【作者】 刘洋；

【导师】 王建中；

【作者基本信息】 辽宁工学院 ， 材料物理与化学， 2007， 硕士

【摘要】 电脉冲对金属凝固有影响已经被众多学者的实验结果所证实,但对其机理的研究严重滞后于实验研究,这给工业应用带来了很大的局限性。为进一步揭示电脉冲对熔体孕育机理,本文采用低熔点的Pb-Sn合金,分别应用脉冲电流、脉冲电场作用过热熔体,从组织、示差扫描量热分析(DSC)、活度等方面探讨了电脉冲对熔体结构的作用。试验发现脉冲电流、脉冲电场作用下Pb-Sn合金单位面积上的晶粒个数显著增加。在脉冲电流作用下最大值为原来的1.6倍,脉冲电场作用下最大值为原来的1.4倍;利用DSC技术,分析了脉冲电流、脉冲电场作用下合金的凝固点变化,实验发现,电脉冲作用下的试样凝固点呈现不同程度的下降并运用经典形核理论对细化机理进行了解释。应用Miedema生成热模型计算了Pb-Sn合金的混合焓,并根据热力学关系计算了过剩吉布斯自由能、过剩熵及活度等热力学量。在液态金属团簇结构假说的基础上建立了Pb-Sn合金熔体结构模型,并根据液态结构模型考察了电脉冲对熔体结构的作用。熔体组分活度与组分分配系数是相关的,分配系数的改变可以反映组元活度的变化。本文应用与金属Pb互不相溶的金属Zn作为平衡体系,考察了金属Sn在Pb和Zn中的分配系数,发现电脉冲能够导致熔体Sn在熔体Pb、Zn中分配系数及活度系数的改变,进一步从活度角度解释了电脉冲对熔体结构的孕育作用。液态是固态的母相,其结构直接对凝固组织有影响。电脉冲能影响熔体结构,进而导致熔体组元活度的变化,因此熔体活度有望成为衡量熔体结构变化的宏观参量。更多还原

【Abstract】 It is proved by experiments that electric pulse has an effect on solidification structure of alloy, but till now it has no consistent view about solidification reason, which impedes the application of electric impulse technique. In order to reveal the modification mechanism of electric pulse deeply, electric pulse’s effect on Pb-Sn alloy molten structure is discussed in this dissertation in terms of Calorimetry(DSC), solidifying texture and activity.Experiments show that solidification structure has been dramatically refined with the treatment of pulse electric field and current. The number of grains in pulse current is increased by 1.6, while the number in pulse field is 1.4. By means of DSC technique, variation of solidifying point of Pb-Sn alloy is studied under pulse electric field and current. It is observed that the freezing point of Pb-Sn alloy is reduced in a various degree. This phenomenon is explained through classical nucleation theory. The mixing enthalpy of Pb-Sn alloy has been calculated based on Miedema Model. Through thermodynamic relations, other thermodynamic functions such as excess Gibbs energy, excess entropy and activity have also been deduced. Based on cluster structure assumption of liquid metal, the model of Pb-Sn liquid structure is established and electric pulse’s effect on molten is evaluated by the model. The component’s activity is correlated to the coefficient of distribution, so measuring the coefficient of distribution is important to understand the activity. Pb and Zn are not dissolved absolutely and mutually, so they are selected as parent phases to study distribution law of Sn in Pb and Zn. Results show that electric pulse can change partition coefficient, which further proves the modification effect of electric pulse.Liquid is the parent phase of solid state. Liquid structure has a direct impact on solidification structure. Electric pulse can modify molten structure, thus lead to alternation of component’s activity in the alloy system, so activity may be a macro-parameter by measuring change of molten structure.更多还原