【作者】 马炳倩；

【导师】 彭志坚； 李建强；

【作者基本信息】 中国地质大学（北京） ， 地质工程， 2014， 博士

【摘要】 难混溶合金由液-液相分离反应生成两个难混溶液相，在一定条件下可凝固形成核壳组织，拓展了该合金体系的应用领域。本文在前人研究成果的基础上，进一步研究核壳结构难混溶合金形成的影响因素及作用机理，取得以下进展：（1）现有文献中制备得到的核壳组织最外层一般被低表面能相包裹。针对该现象，采用浇铸法研究了难混溶区外的亚偏晶和偏晶成分的40Sn60Cu-Bi难混溶合金，得到富Cu-Sn相包裹富Bi相的核壳组织。对比制备了Cu-Pb偏晶合金，得到的合金结构整体为富Cu相枝晶，富Pb相分布在枝晶晶界处。分析认为这种组织差异是合金在偏晶反应后生成的液相与固相间的润湿性差异造成的。（2）采用浇铸法研究了难混溶区合金成分对40Sn60Cu-Bi合金凝固组织的影响。随着富Bi相含量的增加，40Sn60Cu-45%Bi、40Sn60Cu-62.5%Bi和40Sn60Cu-72.5%Bi合金的组织最外层均为富Bi相，并依次形成三层核壳组织、两层核壳组织和富Cu-Sn相弥散分布的组织。（3）采用浇铸法研究了冷却速率对40Sn60Cu-62.5%Bi合金核壳组织形成的影响。计算了三个尺寸合金柱体中富Cu-Sn相液滴的Marangoni对流速率Vm和富Bi相凝固界面推进速率Vi，得到当Vm≥Vi时的临界液滴尺寸。计算和实验结果显示，直径5mm的合金柱体具有最小的临界液滴尺寸，形成的核壳组织的核心面积最大。（4）采用浇铸法研究了稀土元素Ce对40Sn60Cu-60.0%Bi合金核壳组织的影响。结果显示，Ce的掺杂可显著提高合金的界面张力温度系数，使第二相液滴的Marangoni对流运动加强，使形成的核壳组织的核心面积分数提高了20%。（5）研究了气动悬浮条件下Fe-(43±10x)%Cu（x=0、1、2、3）合金的相分离特点。合金凝固组织的形成不仅与第二相液滴的对流运动有关，合金熔体在悬浮状态下的旋转方向也起重要作用。合金组织内部的典型形貌主要分为3类：第二相液滴在基体相中弥散分布的组织、核壳组织和两液相平行分层的组织。其中Fe-23%Cu合金的组织内部为富Fe相包裹富Cu相的核壳结构，可用作金属相变胶囊。更多还原

【Abstract】 Homogeneous immiscible alloys decompose into two immiscible liquids due tothe liquid-liquid decomposition reaction when being cooled into the immiscible zone,and form core-shell structures under certain conditions, which can be applied asmetallic composites in various industrial fields. A substantial research effort has beenundertaken to investigate the formation mechanism of core-shell structuredimmiscible alloys. However, the formation mechanism has not been clarified. Someeffects on the formation mechanism have been studied in this thesis. The followingconclusions have been made.(1) Core-shell immiscible alloys reported have usually been coated by a lay ofone phase with low surface energy, which restricted the potential application fields ofimmiscible alloys. Hypomonotectic and monotectic40Sn60Cu-Bi alloys have beenprepared by a casting method in this work. A core-shell structure which consists of ashell of CuSn-rich phase and a core of Sn-rich phase has been obtained. MonotecticCu-Pb alloy has been casted as well. The morphology of monotectic Cu-Pb alloy wasa network structure formed by Cu dendrites and Pb was distributed at the grainboundary or in the interdendritic regions. The reason for structure difference betweenmonotectic40Sn60Cu-Bi (wt.%) and Cu-Pb alloy was considered to be the differenceof wetting property between the liquid and solid produced by monotectic reaction inthe two alloys.(2) The effect of composition on the formation of40Sn60Cu-Bi hypermonotecticalloys has been studied by the casting method. With the content of Bi increasing, athree-layer core-shell structure, a two-layer core-shell structure and a dispersedstructure with CuSn-rich phase have been observed in40Sn60Cu-45%Bi,40Sn60Cu-62.5%Bi and40Sn60Cu-72.5%Bi alloys, respectively. The periphery of allthe alloys is composed of Bi-rich phase.(3) The effect of cooling rate on the formation of core-shell structure in40Sn60Cu-62.5%Bi alloy has been discussed. The Marangoni moving velocity VmofCuSn-rich droplets and the advancing velocity Viof Bi-rich phase solidification interface have been calculated. For three samples with different radi, the criticaldroplet radius has been got when Vm≥Vi. The least critical droplet radius was gainedand a largest core was obtained as well in the sample with a diameter of5mm.(4) The effect of Ce addition on the formation of core-shell structure in40Sn60Cu-60.0%Bi alloy has been investigated. The results show that the addition ofCe improved the temperature coefficient of liquid-liquid interfacial tension, andtherefore sped up the Marangoni velocity of CuSn-rich droplets. The core fraction hasbeen enlarged by20%with the addition of Ce.(5) Phase separation of Fe-(43±10x) at.%Cu (x=0、1、2、3) alloys underaerodynamic levitation has been studied. Structures of Fe-Cu alloys were determinedby the movement of minor-phase droplets and the rotation direction of alloy spheresin the state of levitated. Three typical kinds of structures have been obtained: adispersed structure, a core-shell structure and a parallel-layer structure. A core-shellstructure with a shell of Fe-rich phase and a core of Cu-rich phase formed inFe-23%Cu alloy, which can be used as metallic phase change capsules.更多还原