Cu-Cr系合金宏观偏析过程的数值模拟

发布时间：2018-10-13 18:47

【摘要】：Cu-Cr系合金是一类拥有良好综合性能的结构功能一体化材料,当第二相弥散分布于基体中时,可使铜合金在获得高强度的同时保持了较好的导电性能。由于合金凝固时存在液-固相变过程,液相Cu易富集于底部,而密度较低的Cr相易于上浮挥发,极易产生偏析现象,恶化其功能特性。本文基于欧拉数值模拟和流体技术,通过数值模拟研究了Cu-Cr系合金中第二相在凝固过程中的偏析行为、温度场以及第三相对合金偏析模式产生的影响,取得如下研究结果。(1)研究了Cu-Cr6.5%合金凝固过程中Cr在基体中的扩散分布面积随时间和位置的变化规律,结果表明:凝固初期Cr相比较均匀的分散在合金基体中,Cr相熔点较高,先发生侧向凝固,形成糊状区;凝固后期基体顶部的Cr会大量聚集,形成顶部偏析,侧向凝固Cr相的形成壁面偏析,对壁面温度场的分布产生影响。(2)分析了合金凝固过程中壁面溶质浓度的变化和柱状晶生长形态,结果表明:液相合金向下流动方向与柱状晶生长方向基本一致,这种流动模式也影响了熔体的组成;随着柱状晶体生长,溶质逐渐向内部富集;凝固后期,当糊状区溶质浓度达到一定程度时,在紊流和重力作用下,柱状晶尖端断裂,成为等轴晶的形核中心。(3)研究了通道偏析的形成规律,结果表明:Cu-Cr通道偏析模型的形成,受到Mo相尺寸和数量的影响。当粒子的大小范围5~25μm形成粒子聚集成团,最终形成通道偏析;当粒子尺寸小于5μm或大于25μm时,颗粒在糊状区之间的相互作用并不会持续太长时间,因此并不能引起通道偏析。(4)研究了Mo相颗粒对Cr相偏析的作用机制,结果表明:颗粒的浮选对通道偏析的形成影响分为两个阶段,即偏析启动阶段和偏析成长阶段。在糊状区附近的局部流速增加将改变Cr相的移动及随后的凝固,从而导致局部Cr相分离和抑制局部凝固,糊状区的凝固速率也将发生变化。通道偏析的形成取决于Mo相颗粒大小和数量,当Mo相颗粒直径逐渐变大时,偏析带逐渐减小。同时Mo相初始粒子的数量增加也增大糊状区的不稳定性,进而引起更多偏析带。
[Abstract]:Cu-Cr alloy is a kind of structure-functional integrative material with good comprehensive properties. When the second phase is dispersed in the matrix, the copper alloy can obtain high strength and good electrical conductivity. Due to the liquid-solid transformation process during solidification, liquid Cu is easy to be enriched at the bottom, while the low density Cr phase is easy to float and volatilize, which is easy to produce segregation phenomenon and deteriorate its functional properties. Based on Euler numerical simulation and fluid technology, the segregation behavior of the second phase in Cu-Cr alloy during solidification, the effect of temperature field and the third relative alloy segregation mode are studied by numerical simulation. The results are as follows. (1) the variation of Cr diffusion area in the matrix during solidification of Cu-Cr6.5% alloy is studied. The results show that the Cr phase is uniformly dispersed in the alloy matrix at the beginning of solidification, and the melting point of Cr phase is higher. In the later stage of solidification, the Cr at the top of the matrix will accumulate in large quantities, forming the top segregation, and forming wall segregation of the Cr phase in the lateral solidification. (2) the variation of solute concentration and the growth morphology of columnar crystals during solidification are analyzed. The results show that the downward flow direction of liquid alloy is basically consistent with that of columnar crystal growth. This flow pattern also affects the composition of the melt; with the growth of columnar crystals, solute gradually enriches internally; at the end of solidification, when the concentration of solute in the paste region reaches a certain level, the columnar crystal tip breaks under the action of turbulence and gravity. (3) the formation of channel segregation is studied. The results show that the formation of Cu-Cr channel segregation model is affected by the size and quantity of Mo phase. When the particle size ranges from 5 渭 m to 25 渭 m, the particle aggregates and forms channel segregation, and when the particle size is less than 5 渭 m or more than 25 渭 m, the interaction between the particles in the paste region does not last for too long. Therefore, channel segregation can not be induced. (4) the mechanism of Mo phase particles acting on Cr phase segregation is studied. The results show that the effect of particle flotation on channel segregation formation is divided into two stages, namely, segregation start-up stage and segregation growth stage. The increase of local velocity near the paste region will change the movement of Cr phase and the subsequent solidification, resulting in local Cr phase separation and inhibition of local solidification, and the solidification rate of the paste region will also change. The formation of channel segregation depends on the size and number of Mo phase particles. When the diameter of Mo phase particles becomes larger, the segregation band gradually decreases. At the same time, the increase of the number of initial particles in Mo phase also increases the instability of the paste region, which leads to more segregation bands.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG146.11

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