偏晶合金液-液相变过程模拟

MODELING OF THE LIQUID-LIQUID PHASE TRANSFOR MATION OF IMMISCIBLE ALLOYS

建立了能描述在弥散相液滴形核、扩散长大、碰撞凝并及两液相空间分离等因素共同作用下,偏晶合金液-液相变过程中组织演变过程的数学模型,将计算的温度场和浓度场与控制凝固组织演变的动力学方程相耦合,模拟研究了单向冷却条件下Al-Pb合金液-液相变过程中的组织演变过程。结果表明,随着冷却的进行,液-液相变区不断由试样底部向试样顶部推进,直至贯穿整个试样,由于在凝固过程中弥散相液滴进行Marangoni迁移和Stokes运动,试样中的某些部位会出现液滴贫化、过饱和度增加和多次形核现象。

A numerical model describing the microstructure evolution under the common action of the nucleation, the diffusional growth, the collisions and coagulations of the minority phase droplets and the spatial separation of the two liquid phases has been developed. The microstructure development in an unidirectionally solidified Al-Pb alloy has been simulated by coupling the calculated temperature and concentration fields with the kinetic equation which controls the microstructure evolution. It is indicated that the liquid-liquid transformation region moves from the bottom to the top of the sample during cooling. The Marangoni migration and the Stokes movement of droplets may cause a decrease of the local number density of droplets and an increase of the local supersaturation. The repeated nucleation of minority phase droplets may, therefore, occur locally.