【作者】 吕海燕；

【导师】 张蓉；

【作者基本信息】 西北工业大学 ， 凝聚态物理， 2004， 硕士

【摘要】 包晶凝固是十分重要的相变过程，许多结构和功能材料的制备都涉及到包晶反应。近年来，包晶凝固研究主要集中在：初生相和包晶相的形核与生长、带状组织、共生生长以及相选择等方面，但对包晶合金定向凝固组织的特征尺度（枝晶间距、相的大小和相体积分数等）随凝固条件的变化规律研究较少。因此，进行这方面研究对于丰富包晶凝固理论以及改善包晶合金性能有重要指导意义。 本文以Cu-Sn合金为研究对象，选Cu-69wt.％Sn、Cu-73wt.％Sn和Cu-75wt.％Sn三组过包晶成分，在1μm／s～5000μm／s的凝固速度区间开展了定向凝固实验研究。通过光学金相、电子显微分析及定量会相技术对凝固组织的形貌、相组成和凝固组织中初生ε相的一次枝晶间距λ、初生ε相与包晶η相的厚度以及共晶体体积分数随凝固条件的变化规律进行了研究。 研究结果表明：所获得的凝固试样都存在一段初始过渡区，加热温度和抽拉速度对过渡区组织和界面位置有影响；在1μm／s～1000μm／s的抽拉速率范围内，Cu-69wt.％Sn和Cu-73wt.％Sn过包晶合金的最终凝固组织由包晶相包裹初生相的板条和其间的共晶体构成，与平衡凝固下的两相组织（包晶η相和共晶体）有很大区别：Cu-69wt.％Sn合金的凝固组织在100～500μm／s抽拉速度区间出现了定向向不定向的转变；初生ε相的厚度在抽拉速度小于5μm／s时变化不大，其后随凝固速度的提高，ε相的厚度逐渐减小，其一次枝晶间距λ与凝固速度V在1μm／s～50μm／s的低速段回归规律符合：λV^0.312=176μm^1.312s^-0.312，50μm／s～1000μm／s中高速段拟合结果满足：λV^0.528=678μm^1.528s^-0.528；共晶体体积分数随凝固速度增加呈现先增加后减小的趋势；包晶相生长机制有三种：包晶反应、包晶转变和直接凝固。凝固速度越慢，包晶转变越充分，对包晶η相层的贡献越大。随凝固速度的增加，包晶η相的厚度在100μm／s以后变化不大，主要是凝固时间和ε枝晶间距的减小对η相的生长有抑制。更多还原

【Abstract】 Peritectic solidification is a very important phase transformation involved in many structural materials and functional materials. Recently, many aspects of peritectic solidification have been investigated including nucleation and growth, banded structure, coupled growth and phase selection. However, the effects of solidification condition on the microstructure characteristic scales, such as primary dendrite arm spacing, size and volume fraction of each phase, deserve further study, which is helpful to improve the property of materials.In this paper, hyperperitectic Cu-Sn alloys with three composition as, Cu-69wt.%Sn, Cu-73wt.%Sn and Cu-75wt.%Sn were studied by directional solidification with drawing velocity range from 1um/s to 5000um/s. The microstructure were analyzed in order to obtain the variation of primary dendrite arm spacing of primary ε phase, thickness of ε and peritectic phase n. and volume fraction of eutectic structure with the solidification velocity.The results show that there exists transition region at the beginning of all samples. The microstructure and length of transition region vary with solidification condition. When the velocity between 1um/s and 1000um/s, the plate-like primary phase is envelopped in the secondary phase in the steady state region. With increasing of growth velocity, the primary ε of Cu-69wt.%Sn becomes more and more thinner. The relation between primary dendrite arm spacing of primary ε andsolidification velocity satisfies λV0.312= 176um1.312-0.312S at low velocity whileλV0.528= 678um1.528-1.528S at high velocity. The volume fraction of eutecticstructure first increases with increasing V and then decreases. The thickness of peritectic phase n rapidly decreases at low velocity and slightly reduces at high velocity. The peritectic transformation mechanism in Cu-Sn is dominant at low velocity.更多还原