spacing and grain size (i.e. grain diameter) measured using Image-Pro Plus software. On condition that the wheel rate is less than 40 m/s, the ribbon microstructural characteristics are divided into two regions, i.e. primary α-Fe phase plus lamellar pseudobinary eutectic near free surface region and anomalous pseudobinary eutectic near roller surface region. As the wheel rate increases from 10 m/s to 30 m/s, lamellar eutectic becomes fragmented and the amount of anomalous pseudobinary eutectic enlarges. Once the wheel rate is up to 40 m/s, anomalous pseudobinary eutectic is the only microstructure of the fishbone-like ribbon. Meanwhile, the alloy droplets with the diameter size ranging from 90 μm to 1500 μm were achieved at the wheel rate of 40 m/s. Owing to the relative low cooling rate, the microstructure of the alloy droplet consist of primary α-Fe phase and lamellar pseudobinary eutectic. As the droplet diameter decreases, the primary α-Fe phase transforms from dendrite to equiaxed grain and the pseudobinary lamellar eutectic is refined.