Design of a cold crucible and characteristics of melting and levitating on materials with a high temperature melting

1.为了评价冷坩埚设计参数对系统性能的影响，建立了一个三维数学模型，采用边界元方法求解了冷坩埚系统周围的磁场分布。通过模型的使用，获得了设计的基本信息。提出了冷坩埚和等离子体相结合的新的复合工艺。这一过程可以熔化氧化物、碳化物和氮化物等材料，这些材料的电导率在固态时相对较低，但在熔点时会急剧增加。此外，还发现该工艺对熔化WC、Mo和Nb等高熔点材料是有用的。利用建立的工艺数学模型和实验结果，阐明了工艺操作条件与物性之间的关系。发展了另一种将自蔓延热锋合成(SHS)反应和冷坩埚相结合的混合工艺。利用该工艺可以成功地熔炼出有望作为下一代耐高温材料的TiAl金属间化合物。该工艺通过控制大气压来抑制Al的汽化，可以精确控制电磁混合所产生的成分，同时由于亚氧化物的蒸发速率较高而降低了氧含量。通过建立SHS反应的数学模型，推导出了热波在稳态下传播的条件。设计了一种新型的集中磁场冷坩埚，并从理论分析和实验两方面对其在区域熔炼过程中的适用性进行了研究。

1. To evaluate the effects of design parameters of a cold Crucible, a three-dimensional mathematical model was developed where the boundary element method was employed to solve the magnetic field distribution around a cold crucible system. The fundamental information for design was obtained by use of the model.2. The new hybrid process which combines a cold crucible and a plasma was proposed. This process can melt materials such as oxide, carbide and nitride, an electric conductivity of which is relatively low in solid state but increase drastically at the melting point. Furthermore, it was found that the process was useful for melting materials with high melting point such as WC, Mo, and Nb. The relations between operating conditions of the process and physical properties were clarified by use of mathematical model developed for the process and by the experimental results.3. Another hybrid process which combines the SHS(Self-propagating heatfront synthesis)reaction and the cold crucible are developed. By use of the process, TiAl intermetallic compound which is promising to use as the high temperature resistance materials in the future generation, could be successfully melted. The process has advantages to suppress Al vaporization by controlling the atmosphere pressure, to allow the precise control of compositions due to electromagnetic mixing and to decrease the oxygen content due to high vaporization rate of suboxides.4. By developing a mathematical model of SHS reaction, the condition for which the heat wave can propagate in the steady state was derived.5. A new type of the cold crucible was designed for concentrating magnetic field and its applicability to the zone melting process was studied by the ways of the theoretical analysis and the experiments.