三种变速条件下共晶生长的多相场法模拟

Multiphase field simulation of the eutectic growth under three schemes of varying velocity

利用多相场模型模拟了共晶合金CBr4-C2Cl6定向凝固变速生长过程,研究了阶跃变速、线性变速以及震荡变速三种变速条件下共晶片层间距的调整以及形态的变化.结果表明:在变速生长过程中,界面平均生长速率与平均过冷度随抽拉速率的变化均产生滞后效应;阶跃增速时,片层间距的调整通过突变分岔形式进行,而阶跃减速时,通过片层的逐步湮没与合并以及自身相的长大方式进行,两个过程表现出强烈的非对称性;线性增速过程,片层间距的调整通过逐步分岔进行,而线性减速过程,片层间距的调整机理与阶跃减速过程类似.线性增速与线性减速过程片层间距的调整具有逆对称性;在震荡变速作用下,片层生长形成类似1λO振荡不稳定性形态.

By multiphase field model method,the unidirectional solidification of eutectic alloy CBr4-C2Cl6 is simulated,and the adjustment of lamellar spacing and morphology evolution have been investigated under three schemes of variable pulling speed, i.e., the stepped change,the linear change and the oscillatory change. The simulation results show that,for the growth under these three schemes,both the interface average velocity and the interface average undercooling show hysteresis effect. When the stepped increase or decrease in velocity is imposed,the lamellar spacing adjustment is realized through abrupt branching or progressive merging and annihilation accompanying the lamellar growing,respectively,and there is strong asymmetry in these two processes during lamellar adjustment. In the case of linear increase in velocity,the lamellar spacing changes by progressive branching,while in the case of linear decrease in velocity,the mechanism of adjustment of lamellar spacing is similar to that of growth under stepped decrease of velocity. The processes for linear increase and decrease in velocity show inverse symmetrical characteristic. A quasi-1λ oscillation mode is present when an oscillatory pulling speed is applied.